The effects of oral doses of theophylline and fenoterol on exercise-induced asthma

The effects of oral doses of theophylline and a β-adrenergic agonist, fenoterol, were examined in 18 asthmatic young adults. Significant bronchodilation was seen with high-dose theophylline (FEV₁ increased 14 percent) and with full 10-mg doses of fenoterol (FEV₁ increased 10 percent). Low-dose theophylline alone (130 mg) increased FEV₁ by 5 percent, but when combined with 5 mg of fenoterol, a 14 percent improvement was seen, demonstrating significant (P = .003) additive effects. The ability of the two drugs to prevent the asthmatic response to exercise was not additive. The mean fall in FEV₁ was not statistically different when subjects exercised after receiving a placebo (32 percent) 130 mg of theophylline (27 percent), or 130 mg of theophylline with 5 mg of fenoterol (18 percent). Furthermore, side effects associated with the two drugs, such as tachycardia, tremor, or CNS stimulation, were significantly increased when the two drugs were given simultaneously. Thus, little therapeutic benefit was gained from simultaneous therapy. Both bronchodilation and toxicity were equivalent to that seen with larger therapeutic doses of either drug given alone, and protection from the effects of a frequently encountered stress was not significantly enhanced.