Maximally effective plasma concentrations of enprofylline and theophylline during constant infusion.

Bronchodilating effects produced by increasing intravenously administered doses of enprofylline and theophylline compared to placebo were evaluated in 20 asthmatic outpatients. Three mean plasma plateaux of enprofylline of 1.5, 2.9 and 4.0 micrograms/ml produced a mean increase in forced expiratory volume in the first second (FEV1.0) as a percentage of baseline, of 12.8%, 18.8% and 30.1%, respectively. Comparable plasma plateaux of theophylline i.e. 5.5, 10.8 and 15.2 micrograms/ml produced a mean increase of FEV1.0 in percent of basal values of 12.4%, 21.6% and 28.2%, respectively. Enprofylline at plasma concentrations above 2.9 micrograms/ml induced more headache and slightly more nausea than theophylline and placebo. Theophylline infusion produced more tremor (finger oscillation) than enprofylline and placebo. Intravenously administered enprofylline produces bronchodilation comparable to theophylline in a mean dose ratio of 3.8.