Drug Interactions between aliskiren / hydrochlorothiazide and cisapride

CONTRAINDICATED: Coadministration with grapefruit juice may increase the plasma concentrations of cisapride. The mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. In a study of 14 healthy volunteers, administration with 250 mL of grapefruit juice increased the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of cisapride (10 mg single dose) by 34% and 39%, respectively, compared to water. A second single-dose study involving 12 healthy volunteers demonstrated an increase of 68% and 51% in cisapride Cmax and AUC, respectively, compared to water. In another 10 healthy volunteers, repeated ingestion of double-strength grapefruit juice (200 mL three times a day for 2 days, then with a 10 mg dose of cisapride and at 0.5 and 1.5 hours afterwards) resulted in an 81% and 144% increase in mean cisapride Cmax and AUC, respectively, compared to water. A high degree of intersubject variability in the grapefruit juice effect was observed in all three studies, but no patient experienced any changes in heart rate, blood pressure, or QT interval. However, high plasma levels of cisapride have been associated with prolongation of the QT interval on the ECG; ventricular arrhythmias including ventricular tachycardia, ventricular fibrillation, and torsade de pointes; cardiac arrest; and sudden death.

GENERALLY AVOID: Coadministration with red wine may increase the plasma concentrations of cisapride in susceptible individuals. The exact mechanism of interaction is unknown but is believed to involve inhibition of CYP450 3A4 in the gut wall similar to grapefruit juice. In 12 healthy volunteers, administration with 250 mL of red wine (cabernet sauvignon) produced only minor and statistically insignificant changes in cisapride pharmacokinetics compared to water. However, one subject had a doubling in cisapride AUC and Cmax with red wine. The same subject also had the largest interaction with grapefruit juice, which suggests that a significant interaction may occur in certain individuals, perhaps those with a preexisting high intestinal CYP450 3A4 content.

MANAGEMENT: Patients receiving cisapride therapy should avoid the consumption of grapefruits and grapefruit juice. Because a significant interaction may occur with red wine in the occasional patient, red wine should preferably be avoided also during cisapride therapy.

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.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.