Drug Interactions between foscarnet and methadone

GENERALLY AVOID: Alcohol may potentiate the central nervous system (CNS) depressant effects of methadone. Concomitant use may result in additive CNS depression and impairment of judgment, thinking, and psychomotor skills. In more severe cases, hypotension, respiratory depression, profound sedation, coma, or even death may occur.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of methadone. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In 8 study subjects stabilized on methadone maintenance treatment, ingestion of regular strength grapefruit juice (200 mL one-half hour before and 200 mL simultaneously with the daily methadone dose) for five days resulted in an approximately 17% mean increase in methadone peak plasma concentration (Cmax) and systemic exposure (AUC) and a 14% mean decrease in apparent clearance for both the R(+) and S(-) enantiomers. Grapefruit juice did not affect the time to peak level (Tmax), terminal half-life, or apparent volume of distribution of methadone. No signs or symptoms of methadone toxicity or changes in intensity of withdrawal symptoms were reported in the study. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict. In addition, high dosages (particularly above 200 mg/day) and high serum levels of methadone have been associated with QT interval prolongation and torsade de pointes arrhythmia.

MANAGEMENT: Patients should not consume alcoholic beverages or use drug products that contain alcohol during treatment with methadone. Any history of alcohol or illicit drug use should be considered when prescribing methadone, and therapy initiated at a lower dosage if necessary. Patients should be closely monitored for signs and symptoms of sedation, respiratory depression, and hypotension. In addition, patients treated with oral methadone should preferably avoid or limit the consumption of grapefruit juice, particularly during the induction of maintenance treatment. Given the interindividual variability in the pharmacokinetics of methadone, a significant interaction with grapefruit juice in certain patients cannot be ruled out. Patients should be advised to seek immediate medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

The use of opiate agonists is contraindicated in patients with acute alcohol intoxication exhibiting depressed vital signs. The central nervous system depressant effects of opiate agonists may be additive with those of alcohol. Severe respiratory depression and death may occur. Therapy with opiate agonists should be administered cautiously in patients who might be prone to acute alcohol intake.

Opiate agonists have the potential to cause dependence and abuse. Tolerance as well as physical and psychological dependence can develop after prolonged use. Abrupt cessation, reduction in dosage, or administration of an opiate antagonist such as naloxone may precipitate withdrawal symptoms. In patients who have developed tolerance to an opiate agonist, overdosage can still produce respiratory depression and death, and cross-tolerance usually will occur with other agents in the class. Addiction-prone individuals, such as those with a history of alcohol or substance abuse, should be under careful surveillance or medical supervision when treated with opiate agonists. It may be prudent to refrain from dispensing large quantities of medication to these patients. After prolonged use or if dependency is suspected, withdrawal of opiate therapy should be undertaken gradually using a dosage-tapering schedule.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Foscarnet is nephrotoxic. Foscarnet crystals may deposit in renal tubules and capillaries, sometimes causing acute tubular necrosis and renal failure. Foscarnet may also concentrate in the urine and cause penile or vulvovaginal irritation. Adequate hydration is crucial to minimize the risk of renal damage and genital ulcerations. Generally, foscarnet should be administered by an infusion pump over 1 to 2 hours accompanied by hydration. The manufacturer recommends 750 to 1000 mL of normal saline or 5% dextrose solution prior to the first infusion of foscarnet to establish diuresis, then 500 mL (for 40 to 60 mg/kg dose of foscarnet) or 750 to 1000 mL (for 90 to 120 mg/kg dose of foscarnet) of hydration fluid concurrently with each subsequent foscarnet infusion. Patients who are dehydrated may be at increased risk for the development of nephrotoxicity and may benefit from additional hydration if tolerated.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Opiate agonists have the potential to cause dependence and abuse. Tolerance as well as physical and psychological dependence can develop after prolonged use. Abrupt cessation, reduction in dosage, or administration of an opiate antagonist such as naloxone may precipitate withdrawal symptoms. In patients who have developed tolerance to an opiate agonist, overdosage can still produce respiratory depression and death, and cross-tolerance usually will occur with other agents in the class. Addiction-prone individuals, such as those with a history of alcohol or substance abuse, should be under careful surveillance or medical supervision when treated with opiate agonists. It may be prudent to refrain from dispensing large quantities of medication to these patients. After prolonged use or if dependency is suspected, withdrawal of opiate therapy should be undertaken gradually using a dosage-tapering schedule.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Opioid analgesics are contraindicated in patients with known or suspected gastrointestinal obstruction, including paralytic ileus.

The hypoventilation associated with administration of opiate agonists, particularly by the intravenous route, can induce cerebral hypoxia and vasodilatation with resultant increase in intracranial pressure. Opiate agonists should not be used in patients with suspected or known head injury or increased intracranial pressure. Also, clinicians treating such patients should be aware that opiate agonists may interfere with the evaluation of CNS function, especially with respect to consciousness levels, respiratory status, and pupillary changes.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Narcotic (opioid) analgesic agents may prolong and/or worsen diarrhea associated with organisms that invade the intestinal mucosa, such as toxigenic Escherichia coli, Salmonella, Shigella, and pseudomembranous colitis due to broad-spectrum antibiotics. These agents decrease gastrointestinal motility, which may delay the excretion of infective gastroenteric organisms and/or their toxins. Other symptoms and complications such as fever, shedding of organisms, and extraintestinal illness may also be increased or prolonged. Therapy with opioids should be avoided or administered cautiously in patients with infectious diarrhea, particularly that due to pseudomembranous enterocolitis or enterotoxin-producing bacteria or if accompanied by high fever, pus, or blood in the stool.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Narcotic (opioid) analgesic agents increase smooth muscle tone in the gastrointestinal tract and decrease peristalsis, which can lead to elevated intraluminal pressure, spasm, and constipation following prolonged use. In patients with severe or acute inflammatory bowel disease, the decrease in colonic motility may induce toxic megacolon. Therapy with opioids should be administered cautiously in patients with gastrointestinal obstruction, constipation, inflammatory bowel disease, or recent gastrointestinal tract surgery. Gastrointestinal effects appear to be the most pronounced with morphine.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

Foscarnet may cause electrolyte disturbances, including hypocalcemia, hypo- or hyperphosphatemia, hypomagnesemia, and hypokalemia. Ionized serum calcium may also demonstrate a dose-dependent (and possibly rate-dependent) decrease that may not be reflected in total serum calcium. Patients should be instructed to report symptoms of low ionized calcium such as perioral tingling, numbness in the extremities, and paresthesias. Other electrolyte-related complications include tetany, seizures, and cardiac disturbances. Therapy with foscarnet should be administered cautiously in patients with preexisting fluid and electrolyte imbalance and those with underlying cardiac or neurologic abnormalities. Serum electrolyte levels should be closely monitored and managed in all patients treated with foscarnet.

The use of narcotic (opioid) analgesic agents is contraindicated in premature infants. These agents may cross the immature blood-brain barrier to a greater extent than in adults, resulting in disproportionate respiratory depression.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Foscarnet is eliminated primarily by the kidney. Patients with renal impairment may be at greater risk for dose-limiting nephrotoxicity and other adverse effects of foscarnet due to decreased drug clearance. Renal function should be closely monitored in all patients receiving therapy with foscarnet, and the dosage adjusted based on serum creatinine. Hydration is recommended to reduce the risk of nephrotoxicity. The manufacturer recommends 750 to 1000 mL of normal saline or 5% dextrose solution prior to the first infusion of foscarnet to establish diuresis, then 500 mL (for 40 to 60 mg/kg dose of foscarnet) or 750 to 1000 mL (for 90 to 120 mg/kg dose of foscarnet) of hydration fluid concurrently with each subsequent foscarnet infusion. Foscarnet should be used with caution in patients with abnormal renal function because reduced plasma clearance of foscarnet will result in elevated plasma levels. Foscarnet dosing must be individualized according to the patient's renal function status. The use of foscarnet is not recommended in patients with severe renal impairment indicated by a CrCl < 0.4 mL/min/kg and in those patients undergoing hemodialysis because dosage guidelines have not been established.

Opiate agonists may produce significant central nervous system and respiratory depression of varying duration, particularly when given in high dosages and/or by rapid intravenous administration. Apnea may result from decreased respiratory drive as well as increased airway resistance, and rigidity of respiratory muscles may occur during rapid IV administration or when these agents are used in the induction of anesthesia. At therapeutic analgesic dosages, the respiratory effects are usually not clinically important except in patients with preexisting pulmonary impairment. Therapy with opiate agonists should be avoided or administered with extreme caution and initiated at reduced dosages in patients with severe CNS depression; sleep apnea; hypoxia, anoxia, or hypercapnia; upper airway obstruction; chronic pulmonary insufficiency; a limited ventilatory reserve; or other respiratory disorders. In the presence of excessive respiratory secretions, the use of opiate agonists may also be problematic because they decrease ciliary activity and reduce the cough reflex. Caution is also advised in patients who may be at increased risk for respiratory depression, such as comatose patients or those with head injury, intracranial lesions, or intracranial hypertension. Clinical monitoring of pulmonary function is recommended, and equipment for resuscitation should be immediately available if parenteral or neuraxial routes are used. Naloxone may be administered to reverse clinically significant respiratory depression, which may be prolonged depending on the opioid agent, cumulative dose, and route of administration.

Opiate agonists can induce vasodilation and significant hypotension, particularly when given in high dosages and/or by rapid intravenous administration. Opiate analgesics cause vasodilatation that may exacerbate hypotension and hypoperfusion and, therefore, are contraindicated in circulatory shock. At therapeutic analgesic dosages, ambulatory patients are more likely to experience dizziness and hypotension than patients who are confined to bed. However, orthostatic hypotension may occur in supine patients upon rising. Therapy with opiate agonists should be administered cautiously and initiated at reduced dosages in patients with hypovolemia, or a predisposition to hypotension. When given by intramuscular or subcutaneous administration, clinicians should also be aware that impaired perfusion in these patients may prevent complete absorption of the drug. With repeated injections, an excessive amount may be absorbed suddenly if normal circulation is reestablished.

Patients with Addison's disease may have increased risk of respiratory depression and prolonged CNS depression associated with the use of narcotic (opioid) analgesic agents. Conversely, these agents may cause or potentiate adrenal insufficiency. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with adrenocortical insufficiency. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

The use of foscarnet is associated with hematologic toxicities, most commonly anemia and granulocytopenia. Thrombocytopenia has been reported rarely. Therapy with foscarnet should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Routine blood counts are recommended.

Opiate agonists have cholinergic activity. Large doses and/or rapid intravenous administration may produce bradycardia and arrhythmias via stimulation of medullary vagal nuclei. Therapy with opiate agonists should be administered cautiously in patients with a history of arrhythmias. Clinical monitoring of cardiovascular status is recommended during therapy.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

The use of foscarnet is associated with hematologic toxicities, most commonly anemia and granulocytopenia. Thrombocytopenia has been reported rarely. Therapy with foscarnet should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Routine blood counts are recommended.

Narcotic (opioid) analgesic agents are extensively metabolized by the liver, and several of them (e.g., codeine, hydrocodone, meperidine, methadone, morphine, propoxyphene) have active metabolites that are further converted to inactive substances. The serum concentrations of these agents and their metabolites may be increased and the half-lives prolonged in patients with impaired hepatic function. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with liver disease. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

The use of foscarnet is associated with hematologic toxicities, most commonly anemia and granulocytopenia. Thrombocytopenia has been reported rarely. Therapy with foscarnet should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Routine blood counts are recommended.

Opioid agonists may cause spasm of the sphincter of Oddi, which may increase biliary tract pressure. Other opioid-induced effects may include a reduction in biliary and pancreatic secretions and transient elevations in serum amylase. Patients with biliary tract disease (including acute pancreatitis) should be regularly evaluated for worsening symptoms. Therapy with opioids should be administered cautiously in patients with biliary tract disease, gallbladder disease, or acute pancreatitis.

Although narcotic (opioid) analgesic agents are generally metabolized by the liver, renal impairment can alter the elimination of these agents and their metabolites (some of which are pharmacologically active), resulting in drug accumulation and increased risk of toxicity. Therapy with opioids should be administered cautiously and initiated at reduced dosages in patients with significantly impaired renal function. Subsequent doses should be titrated based on individual response rather than a fixed dosing schedule.

Narcotic (opioid) analgesic agents may increase the frequency of seizures in patients with seizure disorders, may increase the risk of seizures occurring in other clinical settings associated with seizures, and, at higher dosages, have been reported to induce seizures in patients without history of seizures. Patients with history of seizure disorders should be regularly evaluated for worsened seizure control during therapy. Prolonged meperidine use may increase the risk of toxicity (e.g., seizures) from the accumulation of the active metabolite (normeperidine).

The use of foscarnet is associated with hematologic toxicities, most commonly anemia and granulocytopenia. Thrombocytopenia has been reported rarely. Therapy with foscarnet should be administered cautiously in patients with preexisting blood dyscrasias or bone marrow suppression. Routine blood counts are recommended.

Narcotic (opioid) analgesic agents may inhibit the urinary voiding reflex and increase the tone of the vesical sphincter in the bladder. Acute urinary retention requiring catheterization may occur, particularly in patients with prostatic hypertrophy or urethral stricture and in older adult patients. These agents may also decrease urine production via direct effects on the kidney and central stimulation of the release of vasopressin. Therapy with opioids should be administered cautiously in patients with or predisposed to urinary retention and/or oliguria. The effects on smooth muscle tone appear to be the most pronounced with morphine.