Theophylline: | Frusemide,β-blockers (eg propranolol), isoprenaline, cimetidine, oral contraceptives, aminoglutethimide, carbamazepine, lithium, phenytoin, sulphinpyrazone, rifampicin, erythromycin, ciprofloxacin and other quinolone antibiotics. The handling of theophylline may be influenced by age, smoking, diet and disease including hepatic dysfunction, heart failure, pneumonia, active viral infections and severe (irreversible) airway obstruction. There are conflicting reports concerning potentiation of theophylline by influenza vaccine and physicians should be aware that the interaction may occur. The concomitant use of theophylline and fluvoxamine should usually be avoided. Where this is not possible, patients should have their theophylline dose halved and plasma theophylline should be monitored closely. Plasma concentrations of theophylline can be reduced by concomitant use of the herbal remedy St. John's wort (Hypericum perforatum). Xanthines can potentiate hypokalaemia resulting from β2 agonist therapy, steroids, diuretics and hypoxia. Particular caution is advised in severe asthma. It is recommended that serum potassium levels are monitored in such situations.. |
