Drug Interactions between Buprenex and Halfan

GENERALLY AVOID: Grapefruit juice may increase the plasma concentration of halofantrine. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. After administration of 500 mg with 250 mL regular-strength grapefruit juice daily for 3 days, average halofantrine AUC increased 2.8-fold and peak plasma concentrations increased 3.2-fold, compared to water, in healthy subjects (n=12). QT interval prolongation increased from an average of 17 ms with water to 31 ms with grapefruit juice. Halofantrine, even at recommended doses, can cause dose-related prolongation of the QT interval, resulting in an elevated risk of potentially fatal ventricular arrhythmias including ventricular tachycardia and torsade de pointes.

ADJUST DOSING INTERVAL: The presence of food may increase the absorption and toxicity of halofantrine. Peak plasma concentrations increased seven-fold and AUC increased three-fold in healthy subjects when halofantrine was administered with high-fat food.

MANAGEMENT: The authors of the study recommend that grapefruit juice be avoided during halofantrine therapy. The manufacturer recommends performing an ECG before initiating halofantrine therapy and cardiac monitoring during and for 8 to 12 hours after completion of therapy. Halofantrine should be taken on an empty stomach at least 1 hour before or 2 hours after food.

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GENERALLY AVOID: Concomitant use of buprenorphine with benzodiazepines or other central nervous system (CNS) depressants (e.g., nonbenzodiazepine sedatives/hypnotics, anxiolytics, muscle relaxants, general anesthetics, antipsychotics, other opioids, alcohol) may increase the risk of buprenorphine overdose, severe respiratory depression, coma, and death. Reported cases have primarily occurred in the setting of buprenorphine maintenance treatment for opiate addiction, and many, but not all, involved abuse or misuse of buprenorphine including intravenous self-injection. The mechanism of interaction probably involves some degree of additive pharmacologic effects. Preclinical studies also suggest that benzodiazepines can alter the usual ceiling effect on buprenorphine-induced respiratory depression and render the respiratory effects of buprenorphine appear similar to those of full opioid agonists. Coadministration of buprenorphine with some CNS depressants such as alcohol, benzodiazepines, and phenothiazines may also increase the risk of hypotension.

MANAGEMENT: The use of opioids in conjunction with benzodiazepines or other CNS depressants should generally be avoided unless alternative treatment options are inadequate. If coadministration is necessary, the dosage and duration of each drug should be limited to the minimum required to achieve desired clinical effect. Patients should be monitored closely for signs and symptoms of respiratory depression and sedation, and advised to avoid driving or operating hazardous machinery until they know how these medications affect them. Extreme caution is advised when prescribing buprenorphine to patients who are addicted to opioids and also abusing benzodiazepines or alcohol. Due to potential risk of overdose and death, dependence on sedative-hypnotics such as benzodiazepines or alcohol is considered a relative contraindication for office-based buprenorphine treatment of opioid addiction. For patients who have been receiving extended therapy with both an opioid and a benzodiazepine and require discontinuation of either medication, a gradual tapering of dose is advised, since abrupt withdrawal may lead to withdrawal symptoms. Severe cases of benzodiazepine withdrawal, primarily in patients who have received excessive doses over a prolonged period, may result in numbness and tingling of extremities, hypersensitivity to light and noise, hallucinations, and epileptic seizures.

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