Comparative renal excretion of clofarabine and metformin in the isolated perfused rat kidney model

Purpose: To compare the renal excretion of clofarabine (CLO) and metformin (MET) in the isolated perfused rat kidney (IPK) model. Metformin is a methyl derivative of biguanide with antihyperglycaemic effect which lowers both basal and postprandial plasma glucose levels and improves the insulin resistance in type 2 diabetic mellitus. Clofarabine is a second generation purine nucleoside analog, approved for pediatric patients with relapsed or refractory acute lymphoblastic leukemia. An additional aim of this research was to evaluate a potential renal drug: drug interaction between these two medications.;Method: The IPK experiments were conducted (n=3/group) using the male Sprague-Dawley rats (weighing 320--370 grams) In this research, the excretion of metformin and clofarabine was characterized using the isolated perfused rat kidney (IPK) model. The IPK is well suited for this investigation, since it allows study of renal disposition in the absence of other in vivo processes. This technique has been used to study the renal handling of a wide variety of compounds, including a number of nucleoside analogs. Studies were performed to assess the baseline excretion of metformin and clofarabine separately and to evaluate the effect of inhibitors of organic cation (cimetidine, CMT) transport systems on metformin excretion.;Metformin and clofarabine are administered separately and together, at the clinically relevant concentration of 2 ug/ml to measure baseline excretion and to characterize the drug interaction. Separate methods for HPLC were used to analyze both components separately in both urine and perfusate samples collected after each experiment. The UV spectra of the eluting peaks were determined at a wavelength of 236 nm for Metformin and 264 nm for Clofarabine. GFR of each experiment was calculated by the colorimetric analysis of inulin using anthrone complexation. Preliminary studies found negligible binding to IPK perfusate. Likewise, non-specific binding to the IPK apparatus was ruled out for both metformin and clofarabine.;Results: The renal clearance of metformin alone is 3.9 ml/min with excretion ratio of 5.25 suggesting that metformin undergoes filteration and tubular secretion, but in the presence of cimetidine the renal clearance and excretion ratio is 0.54 ml/min and 0 82, respectively. The renal clearance and excretion ratio of metformin alone and in the presence of Cimetidine were significantly different at 95 % confidence interval. This suggests that metformin is reabsorbed after filteration. In the presence of clofarabine the renal clearance and excretion ratio of metformin is 6.44 ml/min and 7.3 suggests that it undergoes net tubular secretion after filteration and this was not significantly different at 95% confidence interval. The renal clearance of clofarabine alone is 1.1 ml/min and the excretion ratio is 1.56, which suggests that it undergoes net tubular secretion alone. When clofarabine is administered in the presence of metformin, the clearance of clofarabine is 1.4 mllmin and the excretion ratio is 1.9 (not significantly different at 95% confidence interval) which suggests that clofarabine undergoes net tubular secretion in the presence of metformin.;Conclusion: Both metformin and clofarabine display net secretion in the IPK, and renal excretion was significantly inhibited by cimetidine. Although renal OCT transporters appear to play a role in the renal handling of both compounds, the results of this investigation do not provide evidence of a drug: drug interaction between these two medications when they are co-administered.