Acetaminophen; Butalbital; Caffeine
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Classification:
Psychotropic Agents
- Anxiolytics, Sedatives, and Hypnotics
Psychotropic Agents
NOTE: This monograph discusses the use of acetaminophen-butalbital-caffeine combination products for management of mild to moderate pain and headaches. Clinicians may wish to consult the individual monographs for more information about the specific mechanism of action and pharmacokinetics of each agent.
Description: Acetaminophen, butalbital, and caffeine are used together in an oral preparation to treat tension headaches, migraines, and mild to moderate pain, especially when antianxiety or relaxant effects are needed. Treatment of multiple recurrent headaches with this combination has not been well studied. According to published guidelines for the acute management of migraine, the use of butalbital-containing analgesics should be limited and carefully monitored due to concerns of overuse, medication-overuse headache, and withdrawal. Acetaminophen is a non-salicylate analgesic with similar analgesic potency to NSAIDs. Butalbital is a barbiturate that is used in this combination for its sedative and relaxant effects. Caffeine is found in many analgesic formulations and may be beneficial in some vascular headaches such as tension and cluster headaches and migraines. This combination was originally approved by the FDA in November 1984.
Mechanism of Action: The roles and interactions of acetaminophen, butalbital and caffeine in the treatment of tension headaches are not well understood.
- Acetaminophen: Acetaminophen acts primarily in the CNS and increases the pain threshold by inhibiting cyclooxygenase, an enzyme involved in prostaglandin (PG) synthesis. Acetaminophen inhibits both isoforms of central cyclooxygenase, COX-1 and COX-2. Acetaminophen does not inhibit PG synthesis in peripheral tissues, which is the reason for its lack of peripheral anti-inflammatory effects. The antipyretic activity of acetaminophen is exerted by blocking the effects of endogenous pyrogen on the hypothalamic heat-regulating center by inhibiting PG synthesis. Heat is dissipated by vasodilatation, increased peripheral blood flow, and sweating.
- Butalbital: Sedative-hypnotic effects of butalbital are similar to phenobarbital and may result from producing or enhancing the inhibitory affects of gamma-aminobutyric acid (GABA) in the thalamus. Barbiturates inhibit ascending conduction in the reticular formation, which interferes with conduction of impulses to the cortex causing sensory cortex depression, decreased motor activity, drowsiness, sedation and changes in cerebral function. Barbiturates also cause a nonselective depressant effect throughout the CNS and are capable of producing all types of CNS mood alterations. In addition, butalbital may exhibit anticonvulsant affects in high, anesthetic doses.
- Caffeine: Caffeine causes cerebral vasoconstriction, which decreases blood flow and oxygen tension. In combination with acetaminophen, caffeine may provide a quicker onset of action and enhance pain relief allowing for lower doses of analgesics. In some patients, caffeine relieves headaches by treating the effects of caffeine withdrawal.
Chemical Structure For: Acetaminophen; Butalbital; Caffeine
Pharmacokinetics: Acetaminophen-butalbital-caffeine is administered orally. All three components are well absorbed from the GI tract. During migraines gastric stasis may occur which could alter the pharmacokinetic parameters of these agents. Time to onset of analgesia is about 1 - 2 hours. All three agents undergo hepatic metabolism.
- Acetaminophen: Acetaminophen is metabolized in the liver via glucuronidation and sulfate conjugation and is excreted in the urine as glutathione and sulfate conjugates. However about 10 - 15% of the acetaminophen dose undergoes oxidative metabolism via cytochrome P450 isoenzymes (CYP) 2E1 and 1A2 and then glucuronidation to cysteine and mercapturic acid conjugates. In cases of glucuronide depletion, such as acetaminophen overdose, a hepatotoxic metabolite is formed. The half-life of acetaminophen in patients with normal hepatic function is 2 - 4 hours.
- Butalbital: Butalbital is metabolized by the hepatic microsomal system and has a half-life of 35 hours. Butalbital induces hepatic enzymes but to a lesser degree than phenobarbital. Butalbital is renally eliminated as metabolites and unchanged drug (3 - 4%).
- Caffeine: Caffeine undergoes hepatic metabolism to paraxanthine, theobromine, and theophylline. Elimination of caffeine is renal as inactive metabolites. The elimination half-life of caffeine in adults is 3 - 7 hours.
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