Functional classification: Analgesic, opioid
Exact mechanism of action for acetaminophen is not known; however, a centrally mediated mechanism is likely, either via inhibition of central prostaglandin synthesis or effects on serotonergic inhibitory pain pathways. In this formulation, the opiate codeine is added to enhance analgesia.
Effects of codeine are not established in animals. Systemic absorption of codeine from oral administration is small in dogs, and codeine may play only a minor role in analgesia.
Indications and Clinical Uses
Acetaminophen + Codeine is used for analgesia in dogs (e.g., postoperative use). Codeine or codeine with acetaminophen is indicated for treatment of moderate pain. Codeine formulations have also been used as an antitussive. Despite the widespread use of codeine in humans, the efficacy in animals for its antitussive use or analgesic use has not been established. Oral absorption of codeine in dogs is low.
Because codeine is converted to morphine (10% of dose) for its activity and the duration of morphine is short in dogs, the clinical effectiveness of codeine in dogs may be questionable.
Adverse Reactions and Side Effects
Acetaminophen + Codeine is well tolerated in dogs at doses listed; however, high doses have caused liver toxicity.
Contraindications and Precautions
Do not administer to cats because acetaminophen is known to be toxic to cats. Codeine is a Schedule II controlled substance.
In people, other drugs (especially alcohol) will increase risk of hepatotoxicity. It is not known if other drugs increase this risk in animals, but consider this possibility when administering other drugs that may affect hepatic metabolism.
Instructions for Use
Many generic preparations are available. Consider that other ingredients may be present in some combination tablets (e.g., ibuprofen or caffeine).
Patient Monitoring and Laboratory Tests
Monitor liver enzyme levels periodically to look for evidence of hepatotoxicity caused by acetaminophen.
Acetaminophen + Codeine is available in oral solution and tablets. A variety of formulations are available (e.g., 300-mg acetaminophen plus 15-, 30-, or 60-mg codeine).
Stability and Storage
Acetaminophen is stable in aqueous solutions. Maximum stability is at pH of 57.
Small Animal Dosage
Follow dosing recommendations for codeine. Administer dose to deliver doses of codeine equivalent to 0.5-1.0 mg/kg q4-6h PO.
Large Animal Dosage
No dose has been reported for large animals.