Drug Interactions between Subsys and UroAv-81

CONTRAINDICATED: Coadministration of monoamine oxidase inhibitors (MAOIs) with certain opioids has been associated with rare reports of severe and fatal adverse reactions. There appear to be two types of interaction, an excitatory and a depressive one. Symptoms of the excitatory reaction may include agitation, headache, diaphoresis, hyperpyrexia, flushing, shivering, myoclonus, rigidity, tremor, diarrhea, hypertension, tachycardia, seizures, and coma. Death has occurred in some cases. The exact mechanism of interaction is unknown, but may involve excessive serotonergic activity in the central nervous system (i.e., serotonin syndrome). The interaction is unpredictable and has been reported primarily with meperidine or fentanyl and various MAOIs including phenelzine, tranylcypromine, linezolid, moclobemide, and selegiline. Fatal hyperpyrexia and hypertension have also been observed in animal studies with meperidine and phenelzine or furazolidone. In contrast, symptoms of the depressive reaction probably stem from potentiation of CNS effects by MAOIs and include respiratory depression, cyanosis, hypotension, and coma.

MANAGEMENT: Meperidine and fentanyl should not be used with MAOIs or other agents that possess MAOI activity (e.g., furazolidone, linezolid, methylene blue, procarbazine). Some manufacturers of MAOIs also contraindicate the concomitant use of propoxyphene and methadone due to their possible serotonergic effects. At least 14 days should elapse between discontinuation of MAOI therapy and initiation of treatment with these opioids. Although morphine may also have significant CNS interactions with MAOIs, it is generally considered a safer alternative in patients treated with MAOIs who require a narcotic analgesic. A sensitivity test should be performed in which repeated, small, incremental doses of morphine are administered over the course of several hours while overall clinical status and vital signs are carefully monitored.

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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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MONITOR: Coadministration of opioids with anticholinergic agents may result in additive central nervous system (CNS), gastrointestinal, and genitourinary effects. The risk and/or severity of adverse effects such as sedation, dizziness, confusion, cognitive and psychomotor impairment, dry mouth, constipation, and urinary retention may increase. Severe constipation may lead to paralytic ileus in some cases.

MANAGEMENT: Caution and close monitoring of central nervous system, gastrointestinal, and genitourinary adverse effects are recommended when opioids are used with anticholinergic agents. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

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MONITOR: 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.

The risk of seizures induced by the use of bowel cleansing preparations may be increased in patients on concomitant medications that can lower the seizure threshold such as selective serotonin reuptake inhibitors (SSRI antidepressants or anorectics), monoamine oxidase inhibitors, neuroleptic agents, central nervous system stimulants, opioids, tricyclic antidepressants, other tricyclic compounds (e.g., cyclobenzaprine, phenothiazines), systemic steroids, carbapenems, cholinergic agents, fluoroquinolones, interferons, chloroquine, mefloquine, lindane, and theophylline. Rare cases of generalized tonic-clonic seizures and/or loss of consciousness in association with low serum osmolality and electrolyte abnormalities (e.g., hyponatremia, hypokalemia, hypocalcemia, hypomagnesemia) have been reported with the use of bowel cleansing products in patients with no prior history of seizures. The condition resolved with correction of fluid and electrolyte abnormalities.

MANAGEMENT: Caution is advised when bowel cleansing preparations are prescribed in patients treated with agents that can lower the seizure threshold. Bowel cleansing preparations should not be used if these patients have impaired renal function or perfusion, dehydration, or uncorrected electrolyte abnormalities. Baseline and postprocedure labs including serum electrolytes, calcium, phosphate, BUN, and creatinine should be considered, particularly in the elderly. Patients should be advised not to exceed the recommended dosage of their bowel cleansing preparation and to drink sufficient quantities of clear fluids before, during, and after the bowel preparation process. Administration of an electrolyte rehydration solution may help attenuate the electrolyte abnormalities and hypovolemia.

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