Drug Information for ACETAMINOPHEN, ASPIRIN, AND CODEINE* PHOSPHATE CAPSULES: CLINICAL PHARMACOLOGY

Ads
  • Acetaminophen, aspirin, and codeine phosphate capsules combine the analgesic effects of a centrally acting analgesic, codeine, with the peripherally acting analgesics, acetaminophen and aspirin. All ingredients are well absorbed orally. The plasma elimination half-life ranges from 1 to 4 hours for acetaminophen, and from 2.5 to 3 hours for codeine. Although aspirin has a half-life of only about 15 minutes, the apparent biologic half-life of salicylic acid in the therapeutic plasma concentration range is between 6 and 12 hours.

    Codeine retains at least one-half of its analgesic activity when administered orally. A reduced first-pass metabolism of codeine by the liver accounts for the greater oral efficacy of codeine when compared to most other morphine-like narcotics. Following absorption, codeine is metabolized by the liver and metabolic products are excreted in the urine. Approximately 10 percent of the administered codeine is demethylated to morphine, which may account for its analgesic activity.

    Acetaminophen is distributed throughout most fluids of the body, and is metabolized primarily in the liver. Little unchanged drug is excreted in the urine, but most metabolic products appear in the urine within 24 hours.

    Aspirin is rapidly absorbed and almost totally hydrolyzed to salicylic acid following oral administration. Salicylic acid is eliminated by renal excretion and by biotransformation to inactive metabolites. Clearance of salicylic acid in the high-dose range is sensitive to urinary pH and is reduced by renal dysfunction.

  • Drug Information Provided by National Library of Medicine (NLM).
Ads