Drug Interaction Report

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.

ADJUST DOSING INTERVAL: Food enhances the bioavailability of the pharmacologically active metabolite tizoxanide (desacetyl-nitazoxamide) from nitazoxanide administration. According to the product labeling, administration of nitazoxanide tablets with food increases the area under the plasma concentration-time curve (AUC) of tizoxanide and tizoxanide glucuronide in plasma by almost 2-fold and the peak plasma concentration (Cmax) by almost 50%. Administration of nitazoxanide oral suspension with food increases the AUC of tizoxanide and tizoxandie glucuronide by about 45% to 50% and the Cmax by less than 10%.

MANAGEMENT: Nitazoxanide tablets and oral suspension were administered with food in clinical trials and are recommended to be administered with food to ensure maximal drug levels in plasma.