Pirbuterol hydrochloride is a beta 2
adrenergic agonist with a structure similar to that of
albuterol, except for the substitution of a
pyridine ring for the
benzene ring. It is comparable in duration of action to
albuterol when given by inhalation, but it is threefold less potent by weight. In man,
pirbuterol and
albuterol have similar beta 2 selectivity. In the acute
therapy of
chronic obstructive pulmonary disease,
pirbuterol is most effective in oral doses of 15-20 mg, and by
aerosol in doses of 400 micrograms or greater. Long-term studies of oral
pirbuterol in doses between 30-60 mg/day are promising, but further research is warranted. The combination of
pirbuterol's beta 2 and lesser beta1 activity has proven helpful in the
therapy of refractory
congestive heart failure. Improvement of function of both right and left ventricles and systemic and pulmonic circulations has been demonstrated acutely.
Drug effect wanes, as with other
beta adrenergic agonists, due to the development of tolerance; however, long-term benefit appears to persist in both pulmonary and cardiac patients.
Pirbuterol will be marketed in the United States as 10 and 15 mg
tablets and as a 200 micrograms per actuation metered dose
aerosol for use in pulmonary patients only; it will not be approved for use in
congestive heart failure. In terms of beta 2 selectivity, duration of action, potency and frequency of side effects,
pirbuterol is comparable to the two beta 2 agonists already available in the United States,
albuterol and
terbutaline.