Fenoterol: a beta2-adrenergic agonist for use in asthma. Pharmacology, pharmacokinetics, clinical efficacy and adverse effects.

Fenoterol (hydroxyphenylorciprenaline) is chemically closely related to metaproterenol (orciprenaline). It has a higher bronchodilating potency than metaproterenol, albuterol (salbutamol in Europe) or terbutaline. The beta 2 selectivity of fenoterol at normal oral and inhaled doses is the same as for albuterol and terbutaline. Its pharmacodynamic effects are similar to those of other selective beta 2-adrenoceptor agonists. It has a high first-pass metabolism. The long half-life previously reported in the literature (7 hours) is mainly the half-life of inactive fenoterol metabolites. The duration of action at equipotent bronchodilating doses seems to be the same as for albuterol and terbutaline, and not longer, as previously reported. Inhalation of beta-adrenoceptor agonists is the superior route of administration. Side effects do not usually occur at normal therapeutic doses. One puff of fenoterol (200 micrograms) is about equipotent to 2 puffs of albuterol (2 X 100 micrograms) or 2 puffs of terbutaline (2 X 250 micrograms) with the same duration of effect. In patients who overdose with the metered-dose inhaler (MDI), side effects occur at half the number of puffs with fenoterol. Dosage for an acute attack in children is 1 puff (200 micrograms), repeated within 5 minutes if necessary; in adults 1-3 puffs can be given. For maintenance therapy, the dose in adults is 1-2 puffs 2-4 times daily, while in children 1 puff at night and 1 in the morning may be sufficient. The usual oral dosage has been 5-10 mg 3 times daily.