Human pharmacokinetics and comparative bioavailability of loperamide hydrochloride

J Clin Pharmacol. 1979 Apr;19(4):211-8. doi: 10.1002/j.1552-4604.1979.tb01654.x.


A pharmacokinetic study of the antidiarrheal agent loperamide hydrochloride (Imodium) was conducted in six male subjects. The study utilized a random crossover design and employed a 2-mg capsule and a 0.2-mg/ml syrup formulation. Each treatment consisted of a single oral dose of 8 mg loperamide HCl followed by a two-week interval before the next treatment. Serum and urine samples obtained at various times after drug administration were assayed for loperamide using a radioimmunoassay specific for the drug. The mean biologic half-life, calculated from the elimination phase of the log serum concentration-versus-time data, was 10.8 +/- 0.6 hours for the overall study, 10.2 +/- 0.6 hours for the syrup formulation, and 11.2 +/- 0.8 hours for the capsules. The loperamide from the syrup was absorbed more rapidly than from the capsule formulation, with the peak serum levels observed at a mean time of 2.4 +/- 0.7 hours for the syrup and 5.2 +/- 0.3 hours for the capsule formulation. The relative areas under the serum loperamide concentration-versus-time curves suggested that the two formulations have comparable physiologic availability. The maximum observed serum concentrations were also similar, indicating the safety of the syrup formulation. Excretion of approximately 1 per cent of the dose in the urine as unchanged loperamide after seven days was observed independent of the particular dosage form that was administered.

Publication types

  • Clinical Trial
  • Comparative Study
  • Randomized Controlled Trial

MeSH terms

  • Adult
  • Antibody Specificity
  • Biological Availability
  • Capsules
  • Half-Life
  • Humans
  • Kinetics
  • Loperamide / administration & dosage
  • Loperamide / immunology
  • Loperamide / metabolism*
  • Male
  • Piperidines / metabolism*
  • Radioimmunoassay


  • Capsules
  • Piperidines
  • Loperamide