Drug Interactions between MST and norfloxacin

ADJUST DOSING INTERVAL: Concurrent ingestion of meals, dairy products (milk, yogurt) or calcium-fortified foods (i.e., cereal, orange juice) may decrease the absorption of oral norfloxacin. The mechanism is chelation of calcium and the quinolone, resulting in decreased bioavailability. In the case of orange juice, inhibition of intestinal transport mechanisms (P-glycoprotein or organic anion-transporting polypeptides) by flavones may also be involved.

MANAGEMENT: Oral norfloxacin should be taken at least one hour before or two hours after a meal, milk, or other dairy products or calcium-fortified foods.

GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.

GENERALLY AVOID: The oral bioavailability of quinolone and tetracycline antibiotics may be reduced by concurrent administration of preparations containing polyvalent cations such as aluminum, calcium, iron, magnesium, and zinc. Therapeutic failure may result. The proposed mechanism is chelation of quinolone and tetracycline antibiotics by di- and trivalent cations, forming an insoluble complex that is poorly absorbed from the gastrointestinal tract. Reduced gastrointestinal absorption of the cations should also be considered.

MANAGEMENT: Concomitant administration of oral quinolone and tetracycline antibiotics with preparations containing aluminum, calcium, iron, magnesium, and/or zinc salts should generally be avoided. Otherwise, the times of administration should be staggered by as much as possible to minimize the potential for interaction. Quinolones should typically be dosed either 2 to 4 hours before or 4 to 6 hours after polyvalent cation preparations, depending on the quinolone and formulation. Likewise, tetracyclines and polyvalent cation preparations should typically be administered 2 to 4 hours apart. The prescribing information for the antibiotic should be consulted for more specific dosing recommendations.

MONITOR: Coadministration with certain quinolones may increase the plasma concentrations and pharmacologic effects of caffeine due to inhibition of the CYP450 1A2 metabolism of caffeine. Quinolones that may inhibit CYP450 1A2 include ciprofloxacin, enoxacin, grepafloxacin, nalidixic acid, norfloxacin, pipemidic acid, and pefloxacin (not all commercially available). In healthy volunteers, enoxacin (100 to 400 mg twice daily) increased systemic exposure (AUC) of caffeine by 2- to 5-fold and reduced its clearance by approximately 80%. Pipemidic acid (400 to 800 mg twice daily) increased AUC of caffeine by 2- to 3-fold and reduced its clearance by approximately 60%. Ciprofloxacin (250 to 750 mg twice daily) increased AUC and elimination half-life of caffeine by 50% to over 100%, and reduced its clearance by 30% to 50%. Norfloxacin 400 mg twice daily increased caffeine AUC by 16%, while 800 mg twice daily increased caffeine AUC by 52% and reduced its clearance by 35%. Pefloxacin (400 mg twice daily) has been shown to reduce caffeine clearance by 47%.

MANAGEMENT: Patients using caffeine-containing products should be advised that increased adverse effects such as headache, tremor, restlessness, nervousness, insomnia, tachycardia, and blood pressure increases may occur during coadministration with quinolones that inhibit CYP450 1A2. Caffeine intake should be limited when taking high dosages of these quinolones. If an interaction is suspected, other quinolones such as gatifloxacin, gemifloxacin, levofloxacin, lomefloxacin, moxifloxacin, and ofloxacin may be considered, since they are generally believed to have little or no effect on CYP450 1A2 or have been shown not to interact with caffeine.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Quinolones may cause CNS stimulation manifested as tremors, agitation, restlessness, anxiety, confusion, hallucinations, paranoia, insomnia, toxic psychosis, and/or seizures. Benign intracranial hypertension has also been reported. Therapy with quinolones should be administered cautiously in patients with or predisposed to seizures or other CNS abnormalities. In addition, these patients should be advised to avoid the consumption of caffeine-containing products during therapy with some quinolones, most notably ciprofloxacin, enoxacin, and cinoxacin, since these agents can substantially reduce the clearance of caffeine and other methylxanthines, potentially resulting in severe CNS reactions.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Clostridioides difficile-associated diarrhea (CDAD), formerly pseudomembranous colitis, has been reported with almost all antibacterial drugs and may range from mild diarrhea to fatal colitis. The most common culprits include clindamycin and lincomycin. Antibacterial therapy alters the normal flora of the colon, leading to overgrowth of C difficile, whose toxins A and B contribute to CDAD development. Morbidity and mortality are increased with hypertoxin-producing strains of C difficile; these infections can be resistant to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea after antibacterial use. Since CDAD has been reported to occur more than 2 months after antibacterial use, careful medical history is necessary. Therapy with broad-spectrum antibacterials and other agents with significant antibacterial activity should be administered cautiously in patients with history of gastrointestinal disease, particularly colitis; pseudomembranous colitis (generally characterized by severe, persistent diarrhea and severe abdominal cramps, and sometimes associated with the passage of blood and mucus), if it occurs, may be more severe in these patients and may be associated with flares in underlying disease activity. Antibacterial drugs not directed against C difficile may need to be stopped if CDAD is suspected or confirmed. Appropriate fluid and electrolyte management, protein supplementation, antibacterial treatment of C difficile, and surgical evaluation should be started as clinically indicated.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

The use of salicylates, primarily aspirin, in children with varicella infections or influenza-like illnesses has been associated with an increased risk of Reye's syndrome. Although a causal relationship has not been established, the majority of evidence to date seems to support the association. Most authorities, including the American Academy of Pediatrics Committee on Infectious Diseases, recommend avoiding the use of salicylates in children and teenagers with known or suspected varicella or influenza and during presumed outbreaks of influenza. If antipyretic or analgesic therapy is indicated under these circumstances, acetaminophen may be an appropriate alternative. The same precautions should also be observed with related agents such as salicylamide or diflunisal because of their structural and pharmacological similarities to salicylate.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Quinolones have been reported to prolong the QT interval of the electrocardiogram in some patients. QT prolongation may potentiate the risk of ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes. The risk appears to be greatest with grepafloxacin and sparfloxacin (both are no longer marketed in the U.S.), although cardiovascular morbidity and mortality attributable to QT prolongation have also been reported rarely with others like gatifloxacin, levofloxacin, ciprofloxacin, and ofloxacin. Reported cases have primarily occurred in patients with advanced age, cardiac disease, electrolyte disturbances, and/or underlying medical problems for which they were receiving concomitant medications known to prolong the QT interval. Therapy with quinolones should be avoided in patients with known QT prolongation and/or uncorrected electrolyte disorders (hypokalemia or hypomagnesemia) and in patients treated concomitantly with class IA or III antiarrhythmic agents. Cautious use with ECG monitoring is advised in patients with other proarrhythmic conditions such as clinically significant bradycardia, congestive heart failure, acute myocardial ischemia, and atrial fibrillation. As QT prolongation may be a concentration-dependent effect, it is important that the recommended dosages or infusion rates of these drugs not be exceeded, particularly in patients with renal and/or hepatic impairment.

Fluoroquinolones have neuromuscular blocking activity and may exacerbate muscle weakness in persons with myasthenia gravis. Postmarketing serious adverse events, including deaths and requirement for ventilatory support, have been associated with fluoroquinolones use in persons with myasthenia gravis. Fluoroquinolones should be avoided in patients with history of myasthenia gravis.

Tendonitis and ruptures of the shoulder, hand, and Achilles tendons have been reported in patients receiving quinolones, both during and after treatment. Avoid the use of these agents in patients who have a history of tendon disorders or have experienced tendinitis or tendon rupture. Therapy with quinolones should be administered cautiously in patients with patients with kidney, heart, and lung transplant, since it may delay the recognition or confound the diagnosis of a quinolone-induced musculoskeletal effect. Factors that may independently increase the risk of tendon rupture include strenuous physical activity, renal failure, and previous tendon disorders such as rheumatoid arthritis. It is recommended to discontinue these agents if, at any time during therapy, pain, inflammation or rupture of a tendon develops and institute appropriate treatment.

Salicylates, particularly aspirin, can cause dose-related gastrointestinal bleeding and mucosal damage, which may occur independently of each other. Occult, often asymptomatic GI blood loss is quite common with usual dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. In contrast, major upper GI bleeding rarely occurs except in patients with active peptic ulcers or recent GI bleeding. However, these patients generally do not experience greater occult blood loss than healthy patients following small doses of aspirin. Mucosal damage associated with the use of salicylates may lead to development of peptic ulcers with or without bleeding, reactivation of latent ulcers, and ulcer perforation. Therapy with salicylates and related agents such as salicylamide should be considered and administered cautiously in patients with a history of GI disease or alcoholism, particularly if they are elderly and/or debilitated, since such patients may be more susceptible to the GI toxicity of these drugs and seem to tolerate ulceration and bleeding less well than other individuals. Extreme caution and thorough assessment of risks and benefits are warranted in patients with active or recent GI bleeding or lesions. Whenever possible, especially if prolonged use is anticipated, treatment with non-ulcerogenic agents should be attempted first. If salicylates are used, close monitoring for toxicity is recommended. Some adverse GI effects may be minimized by administration with high dosages of antacids, use of enteric-coated or extended-release formulations, and/or concurrent use of a histamine H2-receptor antagonist or a cytoprotective agent such as misoprostol. Patients with active peptic ulceration or GI bleeding treated with salicylates should generally be administered a concomitant anti-ulcer regimen.

The use of quinolones has been associated with an increased risk of peripheral neuropathy. Monitor closely and discontinue their use in patients experiencing symptoms of peripheral neuropathy. It is recommended to avoid these agents in patients who have previously experienced peripheral neuropathy.

Salicylate and its metabolites are eliminated almost entirely by the kidney. Therapy with salicylate drugs should be administered cautiously in patients with renal impairment, especially if it is severe. Reduced dosages may be necessary to avoid drug accumulation. Clinical monitoring of renal function is recommended during prolonged therapy, since the use of salicylate drugs has rarely been associated with renal toxicities, including elevations in serum creatinine, renal papillary necrosis, and acute tubular necrosis with renal failure. Most of the data have been derived from experience with aspirin but may apply to other salicylates as well. In patients with impaired renal function, aspirin has caused reversible and sometimes marked decreases in renal blood flow and glomerular filtration rate. Adverse renal effects have usually reversed rapidly following withdrawal of aspirin therapy.

Tendonitis and ruptures of the shoulder, hand, and Achilles tendons have been reported in patients receiving quinolones, both during and after treatment. Avoid the use of these agents in patients who have a history of tendon disorders or have experienced tendinitis or tendon rupture. Therapy with quinolones should be administered cautiously in patients with patients with kidney, heart, and lung transplant, since it may delay the recognition or confound the diagnosis of a quinolone-induced musculoskeletal effect. Factors that may independently increase the risk of tendon rupture include strenuous physical activity, renal failure, and previous tendon disorders such as rheumatoid arthritis. It is recommended to discontinue these agents if, at any time during therapy, pain, inflammation or rupture of a tendon develops and institute appropriate treatment.

Tendonitis and ruptures of the shoulder, hand, and Achilles tendons have been reported in patients receiving quinolones, both during and after treatment. Avoid the use of these agents in patients who have a history of tendon disorders or have experienced tendinitis or tendon rupture. Therapy with quinolones should be administered cautiously in patients with patients with kidney, heart, and lung transplant, since it may delay the recognition or confound the diagnosis of a quinolone-induced musculoskeletal effect. Factors that may independently increase the risk of tendon rupture include strenuous physical activity, renal failure, and previous tendon disorders such as rheumatoid arthritis. It is recommended to discontinue these agents if, at any time during therapy, pain, inflammation or rupture of a tendon develops and institute appropriate treatment.

Tendonitis and ruptures of the shoulder, hand, and Achilles tendons have been reported in patients receiving quinolones, both during and after treatment. Avoid the use of these agents in patients who have a history of tendon disorders or have experienced tendinitis or tendon rupture. Therapy with quinolones should be administered cautiously in patients with patients with kidney, heart, and lung transplant, since it may delay the recognition or confound the diagnosis of a quinolone-induced musculoskeletal effect. Factors that may independently increase the risk of tendon rupture include strenuous physical activity, renal failure, and previous tendon disorders such as rheumatoid arthritis. It is recommended to discontinue these agents if, at any time during therapy, pain, inflammation or rupture of a tendon develops and institute appropriate treatment.

The use of salicylates, primarily aspirin, in children with varicella infections or influenza-like illnesses has been associated with an increased risk of Reye's syndrome. Although a causal relationship has not been established, the majority of evidence to date seems to support the association. Most authorities, including the American Academy of Pediatrics Committee on Infectious Diseases, recommend avoiding the use of salicylates in children and teenagers with known or suspected varicella or influenza and during presumed outbreaks of influenza. If antipyretic or analgesic therapy is indicated under these circumstances, acetaminophen may be an appropriate alternative. The same precautions should also be observed with related agents such as salicylamide or diflunisal because of their structural and pharmacological similarities to salicylate.

Occult, often asymptomatic GI blood loss occurs quite frequently with the use of normal dosages of aspirin and stems from the drug's local effect on the GI mucosa. During chronic therapy, this type of bleeding may occasionally produce iron deficiency anemia. Other salicylates reportedly cause little or no GI blood loss at usual dosages, but may do so at high dosages. Prolonged therapy with salicylates, particularly aspirin, should be administered cautiously in patients with or predisposed to anemia. Periodic monitoring of hematocrit is recommended. The same precautions should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

All salicylates can interfere with the action of vitamin K and induce a dose-dependent alteration in hepatic synthesis of coagulation factors VII, IX and X. At usual recommended dosages, a slight increase in prothrombin time (PT) may occur. Therapy with salicylates, especially if given in high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

All salicylates can interfere with the action of vitamin K and induce a dose-dependent alteration in hepatic synthesis of coagulation factors VII, IX and X. At usual recommended dosages, a slight increase in prothrombin time (PT) may occur. Therapy with salicylates, especially if given in high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

Crystalluria has been reported rarely during quinolone therapy. Although it is not expected to occur under normal circumstances with usual recommended dosages, patients who are dehydrated (e.g., due to severe diarrhea or vomiting) may be at increased risk and should be encouraged to consume additional amounts of liquid or given intravenous fluid to ensure an adequate urinary output. Alkalinity of the urine should be avoided, since it may also increase the risk of crystalluria. Renal function tests should be performed periodically during prolonged therapy (> 2 weeks).

The use of certain quinolones has been associated with disturbances in blood glucose homeostasis possibly stemming from effects on pancreatic beta cell ATP-sensitive potassium channels that regulate insulin secretion. Hypoglycemia and, less frequently, hyperglycemia have been reported, although the latter may also occur due to infection alone. Hypoglycemia has usually occurred in patients with diabetes receiving concomitant oral hypoglycemic agents and/or insulin. Administration of ciprofloxacin, levofloxacin, norfloxacin, and especially gatifloxacin in patients treated with sulfonylureas or other oral hypoglycemic agents has resulted in severe, refractory hypoglycemia and hypoglycemic coma. Elderly patients and patients with reduced renal function are particularly susceptible. Blood glucose should be monitored more closely whenever quinolones are prescribed to patients with diabetes. Gatifloxacin has been known to cause hypoglycemic episodes generally within the first 3 days of therapy and sometimes even after the first dose, while hyperglycemia usually occurs 4 to 10 days after initiation of therapy. Patients should be counseled to recognize symptoms of hypoglycemia such as headache, dizziness, drowsiness, nausea, tremor, weakness, hunger, excessive perspiration, and palpitations. If hypo- or hyperglycemia occur during quinolone therapy, patients should initiate appropriate remedial therapy immediately, discontinue the antibiotic, and contact their physician.

Crystalluria has been reported rarely during quinolone therapy. Although it is not expected to occur under normal circumstances with usual recommended dosages, patients who are dehydrated (e.g., due to severe diarrhea or vomiting) may be at increased risk and should be encouraged to consume additional amounts of liquid or given intravenous fluid to ensure an adequate urinary output. Alkalinity of the urine should be avoided, since it may also increase the risk of crystalluria. Renal function tests should be performed periodically during prolonged therapy (> 2 weeks).

Salicylates, particularly aspirin, may cause or aggravate hemolysis in patients with pyruvate kinase or glucose-6-phosphate dehydrogenase (G-6-PD) deficiency. However, this effect has not been clearly established. Until more data are available, therapy with salicylates should be administered cautiously in patients with G-6-PD deficiency. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

Salicylate and its metabolites are readily removed by hemodialysis and, to a lesser extent, by peritoneal dialysis. Doses should either be scheduled for administration after dialysis or supplemental doses be given after dialysis.

The use of salicylates has occasionally been associated with acute, reversible hepatotoxicity, primarily manifested as elevations of serum transaminases, alkaline phosphatase and/or, rarely, bilirubin. Hepatic injury consistent with chronic active hepatitis has also been reported in a few patients, which resulted rarely in encephalopathy or death. Salicylate-induced hepatotoxicity appears to be dependent on serum salicylate concentration (> 25 mg/dL) and has occurred most frequently in patients with juvenile arthritis, active systemic lupus erythematosus, rheumatic fever, or preexisting hepatic impairment. Therapy with salicylates, particularly when given in high dosages, should be administered cautiously in these patients, and periodic monitoring of liver function is recommended. The same precautions should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate. A dosage reduction may be necessary if liver function abnormalities develop and serum salicylate concentration exceeds 25 mg/dL, although serum transaminase elevations may sometimes be transient and return to pretreatment values despite continued therapy without dosage adjustment.

Each gram of anhydrous magnesium salicylate contains approximately 6.7 mEq of magnesium. Therapy with products containing magnesium salicylate should be avoided or administered cautiously in patients with renal impairment because of the risk of hypermagnesemia. The use of products containing magnesium salicylate is contraindicated in patients with chronic advanced renal impairment.

Quinolones (except trovafloxacin, moxifloxacin, and nalidixic acid) and their metabolites are eliminated by the kidney. Patients with renal impairment may be at greater risk for adverse effects from quinolones, including nephrotoxicity, due to decreased drug clearance. Dosage adjustments may be necessary and modifications should be based on the degree of renal impairment and severity of infection in accordance with the individual product package labeling. Renal function tests should be performed periodically during therapy.

All salicylates can interfere with the action of vitamin K and induce a dose-dependent alteration in hepatic synthesis of coagulation factors VII, IX and X. At usual recommended dosages, a slight increase in prothrombin time (PT) may occur. Therapy with salicylates, especially if given in high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

All salicylates can interfere with the action of vitamin K and induce a dose-dependent alteration in hepatic synthesis of coagulation factors VII, IX and X. At usual recommended dosages, a slight increase in prothrombin time (PT) may occur. Therapy with salicylates, especially if given in high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

All salicylates can interfere with the action of vitamin K and induce a dose-dependent alteration in hepatic synthesis of coagulation factors VII, IX and X. At usual recommended dosages, a slight increase in prothrombin time (PT) may occur. Therapy with salicylates, especially if given in high dosages, should be administered cautiously in patients with significant active bleeding or a hemorrhagic diathesis, including hemostatic and/or coagulation defects associated with hemophilia, vitamin K deficiency, hypoprothombinemia, thrombocytopenia, thrombocytopathy, or severe hepatic impairment. The same precaution should also be observed with the use of related agents such as salicylamide because of their structural and pharmacological similarities to salicylate.

Crystalluria has been reported rarely during quinolone therapy. Although it is not expected to occur under normal circumstances with usual recommended dosages, patients who are dehydrated (e.g., due to severe diarrhea or vomiting) may be at increased risk and should be encouraged to consume additional amounts of liquid or given intravenous fluid to ensure an adequate urinary output. Alkalinity of the urine should be avoided, since it may also increase the risk of crystalluria. Renal function tests should be performed periodically during prolonged therapy (> 2 weeks).