Factors contributing to variation in clearance of theophylline

Increased clearance

• Enzyme induction by drugs: rifampicin, ethanol, phenobarbitone
• Smoking: tobacco, marijauna
• High-protein, low-carbohydrate diet
• Childhood

Decreased clearance

• Enzyme inhibition by drugs: cimetidine, erythromycin, allopurinol, zafirlukast, ciprofloxacin
• High carbohydrate diet
• Congestive heart failure
• Liver disease
• Pneumonia
• Viral infection and vaccination
• Old age 

Look for mechanism of action of theophylline.