Simple bioequivalence criteria: are they relevant to critical dose drugs? Experience gained from cyclosporine

Comparison of clinical effects, trough and peak levels between branded and generic formulation of Cyclosporine in stable psoriatic patients

BACKGROUND

Cyclosporine A (CyA) is a drug for moderate-to-severe psoriasis. Recently, a generic formulation has been approved as bioequivalent to the branded one. The guidelines for the bioequivalence for critical-dose drugs with a narrow therapeutic range, such as CyA, are questionable. Therefore, it is important to assess the clinical outcome and the pharmacokinetics of different formulations in various patient groups. The current literature lacks of this information in dermatology. The primary objective of this prospective study is to investigate the clinical equivalence (in terms of maintenance of clinical effect) between the generic formulation of CyA and its branded one in patients with psoriasis. A secondary objective is to analyze their trough (C<inf>0</inf>) and peak levels (C<inf>2</inf>).

METHODS

Twenty patients with stable psoriasis under treatment with the branded CyA were monitored in terms of clinical efficacy (psoriasis area severity index, PASI), safety (laboratory values), and their pharmacokinetics utilizing trough (C<inf>0</inf>) and peak plasma concentration (C<inf>2</inf>). The same patients were subsequently shifted to the generic formulation for comparison.

RESULTS

In our sample the efficacy of the two formulations was equal in most cases (P=0.863). A non-significant difference between the C<inf>0</inf> and C<inf>2</inf> of the branded CyA compared to the generic one emerged (respectively P=0.738 and P=0.695).

CONCLUSIONS

The branded and the generic formulations of CyA seem to be not only bioequivalent, but also comparable in terms of clinical efficacy in patients with psoriasis. However, larger samples are required to confirm these findings.

Population pharmacokinetic analysis of tacrolimus in Mexican paediatric renal transplant patients: role of CYP3A5 genotype and formulation

AIMS

The aims of this study were (i) to develop a population pharmacokinetic (PK) model of tacrolimus in a Mexican renal transplant paediatric population (n = 53) and (ii) to test the influence of different covariates on its PK properties to facilitate dose individualization.

METHODS

Population PK and variability parameters were estimated from whole blood drug concentration profiles obtained at steady-state using the non-linear mixed effect modelling software NONMEM® Version 7.2.

RESULTS

Tacrolimus PK profiles exhibited high inter-patient variability (IPV). A two compartment model with first order input and elimination described the tacrolimus PK profiles in the studied population. The relationship between CYP3A5 genotype and tacrolimus CL/F was included in the final model. CL/F in CYP3A5*1/*1 and *1/*3 carriers was approximately 2- and 1.5-fold higher than in CYP3A5*3/*3 carriers (non-expressers), respectively, and explained almost the entire IPV in CL/F. Other covariates retained in the final model were the tacrolimus dose and formulation type. Limustin® showed markedly lower concentrations than the rest of the formulations.

CONCLUSIONS

Population PK modelling of tacrolimus in paediatric renal transplant recipients identified the tacrolimus formulation type as a significant covariate affecting the blood concentrations and confirmed the previously reported significant effect of CYP3A5 genotype on CL/F. It allowed the design of a proposed dosage based on the final model that is expected to help to improve tacrolimus dosing.

Equivalence and interchangeability of narrow therapeutic index drugs in organ transplantation

The calcineurin inhibitors (CNIs), ciclosporin and tacrolimus, are the mainstay of immunosuppression in solid organ transplantation. Generic formulations of these drugs are now available. With increasing pressure on healthcare budgets and the consequent need to match health expectations to available resources, substitution with a generic product appears an attractive option to reduce costs. Approval of generic products differs from innovator drugs, and narrow therapeutic index drugs (NTIs; including CNIs) bring their own particular considerations. With NTIs, small variations in drug exposure could result in reduced immunosuppression or drug toxicity with potentially adverse effects on patient outcomes. NTIs are subject to stricter regulatory approval versus many other generic drugs. However, different generic formulations may still not necessarily be therapeutically equivalent in individuals, raising the possibility of significant differences in exposure between products. Although regional recommendations vary, many guidelines emphasise the need for NTI drug substitution to be initiated by the transplant physician, thus ensuring careful therapeutic monitoring and reduced negative patient impact. The need for therapeutic monitoring during generic substitution has important implications for the overall costs of generic treatment as these costs have to be factored in to the potential savings made from using generic formulations. The reduced acquisition costs of generic products may not necessarily translate into lower overall healthcare costs. This article examines the issue of equivalence and interchangeability of NTI drugs used in organ transplantation, the implications of the approval process for generic drugs on treatment efficacy and safety, and the effective management of substitutions between products.

Cyclosporine: A Commentary on Brand versus Generic Formulation Exchange

The evidence for conversion from brand name to generic equivalent cyclosporine is conflicting. Cyclosporine is a narrow therapeutic-range drug for which small variations in exposure may have severe clinical consequences for transplant patients. There is currently a lack of comparative outcome data relating to the pharmacokinetics of the reference formulation, Neoral, and generic formulations in transplant recipients. A major common concern is the potential inability to attain similar trough levels, an issue that can be easily corrected by ongoing therapeutic drug monitoring to ensure that the new steady state falls within an intended target range. Prospective clinical studies investigating the efficacy and safety of generic formulations in both de novo and long-term transplant patients are also awaited. Until further evidence is available on the conversion of transplant patients to or between generic formulations of cyclosporine, any transfer to a different cyclosporine formulation should be undertaken with close supervision. The best available information to date, however, does not support the frequently held but unsubstantiated belief that generic preparations of immunosuppressive drugs are not as effective as brand names or that conversion from brand to generic is associated with significant danger. This paper attempts to initiate a discussion of these issues.

Therapeutic equivalence and mg:mg switch ability of a generic cyclosporine microemulsion formulation (Sigmasporin Microral) in stable renal transplant patients maintained on Sandimmun Neoral

We tested a hypothesized pharmacokinetic difference between the reference (Sandimmun Neoral) and test (Sigmasporin Microral) products to prove therapeutic equivalence in an open, multiple fixed dose, one-way crossover, multicenter, and multinational study over a period of 29 days. Forty two stable renal transplant recipients maintained on Sandimmun Neoral were enrolled. Whole blood was collected at day 14 of the study at 0, 0.5, 1.0, 1.5, 2, 3, 4, 5, 6, 8, 10, and 12 hours after reference dosing and the same schedule was repeated at day 29 after switching on an mg:mg basis to the test product at day 15 of the study. Analysis of variance was performed for the pharmacokinetic parameters (area under the curve [AUC]0-12, maximum concentration [Cmax]) of cyclosporine using log-transformed values. Tolerability was assessed by vital signs, adverse events, and laboratory investigations. The 90% confidence interval (CI) test for the Ln-transformed, pharmacokinetic parameters was all within the US Food and Drug Administration acceptable range of 80% to 125%, as Ln area under the steady-state curve (AUCss) was within the range of 92.56 to 103.55 and Ln Cmax was within the range of 85.73 to 103.58; the same also applied for AUC0-4, which may be considered the area of greatest inter- and intra-patient variability. Furthermore, in line with the newly adopted recommendations of the Expert Advisory Committee on Bioavailability and Bioequivalence of Health Canada, the 90% CI for AUCss was within the narrow range of 90% to 112%. No significant difference in tolerability was recorded between the two products. Sigmasporin Microral (Julphar) was found to be bioequivalent and clinically interchangeable on an mg:mg basis with Sandimmun Neoral (Novartis).

Bioequivalence of enteric-coated mycophenolate sodium and mycophenolate mofetil: a meta-analysis of three studies in stable renal transplant recipients

BACKGROUND

Mycophenolic acid (MPA) is an inhibitor of lymphocyte proliferation and is well established as an immunosuppressive agent in solid organ transplantation. The initial formulation of the drug was a prodrug formulation, mycophenolate mofetil (MMF, Cellcept), which is well absorbed and rapidly converted to mycophenolate in plasma. However, the use of MMF is associated with adverse gastrointestinal events, which can lead to withdrawal of therapy. In an effort to reduce the gastrointestinal effects of MMF, an enteric-coated formulation of the drug was developed, based on the sodium salt of MPA (EC-MPS, Myfortic).

METHODS

Although bioequivalence has been demonstrated in an individual study in maintenance kidney transplant patients, this manuscript documents bioequivalence in a much larger data set of 82 patients by a meta-analysis of data from clinical trials.

RESULTS

The results confirm the bioequivalence of EC-MPS and MMF for both mycophenolate and metabolite exposure, and for maximum plasma mycophenolate concentrations, across three studies. The 90% confidence interval of the ratio of EC-MPS to MMF for mycophenolate plasma AUC in the 82 patients was 101.1 to 114.5% and for Cmax was 83.0% to 112.7%.

CONCLUSION

These findings provide reassurance to transplant professionals and patients that, when choosing between EC-MPS and MMF, they are choosing between formulations that give equivalent mycophenolate exposure.

Update on the use of ciclosporin in immune-mediated dermatoses

Immune-mediated dermatoses, such as psoriasis and atopic dermatitis, affect a significant proportion of the population. Although most cases are not life threatening, these diseases can have a profound effect on the sufferer's quality of life and that of their family. Systemic therapy, such as ciclosporin, is often indicated for severe or recalcitrant disease. The efficacy of ciclosporin in the treatment of psoriasis and atopic dermatitis has been established and clinical data also demonstrate its efficacy in treating less common but equally challenging conditions such as pyoderma gangrenosum, lichen planus, autoimmune bullous disease, recalcitrant chronic idiopathic urticaria and chronic dermatitis of the hands and feet. The risk of potential adverse events associated with ciclosporin is greatly reduced if current treatment and monitoring guidelines are followed.

Three generations of cyclosporine a formulations: an in vitro comparison

When the microemulsion formulation of the critical dose drug cyclosporine A (CsA) (Sandimmun Optoral) was introduced in the mid-1990s, it became clear that this new formulation improves the oral bioavailability of CsA and has a positive influence on its pharmacokinetic variability. Previous studies with the original CsA formulation (Sandimmun) showed that the size of the emulsion droplets and concomitant food intake has an effect on the absorption of CsA from the small intestine when orally administered. It was suggested that these effects might have an influence on the drugs' pharmacokinetic parameters. In this study, we focused on the two above-mentioned aspects and compared the first and second generations of CsA products (Sandimmun, Sandimmun Optoral) to generic CsA formulations by analyzing the contents of cyclosporine A gel capsules with respect to their emulsion droplet and micelle sizes using photon correlation spectroscopy (PCS). We tried to discern any differences in droplet size between different generations of CsA formulations, primarily the second and third generation, through simple physical tests. Because a high fat content food may influence the absorption of CsA, we also determined the distribution of CsA between hydrophilic and lipophilic phases using high-performance liquid chromatography analysis. It became clear that when compared under simple physical conditions, established cyclosporine formulations and new generic products show significant differences in droplet size and distribution between an aqueous phase and a high fat content food. Whether these differences are of clinical relevance remains to be investigated.

Assessment of the bioequivalence of a generic cyclosporine A by a randomized controlled trial in stable renal recipients

BACKGROUND

The aim of this study was to determine the bioequivalence of Cysporin, a generic cyclosporine A, compared with Neoral in stable renal transplant recipients.

METHODS

Study design consisted of an open label, two-way crossover, randomized controlled trial of Cysporin versus Neoral in stable renal transplant recipients. In all, 33 patients were enrolled; 31 were randomized and 28 were evaluable. AUCs(0-12) were done on day 14 and 28; C(0) and C(2) were done on days 0, 7, 21 and 35. Dose conversion was 1:1. Outcome measures for serum cyclosporin A concentrations expressed as the mean+/-SD were AUC(0-12) (microg x hr/L), C(max) (microg/L), C(2) (microg/L), T(max) (hr) and T(1/2) (hr). Mean and 90% CI of the ratio Cysporin/Neoral of log-transformed data were calculated using a general linear model.

RESULTS

The main pharmacokinetic features were: AUC(0-12): Cysporin 3495+/-1319, Neoral 3853+/-1378 (P<0.05); C(max): Cysporin 755+/-301, Neoral 881+/-368 (P<0.05); C(2): Cysporin 613+/-235, Neoral 672+/-255 (P>0.05); T(max): Cysporin 1.9+/-0.8, Neoral 1.4+/-0.6 (P<0.005); and T1/2: Cysporin 8.8+/-4.3, Neoral 8.7+/-6.2 (P>0.05). Estimated ratios of Cysporin/Neoral were: AUC 0.93 (90% CI 0.88-0.98; P<0.05); C(max) 0.88 (90% CI 0.80-0.97; P<0.05); and T(max) 1.32 (90% CI 1.14-1.53; P<0.005).

CONCLUSIONS

Both the extent and rate of absorption of Cysporin are significantly less than those of Neoral. The 90% CI for the ratios of Cysporin/Neoral for AUC and C(max) lie within 0.80-1.25. Hence in this clinical context Cysporin is pharmacologically bioequivalent with Neoral. This study illustrates the importance of testing bioequivalence of generic cyclosporine A products in transplant recipients not healthy volunteers.

The Utility of the Population Approach Applied to Bioequivalence in Patients

Mixed-effect modeling was used to compare the population pharmacokinetics of 2 formulations of cyclosporine in patients. An open-label, multicenter, conversion study in stable, 6-month post-renal allograft recipients was conducted to compare the safety and pharmacokinetics of oral Pliva Cyclosporine Soft Gelatin Capsules (USP Modified) with Neoral (cyclosporine soft gelatin capsules, USP Modified) in stable post-renal transplant patients. Blood samples were collected predose and for 12 hours postdose on days 1, 14, 15, 28, and 29. Whole-blood samples were analyzed for cyclosporine using high-performance liquid chromatography and mass spectroscopy. Estimates of pharmacokinetic parameters were generated using noncompartmental and population compartmental pharmacokinetic analysis. Moreover, the effects of demographic factors on the pharmacokinetics of cyclosporine were evaluated using the nonlinear mixed-effects modeling program NONMEM. The rate and extent of bioavailability of cyclosporine did not differ between Pliva Cyclosporine Soft Gelatin Capsules and Neoral. In the final model, gender and actual body weight significantly affected the central and peripheral volumes of distribution. In addition, the pharmacokinetics of cyclosporine was defined robustly in this patient population using population pharmacokinetic approaches. Results indicate that the Pliva Cyclosporine Soft Gelatin Capsules and Neoral are bioequivalent when administered to renal transplant patients. Pliva Cyclosporine Soft Gelatin Capsules can then be substituted for Neoral in stabilized patients without anticipating dose adjustments.

Therapeutic drug monitoring of cyclosporine

The introduction of cyclosporine into clinical practice improved transplant outcome. However, the use of cyclosporine is not without problems. A narrow therapeutic index (the drug causes irreversible kidney damage when given in too high a dose) coupled with variable absorption and unpredictable pharmacokinetics has resulted in the need to measure cyclosporine blood concentrations to enable the dose of the drug to be individualised to the patient. When this is done correctly therapeutic efficacy can be maximised while toxicity is kept to a minimum. The evolution of cyclosporine dose optimisation started with the adjustment of empirical fixed doses by clinical "judgement;" progressed to therapeutic drug monitoring of trough, predose, C0 concentration with non specific assays that measured parent drug and metabolite; then on to "specific" cyclosporine C0 measurements; through area under curve monitoring using full profile measurements and limited sampling scheme procedures; and finally ending up with absorption profiling that targets AUC in the first 4 hours or the 2 hour blood cyclosporine concentration, C2. At the same time the formulation of cyclosporine has changed from Sandimmune to Neoral and now generic forms of the latter are available. The evidence base supporting C2 monitoring continues to grow and the technique will need to be customised as new combination therapies emerge. Therapeutic drug monitoring of cyclosporine may also need to be tailored to avoid the potential negative impact of switching patients to generic forms of the drug.

Ciclosporin in psoriasis clinical practice: an international consensus statement

The main recommendations for the use of ciclosporin in the management of psoriasis are: (i) intermittent short courses (average of 12 weeks duration) of ciclosporin are preferable; (ii) ciclosporin should be given in the dose range 2.5-5.0 mg kg(-1) day(-1) (doses greater than 5.0 mg kg(-1) day(-1) should only be given in exceptional circumstances); (iii) treatment regimens should be tailored to the needs of each patient; (iv) selection of patients should take into account psychosocial disability, as well as clinical extent of disease and failure of previous treatment; (v) each patient's renal function (as measured by serum creatinine) should be thoroughly assessed before and during treatment; (vi) each patient's blood pressure should be carefully monitored before and during treatment; (vii) adherence to treatment guidelines substantially reduces the risk of adverse events; (viii) long-term continuous ciclosporin therapy may be appropriate in a subgroup of patients; however, duration of treatment should be kept below 2 years whenever possible; and (ix) when long-term continuous ciclosporin therapy is necessary, annual evaluation of glomerular filtration rate may be useful to accurately monitor renal function.

Clinical pharmacokinetics of tacrolimus in heart transplantation: new strategies of monitoring

The aim of this study was to investigate the absorption profile of tacrolimus (TAC) in heart transplant patients in order to find the best sampling time to predict the total exposure and to explore the target range for optimal clinical immunosuppression. Twenty-five full pharmacokinetic studies were performed in 22 heart transplant patients (11 men and 7 women) at less than 1 year posttransplant. The immunosuppressive treatment was steroids plus azathioprine or mycophenolate mofetil and TAC. The mean age was 55 years (36-64 years) and the mean weight 70.49 kg (50-111 kg). After three days of receiving the same dose, eight blood samples were collected at 0.5, 1, 2, 4, 6, 8, and 12 hours postmorning dose. TAC concentrations were measured by microparticle enzyme immunoassay (IMx). Area under the concentration-time curve(AUC(0-12)) was calculated by the trapezoidal rule. Using 0-4 hours TAC blood concentrations, a projected 12 hours AUC (extrapolated AUC(0-4)) was calculated assuming C0 and C12 were comparable. A high interpatient TAC pharmacokinetics variability that was greater during the absorption phase was observed. A Cmax (30.5+/-13.8 ng/mL) was reached at 2.3+/-1.5 h. When target trough levels were achieved (10-20 ng/mL), the mean tacrolimus exposure was 230.6+/-59.2 ng h/mL (120.14-327.7) (n=19). Correlation between AUC(0-12) and C0 was relatively good (r2=0.74). Between individual time points, C4 showed the best correlation (r2=0.88). In any case the best strategy to monitor is to obtain the extrapolated AUC(0-4) (r2=0.98), as a good approach to patients with a poor response to treatment.

A pharmacokinetic and clinical review of the potential clinical impact of using different formulations of cyclosporin A. Berlin, Germany, November 19, 2001

A meeting of 14 transplant and pharmacokinetic specialists from Europe and North America was convened in November 2001 to evaluate scientific and clinical data regarding the use of different formulations of cyclosporin A (CsA). The following consensus was achieved. (1) CsA is a critical-dose drug with a narrow therapeutic window. Clinical outcomes after transplantation are affected by the pharmacokinetic properties of CsA, particularly by its bioavailability, and by intrapatient variability in CsA exposure. (2) Standard bioequivalence criteria do not address differences in CsA pharmacokinetics between transplant recipients and healthy volunteers, or between subpopulations of transplant recipients. (3) In some circumstances, currently available formulations of CsA that meet standard bioequivalence criteria are likely to be nonequivalent with respect to pharmacokinetic characteristics. (4) The choice of CsA formulation can affect the short- and long-term clinical outcome. Currently, there is a lack of clinical comparisons between generic CsA formulations and the Neoral formulation (Novartis Pharmaceuticals Corporation, East Hanover, New Jersey). Initial retrospective data from the Collaborative Transplant Study suggest that use of generic CsA formulations may result in reduced graft survival at 1 year. (5) Management of transplant recipients by monitoring Neoral concentrations 2 hours after dosing (C(2)) reduces the incidence and severity of acute rejection compared with monitoring of trough concentrations with no increase in toxicity. C(2) monitoring has been developed based on the pharmacokinetics of Neoral only and has not been evaluated or validated for generic formulations of CsA. (6) The major costs of care after transplantation relate to the management of poor clinical outcomes and toxicity. CsA formulations with different pharmacokinetic properties may be associated with varying clinical outcomes, which would be expected to affect total health care costs. (7) The transplant physician is responsible for selecting immunosuppressive agents and formulations for his or her patients. Any switch between CsA formulations in a particular patient should take place only in a controlled setting with adequate pharmacokinetic monitoring.

Cyclosporin monitoring in Australasia: 2002 update of consensus guidelines

Therapeutic drug monitoring of cyclosporin (CsA) has been established as part of the routine clinical treatment of patients following organ transplantation for more than 20 years, and based on contemporary knowledge, many consensus guidelines have been published to assist clinics and laboratories attain optimal strategies for patient care. This article addresses the newer directions in CsA monitoring, with particular reference to the Australasian situation that has evolved since the 1993 Australasian guideline. These changes have included the introduction of alternative assay methodologies, changed CsA formulation from Sandimmun to Neoral throughout Australasia, and alternatives to trough concentration (C0) monitoring, especially 2-hour concentration (C2) monitoring and associated validated dilution protocols to accurately quantitate the higher whole blood CsA concentrations. The revision was prepared following a recent survey of all Australasian CsA-monitoring laboratories where discordant practices were evident.

Randomized, international study of cyclosporine microemulsion absorption profiling in renal transplantation with basiliximab immunoprophylaxis

Increasing information suggests that absorption profiling may be superior to trough level monitoring for optimal concentration control of cyclosporine microemulsion (Neoral) therapy, and that CsA exposure early post-transplant may correlate significantly with reduced risk of acute graft rejection. This randomized, prospective, multicenter international concentration-controlled study was conducted in 21 renal transplant centers in 8 countries to test and compare the clinical feasibility, functionality, accuracy, precision and prediction of rejection by cyclosporine microemulsion absorption profiling to conventional trough-level drug monitoring. Primary or second renal allograft recipients treated with basiliximab, cyclosporine microemulsion and prednisone immunosuppression were randomized to two study groups in which cyclosporine microemulsion therapy was monitored using a multipointalgorithm or by trough levels. The two study arms were comparable in terms of baseline characteristics, treatment and clinical outcomes. Treatment failure, consisting of acute rejection, graft loss or death, occurred with equal incidence in the two groups (30% and 33%, respectively). Diagnostic feasibility, measured as the proportion of samples obtained within the designated time window, was marginally lower in area under the time-concentration curve (AUC) than in trough groups, but the therapeutic accuracy and precision were comparable or superior in the AUC group. Cox regression analysis performed across study groups showed a highly significant correlation between the predicted probability of acute rejection and cyclosporine (CsA) exposure measured by AUC over the entire 12-h dosage interval (AUC[0-12]) (p = 0.0068), AUC over the first 4 h of the 12-h dosage interval (AUC[0-4]) (p = 0.0014) or 2h post-dose (C2) CsA level (p = 0.0027). Day 3 dose- and weight-corrected C2 values (EMIT equivalent) separated patients into low (< 200 microg/L/mg/kg dose), intermediate (200-350 microg/L/mg/kg dose) and high absorber categories (> 350 microg/L/mg/kg dose), defining those at greatest risk. Within these categories, C2 values above approximately 1500 microg/L by day 3 post-transplant were associated with the lowest predicted probability of rejection. Comparable analysis by Cox regression using C0 levels did notreach statistical significance. Absorption profiling is a feasible, accurate and precise method for monitoring cyclosporine microemulsion therapy in clinical practice and, as shown in the companion article, may be simplified by the use of single-point C2 concentrations which accurately predict individual AUC[0-4] exposure levels. Both cyclosporine microemulsion relative absorption (i.e. dose- and weight-corrected exposure) and CsA exposure (measured by predicted AUC or C2 levels) are closely correlated with the risk of rejection, and define patients at high and low risk of acute graft rejection. Trough (C0) levels are not closely correlated with either CsA exposure or rejection risk, and should not be considered reliable for monitoring cyclosporine microemulsion therapy.

Quantitation of cyclosporin A in whole blood by liquid chromatography/stable isotope dilution electrospray ionization mass spectrometry

Therapy with cyclosporin A (CsA) for immunosuppression after organ transplantation requires monitoring of its levels in blood owing to the narrow therapeutic index of the drug and to the high inter-individual variability of the drug absorption and metabolism. We describe the preparation of CsA labelled with stable isotopes ((13)C and (2)H) with an isotopic enrichment of about 99% using labelled glucose and its use as internal standard for quantification of CsA blood levels by isotope dilution/electrospray ionization mass spectrometry. The method was found to be linear in the tested range (1-1000 ng) with and without the matrix. The accuracy of the bracketting calibration curves prepared using 100 ng ml(-1) labelled CsA was within +/-1.7% (bias). The results confirmed the usefulness of the procedure as a reference method for the external quality assessment of the field methods for the evaluation of CsA blood concentration, the imprecision (relative standard deviation) and accuracy (bias) being <2%.

Recommendations for bioequivalence testing of cyclosporine generics revisited

The immunosuppressant cyclosporine is generally considered a critical-dose drug. The validity of standard criteria to establish bioequivalence between cyclosporine formulations has recently been challenged. Recommendations included establishment of individual bioequivalence rather than average bioequivalence, establishment of bioequivalence in transplant patients and in subgroups known to be poor absorbers, as well as long-term efficacy and safety studies in transplant patients. However, at the moment individual bioequivalence is a theoretical concept, the practical benefits of which have not statistically been proven. The proposed patient pharmacodynamic studies can be expected to require an unrealistically high number of subjects to achieve sufficient statistical power. It is well established that the common practice of blood-concentration-guided dosing of cyclosporine efficiently compensates for interindividual and intraindividual variability and allows for safely switching cyclosporine formulations as bioinequivalent as Sandimmune and Neoral. Recent studies comparing the generic cyclosporine formulation SangCya with Neoral, including individual bioequivalence, bioequivalence in transplant patients, and long-term safety after switching from Sandimmune to SangCya, confirmed that it was valid to conclude bioequivalence of both cyclosporine formulations based on standard average bioequivalence criteria. Present FDA guidelines for approving bioequivalence can be considered adequate and sufficient for generic cyclosporine formulations.

Abbreviated tacrolimus area-under-the-curve monitoring for renal transplant recipients

The area under the concentration time curve (AUC) for oral tacrolimus (FK) may provide a more precise model for FK monitoring after renal transplantation. The purpose of this study is to identify a simple, cost-effective method for predicting FK AUC. FK concentrations were measured at 0, 1, 2, 4, 6, 8, and 12 hours after the morning dose. The predicted AUCs (AUC(p)s) derived from regression equations were used to estimate the actual 12-hour AUCs (AUC(12)s). The relationship between AUC(p) and AUC(12) was validated by determining the coefficient of multiple determination (R(2)), percentage of prediction error (PE%), and percentage of absolute prediction error (APE%). Eighteen stable Oriental renal transplant recipients (9 men, 9 women) with a mean age of 42.6 +/- 6 years and mean body weight of 62.7 +/- 10 kg were recruited for the study. The FK AUC(12), trough, 2-hour, and 4-hour concentrations were 125 +/- 24 h. ng/mL (range, 87.7 to 181.9 h. ng/mL), 6 +/- 1.3 ng/mL, 18.1 +/- 4.7 ng/mL, and 11 +/- 2.4 ng/mL, respectively. Trough FK concentration did not have a significant correlation with AUC(12) (r = 0.34; P = 0.17). AUC(p) obtained by a two-time point regression equation using 2-hour (C2) and 4-hour (C4) FK concentrations: (AUC(P) = 16.2 + 2.4*C2 + 5.9*C4) obtained an R(2), PE%, and APE% of 0.93, -0.2% +/- 5.2% (range, -13% to 9.3%), and 3. 6% +/- 3.7% (range, 0.02% to 13%), respectively. We conclude that a two-point sampling method using C2 and C4 may be a more cost-effective FK monitoring strategy than morning FK trough levels in transplant recipients.

Current opinions on therapeutic drug monitoring of immunosuppressive drugs

The pharmacokinetics of the immunosuppressive drugs cyclosporine, tacrolimus, mycophenolate mofetil (MMF), and sirolimus are complex and unpredictable. A narrow therapeutic index unique to each patient, as well as variable absorption, distribution, and elimination, are characteristics of these drugs. Therapeutic drug monitoring plays a key role in helping clinicians maintain blood and plasma levels of immunosuppressive drugs within their respective therapeutic ranges. Variation in concentrations outside the narrow therapeutic ranges can result in adverse clinical outcomes. Therapeutic drug monitoring ensures that concentrations are not too high or too low, thereby reducing the risks of toxicity or rejection, respectively. Therapeutic monitoring of immunosuppressive drugs has been based on several choices of assay and biologic fluid (i.e., whole blood, plasma) appropriate for a particular drug. High-performance liquid chromatography (HPLC) remains the gold standard among assay methods used to monitor immunosuppressive drugs. Although HPLC is the assay of choice for cyclosporine, newer monoclonal assays are suitable as well for routine monitoring. HPLC is also widely used for therapeutic drug monitoring of mycophenolic acid, the active metabolite of MMF, and an immunoassay (used in European centers) has been developed. Therapeutic drug monitoring of tacrolimus has been improved with the recent development of assays with greater sensitivity and specificity for tacrolimus than those previously available. No commercial assays are currently available for the therapeutic monitoring of sirolimus. It is also important to identify a specific pharmacokinetic parameter for each individual drug, whether it is trough or area under the concentration-time curve, that may be most useful as a tool for optimal therapeutic drug monitoring in clinical practice. With an increased understanding of the pharmacokinetics of immunosuppressive drugs, therapeutic drug monitoring guidelines will be more clearly defined to ensure the safe and effective management of transplant recipients.

Issues in cyclosporine drug substitution: implications for patient management

Substantial improvements in short-term and long-term outcomes for kidney transplant recipients have resulted from better use of existing immunosuppressive agents and newer treatment options. Calcineurin inhibitors (e.g., cyclosporine and tacrolimus) remain the foundation of immunosuppressive therapy. These agents are considered critical-dose drugs because of their narrow therapeutic range, variable pharmacokinetics, formulation-dependent bioavailability, and negative clinical consequences of underdosing or overdosing. With the recent introduction of a new cyclosporine formulation, concern exists that current bioequivalence guidelines for generic approval may not provide adequate assessment of the safety and efficacy of critical-dose drugs. Transplant experts at 2 recent conferences recommended more rigorous criteria for bioequivalence testing of critical-dose drugs and adoption of consistent drug substitution practices. Additional recommendations included specifying the intended formulation and instituting appropriate monitoring whenever formulations are switched. A summary of the outcomes of these conferences and practice implications for transplant coordinators is discussed.

Limited sampling model for area-under-the-curve monitoring in pediatric patients receiving either Sandimmune or Neoral cyclosporin A oral formulations

Several limited sampling equations were tested to predict the area under the curve (AUC) of cyclosporin A (CsA) at steady state in 10 children with end-stage renal disease receiving oral CsA 2.5 mg/kg b.i.d. as two different formulations, namely Sandimmune and Neoral, according to a randomized crossover design with a one-month washout period. AUC was significantly correlated with CsA concentration at 5 h. The equation derived from this single concentration time point was able to adequately predict the AUC for Sandimmune but not for Neoral. The equation derived from CsA concentration data, measured at 2 and 12 h, significantly improved predictive performance in terms of bias and precision, allowing adequate AUC predictions in both formulations. CsA concentration at 2 h was also able to predict Cmax, while the concentration at 12 h corresponded to the trough value in a b.i.d. dosing scheme. Therefore, it is concluded that a limited sampling model including concentration data at 2 and 12 h allows the estimation of AUC, Cmax and trough levels, yielding a complete profile in patients exposed to CsA as Sandimmune or Neoral. Hence, this model can be used for therapeutic monitoring of CsA levels in pediatric patients being switched from one formulation to another.

An individual bioequivalence approach to compare the intrasubject variability of two ciclosporin formulations, SangCya and Neoral

A novel bioequivalence testing approach was used to determine intrasubject variability and switchability of two ciclosporin formulations, SangCya (test) and Neoral (reference). Twenty healthy volunteers were enrolled into a single-dose, randomized, open-label, 4-period, 2-sequence study with a crossover replicate design. Subject-by-formulation interaction variances were compared using a mixed effects linear model. Intrasubject variability for ln AUC(0-infinity) and ln C(max) of SangCya and Neoral were not significantly different. The 95% confidence intervals of the intrasubject variability of AUC(0-infinity) (0.94) and C(max) (1.28) as determined using the bootstrap nonparametric percentile method (n = 2,000) were below the individual bioequivalence limit estimated at 2.25. We concluded equivalent intrasubject variability of ciclosporin pharmacokinetics and switchability between SangCya and Neoral.

Drug substitution in transplantation: a National Kidney Foundation White Paper

Specific safeguards to guide the approval process and substitution practices for generic immunosuppressive agents are necessary for the effective delivery of patient care. Currently, the Food and Drug Administration (FDA) requires the demonstration of bioequivalence of generic drugs to innovator drugs in normal healthy subjects, a criterion that may be insufficient for critical-dose drugs. For generic equivalents of critical-dose drugs and for innovator critical-dose drugs, there should be a requirement for replicate studies measuring intrasubject variability and subject-treatment interactions to establish that bioequivalence holds true. Extensive testing of generic drugs in all target patient types is impractical and should not be required. However, when evidence suggests that the bioavailability of a critical-dose drug may vary substantially in certain subgroups, the FDA should require a demonstration of bioequivalence of generic versions to innovator products in these representative target populations. Changes in the approval process for generics should be accompanied by more consistent substitution practices. Pharmacists should notify the prescribing physician and patient whenever a critical-dose drug (generic or brand name) is dispensed in a different formulation from the one the patient has been taking. Therapeutic substitution for such drugs should not be made unless the prescribing physician has granted approval. The health care provider should consider instituting appropriate monitoring whenever patients are switched between generic formulations or between innovator drugs and generic formulations. Patients should be well informed about generic substitutes so that they can participate in treatment choices.