Understanding variability with voriconazole using a population pharmacokinetic approach: implications for optimal dosing.

OBJECTIVES: Voriconazole exhibits highly variable, non-linear pharmacokinetics and is associated with a narrow therapeutic range. This study aimed to investigate the population pharmacokinetics of voriconazole in adults, including the effect of CYP2C19 genotype and drug-drug interactions. METHODS: Non-linear mixed effects modelling (NONMEM) was undertaken of six voriconazole studies in healthy volunteers and patients. Dosing simulations to examine influential covariate effects and voriconazole target attainment (2-5 mg/L) stratified by CYP2C19 phenotype were performed. RESULTS: We analysed 3352 voriconazole concentration measurements from 240 participants. A two-compartment pharmacokinetic model with first-order oral absorption with lag time and Michaelis-Menten elimination best described voriconazole pharmacokinetics. Participants with one or more CYP2C19 loss-of-function (LoF) alleles had a 41.2% lower Vmax for voriconazole. Co-administration of phenytoin or rifampicin, St John's wort or glucocorticoids significantly increased voriconazole elimination. Among patients receiving 200 mg of voriconazole twice daily, predicted trough concentrations on day 7 were <2 mg/L for oral and intravenous regimens for 72% and 63% of patients without CYP2C19 LoF alleles, respectively, with 49% and 35% below this threshold with 300 mg twice daily dosing. Conversely, these regimens resulted in 29%, 39%, 57% and 77% of patients with CYP2C19 LoF alleles with voriconazole trough concentrations ≥5 mg/L. CONCLUSIONS: Current dosing regimens for voriconazole result in subtherapeutic exposure in many patients without CYP2C19 LoF alleles, suggesting the need for higher doses, whereas these regimens result in supratherapeutic exposure in a high proportion of patients with reduced CYP2C19 activity. These findings support the essential role of therapeutic drug monitoring in ensuring efficacious and safe voriconazole exposure.

An audit of a therapeutic drug monitoring service for allopurinol therapy.

BACKGROUND: Oxypurinol, the active metabolite of allopurinol, is the major determinant of the hypouricemic effect of allopurinol. Monitoring oxypurinol concentrations is undertaken to determine adherence to therapy, to investigate reasons for continuing attacks of acute gout and/or insufficiently low plasma urate concentrations despite allopurinol treatment, and to assess the risk of allopurinol hypersensitivity, an adverse effect that has been putatively associated with elevated plasma oxypurinol concentrations. METHODS: An audit of request forms requesting plasma oxypurinol concentration measurements received by the pathology service (SydPath) at St Vincent's Hospital, Darlinghurst, Sydney was undertaken for the 7-year period January 2005-December 2011. Patient demographics, biochemical data, including plasma creatinine and uric acid concentrations, comorbidities, and concomitant medications were recorded. RESULTS: There were 412 requests for determination of an oxypurinol concentration. On 48% of occasions, the time of allopurinol dosing was recorded, while just 79 (19%) blood samples were collected 6-9 hours postdosing, the time window used to establish the therapeutic range for oxypurinol. For these optimally interpretable concentrations, 32 (8%) were within the putative therapeutic range (5-15 mg/L), while 5 (1%) were below and 41 (10%) above this range. The daily dose of allopurinol was documented on only one-third of the request forms. Individually, plasma urate and creatinine concentrations were requested concomitantly with plasma oxypurinol concentrations in 66% and 58% of the cases, respectively; while plasma oxypurinol, urate, and creatinine concentrations were requested concomitantly in 49% of the cases. CONCLUSIONS: Requesting clinicians and blood specimen collectors often fail to provide relevant information (dose, times of last dose, and blood sample collection) to allow the most useful interpretation of oxypurinol concentrations. Concomitant plasma urate and creatinine concentrations should be requested to allow more complete interpretation of the data.

Antifungal use and therapeutic monitoring of plasma concentrations of itraconazole in heart and lung transplantation patients.

BACKGROUND: The prophylactic use of itraconazole has dramatically reduced the incidence of fungal infections in patients after solid-organ transplantation. To further reduce this incidence, it has been suggested that plasma concentrations of itraconazole be monitored and maintained above a putative minimum target concentration of 500 ng/mL. METHODS: A retrospective audit was undertaken of patients who had had a heart or lung transplant over a 14-month period (between January 1, 2010 and March 31, 2011). The itraconazole prophylaxis regimen (dose, time of last dose, time of blood collection) and plasma concentrations were recorded together with the use of concomitant antacid medication. Details of breakthrough fungal infections were documented. RESULTS: Eighty-four heart or lung organ transplantations were undertaken in the study period; 57 were treated prophylactically with itraconazole. Plasma concentrations of itraconazole were monitored in 56% (n = 32) of these cases. Considerable interpatient (range, 50-2000 ng/mL) and intrapatient variability in plasma concentrations was observed. The putative target was not achieved consistently in the majority of cases. All patients were taking a proton pump inhibitor. Six of the cohort developed an invasive fungal infection. None of the 3 patients for whom plasma concentrations were monitored was above the target concentration. CONCLUSIONS: Further clinical studies, involving monitoring of the active metabolite and attention to the importance of the stereoisomers of itraconazole, may give better insight into the appropriateness of the currently suggested minimum target concentration, whose validity remains uncertain. Formulations with improved absorption characteristics could reduce the variability of absorption with the goal of further reducing the incidence of infrequent, but life-threatening, invasive fungal infections.

Multicenter study of posaconazole therapeutic drug monitoring: exposure-response relationship and factors affecting concentration.

Posaconazole has an important role in the prophylaxis and salvage treatment of invasive fungal infections (IFIs), although poor and variable bioavailability remains an important clinical concern. Therapeutic drug monitoring of posaconazole concentrations has remained contentious, with the use of relatively small patient cohorts in previous studies hindering the assessment of exposure-response relationships. This multicenter retrospective study aimed to investigate relationships between posaconazole concentration and clinical outcomes and adverse events and to assess clinical factors and drug interactions that may affect posaconazole concentrations. Medical records were reviewed for patients who received posaconazole and had ≥1 concentration measured at six hospitals in Australia. Data from 86 patients with 541 posaconazole concentrations were included in the study. Among 72 patients taking posaconazole for prophylaxis against IFIs, 12 patients (17%) developed a breakthrough fungal infection; median posaconazole concentrations were significantly lower than in those who did not develop fungal infection (median [range], 289 [50 to 471] ng/ml versus 485 [0 to 2,035] ng/ml; P < 0.01). The median posaconazole concentration was a significant predictor of breakthrough fungal infection via binary logistic regression (P < 0.05). A multiple linear regression analysis identified a number of significant drug interactions associated with reduced posaconazole exposure, including coadministration with proton pump inhibitors, metoclopramide, phenytoin or rifampin, and the H(2) antagonist ranitidine (P < 0.01). Clinical factors such as mucositis, diarrhea, and the early posttransplant period in hematopoietic stem cell transplant recipients were also associated with reduced posaconazole exposure (P < 0.01). Low posaconazole concentrations are common and are associated with breakthrough fungal infection, supporting the utility of monitoring posaconazole concentrations to ensure optimal systemic exposure.

Multicenter study of voriconazole pharmacokinetics and therapeutic drug monitoring.

Voriconazole is a first-line agent in the treatment of many invasive fungal infections and is known to display highly variable pharmacokinetics. Previous studies of voriconazole therapeutic drug monitoring (TDM) have suggested concentration monitoring to be clinically useful but have been limited by small patient samples at a single institution. This multicenter retrospective study aimed to investigate relationships between voriconazole concentration and clinical outcomes and adverse events and to assess clinical factors and drug interactions that may affect voriconazole concentration. Medical records were reviewed for patients who received voriconazole and had at least 1 concentration measured at seven hospitals in Australia. The study included 201 patients with 783 voriconazole trough concentrations. Voriconazole concentrations of <1.7 mg/liter were associated with a significantly greater incidence of treatment failure (19/74 patients [26%]) than concentrations of ≥1.7 mg/liter (6/89 patients [7%]) (P < 0.01). Neurotoxic adverse events (visual and auditory hallucinations) occurred more frequently at voriconazole concentrations of >5 mg/liter (10/31 patients [32%]) than at concentrations of ≤5 mg/liter (2/170 patients [1.2%]) (P < 0.01). Multiple regression analysis of voriconazole concentration identified associations between increasing patient weight, oral administration of voriconazole, and coadministration of phenytoin or rifampin and significantly reduced concentrations, and associations between increasing patient age and coadministration of proton pump inhibitors and increased concentrations. Coadministration of glucocorticoids was found to significantly reduce voriconazole concentrations, inferring a previously unreported drug interaction between glucocorticoids and voriconazole.

A randomized study of pharmacokinetics, efficacy, and safety of 2 raltegravir plus atazanavir strategies in ART-treated adults.

BACKGROUND: New antiretroviral drug classes provide opportunities to explore novel regimens. METHODS: HIV+ adults (<50 copies/mL) receiving atazanavir (ATV) were randomized to raltegravir (RAL) 400 mg + ATV 300 mg twice daily (q12h) for 4 weeks followed by RAL 800 mg + ATV/ritonavir 300/100 mg once daily (q24h) for 4 weeks or vice versa. Validated assays quantitated RAL and ATV plasma concentrations. Primary endpoint was geometric mean ratio (GMR) of ATV minimum concentration (Cmin) for q24h/q12h. Equivalence was 90% confidence interval (CI) of GMR lying between 0.80 and 1.25. Participants could consent to a total 48-week follow-up. RESULTS: Twenty-five men, mean age 45 (range, 35-57) years, were evaluated. ATV and RAL demonstrated considerable pharmacokinetic variability. There was no period or sequence effect for pharmacokinetic parameters (P > 0.1 all measures). Ninety percent CIs of ATV GMR C(min) [1.30 (90% CI: 1.08 to 1.58)] and RAL GMR C(min) [0.48 (90% CI: 0.31 to 0.75)] demonstrated nonequivalence. Seventy-six percent consented to follow-up. There were no serious adverse events and no discontinuations due to adverse events over 48 weeks; HIV RNA remained undetectable. CONCLUSIONS: In virologically suppressed adults, regimens comprising ATV plus RAL were efficacious and safe. ATV q12h troughs were lower than ritonavir-boosted atazanavir q24h; RAL q24h troughs were lower than q12h.

Posaconazole exposure-response relationship: evaluating the utility of therapeutic drug monitoring.

Posaconazole has become an important part of the antifungal armamentarium in the prophylaxis and salvage treatment of invasive fungal infections (IFIs). Structurally related to itraconazole, posaconazole displays low oral bioavailability due to poor solubility, with significant drug interactions and gastrointestinal disease also contributing to the generally low posaconazole plasma concentrations observed in patients. While therapeutic drug monitoring (TDM) of plasma concentrations is widely accepted for other triazole antifungal agents such as voriconazole, the utility of TDM for posaconazole is controversial due to debate over the relationship between posaconazole exposure in plasma and clinical response to therapy. This review examines the available evidence for a relationship between plasma concentration and clinical efficacy for posaconazole, as well as evaluating the utility of TDM and providing provisional target concentrations for posaconazole therapy. Increasing evidence supports an exposure-response relationship for plasma posaconazole concentrations for prophylaxis and treatment of IFIs; a clear relationship has not been identified between posaconazole concentration and toxicity. Intracellular and intrapulmonary concentrations have been studied for posaconazole but have not been correlated to clinical outcomes. In view of the high mortality and cost associated with the treatment of IFIs, increasing evidence of an exposure-response relationship for posaconazole efficacy in the prevention and treatment of IFIs, and the common finding of low posaconazole concentrations in patients, TDM for posaconazole is likely to be of significant clinical utility. In patients with subtherapeutic posaconazole concentrations, increased dose frequency, administration with high-fat meals, and withdrawal of interacting medications from therapy are useful strategies to improve systemic absorption.

Clinical pharmacokinetics of metformin.

Metformin is widely used for the treatment of type 2 diabetes mellitus. It is a biguanide developed from galegine, a guanidine derivative found in Galega officinalis (French lilac). Chemically, it is a hydrophilic base which exists at physiological pH as the cationic species (>99.9%). Consequently, its passive diffusion through cell membranes should be very limited. The mean ± SD fractional oral bioavailability (F) of metformin is 55 ± 16%. It is absorbed predominately from the small intestine. Metformin is excreted unchanged in urine. The elimination half-life (t(½)) of metformin during multiple dosages in patients with good renal function is approximately 5 hours. From published data on the pharmacokinetics of metformin, the population mean of its clearances were calculated. The population mean renal clearance (CL(R)) and apparent total clearance after oral administration (CL/F) of metformin were estimated to be 510 ± 130 mL/min and 1140 ± 330 mL/min, respectively, in healthy subjects and diabetic patients with good renal function. Over a range of renal function, the population mean values of CL(R) and CL/F of metformin are 4.3 ± 1.5 and 10.7 ± 3.5 times as great, respectively, as the clearance of creatinine (CL(CR)). As the CL(R) and CL/F decrease approximately in proportion to CL(CR), the dosage of metformin should be reduced in patients with renal impairment in proportion to the reduced CL(CR). The oral absorption, hepatic uptake and renal excretion of metformin are mediated very largely by organic cation transporters (OCTs). An intron variant of OCT1 (single nucleotide polymorphism [SNP] rs622342) has been associated with a decreased effect on blood glucose in heterozygotes and a lack of effect of metformin on plasma glucose in homozygotes. An intron variant of multidrug and toxin extrusion transporter [MATE1] (G>A, SNP rs2289669) has also been associated with a small increase in antihyperglycaemic effect of metformin. Overall, the effect of structural variants of OCTs and other cation transporters on the pharmacokinetics of metformin appears small and the subsequent effects on clinical response are also limited. However, intersubject differences in the levels of expression of OCT1 and OCT3 in the liver are very large and may contribute more to the variations in the hepatic uptake and clinical effect of metformin. Lactic acidosis is the feared adverse effect of the biguanide drugs but its incidence is very low in patients treated with metformin. We suggest that the mean plasma concentrations of metformin over a dosage interval be maintained below 2.5 mg/L in order to minimize the development of this adverse effect.

Current status of therapeutic drug monitoring in Australia and New Zealand: a need for improved assay evaluation, best practice guidelines, and professional development.

The measurement of drug concentrations, for clinical purposes, occurs in many diagnostic laboratories throughout Australia and New Zealand. However, the provision of a comprehensive therapeutic drug monitoring (TDM) service requires the additional elements of pre- and postanalytical advice to ensure that concentrations reported are meaningful, interpretable, and clinically applicable to the individual patient. The aim of this project was to assess the status of TDM services in Australia and New Zealand. A range of professions involved in key aspects of TDM was surveyed by questionnaire in late 2007. Information gathered included: the list of drugs assayed; analytical methods used; interpretation services offered; interpretative methods used; and further monitoring advice provided. Fifty-seven responses were received, of which 42% were from hospitals (public and/or private); 11% a hospital (public and/or private) and pathology provider; and 47% a pathology provider only (public and/or private). Results showed that TDM is applied to a large number of different drugs. Poorly performing assay methods were used in some cases, even when published guidelines recommended alternative practices. Although there was a wide array of assays available, the evidence suggested a need for better selection of assay methods. In addition, only limited advice and/or interpretation of results was offered. Of concern, less than 50% of those providing advice on aminoglycoside dosing in adults used pharmacokinetic tools with six of 37 (16.2%) respondents using Bayesian pharmacokinetic tools, the method recommended in the Australian Therapeutic Guidelines: Antibiotic. In conclusion, the survey highlighted deficiencies in the provision of TDM services, in particular assay method selection and both quality and quantity of postanalytical advice. A range of recommendations, some of which may have international implications, are discussed. There is a need to include measures of impact on clinical decision-making when assessing assay methodologies. Best practice guidelines and professional standards of practice in TDM are needed, supported by an active program of professional development to ensure the benefits of TDM are realized. This will require significant partnerships between the various professions involved.

Correlation between HIV-1 RNA load in blood and seminal plasma depending on antiretroviral treatment status, regimen and penetration of semen by antiretroviral drugs.

To assess the correlation between HIV-1 RNA load in blood and semen by antiretroviral therapy status and the relative penetration of antiretroviral drugs in seminal plasma. We performed a cross-sectional cohort study of 119 HIV-1 subjects divided into three groups according to treatment status. Blood and semen were collected concurrently. Seminal viral load determined by NucliSens HIV-1 QT PCR (BioMerieux). Viral suppression over time was assessed in a second semen sample collected from 10 treated subjects. Antiretroviral plasma concentrations were measured by high performance liquid chromatography and recovery experiments were performed on semen samples to validate quantitation in this matrix. All subjects taking non nucleoside reverse transcriptase inhibitors (n = 36, mean treatment 33 months +/- 14) or protease inhibitors (n = 45, mean treatment 31 months +/- 25) had blood viral load < 50 copies/mL and seminal viral load < 250 copies/mL. In untreated subjects (n = 38), blood and semen viral loads were positively correlated (Spearman's rho = 0.489, p = 0.002). Blood and semen nevirapine concentrations were positively correlated (r(2) = 0.795, p = 0.005) and therapeutic concentrations achieved in both compartments. Lopinavir and atazanavir also penetrated semen but efavirenz did not. We find that there is compartmentalisation of HIV-1 within the male genital tract and propose that new infections may originate from untreated men and that suppressive antiretroviral regimens may reduce the risk of sexual transmission.

Quantification of antiretroviral drugs for HIV-1 in the male genital tract: current data, limitations and implications for laboratory analysis.

Antiretroviral therapy has reduced the morbidity and mortality associated with HIV-1/AIDS in developed countries. Viral replication in blood plasma is suppressed by antiretroviral drugs, whereas virus in the male genital tract is genetically and phenotypically unique and may not be suppressed. This viral compartmentalization affects antiretroviral drug penetration of the male genital tract and capacity for antiretroviral therapy to reduce sexual transmission. The problem of having two distinct viral populations within any given individual is compounded by the fact that antiretroviral drugs penetrate semen to varying degrees. Incomplete suppression of genital tract virus may yield drug-resistant virus and increase the risk of sexual transmission. This review critically appraises current studies of antiretroviral drug quantification in semen and suggests recommendations to address observed limitations.

Decision support tool to individualize cyclosporine dose in stable, long-term heart transplant recipients receiving metabolic inhibitors: overcoming limitations of cyclosporine C2 monitoring.

BACKGROUND: Monitoring of the 2-hour post-dose sample (C(2)) for cyclosporine (CsA) has gained favor; however, choosing a single-point surrogate marker of therapeutic effect for a drug with extensive pharmacokinetic variability is problematic and has limitations. METHODS: A Bayesian decision support tool was developed using published pharmacokinetic information implemented using ABBOTTBASE pharmacokinetic software. The model was evaluated in 47 stable heart transplant recipients who received concomitant administration of drugs known to inhibit CsA metabolism: diltiazem; ketoconazole; and a combination of diltiazem and ketoconazole. RESULTS: A 3-point feedback strategy with samples collected at 0, 1 and 2 hours after an oral CsA dose was used to predict area under the concentration-time curve in the first 12 hours post-dose (AUC(0-12)). In Group A, patients who received CsA alone showed a good correlation between observed and model-predicted CsA AUC(0-12) (r(2) = 0.871, p < 0.001, precision of 12%, accuracy of 13%). Furthermore, the Bayesian model provided acceptable predictions in patients who received CsA with metabolic inhibitors: Group B (diltiazem), r(2) = 0.791, p < 0.001, precision of 19%, accuracy of 22%; Group C (ketoconazole), r(2) = 0.761, p < 0.001, precision of 4%, accuracy of 12%; and Group D (diltiazem plus ketoconazole), r(2) = 0.818, p < 0.001, precision of 14%, accuracy of 17%. CONCLUSIONS: A Bayesian decision support tool is described that can predict CsA AUC(0-12) in a cohort of patients with variable CsA absorption who received metabolic inhibitors. Bayesian modeling offers a number of advantages over single point metrics that are used to adjust CsA dose and may provide another refinement to optimize CsA therapy.

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.

Therapeutic drug monitoring of atazanavir: surveillance of pharmacotherapy in the clinic.

BACKGROUND: Therapeutic failure with antiretroviral therapy (ART) is a substantial issue where viral rebound, viral resistance and drug-related toxicity remain serious concerns. Drug exposure-response relationships have been described for the protease inhibitors, pharmacokinetic variability is substantial for this class of drugs and drug interactions can also alter ART exposure. Given this background we established a therapeutic drug monitoring (TDM) service to monitor atazanavir (ATV) plasma concentrations early after the therapy was made available to treatment-experienced people infected with HIV who were managed in a clinical setting. METHODS: This was a prospective observational study which evaluated plasma samples from 110 highly treatment-experienced people with HIV using TDM and applied pharmacokinetic analysis over a five month period. RESULTS: ATV trough concentrations exhibited substantial intersubject variability (<25-2108 microg l(-1)). A substantial number of subjects (50%,13/26) who received ATV400 mg daily had low exposure to ATV. Serum bilirubin concentrations correlated significantly with higher ATV trough concentrations (rho = 0.803; P < 0.001) and 55% (29/53) of subjects who received ATV300/100 mg RTV daily had plasma concentrations above a proposed target concentration associated with elevated bilirubin concentrations. This study confirmed low ATV exposure in eight subjects with HIV receiving ATV 400 mg daily. Reasons for low ATV exposure in this cohort include administration of interacting drugs, including a possible interaction with ritonavir, fluticasone and ATV, impaired ATV absorption secondary to suspected achlorhydria and potential interactions with colchicine and nandrolone. Viral load remained undetectable in most of these subjects with low ATV exposure. CONCLUSIONS: TDM and targeted pharmacokinetic studies should be viewed as fundamental tools in the development and clinical application of ART, to improve pharmacotherapy for people with HIV.

Cyclosporin C(2) and C(0) concentration monitoring in stable, long-term heart transplant recipients receiving metabolic inhibitors.

BACKGROUND: Cyclosporin (CsA) dose selection is complicated by significant pharmacokinetic variability between patients. Although therapeutic drug monitoring (TDM) has proven to be a useful tool for dose individualization, the search for an effective and practical measure of clinical effect has uncovered a number of options. Monitoring the CsA concentration in a blood sample taken 2 hours after the dose (C(2)) has been utilized but has not been rigorously evaluated in all clinical situations. The aim of this study was to evaluate C(2) and trough (C(0)) CsA concentrations as surrogate markers of area under the concentration-time curve (AUC) in stable, long-term heart transplant recipients receiving CsA alone or with diltiazem and/or ketoconazole. METHODS: CsA blood concentration-time data were collected at steady state for 47 stable heart transplant recipients after the morning dose of Neoral. CsA concentration in whole blood was quantitated using the EMIT immunoassay. Patients were stratified into 4 groups, depending on the long-term concomitant administration of drugs known to inhibit CsA metabolism, as part of their routine therapy: Group A (n = 11), CsA alone; Group B (n = 10), CsA with slow-release diltiazem; Group C (n = 13), CsA with ketoconazole; and Group D (n = 12), CsA with a combination of diltiazem and ketoconazole. RESULTS: In Group A, C(2) correlated poorly with AUC(0-5) (r(2) = 0.197; p = 0.17), whereas C(0) (trough blood sample) showed a stronger correlation (r(2) = 0.710; p = 0.001). Correlations of C(0) and C(2) with AUC(0-5) were the same, but weaker in patients receiving CsA and diltiazem (r(2) = 0.650; p = 0.005); however, C(2) correlated strongly with AUC(0-5) in patients receiving ketoconazole (r(2) = 0.870; p < 0.0001) or ketoconazole with diltiazem (r(2) = 0.898; p < 0.0001). C(0) was a poor predictor of AUC(0-5) in the latter 2 groups. CONCLUSIONS: C(2) showed a strong correlation with AUC(0-5) in cardiothoracic transplant recipients receiving CsA with ketoconazole, but not with CsA alone or diltiazem. TDM using C(2) as an estimate of AUC requires further evaluation before being applied in long-term, stable cardiac transplant patients, as it may lead to inappropriate dose adjustment of CsA in patients receiving concomitant metabolic inhibitors.

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.