Three-year follow-up of the European Multicenter Tacrolimus (FK506) Liver Study

Immunosuppressive Drugs in Liver Transplant: An Insight

Liver transplantation (LT) is the standard of care for end-stage liver failure and hepatocellular carcinoma. Over the years, immunosuppression regimens have improved, resulting in enhanced graft and patient survival. At present, the side effects of immunosuppressive agents are a significant threat to post-LT quality of life and long-term outcome. The role of personalized immunosuppression is to reach a delicate balance between optimal immunosuppression and minimal side effects. Today, immunosuppression in LT is more of an art than a science. There are no validated markers for overimmunosuppression and underimmunosuppression, only a few drugs have therapeutic drug monitoring and immunosuppression regimens vary from center to center. The immunosuppressive agents are broadly classified into biological agents and pharmacological agents. Most regimens use multiple agents with different modes of action to reduce the dosage and minimize the toxicities. The calcineurin inhibitor (CNI)-related toxicities are reduced by antibody induction or using mTOR inhibitor/antimetabolites as CNI sparing or CNI minimization strategies. Post-liver transplant immunosuppression has an intensive phase in the first three months when alloreactivity is high, followed by a maintenance phase when immunosuppression minimization protocols are implemented. Over time some patients achieve "tolerance," defined as the successful stopping of immunosuppression with good graft function and no indication of rejection. Cell-based therapy using immune cells with tolerogenic potential is the future and may permit complete withdrawal of immunosuppressive agents.

Induction Therapy With Antithymocyte Globulin and Delayed Calcineurin Inhibitor Initiation for Renal Protection in Liver Transplantation: A Multicenter Randomized Controlled Phase II-B Trial

BACKGROUND

Calcineurin inhibitor (CNI) based immunosuppression in liver transplantation (LTx) is associated with acute and chronic deterioration of kidney function. Delaying CNI initiation by using induction rabbit anti-thymocyte globulin (rATG) may provide kidneys with adequate time to recover from a perioperative insult reducing the risk of early post-LTx renal deterioration.

METHODS

This was an open-label, multicenter, randomized controlled clinical trial comparing use of induction rATG with delayed CNI initiation (day-10) against upfront CNI commencement (SOC; standard of care) in those patients deemed at standard risk of postoperative renal dysfunction following LTx. The primary end point was change in (delta) creatinine from baseline to month-12.

RESULTS

Fifty-five patients were enrolled in each study arm. Mean Tacrolimus levels remained comparable in both groups from day-10 throughout the study period. A significant difference in delta creatinine was observed between rATG and SOC groups at 9-months (p=0.03) but not at month-12 (p=0.05). eGFR levels remained comparable between cohorts at all time points. Rates of biopsy-proven acute rejection at 1-year were similar between groups (16.3 vs 12.7%, p= 0.58). rATG showed no significant adverse effects. Survival at 12-months was comparable between groups (p= 0.48).

CONCLUSIONS

Although the use of induction rATG and concurrent CNI deferral in this study did not demonstrate a significant difference in delta creatinine at 1 year, these results indicate a potential role for rATG in preserving early kidney function, especially when considered with CNI deferral beyond 10 days and/or lower target Tacrolimus levels, with acceptable safety and treatment efficacy.

Toward immunosuppressive effects on liver transplantation in rat model: tacrolimus loaded poly(ethylene glycol)-poly(D,L-lactide) nanoparticle with longer survival time

In this study, tacrolimus (FK506) was encapsulated into a biodegradable poly(ethylene glycol)-poly(D,L-lactide) (MPEG-PLA) block copolymer using a double emulsion-solvent evaporation technique. Drug loading (DL) and encapsulation efficiency (EE) can be changed by varying the mass ratio of FK506/MPEG-PLA. Furthermore, transmission electron microscope (TEM) and Malvern Zetasizer were used to investigate the properties of FK506/MPEG-PLA nanoparticles (DL=9.5%), which were monodisperse (PDI=0.100 ± 0.023) with a mean particle size of 90.5 ± 1.5 nm. Compared with FK506 capsule, in vitro release profile showed that FK506/MPEG-PLA nanoparticles exhibited sustained release. Meanwhile, the higher concentration and longer retention time in plasma were also confirmed in vivo. We further preliminarily evaluated immunosuppressive effect on liver transplantation in rat model. The survival time of the rat administrated FK506/MPEG-PLA nanoparticles was obviously prolonged than that of the control group administrated FK506 capsule.

Current status of immunosuppression in liver transplantation

With advancements in immunosuppressive strategies and availability of better immunosuppressive agents, survival rate following liver transplantation has improved significantly in the recent times. Besides improvements in surgical techniques, the most important factor that has contributed to this better outcome is the progress made in the field of immunosuppression. Over the last several years, the trend has changed to tailored immunosuppression with the aim of achieving optimal graft function while avoiding its undesirable side effects. Induction agents are no longer used routinely and the aim is to provide minimal immunosuppression in the maintenance phase. The present review discusses the various types of immunosuppressive agents, their mechanism of action, clinical utility, advantages and disadvantages, and their side effects in short and long-term. It also discusses about tailoring immunosuppression in presence of various situations such as renal dysfunction, metabolic syndrome, hepatitis C recurrence, cytomegalovirus infections and so on. The issue of chronic kidney disease and the available renal sparing immunosuppressive strategies has been particularly stressed upon. Finally, it discusses about the practical aspects of various immunosuppression regimens including drug monitoring.

Safety and efficacy of four steroid-minimization protocols in liver transplant recipients: 3-year follow-up in a single center

OBJECTIVE

To evaluate the safety and efficacy of steroid-minimization therapy in liver transplantation (LT) recipients with hepatitis B virus-related diseases in China.

METHODS

From March 2000 to June 2007, 502 adult LT recipients, mostly with hepatitis B (HBV)-related diseases, were enrolled in our study. Four study groups were setup according to the steroid-minimization protocols: tacrolimus (TAC) with 6 months steroids withdrawal (6M SW), TAC with 3 months SW (3M SW), TAC with 14 days SW (14d SW), and TAC with basiliximab induction and steroids avoidance (Bas SA). All patients were followed up for at least 36 months after LT.

RESULTS

There were no significant differences in the overall 3-year survival rates of the patients and graft, and chronic rejection among the four groups (P = 0.092, P = 0.113 and P = 0.684, respectively). There was also no difference in acute rejection within 12 months after LT (P = 0.514). The 3-year recurrence rates of HBV infection and hepatocellular carcinoma (HCC) after LT were significantly different among all the groups (lowest in TAC/Bas SA group; P = 0.037 and P = 0.029, respectively). The overall incidence of infection was significantly higher in the 6M SW group (62.2% vs 56.1% in 3M SW, 30.5% in 14d SW, 20.5% in Bas SA; P < 0.01). By the end of the 3-year follow-up, more than 90% of the surviving patients could safely receive TAC monotherapy.

CONCLUSION

Bas SA immunosuppressive protocol can be achieved safely in LT and reduce HBV infection and HCC recurrence and side effects of steroids after LT.

Chronic rejection of the liver: the role of immunosuppression

Liver transplantation is now widely recognised as an effective treatment option for patients with advanced liver disease. Many units now achieve greater than 85% survival at 1 year, with the majority of patients having a high quality of life. The maintenance of a high quality of life requires careful clinical management to ensure that the continued maintenance of excellent liver graft function is not achieved at the expense of immunosuppressive drug complications or morbidity. Acute liver rejection will occur in between 30 to 45% of patients, although with modern immunosuppressive protocols, usually combining one of the calcineurin agents, either cyclosporin or tacrolimus, with both azathioprine and corticosteroids (prednisolone) ensures that relatively few grafts are lost from severe acute rejection. While the incidence and severity of acute rejection may be one factor in raising the risk of chronic rejection, it may not be the principal one in many patients. It is important to recognise that the frequency of rejection also varies with the primary underlying liver disease, with patients with hepatitis B or alcoholic liver disease having relatively low rejection rates, compared with patients with primary biliary cirrhosis (PBC) or primary sclerosing cholangitis (PSC), which range between 20 to 70%. Chronic rejection will account for some 5% of grafts lost in the first 3 to 5 years. Indeed, there is some evidence that the incidence of chronic rejection is actually declining over the past few years. While the reason for this apparent decline is uncertain, and it could relate to better immunosuppression management, or more likely to the growing recognition that chronic graft dysfunction may be due to recurrent liver disease, such as autoimmune hepatitis, PBC, PSC, or recurrent hepatitis C. The differentiation of recurrent primary liver disease from chronic rejection can prove to be very difficult in clinical practice. Thus, the clinician must carefully monitor liver and graft function, evaluate any biochemical changes, and try to reach a clear diagnosis before considering any modification of immunosuppressive schedules.

Overview of immunosuppression in liver transplantation

Continued advances in surgical techniques and immunosuppressive therapy have allowed liver transplantation to become an extremely successful treatment option for patients with end-stage liver disease. Beginning with the revolutionary discovery of cyclosporine in the 1970s, immunosuppressive regimens have evolved greatly and current statistics confirm one-year graft survival rates in excess of 80%. Immunosuppressive regimens include calcineurin inhibitors, anti-metabolites, mTOR inhibitors, steroids and antibody-based therapies. These agents target different sites in the T cell activation cascade, usually by inhibiting T cell activation or via T cell depletion. They are used as induction therapy in the immediate peri- and post-operative period, as long-term maintenance medications to preserve graft function and as salvage therapy for acute rejection in liver transplant recipients. This review will focus on existing immunosuppressive agents for liver transplantation and consider newer medications on the horizon.

Minimization of steroids in liver transplantation

Because of the markedly improved short-term results of liver transplantation (LT) and persistently high number of long-term complications, the attention of transplant physicians should be focused on minimizing immunosuppressive therapy as much as possible. Steroid-based immunosuppression is responsible for a substantial post-LT morbidity and mortality, hence, minimization of its use is of utmost importance to improve the quality of life of the successfully transplanted liver recipient. This literature review shows that LT can be performed safely with steroid-minimal immunosuppression without compromising graft and patient survival. The tendency in clinical practice is to move more and more from steroid withdrawal to steroid avoidance protocols.

Conversion From Cyclosporine to Tacrolimus for Chronic Allograft Nephropathy

We investigate the effect of conversion from a cyclosporine (CsA) based-regimen to a tacrolimus (FK506)-based regimen with respect to graft renal function induced by chronic allograft nephropathy (CAN). Thirty-one patients with a histological diagnosis of CAN were included after other causes of chronic graft dysfunction had been excluded. Conversion to FK506 was undertaken at an initial dose of 0.15 mg/kg/d, which was subsequently adjusted to maintain FK506 whole blood trough levels between 5 and 10 mug/L. The rate of decline of renal function before and after the FK506 conversion was represented by regression lines (slope) of the reciprocal of serum creatinine versus time. To evaluate the effect of conversion on allograft function, we gathered data on serum lipids, blood glucose, proteinuria, and hypertension. When postconversion slopes were compared to preconversion slopes for each patient, 20 patients (64.5%) showed positive regression lines and four patients (12.9%), less negative. Seven patients (22.6%) displayed an increased rate of decline in renal function with regression lines becoming more negative. FK506 was associated with a significant decrease in lipid levels, proteinuria, and hypertension. No patient returned to dialysis at the end of the 36-month follow-up. Conversion from a CsA-based regimen to a tacrolimus-based regimen was an effective alterative for salvage of patients with abnormal graft renal function induced by CAN.

Randomized controlled trial of tacrolimus versus microemulsified cyclosporin (TMC) in liver transplantation: poststudy surveillance to 3 years

The 1-year results of the tacrolimus versus microemulsified cyclosporin (TMC) study found a benefit with tacrolimus immunosuppression after primary liver transplants in adults with respect to freedom from graft loss and immunological failure. The integrity of the randomization process was preserved for a further 2 years for poststudy surveillance. The data after 3 years confirms the significant difference between tacrolimus and cyclosporin with tacrolimus less likely to meet the composite primary endpoint (log rank p = 0.01; relative risk 0.75; 95% CI 0.60-0.95; p = 0.016). However, freedom from death or retransplantation no longer achieves statistical significance (relative risk 0.79; 95% CI 0.62-1.02; p = 0.065). A total of 62.1% of patients randomized to tacrolimus were alive at 3 years with their original graft and still on their allocated study medication, as compared with only 41.6% in the cyclosporin limb (p < 0.001). No difference was detected between tacrolimus and cyclosporin in hepatitis-C-positive patients with the available data. The TMC study confirms after 3 years of follow-up the benefits of tacrolimus-based immunosuppression over cyclosporin using C(0) monitoring.

Immunosuppressive agents in solid organ transplantation: Mechanisms of action and therapeutic efficacy

Effective immunosuppression is an essential pre-requisite for successful organ transplantation and improvements in outcome after transplantation have to a large extent been dependent on developments in immunosuppressive therapy. Here we provide an overview of the different immunosuppressive agents currently used in solid organ transplantation. A historical perspective on the development of immunosuppression for organ transplantation is followed by a review of the individual agents, with a focus on their mechanism of action and efficacy. Steroids, anti-proliferative agents (azathioprine and mycophenolate), calcineurin inhibitors (cyclosporine and tacrolimus) and TOR inhibitors (sirolimus and everolimus) are discussed along with both polyclonal and monoclonal antibody preparations. Many of the key clinical trials that underpin current clinical usage of these agents are described and side-effects of the different agents are highlighted. Finally, a number of newer agents still in various stages of clinical development are briefly considered.

Five-year follow-up of a trial comparing Tacrolimus and cyclosporine microemulsion in liver transplantation

We evaluate 5-year results of a prospective randomized trial that compared cyclosporine microemulsion (CsA-me) and Tacrolimus (Tac) for primary immunosuppression. One hundred one adult patients undergoing liver transplantation were randomized to receive Tac (n = 50) or CsA-me (n = 51). The most frequent indication for the procedure was cirrhosis due to virus C followed by alcoholism. Survival rates at 1, 3, and 5 years were 86%, 75%, and 72%, respectively; there was no significant difference between CsA-me versus Tac arms. Acute rejection occurred in 30 cases (30%), independent of the type of primary immunosuppression. Serious adverse events were reported significantly more among patients under CsA-me (48 episodes) than under Tac (32 episodes). Nineteen patients were switched to the other calcineurin inhibitor. The switch was much more frequent from CsA-me to Tac (n = 15; 29.4%), mainly because of lack of efficacy (n = 10; 19.6%). There were no cases of chronic rejections in the Tac arm. Four patients were switched from Tac to CsA-me for side effects; only 1 remains alive, after treatment was changed from CsA-me to an antimetabolite. There were no statistical differences in renal dysfunction, diabetes, hypertension, neurologic disorders, new-onset malignancies, or infections. There were no differences in survival or rejection among the intention-to-treat groups. Serious adverse events, total patients with switch of calcineurin inhibitor, as well as switches due to lack of efficacy, were statistically more frequent under CsA-me. Tacrolimus seems to be a more appropriate drug to be used for primary immunosuppression in liver transplantation.

A comparison of tacrolimus and cyclosporine in liver transplantation: effects on renal function and cardiovascular risk status

A retrospective chart review of 1065 consecutive liver allograft recipients in 11 centers from January 1997 to September 1998 was performed. Patients were followed for 3 years or until graft loss. Patients received either tacrolimus (n = 594), cyclosporine (n = 450) or no calcineurin inhibitor (n = 21). Model for end-stage liver disease (MELD) scores at time of transplant were similar between the two groups. During follow-up, more patients switched from cyclosporine to tacrolimus (26.7%) than from tacrolimus to cyclosporine (12.8%; p < 0.0001). Patient and graft survival were equivalent. Corticosteroid use was more common in cyclosporine-treated patients (p < 0.00001). Patients receiving tacrolimus experienced lower serum creatinine levels at months 3 through 36 (p < 0.0001). Systolic blood pressure was lower in patients receiving tacrolimus (p < 0.001) despite a reduced requirement for anti-hypertensive agents (p < 0.0001). In addition, tacrolimus was associated with lower total cholesterol and triglyceride levels for months 3 through 24 and 3 through 12, respectively (p < 0.01), despite a reduced requirement for anti-hyperlipidemic agents. The incidence of new-onset diabetes mellitus was similar in both groups. While both calcineurin inhibitors were associated with excellent patient and graft survival, renal function, blood pressure and serum lipid levels were significantly better with tacrolimus treatment.

Calcineurin Inhibitor‐Induced Headache: Clinical Characteristics and Possible Mechanisms

OBJECTIVE

To classify the headache syndromes under treatment with calcineurin inhibitors and to investigate whether the latter influence the nitric oxide production of human brain microvascular cells (HBMEC).

BACKGROUND

Single cases of cyclosporine-induced headaches have been reported. Since calcineurin inhibitors are known to influence the renal metabolism of NO, a key molecule in tension-type headache and migraine, we were interested whether calcineurin inhibitors might change NO metabolism in HBMEC as well.

DESIGN AND METHODS

Headache symptoms of 74 patients receiving cyclosporine and/or tacrolimus for organ transplantation were retrospectively assessed. Furthermore, the effect of cyclosporine and tacrolimus on nitric oxide production in human brain microvascular endothelial cells was investigated after incubation.

RESULTS

Only 18 of the 74 patients reported no headache 1-36 months after liver, lung, or bone-marrow transplantation, 28 reported a new headache, and 17 an increase in the frequency or intensity of a pre-existing headache. The headache was generally classified as migraine without aura (IHS 1.1) or migraine-like headache (IHS 1.6). Furthermore, we found significantly increased NO production after co-incubation of calcineurin inhibitors with human brain microvascular endothelial cells.

CONCLUSION

The pathophysiological mechanism of these headaches may be connected with an endothelial dysfunction in terms of increased production of NO.

Comparison of low and high initial tacrolimus dosing in primary heart transplant recipients: a prospective European multicenter study

BACKGROUND

The purpose of this prospective, randomized, open-label, phase II, multicenter study was to optimize the initial oral dose of tacrolimus.

METHODS

A total of 113 patients were randomly assigned to initial low-dose (0.075 mg/kg/day, n=55) or high-dose (0.15 mg/kg/day, n=58) oral tacrolimus and followed for 3 months. Target whole-blood trough levels were 10 to 20 ng/mL. Prophylactic use of corticosteroids and azathioprine was identical in both groups, and antibody induction was mandatory. The primary endpoint was the time to and incidence of the initial oral tacrolimus dose adjustment because of toxicity or rejection, or withdrawal before initial dose change. Efficacy was assessed by the occurrence of biopsy-proven rejection (International Society for Heart and Lung Transplantation grade > or =1B).

RESULTS

In the primary endpoint, no significant difference was observed between the low- and high-dose groups. After 3 months, there was no difference in freedom from initial oral tacrolimus dose change because of rejection, toxicity, or withdrawal (89.0% vs. 87.6%; not significant [NS]). In both groups, dose adjustments were mainly required to achieve and maintain target blood levels (80.0% vs. 82.8%; NS). Patient survival was 92.7% and 98.3% (NS). There was no significant difference between groups regarding freedom from biopsy-proven acute rejection (57.1% vs. 66.3%; NS). The overall safety profiles indicated a tendency toward better tolerability in the low-dose group.

CONCLUSIONS

Although low-dose and high-dose tacrolimus had similar efficacy, low-dose tacrolimus was associated with a more favorable safety profile. Therefore we recommend starting tacrolimus therapy after antibody induction at 0.075 mg/kg and adjust dose according to whole-blood trough levels.

Tacrolimus in liver transplantation

Tacrolimus has been in clinical use for ten years. It was launched in a hail of publicity following the successful treatment of cases with apparently irreversible rejection using conventional immunosuppressive therapies. Since that time, the overall experience with the drug has increased considerably. The purpose of this article is to review tacrolimus comprehensively, including evidence derived from major clinical trials, to enable the reader to become familiar with its clinical role, including a comparison with its main competitor, cyclosporin. Tacrolimus was discovered in 1984, it predominantly acts via inhibition of T-cell mediated immunity, and to a lesser extent B-cell humoral immunity. The agent was introduced into clinical medicine in 1989 and was soon shown to be a highly effective immunosuppressive agent, receiving approval in 1994 by the Food and Drug Administration (FDA) for primary immunosuppression in adult and paediatric liver transplantation. Tacrolimus has proved to be a major development in transplantation. Whilst the available data have been hindered to some extent by deficiencies of trial design in the major studies, there is still more comparative clinical data available for tacrolimus than for any of its predecessors. The overall balance of risk benefit is considered by many to be tipped in favour of tacrolimus; it is likely that with more long-term follow-up results becoming available in liver and other solid organ transplants, the benefits will appear clearer.

Liver transplantation of patients in end-stage cirrhosis

The success of liver transplantation has resulted in its widespread use for end-stage liver disease; 1- and 5-year survival rates of 70-90% and 60-80% respectively have been reported. Indications for assessment for liver transplantation are now evidence-based and early referral is recommended, correlating with improved patient survival. The management of patients on the waiting list for liver transplantation is designed to prevent complications of liver disease and to avoid therapeutic misadventures. Following transplantation, rejection and infection dominate post-operative complications, and improvements in their prevention and treatment have also correlated with improved patient survival. The development and introduction into clinical practice of a variety of immunosuppressive agents has offered a bewildering array of therapeutic options but with a lack of evidence on which to select optimal immunosuppression. Similarly, difficulties remain in the treatment of some of the complications arising from liver transplantation such as recurrence of disease and complications of immunosuppression.

Modern immunosuppression

The current treatment of posttransplant lymphoproliferative disease (PTLD) includes prophylaxis at the time of transplant, decreasing or stopping immunosuppresion and initiation of antiviral therapy in patients with polymerase chain reaction or clinical evidence of PTLD, and judicial reintroduction of immunosuppression in patients who have cleared their PTLD and have begun to have rejection. The pharmacology, pharmacokinetics, notable side effects, and toxicities of the immunosuppressive agents are described in this article. At the conclusion of each section the author's current practice with these agents and treatment strategies are described.

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.

Tacrolimus: a further update of its pharmacology and therapeutic use in the management of organ transplantation

Tacrolimus (FK-506) is an immunosuppressant agent that acts by a variety of different mechanisms which include inhibition of calcineurin. It is used as a therapeutic alternative to cyclosporin, and therefore represents a cornerstone of immunosuppressive therapy in organ transplant recipients. Tacrolimus is now well established for primary immunosuppression in liver and kidney transplantation, and experience with its use in other types of solid organ transplantation, including heart, lung, pancreas and intestinal, as well as its use for the prevention of graft-versus-host disease in allogeneic bone marrow transplantation (BMT), is rapidly accumulating. Large randomised nonblind multicentre studies conducted in the US and Europe in both liver and kidney transplantation showed similar patient and graft survival rates between treatment groups (although rates were numerically higher with tacrolimus- versus cyclosporin-based immunosuppression in adults with liver transplants), and a consistent statistically significant advantage for tacrolimus with respect to acute rejection rate. Chronic rejection rates were also significantly lower with tacrolimus in a large randomised liver transplantation trial, and a trend towards a lower rate of chronic rejection was noted with tacrolimus in a large multicentre renal transplantation study. In general, a similar trend in overall efficacy has been demonstrated in a number of additional clinical trials comparing tacrolimus- with cyclosporin-based immunosuppression in various types of transplantation. One notable exception is in BMT, where a large randomised trial showed significantly better 2-year patient survival with cyclosporin over tacrolimus, which was primarily attributed to patients with advanced haematological malignancies at the time of (matched sibling donor) BMT. These survival results in BMT require further elucidation. Tacrolimus has also demonstrated efficacy in various types of transplantation as rescue therapy in patients who experience persistent acute rejection (or significant adverse effect's) with cyclosporin-based therapy, whereas cyclosporin has not demonstrated a similar capacity to reverse refractory acute rejection. A corticosteroid-sparing effect has been demonstrated in several studies with tacrolimus, which may be a particularly useful consideration in children receiving transplants. The differences in the tolerability profiles of tacrolimus and cyclosporin may well be an influential factor in selecting the optimal treatment for patients undergoing organ transplantation. Although both drugs have a similar degree of nephrotoxicity, cyclosporin has a higher incidence of significant hypertension, hypercholesterolaemia, hirsutism and gingival hyperplasia, while tacrolimus has a higher incidence of diabetes mellitus, some types of neurotoxicity (e.g. tremor, paraesthesia), diarrhoea and alopecia.

CONCLUSION

Tacrolimus is an important therapeutic option for the optimal individualisation of immunosuppressive therapy in transplant recipients.

Cyclosporine and tacrolimus (FK506): a comparison of efficacy and safety profiles

Multicenter clinical trials conducted in the United States and Europe to compare the efficacy and safety of cyclosporine with tacrolimus (FK506) have demonstrated comparable long-term patient survival and graft survival in liver and renal transplant recipients. Importantly, treatment with tacrolimus was associated with reductions in the incidence and severity of acute rejection episodes. However, tacrolimus-based therapy was also associated with increased toxicities in comparison to conventional cyclosporine-based therapy. It is becoming increasingly accepted that earlier trials may have employed high or supratherapeutic doses of tacrolimus and may have been unbalanced with respect to study design. In addition, these pivotal comparative trials were performed with the original formulation of cyclosporine, and not the cyclosporine microemulsion preparation. This critical review of the literature focuses on the United States and European tacrolimus multicenter clinical trials and examines the efficacy and safety of the two primary immunosuppressants, cyclosporine and tacrolimus, obtained in these and other studies. The preliminary findings of ongoing studies comparing the efficacy and safety of the improved formulation, cyclosporine microemulsion, with tacrolimus are also discussed. The overall efficacy of the two agents appears to be similar. The safety profile shows differing toxicities of the two medications. The availability of these two immunosuppressants allows the clinician improved options when choosing an immunosuppressive regimen in solid organ transplantation.

Potential for improved therapeutic index of FK506 in liposomal formulation demonstrated in a mouse cardiac allograft model

BACKGROUND

FK506 is a potent immunosuppressant that has improved clinical outcomes in kidney and liver transplantation both as a primary and as a rescue immunosuppressive agent. Despite these benefits, the potential value of FK506 is limited by toxic side effects that result in a narrow therapeutic index. By encapsulating the active drug within liposomes (LipoFK506), a new formulation has been developed that might improve this therapeutic index.

METHODS

The biodistribution of tritiated-FK506 administered i.v. showed that the drug remained associated with the liposomal carrier in vivo, and that its tissue distribution was increased in heart and spleen compared to nonliposomal FK506. The immunosuppressive efficacy of lipoFK506 compared with conventional FK506 formulation was tested in vivo. CBA (H2k) mice were engrafted with BALB/c (H2d) mouse hearts with daily immunosuppression using either 1 mg/kg FK506, or 1 mg/kg LipoFK506, from day 0 to 14.

RESULTS

At day 7 the blood trough level of FK506 in the FK506 group was 10-fold higher (25 microg/L) than that in the LipoFK506 group. In both groups the median heart allograft survival was similar at around 26 days. The possibility that FK506, or LipoFK506, might influence antibody-mediated tolerogenesis was addressed in the same model: neither formulation prevented tolerance induction by CD4 and CD8 blockade.

CONCLUSION

LipoFK506 is a novel formulation of FK506 that is efficacious at low blood trough FK506 levels. This property has a direct potential benefit for clinical organ transplantation.