Influence of chronic ingestion of grapefruit juice on steady-state blood concentrations of cyclosporine A in renal transplant patients with stable graft function.

Ingestion of grapefruit juice has been shown to increase the oral bioavailability of several dihydropyridines and cyclosporine A [1, 2], with the suggested mechanism being inhibition of presystemic metabolism by CYP3A4 [2-5]. The clinical significance of these interactions is uncertain because of a lack of chronic dosing studies [2] and a paucity of pharmacodynamic data [2, 5]. One study has reported increased trough concentrations of cyclosporine in patients dosed chronically with grapefruit juice [5]. We confirm this finding. Ten medically stable renal transplant out-patients (five males, five females, mean age 51 and 45 years, respectively) receiving continuous cyclosporine therapy (mean dose 3.6 mg kg-' day-, range 2.34 to 6.25) were recruited after giving informed consent and approval of the study by the institutional ethics committee. Transplants had been performed between 1.5 and 11.8 years prior to the study. Only one patient received a concomitant low constant dosage of a drug (verapamil) known to effect CYP3A4. A crossover design with 7 days between arms was used, and patients were randomized to receive either 175 ml of 'Hitchcock'® grapefruit juice from a single commercial batch or the same volume of mineral water with twice daily cyclosporine capsules (Sandimmum®) for a period of 7 days each. On day 6 of each arm, patients fasted overnight beginning at 22.00 h. The next morning, cyclosporine was taken 12 h after the previous evening's dose, followed by ingestion of grapefruit juice or mineral water. A small breakfast was served 1 h and a full meal 5 h after dosage. Patients were requested to drink 200 ml mineral water hourly. The second dose of cyclosporine was taken 12 h after the first. Blood samples were collected into plastic EDTA tubes (Monovette®, Sarstedt, Numbrecht, Germany) immediately before dosage and at 1, 2, 3, 4, 5, 6, 7, 9 and 12 h thereafter, and deep frozen at -35° C. Whole blood cyclosporine and metabolite concentrations were assayed using TDx® cyclosporine monoclonal and TDx® cyclosporine and metabolite kits (Abbott Laboratories, Abbott Park, IL 60064). Between-run coefficients of variation were 4.6% at 151.5 gg 1-1 and 3.7% at 864.6 kg 1-1 (monoclonal) and 7.8% at 350.7 kg 1-1 and 4.5% at 1650.1 kg 1-l (nonspecific assay). Corresponding within-run values were 3.0%/1.7% and 3.4%/2.8%, respectively. The working analytical ranges were 25-1500 jg 1-1 and 60-2000 kg 1-1. Values of Cmni, Gmax (kg l ), and tmax (h) were noted directly from the day 7 data. AUC values (kg 1-l h) for the dosing interval (AUC(r)) were calculated using the linear trapezoidal rule. Total metabolites were estimated by subtracting the values obtained with the monoclonal assay from those of the nonspecific assay. Ingestion of grapefruit juice was associated with a significant increase in mean Cmin (136 + 21 s.d. vs 241 + 84 s.d.; 95% CI of difference, 43 to 166) and AUC(r) (3241 ± 481 vs 4329 ± 1272; 95% CI of difference, 187 to 1989) values of unchanged cyclosporine, but no significant change in Cmax (655 ± 137 vs 718 ± 311; 95% CI of difference, -181 to 308). Median values of tmax were 2 (range: 1-3) and 3 (range: 1-8). Total metabolites showed a corresponding significant increase in mean Cmin (191 ± 48 vs 310 ± 160; 95% CI of difference, 32 to 205) and of AUC(t) (2899 + 805 vs 4493 ± 2167; 95% CI of difference, 391 to 2798) without significant change in Cmax (431 ± 146 vs 522 ± 261; 95% CI of difference, -92 to 276). Median values of tmax were 2 (range: 1-3) and 4 (range 2-7). The mean metabolite/cyclosporine AUC(r) ratios were 0.887 ± 0.168 vs 1.027 ± 0.352 with a 95% CI of difference of -0.038 to 0.318. Thus, the results indicate a mean increase of 77% and 62% in the trough concentrations of cyclosporine and its metabolites, respectively, and a 34% and 55% increase in the AUC(t) during continuous ingestion of grapefruit juice, confirming previous findings [5]. It has been suggested that such changes are caused by inhibition of the pre-hepatic CYP3A4-mediated metabolism of cyclosporine in the gut wall [2, 5]. However, we did not demonstrate a lower metabolite/cyclosporine ratio in blood.