Drug Therapy in Transplant Recipients

Use of a cocktail probe to assess potential drug interactions with cytochrome P450 after administration of belatacept, a costimulatory immunomodulator

Aim

This open‐label study investigated the effect of belatacept on cytokine levels and on the pharmacokinetics of caffeine, losartan, omeprazole, dextromethorphan and midazolam, as CYP probe substrates after oral administration of the Inje cocktail in healthy volunteers.

Methods

Twenty‐two evaluable subjects received the Inje cocktail on Days 1, 4, 7 and 11 and belatacept infusion on Day 4.

Results

Since belatacept caused no major alterations to cytokine levels, there were no major effects on CYP‐substrate pharmacokinetics, except for a slight (16–30%) increase in omeprazole exposure, which was probably due to omeprazole‐mediated, time‐dependent CYP inhibition. Belatacept did not cause major alterations in the pharmacokinetics, as measured by the geometric mean ratios and associated 90% confidence interval for area under the plasma concentration ‐time curve from time zero to infinity on Day 7 comparing administration with and without belatacept for caffeine (1.002 [0.914, 1.098]), dextromethorphan (1.031 [0.885, 1.200]), losartan (1.016 [0.938, 1.101)], midazolam (0.968 [0.892, 1.049]) or their respective metabolites.

Conclusions

Therefore, no dose adjustments of CYP substrates are indicated with belatacept coadministration.

Pharmacokinetics and pharmacodynamics of immunosuppressive drugs in elderly kidney transplant recipients

Elderly patients are a fast growing population among transplant recipients over the past decades. Both the innate and adaptive immune reactivity decrease with age, which is believed to contribute to the decreased incidence of acute rejection and increased infectious death rate in elderly transplant recipients. In contrast to recipient age, donor age is associated with a higher incidence of acute rejection. Pharmacokinetic studies in renal transplant recipients show that CNI troughs are >5% higher in elderly compared to younger patients given the same dose normalized by body weight. This may impact the starting dose of tacrolimus and cyclosporine. Possibly in elderly patients the intracellular (in lymphocyte) concentrations are relatively high in relation to the whole blood concentration, resulting in a stronger pharmacodynamic effect at the same whole blood trough concentration. For cyclosporine this has been shown, but it is not clear if the same is true for other immunosuppressive drugs. Pharmacodynamic studies have compared the inhibition of target enzymes, or more downstream effects of immunosuppressive drugs, in younger and older patients. Measurement of nuclear factor of activated T-cell (NFAT)-regulated gene expression (RGE), a pharmacodynamic read-out of CNI, is a promising biomarker of immunosuppression. Low levels of NFAT RGE are associated with increased risk of infection and non-melanoma skin cancer in elderly patients. Clinical trials to evaluate the safety and efficacy of immunosuppression regimens in this specific patient population, which is underrepresented in published trials, are lacking. More studies in elderly patients are needed to investigate the impact of age on the pharmacokinetics or pharmacodynamics of immunosuppressive drugs, and to decide on the optimal regimen and target levels for elderly transplant recipients.

Immunosenescence and organ transplantation

Increasing numbers of elderly transplant recipients and a growing demand for organs from older donors impose pressing challenges on transplantation medicine. Continuous and complex modifications of the immune system in parallel to aging have a major impact on transplant outcome and organ quality. Both, altered alloimmune responses and increased immunogenicity of organs present risk factors for inferior patient and graft survival. Moreover, a growing body of knowledge on age-dependent modifications of allorecognition and alloimmune responses may require age-adapted immunosuppression and organ allocation. Here, we summarize relevant aspects of immunosenescence and their possible clinical impact on organ transplantation.

Primary care of the renal transplant patient

There has been a remarkable rise in the number of kidney transplant recipients (KTR) in the US over the last decade. Increasing use of potent immunosuppressants, which are also potentially diabetogenic and atherogenic, can result in worsening of pre-existing medical conditions as well as development of post-transplant disease. This, coupled with improving long-term survival, is putting tremendous pressure on transplant centers that were not designed to deliver primary care to KTR. Thus, increasing numbers of KTR will present to their primary care physicians (PCP) post-transplant for routine medical care. Similar to native chronic kidney disease patients, KTRs are vulnerable to cardiovascular disease as well as a host of other problems including bone disease, infections and malignancies. Deaths related to complications of cardiovascular disease and malignancies account for 60-65% of long-term mortality among KTRs. Guidelines from the National Kidney Foundation and the European Best Practice Guidelines Expert Group on the management of hypertension, dyslipidemia, smoking, diabetes and bone disease should be incorporated into the long-term care plan of the KTR to improve outcomes. A number of transplant centers do not supply PCPs with protocols and guidelines, making the task of the PCP more difficult. Despite this, PCPs are expected to continue to provide general preventive medicine, vaccinations and management of chronic medical problems. In this narrative review, we examine the common medical problems seen in KTR from the PCP's perspective. Medical management issues related to immunosuppressive medications are also briefly discussed.

Prevalence and Correlates of Influenza Vaccination among Kidney Transplant Patients

Context

Immunosuppressive regimens increase kidney transplant patients' risk of contracting life-threatening influenza. However, little information exists about the prevalence and correlates of influenza vaccinations in this population.

Objective

To determine the prevalence and explore correlates of influenza vaccination in kidney transplant recipients.

Design, Sample, and Setting

This cross-sectional study used data from the Supporting Medication Adherence in Renal Transplantation study. The convenience sample consisted of 356 adult kidney transplant recipients (58.1% male; mean age, 52.9 [SD 13.53] years) recruited from 2 Swiss transplant outpatient clinics. Influenza vaccination status was assessed by self-report (yes/no).

Main Outcome Measure

Known correlates of vaccination in chronically ill patients (older age, cohabitation, higher education, higher socioeconomic status, financial stability, more comorbid diseases, nonsmoking status, and clinical site where care is received) were entered into a multiple logistic regression model.

Results

Of the 356 patients, only 83 (23.3%) reported having been vaccinated against influenza in the previous year. Positive vaccination status was significantly related to older age (odds ratio, 1.04; 95% confidence interval, 1.02–1.06).

Conclusion

Despite national and international guidelines recommending influenza vaccination in kidney transplant recipients, the prevalence of influenza vaccination in this sample was low. This study's results suggest that transplant centers need to implement policies to maximize influenza vaccination of their patients.

Immunotherapy in elderly transplant recipients: a guide to clinically significant drug interactions

Currently, >50% of candidates for solid organ transplantation in Europe and the US are aged >50 years while approximately 15% of potential recipients are aged >or=65 years. Elderly transplant candidates are characterized by specific co-morbidity profiles that compromise graft and patient outcome after transplantation. The presence of coronary artery or peripheral vascular disease, cerebrovascular disease, history of malignancy, chronic obstructive lung disease or diabetes mellitus further increases the early post-transplant mortality risk in elderly recipients, with infections and cardiovascular complications as the leading causes of death. Not only are elderly patients more prone to developing drug-related adverse effects, but they are also more susceptible to pharmacokinetic and pharmacodynamic drug interactions because of polypharmacy. The majority of currently used immunosuppressant drugs in organ transplantation are metabolized by cytochrome P450 (CYP) or uridine diphosphate-glucuronosyltransferases and are substrates of the multidrug resistance (MDR)-1 transporter P-glycoprotein, the MDR-associated protein 2 or the canalicular multispecific organic anion transporter, which predisposes these immunosuppressant compounds to specific interactions with commonly prescribed drugs. In addition, important drug interactions between immunosuppressant drugs have been identified and require attention when choosing an appropriate immunosuppressant drug regimen for the frail elderly organ recipient. An age-related 34% decrease in total body clearance of the calcineurin inhibitor ciclosporin was observed in elderly renal recipients (aged >65 years) compared with younger patients, while older recipients also had 44% higher intracellular lymphocyte ciclosporin concentrations. Similarly, using a Bayesian approach, an inverse relationship was noted between sirolimus clearance and age in stable kidney recipients. Ciclosporin and tacrolimus have distinct pharmacokinetics, but both are metabolized by intestinal and hepatic CYP3A4/3A5 and transported across the cell membrane by P-glycoprotein. The most common drug interactions with ciclosporin are therefore also observed with tacrolimus, but the two drugs do not interact identically when administered with CYP3A inhibitors or inducers. The strongest effects on calcineurin-inhibitor disposition are observed with azole antifungals, macrolide antibacterials, rifampicin, calcium channel antagonists, grapefruit juice, St John's wort and protease inhibitors. Drug interactions with mycophenolic acids occur mainly through inhibition of their enterohepatic recirculation, either by interference with the intestinal flora (antibacterials) or by limiting drug absorption (resins and binders). Rifampicin causes a reduction in mycophenolic acid exposure probably through induction of uridine diphosphate-glucuronosyltransferases. Proliferation signal inhibitors (PSIs) such as sirolimus and everolimus are substrates of CYP3A4 and P-glycoprotein and have a macrolide structure very similar to tacrolimus, which explains why common drug interactions with PSIs are comparable to those with calcineurin inhibitors. Ciclosporin, in contrast to tacrolimus, inhibits the enterohepatic recirculation of mycophenolic acids, resulting in significantly lower concentrations and hence risk of underexposure. Therefore, when switching from tacrolimus to ciclosporin and vice versa or when reducing or withdrawing ciclosporin, this interaction needs to be taken into account. The combination of ciclosporin with PSIs requires dose reductions of both drugs because of a synergistic interaction that causes nephrotoxicity when left uncorrected. Conversely, when switching between calcineurin inhibitors, intensified monitoring of PSI concentrations is mandatory. Increasing age is associated with structural and functional changes in body compartments and tissues that alter absorptive capacity, volume of distribution, hepatic metabolic function and renal function and ultimately drug disposition. While these age-related changes are well-known, few specific effects of the latter on immunosuppressant drug metabolism have been reported. Therefore, more clinical data from elderly organ recipients are urgently required.

Renal transplantation outcomes: a comparative analysis between elderly and younger recipients

Renal transplantation is presently the best treatment for end-stage renal disease, although considered contraindicated for elderly patients. However, more investigation is needed due to higher life expectancy rates of the general population and the increasing number of over 60-yr-old patients with chronic renal failure dependent upon dialysis. This study aims to determine graft and patient survival rates of renal transplant patients 60 yr and older compared to a younger group (50-59 yr old). Relevant pre- and post-transplant clinical data related to graft and patient survival in both groups were also investigated. Three-hundred and twenty consecutive renal transplant patients were enrolled in this study and grouped based on age at the time of the transplantation: one-hundred and ten patients at or over 60 yr old (elderly group) and 210 patients ranging from 50 to 59 yr old (younger group). There were no statistical differences in either group regarding clinical characteristics and immunological risk factors. The incidence of acute rejection was higher in the younger group (37.6%) than in the elderly (22.7%) (p = 0.01). Censored to death graft survivals at five yr were respectively 86.7% for patients > or = 60 yr and 82.1% for patients 50-59 yr old (p = 0.49). Patient survival rates at five yr were respectively 76.2% for patients > or = 60 yr and 81.6% for patients 50-59 yr old (p = 0.33). Our data show that renal transplantation for elderly patients has similar results to those found in younger individuals, which does not make age, in and of itself, a contraindication for transplantation.

Immunosuppression of the elderly kidney transplant recipient

The growing number of elderly patients with end-stage kidney disease awaiting transplantation has resulted in a corresponding rise in the number of elderly transplant recipients. In this paper, we review existing literature on age-related changes, transplant outcomes, and complications in the elderly in an attempt to propose a tailored approach to immunosuppression management in this group of patients. Despite the fact that the benefit of transplantation in the elderly is well established, clinical trials evaluating the safety and efficacy of immunosuppression regimens are lacking. Until such data exists, immunosuppression of the elderly transplant recipient should be based on the traditional principles which guide all transplant protocols and consideration of factors that are unique to the elderly. There are limited data regarding age-related changes in immune function and metabolism of immunosuppression agents in this population. Results of registry data analyses suggest that the risk of acute rejection decreases with age; however, the impact of acute rejection on long-term allograft function is greater in this population. There is also an increased risk of infection and adverse events posttransplantation among these patients. Elderly patients are more likely to receive organs from extended criteria donors and the impact of donor factors on transplant outcomes must therefore be considered. Taking these factors into consideration, we propose an approach to immunosuppression in the elderly based on individual risk stratification of treatment failure and the potential for adverse events.

A Single-Center Experience of Renal Transplantation in Elderly Patients: A Paired-Kidney Analysis

BACKGROUND

Chronic renal failure is a disease of the elderly. The elderly are the fastest growing population among dialysis patients and also on waiting lists for kidney transplantation. The objective for this study was to analyze the results of the renal transplantation in recipients elder than 60 years. To minimize the donor variability and bias, a paired kidney analysis was used.

METHODS

The older renal transplantation (ORT) group included 44 patients (30 men, 14 women) aged 60 to 72 (mean 64+/-3) years. Their pairs created a younger renal transplantation (YRT) group consisting of 44 patients (30 men, 14 women) aged 14 to 59 (mean 40+/-12) years.

RESULTS

Graft function estimated 1 year after transplantation applying abbreviated Modification of Diet in Renal Disease formula was significantly better in ORT (46.8+/-10.2 ml/min) versus YRT (43.7+/-16.8 ml/min). Studied groups (ORT vs. YRT) did not differ significantly with respect to 1-year patient survival (93.2% vs. 95.5%), 1-year graft survival (88.6% vs. 86.3%), 1-year death-censored graft survival (93% vs. 90.1%), and the incidences of delayed graft function and acute rejection. The most common complications noticed after ORT were cardiovascular complications, surgical complications, and infections.

CONCLUSIONS

Our single-center results confirm that renal transplantation is a good option of renal replacement therapy in patients older than 60 years. Thorough recipient selection and preparation as well as customized immunosuppressive protocols are particularly important in that group of renal transplant recipients.

Pharmacokinetic Considerations Relating to Tacrolimus Dosing in the Elderly

Relaxation of the upper age limits for solid organ transplantation coupled with improvements in post-transplant survival have resulted in greater numbers of elderly patients receiving immunosuppressant drugs such as tacrolimus. Tacrolimus is a potent agent with a narrow therapeutic window and large inter- and intraindividual pharmacokinetic variability. Numerous physiological changes occur with aging that could potentially affect the pharmacokinetics of tacrolimus and, hence, patient dosage requirements. Tacrolimus is primarily metabolised by cytochrome P450 (CYP) 3A enzymes in the gut wall and liver. It is also a substrate for P-glycoprotein, which counter-transports diffused tacrolimus out of intestinal cells and back into the gut lumen. Age-associated alterations in CYP 3A and P-glycoprotein expression and/or activity, along with liver mass and body composition changes, would be expected to affect the pharmacokinetics of tacrolimus in the elderly. However, interindividual variation in these processes may mask any changes caused by aging. More investigation is needed into the impact aging has on CYP and P-glycoprotein activity and expression. No single-dose, intense blood-sampling study has specifically compared the pharmacokinetics of tacrolimus across different patient age groups. However, five population pharmacokinetic studies, one in kidney, one in bone marrow and three in liver transplant recipients, have investigated age as a co-variate. None found a significant influence for age on tacrolimus bioavailability, volume of distribution or clearance. The number of elderly patients included in each study, however, was not documented and may have been only small. It is likely that inter- and intraindividual pharmacokinetic variability associated with tacrolimus increase in elderly populations. In addition to pharmacokinetic differences, donor organ viability, multiple co-morbidity, polypharmacy and immunological changes need to be considered when using tacrolimus in the elderly. Aging is associated with decreased immunoresponsiveness, a slower body repair process and increased drug adverse effects. Elderly liver and kidney transplant recipients are more likely to develop new-onset diabetes mellitus than younger patients. Elderly transplant recipients exhibit higher mortality from infectious and cardiovascular causes than younger patients but may be less likely to develop acute rejection. Elderly kidney recipients have a higher potential for chronic allograft nephropathy, and a single rejection episode can be more devastating. There is a paucity of information on optimal tacrolimus dosage and target trough concentration in the elderly. The therapeutic window for tacrolimus concentrations may be narrower. Further integrated pharmacokinetic-pharmacodynamic studies of tacrolimus are required. It would appear reasonable, based on current knowledge, to commence tacrolimus at similar doses as those used in younger patients. Maintenance dose requirements over the longer term may be lower in the elderly, but the increased variability in kinetics and the variety of factors that impact on dosage suggest that patient care needs to be based around more frequent monitoring in this age group.