Pharmacokinetics and metabolism of salbutamol in premature labour.

1 The pharmacokinetics of salbutamol and its sulphate conjugate were examined during intravenous and steady-state oral administration in nine patients receiving the drug for the prevention or treatment of premature labour. 2 Uterine contractions were inhibited by plasma salbutamol concentrations in the range 8-33 ng ml-1 in six of the seven patients who were receiving intravenous drug. 3 By comparison with our previous study in a control group of healthy males and nonpregnant females, the total clearance of salbutamol in premature labour (501; s.d. 185 ml min-1) was similar to that in the control group (480; s.d. 123 ml min-1). Renal salbutamol clearance (208; s.d. 51 ml min-1), however, was significantly less than that in the control group (283; s.d. 51 ml min-1). 4 The systemic availability (n = 3), urinary recovery of unchanged oral salbutamol and area under the plasma curve during the oral dosage interval (n = 5) were all only slightly lower (10-20%) than control values, suggesting slightly lower oral absorption. 5 Formation and elimination of the sulphate conjugate were similar to those observed in control subjects suggesting that first-pass sulphation in the gut wall is unchanged in pregnancy. Overall there were only minor differences in salbutamol pharmacokinetics between control subjects and patients in premature labour.