[Pharmacokinetics and pharmacodynamics of hydrocortisone in asthmatic children]

Corticosteroids are very efficacious in the treatment of asthma. In the present study, the conversion rate of hydrocortisone succinate (HCS) to hydrocortisone in plasma was examined and pharmacokinetic study was carried out for the two compounds after a single intravenous injection of hydrocortisone sodium succinate (HCSS). Moreover, it was examined whether hydrocortisone improved acute asthmatic attacks. In a randomised cross-over trial at 5 to 7 days intervals, 10 asthmatic children aged 9-14 years were treated with a single intravenous injection of HCSS in a dose of 5 mg hydrocortisone/kg body weight or without HCSS. After 4-hour pulmonary function studies, they were received a subcutaneous injection of epinephrine (0.004 mg/kg). The plasma concentrations of HCS and hydrocortisone were measured by the HPLC and/or radioimmunoassay. The mean of maximum concentration of HCS was 26.38 mg/L. The concentration of HCS decreased rapidly with a half-life of 0.09 hr (5.38 min). The concentration of hydrocortisone reached to a peak value of 4.96 mg/L after 10 min, and then decreased with a half-life of 1.24 hour. It is predicted that an intravenous injection of HCSS every 6 hours in a dose of 5 mg hydrocortisone/kg would maintain hydrocortisone level at 100 to 150 micrograms/dl. HCSS did not show a rapid improvement of the pulmonary functions, but showed a tendency to improve the functions over 4 hours. Subcutaneous injection of epinephrine after HCSS resulted in a significant improvement of pulmonary functions compared to those by epinephrine alone. We concluded that hydrocortisone showed a slowly evolving improvement of pulmonary function and increased the responsiveness to beta-agonists.