Calculation skills for nurses: Co-trimoxazole

Abstract

T topic of calculation skills this month is dosage calculation using co-trimoxazole. The licensed indications for co-trimoxazole are restricted because of serious side effects, including blood dyscrasias and StevensJohnson syndrome, to the treatment of and prophylaxis against serious infections such as Pneumocystis jirovecii (previously known as Pneumocystis carinii) pneumonia. However, it is also used to treat toxoplasmosis and nocardiosis. It may be used to treat acute exacerbations of chronic bronchitis and urinary tract infections in adults and acute otitis media in children only where bacteriological testing shows good evidence of sensitivity to this drug combination (1-part trimethoprim with 5-parts sulfamethoxazole) and where there are good reasons to select this drug combination over a single drug alternative. Prophylactic use is common in immunocompromised patients, including those with human immunodeficiency virus (HIV) or those receiving chemotherapy or organ transplantation, to reduce the risk of opportunistic infection. The British National Formulary (BNF) (Joint Formulary Committee, 2013) recommends a treatment dose by mouth or by intravenous (IV) infusion for Pneumocystis jirovecii infection in adults (and children over 4 weeks old) of 120 mg/kg daily in two to four divided doses for 14–21 days. However, the BNF for Children 2013–2014, the preferred reference source for children, gives the amount per dose for oral/IV treatment as 60 mg/kg every 12 hours for 14– 21 days for children aged 1 month to 18 years. It states that the total daily dose can alternatively be divided into 3–4 divided doses and the oral route is preferred. In the adult BNF, the prophylactic dose is related to age rather than weight. In the BNF for Children 2013–14, the oral/IV prophylactic dose is stated for children aged 1 month to 18 years as 450 mg/m (maximum 960 mg) twice daily for three days of the week, to be given either consecutively or on alternate days. In patients with renal impairment, the dose is reduced to half the normal dose in adults and children if the estimated glomerular filtration rate (eGFR) is 15–30 ml/min/1.73 m. If the eGFR is less than 15 ml/min/1.73 Alison Eggleton