Renal drug dosing recommendations: evaluation of product information for brands of the same drug

Objectives: To review the product information (PI) for various brands of the same generic drugs and investigate the extent to which information is currently available on dosing in renal impairment and the concordance between the dosing recommendations for the same generic drug.

Method: The Monthly Index of Medical Specialities (MIMS) was examined for 28 generic drugs recommended to be used with caution in renal impairment. For each generic drug all available brands listed as having solid oral dosage form were recorded. For each identified brand, the current PI was consulted and data referring to renal impairment was collated. The dissimilarity between these PI regarding the renal dosage recommendation was determined.

Results: There was generally a lack of detailed information in the PI on the use of drugs in patients with renal impairment. The majority of PI documents (88 of 155 PI; 57%) provided quantitative dosage recommendations, but this was often not detailed enough to help users to make an informed decision. For 37 PI documents (24%), an altered dosage regimen was proposed without a quantifiable measure of renal function reported in the dose recommendation. The renal function severity category terms used and the associated quantitative values were also not consistent. It was observed that the recommendations varied among different brands of hydromorphone, morphine, oxycodone, tramadol, metformin and topiramate.

Conclusion: The reporting of renal function quantification methods, and associated dosage recommendations, in PI requires standardisation to ensure optimal drug dosing. Regularly updating of PI is also necessary.