Low-dose oral methotrexate is associated with wrong frequency dosing errors, when taken once daily instead of the intended once weekly schedule. The Institute for Safe Medication Practices (ISMP) has classified methotrexate as a risk medication that can cause fatal and harmful errors in patients, despite warnings. However, the incidence of wrong frequency errors is unknown. A chart confirmed analysis was conducted in one Sentinel Data Partner (Kaiser Permanente Northern California) and found the incidence of low-dose oral methotrexate wrong frequency dosing errors to be 0.4%. FDA is using these findings to determine appropriate regulatory action.