Population pharmacokinetics of posaconazole in allogeneic haematopoietic stem cell transplant patients.

BACKGROUND: Invasive fungal disease (IFD) in the early post-allogeneic HSCT (alloHCT) period is associated with increased likelihood of catastrophic outcomes. The utility of oral modified release (MR) posaconazole tablets is limited by reduced drug absorption from gastrointestinal toxicity induced by cytotoxic chemotherapy, necessitating a switch to the IV posaconazole formulation. OBJECTIVES: To describe the population pharmacokinetics of posaconazole for oral MR and IV formulations in alloHCT patients and determine dosing regimens likely to achieve therapeutic exposures. METHODS: We performed a prospective observational pharmacokinetic study in adult patients in the early post-alloHCT period requiring a change in posaconazole formulation (oral to IV). Samples were analysed using a validated LC-MS/MS method. Population pharmacokinetic analysis and Monte Carlo simulations (n = 1000) were performed using Pmetrics for R. RESULTS: Twenty patients aged between 21 and 70 years were included in the study. A two-compartment model, incorporating mucositis/diarrhoea to modify the bioavailability for oral administration best described the data. To achieve ≥90% PTA, simulations showed that higher than currently recommended doses of oral MR posaconazole were required for prophylaxis Cmin targets (≥0.5 and ≥0.7 mg/L), while increased doses of both formulations were required for IFD treatment PK/PD targets, with patients experiencing oral mucositis/diarrhoea unlikely to achieve these. CONCLUSIONS: Increased doses of posaconazole should be considered for both prophylaxis and treatment of IFD to increase the proportion of alloHCT patients achieving therapeutic exposures, particularly the oral formulation in patients with mucositis and/or diarrhoea. Posaconazole therapeutic drug monitoring should be considered for all formulations in this setting.

Consistency of remifentanil concentrations in propofol-Remifentanil infusions. A laboratory-based study.

BACKGROUND: There is increasing interest in two-agent single-pump intravenous infusions for anesthesia and sedation in pediatric patients. Propofol-remifentanil is one such mixture. The poor miscibility of such admixtures when remifentanil is added in very high concentrations and when the admixtures are maintained in static conditions has been demonstrated; however, these physiochemical properties have not been examined in clinically relevant concentrations or settings. AIM: To examine if propofol-remifentanil admixtures maintain consistent remifentanil delivery when mixed in clinically relevant remifentanil concentrations and subjected to the physical effects of an actively infusing, directly-engaged syringe driver system with an extension line, as occurs when propofol-remifentanil is administered to a patient. METHODS: A propofol 10 mg.ml-1 combined with remifentanil 5 mcg.ml-1 solution was run using a Paedfusor® propofol target-controlled infusion model for 10 kg and 20 kg children for 57 min at a target plasma concentration of 3 mcg.ml-1 through a 30 ml syringe, 180 cm minimum volume extension line, lever lock cannula, interlink injection site, and 22 g intravenous cannula into sample pots. Samples were taken at the completion of the loading bolus, 1 and 2 min postcompletion of loading bolus, and every 5 min thereafter. The remifentanil concentration in these samples was then assayed using chromatography. RESULTS: There was no difference in the concentration of remifentanil in the samples based on the duration of infusion to the endpoint of 1 h, or on the patient weight model used. The concentration remained 5 mcg.ml-1 +/- 0.5 mcg.ml-1 per sample. The measurement uncertainty for the assay at 0.5 mcg.ml-1 is +/- 0.2 mcg.ml-1 . CONCLUSION: The concentration of remifentanil was 5 mcg.ml-1 +/- 0.5 mcg.ml-1 and was consistent across 57 min of infusion, and two different pediatric weight profiles.

Validation of a High-Performance Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Perhexiline and Cis-Hydroxy-Perhexiline Plasma Concentrations.

BACKGROUND: The polymorphic nature of cytochrome P450 2D6 has made therapeutic drug monitoring of the anti-anginal agent perhexiline a compulsory step in reducing adverse events associated with plasma concentrations above the therapeutic range (0.15-0.60 mg/L). The aim of this study was to develop a high-performance liquid chromatography-mass spectrometry/mass spectrometry method for the determination of plasma perhexiline concentrations and its major metabolite cis-hydroxy-perhexiline to reduce sample extraction procedures and improve sample turnaround times. METHODS: The method was validated by determining the precision and accuracy of calibrators and quality control material, comparing quality assurance program samples and patient samples measured by a previously reported liquid-liquid extraction fluorescence (FL) detection high-performance liquid chromatography method and performing matrix effects investigations. RESULTS: Replicates of calibrators at concentrations of 3.00 and 0.05 mg/L demonstrated imprecision of <10.8% and inaccuracy of <8.2% for perhexiline and <10.1% and <4.5% for cis-hydroxy-perhexiline, respectively. All samples measured by the 2 methods (n = 102) demonstrated Deming regression of perhexiline = 1.20 FL + 0.00 (Sy.x = 0.08, 1/slope = 0.67); cis-hydroxy-perhexiline = 1.48 FL - 0.20 (Sy.x = 0.40, 1/slope = 0.67). CONCLUSIONS: The assay performance was deemed acceptable and integrated into the routine therapeutic drug monitoring program of the department.

Ropivacaine (total and unbound) and AGP concentrations after transversus abdominis plane block for analgesia after abdominal surgery.

BACKGROUND: The goal of this study was to assess the safety of single bolus dose of ropivacaine (ROP) followed by continuous infusion through transversus abdominis plane block catheter. The aim was to determine ROP absorbed from the infusion site, changes in protein binding after surgery, and clinical determinants of adverse effects. METHODS: Twelve patients undergoing laparotomy, received bilateral transversus abdominis plane block under ultrasound guidance using a 20-mL bolus of 0.5% ROP followed by 10 mL/h of 0.2% ROP infusion for 48 hours. Serial blood samples were drawn presurgery and to 48 hours postbolus. Plasma concentrations of total and unbound ROP were measured by high performance liquid chromatography with ultraviolet detection. Alpha-1 acid glycoprotein concentrations were measured by enzyme-linked immunosorbent assay. Patients were monitored for any signs or symptoms of central nervous system and chorionic villus sampling toxicity. RESULTS: After the bolus dose, the mean (±SD) peak plasma total (bound plus unbound) ROP concentration (Cmax) was 2.1 (±0.8) mg/L and unbound ROP concentration was 0.04 (±0.02) mg/L. During the infusion phase, total ROP concentration continued to rise to a mean (±) Cmax of 3.3 (±1.6) mg/L, and the peak unbound concentration was 0.06 (±0.0) mg/L. No patients showed symptoms of ROP toxicity or unacceptable QTc intervals. CONCLUSIONS: Although the total ROP concentrations approached or exceeded reported neurotoxicity thresholds, no patients had unbound ROP concentrations approaching the unbound toxicity threshold, nor showed any signs or symptoms of toxicity. This result was consistent with changes in protein binding to alpha-1 acid glycoprotein after surgery.

A randomized double-blind clinical trial of a continuous 96-hour levobupivacaine infiltration after open or laparoscopic colorectal surgery for postoperative pain management--including clinically important changes in protein binding.

BACKGROUND: Continuous local anesthetic infiltration has been used for pain management after open colorectal surgery. However, its application to patients undergoing laparoscopic colorectal surgery has not been examined. The aim of this prospective, randomized, double-blind, placebo-controlled clinical trial was to study the use of a commercial infiltration device in patients undergoing open or laparoscopic colorectal surgery, along with plasma concentrations of levobupivacaine, its acute-phase binding protein (alpha-1 acid glycoprotein, AAG), and the stress marker, cortisol. METHODS: Eligible patients were randomized (2:1) to receive a continuous infiltration of either levobupivacaine or placebo using a commercial device (ON-Q PainBuster) inserted in the preperitoneal layer at the end of surgery. Blood was sampled for determination of levobupivacaine and AAG and cortisol concentrations. Other outcomes measured were pain scores, morbidity and mortality, time to bowel movement, mobilization, and length of hospitalization. RESULTS: In patients having open surgery, the levobupivacaine treatment showed a trend toward reduced total opioid consumption. No patients reported adverse effects attributable to levobupivacaine, despite 11 patients having concentrations at some time(s) during the 96-hour infiltration of up to 5.5 mg/L exceeding a putative toxicity threshold of 2.7 mg/L. AAG concentrations measured postsurgery increased by a mean of 55% (P < 0.001) at 48 hours. Cortisol concentrations also increased significantly by a mean of 191% at 1 hour. CONCLUSIONS: Continuous local anesthetic infiltration may be more beneficial in open surgery. The threshold for adverse effects from highly bound local anesthetic drugs established in healthy volunteers is of limited usefulness in clinical scenarios in which AAG concentration increases in response to surgical stress. Hence, there is scope to adopt higher doses to enhance therapeutic benefit.

Interaction of terbinafine (anti-fungal agent) with perhexiline: a case report.

Perhexiline is a unique anti-anginal agent that is frequently used in the treatment of chronic refractory angina. Its utility has been limited because of its complex pharmacokinetics that were only appreciated following the development of a therapeutic perhexiline assay. Perhexiline is cleared primarily via formation of mono-hydroxy metabolites (OH-perhexiline) by cytochrome P450 2D6 (CYP2D6). Drugs that are inhibitors of CYP2D6 may therefore inhibit perhexiline metabolism, increase plasma perhexiline concentration and may consequently increase the risk of toxicity. We report a case of a rise in perhexiline plasma concentration to a toxic level following the introduction of terbinafine hydrochloride; a moderate CYP2D6 inhibiting drug.

The effect of cognitive behavioral stress management on perceived stress, biological stress markers and weight loss/regain, from a diet-induced weight loss program: A randomized controlled trial.

Obesity and psychosocial stress are inter-related chronic conditions which lead to increased cardiovascular morbidity and mortality. The aim of this parallel randomized controlled trial was to determine whether the addition of a structured cognitive behavioral stress management (CBSM) on to a commercial online weight loss program, resulted in greater weight loss than the standard weight loss program in isolation. Eligible participants were adults between the ages 18-65, BMI 30-45 kg/m2, with no major systemic or psychiatric conditions. Seventy-four participants were assigned according to simple randomization using computer generated random numbers to either a 3-month online Weight Watchers® program (n = 36), or Weight Watchers® plus 10 weekly sessions of CBSM (n = 38). The primary outcome was weight at 3 months compared to baseline. Secondary outcomes were weight at 12 months and subjective/objective stress system measures and metabolic markers at 3 and 12 months. The study was powered at 90% to detect a 5 kg difference in weight between the two groups at 3 months. Independent sample t-tests were used to analyze the difference in weight (in kg) between the groups and paired sample t-tests were used to analyze the difference within group at different time intervals. At follow-up, there was no significant difference in weight loss between the groups (1.8 kg, 2.1 kg). However, CBSM was effective in reducing psychological measures of stress (p < 0.05) and salivary cortisol (waking, 20-min post-waking) at 3-months; with the effect on stress persisting at 12-months within the CBSM group. The reduction in PSS at 3 months was significantly greater in the CBSM group (3.84, p = 0.028) compared to WW only group at 3 months. Addition of CBSM to a standard weight loss intervention did not improve the weight loss over the standard approach on its own, but the CBSM intervention improved psychological stress parameters and cortisol secretion in participants living with obesity.

Maternal thiopurine metabolism during pregnancy in inflammatory bowel disease and clearance of thiopurine metabolites and outcomes in exposed neonates.

BACKGROUND: Azathioprine and mercaptopurine are considered safe during pregnancy. However, the pharmacokinetic effects of pregnancy on thiopurine metabolism are undefined. AIMS: To characterise thiopurine metabolism in pregnancy and measure infant metabolite levels and outcomes. METHODS: Women with IBD who were taking a thiopurine and pregnant or trying to conceive were recruited. Maternal thiopurine metabolites were measured pre-conception, in each trimester, at delivery and post-partum. Infant metabolite levels, full blood examination and liver function testing were performed at birth, and repeated until levels undetectable and haematological and biochemical abnormalities resolved. RESULTS: Forty patients were included with measurements on at least two occasions, and two with only mother-baby levels at delivery. The median maternal 6-TGN level dropped in the second trimester compared with post-partum (179.0 vs 323.5 pmol/8 × 108 RBCs, P < 0.001) and the median 6-MMP level increased in the second trimester compared with post-partum (1103.0 vs 329.5 pmol/8 × 108 RBCs, P < 0.01). At delivery, the median 6-TGN level was lower in infants (n = 20) than mothers (78.5 vs 217 pmol/8 × 108 RBCs) (P < 0.001). Metabolites were not detected at 6 weeks in any infants. Anaemia was not seen, but thrombocytosis and abnormal liver biochemistry were detected in 80% of infants from 6 weeks, which gradually improved. CONCLUSIONS: 6-TGN levels decrease and 6-MMP levels increase in the second trimester of pregnancy. Infants are exposed to thiopurine metabolites at low levels with clearance by 6 weeks and no anaemia. The cause of infant thrombocytosis and abnormal liver biochemistry in the absence of metabolites is unclear.

Opportunities to optimize tacrolimus therapy in solid organ transplantation: report of the European consensus conference.

In 2007, a consortium of European experts on tacrolimus (TAC) met to discuss the most recent advances in the drug/dose optimization of TAC taking into account specific clinical situations and the analytical methods currently available and drew some recommendations and guidelines to help clinicians with the practical use of the drug. Pharmacokinetic, pharmacodynamic, and more recently pharmacogenetic approaches aid physicians to individualize long-term therapies as TAC demonstrates a high degree of both between- and within-individual variability, which may result in an increased risk of therapeutic failure if all patients are administered a uniform dose. TAC has undoubtedly benefited from therapeutic drug monitoring, but interpretation of the blood concentration is confounded by the relative differences between the assays. Single time points, limited sampling strategies, and area under concentration-time curve have all been considered to determine the most appropriate sampling procedure that correlates with efficacy. Therapeutic trough TAC concentration ranges have changed since the initial introduction of the drug, while still maintaining adequate immunosuppression and avoiding drug-related adverse effects. Pharmacodynamic markers have also been considered advantageous to the clinician, which may better reflect efficacy and safety, taking into account the between-individual variability rather than whole blood concentrations. The choice of method, differences between methods, and potential pitfalls of the method should all be considered when determining TAC concentrations. The recommendations of this consensus meeting regarding the analytical methods include the following: encourage the development and promote the use of analytical methods displaying a lower limit of quantification (1 ng/mL), perform careful validation when implementing a new analytical assay, participate in external proficiency testing programs, promote the use of certified material as calibrators in high-performance liquid chromatography with mass spectrometric detection methods, and take account of the assay and intermethod bias when comparing clinical trial outcomes. It is also important to consider that TAC concentrations may also be influenced by other factors such as specific pharmacokinetic characteristics associated with the population, drug interactions, pharmacogenetics, adverse events that may alter TAC concentrations, and any change in the oral formulation that may result in pharmacokinetic changes. This meeting emphasized the importance of obtaining multicenter prospective trials to assess the efficacy of alternative strategies to TAC trough concentrations whether it is other single time points or area under the concentration-time curve Bayesian estimation using limited sampling strategies and to select, standardize, and validate routine biomarkers of TAC pharmacodynamics.

Glucuronidation of mycophenolic acid by Wistar and Mrp2-deficient TR- rat liver microsomes.

In humans, mycophenolic acid (MPA) is metabolized primarily by glucuronidation in the liver to mycophenolate ether glucuronide (MPAGe) and mycophenolate acyl glucuronide (MPAGa). We have previously reported that in perfused livers of TR(-) rats (lacking the Mrp2 transporter), the clearance and hepatic extraction ratio of MPA were significantly lower compared with control Wistar rats, suggesting a difference in the capacity of the TR(-) rats to metabolize MPA in situ. There is very little information regarding the phase II metabolic capabilities of TR(-) rats; therefore, the aim of this study was to investigate the in vitro glucuronidation of MPA in Wistar and TR(-) rat liver microsomal protein. A second aim was to determine whether MPAGa, cyclosporine (CsA), and/or its metabolites AM1, AM1c, and AM9 inhibit the metabolism of MPA to MPAGe in rat liver microsomes. MPAGe formation rates by Wistar and TR(-) microsomes were 0.48 and 0.65 nmol/min/mg, respectively (p = 0.33). K(m) values for control and TR(-) microsomes were 0.47 and 0.50 mM, respectively (p = 0.81). The mean (S.E.M.) ratios of MPAGe formation by Wistar rat liver microsomes incubated with 50 microM MPA plus inhibitor versus 50 microM MPA alone were MPAGa 1.2 (0.1), CsA 0.7 (0.1) (p < 0.05), AM1 2.2 (0.3) (p < 0.05), AM1c 1.2 (0.2), and AM9 1.0 (0.2). Our results suggest that lower in situ glucuronidation of MPA in TR(-) rats may be because of inhibition of glucuronidation by endogenous and exogenous compounds that accumulate in the transporter-deficient rat. Whereas CsA inhibits glucuronidation of MPA, its metabolite AM1 enhances MPAGe formation by rat liver microsomes.

Seradyn quantitative microsphere system lamotrigine immunoassay on a Hitachi 911 analyzer compared with HPLC-UV.

Lamotrigine (LTG) is used currently as monotherapy or, more frequently, as add-on therapy with other antiepileptic drugs. It demonstrates efficacy against partial seizures, primary and secondary tonic clonic seizures, absence seizures, and drop attacks. LTG pharmacokinetics is complicated by coadministration with other antiepileptic drugs such as valproic acid, phenytoin, or carbamazepine. The wide interpatient variability in LTG dosage required to attain therapeutic plasma LTG concentrations for seizure control suggests that LTG is a good candidate for therapeutic drug monitoring (TDM). In this study, we compared the quantitative microsphere system (QMS) LTG immunoassay with the LTG high-performance liquid chromatography-ultra violet (HPLC-UV) assay routinely employed for TDM in our laboratory. Samples tested by these methods were patient samples presented for TDM and from a quality assurance program. Quality control material demonstrated within- and between-run (n = 6) coefficient of variation and biases of less than 10%. Patient samples demonstrated a Deming regression of QMS = 1.09 HPLC-UV - 0.17 and quality assurance program samples had a Deming regression of QMS = 1.03 HPLC-UV - 0.11. Patient samples demonstrated a mean bias of 6.1% and quality assurance program samples had a mean bias of 0.2%. The QMS LTG assay had a clinically small but significant overestimation of plasma LTG concentrations. It may be useful as a convenient alternative method that would provide TDM guidance if a chromatographic assay was not available.

Validation of a high-performance liquid chromatography method for the measurement of mycophenolic acid and its glucuronide metabolites in plasma.

OBJECTIVES: The need for therapeutic drug monitoring of the immunosuppressant mycophenolic acid is becoming more evident. This paper describes a simple high-performance liquid chromatography procedure for the simultaneous quantitation of mycophenolic acid (MPA) and its glucuronide metabolites in plasma using protein precipitation followed by HPLC analysis with isocratic elution and UV detection. DESIGN AND METHODS: The performance of this method is compared to the EMIT 2000 MPA immunoassay (Dade Behring Diagnostics Inc., Cupertino, California, USA). RESULTS AND CONCLUSION: Intra-assay precision and accuracy of calibrators were determined for MPA at 0.5 and 20 mg/L, MPAGe at 5 and 200 mg/L, and MPAGa at 2.5 and 100 mg/L and showed coefficients of variation of less than 5.0% and biases of less than 14.0%. Inter-assay precision and accuracy of quality control samples were determined for MPA at 2 and 15 mg/L, MPAGe at 20 and 150 mg/L and showed CVs of less than 5.0% and biases of less than 14%. The lower limit of quantitation of the method was determined for MPA at 0.25 mg/L, MPAGe at 0.5 mg/L, and MPAGa at 0.25 mg/L and showed CVs of less than 19% and biases of less than 20%. This method, compared to the EMIT 2000 MPA immunoassay, showed a linear regression analysis relationship of EMIT = 0.973 HPLC + 0.55 (r(2) = 0.851), and was determined to be suitable for therapeutic drug monitoring and pharmacokinetic studies of MPA.

Cloned enzyme donor immunoassay tacrolimus assay compared with high-performance liquid chromatography-tandem mass spectrometry and microparticle enzyme immunoassay in liver and renal transplant recipients.

The immunosuppressant drug tacrolimus has a narrow therapeutic index and is subject to a large variation in individual bioavailability and clearance. With its narrow therapeutic index, therapeutic drug monitoring is standard clinical practice in the management of transplant recipients. In this study, we report the evaluation of the cloned enzyme donor immunoassay (CEDIA) for the determination of whole-blood tacrolimus concentrations compared with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) and microparticle enzyme immunoassay (MEIA) using samples obtained from liver (n = 100) and renal (n = 88) transplant recipients. Linear regression analysis showed a relationship of CEDIA = 1.24 HPLC-MS/MS -0.18 (r = 0.81). The mean bias (+/-SEM) for all patients when compared with HPLC-MS/MS was 22.2% (+/-2.1%). The precision of the CEDIA method for all samples showed a root mean square error of 3.1 microg/L. Liver transplant recipient samples showed a mean (+/-SEM) bias compared with HPLC-MS/MS of 12.5% (+/-1.6%). The precision of the CEDIA method for these samples showed a root mean square error of 1.5 microg/L. The data suggest that in the renal transplant group, the CEDIA and MEIA methods have a bias of 33.3% and 20.1%, respectively, compared with HPLC-MS/MS. The CEDIA tacrolimus immunoassay has been shown to be a rapid method for the determination of whole-blood tacrolimus concentrations and may be considered when HPLC-MS/MS is not available. When used in the clinical setting with other parameters, it would be a useful adjunct in the management of liver transplant recipients, but a significant bias in renal transplant patients needs to be further investigated.

CEDIA mycophenolic acid assay compared with HPLC-UV in specimens from transplant recipients.

Routine monitoring of mycophenolic acid (MPA) has been accepted as an essential tool in the management of this therapy in transplant recipients. The availability of simple, sensitive assays that measure MPA in plasma permits individualization of dosing regimens according to pharmacokinetic principles. We report the results of an evaluation of the CEDIA Mycophenolic Acid Immunoassay (Microgenics Corporation, Fremont, California) for the measurement of plasma MPA concentrations in a range of transplant indications and compare its performance and specificity to an established HPLC/UV method. Precision and accuracy were determined both within and between runs using the quality control materials provided with the CEDIA MPA assay, which produced within run (n = 21) coefficients of variation (CV%) and biases of less than 5%. The between run analyses, performed over consecutive days following daily calibration of the assay, showed CVs and biases of less than 7%. Routine patient samples (n = 298) from 142 patients of varying transplant type were analyzed using the CEDIA MPA kit and HPLC/UV methods. Regression analysis of the patient samples gave an equation of CEDIA = 1.18 HPLC/UV + 0.45 (r = 0.83). According to the manufacturer's product information, there is 192% cross reactivity with the active mycophenolate acyl glucuronide. The data presented suggest that the CEDIA MPA immunoassay, run on the Hitachi 911 analyzer, over-estimates plasma MPA concentrations with a magnitude that is influenced by transplant type. Hence, users must interpret the immunoassay results with caution and not assume that the metabolite fraction is constant in recipients of the same organ type or in different organ transplant populations.

Role of Mrp2 in the hepatic disposition of mycophenolic acid and its glucuronide metabolites: effect of cyclosporine.

Mycophenolic acid (MPA) is part of the immunosuppressant therapy for transplant recipients. This study examines the role of the canalicular transporter, Mrp2, and the effect of cyclosporin A (CsA), on the biliary secretion of the ether (MPAGe) and acyl (MPAGa) glucuronides of MPA. Isolated livers from Wistar rats (n = 6), or Wistar TR- rats (n = 6) were perfused with MPA (5 mg/l). A third group of Wistar rats (n = 6) was perfused with MPA and CsA (250 microg/l). There was no difference in the half-life, hepatic extraction ratio (E(H)), clearance or partial clearance of MPA to MPAGe, but there was a difference in partial clearance to MPAGa between control and CsA groups (0.9 +/- 0.4 versus 0.5 +/- 0.1 ml/min). TR- rats had a lower E(H) (0.59 +/- 0.30 versus 0.95 +/- 0.30), a lower clearance (18 +/- 8 versus 29 +/- 7 ml/min), and a longer half-life (19.5 +/- 10.3 versus 10.1 +/- 2.4 min) than controls. Compared to controls, MPAGe and MPAGa biliary excretion was reduced by 99% and 71.8%, respectively, in TR- rats, and 17.5% and 53.8%, respectively, in the MPA-CsA group. The biliary excretion of MPAGe is mediated by Mrp2, whereas that of MPAGa seems to depend on both Mrp2 and another unidentified canalicular transporter. Although CsA can inhibit Mrp2, our data suggest that it may also inhibit the hepatic glucuronidation of MPA in Wistar rats.

Evaluation of the immunotech cyclosporine direct radioimmunoassay for the determination of whole-blood cyclosporine in renal transplant patients.

Therapeutic drug monitoring (TDM) of cyclosporine (CsA) has been an accepted as an essential tool in the management of solid organ transplant recipients. The authors evaluated a new CsA method, Immunotech cyclosporine direct radioimmunoassay (Beckman Coulter, Prague, Czech Republic), for the measurement of whole-blood CsA concentrations. The performance was compared with CEDIA Plus method as well as group mean data for HPLC and other immunoassays available from the International CsA Proficiency Testing Program (www.bioanalytics.co.uk). Regression analysis of patient samples gave a relationship of RIA = 1.0822 CEDIA(+) + 69.84 (r(2) = 0.933). External CsA-spiked proficiency-testing (PT) samples gave a regression equation of RIA = 0.9672 CEDIA(+) + 4.99 (r(2) = 0.996). The correlation with the CEDIA Plus method using patient specimens (hence, including CsA metabolites) suggested that the test RIA method possibly had slightly inferior specificity for parent CsA. The results suggest that the Immunotech cyclosporine direct RIA kit is suitable for the measurement of whole-blood CsA concentrations and maintained clinically acceptable analytic precision and accuracy, displaying CVs of less than 15% and biases of less than 10%. The PT program CsA-metabolite-free samples showed that calibration between methods was comparable with the possible exception of mFPIA/TDx.

CEDIA sirolimus assay compared with HPLC-MS/MS and HPLC-UV in transplant recipient specimens.

The role of the therapeutic drug monitoring laboratory in support of immunosuppressant drug therapy is well established, and the introduction of sirolimus (SRL) is a new direction in this field. The lack of an immunoassay for several years has restricted the availability of SRL assay services. The recent availability of a CEDIA SRL assay has the potential to improve this situation. The present communication has compared the CEDIA SRL method with 2 established chromatographic methods, HPLC-UV and HPLC-MS/MS. The CEDIA method, run on a Hitachi 917 analyzer, showed acceptable validation criteria with within-assay precision of 9.1% and 3.3%, and bias of 17.1% and 5.8%, at SRL concentrations of 5.0 microg/L and 20 microg/L, respectively. The corresponding between-run precision values were 11.5% and 3.3% and bias of 7.1% and 2.9% at 5.0 microg/L and 20 microg/L, respectively. The lower limit of quantification was found to be 3.0 microg/L. A series of 96 EDTA whole-blood samples predominantly from renal transplant recipients were assayed by the 3 methods for comparison. It was found that the CEDIA method showed a Deming regression line of CEDIA=1.20xHPLC-MS/MS-0.07 (r=0.934, SEE=.47), with a mean bias of 20.4%. Serial blood samples from 8 patients included in this evaluation showed that the CEDIA method reflected the clinical fluctuations in the chromatographic methods, albeit with the variable bias noted. The CEDIA method on the H917 analyzer is therefore a useful adjunct to SRL dosage individualization in renal transplant recipients.

Pharmacokinetics of the antianginal agent perhexiline: relationship between metabolic ratio and steady-state dose.

AIMS: 1) To develop an estimate of oral clearance (CL(Px)/F) for the antianginal agent perhexiline based on the ratio of cis-OH-perhexiline metabolite/parent perhexiline plasma concentrations at steady-state (C(OHPx,ss)/C(Px,ss)). 2) To determine whether the ratio measured in the first fortnight of treatment (C(i)(OHPx)/C(i)(Px)) may be used to guide patient dosing with perhexiline, a drug with a narrow therapeutic index, long half-life and saturable metabolism via CYP2D6. METHODS: Two retrospective studies were conducted reviewing patient records and data obtained from routine monitoring of plasma perhexiline and cis-OH-perhexiline concentrations. RESULTS: Study 1 (n=70). At steady-state, the frequency distributions of CL(Px)/F and C(OHPx,ss)/C(Px,ss) were consistent with CYP2D6 metabolism. Putative poor metabolizers (approximately 8%) were identified by CL(Px)/F< or =50 ml min(-1) or C(OHPx,ss)/C(Px,ss)< or =0.3. A group of patients with CL(Px)/F> or =950 ml min(-1) may have been ultra-rapid metabolizers. In this group, the high CL(Px)/F values suggest extensive first-pass metabolism and poor bioavailability. In patients with therapeutic plasma perhexiline concentrations (0.15-0.60 mg l(-1)), the variability in dose appeared directly proportional to CL(Px)/F (r2=0.741, P<0.0001). Study 2 (n=23). Using C(i)(OHPx)/C(i)(Px) patients were tentatively identified as poor, extensive and ultra-rapid metabolizers, with CL(Px)/F of 23-72, 134-868 and 947-1462 ml min(-1), respectively, requiring doses of 10-25, 100-250 and 300-500 mg day(-1), respectively. CONCLUSIONS: The cis-OH-perhexiline/perhexiline concentration ratio may be useful for optimizing individual patient treatment with the antianginal agent perhexiline.