Drug Interactions between AccessPak for HIV PEP Expanded with Kaletra and donepezil / memantine

MONITOR: Since acetylcholinesterase inhibitors can cause bradycardia and heart block due to vagotonic effects on the sinoatrial and atrioventricular nodes, additive effects may occur with other agents that also possess bradycardic effects such as beta-blockers, calcium channel blockers, digitalis, some protease inhibitors (atazanavir, lopinavir-ritonavir, saquinavir), amiodarone, dronedarone, moricizine, lacosamide, and mefloquine. A group of French investigators conducted a retrospective analysis of spontaneous reports in the French Pharmacovigilance Database concerning adverse drug reactions (ADRs) associated with use of the acetylcholinesterase inhibitors donepezil, galantamine, and rivastigmine. Two hundred and five cases of potential drug-drug interaction with bradycardic drugs (beta-blockers, calcium channel blockers, amiodarone, digoxin) were identified, 73 of which were associated with serious ADRs including five deaths due to syncope, bradycardia, arrhythmia, or cardiac arrest. However, no details on the individual cases such as patient characteristics or concomitant risk factors were provided, making the contribution of a potential drug interaction difficult to evaluate. The remainder of the cases were of no apparent clinical consequences. In contrast, a phase III trial of donepezil consisting of 1035 patients reported no significant increase in risk ratios for bradycardia during concomitant use of beta-blockers, nondihydropyridine calcium channel blockers, or digoxin.

MANAGEMENT: Caution is advised if acetylcholinesterase inhibitors are used concomitantly with bradycardic drugs. Patients with underlying structural heart disease, preexisting conduction system abnormalities, ischemic heart disease, or cardiomyopathies may be at increased risk for developing cardiac conduction disturbances and atrioventricular block. Patients should be advised to notify their physician if they experience dizziness, lightheadedness, fainting, or irregular heartbeat.

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MONITOR: Coadministration with ritonavir, with or without lopinavir, has been suggested in postmarketing reports to increase the proximal tubular intracellular concentrations of tenofovir and potentiate the risk of tenofovir-induced nephrotoxicity. The proposed mechanism is ritonavir inhibition of tenofovir renal tubular secretion into the urine via multidrug resistance protein MRP2. Analysis of data from a compassionate access study in which 271 patients with advanced HIV disease received the combination for a mean duration of 63 weeks revealed no clinically significant nephrotoxicity associated with coadministration. However, there have been case reports of renal failure associated with acute tubular necrosis, Fanconi's syndrome, and nephrogenic diabetes insipidus in patients treated with tenofovir disoproxil fumarate in combination with ritonavir. Some patients had incomplete recovery of renal function more than a year after cessation of tenofovir therapy. Ritonavir given in combination with lopinavir has also been reported to modestly increase the plasma concentrations of tenofovir. In contrast, both slight decreases and no change in lopinavir and ritonavir concentrations have been reported.

MANAGEMENT: Caution is advised if tenofovir disoproxil fumarate is prescribed with ritonavir. Renal function should be monitored regularly, including surveillance for signs of tubulopathy such as glycosuria, acidosis, increases in serum creatinine level, electrolyte disturbances (e.g., hypokalemia, hypophosphatemia), and proteinuria. The same precaution may be applicable during therapy with other protease inhibitors based on their similar pharmacokinetic profile, although clinical data are lacking. Nelfinavir reportedly does not alter the pharmacokinetics of tenofovir, or vice versa. Tenofovir administration should be discontinued promptly if nephropathy develops.

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MONITOR: Coadministration with ritonavir, with or without lopinavir, has been suggested in postmarketing reports to increase the proximal tubular intracellular concentrations of tenofovir and potentiate the risk of tenofovir-induced nephrotoxicity. The proposed mechanism is ritonavir inhibition of tenofovir renal tubular secretion into the urine via multidrug resistance protein MRP2. Analysis of data from a compassionate access study in which 271 patients with advanced HIV disease received the combination for a mean duration of 63 weeks revealed no clinically significant nephrotoxicity associated with coadministration. However, there have been case reports of renal failure associated with acute tubular necrosis, Fanconi's syndrome, and nephrogenic diabetes insipidus in patients treated with tenofovir disoproxil fumarate in combination with ritonavir. Some patients had incomplete recovery of renal function more than a year after cessation of tenofovir therapy. Ritonavir given in combination with lopinavir has also been reported to modestly increase the plasma concentrations of tenofovir. In contrast, both slight decreases and no change in lopinavir and ritonavir concentrations have been reported.

MANAGEMENT: Caution is advised if tenofovir disoproxil fumarate is prescribed with ritonavir. Renal function should be monitored regularly, including surveillance for signs of tubulopathy such as glycosuria, acidosis, increases in serum creatinine level, electrolyte disturbances (e.g., hypokalemia, hypophosphatemia), and proteinuria. The same precaution may be applicable during therapy with other protease inhibitors based on their similar pharmacokinetic profile, although clinical data are lacking. Nelfinavir reportedly does not alter the pharmacokinetics of tenofovir, or vice versa. Tenofovir administration should be discontinued promptly if nephropathy develops.

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Coadministration with inhibitors of CYP450 2D6 and/or 3A4 may increase the plasma concentrations of donepezil, which is primarily metabolized by these isoenzymes. In a 7-day crossover study in 18 healthy volunteers, the potent CYP450 3A4 inhibitor ketoconazole (200 mg once daily) increased the mean peak plasma concentration (Cmax) and systemic exposure (AUC) of donepezil (5 mg once daily) by approximately 36% each. The clinical relevance of these increases is unknown. A prolonged duration of monitoring for adverse effects may be required depending on the elimination half-life of the concomitant drug. For example, it should be noted that rolapitant, a moderate CYP450 2D6 inhibitor, can increase plasma concentrations and the risk of adverse effects of donepezil for at least 28 days after administration of rolapitant.

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Theoretically, the concomitant administration of memantine and other drugs that undergo active renal tubular secretion may result in altered plasma levels of both drugs. The clinical significance is unknown. When hydrochlorothiazide/triamterene and memantine were coadministered in a clinical study, the bioavailability of hydrochlorothiazide decreased by 20% and there was no change in memantine or triamterene bioavailability.

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