Drug Interactions between Biltricide and clarithromycin

ADJUST DOSING INTERVAL: Administration with food increases the oral bioavailability of praziquantel. The mechanism has not been described. In nine healthy volunteers, administration of praziquantel (1800 mg single oral dose) following a high-fat meal increased the mean praziquantel peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) by 243% and 180%, respectively, compared to administration under fasting conditions. Administration with a high-carbohydrate meal increased these values by 515% and 271%, respectively, compared to fasting. Overall, the relative bioavailability was increased by a factor of 2.72 and 3.98 with the high-fat and high-carbohydrate meals, respectively. The time to reach peak concentration (Tmax) and elimination half-life (T1/2) were not significantly altered.

Coadministration with grapefruit juice may increase the oral bioavailability of praziquantel. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall induced by certain compounds present in grapefruit. In 18 healthy volunteers, administration of praziquantel (1800 mg single oral dose) with 250 mL of commercially squeezed grapefruit juice resulted in increases in the mean praziquantel Cmax and AUC of 63% and 90%, respectively, compared to administration with water. The Tmax and T1/2 were not significantly altered. The pharmacokinetics of praziquantel were subject to a high degree of interpatient variability with and without grapefruit juice.

MANAGEMENT: To ensure maximal oral absorption, praziquantel should be administered with meals. Administration with grapefruit juice may further increase pharmacologic effects of praziquantel, including adverse effects such dizziness, abdominal discomfort, and nausea.

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Grapefruit juice may delay the gastrointestinal absorption of clarithromycin but does not appear to affect the overall extent of absorption or inhibit the metabolism of clarithromycin. The mechanism of interaction is unknown but may be related to competition for intestinal CYP450 3A4 and/or absorptive sites. In an open-label, randomized, crossover study consisting of 12 healthy subjects, coadministration with grapefruit juice increased the time to reach peak plasma concentration (Tmax) of both clarithromycin and 14-hydroxyclarithromycin (the active metabolite) by 80% and 104%, respectively, compared to water. Other pharmacokinetic parameters were not significantly altered. This interaction is unlikely to be of clinical significance.

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