Knowledge of dosing directions among current users of acetaminophen-containing medications.

OBJECTIVES: Users should know the active ingredients and dosing directions to optimize the safe use of acetaminophen-containing medications. The aim of this work was to examine knowledge of acetaminophen-containing medication directions among current users.

DESIGN, SETTING, AND PARTICIPANTS: An Internet panel diary study (2012-2016) of 1-week usage of acetaminophen medications (over-the-counter [OTC] and prescription), recorded daily; 9629 participants. Users were asked about ingredients of medications taken; specific dosing instructions were asked for each OTC medication taken. Subjects were considered to be correct only if an accurate response was provided for all of the medications they used.

OUTCOME MEASURES: Analyses examined prevalence of several aspects of knowledge and their relation to the corresponding deviations from directions. Knowledge that acetaminophen was an ingredient was compared between medication types.

RESULTS: Two-thirds of 5161 participants who used only 1 acetaminophen medication knew the ingredient; the proportion was almost halved in 4468 users of 2 or more. Ingredient knowledge was highest for single-ingredient medications (74%); for combination medications it ranged from 39% (cough or cold) to 61% (sleep or other non-pain). About one-third knew the prohibition against concomitant use of multiple acetaminophen medications; 85% knew the maximum one-time OTC dose, but only 47% knew the minimum interval between doses. Correct knowledge was inversely associated with violating the relevant label directions; in particular, knowing the one-time dose decreased the odds of taking too much at one time fivefold. Knowing both the ingredient and the concomitant use prohibition decreased the odds of concomitant use by 50%.

CONCLUSIONS: Knowledge of directions for safe use of acetaminophen-containing medications is poor, and its deficiency is associated with corresponding deviations from label instructions. This study demonstrates a need for education about safe use of acetaminophen-containing medications, particularly for combination products.