Drug Interaction Report

MONITOR: Orlistat may theoretically reduce the gastrointestinal absorption and therapeutic efficacy of antiretroviral agents. The mechanism may involve retention of lipophilic medicines in the gastrointestinal tract or reduced gastrointestinal tract transit time. Data have been reported for efavirenz and lopinavir. Other antiretroviral agents may also be affected.

MANAGEMENT: The potential reduction in antiretroviral efficacy should be considered before initiating treatment with orlistat. Patients who take antiretroviral medications should be advised to consult their physician before using the non-prescription brand of orlistat.

ADJUST DOSING INTERVAL: According to the manufacturer, coadministration with a meal high in calories, fat, and protein reduces the absorption of indinavir. In ten patients given indinavir in this manner, the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of indinavir decreased by an average of 84% and 77%, respectively. In contrast, grapefruit juice may have only minor effects on the oral bioavailability of indinavir. The manufacturer's package labeling states that administration of a single 400 mg dose of indinavir with 8 oz. of grapefruit juice decreased indinavir AUC by an average of 26%. Likewise, a study consisting of 14 HIV-infected subjects found no uniform nor significant changes in steady-state indinavir AUC during administration with double-strength grapefruit juice compared to water. There was, however, a delay in absorption (Tmax) due to grapefruit juice that is unlikely to be of clinical significance.

MANAGEMENT: To ensure maximal oral absorption, indinavir should be administered without food but with water 1 hour before or 2 hours after a meal. Alternatively, indinavir may be administered with other liquids such as skim milk, juice, coffee, or tea, or with a light meal (e.g., dry toast with jelly, juice, and coffee with skim milk and sugar; corn flakes, skim milk and sugar).