Drug Interactions between hyoscyamine / methenamine / methylene blue / phenyl salicylate / sodium biphosphate and Polycitra

CONTRAINDICATED: The following interaction does not apply to all products containing potassium citrate. It is applicable to certain oral solid formulations of potassium citrate used primarily for potassium supplementation, and the prescriber should consult the individual product labeling for more specific information and guidance.

Concomitant use of agents with anticholinergic properties (e.g., antihistamines, antispasmodics, neuroleptics, phenothiazines, skeletal muscle relaxants, tricyclic antidepressants, the class IA antiarrhythmic disopyramide) may potentiate the risk of upper gastrointestinal injury associated with oral solid formulations of potassium citrate. The proposed mechanism involves increased gastrointestinal transit time due to reduction of stomach and intestinal motility by anticholinergic agents, thereby creating a high localized concentration of potassium ions in the region of a dissolving tablet or capsule and increasing the contact time with GI mucosa. Solid formulations of potassium chloride have been associated with upper GI bleeding and small bowel ulceration, stenosis, perforation, and obstruction. Deaths have been reported rarely. In clinical studies, short-term coadministration of wax-matrix or microencapsulated formulations of potassium chloride and potassium citrate at high dosages in combination with an anticholinergic agent such as glycopyrrolate resulted in more frequent and more serious endoscopic lesions than potassium therapy alone. However, the lesions were not accompanied by bleeding or epigastric symptoms. Some investigators have suggested a higher risk of upper GI lesions with wax-matrix than microencapsulated formulations, although existing data are limited and conflicting.

MANAGEMENT: The use of oral solid formulations of potassium citrate is considered contraindicated in patients receiving agents with anticholinergic properties at sufficient doses to exert anticholinergic effects. A liquid formulation of potassium citrate should be considered. Patients prescribed a solid oral formulation should be advised to discontinue potassium therapy and contact their physician if they experience potential symptoms of upper GI injury such as severe vomiting, abdominal pain, distention, and gastrointestinal bleeding.

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MONITOR CLOSELY: The following interaction applies only to products containing sodium biphosphate that are used for bowel cleansing. It does not apply to products containing sodium biphosphate that are used for other, non-laxative related purposes.

Coadministration with agents that affect renal function or perfusion such as diuretics, ACE inhibitors, angiotensin receptor blockers, and nonsteroidal anti-inflammatory drugs (NSAIDs) may increase the risk of acute phosphate nephropathy associated with the use of bowel-cleansing phosphate solutions. The risk and/or severity of fluid and electrolyte disturbances may also be increased, which can lead to serious adverse events including cardiac arrhythmias, seizures, and renal impairment. Acute phosphate nephropathy is a rare adverse event that presents as acute renal failure with minimal proteinuria and a bland urine sediment. Renal biopsy findings are consistent with nephrocalcinosis and include acute and/or chronic renal tubular injury, calcium-phosphate crystal deposition in the distal tubules and collecting ducts, and no other pattern of histological injury. The risk of acute phosphate nephropathy stems from the large phosphate load, fluid shifts, and decreased intravascular volume, which can be exacerbated in the presence of medications that affect renal perfusion or function. In reported cases, acute renal failure was typically diagnosed within two to five months of colonoscopy. These cases often resulted in permanent impairment of renal function, some requiring long-term dialysis.

MANAGEMENT: Caution is advised when bowel-cleansing phosphate preparations are prescribed in patients treated with agents that affect renal function or perfusion, particularly if they are frail or elderly. Bowel-cleansing phosphate preparations should not be used in patients who have impaired renal function or perfusion, dehydration, or uncorrected electrolyte abnormalities. In patients at risk for acute phosphate nephropathy, baseline and postprocedure labs including serum electrolytes, calcium, phosphate, BUN, and creatinine should be performed. Patients should be advised not to exceed the recommended dosage of their bowel-cleansing preparation and to drink sufficient quantities of clear fluids during before, during, and after bowel cleansing. Limited data suggest that administration of an electrolyte rehydration solution may attenuate the electrolyte abnormalities and hypovolemia. Hospitalization and intravenous fluid hydration may be appropriate for frail or elderly patients who may be unable to drink an adequate volume of fluid.

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GENERALLY AVOID: Agents that can alkalinize the urine such as thiazide diuretics, carbonic anhydrase inhibitors, and antacids may decrease the antibacterial effectiveness of methenamine by inhibiting its conversion to formaldehyde. Methenamine is most effectively converted in an acidic milieu of pH less than 5.5.

MANAGEMENT: Concomitant use of methenamine-containing preparations with thiazide diuretics, carbonic anhydrase inhibitors, or large doses of antacids should be avoided if possible. Otherwise, frequent urine pH testing may be considered. Some methenamine products may be used with antacids if dosing times are separated by at least one hour. Consult the manufacturer's product labeling for specific recommendations.

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MONITOR: Agents that cause urinary alkalinization can reduce serum salicylate concentrations in patients receiving anti-inflammatory dosages of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to increased urinary pH, resulting in increased renal salicylate clearance especially above urine pH of 7. This interaction is sometimes exploited in the treatment of salicylate toxicity.

MANAGEMENT: Patients treated chronically with urinary alkalinizers and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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GENERALLY AVOID: Agents that can alkalinize the urine such as thiazide diuretics, carbonic anhydrase inhibitors, and antacids may decrease the antibacterial effectiveness of methenamine by inhibiting its conversion to formaldehyde. Methenamine is most effectively converted in an acidic milieu of pH less than 5.5.

MANAGEMENT: Concomitant use of methenamine-containing preparations with thiazide diuretics, carbonic anhydrase inhibitors, or large doses of antacids should be avoided if possible. Otherwise, frequent urine pH testing may be considered. Some methenamine products may be used with antacids if dosing times are separated by at least one hour. Consult the manufacturer's product labeling for specific recommendations.

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MONITOR: Agents that cause urinary alkalinization can reduce serum salicylate concentrations in patients receiving anti-inflammatory dosages of aspirin or other salicylates. The mechanism involves reduction in salicylate renal tubular reabsorption due to increased urinary pH, resulting in increased renal salicylate clearance especially above urine pH of 7. This interaction is sometimes exploited in the treatment of salicylate toxicity.

MANAGEMENT: Patients treated chronically with urinary alkalinizers and large doses of salicylates (i.e. 3 g/day or more) should be monitored for potentially diminished or inadequate analgesic and anti-inflammatory effects, and the salicylate dosage adjusted if necessary.

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