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David W Holt

Publications and source records attributed to David W Holt.

At least 19 recordsLinked to original sources

Bioequivalence of enteric-coated mycophenolate sodium and mycophenolate mofetil: a meta-analysis of three studies in stable renal transplant recipients.

BACKGROUND: Mycophenolic acid (MPA) is an inhibitor of lymphocyte proliferation and is well established as an immunosuppressive agent in solid organ transplantation. The initial formulation of the drug was a prodrug formulation, mycophenolate mofetil (MMF, Cellcept), which is well absorbed and rapidly converted to mycophenolate in plasma. However, the use of MMF is associated with adverse gastrointestinal events, which can lead to withdrawal of therapy. In an effort to reduce the gastrointestinal effects of MMF, an enteric-coated formulation of the drug was developed, based on the sodium salt of MPA (EC-MPS, Myfortic). METHODS: Although bioequivalence has been demonstrated in an individual study in maintenance kidney transplant patients, this manuscript documents bioequivalence in a much larger data set of 82 patients by a meta-analysis of data from clinical trials. RESULTS: The results confirm the bioequivalence of EC-MPS and MMF for both mycophenolate and metabolite exposure, and for maximum plasma mycophenolate concentrations, across three studies. The 90% confidence interval of the ratio of EC-MPS to MMF for mycophenolate plasma AUC in the 82 patients was 101.1 to 114.5% and for Cmax was 83.0% to 112.7%. CONCLUSION: These findings provide reassurance to transplant professionals and patients that, when choosing between EC-MPS and MMF, they are choosing between formulations that give equivalent mycophenolate exposure.

Glucuronides↗

Multidrug resistance gene-1 (MDR-1) haplotypes have a minor influence on tacrolimus dose requirements.

P-glycoprotein (P-gp) and the drug metabolizing enzymes have major pharmacokinetic effects. Variability in tacrolimus absorption is influenced by P-gp activity which, in turn, is affected by single nucleotide polymorphisms (SNPs) within the multidrug resistance-1 gene (MDR-1). Tacrolimus dose requirements of 206 stable renal transplant patients were related to MDR-1 genotypes of SNPs C1236T, G2677T/A and C3435T, as well as haplotypes: C-G-C and T-T-T. Lower dose-normalized blood tacrolimus concentrations were achieved for: 2677-GG genotype patients, as compared to 2677-TT, and for 3435-CC patients as compared to 3435-TT patients. There was a small, but significant, difference in dose requirements between haplotypes C-G-C and T-T-T patients, which was not significant when patients were subclassified as producers and non-producers of cytochrome P450 3A5 (CYP3A5). The activities of CYP3A5 and P-gp have been shown to influence bioavailability of several drugs. Our data suggest that MDR-1 haplotypes have a relatively minor association with tacrolimus pharmacokinetics.

Adolescent↗

Therapeutic drug monitoring of mycophenolate mofetil in transplantation.

A roundtable meeting to discuss the use of therapeutic drug monitoring (TDM) to guide immunosuppression with mycophenolate mofetil was held in New York in December 2004. Existing recommendations for the initial months after transplantation were updated. After ensuring adequate levels of mycophenolic acid (MPA, the active metabolite of mycophenolate mofetil) immediately after transplantation, optimal efficacy may require only a few dose adjustments, because intrapatient variability in exposure seems low. Recommendations based on current knowledge were made for posttransplantation sampling time points and for target MPA concentrations. Algorithms for estimating MPA exposure using limited sampling strategies were presented, and a new assay for MPA discussed. It was agreed that because of interpatient variability and the influence of concomitant immunosuppressants, TDM might help optimize outcomes, especially in patients at higher risk of rejection. The value of TDM in the general transplant population will be assessed from large, ongoing, randomized studies.

Algorithms↗

Effects of conventional ultrafiltration on renal performance during adult cardiopulmonary bypass procedures.

Ultrafiltration has been used successfully in a variety of applications in the perioperative setting to assist in hemoconcentration and volume reduction. This study was designed to investigate the effects of aggressive conventional hemofiltration on bypass urine production, fluid balance, and renal performance in the 24 hours after bypass procedures in the adult population. A prospective, randomized study was designed to determine the effects of conventional ultrafiltration (CUF) during bypass while monitoring urine dynamics intraoperatively and in the 24-hour post-bypass period. Study group 1 (CUF, n = 49) was compared to control group 2 (non-CUF, n = 47) by monitoring urine values, volume additions, and packed red cell (PRC) use throughout the procedure. The mean total CUF volume removed from group 1 was 5781 +/- 2612. There were no differences in pre-bypass, total bypass, or total operating room (OR) urine between the two groups. The 24-hour urine totals were significantly higher in group 2 (2389 +/- 895) than in group 1 (2035 +/- 895). The ending bypass hematocrit was also lower in group 2 (26 +/- 2.0) than in group 1 (30 +/- 6.0). OR PRC additions were higher in group 2 (395 +/- 699) than group 1 (204 +/- 300). The non-CUF control group 2 experienced significantly greater ending fluid balance (3006 +/- 868) compared with group 1 (744 +/- 1271). No significant differences in pre- or postoperative creatinine values were observed. Aggressive CUF can be safely used during cardiopulmonary bypass in the adult population to reduce fluid accumulation and elevate bypass hematocrit without effecting bypass or intraoperative urine production.

Aged↗

Normoxia vs. hyperoxia: impact of oxygen tension strategies on outcomes for patients receiving cardiopulmonary bypass for routine cardiac surgical repair.

Oxygen pressure field theory (OPFT) was originally described in the early 1900s by Danish physiologist, Dr. August Krogh. This revolutionary theory described microcirculation of blood gases at the capillary level using a theoretical cylindrical tissue model commonly referred to as the Krogh cylinder. In recent years, the principles and benefits of OPFT in long-term extracorporeal circulatory support (ECMO) have been realized. Cardiac clinicians have successfully mastered OPFT fundamentals and incorporated them into their clinical practice. These clinicians have experienced significantly improved survival rates as a result of OPFT strategies. The objective of this study was to determine if a hyperoxic strategy can lead to equally beneficial outcomes for short-term support as measured by total ventilator time and total length of stay in intensive care unit (ICU) in the cardiopulmonary bypass (CPB) patient at a private institution. Patients receiving traditional blood gas management while on CPB (group B, n = 17) were retrospectively compared with hyperoxic patients (group A, n = 19). Hyperoxic/OPFT management was defined as paO2 values of 300-350 mmHg and average VSAT > 75%. Traditional blood gas management was defined as paO2 values of 150-250 mmHg and average VSAT < 75%. No significant differences between treatment groups were found for patient weight, CPB/AXC times, BSA, pre/post Hgb, pre/post-platelet (PLT) counts, pre/post-creatinine levels, pre/ post-BUN, UF volumes, or CPB urine output. Additionally, no significant statistical differences were found between treatment groups for total time in ICU (T-ICU) or total time on ventilator (TOV). Hyperoxic management strategies provided no conclusive evidence of outcome improvement for patients receiving CPB for routine cardiac surgical repair. Additional studies into the impact of hyperoxia in short-term extracorporeal circulatory support are needed.

Arteries↗

Relationship among pregnancy associated plasma protein-A levels, clinical characteristics, and coronary artery disease extent in patients with chronic stable angina pectoris.

AIMS: To assess, in chronic stable angina (CSA) patients, the relationship among clinical characteristics and cardiovascular risk factors, extent of coronary artery disease (CAD), and pregnancy-associated plasma protein-A (PAPP-A) levels. METHODS AND RESULTS: We studied 643 CSA patients (63+/-10 years, 482 men) undergoing diagnostic coronary angiography; 97 with angiographically normal coronary arteries or <50% stenosis, 127 with single vessel disease (VD), and 419 with multi-VD. Patients' age, gender, cardiovascular risk factors, body mass index, history of previous myocardial infarction, angina class, left ventricular ejection fraction (LVEF), and treatment were assessed at study entry. PAPP-A levels (mIU/L) were higher in men than in women (6.2+/-2.4 vs. 5.2+/-1.8; P<0.001) and in hypertensive vs. normotensive patients (6.4+/-2.8 vs. 5.8+/-2.1; P=0.01). PAPP-A correlated directly with age (r=0.19, P<0.001) and inversely with LVEF (r=-0.11, P=0.01). Patients with multivessel disease (VD) had higher PAPP-A levels (6.45+/-2.58) than those with single-VD (5.49+/-1.54, P<0.001) or normal coronaries (4.62+/-1.17, P<0.001). Male gender, age, history of a previous MI, hypercholesterolaemia, and PAPP-A levels were independent predictors for the presence of CAD. CONCLUSION: In CSA patients PAPP-A levels correlate with age, male gender, hypertension, and CAD extent. In the present study, PAPP-A was an independent predictor for the presence and extent of CAD.

Angina Pectoris↗

Effective synthesis of 1beta-acyl glucuronides by selective acylation.

[reaction: see text] Acyl glucuronides are vital metabolites for many carboxylic acid containing drugs. We report an efficient new method for the chemical synthesis of these molecules by selective 1beta-acylation of allyl glucuronate with carboxylic acids catalyzed by HATU and then mild deprotection through treatment with Pd(PPh(3))(4) and morpholine. The method is effective for a range of aryl and alkyl carboxylic acids, including important drugs.

Acylation↗

Tacrolimus pharmacogenetics: the CYP3A5*1 allele predicts low dose-normalized tacrolimus blood concentrations in whites and South Asians.

Previously, we demonstrated that the dose-normalized tacrolimus blood concentration after renal transplantation was associated with a single nucleotide polymorphism (SNP) in the CYP3AP1 gene, probably through linkage with an SNP in the CYP3A5 gene. Individuals with at least one CYP3A5*1 allele synthesize CYP3A5 and CYP3A5*3/*3 homozygotes do not. We now present results with direct typing of the CYP3A5 genotype for this group of 180 kidney-only transplant recipients from a single center. South Asian and white patients with at least one CYP3A5*1 allele achieved twofold lower dose-normalized tacrolimus blood concentrations compared with CYP3A5*3/*3 homozygotes, confirming our previous findings for the CYP3AP1 SNP. There was a significant delay in achieving target blood concentrations in those with at least one CYP3A5*1 allele. Determination of the CYP3A5*1/*3 genotype could be used to predict the tacrolimus dose requirement and, given incomplete linkage, would be better than determination of the CYP3AP1 genotype.

Adolescent↗

Analysis for identification in amnesty bin samples from dance venues.

The analysis of unknown substances discarded in amnesty bins, first described by Ramsey et al, from a large central London club and 7 smaller clubs in Manchester, UK are described. The contents of the bins were collected between July 2003 and March 2004. Solid dosage formulations were identified using the TICTAC database, chemical tests, and GC-MS screening. Drugs that could not be readily identified were subjected to other analytical techniques. The goal was to document the current range of drugs available on the dance scene and compare the findings between the London club, which had been the subject of a previous survey, and Manchester clubs. More than 1000 tablets, capsules, and powder doses were discarded in the amnesty bins. Tablets containing only MDMA (ecstasy) were found to be >94% and >84% of the total in London and Manchester, respectively. Although the quantities of tablets and powders recovered were different between London and Manchester, the proportions of the drugs were remarkably similar. The most common drugs found in powders in London and Manchester respectively were cocaine (29%, 40%), amphetamine (25%, 26%), ketamine (19%, 20%), and MDMA (19%, 11%).

Adolescent↗

Bone metabolism in renal transplant patients treated with cyclosporine or sirolimus.

Sirolimus is a new immunosuppressive agent used as treatment to prevent acute renal allograft rejection. One of the complications of renal transplantation and subsequent long-term immunosuppression is bone loss associated with osteoporosis and consequent fracture. Two open-label, randomized, phase 2 studies comparing sirolimus versus cyclosporine (CsA) included indices of bone metabolism as secondary end-points. Markers of bone turnover, serum osteocalcin and urinary N-telopeptides, were measured over a 1-year period in 115 patients receiving either CsA or sirolimus as a primary therapy in combination with azathioprine and glucocorticoids (study A) or mycophenolate mofetil (MMF) and glucocorticoids (study B). Urinary excretion of N-telopeptides and the concentrations of serum osteocalcin were consistently higher in the CsA-treated patients and significantly different at week 24 for N-telopeptides and at weeks 12, 24, and 52 for osteocalcin. In conclusion, future trials are warranted to test whether a sirolimus-based regimen conserves bone mineral density compared with a CsA-based regimen.

Adult↗

Genotyping cytochrome P450 3A5 using the Light Cycler.

Cytochrome P450 3A5 (CYP3A5) is involved in the biotransformation of many orally administered drugs, some of which are dose optimized using therapeutic drug monitoring. The CYP3A5 gene exhibits variable inter-individual expression, which is related to a single-nucleotide polymorphism. Producers of the enzyme possess at least one CYP3A5*1 allele. Knowledge of patients' CYP3A5 genotype, in conjunction with therapeutic drug monitoring (TDM), may aid patient management. Real-time polymerase chain reaction (PCR) was used to genotype the A6986G mutation of the CYP3A5 gene. Specific primers were employed to generate a DNA product, co-amplified with two internal hybridization probes, using a LightCycler. DNA melt curve analysis readily identified the genotypes CYP3A5*1/*1, CYP3A5*1/*3 and CYP3A5*3/*3. Results were confirmed using DNA sequencing with 100% correlation. Genotypes were determined from 263 individuals and compared with the genotypes of a pseudogene CYP3AP1, which is in disequilibrium with CYP3A5. This is a rapid and reliable method for genotyping the CYP3A5 polymorphism which may be used as an important adjunct to the TDM service offered by laboratories to optimize drug prescription.

Base Sequence↗

Does pharmacogenetics have the potential to allow the individualisation of immunosuppressive drug dosing in organ transplantation?

The immunosuppressive drugs used in organ transplantation have a narrow therapeutic index, with rejection occurring as a consequence of underdosing and infection, malignancy and a number of drug-specific side effects with excessive dosing. Significant heterogeneity in the dose of drug required to achieve therapeutic blood concentrations adds to the complexity of the problem, which has been partly resolved by therapeutic drug monitoring. Single nucleotide polymorphisms have been identified in genes encoding metabolic enzymes, drug efflux pumps and drug targets for most of the drugs in widespread use. A pharmacogenetic approach to immunosuppressive drug prescribing remains to be tested. Based on current evidence, the most promising strategy would be use of the cytochrome P450 3A5 expressor genotype to guide initial dosing with tacrolimus.

Animals↗