Phenylephrine hypertension caused

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. 

SYMPATHOMIMETICS CYTOTOXICS -PROCARBAZINE Co-administration of ephedrine, metaraminol, methylphenidate, phenylephrine or pseudoephedrine (including nasal and ophthalmic solutions) with procarbazine may cause a prolongation and t intensity of the cardiac stimulant effects and effects on BP, which may lead to headache, arrhythmias, hypertensive or hyperpyretic crisis The metabolism of sympathomimetics is impaired due to an inhibition of MAO It is recommended that sympathomimetics not be administered during and within 14 days of stopping procarbazine. Do not use any OTC nasal decongestants (sprays or oral preparations) or asthma relief agents without consulting the pharmacist/doctor... 

Phenylephrine eye drops given to patients undergoing general anaesthesia caused marked cyanosis and bradycardia in a baby, and hypertension in a woman. 

However, no change in blood pressure was seen in a study in both nor-motensive subjects and patients taking metoprolol who were given 0.5 to 4-mg doses of phenylephrine intranasally every hour, to a total of 7.5 to 15 mg (4 to 30 times the usual dose). Similarly, in a placebo-controlled study in 12 hypertensive patients, neither propranolol nor metoprolol significantly altered the dose of intravenous phenylephrine required to cause a 25 mmHg increase in systolic blood pressure. 

Phenylephrine causes vasoconstriction, which can raise the blood pressure. Normally this would be limited by a baroreflex mediated by the vagus nerve, but if this cholinergic mechanism is blocked by atropine or other antimuscarinics, the rise in blood pressure is largely uncontrolled. Severe hypertension may occur, and other adverse cardiae events such as acute cardiac failure may follow. 

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. 

Morales-Carpi C, Torres-Chazarra C, Lurbe E, Torro I, Morales-Olivas FJ. Cold medication containing phenylephrine as a cause of hypertension in children. Eur J Pediatr 2008 167(8) 947-8. 

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