Errors associated with co-names of medicines: The nomenclature of combination medicinal products

In comparison to the efforts required to bring a new drug or formulation to the clinic, bestowing a name on a medicine is relatively simple. However, if the name we choose causes confusion-by making its contents ambiguous or if it is too alike another drug-it can precipitate clinical errors. This prompted the World Health Organization to set up the International Nonproprietary Naming Committee in the 1970s to select unambiguous names for drugs. Unfortunately, multidrug products-which are becoming increasingly popular-do not fall under the remit of conventional International Non-proprietary Nomenclature. We have identified 26 combination formulations that have been historically named with the co-drug format in the United Kingdom. Most of them have also been prescribed in the United Kingdom in the past year, and although several of them are not prescribed very often, 11 were prescribed more than 2000 times. In this paper, we have explored the literature to identify prescribing errors with co-drug products and found several idiosyncrasies that have caused drug errors in the past. We advocate for a standard nomenclature (state the international nonproprietary name [INN] of each component followed by dose information in the x + y format) for these products on the box and in prescribing resources. We hope that this will enhance clarity and safety during prescribing and administration, particularly for high-volume drugs like paracetamol + codeine (co-codamol), amoxicillin + clavulanic acid (co-amoxiclav) and trimethoprim + sulfamethoxazole (co-trimoxazole).