Safer loading doses of medicines: summary of a safety report from the National Patient Safety Agency

Some medicines need to be given at high initial doses (loading doses) at the start of treatment, before being reduced to a lower, maintenance dose. Reasons vary for the need for loading doses. In some patients the therapeutic level is needed very quickly—for example, phenytoin to stabilise a patient after a seizure. Loading doses are also needed for medicines that would otherwise take a long time to reach the desired therapeutic levels—for example, without a loading dose, it might take a month for a patient with heart failure to benefit from amiodarone.

Loading doses are complex to prescribe, as they require multistep calculations using information about the patient (such as weight) and the medicine (such as estimated volume of distribution or half life). Staff may mistakenly continue loading doses instead of lowering to maintenance doses, particularly when patients move between settings (for example, from emergency departments to general wards or from hospital back to the community). Little evidence exists in the formal literature on frequency of error or harm, except for isolated case reports.1

From January 2005 to April 2010, staff in England and Wales reported 1165 patient safety incidents relating to loading dose errors. These included two deaths, four cases of severe harm, and 102 of moderate harm. A further death was reported by a coroner.

A typical incident report reads: “Patient prescribed loading dose of 1 g phenytoin on [ward name] then maintenance dose of 1 g BD [twice daily] (usual maintenance dose is around 300 mg OD [once daily]) on Friday … Five 1 …