Drug Interaction Report

GENERALLY AVOID: Licorice use has been associated with hypertension and may antagonize the effects of antihypertensive agents or effects of agents with hypotensive properties. Glycyrrhizic acid, a component of licorice, is hydrolyzed in the intestine to a metabolite (glycyrrhetinic acid) that causes mineralocorticoid and renin-suppressing effects. In one study, licorice was found to increase blood pressure in a dose-dependent manner. Healthy volunteers who consumed licorice 50 to 200 g/day (corresponding to 75 to 540 mg/day of glycyrrhetinic acid) for two to four weeks had a 3.1 to 14.4 mmHg increase in their systolic blood pressure. Even the lowest dosage demonstrated a significant effect. In another study, plasma potassium levels decreased by 0.3 to 1.5 mEq/L in 12 out of 14 healthy volunteers who ingested licorice 100 or 200 g/day (equivalent to 700 to 1400 mg/day of glycyrrhizic acid) for one to four weeks, including four who had to be withdrawn from the study because of hypokalemia. Two more subjects were withdrawn due to edema of the face, hands, and ankles. Other side effects reported include mild, transient generalized edema; headache; sodium retention; and weight gain (1 to 4 kg, mean 1.5 kg). Signs of renin-angiotensin-aldosterone suppression were observed in all subjects, especially plasma renin activity and urinary aldosterone concentrations, which fell to subnormal or undetectable levels in the majority of subjects. There have been various published case reports of refractory hypertension, severe hypokalemia (life-threatening hypokalemic paralysis, myopathy, arrhythmia, or cardiac arrest), and hypertensive encephalopathy in association with licorice intoxication. Hypertension and hypokalemia have also been reported with moderate doses of licorice in the form of licorice-flavored chewing gum or candy, chewing tobacco, or licorice-based foods and beverages consumed on a chronic basis. Prolonged use of licorice has led to a hypermineralocorticoid (pseudohyperaldosteronism) syndrome characterized by hypertension, hypernatremia, hypokalemia, metabolic alkalosis, renin-angiotensin-aldosterone suppression, and edema. In studies and case reports, licorice toxicity has generally been completely reversible within one to several weeks of licorice discontinuation. However, renin-angiotensin-aldosterone axis may be suppressed for up to several months.

MANAGEMENT: Patients receiving antihypertensive therapy or agents with hypotensive properties should avoid or limit the consumption of licorice-containing products. Even relatively moderate doses of licorice may be problematic in susceptible patients when ingested regularly for prolonged periods.

MONITOR: Like many CNS-active agents, alcohol can exhibit hypotensive effects. Coadministration with antihypertensive agents including diltiazem may result in additive effects on blood pressure and orthostasis.

MONITOR: Grapefruit juice may increase the plasma concentrations of orally administered diltiazem in some patients. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. In a study of ten healthy male volunteers, administration of a single 120 mg oral dose of immediate-release diltiazem in combination with 250 mL of grapefruit juice increased the diltiazem peak plasma concentration (Cmax) and systemic exposure (AUC) by an average of 22% and 20%, respectively, compared to administration with water. The time to reach Cmax (Tmax) and the terminal half-life were not affected, and no statistically significant differences in blood pressure and heart rate were observed during administration with grapefruit juice relative to water. In a different study, repeated administration of 200 mL of grapefruit juice at 0, 2, 4, 8 and 12 hours had no significant effect on the Cmax or AUC of a single 120 mg oral dose of diltiazem, but increased its half-life from 4.1 to 5.1 hours. The ratios for the N-demethyl and deacetyl metabolites to diltiazem were also not affected by grapefruit juice. However, because pharmacokinetic interactions involving grapefruit juice are often subject to a high degree of interpatient variability, the extent to which a given patient may be affected is difficult to predict.

MANAGEMENT: Patients should be advised that alcohol may potentiate the hypotensive effects of diltiazem, especially during the initiation of therapy and following a dosage increase. Caution should be exercised when rising from a sitting or recumbent position, and patients should notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients who regularly consume grapefruit or grapefruit juice should be monitored for increased adverse effects of diltiazem such as such as headache, irregular heartbeat, edema, unexplained weight gain, and chest pain. Grapefruit and grapefruit juice should be avoided if an interaction is suspected.

MONITOR: Calcium-containing products may decrease the effectiveness of calcium channel blockers by saturating calcium channels with calcium. Calcium chloride has been used to manage acute severe verapamil toxicity.

MANAGEMENT: Management consists of monitoring the effectiveness of calcium channel blocker therapy during coadministration with calcium products.