Drug Interactions between Diltiazem Hydrochloride CD and safinamide

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.

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GENERALLY AVOID: Foods that contain large amounts of tyramine may precipitate a hypertensive crisis in patients treated with safinamide. The proposed mechanism involves potentiation of the tyramine pressor effect due to inhibition of monoamine oxidase (MAO) by safinamide. Monoamine oxidase in the gastrointestinal tract and liver, primarily type A (MAO-A), is the enzyme responsible for metabolizing exogenous amines such as tyramine and preventing them from being absorbed intact. Once absorbed, tyramine is metabolized to octopamine, a substance that is believed to displace norepinephrine from storage granules causing a rise in blood pressure. In vitro, safinamide inhibits MAO-B with greater than 1000-fold selectivity over MAO-A, and neither safinamide nor its major metabolites inhibit MAO-A at clinically relevant concentrations. Results from an oral tyramine challenge study also suggest that safinamide is a selective inhibitor of MAO-B at the recommended dosages of 50 or 100 mg/day. However, this selectivity is not absolute and may diminish in a dose-related manner above the maximum recommended daily dosage. In clinical trials, the incidence of hypertension was 7% and 5% for safinamide 50 mg and 100 mg, respectively, versus 4% for placebo. There were no reported cases of hypertensive crisis.

Administration of safinamide following intake of a high-fat, high-caloric breakfast resulted in a slight delay in the absorption of safinamide, but had no effects on safinamide peak plasma concentration (Cmax) and systemic exposure (AUC) compared to administration under fasted conditions.

MANAGEMENT: Dietary restriction is not ordinarily required during safinamide treatment with respect to most foods and beverages that contain tyramine, which usually include aged, fermented, cured, smoked, or pickled foods (e.g., air-dried and fermented meats or fish, aged cheeses, most soybean products, yeast extracts, red wine, beer, sauerkraut). However, certain foods like some of the aged cheeses (e.g., Boursault, Liederkrantz, Mycella, Stilton) and pickled herring may contain very high amounts of tyramine and could potentially cause a hypertensive reaction in patients taking safinamide, even at recommended dosages, due to increased sensitivity to tyramine. Patients should be advised to avoid the intake of very high levels of tyramine (e.g., greater than 150 mg) and to promptly seek medical attention if they experience potential signs and symptoms of a hypertensive crisis such as severe headache, visual disturbances, confusion, stupor, seizures, chest pain, unexplained nausea or vomiting, and stroke-like symptoms. Blood pressure should be regularly monitored and managed accordingly. Medication adjustment may be necessary if blood pressure elevations are sustained or not adequately controlled. Safinamide should not be used at dosages exceeding 100 mg/day, or 50 mg/day in patients with moderate hepatic impairment (Child-Pugh B, 7-9), as it may increase the risk of hypertensive crisis and other adverse reactions associated with nonselective inhibition of MAO. Safinamide can be administered with or without food.

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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.

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