Theophylline - serum

5 mL blood in plain tube.

Preferably collected pre-dose; timing of post-dose peak varies with formulation.

Neonate: 33-66 µmol/L (6-12 mg/L)

Child, adult: 55-110 µmol/L (10-20 mg/L)

During acute illness, the half-life may be prolonged beyond the usual range of 3-9 hours.

Toxicity may develop if the dosage is not reduced. Toxicity may occur within the therapeutic interval in some patients.

Cigarette smoking reduces the half-life and therefore decreases levels significantly.