Drug Interaction Report

MONITOR: Coadministration with tolvaptan can potentiate the risk of hyperkalemia in patients treated with other drugs that are known to increase serum potassium. Tolvaptan alone can increase serum potassium by causing an acute reduction of the extracellular fluid volume. In clinical studies, adverse reactions of hyperkalemia were approximately 1% to 2% higher when tolvaptan was used concomitantly with ACE inhibitors, angiotensin II receptor antagonists, or potassium sparing diuretics compared to administration of these medications with placebo.

MANAGEMENT: Serum potassium levels should be checked regularly during concomitant therapy with tolvaptan and other agents that can increase serum potassium such as ACE inhibitors, angiotensin II receptor antagonists, potassium-sparing diuretics, aldosterone antagonists, and miscellaneous agents like cyclosporine, heparin, tacrolimus, and trimethoprim. Particular caution is warranted in patients with renal impairment, diabetes, old age, severe or worsening heart failure, or dehydration. Patients should be advised to seek medical attention if they experience signs and symptoms of hyperkalemia such as nausea, vomiting, weakness, listlessness, tingling of the extremities, paralysis, confusion, weak pulse, and a slow or irregular heartbeat.

GENERALLY AVOID: Coadministration with grapefruit juice may increase the plasma concentrations of eplerenone. The primary mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. Inhibition of hepatic CYP450 3A4 may also contribute. In drug interaction studies, administration of a single 100 mg dose of eplerenone in combination with grapefruit juice resulted in a 25% increase in eplerenone systemic exposure (AUC). High blood levels of eplerenone can increase the risk of side effects including hyperkalemia. In general, the effect of grapefruit juice is concentration-, dose- and preparation-dependent, and can vary widely among brands. Certain preparations of grapefruit juice (e.g., high dose, double strength) have sometimes demonstrated potent inhibition of CYP450 3A4, while other preparations (e.g., low dose, single strength) have typically demonstrated moderate inhibition.

MANAGEMENT: It may be advisable for patients to avoid the consumption of grapefruit, grapefruit juice, or supplements that contain grapefruit during treatment with eplerenone.

GENERALLY AVOID: Grapefruit juice may significantly increase the plasma concentrations of tolvaptan. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. According to the product labeling, administration of tolvaptan with grapefruit juice resulted in a 1.8-fold increase in tolvaptan systemic exposure. The clinical significance is unknown, although increased pharmacologic effects may be expected. Too rapid correction of hyponatremia increases the risk of osmotic demyelination syndrome, which is associated with dysarthria, mutism, dysphagia, lethargy, affective changes, spastic quadriparesis, seizures, coma, and death.

MANAGEMENT: Patients treated with tolvaptan should avoid consumption of grapefruits and grapefruit juice.