Drug Interactions between emtricitabine / lopinavir / ritonavir / tenofovir and eszopiclone

ADJUST DOSE: Coadministration with potent inhibitors of CYP450 3A4 may increase the plasma concentrations of both zopiclone and its pharmacologically active S(-) enantiomer, eszopiclone. Zopiclone has been shown in vitro to be metabolized by CYP450 3A4 and CYP450 2C8, while eszopiclone is primarily metabolized by CYP450 3A4 and 2E1 via demethylation and oxidation. In 18 healthy subjects, administration of a single 3 mg dose of eszopiclone with the potent CYP450 3A4 inhibitor ketoconazole (400 mg daily for 5 days) increased eszopiclone half-life, peak plasma concentration (Cmax) and systemic exposure (AUC) by 1.3-, 1.4- and 2.2-fold, respectively. In 10 healthy young subjects, itraconazole 200 mg daily given for 4 days increased the Cmax and AUC of a single 7.5 mg dose of zopiclone by 29% and 73%, respectively, and prolonged its half-life by 40%. The pharmacokinetics of eszopiclone were not reported in this study. A case report describes an 86-year-old woman who experienced morning drowsiness during coadministration of zopiclone and nefazodone, a known potent CYP450 3A4 inhibitor. Zopiclone plasma concentrations were measured both during and after withdrawal of nefazodone therapy. Following discontinuation of nefazodone due to lack of therapeutic effect, the plasma concentration of S(-) zopiclone decreased from 107 to 16.9 ng/mL, and that of R(+) zopiclone decreased from 20.6 to 1.45 ng/mL.

MANAGEMENT: Due to increased risk of next-day psychomotor impairment, the dosages of eszopiclone and zopiclone should be reduced when used with potent CYP450 3A4 inhibitors. The manufacturers recommend that total dose of eszopiclone not exceed 2 mg. An initial dose of 3.75 mg is recommended for zopiclone, which may be increased up to 5 mg if clinically indicated. Patients should be advised to avoid driving or operating hazardous machinery until they know how these medications affect them, preferably at least 12 hours after administration of the hypnotic.

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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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