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1. Adjust dosage carefully
Theophylline has a relatively long half-life in certain patient populations (the elderly and CHF patients), consequently it may take several days to reach steady state. Dosage increases should be made with caution. The patient must be followed closely for signs of toxicity.
2. Proper serum sampling is important when monitoring oral theophylline.
Suggested serum sampling times:
3. Factors affecting theophylline elimination
Patients with decompensated cirrhosis, acute hepatitis, and, possible, cholestasis have reduced theophylline clearance. A correlation between slow hepatic metabolism and serum albumin and bilirubin concentration has been made in patients with cirrhosis.
Patients with CHF have decreased theophylline clearance due to diminished blood flow to the liver. With treatment of CHF, theophylline clearance increases.
Acute illnesses associated with fever have been reported to prolong theophylline half-life. If fever is high and sustained, e.g., >102 for >24 hours, dosage should be reduced.
Ingestion of a high protein, low carbohydrate diet accelerates theophylline metabolism presumably by increasing liver enzyme activity. Dietary intake of methylxanthines, caffeine in particular, decreases theophylline metabolism by acting as a Substrate for metabolizing enzymes.
Smoking of cigarettes has a profound effect on theophylline metabolism. There is a dose-related increase in theophylline clearance, with heavy smokers metabolizing theophylline twice as fast as nonsmokers.
Cimetidine, macrolide antibiotics, and quinolones significantly decrease theophylline metabolism. Phenytoin, phenobarbital, and rifampin significantly increase theophylline metabolism.
Most studies report slower clearance in the elderly.