Theophylline stimulates the CNS and skeletal muscles, stimulates cardiac muscle, relaxes certain smooth muscles including those of the bronchi, produces diuresis, and causes an increase in gastric secretion. Phyllocontin and Phyllocontin-350 tablets are sustained release tablets which produce peak blood levels of theophylline between 3 and 5 hours. Once the steady state level has been reached, the therapeutic blood levels persist for 12 hours. Theophylline is usually readily absorbed following oral administration. The extent of absorption is negligibly influenced by food.
Theophylline is distributed in the extracellular fluids and uniformly to all tissues.
The drug has a mean biological half-life of 5 hours in adults and 3.5 hours in children with great individual variability. Theophylline is metabolized in the liver. The enzymes involved in theophylline metabolism are unknown, but do not include xanthine oxidase. Serum uric acid concentrations are not increased during theophylline administration and the drug is not contraindicated in the presence of gout or allopurinol administration. Theophylline clearance is markedly increased in smokers, likely due to stimulation of the metabolizing enzymes.