Drug Interactions between safinamide and vardenafil

MONITOR: Grapefruit juice may increase the plasma concentrations of orally administered drugs that are substrates of the CYP450 3A4 isoenzyme. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit. Because grapefruit juice inhibits primarily intestinal rather than hepatic CYP450 3A4, the magnitude of interaction is greatest for those drugs that undergo significant presystemic metabolism by CYP450 3A4 (i.e., drugs with low oral bioavailability). 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. Pharmacokinetic interactions involving grapefruit juice are also subject to a high degree of interpatient variability, thus the extent to which a given patient may be affected is difficult to predict.

MANAGEMENT: Patients who regularly consume grapefruit or grapefruit juice should be monitored for adverse effects and altered plasma concentrations of drugs that undergo significant presystemic metabolism by CYP450 3A4. Grapefruit and grapefruit juice should be avoided if an interaction is suspected. Orange juice is not expected to interact with these drugs.

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.