Pseudoephedrine × Selegiline

Selegiline irreversibly inhibits monoamine oxidase type B (MAO-B), and enzyme activity recovers only as new enzyme is made (selegiline summary of product characteristics, SmPC, section 5.2). After a single 10 mg dose, platelet MAO-B activity returns to normal in about 2 weeks (selegiline SmPC, section 5.2). Pseudoephedrine constricts blood vessels through alpha-1 adrenergic receptors. It also enters sympathetic nerve fibres, where it displaces noradrenaline from storage vesicles (pseudoephedrine SmPC, section 5.1). Monoamine oxidase (MAO) inhibitors, selegiline included, increase catecholamine release and can prolong and intensify the vasopressor and cardiac stimulant effects of pseudoephedrine (pseudoephedrine SmPC, section 4.5). Selegiline should not be combined with sympathomimetics because of the risk of hypertension (selegiline SmPC, section 4.5). Above the recommended 10 mg, it may lose its selectivity for MAO-B, which raises the risk of hypertension (selegiline SmPC, section 4.4).

According to the pseudoephedrine summary of product characteristics (SmPC), combining it with monoamine oxidase (MAO) inhibitors can cause severe hypertension, hyperpyrexia and headache (section 4.5). Uncontrolled hypertension, including hypertensive crisis, has been reported when the usual dose of selegiline was combined with ephedrine, of which pseudoephedrine is a stereoisomer (selegiline labels, US Food and Drug Administration, FDA; pseudoephedrine SmPC, section 5.1). Pseudoephedrine alone at the usual dose can raise blood pressure, cause tachycardia and stimulate the central nervous system (pseudoephedrine SmPC, section 4.4). Warning signs that call for stopping pseudoephedrine are hypertension, tachycardia, palpitations, arrhythmias, nausea, and new or worsening headache (pseudoephedrine SmPC, section 4.4).

The combination is contraindicated. The selegiline summary of product characteristics (SmPC) rules it out (sections 4.3 and 4.5). The pseudoephedrine SmPC names selegiline among the monoamine oxidase inhibitors, or MAOIs (sections 4.3 and 4.5). The over-the-counter pseudoephedrine label of the US Food and Drug Administration (FDA) also rules out the combination. Selegiline should not be combined with any sympathomimetic, nasal decongestants included (selegiline SmPC, sections 4.3 and 4.5). Do not take pseudoephedrine within 2 weeks after stopping selegiline (pseudoephedrine SmPC, section 4.3; FDA pseudoephedrine label). Section 4.5 of the pseudoephedrine SmPC gives 15 days. Ask the patient to report all prescription and over-the-counter medicines they take or plan to take, especially cold medicines (FDA label of selegiline orally disintegrating tablets, section 17). Patients who are not sure whether a prescription drug is an MAOI are advised to check before taking pseudoephedrine (FDA pseudoephedrine label). Stop pseudoephedrine if hypertension, tachycardia, palpitations, arrhythmias, nausea or headache appear (pseudoephedrine SmPC, section 4.4). The patient should report severe headache, unusual new symptoms or very high blood pressure to a doctor straight away (FDA label of selegiline orally disintegrating tablets, section 17). Do not raise the dose of selegiline tablets or capsules above 10 mg a day (selegiline SmPC, sections 4.2 and 4.4; FDA selegiline capsules label).