Tacrolimus (FK506) and the pharmaceutical/academic/regulatory gauntlet

Thirty Years of Tacrolimus in Clinical Practice

Tacrolimus was discovered in 1984 and entered clinical use shortly thereafter, contributing to successful solid organ transplantation across the globe. In this review, we cover development of tacrolimus, its evolving clinical utility, and issues affecting its current usage. Since earliest use of this class of immunosuppressant, concerns for calcineurin-inhibitor toxicity have led to efforts to minimize or eliminate these agents in clinical regimens but with limited success. Current understanding of the role of tacrolimus focuses more on its efficacy in preventing graft rejection and graft loss. As we enter the fourth decade of tacrolimus use, newer studies utilizing novel combinations (as with the mammalian target of rapamycin inhibitor, everolimus, and T-cell costimulation blockade with belatacept) offer potential for enhanced benefits.

Effects of Tacrolimus and Other Immune Targeting Compounds on Binge-Like Ethanol Drinking in High Drinking in the Dark Mice

High Drinking in the Dark (HDID-1) mice represent a unique genetic risk model of binge-like drinking and a novel means of screening potential pharmacotherapies to treat alcohol use disorders (AUDs). We tested the effects of tacrolimus (0, 0.5, 1, and 2 mg/kg), sirolimus (0, 5, 10, and 20 mg/kg), palmitoylethanolamide (PEA; 0, 75, 150, and 225 mg/kg), and secukinumab (0, 5, 20, and 60 mg/kg) on binge-like ethanol intake (2-day, "Drinking in the Dark" [DID]) and blood alcohol levels (BALs) in HDID-1 mice. Tacrolimus reduced ethanol intake and BALs. Tacrolimus had no effect on water intake, but reduced saccharin intake. There was no effect of sirolimus, PEA, or secukinumab on ethanol intake or BALs. These results compare and contrast with previous work addressing these compounds or their targeted mechanisms of action on ethanol drinking, highlighting the importance of screening a wide range of models and genotypes to inform the role of neuroimmune signaling in AUDs.

Clinical Evaluation of Modified Release and Immediate Release Tacrolimus Formulations

The science of drug delivery has evolved considerably and has led to the development of multiple sustained release formulations. Each of these formulations can present particular challenges in terms of clinical evaluation and necessitate careful study to identify their optimal use in practice. Tacrolimus is an immunosuppressive agent that is widely used in organ transplant recipients. However, it is poorly soluble, has an unpredictable pharmacokinetic profile subject to important genetic polymorphisms and drug-drug interactions, and has a narrow therapeutic index. For these reasons, it represents an agent that could benefit from modified release formulations to overcome these limitations. The objective of this review is to discuss the clinical evaluation of immediate and modified release tacrolimus formulations in renal transplant recipients. Clinical trials from early development of immediate release tacrolimus to formulation-specific post-marketing trials of modified release tacrolimus formulations are reviewed with an emphasis on key elements relating to trial design end endpoint assessment. Particular elements that can be addressed with formulation alterations, such as pharmacokinetics, pharmacogenomics, and toxicity and corresponding clinical evaluations are discussed. In addition, current knowledge gaps in the clinical evaluation of immediate and modified release tacrolimus formulations are discussed to highlight potential avenues for the future development of different tacrolimus formulations with outcomes relevant to the regulators, the transplant community, and to transplant recipients. This review shows that new formulations may alter tacrolimus bioavailability, alleviate certain adverse events while potentially enhancing patient convenience.

Update on liver transplantation using cyclosporine

After the introduction of cyclosporine into liver transplantation in 1983, 1-year patient survival more than doubled. Later, with the improved microemulsified formulation of cyclosporine (Neoral) more stable pharmacokinetics were achieved. Today, C(2) monitoring of cyclosporine blood levels allows a more accurate estimation of the area under the concentration-versus-time curve as the single best indicator of cyclosporine exposure. As a consequence, with better control of side effects as well as desired effects the results of cyclosporine in liver transplantation have been further improved. The introduction of mycophenolate mofetil and basiliximab/daclizumab combination therapy has provided new options for the prevention of allograft rejection. The safety profile of individual immunosuppressive regimens comes more into focus since acute allograft rejection may be controlled successfully with competing strategies. As the focus in liver transplantation is shifting toward greatly improved long-term results, late posttransplant mortality with a functioning graft is a major concern. Prevention of long-term complications associated with highly effective immunosuppressants--posttransplant lymphoproliferative disease, cytomegalovirus infection, diabetes, hypertension, and hyperlipidemia-gains importance. Technical advances in living-related and cadaveric split-liver transplantation have lead to increasing use of segmental liver transplantation with the need to consider the effects of immunosuppression on liver regeneration and metabolism. The individualized orchestration of immunosuppression taking into account the underlying liver disease as well as other individual predispositions remains a future challenge.

Immunologic Aspects of Transplant Management: Pharmacotherapy and Rejection

The intensivist caring for the critically ill transplant patient must be knowledgeable in the management of immunosuppression or have expert help. Critical illness often has a major impact on the absorption and metabolism of immunosuppressive drugs, increasing or decreasing net immunosuppression. Too little immunosuppression brings the risk of graft loss, while too much increases the morbidity and mortality of serious infection. Optimum management often requires the skillful manipulation of dosage and/or routes of drug delivery. In many cases of life-threatening infection, immunosuppression must be discontinued altogether and restarted prior to significant graft injury. The cost of miscalculation is very high. Loss of a renal, pancreas, or small bowel transplant is tragic, while loss of a heart, lung, or liver is usually fatal. Unfortunately the management of immunosuppression is becoming more complex. As the field of transplantation matures, new immunosuppressants are being introduced. Also, more experience and growing numbers of clinical trials are making the required knowledge base ever larger. Each type of transplant has its own set of evolving immunosuppression strategies. This review presents the basic mechanisms of the most widely used drugs and the dangers of immunosuppression. The drugs are then discussed in the context of liver, small bowel, kidney, pancreas, heart, and lung transplantation. Finally, a brief section on the practical pharmacokinetics of the drugs is presented.

Hand transplantation: pertinent data and future outlook

Transplantation of composite tissue allografts, such as a hand, offers immense potential in reconstructive surgery. Review of current replantation literature suggests the prospect for significant functional return following hand transplant, provided appropriate patient is selected and allograft rejection is prevented. Experimental studies of limb transplantation in rodents have demonstrated the efficacy of combination therapy using multiple immunosuppressants. However, long-term survival of limb allografts could not be achieved in large animal models without significant drug toxicity. Given the potential for organ failure, opportunistic infection, and malignancy resulting from long-term immunosuppression, the risk-benefit ratio for hand transplant must be carefully weighed. Our laboratory has been able to achieve allograft survival with minimum immunosuppression by MHC matching or donor antigen exposure prior to immune maturity in the swine. Future transplantation of composite tissue allografts, therefore, may depend upon such modalities to induce host tolerance without long-term immunosuppression.

Evolving trends in liver transplantation: an outcome and charge analysis

BACKGROUND

Due to the limited supply and increased demand for donor livers, waiting times are progressively lengthening, which may lead to transplantation at more advanced and less cost-effective stages of disease. The purpose of this study was to evaluate the outcomes and hospital charges of liver transplantation during two recent eras to identify areas for providing more cost-effective care.

METHODS

A total of 144 primary liver allografts were performed from 1991 to 1996. Patient characteristics, outcome measures, and hospital charges were compared for patients receiving allografts between 1991 and 1993 (group A) versus those receiving grafts between 1994 and 1996 (group B) using unpaired Student t tests for continuous data and chi-squared tests for categorical data.

RESULTS

In comparing groups A and B, no significant differences in patient demographics, relative contraindications, or indication for transplantation existed; median waiting time from date of listing until transplant increased from 88 days to 159 days; and a shift in UNOS priority status at time of transplantation occurred, as the percentage of patients requiring inpatient care increased from 58% to 75% (P=0.034). Despite this, patient hospital and 1-year survival significantly improved from 75.0% to 90.3% (P=0.016), and from 68.1% to 88.9% (P=0.002), respectively. Total hospital charges, without correction for inflation, were $174,908+/-16,388 in A and $193,525+/-14,444 in B (P=0.288). The increased charges were associated with longer inpatient length of stay (LOS) before transplant, resulting in increased pretransplant charges from $24,088+/-4134 (A) to $39,490+/-6,196 (B) (P=0.011). Room and service (54%) was the largest pretransplant contributor to charges, while blood products (23%), room and service (21%), organ acquisition (13%), and operating room charges (11%) contributed the most after transplant.

CONCLUSIONS

Longer waiting times resulting in transplantation at later stages of disease have occurred, leading to longer pretransplant LOS and its associated charges. Despite more advanced disease, patient survival rates have significantly improved with fewer infection-related deaths. LOS pretransplant, blood products, and operating room services represent potential areas for providing more cost-effective care.