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Pharmacology: Pharmacodynamics: Doxofylline, a bronchodilator, differs from theophylline by the presence of a dioxolane group in position 7. Doxofylline inhibits phosphodiesterase enzymes followed by an increase in cyclic-3',5'-adenosine monophosphate (cAMP). cAMP mediates cellular responses such as bronchial smooth muscle relaxation resulting in bronchodilation.
The decreased affinity of doxofylline for adenosine A1and A2 receptors has been suggested to account for its better safety profile compared with theophylline. Studies on doxofylline have shown less pronounced clinically important arrhythmogenic and cardiostimulant effects.
Pharmacokinetics: Doxofylline is rapidly absorbed following an oral dose of 400 mg, with peak serum concentration being reached after 1 hour and steady state in 4 days. Absolute bioavailability is about 62.6%. Plasma protein binding is about 48%. Doxofylline is almost completely metabolized in the liver, with only one detectable metabolite (hydroxymethyltheophylline). Less than 4% of an orally administered dose is excreted unchanged in the urine. The mean elimination half-life is 7.01 ± 0.8 hours.
