Drug Interactions between Omeclamox-Pak and saquinavir

CONTRAINDICATED: Saquinavir 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 59 healthy volunteers aged 18 to 55 years who were administered saquinavir/ritonavir at a therapeutic dosage of 1000 mg/100 mg twice daily and a supratherapeutic dosage of 1500 mg/100 mg twice daily, the maximum mean QT prolongation (QTcS; study-specific QT interval correction) on treatment day 3 was 18.9 msec for the lower dosage and 30.2 msec for the supratherapeutic dosage, compared to 12.2 msec for the active control (moxifloxacin 400 mg). The majority of subjects (89% and 80% in the therapeutic and supratherapeutic groups, respectively) had a QTcS less than 450 msec, and none had a QTc interval exceeding the potentially clinically relevant threshold of 500 msec. 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 ritonavir-boosted saquinavir with other drugs that can prolong the QT interval is considered contraindicated.

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MONITOR: The concomitant administration of some proton pump inhibitors with saquinavir, with or without ritonavir, may significantly increase exposure to saquinavir. When omeprazole 40 mg once daily and saquinavir/ritonavir 1000 mg/100 mg twice daily were administered to healthy subjects (n=18), the steady-state area under the concentration-time curve (AUC) and maximum plasma concentrations (Cmax) of saquinavir were increased by an average of 82 % (range, 37% to 234%) and 75 % (range, 31% to 234%), respectively, compared to saquinavir/ritonavir. Ritonavir concentrations were not changed significantly. The mechanism is unknown.

MANAGEMENT: Clinical and laboratory monitoring for saquinavir toxicity is recommended during concurrent use of a proton pump inhibitor. According to some authorities, a dose reduction for saquinavir may be considered.

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Although some in vitro data indicate synergism between macrolide antibiotics and penicillins, other in vitro data indicate antagonism. When these drugs are given together, neither has predictable therapeutic efficacy. Data are available for erythromycin, although theoretically this interaction could occur with any macrolide. Except for monitoring of the effectiveness of antibiotic therapy, no special precautions appear to be necessary.

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Clarithromycin may increase and prolong the omeprazole plasma concentration. The mechanism may be related to clarithromycin inhibition of hepatic cytochrome P450 enzymes responsible for omeprazole metabolism. Coadministration of omeprazole may result in an increase in clarithromycin and 14-(R)-hydroxyclarithromycin plasma concentrations. These increases may be due to the effect of omeprazole on gastric pH.

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