A population study of the frequency of high-dose acetaminophen prescribing and dispensing.

BACKGROUND: Recurrent intake of 4 g/day or more of acetaminophen has been associated with elevation of serum alanine aminotransferase (ALT) levels in 30-40% of the exposed population and may result in hepatotoxicity.

OBJECTIVE: To describe the frequency that patients are prescribed acetaminophen doses that exceed 4 g/day across a large population.

METHODS: Using California's Medicaid (Medi-Cal) fee-for-service population, pharmacy claims including over-the-counter (OTC) medications were examined for prescriptions that could result in acetaminophen doses of 4 g/day or more. The period studied, October 2004 through September 2005, was before the Part D pharmacy benefit was available to dually eligible Medicare patients when all prescriptions were covered by the Medi-Cal claims process.

RESULTS: During the pre-Part D evaluation period, approximately 3.27 million beneficiaries were enrolled in the fee-for-service Medi-Cal program. A total of 192,716 (5.9%) were potentially exposed to at least 1 day of 4 g/day or more of acetaminophen. Of those, 769 patients were potentially exposed to at least 1 day of 16 g/day or more. A total of 2664 beneficiaries were dispensed prescriptions and OTC products that, if taken as directed, would have resulted in more than 100 days of acetaminophen doses of 4 g/day or more during the study year.

CONCLUSIONS: Despite electronic systems designed to warn dispensing pharmacists of duplications of drug class and cumulative excessive doses, potentially toxic amounts of acetaminophen are commonly prescribed and dispensed to this population. Better systems, increased awareness, and education of patients, prescribers, and pharmacists are needed to reduce this potential toxic exposure.