Peter I. Pillans

Free mycophenolic acid should be monitored in renal transplant recipients with hypoalbuminemia

The current approach for therapeutic drug monitoring in renal transplant recipients receiving mycophenolate mofetil (MMF) is measurement of total mycophenolic acid (MPA) concentration. Because MPA is highly bound, during hypoalbuminemia the total concentration no longer reflects the free (pharmacologically active) concentration. The authors investigated what degree of hypoalbuminemia causes a significant change in protein binding and thus percentage free MPA. Forty-two renal transplant recipients were recruited for the study. Free and total concentrations of MPA (predose, and 1, 3, and 6 hours post-MMF dose samples) and plasma albumin concentrations were determined on day 5 posttransplantation. Six-hour area under the concentration-time curve (AUC0–6) values were calculated for free and total MPA, and percentage free MPA was determined for each patient. The authors found a significant relationship between low albumin concentrations and increased percentage free MPA (Spearman correlation = −0.54, P < 0.0001). Receiver operating characteristic (ROC) curve analysis was performed on the albumin versus percentage free MPA data. The cutoff value of albumin determined from the ROC analysis that differentiated normal from elevated percentage free MPA (defined as ≥3%) in this patient population was 31 g/L. At this cutoff value albumin was found to be a good predictor of altered free MPA percentage, with a sensitivity and specificity of 0.75 and 0.80, respectively, and an area under the ROC curve of 0.79. To rationalize MMF dosing regimens in hypoalbuminemic patients (plasma albumin ≤ 31 g/L), clinicians should consider monitoring the free MPA concentration.

A retrospective analysis of mycophenolic acid and cyclosporin concentrations with acute rejection in renal transplant recipients.

OBJECTIVES Although monitoring of cyclosporin (CsA) is standard clinical practice postrenal transplantation, mycophenolic acid (MPA) concentrations are not routinely measured. There is evidence that a relationship exists between MPA area under the concentration-time curve (AUC) and rejection. In this study, a retrospective analysis was undertaken of 27 adult renal transplant recipients. METHODS Patients received CsA and MPA therapy and had a four-point MPA AUC investigation. The relationship between MPA AUC performed in the first week after transplantation, as well as median trough cyclosporin concentrations, and clinical outcomes in the first month posttransplant were evaluated. RESULTS A total of 12 patients experienced biopsy proven rejection (44.4%) and 4 patients had gastrointestinal adverse events (14.8%). A statistically significant relationship was observed between the incidence of biopsy proven rejection and both MPA AUC (p = 0.02) and median trough CsA concentration (p = 0.008). No relationship between trough MPA concentration and rejection was observed (p = 0.21). Only 3 of 11 (27%) patients with an MPA AUC > 30 mg x h/L and a median trough CsA > 175 microg/L experienced acute rejection, compared with a 56% incidence of rejection for the remaining 16 patients. Patients who experienced adverse gastrointestinal events had significantly lower MPA AUC (p = 0.04), but median trough CsA concentrations were not significantly different (p = 0.24). Further, 3 of these 4 patients had rejection episodes. CONCLUSIONS In addition to standard CsA monitoring, we propose further investigation of the use of a 4-point sampling strategy to predict MPA AUC in the first week posttransplant, which may facilitate optimization of mycophenolate mofetil dose at a time when patients are most vulnerable to acute rejection.

Deciding when to stop: towards evidence-based deprescribing of drugs in older populations.

Minimising the harm from inappropriate prescribing in older populations is a major urgent concern for modern healthcare systems. In everyday encounters between prescribers and patients, opportunities should be taken to identify patients at high risk of harm from polypharmacy and reappraise their need for specific drugs. Attempts to reconcile life expectancy, comorbidity burden, care goals and patient preferences with the benefits and harms of medications should be made in every patient at significant risk. Drugs identified by this process of reconciliation as conferring little or no benefit and/or excessive risk of harm should be candidates for discontinuation. Evidence supporting a structured approach to drug discontinuation (or deprescribing) is emerging, and while many barriers to deprescribing exist in routine practice, various enabling strategies can help overcome them.

Evaluation of Limited Sampling Strategies for Estimation of 12-hour Mycophenolic Acid Area Under the Plasma Concentration–time Curve in Adult Renal Transplant Patients

Mycophenolate mofetil, the oral prodrug of mycophenolic acid, is indicated as immunosuppressive therapy after renal transplantation. To aid in the investigation of pharmacokinetic–pharmacodynamic relationships of mycophenolic acid in the clinical setting, limited blood sampling strategies have been proposed, and models from these developed, for the estimation of mycophenolic acid area under the concentration–time curve (AUC). In the current study, the authors investigated the predictive performance of six published models to estimate AUC. A total of 49 profiles from 25 renal transplant patients were used to test each models performance against a full 14 time-point AUC. A wide range of agreement was found when predicted AUCs were compared with full AUCs using linear regression analysis (range:r2 = 0.499 to 0.836). Model 1, which uses 4 time-points over 6 hours, was found to be superior to all other models. The range of time-points used in this model takes into account patients with variable absorption. This model should be further tested on data sets from other centers. The relatively poor performance of the other models may be caused by their inability to describe the peak concentration in these patients. Caution is warranted when using limited sampling strategies on patients whose absorption of mycophenolic acid is altered, compared with those of the pharmacokinetic profiles from which the model was developed.

Use and monitoring of low dose rituximab in myasthenia gravis

Background Myasthenia gravis is an autoimmune disorder of the neuromuscular junction. Rituximab (RTX), a monoclonal antibody to CD20, leads to B lymphocyte depletion and has been used in some autoimmune disorders, including small case series of myasthenia gravis patients. Methods A retrospective analysis was performed of all patients with acetylcholine receptor (AChR) (11 subjects) or muscle specific kinase antibody (MuSK) positive myasthenia gravis (three subjects), who had been treated with RTX in Brisbane, Australia. In most patients 1 g of RTX, in two divided doses, was given. Patients were monitored by serial clinical assessments, flow cytometry of peripheral blood B lymphocytes and antibody testing. Results RTX led to a significant improvement in symptoms in 11 of 14 patients. Doses of immunosuppressive medications were able to be reduced in 12 of 14 patients but medications could be completely ceased in only one patient. A demonstrable reduction of autoantibody levels was found in only three AChR positive patients and one MuSK positive patient, independent of clinical improvement. Peripheral blood B lymphocyte depletion was achieved in 13 out of 14 patients. B lymphocyte recovery occurred between 9 and 30 months post RTX (median 12.3 months) and was consistently associated with worsening of clinical symptoms. Conclusion Rituximab at a dose of 1 g appears to be beneficial in the treatment of patients with severe myasthenia gravis. Serial monitoring of peripheral blood B lymphocytes appears to be useful in guiding the need for further RTX therapy.

Simultaneous Quantification of Tacrolimus and Sirolimus, in Human Blood, by High-Performance Liquid Chromatography-Tandem Mass Spectrometry

In this paper the authors present a validated method for the simultaneous analysis of tacrolimus and sirolimus in human blood by high-performance liquid chromatography–electrospray tandem mass spectrometry. Blood samples (500 &mgr;L) were prepared by C18 solid-phase extraction. Mass spectrometric detection was by selected reaction monitoring. The assay was linear for both compounds over the range 0.25–100 &mgr;g/L (r2 > 0.996, n = 7). At the limit of quantification (0.25 &mgr;g/L), for both sirolimus and tacrolimus, the interday imprecision was <3% and the analytical recovery was between 97.0% and 102%, respectively. The interbatch and intrabatch coefficients of variation of the method for both analytes, at the three quality control concentrations (0.5, 20, and 80 &mgr;g/L), were <16% and <10%, respectively. The analytical recovery, at the three control concentrations, ranged from 99.2% to 104% of the nominal concentration. The mean absolute recovery (±standard deviation) of tacrolimus, sirolimus, and internal standard was 82 ± 7%, 89 ± 12%, and 77 ± 8%, respectively (n = 12). In conclusion, the method presented can be used for simultaneous determination of tacrolimus and sirolimus and will aid in pharmacokinetic studies and therapeutic drug monitoring of these drugs. Furthermore, this method has economic benefits in the clinical setting where these drugs are coadministered.

The quantification of sirolimus by high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in renal transplant recipients

BACKGROUND Sirolimus, an immunosuppressive agent, is undergoing clinical trials in the prophylaxis of organ rejection. OBJECTIVES The aim of this study was to compare the performance of the semi-automated prototype (mode IA) microparticle enzyme immunoassay (MEIA) against a validated high-performance liquid chromatography-mass spectrometry (HPLC-MS) method for measuring sirolimus concentrations. A secondary objective was to identify potential factors that may influence sirolimus measurement. METHODS The comparison was based on predose samples (n = 841) from 74 renal transplant patients receiving sirolimus therapy. Samples were collected up to 12 months after transplantation. RESULTS The mean (+/- SD) overestimation by MEIA was 42.5%+/-16.9%. Several variables were investigated to determine potential contributors to the observed overestimation. Stratification of the data based on the mean sirolimus concentrations determined by both assays yielded no statistically significant differences in bias between concentration subgroups within the clinically relevant range. Multiple linear regression analysis identified HPLC-MS sirolimus concentration (P = 0.03), hemoglobin concentration (P < 0.001), and time after transplantation (P < 0.001) as significant variables in the prediction of overestimation by MEIA. Analysis of the effect of time after transplantation on overestimation yielded a statistically significant difference up to 6 months after transplantation (35.6% to 46.4%) compared with 9 (23.9%) and 12 months (24.4%). A relationship between hemoglobin concentration and time after transplantation may explain the reduction in bias observed after 6 months. CONCLUSION The MEIA overestimates sirolimus concentrations in renal transplant patients compared with HPLC-MS. The clinical importance of this observed overestimation requires further investigation.

The current role of liquid chromatography-tandem mass spectrometry in therapeutic drug monitoring of immunosuppressant and antiretroviral drugs

Therapeutic drug monitoring of critical dose immunosuppressant drugs is established clinical practice and there are similar good reasons to monitor antiretrovirals. The aim of this article is to review the recent literature (last five years), with particular reference to the use of liquid chromatography-tandem mass spectrometry (LC-MS/MS). LC-MS/MS offers many potential advantages. The superior selectivity of LC-MS/MS over immunoassays for immunosuppressant drugs has been widely reported. Simultaneous measurement of a number of drugs can be performed. It is currently routine practice for the four major immunosuppressants (cyclosporin, tacrolimus, sirolimus and everolimus) to be simultaneously measured in whole blood. While up to 17 antiretroviral drugs have been simultaneously measured in plasma. The exquisite sensitivity of LC-MS/MS also provides the opportunity to measure these drugs in alternative matrices, such as dried blood spots, saliva, peripheral blood mononuclear cells and tissue. However, the clinical utility of measuring these classes of drugs in alternative matrices is still to be determined.

Severe toxicity associated with a markedly elevated mycophenolic acid free fraction in a renal transplant recipient.

A 58-year-old man with end-stage renal failure secondary to polycystic kidney disease developed a profoundly elevated mycophenolic acid (MPA) free fraction and associated severe toxicity after cadaveric renal transplantation. Initial immunosuppressive therapy was 4 mg/kg body weight bid cyclosporin (Neoral; Novartis Pharmaceutical Co Ltd, Sydney, Australia) given orally with 1 g bid mycophenolate mofetil (MMF) (CellCept; Roche Products Pty Ltd, Sydney, Australia). In the first 5 days posttransplantation, the serum creatinine concentration fell, and the patient developed profound hypoalbuminemia (serum albumin <20 g/L) and hyperbilirubinemia (serum bilirubin >150 micromol/L) that resulted from progressing biliary obstruction. On day 5 posttransplantation, the 2-hour whole-blood cyclosporin concentration and total MPA area under the curve (AUC(0-6)) were low (837 microg/L and 12.6 mg x h/L, respectively), while the total mycophenolic acid glucuronide (MPAG) AUC(0-6) was elevated (1317 mg x h/L). MMF was continued at the same dose, but tacrolimus substituted for cyclosporin. The patient subsequently experienced severe nausea, vomiting, hematemesis, and pancytopenia (nadir white cell count 1.6 x 10(9)/L, platelet count 32 x 10(9)/L, and hemoglobin 73 g/L) that were normalized after cessation of MMF. Retrospective measurement of the free MPA concentration on day 5 showed that free MPA AUC(0-6) was markedly elevated at 2.3 mg x h/L, as was the free fraction, at 18.3%. This case illustrates how altered protein binding can be associated with severe MMF toxicity caused by an increased free MPA concentration despite relatively low total MPA. These data support the monitoring of free MPA concentrations in those patients considered at risk for MMF-related toxicity.

Evaluation of dosage adjustment in patients with renal impairment

Abstract