CYP3A5 genotype had no impact on intrapatient variability of tacrolimus clearance in renal transplant recipients.

BACKGROUND: The risk of long-term chronic allograft nephropathy and graft loss after kidney transplantation is increased in patients with a high intrapatient variability in the clearance of tacrolimus. CYP3A5 genotype has a significant influence on the oral bioavailability of tacrolimus and is a potential influence on variability of exposure. METHODS: The study population consisted of 118 renal transplant recipients with stable renal function 12 months after transplant. The intrapatient variability of tacrolimus concentration was calculated. The patients were divided into low- and high-intraindividual variability groups using the median variability of tacrolimus clearance as the cutoff value. RESULTS: No differences in baseline characteristics were observed between the expressers (n = 37) and nonexpressers (n = 81) except for ethnicity, which is in line with previous observations. Tacrolimus dose requirement was significantly higher in patients expressing CYP3A5, confirming earlier observations (P < 0.0001). However, intraindividual variability of tacrolimus clearance was not related to CYP3A5 genotype (P = 0.3331). CONCLUSIONS: The intrapatient variability of tacrolimus clearance was not associated with CYP3A5 genotype in stable renal transplant recipients.

Osteoarthritis in temporomandibular joint of Col2a1 mutant mice.

OBJECTIVE: Col2a1 gene mutations cause premature degeneration of knee articular cartilage in disproportionate micromelia (Dmm) and spondyloepiphesial dysplasia congenita (sedc) mice. The present study analyses the temporomandibular joint (TMJ) in Col2a1 mutant mice in order to provide an animal model of TMJ osteoarthritis (OA) that may offer better understanding of the progression of this disease in humans. DESIGN: Dmm/+ mice and controls were compared at two, six, nine and 12 months. Craniums were fixed, processed to paraffin sections, stained with Safranin-O/Fast Green, and analysed with light microscopy. OA was quantified using a Mankin scoring procedure. Unfolded protein response (UPR) assay was performed and immunohistochemistry (IHC) was used to assay for known OA biomarkers. RESULTS: Dmm/+ TMJs showed fissuring of condylar cartilage as early as 6 months of age. Chondrocytes were clustered, leaving acellular regions in the matrix. Significant staining of HtrA1, Ddr2 and Mmp-13 was observed in Dmm/+ mice (p<0.01). We detected upregulation of the UPR in knee but not TMJ. CONCLUSIONS: Dmm/+ mice are subject to early-onset OA in the TMJ. We observed upregulation of biomarkers and condylar cartilage degradation concomitant with OA. An upregulated UPR may exacerbate the onset of OA. The Dmm/+ mouse TMJ is a viable model for the study of the progression of OA in humans.

Acute kidney injury reduces the hepatic metabolism of midazolam in critically ill patients.

INTRODUCTION: Acute kidney injury (AKI) is a common and serious complication increasing morbidity and mortality from all causes of hospital admission. We have previously shown that AKI decreases midazolam metabolism, a substrate of the cytochrome P450 3A (CYP3A) enzymes and our primary aim was to determine if this effect is dependent on the severity of AKI. We also present preliminary data on the functional impact of different genotypes of CYP3A. METHODS: Critically ill patients at risk of AKI and admitted to a general intensive care unit were categorised after initial resuscitation according to the RIFLE criteria for AKI. Midazolam (1mg) was administered and the serum concentration of midazolam measured at 4 h. Samples were taken for CYP3A genotyping. RESULTS: Seventy-three patients were assigned to categories R, I and F of the RIFLE criteria or C (controls). Midazolam concentrations (ng mL(-1)) increased significantly (p = 0.002) as the severity of AKI worsened [control 3.1 (1.4-5.9), risk 4.7 (1.3-10.3), injury 3.9 (2.0-11.1) and failure 6.8 (2.2-113.6)] and were predicted by the duration of AKI (p = 0.000) and γ-glutamyl transferase (p = 0.005) concentrations. Increasing BMI negatively predicted the midazolam concentration (p = 0.001). Preliminary data suggest this effect is diminished if the patient expresses functional CYP3A5. CONCLUSION: Increasing severity and duration of AKI are associated with decreased midazolam elimination. We propose that this is caused by impaired CYP3A activity secondary to AKI. The exact mechanism remains to be elucidated. This may have important implications for our drug treatment of critically ill patients.

A systematic evaluation of the core communication skills expected of a perfusionist.

BACKGROUND: The objective of this systematic evaluation was to identify the sentinel standards necessary to obtain a core level of communication required of a clinical perfusionist during cardiopulmonary bypass (CPB). Once these sentinel standards were identified and a core level of communication was established (via four simulated case scenarios), a team of cardiac healthcare professionals was assembled to interpret both the accuracy of response and the speed of response encountered in each case scenario. METHODS: Four simulated case scenarios were utilized in order to replicate the typical patterns of verbal exchange that occur during surgeries using extracorporeal technology. The simulated case scenarios included CPB interactions associated with preparation, initiation, maintenance, termination and post CPB. For all CPB interactions, two variables were measured: accuracy of the perfusionist's response and speed of the perfusionist's response. The cases took place in a controlled setting within an empty operating room at The Children's Hospital of Philadelphia. Four clinical perfusionists each represented the role of the "perfusionist" in all simulated case scenarios. RESULTS: When analyzing the accuracy and speed of the responses, each clinical perfusionist recorded an average score of 96.3% or higher with all case scenarios. Since the clinical perfusionists who participated in the scenarios were primarily pediatric perfusionists, the scores were best during the pediatric case scenario, 99.3% (Case Scenario #4). The lowest scores were captured during Case Scenario #3 (96.3%) which involved a more intense adult patient scenario. CONCLUSION: The systematic evaluation of both response accuracy and response time (presented in various adult and pediatric patient case scenarios) can be beneficial within the realm of perfusion education. Students will be introduced to core communication concepts within the clinical realm. This study supports the idea that simulation and evaluation may ease the transition for students from the didactic to clinical realm in terms of communication. Further studies need to be developed in order to define "standard" CPB communication guidelines for perfusion students.

Osteoarthritis-like changes in the heterozygous sedc mouse associated with the HtrA1-Ddr2-Mmp-13 degradative pathway: a new model of osteoarthritis.

OBJECTIVE: To test the hypothesis that the spondyloepiphyseal dysplasia congenita (sedc) heterozygous (sedc/+) mouse, a COL2A1 mutant, is a model for the study of osteoarthritis (OA) in the absence of dwarfism and to investigate the presence of HtrA1, Ddr2, and Mmp-13 and their possible involvement in a universal mechanism leading to OA. DESIGN: Whole mount skeletons of adult animals were analyzed to determine whether sedc/+ mice exhibit dwarfism. To characterize progression of osteoarthritic degeneration over time, knee and temporomandibular joints from sedc/+ and wild-type mice were analyzed histologically, and severity of articular cartilage degradation was graded using the Osteoarthritis Research Society International (OARSI) scoring system. Immunohistochemistry was used to detect changes in expression of HtrA1, Ddr2, and Mmp-13 in articular cartilage of knees. RESULTS: As previously reported, the sedc/+ skeleton morphology was indistinguishable from wild type, and skeletal measurements revealed no significant differences. The sedc/+ mouse did, however, show significantly higher OARSI scores in knee (9, 12 and 18 months) and temporomandibular joints at all ages examined. Histological staining showed regions of proteoglycan degradation as early as 2 months in both temporomandibular and knee joints of the mutant. Cartilage fissuring and erosion were observed to begin between 2 and 6 months in temporomandibular joints and 9 months in knee joints from sedc/+ mice. Immunohistochemistry of mutant knee articular cartilage showed increased expression of HtrA1, Ddr2, and Mmp-13 compared to wild type, which upregulation preceded fibrillation and fissuring of the articular surfaces. CONCLUSIONS: With regard to skeletal morphology, the sedc/+ mouse appears phenotypically normal but develops premature OA as hypothesized. We conclude that the sedc/+ mouse is a useful model for the study of OA in individuals with overtly normal skeletal structure and a predisposition for articular cartilage degeneration.

Tribal ethnicity and CYP2B6 genetics in Ugandan and Zimbabwean populations in the UK: implications for efavirenz dosing in HIV infection.

OBJECTIVES: To determine differences in CYP2B6 loss of function (LoF) single nucleotide polymorphisms (SNPs) and haplotypes between Zimbabweans and Ugandans, and within Ugandan populations (Bantu and Nilotic). METHODS: Genetic epidemiological study enrolling adult black African Ugandan and Zimbabwean patients attending a UK HIV-1 clinic, irrespective of antiretroviral therapy status. Genomic DNA was extracted from whole blood and the presence of CYP2B6 alleles was determined by direct sequencing of all nine exons of the CYP2B6 gene. Blood was also collected, where appropriate, for determination of efavirenz concentrations. Frequency of SNPs in all patients and LoF haplotype frequencies were calculated. The relationship between the number of LoF haplotype alleles possessed and efavirenz trough concentration (ETC) was determined. RESULTS: Thirty-six Zimbabweans and 74 Ugandans (58 Bantu and 16 Nilotic) were recruited. The definite haplotypes determined were *6, *18, *20 and *27 as LoF and *4 as gain of function. Among those with definite genotypes, the frequency of LoF alleles was 65% [95% confidence interval (95% CI): 51-80] of Zimbabweans versus 22% (95% CI: 12-31) of Ugandan Bantus (P = 10(-6)) and versus 39% (95% CI: 14-64) of Ugandan Nilotics (P = 0.09). Among the 19 patients with definite genotype and with available ETCs, log ETCs were associated with a greater number of LoF haplotype alleles [848 ng/mL (n = 12), 1069 ng/mL (n = 4) and 1813 ng/mL (n = 3) for 0, 1 or 2 LoF haplotypes, respectively (P = 0.016)]. CONCLUSIONS: Among Zimbabweans, LoF haplotypes constitute the majority of CYP2B6 alleles and are significantly higher in prevalence compared with Ugandans. Frequencies of LoF haplotypes and SNPs in Ugandan Nilotics appear to lie between those of Zimbabweans and Ugandan Bantus. These findings may have relevance to pharmacokinetics and dosing of efavirenz in African populations.

Buying 'legal' recreational drugs does not mean that you are not breaking the law.

BACKGROUND: Recreational drug use in the UK is common; sources of recreational drugs are changing, with increasing purchase of legal highs from the Internet. Previous studies have shown that there is not consistency of active ingredient(s) in legal highs purchased from the Internet. AIM: The aim of this study was to determine the impact of the 16 April 2010 change to the Misuse of Drugs Act (1971) on the content of 'legal highs' purchased over the Internet and supplied within the UK. METHODS: Legal highs were purchased from a number of different Internet suppliers and the active ingredients determined by analysis undertaken within a Home Office approved and licensed laboratory set in a UK academic institution. The active ingredient(s) detected on screening were then compared to the UK legislation in force at the time of purchase to determine whether each individual 'legal' high was in fact legal or not. RESULTS: All 18 products purchased prior to the change in the UK legislation contained active ingredients that were legal under the Misuse of Drugs Act (1971) in force at that time. Six products were purchased and analysed after the changes to the UK Misuse of Drugs Act (1971) on the 16 April 2010. Five of the products contained information, either on the Internet site or the packaging, stating that the product contained legal substances; the final product did not specify the active ingredient and so purchasers would be unable to determine if this was truly a legal product. Five of the six products contained an active ingredient that is a Class B drug under the Misuse of Drugs Act (1971); the other product contained an unlicensed medicine not controlled under the Misuse of Drugs Act (1971). CONCLUSION: We have shown in this study that some drugs sold as 'legal' highs contain drugs that are controlled under the Misuse of Drugs Act (1971). Under current UK legislation, individuals purchasing legal highs that contained controlled drugs would be subject to the same penalties as if they had knowingly purchased a controlled drug. Dissemination of information on the harm associated with the use of legal highs should also inform individuals that they may be purchasing controlled substances and the potential legal consequences of this.

Purchasing 'legal highs' on the Internet--is there consistency in what you get?

BACKGROUND: The supply of recreational drugs has changed and users increasingly buy 'legal highs' over the Internet. Use of these is common and there is a potential for significant toxicity associated with their use. AIM: To determine the content of legal highs available for purchase in the UK and whether the content of these remains consistent. METHODS: Twenty-six legal highs were purchased monthly from five different Internet sites over 6 months. These were analysed to determine the drugs in the products and whether there were any changes in their content over this time period. RESULTS: All products were supplied initially, but there was a decline in supply of products month by month. The following drug classes were detected: piperazines, cathinones, caffeine/ephedrine or products in which no psychoactive drugs were detected. Of the products supplied on more than one occasion, 15 (75%) contained the same compounds on each occasion. In three products there was a change in the piperazine detected, with 1-benzylpiperazine being substituted for 1-methyl-4-benzylpiperazine or vice versa. In two other products there was a cathinone [4-fluorophenylpiperazine (pFPP) or 3-fluromethcathinone (3FMC)] detected in products purchased in Month 1 that was not present in the products purchased in subsequent months. CONCLUSION: Whilst there was no variation in the composition of most legal highs supplied over 6 month, there was significant variation in the piperazine or cathinone content of one quarter of the products. This variation could be of clinical significance as the cathinone and piperazine products can be associated with significant toxicity.

The acute effects of synthetic intravenous Delta9-tetrahydrocannabinol on psychosis, mood and cognitive functioning.

BACKGROUND: Recent work suggests that heavy use of cannabis is associated with an increased risk of schizophrenia-like psychosis. However, there is a dearth of experimental studies of the effects of the constituents of cannabis, such as Delta9-tetrahydrocannabinol (THC). In a study of intravenous (i.v.) synthetic THC in healthy humans, we aimed to study the relationship of the psychotic symptoms induced by THC to the consequent anxiety and neuropsychological impairment. METHOD: Twenty-two healthy adult males aged 28+/-6 years (mean+/-s.d.) participated in experimental sessions in which i.v. THC (2.5 mg) was administered under double-blind, placebo-controlled conditions. Self-rated and investigator-rated measurements of mood and psychosis [the University of Wales Institute of Science and Technology Mood Adjective Checklist (UMACL), the Positive and Negative Syndrome Scale (PANSS) and the Community Assessment of Psychic Experiences (CAPE)] were made at baseline and at 30, 80 and 120 min post-injection. Participants also completed a series of neuropsychological tests [the Rey Auditory Verbal Learning Task (RAVLT), Digit Span, Verbal Fluency and the Baddeley Reasoning Task] within 45 min of injection. RESULTS: THC-induced positive psychotic symptoms, and participant- and investigator-rated measurements of these were highly correlated. Participants showed an increase in anxiety ratings but there was no relationship between either self- or investigator-rated positive psychotic symptoms and anxiety. THC also impaired neuropsychological performance but once again there was no relationship between THC-induced positive psychotic symptoms and deficits in working memory/executive function. CONCLUSIONS: These findings confirm that THC can induce a transient, acute psychotic reaction in psychiatrically well individuals. The extent of the psychotic reaction was not related to the degree of anxiety or cognitive impairment.

Medical and legal confusion surrounding gamma-hydroxybutyrate (GHB) and its precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4BD).

BACKGROUND: Gamma-hydroxybutyrate (GHB) is used as a recreational drug, with significant associated morbidity and mortality; it is therefore a class C drug under the Misuse of Drugs Act (1971). However, its precursors gamma-butyrolactone (GBL) and 1,4-butanediol (1,4BD) remain legally available despite having similar clinical effects. AIM: The aim of this study was to determine whether the relative proportions of self-reported ingestions of GHB or its precursors GBL and 1,4BD were similar to those seen in analysis of seized drugs. DESIGN AND METHODS: Retrospective review of our clinical toxicology database to identify all cases of self-reported recreational GHB, GBL and 1,4BD use associated with ED presentation in 2006. Additionally all seized substances on people attending local club venues were analysed by a Home Office approved laboratory to identify any illicit substances present. RESULTS: In 2006, there were a total of 158 ED presentations, of which 150 (94.9%) and 8 (5.1%) were GHB and GBL self-reported ingestions respectively; 96.8% (153) were recreational use. Of the 418 samples seized, 225 (53.8%) were in liquid form; 85 (37.8%) contained GHB and 140 (62.2%) contained GBL. None of the seized samples contained 1,4BD and there were no self-reported 1,4BD ingestions. CONCLUSION: Self-reported GHB ingestion was much more common than GBL ingestion, whereas GBL was more commonly found in the seized samples. These differences suggest that GBL use may be more common than previously thought and we suggest that there should be further debate about the legal status of the precursors of GHB.

What evidence is there that the UK should tackle the potential emerging threat of methamphetamine toxicity rather than established recreational drugs such as MDMA ('ecstasy')?

BACKGROUND: There is increasing interest in whether methamphetamine is an emerging recreational drug in the UK. AIM: To determine what evidence is there that methamphetamine use is an emerging drug in the UK compared to established recreational drugs such as MDMA. DESIGN AND METHODS: We undertook a retrospective study collating data on the number of enquiries to both our poisons centre and the UK National Poisons Information Service (NPIS) relating to all recreational drugs, methamphetamine and MDMA; presentations to our Emergency Department (ED) with acute methamphetamine toxicity and the frequency of positive urine tests for methamphetamine and MDMA in workplace drug screening programmes. RESULTS: There was a small increase in the number of methamphetamine-related calls to our poisons centre, but it remained uncommon (0.1% of all recreational drugs cases in 2000 to 1.23% in 2006) compared to MDMA (17.3-42.7% of all recreational drugs cases). The number of 2005/6 enquiries to the UK NPIS for methamphetamine was 12, compared to 455 MDMA enquiries (0.014 and 0.52% of all enquiries, respectively). There were five presentations to our ED relating to methamphetamine over a 15-month period compared to 171 for MDMA. Of the 254 440 urine samples screened for the presence of drugs in the workplace (2000-06), three were positive for methamphetamine and 147 for MDMA. CONCLUSION: There is no evidence of increasing use of methamphetamine or that acute methamphetamine poisoning is a significant clinical problem compared to established recreational drugs such as MDMA. In our opinion, healthcare, educational and law enforcement resources should be proportionally directed towards tackling drugs that pose an immediate and continuing healthcare risk to the population rather than emerging recreational drugs.

Can vacuum assisted venous drainage be achieved using a roller pump in an emergency? A pilot study using neonatal circuitry.

There has been much advancement in perfusion technology over its 50 years of progression. One of these techniques is vacuum-assisted venous drainage (VAVD). Many perfusionists augment venous drainage using VAVD, typically from a wall vacuum source. This study explores alternates to providing VAVD if the wall vacuum fails. In two porcine laboratories, approximately 36 in. of 3/16-in. tubing was connected to a sucker return port and placed into the roller head next to the arterial pump. The vacuum was monitored with a DLP pressure monitoring system (Medtronic). This system was connected to small-bore tubing and attached to a stopcock on top of the reservoir. The vacuum was regulated using another stopcock connected to a non-filtered luer lock port on top of the reservoir or by a segment of 3 x 0.25-in.-diameter tubing attached to the vent port with a c-clamp. Vacuum drainage was achieved, ranging from -18 mmHg to -71 mmHg by manipulating the stopcock or c-clamp. Changes in venous drainage were seen by volume fluctuations in the venous reservoir. The vacuum was adjusted to account for dramatic changes. Augmented venous drainage using a roller pump can be achieved successfully during cardiopulmonary bypass (CPB). This method of active drainage can be used in lieu of wall suction or during times of emergency if wall suction fails.

Paradoxical response to tacrolimus assessed by interleukin-2 gene expression.

BACKGROUND: The calcineurin inhibitors cyclosporine and tacrolimus are potent immunosuppressive drugs, used mainly after organ transplantation. Methods to monitor their pharmacodynamic effects are not well established. METHODS: Whole blood samples from healthy volunteers (n = 16) were incubated for 24 hours in culture medium; each sample was preincubated for 2 hours with or without tacrolimus. An identical procedure was performed for 7 samples using blood from renal transplant patients before transplantation. Following the culture period, total RNA was isolated and quantitative reverse transcriptase polymerase chain reaction, using TaqMan probes, was employed to quantify interleukin-2 (IL-2) mRNA expression, and IL-2 mRNA copy number was reported by reference to a standard curve. RESULTS: IL-2 mRNA synthesis was suppressed by the presence of tacrolimus in most cases, compared with a control sample. However, some samples demonstrated up-regulation of mRNA expression. In the patient samples, there was up-regulation of IL-2 mRNA in two samples and, after transplantation, these patients developed acute rejection. CONCLUSION: Quantitative measurement of cytokine IL-2 regulated gene expression may represent a method to assess the efficacy of calcineurin inhibitor drugs.

Validation of high-performance liquid chromatographic-mass spectrometric method for the analysis of lidocaine in human plasma.

A sensitive and simple liquid chromatography-tandem mass spectrometry method is developed and validated for the determination of lidocaine in human plasma. Bupivacaine is used as an internal standard, and the plasma extraction is performed by a simple liquid-liquid extraction. The limit of quantitation (LOQ) is 0.5 ng/mL with a signal-to-noise ratio greater than 5. The calibration curve is linear from 0.5 to 250 ng/mL with an r2 greater than 0.99. The coefficients of variation for within- and between-assay imprecision, including LOQ, are < or = 13% and < or = 8%, respectively. The percentage of inaccuracy for within- and between-assay, including LOQ, are < or = 9% and < or = 5%, respectively. The absolute recovery of lidocaine and bupivacaine are greater than 84% and 82%, respectively. The higher sensitivity and accuracy of this method allow the measurement of low concentrations of lidocaine in plasma from a clinical study of topically applied lidocaine in healthy subjects.

A microparticle enzyme immunoassay to measure sirolimus.

Measurement of sirolimus as a guide to therapy is widely accepted. Since the commercial introduction of the drug, the only method available to measure blood concentrations has been high-performance liquid chromatography (HPLC). Only a limited number of centers have the facilities to perform this technique and, as a result, the measurement of the drug has been performed in central laboratories, often some distance from the clinical centers. This article describes a single-center assessment of a new immunoassay to measure sirolimus, including a comparison between immunoassay results and a chromatographic technique. Calibration accuracy was good, reproducibility at 11 ng/mL was better than 6%, and sensitivity was better than 2 ng/mL; all these parameters are appropriate for routine clinical use. There was a mean positive bias of almost 20% for the measurement of sirolimus in clinical samples from kidney transplant patients receiving the drug, compared with HPLC. This bias was most likely due to cross-reactivity with metabolites of the drug and was of the order noted when an earlier configuration of this immunoassay was used in clinical practice. We conclude that, despite the analytical bias, this immunoassay offers a viable alternative to the use of HPLC and would be an assay suitable for implementing at local centers.

Therapeutic drug monitoring of cyclosporine.

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

The relative proportions of sirolimus metabolites in blood using HPLC with mass-spectrometric detection.

Measurement of sirolimus in blood as a guide to dose adjustment is an accepted practice. To date, most data have resulted from the use of a chromatographic technique. With the imminent introduction of an immunoassay into this field, there is a need to know whether metabolites that could interfere with the performance of this assay, causing a bias compared with measurements made by a chromatographic assay, vary over a period of time or with changes in concomitant immunosuppressive therapy. This preliminary study measured several sirolimus metabolites in blood samples from a variety of clinical settings, using high-performance liquid chromatography with tandem mass-spectrometric detection. Two metabolites known to cross-react in one immunoassay system, single hydroxylation products and 41-O-demethyl rapamycin, were found to constitute the bulk of the metabolic products. They were also found to form a remarkably stable proportion of all metabolites measured, both with respect to the time since transplantation and the concomitant use of cyclosporine or tacrolimus. It is concluded that the analytical bias due to cross-reactivity with metabolites, inherent in this immunoassay, should be consistent across a wide spectrum of patients receiving the drug.

A survey to determine the blood concentration of cyclosporine 2 hours postdose in stable renal transplant patients.

The current method for monitoring cyclosporine measures predose concentrations (C0). A better method has been developed, namely, measurement of the blood cyclosporine concentration at 2 hours postdose (C2). The aim of this survey was to determine the variability of C0 and C2 concentrations among stable renal transplant patients. One hundred two stable renal transplant patients who were at least 6 months posttransplant were recruited from the renal transplant outpatient clinic. The cyclosporine dose was between 100 and 500 mg daily; all patients had been monitored using C0 concentrations. Blood samples for cyclosporine concentration measurements were taken at both C0 and C2 at two consecutive clinic visits. The within- and between-patient variabilities were calculated using nested analysis of variance. The mean age was 50 years (21 to 81); the mean weight was 75 kg. The mean cyclosporine dose was 3.18 mg/kg/d (1.2 to 8.8). The average serum creatinine was 174 micromol/L (77 to 626) and the average cholesterol was 5 micromol/L (3 to 9). The mean (+/-SD) C0 concentration was 150 (47.31) microg/L and C2=895 (239) microg/L. The C0 concentration varied over 16-fold between patients compared to a sevenfold variation in C2. The between-subject coefficient of variation (CV) was 35% for C0 and 30% for C2 and the within subject CV was 23% for C0 and 20% for C2. The results suggest that cyclosporine concentrations at C0 are slightly more variable than those at C2. Whether this modest reduction in variability results in better patient outcomes is the subject of the next phase of this study.

Therapeutic monitoring of sirolimus: its contribution to optimal prescription.

It is now common practice to measure immunosuppressive drugs in blood as a guide to therapy. The immunosuppressive drug sirolimus, recently approved for use following kidney transplantation, was developed in the context of this clinical approach. Throughout the early clinical studies, validated analytical techniques based on chromatographic techniques were used to measure the drug. After a brief period in which an immunoassay was available, routine measurements are again being performed by chromatographic assays. In this article the use of blood concentration measurements in the assessment of the early and pivotal clinical trials of the drug is documented. Then, the rationale for the routine monitoring of the drug in clinical practice, a regulatory requirement in some countries, is set out. It is concluded that the development of this compound has benefited from experience gained during the pharmacokinetic assessment of other immunosuppressive drugs. The pharmacokinetic data accumulated on sirolimus have been a key element in formulating guidelines on dosing with this drug, both when used in combination with cyclosporine and when used after cyclosporine withdrawal.

Sirolimus: has it gained from experience with older drugs?

The immunosuppressive drug sirolimus, recently licensed in Europe for use following kidney transplantation, was developed against a background in which it was common practice to use blood concentration measurements as a guide to therapy. This article sets out to document the use of blood concentration measurements in the assessment of the early and pivotal clinical trials of the drug and the attention that has been paid to the validation of analytical techniques used to measure the drug. It is concluded that, building on experience from the older drugs used for immunosuppression, data relating drug concentrations with efficacy outcomes have played a significant role in formulating guidelines on sirolimus dosing.