The pharmacokinetics and bioavailability of clemastine and phenylpropanolamine in single-component and combination formulations.

Studies were conducted in healthy male volunteers (n = 171; age range, 19-49 years; 22-27 subjects per study) to examine the following: pharmacokinetics and dose proportionality of the antihistamine clemastine; the effect of coadministration of phenylpropanolamine and clemastine on the pharmacokinetics of the two drugs; and the bioavailability of clemastine tablets and combination tablets of clemastine and sustained-release phenyl-propanolamine under fasted and fed conditions after single-dose administration and at steady state. All studies used crossover designs, with randomized drug treatments separated by a 7-day washout period for the single-dose studies, and with administration every 6 or 12 hours for 7 days per treatment for the steady-state studies. After single oral doses of clemastine solution (1,2, and 4 mg), the area under the concentration-time curve (AUC) and maximum concentration (Cmax) were dose proportional. Clemastine showed a first-pass reduction in the extent of absorption, with oral bioavailability calculated as 39.2 +/- 12.4%. Extravascular distribution of drug was suggested by the high volume of distribution (799 +/- 315 L) and low Cmax (0.577 +/- 0.252 ng/mL/mg) observed at 4.77 +/- 2.26 hours after administration, and by the biphasic decline in plasma concentration. The terminal elimination half-life (t1/2) of clemastine was 21.3 +/- 11.6 hours. Steady-state concentrations of clemastine were consistent with linear pharmacokinetic processes, and clearance was unaffected by age in the range studied, or by race. Clemastine solution and tablets were bioequivalent, and food had no significant effect on rate and extent of absorption of clemastine. The 1- and 2-mg clemastine tablets showed proportional bioavailability. Coadministration of clemastine with phenylpropanolamine did not significantly influence the pharmacokinetics of clemastine or the AUC and elimination t1/2 of phenylpropanolamine, but reduced the rate of absorption of phenylpropanolamine. Combination tablets containing 1 mg or 2 mg of immediate-release clemastine plus 75 mg of sustained-release phenylpropanolamine for twice daily administration were bioequivalent to the separate components and showed no significant interaction with food.

Effect of current magnitude and drug concentration on iontophoretic delivery of octreotide acetate (Sandostatin) in the rabbit.

The effect of current magnitude and drug concentration on transdermal iontophoretic delivery of octreotide acetate (Sandostatin) was examined in the rabbit. Plasma samples were collected over 24 hours and octreotide concentrations were determined by a radioimmunoassay. Without an electrical current, negligible plasma concentrations of octreotide were obtained. Following initiation of iontophoresis, plasma concentrations of octreotide increased rapidly, although did not sustain at a plateau level during the dosing period. Octreotide concentrations declined rapidly after removal of the device. Increasing the electrical current from 50 microA/cm2 to 150 microA/cm2 yielded a proportional increase in the delivery. Increasing the drug concentration in the device from 2.5 mg/mL to 5 mg/mL resulted in approximately proportional increase in plasma octreotide concentrations; however, further increase in plasma concentrations was not observed for drug concentrations beyond 5 mg/mL. Iontophoretic delivery at the conditions which yielded the highest octreotide concentrations in this study (5 mg/mL solution at 150 microA/cm2 for 8 hours) yielded an apparent bioavailability (which represents an underestimate of the absolute bioavailability determined when the patches are run to exhaustion) of approximately 8%.