NCPDP recommendations for standardizing dosing in metric units (mL) on prescription container labels of oral liquid medications, version 2.0

Purpose: Best practices and guidance are provided for standardizing dosing instructions on prescription container labels of oral liquid medications by eliminating use of U.S. customary (household) units and adopting metric units universally, with the goal of decreasing the potential for error and improving safety and outcomes when patients and caregivers take and administer these medications.

Summary: Despite decades of best practice use of metric units in organized healthcare settings and advocacy by various professional societies, medication safety experts, and standards setting organizations, use of household units (e.g., teaspoon) on prescription container labeling instructions for oral liquid medications persists in community pharmacy settings. Five years after publication of the National Council for Prescription Drug Programs' (NCPDP's) original white paper advocating metric-only dosing, very few community pharmacy companies appear to require oral liquid dosing instructions be presented in metric-only units (mL). Error-prone dosing designations contribute to medication errors and patient harm. Use of both multiple volumetric units (e.g., teaspoonsful, tablespoonsful) and multiple abbreviations for the same volumetric units (e.g., mL, cc, mls; tsp, TSP, t) increases the likelihood of dosing errors. Opportunities for error exist with each administration of an oral liquid medication and, unless coordinated with dispensing of appropriate oral dosing devices and optimal counseling, can result in use of household utensils (e.g., uncalibrated teaspoons) or discordantly marked devices that can further exacerbate the risk of error. Since publication of NCPDP's original white paper, new standards have been adopted governing official liquid volume representation, calibrated dosing devices, and e-prescribing software which support the elimination of non-metric units to reduce use of dosing practices that are error-prone. In each case, U.S. customary (household) units have been eliminated in official standards and certification requirements. Therefore, use of non-metric units for oral dosing of liquid medications no longer is an acceptable practice.

Conclusion: Key factors contributing to dosing errors with oral liquid medications include use of multiple volumetric units and abbreviations; failure to institute policies and procedures that eliminate the use of non-metric (e.g., household) units and universally adopt metric-only dosing instructions in all settings; failure to coordinate dosing instructions with dosing device markings, appropriate type (oral syringe versus cup), and optimal volumes (e.g., 1-, 5-, or 10-mL devices); failure to adequately counsel patients about appropriate measurement and administration of oral liquid medication doses; and use or error-prone practices such as missing leading zeros and elimination of trailing zeros in prescriptions and container labels. Adoption of this white paper's recommendations will align dosing designations for oral liquid medications in all settings with current standards and attain universal metric-only practice.