Exceeding the maximum daily dose of acetaminophen with use of different single-ingredient OTC formulations.

Objectives: To assess whether there are differences in the likelihood of exceeding the daily limit of 4 grams of acetaminophen when using different formulations (325 mg, 500 mg, 650 mg) of OTC single-ingredient (SI) acetaminophen medications.

Design And Setting: Multiyear observational study of acetaminophen use via daily online acetaminophen-usage diaries completed for 7 days.

Participants: A total of 7579 U.S. adults from online research panels who used acetaminophen in the month preceding enrollment and used an OTC SI acetaminophen medication during the study.

Outcome Measure: Exceeding the daily dose.

Results: On days when 325-mg or 500-mg OTC SI formulations were taken, users were not significantly more likely to exceed 4 grams than on days when OTC SI formulations were not used. On days when 650-mg extended-release (ER) formulations were taken, exceeding 4 grams was significantly more likely (8.9% of days vs. 4.4%; P < 0.0001; median on those days was 5.2 g) than on days with 325- or 500-mg OTC SI formulations. Users of 650-mg ER formulations were significantly less likely to know their dosing interval of 8 hours (33% vs. 49%; P < 0.0001) and more likely to redose too soon (26% vs. 10%; P < 0.0001) and to use other acetaminophen medications concomitantly (14% vs. 7%; P < 0.0001). These patterns were strongest among 650-mg ER products that did not include "8-Hour" in the product name.

Conclusion: Usage of 500-mg OTC SI acetaminophen formulations does not contribute differently to exceeding dosage compared with other OTC SI acetaminophen formulations. Exceeding 4 grams is more likely when 650-mg ER formulations are used. Improved consumer information on the packages and counseling from pharmacists may help to reduce practices that contribute to exceeding the labeled daily limit of these medications.