Renal impairment (RI) significantly impacts the clearance of drugs through changes in the glomerular filtration rate, protein binding and alterations in the expression of renal drug transport proteins and hepatic metabolizing enzymes. The objectives of this study were to evaluate quantitatively the effects of renal impairment on the pharmacokinetics of drugs undergoing renal transporter-mediated reabsorption. A previously published semi-mechanistic kidney model incorporating physiologically relevant fluid reabsorption and transporter-mediated active renal reabsorption (PMID: 26341876) was utilized in this study. The probe drug/transporter pair utilized was γ-hydroxybutyric acid (GHB) and monocarboxylate transporter 1 (SCL16A1, MCT1). γ-Hydroxybutyric acid concentrations in the blood and amount excreted into urine were simulated using ADAPT 5 for the i.v. dose range of 200-1500 mg/kg in rats and the impact of renal impairment on CLR and AUC was evaluated. A 90% decrease in GFR resulted in a > 100-fold decrease in GHB CLR . When expression of reabsorptive transporters was decreased and fu was increased, CLR approached GFR. The effect of renal impairment on CLR was reduced when the expression of drug metabolizing enzymes (DME) was increased as a result of increased metabolic clearance; the converse held true when the DME expression was decreased. In conclusion, this study quantitatively demonstrated that the effects of renal insufficiency on the clearance of drugs is modulated by transporter expression, contribution of renal clearance to overall clearance, expression of drug metabolizing enzymes, fraction unbound and drug-drug interactions with inhibitors of renal transporters that may be increased in the presence of renal impairment.
Keywords: GFR; GHB; kidney disease; pharmacokinetics; renal transport.
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