Standardised nomenclature for combination formulations could “minimise confusion and prevent medication errors”, suggests recently published research.

The authors identified 26 combination formulations with ‘co-drug’ names in the UK. Eleven were prescribed more than 2,000 times during 2023, including paracetamol + codeine (co-codamol), which saw an average of 1.26 million items dispensed each month; carbidopa + levodopa (co-careldopa – 114,656 items a month); dihydrocodeine + paracetamol (co-dydramol – 110,506 average monthly items; and amoxicillin + clavulanic acid (co-amoxiclav), with an average of 106,504 items a month.

A literature review found examples of errors involving, with decreasing frequency, co-amoxiclav, co-amilofruse, co-beneldopa, co-careldopa, co-codamol, co-dydramol and co-trimoxazole. 

The authors noted that packaging of co-drugs can also be inconsistent. For example, some co-codamol products do not prominently display the individual active ingredients, while the strength is unclear on others. To reduce the risk of errors, the authors advocate a standardised nomenclature on the box and in prescribing resources so that the international non-proprietary name (INN) of each component is followed by the strengths in the x + y format. 

For example, trimethoprim-sulfamethoxazole 800/160mg becomes trimethoprim 800mg + sulfamethoxazole 160mg. Symtuza, which contains darunavir/cobicistat/emtricitabine/tenofovir alafenamide 800/150/200/10mg, would become darunavir 800mg + cobicistat 150mg + emtricitabine 200mg + tenofovir alafenamide 10mg. Packs and information should also include the co-name to avoid confusion, for example: co-codamol: paracetamol 500mg + codeine 30mg. 

The authors argue that this nomenclature should apply to proprietary, generic and unlicensed products, including oral contraceptives and inhaled formulations. “We hope that this will enhance clarity and safety during prescribing and administration, particularly for high volume drugs,” they say.