Drug Interactions between aliskiren and P-A-C

GENERALLY AVOID: Coadministration with orange, apple, or grapefruit juice may significantly decrease the oral bioavailability and renin-inhibiting effect of aliskiren. The exact mechanism of interaction is unknown, but may include inhibition of OATP2B1-mediated influx of aliskiren in the small intestine, formation of insoluble complexes between fruit juice constituents and aliskiren, and/or increased ionization of aliskiren due to reduced intestinal pH. In 12 healthy volunteers, 200 mL of either orange juice or apple juice administered three times daily for 5 days in combination with a single 150 mg oral dose of aliskiren on day 3 reduced the mean aliskiren peak plasma concentration (Cmax) and systemic exposure (AUC) by approximately 80% and 60%, respectively, compared to water. Plasma renin activity was 87% and 67% higher at 24 hours postdose when aliskiren was administered with orange juice and apple juice, respectively, compared to water. No significant differences were observed in the blood pressure or heart rate between treatments. However, this may be due to the delayed onset of aliskiren's blood pressure-lowering effect, which would not be apparent following a single dose. A similar pharmacokinetic interaction has been reported with grapefruit juice. In 11 healthy volunteers, 200 mL of normal strength grapefruit juice administered three times daily for 5 days in combination with a single 150 mg oral dose of aliskiren on day 3 reduced the mean aliskiren Cmax and AUC by 81% and 61%, respectively, but there was no change in plasma renin activity compared to water. A high degree of interpatient variability was observed with all three interactions.

MONITOR: High-fat meals can substantially reduce the gastrointestinal absorption of aliskiren. According to the product labeling, administration of aliskiren with a high-fat meal decreased the mean peak plasma concentration (Cmax) and systemic exposure (AUC) by 85% and 71%, respectively. In clinical trials, however, aliskiren was administered without a fixed requirement in relation to meals.

MANAGEMENT: To ensure steady systemic drug levels and therapeutic effects, patients should establish a routine pattern for administration of aliskiren with regard to meals. Coadministration with orange, apple, or grapefruit juice should be avoided, especially if these juices are to be consumed on a regular basis or shortly before or after aliskiren dosing.

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GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.

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The effect of grapefruit juice on the pharmacologic activity of caffeine is controversial. One report suggests that grapefruit juice increases the effect of caffeine. The proposed mechanism is inhibition of cytochrome P-450 metabolism of caffeine. However, a well-conducted pharmacokinetic/pharmacodynamic study did not demonstrate this effect. The clinical significance of this potential interaction is unknown.

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One study has reported that coadministration of caffeine and aspirin lead to a 25% increase in the rate of appearance and 17% increase in maximum concentration of salicylate in the plasma. A significantly higher area under the plasma concentration time curve of salicylate was also reported when both drugs were administered together. The exact mechanism of this interaction has not been specified. Physicians and patients should be aware that coadministration of aspirin and caffeine may lead to higher salicylate levels faster.

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