Abstract

Liquid preparations of penicillin V (phenoxymethylpenicillin) come in several different strengths, ranging from Phenoxymethylpenicillin Mixture BNF, which contains 62.5 mg in 5 ml, to Penicals 333 (Leo), which has 333 mg in 5 ml (see table). It is worth noting that some preparations with the same brand name are marketed in more than one strength. Children over the age of one year require a dose of 125 mg or more six-hourly and most of the proprietary preparations provide this amount in 5 ml. Failure to realise that the BNF mixture contains only 62.5 mg/5 ml can inadvertently lead to inadequate treatment, if phenoxymethylpenicillin mixture is prescribed in terms of volume only (one teaspoonful, or 5 ml, six-hourly). The dose should therefore always be stated in mg of penicillin. The pharmacist who checks with the prescriber in any instance of apparent urderdosage (e.g. ‘Penicillin V mixture 5 ml, six-hourly’ for a two-year-old, i.e. only 62.5 mg in the present BNF formulation) deserves thanks.