Pharmacokinetics of theophylline in infants with bronchiolitis.

Theophylline pharmacokinetics were studied in 12 infants (age 3 weeks-6.5 months) with bronchiolitis. 9 of the 12 patients received a single dose of aminophylline (5.0-8.5 mg/kg) whereas the remainder were at steady-state receiving multiple doses (2.5-5.0 mg/kg) of aminophylline. The dose was administered IV over 0.5-1.0 h. An HPLC method was used to measure theophylline concentrations in serum and urine. Peak serum concentrations of theophylline measured by HPLC ranged from 8.48-21.6 micrograms/ml. Total, renal and nonrenal clearance of theophylline ranged from 4.66 to 19.25, 1.07 to 5.76 and 3.59 to 16.83 ml/min/m2, respectively. Mean apparent volume of distribution and elimination half-life were 8.75 l/m2 and 11.38 h, respectively. Although no significant correlation was observed between age and theophylline kinetic parameters, clearance appeared to increase and half-life decrease with age. Our patients had a substantially lower clearance and longer half-life as compared to published data in children greater than 1 year of age. A five-fold variation in theophylline clearance demonstrates the need for monitoring theophylline serum concentration to minimize the risk of potential toxicity.