Pharmacology. Phenylephrine directly and preferentially stimulates alpha1-adrenergic receptors, although at higher doses it may also stimulate alpha2– and beta1-adrenergic receptors. It is a potent vasoconstrictor with little inotropic or chronotropic effects. Thus, in poisonings it is used primarily as a vasopressor to increase systemic vascular resistance. The onset of action following intravenous administration is immediate, and the effect persists for 15–30 minutes after infusion has stopped.

Indications. Phenylephrine is used to increase blood pressure in patients with hypotension caused by vasodilation or low systemic vascular resistance. Phenylephrine may be particularly useful in patients with tachycardia or dysrhythmias that might otherwise be exacerbated by the use of beta-adrenergic agents. Volume resuscitation should be done before or during administration of phenylephrine.

Contraindications

1. 
   

   Uncorrected hypovolemia.

   
   
2. 
   

   Relatively contraindicated in patients with peripheral vascular disease accompanied by severe localized ischemia or thrombosis.

   
   
3. 
   

   Use with caution in patients with bradycardia or hyperthyroidism.

Adverse effects

1. 
   

   Hypertension.

   
   
2. 
   

   Decreased cardiac output.

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