Background Inpatients frequently require dose adjustments of medicines due to acute changes in renal function. The FDA recommend adjusting medicines according to the estimated glomerular filtration obtained with the Cockcroft-Gault formula. However the Modification of Diet in Renal Disease (MDRD) study equation is widely recognised as more accurate than Cockcroft-Gault, which confuses clinicians because they do not know its utility for adjusting drug doses.

Purpose To compare the incidence in inpatients of medicine dosing errors depending on the type of equation used to estimate it: Cockcroft-Gault or MDRD.

Materials and Methods A cross-sectional study was conducted in a low complexity unit. Patients were included with impaired renal function who were not on haemodialysis.

We used the FDA guidelines to determine the incidence of errors.

Fisher’s test was used to compare the groups, with statistical significance level <0.05.

Results We included 56 inpatients and 214 prescriptions. 58% were women and 68% were older than 65. We detected 42% and 28% of errors using CG and MDRD, respectively (p = 0.014). The most common error was an overdose (79%) followed by an underdose (12%) and contraindication (9%).

Further analysis found that the difference between the two equations occurred only in the following subgroups of patients: patients with mild to moderate impairment of renal function (38% versus 23%, p = 0.03), older than 65 years (51% versus 30%, p = 0.01) and low body weight (37% versus 31%, p = 0.04).The distribution of types of errors was similar in the three subgroups.

Conclusions The percentage of dosing error for both methods was similar to that reported in the literature.

The two equations were not discordant except in the elderly, in patients with low body weight and with mild renal dysfunction. This could explain why there were differences in the incidence of medicine errors in these subgroups.

In the absence of a gold standard to assess the acute deterioration of renal function and considering the limitations in estimating renal function with these equations, clinicians should include clinical judgement when determining the dose for each patient. The dose should be determined by weighing the risk of toxicity with higher doses versus the risk of treatment failure with lower doses, especially in elderly and low body weight patients.

No conflict of interest.