Drug Interactions between AccessPak for HIV PEP Expanded with Kaletra and Zubsolv

MONITOR: Coadministration with inhibitors of CYP450 3A4 may increase the plasma concentrations and pharmacologic effects of buprenorphine, which is partially metabolized (approximately 30%) by the isoenzyme. The interaction appears to be dependent, in part, on the route of administration of buprenorphine. When administered transdermally, buprenorphine peak plasma concentration (Cmax) and systemic exposure (AUC) were not significantly affected by ketoconazole, a potent CYP450 3A4 inhibitor. However, it was reported in another study that ketoconazole increased the Cmax and AUC of buprenorphine (route unspecified) by approximately 70% and 50%, respectively, and to a lesser extent, of the metabolite norbuprenorphine. The interaction has also been reported with atazanavir/ritonavir. A case series describes three patients who experienced excessive opiate effects of buprenorphine during concomitant antiretroviral therapy with atazanavir, ritonavir, and various nucleoside reverse transcriptase inhibitors. Two of the patients had been on their antiretroviral regimen for several months and reported doped-up feeling, dizziness, and feeling high following initiation of buprenorphine 8 mg/day. The dosage was reduced to 8 mg every other day. One was maintained on this dosage while the other had dosage increased up to 12 mg/day, whereupon he developed hypersomnolence but managed to maintain that dosage. The third patient had been inducted with buprenorphine and titrated to a stable dose of 14 mg/day for two days prior to beginning antiretroviral therapy. The next day, the patient complained of daytime somnolence and decreased mental functioning. His buprenorphine dosage was decreased to 8 mg/day, and he developed tolerance to the sedative effects within 7 days.

MANAGEMENT: Caution is advised if buprenorphine is prescribed with CYP450 3A4 inhibitors. Induction with buprenorphine should begin at a reduced dosage, and dosage escalation should occur more slowly to allow for assessment of opiate effects and development of patient tolerance. In patients who are already stabilized on buprenorphine, pharmacologic response and vital signs should be monitored more closely whenever a CYP450 3A4 inhibitor is added to or withdrawn from therapy, and the buprenorphine dosage adjusted as necessary. Ambulatory patients should be counseled to avoid hazardous activities requiring complete 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. Patients should seek medical attention if potential signs and symptoms of toxicity occur such as dizziness, confusion, fainting, extreme sedation, bradycardia, slow or difficult breathing, and shortness of breath.

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GENERALLY AVOID: Lopinavir in combination with ritonavir may cause dose-related prolongation of the QT interval. Theoretically, coadministration with other agents that can prolong the QT interval may result in additive effects and increased risk of ventricular arrhythmias including torsade de pointes and sudden death. In a study of 39 healthy adults who were administered lopinavir-ritonavir at a therapeutic dosage of 400 mg-100 mg twice daily and a supratherapeutic dosage of 800 mg-200 mg twice daily, the maximum mean time-matched difference in QTcF interval from placebo (after baseline correction) was 5.3 msec for the lower dosage and 15.2 msec for the supratherapeutic dosage in the 12 hours post-dose on treatment day 3 when exposures were approximately 1.5 and 3-fold higher, respectively, than those observed with recommended once-daily or twice-daily dosages of lopinavir-ritonavir at steady state. No subject experienced an increase in QTcF greater than 60 msec from baseline or a QTcF interval exceeding the potentially clinically relevant threshold of 500 msec. There have been cases of QT interval prolongation and torsade de pointes arrhythmia during postmarketing use of lopinavir-ritonavir, although causality could not be established. In general, the risk of an individual agent or a combination of agents causing ventricular arrhythmia in association with QT prolongation is largely unpredictable but may be increased by certain underlying risk factors such as congenital long QT syndrome, cardiac disease, and electrolyte disturbances (e.g., hypokalemia, hypomagnesemia). In addition, the extent of drug-induced QT prolongation is dependent on the particular drug(s) involved and dosage(s) of the drug(s).

MANAGEMENT: Coadministration of lopinavir-ritonavir with other drugs that can prolong the QT interval should generally be avoided. Patients treated with any medication that can cause QT prolongation should be advised to seek prompt medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

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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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