Thomas Vanhove

Clinical determinants of calcineurin inhibitor disposition: a mechanistic review

Abstract The calcineurin inhibitors (CNIs) tacrolimus and cyclosporine are widely used immunosuppressive drugs characterized by high pharmacokinetic and pharmacodynamic variability, both between and within patients. CNIs are highly lipophilic, poorly soluble, undergo extensive first-pass metabolism and are cleared by the liver. In both gut and liver, CNIs are substrates for the cytochrome P450 (CYP) enzymes 3A4 and 3A5 as well as the P-glycoprotein (P-gp) transporter, whose functions are determined by a complex interplay between genetic polymorphisms, the inductive or inhibitory effects of many drugs, herbs, food constituents and endogenous substances such as uremic toxins in case of end-stage renal disease. The current literature is reviewed for all common clinical determinants of variability in CNI disposition such as food intake, diarrhea and other intestinal pathology, anemia, hypoalbuminemia, hyperlipidemia, liver and kidney disease, aging, ethnicity, formulation and time post-transplant, focusing on the underlying mechanisms. Drugs and herb- and food constituents mainly interact with CNIs at the gut level by affecting bioavailability, with interactions generally being much more pronounced in case of oral compared with intravenous co-administration. Cyclosporine disposition is less susceptible to these interactions compared with tacrolimus, possibly because cyclosporine is itself a moderately strong CYP3A4- and strong P-gp inhibitor, blunting the effect of additional inhibitors. P-gp also has a major role in limiting distribution of CNI to tissues such as the brain, placenta, lymphocytes and kidney. Inactivating polymorphisms and inhibition of P-gp have the potential to significantly increase CNI exposure in these tissues with possible implications for toxicity and efficacy.

Reasons for dose reduction of mycophenolate mofetil during the first year after renal transplantation and its impact on graft outcome

Mycophenolate mofetil (MMF) decreases the risk of acute rejection and is associated with improved graft survival in renal transplant recipients. However, MMF‐related side effects often necessitate dose reduction, which may expose patients to a higher risk of acute rejection and graft loss. This studys aim was to examine the reasons for MMF dose reduction during the first post‐transplant year and its impact on acute rejection, overall and death‐censored graft loss. Methods: Single‐center retrospective analysis of 749 renal transplant recipients treated with MMF in their initial maintenance immunosuppressive protocol. Results: In 365 patients (48.7%) a total of 530 MMF dose reductions were done. Reasons for reduction were hematologic toxicity (46.5%), infection (16.1%), gastrointestinal side effects (12.3%), malignancy (2.1%), study protocol (14.6%), and unknown (13.5%). MMF dose reduction as such was not an independent predictor of acute rejection or graft survival, although reductions in ≥50% of initial dose were significantly associated with acute rejection. Conclusions: In this retrospective cohort, by far the most important reason for MMF dose reduction during the first post‐transplantation year was hematologic. MMF dose reductions in ≥50% increased the risk of acute rejection but did not compromise graft survival.

High Intrapatient Variability of Tacrolimus Concentrations Predicts Accelerated Progression of Chronic Histologic Lesions in Renal Recipients

High intrapatient variability (IPV) of tacrolimus concentrations is increasingly recognized as a predictor of poor outcome in solid organ recipients. How it relates to evolution of histology has not been explored. We analyzed tacrolimus IPV using the coefficient of variability (CV) from months 6–12 after transplantation in a cohort of 220 renal recipients for whom paired protocol biopsies at 3 mo and 2 years were available. Recipients in the highest CV tertile had an increased risk of moderate to severe fibrosis and tubular atrophy by 2 years compared with the low‐IPV tertile (odds ratio [OR] 2.47, 95% confidence interval [CI] 1.09–5.60, p = 0.031; and OR 2.40, 95% CI 1.03–5.60, p = 0.043, respectively). Other predictors were donor age, severity of chronic lesions at 3 mo, and presence of borderline or subclinical rejection at 3 mo. Chronicity score increased significantly more in the high CV tertile group than in the middle and low tertiles (mean increase 1.97 ± 2.03 vs. 1.18 ± 2.44 and 1.12 ± 1.80, respectively; p < 0.05). CV did not predict evolution of renal function, which did not deteriorate within the 2‐year follow‐up period. These results indicate that high IPV is related to accelerated progression of chronic histologic lesions before any evidence of renal dysfunction.

Progressive decline in tacrolimus clearance after renal transplantation is partially explained by decreasing CYP3A4 activity and increasing haematocrit

AIMS The long-term disposition of tacrolimus following kidney transplantation is characterized by a gradual decrease in dose requirements and increase in dose-corrected exposure. This phenomenon has been attributed to a progressive decline in cytochrome P450 3A4 (CYP3A4) activity, although this has never been demonstrated in vivo. METHODS Sixty-five tacrolimus- and 10 cyclosporine-treated renal transplant recipients underwent pharmacokinetic testing at day 7 and months 1, 3, 6 and 12 after transplantation, including 8-h area under the concentration-time curve (AUC) for tacrolimus or cyclosporine and assessment of CYP3A4 activity using oral and intravenous midazolam (MDZ) drug probes. RESULTS Tacrolimus clearance decreased gradually throughout the entire first year but only in CYP3A5*3/*3 homozygous recipients (25.6 ± 11.1 l h(-1) at day 7; 17 ± 9.1 l h(-1) at month 12; P < 0.001). In mixed model analysis, decreasing CYP3A4 activity, measured by apparent oral MDZ clearance (924 ± 443 ml min(-1) at day 7 vs. 730 ± 344 ml min(-1) at month 1; P < 0.001), explained 55.4% of the decline in tacrolimus clearance in the first month. CYP3A4 activity decreased by 18.9 ml min(-1) for every milligram of methylprednisolone dose tapering within the first month; beyond this point it remained stable. A gradual rise in haematocrit throughout the entire first year explained 31.7% of the decrease in tacrolimus clearance in the first month and 23.6% of the decrease between months 1 and 12. Cyclosporine clearance did not change over time. CONCLUSIONS The maturation of tacrolimus disposition in the first year after renal transplantation observed in CYP3A5*3/*3 homozygous patients can partly be explained by a (steroid tapering-related) decline in CYP3A4 activity and a progressive increase in haematocrit.

Effect of the Direct Oral Anticoagulants Rivaroxaban and Apixaban on the Disposition of Calcineurin Inhibitors in Transplant Recipients.

Background: Calcineurin inhibitors (CNIs) and direct oral anticoagulants (DOACs) share certain metabolic pathways, but whether DOACs influence CNI exposure has not been assessed. Methods: A single-center retrospective analysis was performed including 39 organ recipients treated with the combination of a CNI and rivaroxaban (n = 29) or apixaban (n = 10). Dose-corrected CNI trough concentrations (C0/D) during 200 days before and after DOAC initiation were recorded (n = 261), together with covariates known to influence CNI disposition such as steroid dose and hematocrit. The average C0/D before and during DOAC therapy was compared using paired samples t test. Multivariable mixed models were constructed to estimate the effect of DOAC and other predictors on C0/D at each time point. Results: Group average C0/D was not significantly different before and during DOAC therapy for any CNI–DOAC combination (P = 0.089–0.761), although C0/D changed >20% in 19/39 patients (13 increases, 6 decreases). In multivariable analysis, independent predictors of tacrolimus C0/D were methylprednisolone dose (P = 0.039) and concomitant use of a CYP3A inhibitor (P = 0.007). The subgroup analysis per DOAC showed a limited but significant effect of rivaroxaban on tacrolimus C0/D (9.2% increase, P = 0.042). Independent predictors of ciclosporin C0/D were age (P = 0.018) and use of any DOAC (12.1% increase, P = 0.020). Conclusions: Apixaban, and particularly rivaroxaban, may cause a limited (<20%) increase in CNI trough concentration, an effect that is unlikely to trigger a dose change. It may be prudent to perform an additional CNI trough concentration measurement 5–7 days after DOAC initiation, but preemptive CNI dose changes are not warranted based on these observations.

Effect of ABCB1 diplotype on tacrolimus disposition in renal recipients depends on CYP3A5 and CYP3A4 genotype

The relevance of most genetic polymorphisms beyond CYP3A5*1 on tacrolimus disposition remains unclear. We constructed a predictive mixed model for tacrolimus dose-corrected trough concentration (C0/dose) at months 3, 12 and 24 after transplantation in a retrospective cohort of 766 predominantly Causasian adult renal recipients (n=2042 trough concentrations). All patients were genotyped for 32 single-nucleotide polymorphisms with a proven or possible relevance to tacrolimus disposition based on the previous studies. Of these, ABCB1, ABCC2, OATP1B1, COMT, FMO, PPARA and APOA5 were analyzed as (functional) diplotype groups. Predictors of C0/dose were CYP3A5*1, hematocrit, age, CYP3A4*22, use of concomitant CYP3A4 inhibitor or inducer, ALT, estimated glomerular filtration rate, tacrolimus formulation (once vs twice daily), ABCB1 diplotype and time after transplantation. The effect of ABCB1 diplotype was small but strongly accentuated in CYP3A4*22 carriers and non-existent in CYP3A5 expressors. ABCC2 diplotype had a limited effect on C0/dose that was only statistically significant in CYP3A5 non-expressors.

Determinants of the Magnitude of Interaction Between Tacrolimus and Voriconazole/Posaconazole in Solid Organ Recipients

Administration of azole antifungals to tacrolimus‐treated solid organ recipients results in a major drug–drug interaction characterized by increased exposure to tacrolimus. The magnitude of this interaction is highly variable but cannot currently be predicted. We performed a retrospective analysis of 126 solid organ recipients (95 lung, 31 kidney) co‐treated with tacrolimus and voriconazole (n = 100) or posaconazole (n = 26). Predictors of the change in tacrolimus dose‐corrected trough concentrations (C/D) between baseline and tacrolimus–azole co‐therapy were assessed using linear mixed modeling. Patients were genotyped for relevant polymorphisms in CYP3A4, CYP3A5, MDR1, CYP2C19, POR, and UGT1A4. Tacrolimus C/D increased by a factor 5.0 ± 2.7 (range 1.0–20.2) for voriconazole and 4.4 ± 2.6 (range 0.9–18.0) for posaconazole, suggesting that a 66% dose reduction is insufficient for the majority of patients. Change in C/D was blunted in CYP3A5 expressors (estimated effect: ‐43%, p = 0.017) and affected by hematocrit (+8% per %, p = 0.004), baseline C/D (‐14% per 100% increase, p < 0.001), and age (+1%, p = 0.008). However, the final model explained only 22% of interindividual variability in C/D change. In conclusion, CYP3A5 genotype and several clinical variables were identified as modulators of the tacrolimus–azole interaction, but these did not permit accurate predictions in individual patients.

Fexofenadine, a Putative In Vivo P‐glycoprotein Probe, Fails to Predict Clearance of the Substrate Tacrolimus in Renal Recipients

Whether the combined use of probe drugs for CYP3A4 and P‐glycoprotein can clarify the relative contribution of these proteins to pharmacokinetic variability of a dual substrate like tacrolimus has never been assessed. Seventy renal recipients underwent simultaneous 8‐h pharmacokinetic profiles for tacrolimus, the CYP3A4 probe midazolam, and the putative P‐glycoprotein probe fexofenadine. Patients were genotyped for polymorphisms in CYP3A5, CYP3A4, ABCB1, ABCC2 and SLCO2B1, ‐1B1, and 1B3. Carriers of the ABCB1 2677G>A polymorphism displayed lower fexofenadine Cmax (–66%; P = 0.012) and a trend toward higher clearance (+157%; P = 0.078). Predictors of tacrolimus clearance were CYP3A5 genotype, midazolam clearance, hematocrit, weight, and age (R2 = 0.61). Fexofenadine pharmacokinetic parameters were not predictive of tacrolimus clearance. In conclusion, fexofenadine pharmacokinetics varied considerably between renal recipients but most of this variability remained unexplained, with only minor effects of genetic polymorphisms. Fexofenadine cannot be used to assess in vivo CYP3A4–P‐glycoprotein interplay in tacrolimus‐treated renal recipients.

A noninferiority trial comparing a heparin-grafted membrane plus citrate-containing dialysate versus regional citrate anticoagulation: results of the CiTED study

Background Anticoagulation is a prerequisite for successful haemodialysis. Heparin and low-molecular weight heparins are routinely used despite increased bleeding risk. Regional citrate anticoagulation (RCA) is efficacious, but is laborious and may induce metabolic disturbances. Heparin-grafted membranes are less efficacious. It is not known whether combining citrate-containing dialysate and a heparin-grafted membrane is a valid anticoagulation strategy. Methods We performed a randomized crossover noninferiority trial, with a prespecified noninferiority threshold of 10% in maintenance dialysis patients ( n  = 25). We compared the combination of citrate-containing dialysate plus a heparin-grafted membrane [CiTrate and EvoDial (CiTED) protocol] with RCA. The primary endpoint was completion of dialysis without significant clotting. Secondary endpoints included time to clotting, achieved Kt / V urea , loss of total cell volume, venous air chamber clotting score and systemic-ionized calcium concentration. Results In total, 1284 sessions were performed according to study protocol, 636 in the CiTED arm and 648 in the RCA arm. The primary outcome of preterm interruption due to clotting occurred in 36 (5.7%) of sessions in the CiTED arm, and in 40 (6.2%) sessions in the RCA arm, thereby meeting noninferiority criteria (P < 0.0001). Most of the clotting events occurred in the fourth hour of dialysis. Repetitive clotting occurred in four patients in the CiTED arm and one patient in the RCA arm. Time to preterm interruption due to clotting and achieved Kt / V urea was not significantly different. Systemic-ionized calcium levels during treatment were significantly lower in the RCA arm and clinically relevant hypocalcaemia was noted only in the RCA arm. Conclusion The combination of citrate-containing dialysate and a heparin-grafted membrane is a valid alternative to RCA.

Drug-drug interactions between immunosuppressants and antidiabetic drugs in the treatment of post-transplant diabetes mellitus.

Post-transplant diabetes mellitus is a frequent complication of solid organ transplantation that generally requires treatment with lifestyle interventions and antidiabetic medication. A number of demonstrated and potential pharmacokinetic drug-drug interactions (DDIs) exist between commonly used immunosuppressants and antidiabetic drugs, which are comprehensively summarized in this review. Cyclosporine (CsA) itself inhibits the cytochrome P450 (CYP) 3A4 enzyme and a variety of drug transporters. As a result, it increases exposure to repaglinide and sitagliptin, will likely increase the exposure to nateglinide, glyburide, saxagliptin, vildagliptin and alogliptin, and could theoretically increase the exposure to gliquidone and several sodium-glucose transporter (SGLT)-2 inhibitors. Currently available data, although limited, suggest that these increases are modest and, particularly with regard to gliptins and SGLT-2 inhibitors, unlikely to result in hypoglycemia. The interaction with repaglinide is more pronounced but does not preclude concomitant use if repaglinide dose is gradually titrated. Mycophenolate mofetil and azathioprine do not engage in DDIs with any antidiabetic drug. Although calcineurin inhibitors (CNIs) and mammalian target of rapamycin inhibitors (mTORi) are intrinsically prone to DDIs, their disposition is not influenced by metformin, pioglitazone, sulfonylureas (except possibly glyburide) or insulin. An effect of gliptins on the disposition of CNIs and mTORi is unlikely, but has not been definitively ruled out. Based on their disposition profiles, glyburide and canagliflozin could affect CNI and mTORi disposition although this requires further study. Finally, delayed gastric emptying as a result of glucagon-like peptide-1 agonists seems to have a limited, but not necessarily negligible effect on CNI disposition.