Andrew K. Trull

Distribution of cyclosporin in organ transplant recipients.

AbstractCyclosporin is an immunosuppressive agent with a narrow therapeutic index. The total concentration of cyclosporin in blood is usually monitored to guide dosage adjustment and to compensate for substantial interindividual and intraindividual variability in cyclosporin pharmacokinetics. Cyclosporin is a highly lipophilic molecule and widely distributes into blood, plasma and tissue components. It mainly accumulates in fat-rich organs, including adipose tissue and liver. In blood, it binds to erythrocytes in a saturable fashion that is dependent on haematocrit, temperature and the concentration of plasma proteins. In plasma, it binds primarily to lipoproteins, including high-density, low-density and very-low-density lipoprotein, and, to a lesser extent, albumin. The unbound fraction of cyclosporin in plasma (CsAfu) expressed as a percentage is approximately 2%.It has been shown that both the pharmacokinetic and pharmacodynamic properties of cyclosporin are related to its binding characteristics in plasma. Furthermore, there is some evidence to indicate that the unbound concentration of cyclosporin (CsAU) has a closer association with both kidney and heart allograft rejection than the total (bound + unbound) concentration. However, the measurement of CsAfu is inherently complex and cannot easily be performed in a clinical setting. Mathematical models that calculate CsAfu, and hence CsAU, from the concentration of plasma lipoproteins may be a more practical option, and should provide a more accurate correlate of effectiveness and toxicity of this drug in transplant recipients than do conventional monitoring procedures.In conclusion, the distribution characteristics of cyclosporin in blood, plasma and various tissues are clinically important. Further investigations are needed to verify whether determination of CsAU improves the clinical management of transplant recipients.

Randomized, trough blood cyclosporine concentration-controlled trial to compare the pharmacodynamics of Sandimmune and Neoral in de novo lung transplant recipients

The greater and more consistent absorption of cyclosporine from the microemulsion formulation (Neoral; Novartis Pharmaceuticals Ltd., Frimley, UK) when compared with that from the original form (Sandimmune; Novartis Pharmaceuticals Ltd., Frimley, UK) results in greater systemic exposure. Lung transplant recipients could particularly benefit from this enhanced exposure, but not at the expense of excessive cyclosporine toxicity. We compared the pharmacodynamics of Neoral and Sandimmune over the first postoperative year in 50 lung transplant recipients. Twenty-eight patients were randomly selected to receive Neoral and 22 to receive Sandimmune. Nine patients with cystic fibrosis (CF) were randomly selected independently (5, Neoral; 4, Sandimmune). Patients were maintained on similar trough blood cyclosporine concentrations (C0) throughout the 12-month follow-up. A limited blood sampling strategy was adopted to compare the pharmacokinetics of the two formulations at the end of weeks 1 to 4, and of weeks 13, 26, 39, 52. The influence of any difference between the pharmacokinetics of Neoral and Sandimmune on either efficacy or toxicity of the drug was investigated during the follow-up period. Patients in the Neoral and the Sandimmune groups were matched demographically. There were no differences in dose-normalized blood cyclosporine concentrations measured predose (C0) or 6 hours postdose between the two groups. However, the measurement at 2 hours postdose (C2) and the total AUC0-6 were significantly greater in the Neoral group in both CF and non-CF patients at all visits (p < 0.001). Non-CF patients required 9% lower doses of Neoral to achieve comparable C0 measurements to those patients receiving Sandimmune. However, patients with CF required 2 to 3 times the dose of both Neoral and Sandimmune to achieve the same C0 as non-CF patients. The linear rejection rate in the Sandimmune group was 1.87 episodes per patient year, which was similar to the rejection rate of 1.97 episodes per patient year in the Neoral group. Serial lung function, blood biochemistry and hematology, mortality and the incidence of severe renal dysfunction, hypertension, infection, seizures, and new-onset diabetes were all similar in the two groups. Despite equivalent C0, those in the Neoral group were consistently exposed to greater blood cyclosporine concentrations during the dosing interval than those in the Sandimmune group. This did not increase the incidence of serious cyclosporine-associated side effects or influence the rate of acute rejection either. When data from the Neoral and Sandimmune groups were combined, measurements of C0 but not C2 or C6 were associated with the risk of acute lung allograft rejection.

Randomized trial to evaluate the clinical benefits of serum alpha-glutathione S-transferase concentration monitoring after liver transplantation

BACKGROUND An increase in serum alpha-glutathione S-transferase concentration (GST) has been shown to be a more sensitive and specific marker of hepatocellular damage than equivalent increases in transaminase activities. A randomized clinical trial of 60 liver transplants in 49 patients was carried out to assess the clinical benefits of GST monitoring as a supplementary test to routine liver function tests during the first 3 postoperative months after liver transplantation. METHODS Mortality and morbidity were compared in graft recipients who had their GST reported daily to the ward (reporting group) and graft recipients who did not. RESULTS The 3-month survival rate was significantly greater in the reporting group (P=0.033) and the risk of graft loss was halved (relative hazard ratio=0.50; P=0.29). The reporting group also had significantly more patients who spent less than 3 weeks in the hospital throughout the follow-up period (P=0.036). In addition, the reporting group experienced a lower frequency of biopsies per graft (P=0.038), less severe rejection (P=0.015), and a lower incidence of infection episodes per graft (P=0.03). GST increased by >50% above the upper limit of the reference range at a median of 1 day before the equivalent change in alanine transaminase in association with allograft rejection in the combined groups (95% confidence interval=1 to 2 days) but was lower on the day of diagnosis of rejection in the reporting group (P=0.02). This is compatible with the earlier diagnosis of rejection in the reporting group. CONCLUSIONS We conclude that the monitoring of GST may improve patient care, reducing both mortality and morbidity.

Risk factors for the development and progression of dyslipidemia after heart transplantation.

Background. Hyperlipidemia is an important complication after organ transplantation and contributes to the development of posttransplant accelerated coronary artery diseases. Methods. We have retrospectively evaluated the relative contribution of various risk factors associated with the development and progression of hyperlipidemia in 194 heart transplant recipients by the use of mixed effects multiple linear regression analysis. The demographic characteristics evaluated were primary diagnosis of ischemic heart disease (IHD), gender, and age. Postoperative characteristics included number of treated rejections, dosage of cyclosporine (CYA), tacrolimus (TAC), prednisolone and azathioprine, and concentration of serum creatinine and glucose. The effects of administration of antihypertensive agents, diuretics, and lipid lowering agents were also studied. Results. The total cholesterol concentration increased significantly in the first 3 months posttransplant but gradually decreased thereafter. Total cholesterol and the ratio of low density lipoprotein (LDL) cholesterol to high density lipoprotein (HDL) cholesterol (LDL-C/HDL-C) increased to a greater extent in patients with IHD although female transplant recipients had a greater increase in the total cholesterol concentration. Each episode of rejection increased serum cholesterol by 0.306 mmol/liter (0.258, 0.355) [mean (95% C.I.)] and serum triglyceride by 0.164 mmol/liter (0.12, 0.209) although switching to TAC improved total cholesterol and LDL-C/HDL-C. Administration of frusemide, increased the total cholesterol and LDL-C/HDL-C whereas administration of bumetanide or metolazone increased the concentration of serum triglyceride. Serum glucose was associated with hypertriglyceridemia whereas serum creatinine was associated with increases in the total cholesterol, LDL-C/HDL-C and triglyceride. Conclusions. We have identified demographic and postoperative covariables that predispose heart transplant recipients to hyperlipidemia. Some of these risk factors, such as the effect of diuretics, have not been identified before in this group of patients and may be amenable to modification or closer control. TAC rather than CYA may be the immunosuppressive of choice for patients who are at greater risk of developing hyperlipidemia.

Simultaneous determination of plasma prednisolone, prednisone, and cortisol levels by high-performance liquid chromatography.

Recipients of organ transplants remain particularly dependent on prednisolone as part of their maintenance immunosuppression. Despite this, the pharmacokinetics of prednisolone have never been fully characterized in these patients, and consequently dosing remains empirical. Accurate monitoring of prednisolone, its primary metabolite prednisone, and endogenous cortisol suppression in such patients may provide a means of improving the clinical outcome by adjusting for variability in prednisolone pharmacokinetics and pharmacodynamics. Measurement of endogenous cortisol may provide an independent marker of prednisolone pharmacodynamics. A simple isocratic reverse-phase high-performance liquid chromatography procedure, using betamethasone as an internal standard, was developed to quantify plasma prednisolone, prednisone, and cortisol simultaneously. The steroids were extracted from 0.5 mL plasma with 3 mL (1:1 v/v) ethyl acetate/tert-methyl butyl ether and 0.1 mL phosphoric acid, washed in 0.1 mol/L NaOH before a final drying step and reconstitution in mobile phase for injection. Separation was achieved using a Supelcosil LC-18-DB, 150 × 4.6-mm, 5-&mgr;m particle size, reverse-phase column attached to a Newguard 15 × 3-mm, RP8 guard column maintained at 25°C, with ultraviolet detector set at 254 nm. The mobile phase consisted of 16% isopropanol in water containing 0.1% trifluoroacetic acid, set at a flow rate of 1.2 mL/min. The assay was linear up to 1,002 &mgr;g/L for prednisolone, 982 &mgr;g/L for prednisone, and 545 &mgr;g/L for cortisol. Mean intra-assay and interassay imprecision levels were 6.0% and 7.2%, respectively, for prednisolone, 5.8% and 7.2% for prednisone, and 5.6% and 7.9% for cortisol. Intra-assay inaccuracy was <7% of nominal values for prednisolone, prednisone, and cortisol. The lower limit of quantification was 7 &mgr;g/L for prednisolone and prednisone and 10 &mgr;g/L for cortisol. Corticosteroid recoveries were 73%, 74%, and 90% for prednisolone, prednisone, and cortisol, respectively. The authors describe a robust, inexpensive, and simple method suitable for therapeutic drug monitoring or pharmacokinetic studies of prednisolone; it may also be used to measure the suppression of endogenous cortisol production.

Pharmacokinetics of cyclosporine in heart and lung transplant candidates and recipients with cystic fibrosis and Eisenmenger's syndrome.

Objective: To compare the pharmacokinetics of cyclosporine in patients with either cystic fibrosis or Eisenmengers syndrome.

Population pharmacokinetics of cyclosporine in cardiopulmonary transplant recipients.

A population pharmacokinetic analysis of cyclosporine (CsA) was performed, and the influence of covariates on CsA oral clearance and relative bioavailability was investigated. Data from 48 recipients of heart-lung (n = 21) or single (n = 18) or double (n = 9) lung transplant were included in the study. Patients received oral CsA as either a conventional formulation (Sandimmune™) or a microemulsion (Neoral™). Steady-state CsA concentrations were measured before and at approximately 2 and 6 hours after the morning dose of CsA at the end of weeks 1, 2, 3, 4, 13, 26, 39, and 52 posttransplantation. A total of 1004 CsA concentration observations were analyzed using mixed effects-modeling (NONMEM). A 1-compartment pharmacokinetic model and first-order oral absorption were used to fit the data. The absorption rate constants were fixed at 0.25 L/h for Sandimmune and 1.35 L/h for Neoral formulations. Oral clearance (CL/F) was estimated to be 22.1 L/h (95% confidence intervals [CI] 19.5-24.7 L/h). Itraconazole (ITRA), cystic fibrosis (CF), and weight (WT) were identified as significant covariates for CL/F according to the final model: CL/F = 22.1 − 11.3 × ITRA + 23.5 × CF + 0.129 × (WT − 58.7) L/h; where ITRA = 1 if the patient was taking concomitant itraconazole, otherwise 0; CF = 1 if the patient had cystic fibrosis, otherwise CF = 0; and WT is patient weight in kilograms. The relative oral bioavailability of Sandimmune to Neoral was 0.82. The bioavailability of both preparations increased during the first month posttransplantation. Age, gender, and type of transplant (single, double, or heart-lung) were not identified as significant covariates for CsA clearance. The population pharmacokinetic model developed identified some sources of variability in CsA pharmacokinetics; however, an appreciable degree of variability is still present in this patient population.

Altered pharmacokinetics of cyclosporin in heart-lung transplant recipients with cystic fibrosis.

The cyclosporin dose versus blood concentration relationship for 11 heart-lung transplant recipients with cystic fibrosis was studied retrospectively. Eleven patients, closely matched for age and gender, who received heart-lung transplantation for other diseases were selected as controls. Cystic fibrosis patients received 16.7 (SD 7.2) mg/kg/day of oral cyclosporin compared with 8.2 (SD 1.9) mg/kg/day given to the control patients (p < 0.01). Nine of the cystic fibrosis patients received higher mean daily doses of cyclosporin. Mean blood cyclosporin concentrations were, however, not significantly different (p = 0.58), and there were no apparent differences in clinical outcome in terms of rejection, infection, and nephrotoxicity in the two groups. The apparent oral clearance of cyclosporin was significantly higher (p < 0.01) in cystic fibrosis patients. Cyclosporin dosage individualization with the aid of cyclosporin blood concentration measurements is critically important in this subpopulation of heart-lung transplant recipients.

Evaluation of an Enzyme-Immunometric Assay for Serum α-Glutathione S-Transferase

A commercially available enzyme-immunometric assay for serum α-glutathione S-transferase (GST) was evaluated. Endogenous serum α-GST diluted linearly within the calibration range. However, we recommend that the sample and second antibody reagent are always added sequentially in the assay to avoid hook effect. Between-assay variability was below 7% across the calibration range and the upper limit of the reference range in adults (n = 219) was 11 · 4 μg/L. Within-individual variability in serum α-GST concentrations measured over a 4–6 week period in 4 healthy adults was small. Serum α-GST concentrations did not change significantly 6 h after a therapeutic dose of paracetamol. Studies in two patients after liver transplantation showed that serum α-GST is a better discriminant of acute changes in liver function than conventional tests. Serum α-GST concentrations were unaffected by gross muscle damage, extra-hepatic inflammation, or haemolysis and thus appear to be more liver specific than transaminase activities. The effect of renal impairment on serum α-GST concentrations requires further investigation.

Monitoring eosinophil activation and liver function after liver transplantation.

BACKGROUND Portal tract eosinophil infiltration and an increase in the blood eosinophil count (EOS) have been shown to be specific markers of liver allograft rejection. The graft eosinophil infiltration is associated with the local release of eosinophil cationic protein. Therefore, serum eosinophil cationic protein concentration (ECP) is a potential marker for acute allograft rejection. We investigated the chronological relationship among and diagnostic value of serial changes in EOS, ECP, and liver function tests (LFTs) following liver transplantation. METHODS EOS, ECP, serum alpha-glutathione S-transferase concentration, and conventional LFTs were measured in serial samples collected over the first 3 postoperative months following 58 liver transplants. The diagnostic potential of each test, alone or in combination, was reviewed over the entire follow-up period. RESULTS EOS and ECP increased at a median period of 3.5 and 4 days, respectively, before the diagnosis of acute rejection, and this increase was significantly earlier than the corresponding changes in LFTs (P<0.05). There was a significant correlation between the day of the first increase in EOS and alpha-glutathione S-transferase (rs=0.535; P=0.009) and EOS and alanine transaminase (rs=0.629; P=0.004). The optimum combination of tests for the diagnosis of acute rejection was an increase in both EOS and GST with a predictive efficiency of 84%. CONCLUSIONS Increases in EOS and ECP are early indicators of acute liver allograft rejection and precede evidence of hepatocellular damage. However, an increase in ECP was also frequently associated with infection. Therefore, we recommend the regular monitoring of EOS in conjunction with routine LFTs after liver transplantation as an aid to the early diagnosis of acute rejection.