084: Exploration of Estimated Renal Function & Gabapentin Clearance in Older Adults

This study determined the proportion of older adults who would be predicted to need a GBP dose adjustment based on their eGFR calculated by different established equations that incorporate serum creatinine, cystatin C, age or race.

Description of Methods & Materials:

A total of 222 GBP plasma and serum creatinine concentrations from 59 older adults who were at least 60 years of age were collected from seven nursing homes in Minnesota and California. Plasma GBP concentrations and serum creatinine were measured at the University of Minnesota. Cystatin C concentrations were obtained from the UCSF Medical Center laboratory. Renal function was estimated using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI released in 2012 and updated in 2021^2,3 Cockcroft-Gault (CG)⁴ and Modifications Diet in Renal Disease (MDRD)⁵. We developed a population pharmacokinetic analysis to obtain individual GBP clearance values (CLi~GBP). Subsequently, we determined the correlation between CLi~GBP and eGFR values by using the Spearman’s rank correlation test. Then, we calculated the proportion of patients that were predicted to need dosage adjustments according to the consensus guidelines for oral dosing of primarily renally cleared medications in older adults¹ and the GBP package insert.⁶

Data & Results:

The correlation between CLi~GBP and eGFR formulas ranged from 0.68 to 0.75. The strongest correlation (r=0.75) was seen with the CKD-EPI 2021, which incorporates serum creatinine and cystatin c, but not race, and the lowest (r=0.67) with the CG formula. The proportion of older adults that would need a GBP dose adjustment by using consensus guidelines was 79% (CKD-EPI 2021) and 81% (CG), respectively. On the other hand, based on the GBP package insert recommendation, the proportion of subjects needing GBP dose adjustment using these two different equations was the same, 56%.

Interpretation, Conclusion or Significance:  CONCLUSION: The eGFR calculated from the CKD-EPI equation updated 2021 showed the strongest correlation with GBP clearance. Regardless, if using CKD-EPI 2021 or CG, the proportion of patients predicted to need a GBP dose adjustment is higher based on consensus than on the package insert recommendations. The expansion of this study will include more samples per individual to characterize the intra-individual variability of eGFR over time and its utility for guiding the dosing of this renally cleared medication

Disclosures:

Disclosure: This study was funded in part by the National Institute on Aging of the National Institutes of Health  

                 R01AG026390. JS is a graduate student funded by Fulbright.

Citations/References:

1. Hanlon JT, Aspinall SL, Semla TP, Weisbord SD, Fried LF, Good CB, et al. Consensus guidelines for oral dosing of primarily renally cleared medications in older adults. J Am Geriatr Soc. 2009;57(2):335–40.