Theophylline

Theophylline is prescribed for bronchial asthma, for chronic obstructive pulmonary disease, and for newborn apnea. The drug is extensively metabolized¹ with peak serum levels reached four hours after oral dose. Troleandomycin and erythromycin may slow theophylline elimination. Heart failure, liver disease, prolonged fever, certain infections, and obesity may have similar effects. Prolonged half-life occurs in premature infants. Dosage should be reduced in these situations.

By contrast, half-life is shortened in smokers, variable with phenobarbital administration; higher doses are also tolerated in acidemia. Smokers on the average are reported to need 1.5 to 2 times as much of the drug as nonsmokers to achieve the same effects. Optimal resampling time after change in dosage is 48 hours for adults, one to two days for children. The half-life of theophylline is from 3 to 10 hours for adults and 1.4 to 7.9 hours for children, but varies between individuals.

Studying serum concentrations and toxic effects, Bertino et al found toxicity with peak theophylline concentrations as low as 19.4 mg/L. Recognizing theophylline toxicity over a wide range of theophylline levels, these authors questioned the association between the severity of toxic effects and serum concentrations.² Aitken and Martin also found lack of correlation between serum theophylline level and toxic effects.³

Blood levels should be interpreted in light of the patient's clinical status and use of other medications.

Toxic effects include nausea, vomiting, diarrhea, headache, atrial and ventricular arrhythmias, tremors, and convulsions.