Phenylephrine MAOIs

Ephedrine —contraindicated with MAOIs Pseudoephedrine —contraindicated with MAOIs Phenylephrine —contraindicated with MAOIs Phenylpropanolamine —contraindicated with MAOIs Seriously elevated blood pressure (hypertensive crisis), elevated temperature, seizures, cerebral hemorrhage, death... 

Predictable interactions occur between the MAOIs and any amine precursors, or directly or indirectly acting sympathomimetic amines (e.g. the amphetamines, phenylephrine and tyramine). Such interactions can cause pronounced hypertension and, in extreme cases, stroke. 

Interactions of MAOIs with other sympathomimetic drugs are well known. The increased neuronal stores of NE represent a booby-trap hazard that can easily be triggered by indirectly acting adrenergic agents such as the amphetamines found in many antiobesity preparations. Drugs such as ephedrine, phenylpropanolamine, and phenylephrine are potentially more dangerous because of their ready availability to the public in over-the-counter medications such as cold medicines and nose drops. 

A 15-year-old girl taking phenelzine 15 mg three times daily (as well as thioridazine, procyclidine and metronidazole) took 13 capsules of Romilar CF (containing dextromethorphan hydrobromide 15 mg, phenindamine tartrate 6.25 mg, phenylephrine hydrochloride 5 mg and paracetamol (acetaminophen) 120 mg in each capsule). She became comatose, hyper-pyrexic (lOS F), had a blood pressure of 100/60 mmHg, a pulse of 160 bpm and later died ofa cardiac arrest. This case is complicated by the overdosage and multiplicity of drugs present, particularly the phenylephrine. See MAOIs or RIMAs + Sympathomimetics Phenylephrine , p.1148. 

Note that drugs with directly-acting sympathomimetic effects (of which beta agonists are an example) do not normally interact to cause hypertension with MAOIs, see sympathomimetics directly-acting , (below). However, phenylephrine (which has some indirect actions, see sympathomimetics phenylephrine , (p.l 148)) may have contributed to the reaction between toloxatone and terbutaline, and the fact that terbutaline seems to have been given orally would also have eontributed. The hypomania reaction is not understood. 

The interaction between phenylephrine and the MAOIs is dealt with elsewhere (see MAOIs orMMAs + Sympathomimetics Phenylephrine , p. 1148). Consider also MAOIs or RIMAs + Sympathomimetics Beta-agonist bronchodilators , p.ll46 and Inotropes and Vasopressors Dopamine + Selegiline , p.893, for dosing advice with when dopamine is given to patients taking MAOIs. 

The concurrent use of oral phenylephrine and the non-selective MAOIs can result in a potentially life-threatening hypertensive crisis. Phenyiephrine is commonly found in proprietary cough, coid and influenza preparations. The effects of parenterai phenyiephrine may be approximately doubled by MAOIs. Some interaction occurs between phenylephrine and the RIMAs mociobemide or brofaromine, but the biood pressure response appears to be much smaller than that seen with the non-seiective MAOIs. 

The interaction between the MAOIs and oral phenylephrine is established, serious and potentially life-threatening. Phenylephrine commonly occurs in oral non-prescription cough, cold and influenza preparations, so patients should be strongly warned about them. Whether the effects of nasal drops and sprays and eye drops are also enhanced is uncertain, but it would be prudent to avoid them until they have been shown to be safe. The response to parenteral administration is also approximately doubled, so that a dosage reduction is necessary. 

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