Drug Interactions between CPM-PSE DM Drops and propoxyphene

MONITOR CLOSELY: Sedatives, tranquilizers, muscle relaxants, antidepressants, and other central nervous system (CNS) depressants may have additive CNS- and/or respiratory-depressant effects with propoxyphene. Misuse of propoxyphene, either alone or in combination with other CNS depressants, has been a major cause of drug-related deaths, particularly in patients with a history of emotional disturbances, suicidal ideation, or alcohol and drug abuse. In a large Canadian study, propoxyphene use was also associated with a 60% increased risk of hip fracture in the elderly, and the risk was further increased by concomitant use of psychotropic agents (sedatives, antidepressants, neuroleptics), presumably due to additive psychomotor impairment. Therefore, these drugs may constitute a dangerous combination in certain susceptible populations. Pharmacokinetically, propoxyphene is an inhibitor of CYP450 2D6 and may increase the plasma concentrations of many psychotropic agents that are metabolized by the isoenzyme such as phenothiazines, haloperidol, risperidone, phenobarbital, and some tricyclic antidepressants and serotonin reuptake inhibitors.

MANAGEMENT: Caution is advised if propoxyphene is used with sedatives, tranquilizers, muscle relaxants, antidepressants, and other CNS depressants, particularly in the elderly and in patients with a history of emotional disturbances, suicidal ideation, or alcohol and drug abuse. Dosage reductions may be appropriate. Patients should be monitored for potentially excessive or prolonged CNS and respiratory depression and other CNS adverse effects. Patients should be warned not to exceed recommended dosages, to avoid alcohol, and to avoid activities requiring mental alertness until they know how these agents affect them.

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MONITOR: Central nervous system- and/or respiratory-depressant effects may be additively or synergistically increased in patients taking multiple drugs that cause these effects, especially in elderly or debilitated patients. Sedation and impairment of attention, judgment, thinking, and psychomotor skills may increase.

MANAGEMENT: During concomitant use of these drugs, patients should be monitored for potentially excessive or prolonged CNS and respiratory depression. Cautious dosage titration may be required, particularly at treatment initiation. 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: Coadministration with CYP450 2D6 inhibitors may increase the plasma concentrations of dextromethorphan in patients who are extensive metabolizers of this isoenzyme (approximately 93% of Caucasians and more than 98% of Asians and individuals of African descent). The proposed mechanism is inhibition of the CYP450 2D6-mediated O-demethylation of dextromethorphan. Increased plasma concentrations increase the risk of dextromethorphan-related adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome. Coadministration of dextromethorphan (60 mg orally, once) with the CYP450 2D6 inhibitor panobinostat (20 mg orally once a day on days 3, 5, and 8) in 14 patients with advanced cancer had a highly variable effect on dextromethorphan levels, increasing the peak plasma concentration (Cmax) of dextromethorphan by 20% to 200%, and total systemic exposure (AUC 0 to infinity) by 20% to 130%, compared to dextromethorphan given alone. In addition, multiple doses of the potent CYP450 2D6 inhibitor cinacalcet (50 mg daily), increased the AUC of a single 30 mg dextromethorphan dose by 11-fold in extensive metabolizers of this isoenzyme. The moderate CYP450 2D6 inhibitor asunaprevir, given at 200 mg twice daily, also increased Cmax and AUC of a single 30 mg dose of dextromethorphan by 2.7- and 3.9-fold, respectively, in 17 study subjects.

MANAGEMENT: Caution should be exercised if these drugs must be used together. Patients should be monitored for signs of dextromethorphan adverse effects (e.g., agitation, confusion, tremor, insomnia, diarrhea, and respiratory depression) and serotonin syndrome, and advised to notify their health care professional if these adverse effects develop or worsen. Dose reduction of dextromethorphan may also be required.

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