Single dose (SD) pharmacokinetics (PK) of terbutaline (T) in pediatric patients with status asthmaticus

Severe childhood asthma unresponsive to maximal therapy(MT: IV aminophylline, steroids, continuous albuterol, oxygen, ±anticholinergic aerosols) progressing to respiratory failure is a medical emergency. Continuous infusion T is often added to enhance MT, but the lack of rigorous PK data has hampered optimal age-based dosing recommendations. We undertook a SD T, dose-escalation (10,20,30 mcg/Kg) study in 41 infants & children receiving MT. Patients were enrolled into 1 of 4 age groups. Timed serum samples (0-32hrs) analyzed by HPLC were obtained. No differences in T PK were observed relative to dose, thus data are pooled below; mean(SD). Age Group t1/2(hr) MRT(hr) Vdss (l/Kg) <1 yr (n=4) 1.3(0.3) 1.3(0.5) 0.5(0.4) 1-<5 yr (n=11) 2.9(0.7) 2.5(0.5) 0.7(0.1) 5-10 yr (n=9) 1.9(0.4) 1.7(0.4) 0.7(0.1) 11-17 yr(n=10) 2.3(0.3) 2.1(0.1) 0.6(0.2) No changes in baseline HR,BP,RR or 0₂ sat after T was observed in any patient. No age-related differences were observed in T t1/2, MRT or Vdss. T clearance(Cl) increases over the first 4 years of life, remaining elevated up to age 10, gradully falling to adult values by age 15. Children 4-9 years of age may require higher doses than younger infants and adults.