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David W Johnson

Publications and source records attributed to David W Johnson.

At least 73 records · Page 4Linked to original sources
PubMed2004

Free mycophenolic acid should be monitored in renal transplant recipients with hypoalbuminemia.

The current approach for therapeutic drug monitoring in renal transplant recipients receiving mycophenolate mofetil (MMF) is measurement of total mycophenolic acid (MPA) concentration. Because MPA is highly bound, during hypoalbuminemia the total concentration no longer reflects the free (pharmacologically active) concentration. The authors investigated what degree of hypoalbuminemia causes a significant change in protein binding and thus percentage free MPA. Forty-two renal transplant recipients were recruited for the study. Free and total concentrations of MPA (predose, and 1, 3, and 6 hours post-MMF dose samples) and plasma albumin concentrations were determined on day 5 posttransplantation. Six-hour area under the concentration-time curve (AUC(0-6)) values were calculated for free and total MPA, and percentage free MPA was determined for each patient. The authors found a significant relationship between low albumin concentrations and increased percentage free MPA (Spearman correlation = -0.54, P < 0.0001). Receiver operating characteristic (ROC) curve analysis was performed on the albumin versus percentage free MPA data. The cutoff value of albumin determined from the ROC analysis that differentiated normal from elevated percentage free MPA (defined as > or = 3%) in this patient population was 31 g/L. At this cutoff value albumin was found to be a good predictor of altered free MPA percentage, with a sensitivity and specificity of 0.75 and 0.80, respectively, and an area under the ROC curve of 0.79. To rationalize MMF dosing regimens in hypoalbuminemic patients (plasma albumin < or = 31 g/L), clinicians should consider monitoring the free MPA concentration.

Adult↗
PubMed2004

Severe toxicity associated with a markedly elevated mycophenolic acid free fraction in a renal transplant recipient.

A 58-year-old man with end-stage renal failure secondary to polycystic kidney disease developed a profoundly elevated mycophenolic acid (MPA) free fraction and associated severe toxicity after cadaveric renal transplantation. Initial immunosuppressive therapy was 4 mg/kg body weight bid cyclosporin (Neoral; Novartis Pharmaceutical Co Ltd, Sydney, Australia) given orally with 1 g bid mycophenolate mofetil (MMF) (CellCept; Roche Products Pty Ltd, Sydney, Australia). In the first 5 days posttransplantation, the serum creatinine concentration fell, and the patient developed profound hypoalbuminemia (serum albumin <20 g/L) and hyperbilirubinemia (serum bilirubin >150 micromol/L) that resulted from progressing biliary obstruction. On day 5 posttransplantation, the 2-hour whole-blood cyclosporin concentration and total MPA area under the curve (AUC(0-6)) were low (837 microg/L and 12.6 mg x h/L, respectively), while the total mycophenolic acid glucuronide (MPAG) AUC(0-6) was elevated (1317 mg x h/L). MMF was continued at the same dose, but tacrolimus substituted for cyclosporin. The patient subsequently experienced severe nausea, vomiting, hematemesis, and pancytopenia (nadir white cell count 1.6 x 10(9)/L, platelet count 32 x 10(9)/L, and hemoglobin 73 g/L) that were normalized after cessation of MMF. Retrospective measurement of the free MPA concentration on day 5 showed that free MPA AUC(0-6) was markedly elevated at 2.3 mg x h/L, as was the free fraction, at 18.3%. This case illustrates how altered protein binding can be associated with severe MMF toxicity caused by an increased free MPA concentration despite relatively low total MPA. These data support the monitoring of free MPA concentrations in those patients considered at risk for MMF-related toxicity.

Humans↗
PubMed2004

Identification of hemodynamic compromise by cerebrovascular reserve and oxygen extraction fraction in occlusive vascular disease.

Cerebrovascular reserve (CVR) and oxygen extraction fraction (OEF) are used to identify hemodynamic compromise in symptomatic patients with carotid occlusive vascular disease, but evidence suggests that they are not equivalent. The authors studied the relationship between CVR and OEF to evaluate their equivalence and stages of hemodynamic compromise. Symptomatic patients (N = 12) with carotid occlusion were studied by stable xenon-computed tomography CBF after intravenous acetazolamide administration for CVR, followed within 24 hours by positron emission tomography (PET) for OEF. Middle cerebral artery territories were analyzed by hemisphere and level. Hemispheric subcortical white matter infarctions were graded with magnetic resonance imaging. Both hemispheric and level analysis of CVR and OEF showed a significant (P = 0.001), negative linear relationship [CVR (%) = -1.5 (OEF) + 83.4, (r = -0.57, P = 0.001, n = 24]. However, 37.5% of the hemispheres showed compromised CVR but normal OEF and were associated (P = 0.019) with subcortical white matter infarction. CMRO2 was elevated in stage II hemodynamic compromise (CVR < 10%, OEF > 50%). CVR and OEF showed a significant negative linear relationship in stage II hemodynamic compromise but revealed hemispheres in hemodynamic compromise by CVR but normal OEF that were associated with subcortical white matter infarction.

Aged↗
PubMed2004

Medicinal herbal extracts -- renal friend or foe? Part one: the toxicities of medicinal herbs.

In recent years, an increasing percentage of people from industrialized countries have been using complementary and alternative medicines (CAM). This, combined with numerous warnings regarding the potential toxicity of these therapies, suggests the need for practitioners to keep abreast of the reported incidence of renal toxicity caused by the ingestion of medicinal herbs. The goal of the present two-part series, on the toxic or beneficial effects of medicinal herbs on renal health, is to provide practitioners with a summary of the most recent information as well as the means by which evidence for benefit or toxicity has been found. In this first article, we explore in vivo evidence of toxicity. Included are nephrotoxicity from aristolochic acid and other components within herbs, herb--drug interactions resulting in adverse renal effects, and renal toxicity from contaminants within the extracts. The review aims to provide a guide to encourage future toxicity studies and rigorous clinical trials.

Aristolochic Acids↗
PubMed2004

Increases in peritoneal small solute transport in the first month of peritoneal dialysis predict technique survival.

BACKGROUND: Peritoneal transport of small solutes generally increases during the first month of peritoneal dialysis (PD). The aim of this study was to prospectively evaluate the ability of the peritoneal equilibration test (PET), carried out 1 and 4 weeks after the commencement of PD, to predict subsequent technique survival. METHODS: Fifty consecutive patients commencing PD at the Princess Alexandra Hospital between 1 February 2001 and 31 May 2003 participated in the study. Paired 1 week and 1 month PET data were collated and correlated with subsequent technique survival. RESULTS: A significant increase was observed in the dialysate : plasma creatinine ratio at 4 h (D/P Cr) between 1 and 4 weeks after the onset of PD (0.55 +/- 0.12 vs 0.66 +/- 0.11, P <0.001). Mean death-censored technique survival was superior in patients who experienced > or =20% rise in D/P Cr during the first month of PD compared with those who did not (2.3 +/- 0.2 vs 1.6 +/- 0.2 years, P <0.05). Using a multivariate Cox proportional hazards model analysis, the significant independent predictors of death-censored technique survival were an increase in D/P Cr of greater than 20% during the first month (adjusted hazard ratio [HR] 0.20, 95% CI 0.05-0.75), the absence of diabetes mellitus, the absence of ischaemic heart disease, body mass index and baseline peritoneal creatinine clearance. CONCLUSIONS: A 20% or greater rise in D/P Cr during the first month of commencing PD is independently predictive of PD technique survival. Further investigations of the mechanisms underlying this phenomenon are warranted.

Biological Transport↗
PubMed2004

Efficacy and side-effect profile of sevelamer hydrochloride used in combination with conventional phosphate binders.

BACKGROUND: Poor phosphate control is common among patients with end-stage renal disease. Sevelamer hydrochloride has been demonstrated to be a safe and effective phosphate binder when used as a monotherapy. However, cost limits its usefulness in many countries. Data assessing its effectiveness and safety in combination with conventional phosphate binders are lacking. METHODS: Dialysis patients meeting the following inclusion criteria participated in this study: (i) hyperphosphataemia >1.8 mmol/L (5.6 mg/dL); and (ii) an inability to tolerate currently available binders. The trial was conducted in three phases each lasting 3 months: (i) an observation phase (patients continued on their regular phosphate binders); (ii) a titration phase (sevelamer was added at a dose of 403 mg three times daily with meals, titrated to a maximum of 1209 mg three times daily); and (iii) a maintenance phase. RESULTS: Twenty-five patients were recruited into the study. Eighteen patients completed all three trial phases. Mean serum phosphate dropped from 2.11 +/- 0.06 mmol/L (6.6 +/- 0.2 mg/dL) during the observation period to 1.91 +/- 0.01 mmol/L (5.9 +/- 0.003 mg/dL) during the maintenance phase (P=0.02). Calcium x phosphate product fell from 5.49 +/- 0.17 mmol2/L2 (68.64 +/- 2.11 mg2 dL2) to 4.89 +/- 0.27 mmol2/L2 (61.36 +/- 3.35 mg2 dL2) (P=0.02). There was no significant change in serum calcium or parathyroid hormone. Total serum cholesterol fell from 3.8 mmol/L (3.4-4.37) 147 mg/dL (131-169) to 3.55 mmol/L (2.97-4.2) 137 mg/dL (115-162) (P=0.02). Serum low-density lipoprotein cholesterol also fell significantly from 1.67 +/- 0.10 mmol/L (65 +/- 4 mg/dL) to 1.52 +/- 0.11 mmol/L (59 +/- 4 mg/dL) (P=0.04). The average prescribed dose of sevelamer was 2.4 g/day. Elemental calcium dropped from 3.4 g/day (1.4 to 4.6) to 1.2 g/day (0.6-2.4) (P=0.04). Seventy-two per cent of patients reported mild flatulence, nausea and indigestion. Three patients discontinued treatment because of adverse effects. CONCLUSIONS: Sevelamer in combination with conventional phosphate binders is effective in lowering serum phosphate and calcium-phosphate product in patients with refractory hyperphosphataemia. Beneficial effects on lipid profile were also observed. Mild gastrointestinal upset is common.

Aluminum Hydroxide↗
PubMed2004

Medicinal herbal extracts--renal friend or foe? Part two: herbal extracts with potential renal benefits.

In this second of two articles regarding the renal toxicities or benefits of medicinal herbs, herbs are reported as being 'potentially beneficial' to the kidneys if there is strong in vivo evidence of renal protection from toxic substances or drugs; potent, specific renal anti-oxidant effects; in vivo cancer antiproliferative effects specific to the kidneys; or in vivo evidence of being beneficial in renal disease or failure. Among the herbs, polyherbal formulae and fungi with potential renal benefits are Cordyceps sinensis, Sairei-to, Rheum spp., Salvia miltiorrhiza and its component, magnesium lithospermate B and others.

Animals↗
PubMed2004

The roles of IGF-I and IGFBP-3 in the regulation of proximal tubule, and renal cell carcinoma cell proliferation.

BACKGROUND: Insulin-like growth factor I (IGF-I), a potent proximal tubule cell (PTC) mitogen, has been implicated in the progression of many human cancers. Our previous work on human renal tissues has suggested that IGF-I and several of its binding proteins (IGFBP-3 and -6) are up-regulated in clear cell renal cell carcinoma (RCC). METHODS: To further elucidate the role of IGF-I and IGFBPs in RCC growth, immunohistochemistry, thymidine incorporation, and Western analysis were performed in primary cultures of normal PTC (priPTC) and clear-cell RCC (priRCC), as well as in SN12K1 cells (a cell line derived from metastatic RCC). RESULTS: By immunohistochemistry, IGFBP-3 and IGF-I were prominently expressed in SN12K1 cells, and weakly expressed in priPTC and priRCC. Incubation with 100 ng/mL IGF-I significantly augmented DNA synthesis by priPTC (mean +/- SD 120.7%+/- 19.7% of controls, P < 0.05), priRCC (238.7%+/- 279.9% of controls, P < 0.01), and SN12K1(120.0%+/- 22.9% of controls, P < 0.05). Neutralizing antibodies to IGF-I and IGF-I receptor significantly suppressed SN12K1 growth (81.9%+/- 13.5% of control, P < 0.01 and 87.4%+/- 16.2% of control, P < 0.05, respectively). Removal of endogenous IGFBP-3 by an anti-IGFBP-3 increased SN12K1 DNA synthesis (243.9%+/- 35.3% of control, P < 0.001), which was partially abrogated by coincubation with exogenous IGFBP-3 (135.97%+/- 5.9% of controls, P < 0.001). Using Western analysis, IGFBP-3 expression was enhanced in IGF-I-stimulated SN12K1 cells exposed to exogenous IGF-I. Coincubation with anti-IGFBP-3 further enhanced IGF-I-induced DNA synthesis. CONCLUSION: RCC cells express IGF-I and IGFBP-3, and are responsive to exogenous IGF-I stimulation. Moreover, in SN12K1 cells (derived from metastatic RCC), autocrine IGF-I and IGFBP-3 actions, respectively, stimulated and inhibited growth. These results suggest that IGF-I and IGFBP-3 may be potential candidates for therapeutic manipulation in patients with advanced RCC.

Antibodies↗
PubMed2004

Practice variation among pediatric emergency departments in the treatment of bronchiolitis.

OBJECTIVES: Bronchiolitis is the most common disease of the lower respiratory tract in the first year of life. Treatment is controversial, with studies giving conflicting views on the benefits of bronchodilators and steroids. The objectives of this study were 1) to characterize the management of bronchiolitis in pediatric emergency departments (PEDs) in Canada, 2) to determine patient outcomes following emergency department (ED) visits, and 3) to provide descriptive data regarding bronchiolitis symptoms and family/personal medical history of these patients. METHODS: A prospective consecutive cohort of children with bronchiolitis presenting to seven Canadian PEDs was enrolled during a seven-to-21-day period. Standardized interviews with parents provided data regarding symptoms, previous treatment, and past history. Charts were reviewed for treatment, investigations, and disposition. Telephone follow-up at two to three weeks collected information regarding duration of illness and return visits. RESULTS: Two hundred thirty-seven (91%) of 260 eligible patients were enrolled. One hundred eighty-nine patients (80%) had both an interview and chart review, and 48 (20%) had only chart reviews; follow-up was completed for 163 (69%) patients. One hundred fifteen (63%) had seen their primary care provider during their illness prior to the ED visit. Seventy-three percent of patients (range per site 59-100%) were treated in the ED with bronchodilators (usually salbutamol or epinephrine) and 5% (range per site 0-14%) with oral steroids. Twenty-four percent (58/237) were prescribed bronchodilators on discharge, 3% (7/237) inhaled steroids, and 2% (5/237) oral steroids. Chi-square tests indicated significant practice variation by site in ED bronchodilator use (p < 0.001) and bronchodilator use at discharge (p = 0.0003). Admission rate was 31% (range by site 22-43%), 17% of patients had more than one ED visit, and 1% were admitted more than once. Admission rates were increased in younger children, children with comorbidities, and children with lower oxygen saturation. Viral studies were obtained in 53%, with 76% of these positive for respiratory syncytial virus (RSV). Median duration of cough was 12 days, poor sleeping and irritability eight days, and wheeze and poor feeding seven days. CONCLUSIONS: This study prospectively describes the treatment of bronchiolitis in the pediatric ED. The findings are consistent with the literature regarding the reported use of bronchodilators; however, use of steroids was found to be much lower than reported in other studies. Bronchodilator use in the ED and at discharge varied significantly by site. The results capture variation in treatment practices in Canadian PEDs, which may be the result of discordant randomized controlled trial evidence. Further research is needed to establish best practices.

Bronchiolitis↗
PubMed2003

Measurement of plasma pristanic, phytanic and very long chain fatty acids by liquid chromatography-electrospray tandem mass spectrometry for the diagnosis of peroxisomal disorders.

High pressure liquid chromatography with a narrow bore C8 column has been used to separate pristanic, phytanic and very long chain fatty acids, important in the diagnosis of peroxisomal disorders, for their accurate isotope dilution quantification by tandem mass spectrometry. The fatty acids, isolated from plasma, were analysed as trimethylaminoethyl ester (quaternary ammonium) derivatives. Analysis time was 2.5 h and sample requirement was 10 microl of plasma. Good agreement with GC-MS methods for the levels of pristanic and phytanic acids, C26:0/C22:0 and C24:0/C22:0 ratios were obtained for 12 plasma samples from peroxisomal disorder patients and a set of controls.

Chromatography, High Pressure Liquid↗
PubMed2003

Frequency and severity of acute rejection in live- versus cadaveric-donor renal transplants.

BACKGROUND: Live donors are an increasingly important source of kidneys for transplantation in Australia. The aim of this study was to compare the rate and severity of rejection between patients receiving kidney transplants from live versus cadaveric donors. METHODS: A retrospective analysis was undertaken of all patients receiving live-donor (n=109) and cadaveric-donor (n=389) renal transplants at our institution between April 1, 1994, and March 31, 2000. Follow-up was completed on all patients until graft loss, death, or May 31, 2001. RESULTS: The baseline characteristics of the live-donor and cadaveric groups were similar, except for recipient age (mean+/-SD, 36.3+/-15.6 vs. 44.5+/-14.4 years, respectively; P<0.001); donor age (46.1+/-11.3 vs. 36.1+/-16.4 years, P<0.001); pretransplant dialysis duration (1.36+/-2.1 vs. 3.4+/-4.4 years, P<0.001); and the proportions of patients receiving first allografts (95% vs. 88%, respectively; P<0.05), antibody induction (8% vs. 20%, P<0.01), and mycophenolate mofetil (MMF) (60% vs. 37%, P<0.001). Acute rejection was observed in 48 (44%) live-donor and 108 (28%) cadaveric transplants (P=0.001). Cadaveric donor type was independently predictive of less acute rejection both on logistic regression (adjusted odds ratio [AOR], 0.47; 95% confidence interval [CI], 0.30-0.73; P=0.001) and multivariate Cox proportional hazards model analysis (hazard ratio, 0.49; 95% CI, 0.34-0.69; P<0.001). Patients receiving cadaveric-donor transplants were also significantly less likely to receive antibody therapy for rejection (univariate, 18% vs. 9%; P=0.006; multivariate AOR, 0.45; 95% CI, -0.25-0.82; P<0.01), independent of recipient age, gender, race, transplant number, human leukocyte antigen mismatch, sensitization, induction therapy, delayed graft function, MMF use, tacrolimus or cyclosporine A use, sirolimus-everolimus use, year of transplant, donor age, or dialysis duration. However, donor type did not independently influence graft survival, immunologic graft survival, or patient survival. CONCLUSIONS: Live-donor kidney transplant recipients had a higher rate and severity of rejection and a shorter rejection-free period than cadaveric renal transplant recipients. Further consideration of the reasons for this difference and the use of alternative immunosuppressive strategies for live-donor transplants are recommended.

Acute Disease↗
PubMed2003

The importance of multiphase and multicomponent modeling in consequence and risk analysis.

The ability to accurately predict the consequences of hazardous fluid release is dependent on three things: the knowledge of the modeler, the quality of the model that is used, and the quality of the input parameters. One of the most difficult problems in consequence modeling is the prediction of post-release multiphase behavior, especially when a multicomponent mixture is involved. Releases from gas/oil wells often fit this description. The wellstream will produce a light crude oil and a gas stream when flashed into a separator. If accidentally released to the atmosphere, the gas, aerosol, and liquid fractions rarely match the phase separations in the separator, or the expectations of the modeler. And, since the wellstream has a wide range of hydrocarbon components, the need to accurately predict the multicomponent behavior becomes more important. Over the years, modelers have used several "rules of thumb" to provide the source term input parameters for modeling multiphase/multicomponent releases and subsequent dispersion. These modeling assumptions can lead to hazard predictions that are very different from reality. The biggest problem with rules of thumb is their inability to account for thermodynamics; thus, they cannot approximate the phase splits and composition changes that do occur. The aim of this paper is to improve the knowledge of the modeler by providing some insight into the selection of the proper input parameters for multiphase releases of multicomponent fluids. The application of a multiphase release model with multicomponent thermodynamics to a wellstream release is used to illustrate the importance of good modeling techniques.

Hazardous Substances↗
PubMed2003

Cyclosporine excretion into breast milk.

Although many female patients of childbearing age who are receiving cyclosporine have successful pregnancies, these women may be advised not to breast-feed. During recent years, cases of uneventful pregnancies and subsequent successful breast-feeding have been reported in the literature. The infant's blood cyclosporine concentration was usually very low. Based on these findings and the lack of detectable adverse effects, some investigators have suggested that women on cyclosporine may breast-feed, challenging the conventional view that cyclosporine is contraindicated during breast-feeding. Here, we report our experience with cyclosporine use during breast-feeding in five mother-infant pairs. We show a wide range of infant exposures to the drug in milk, noting that one of the infants had therapeutic blood concentrations of cyclosporine despite relatively low concentrations of the drug in milk.

Cyclosporine↗
PubMed2003

A single-centre experience of post-renal transplant lymphoproliferative disorder.

Post-transplant lymphoproliferative disorder (PTLD) complicates 1 to 10% of all transplantations. Previous clinicopathological studies of PTLD have been limited by small numbers, short follow-up times, outdated data, heterogeneity of pooled solid-organ transplant results, and selective inclusion of early-onset disease. We therefore undertake here a retrospective analysis and identify all cases of PTLD that complicated renal transplantation at the Princess Alexandra Hospital between 30 June 1969 and 31 May 2001. Tumour samples were subsequently retrieved for pathological review and for Epstein-Barr virus-encoded RNA in situ hybridisation (EBER-ISH). Of 2,030 renal transplantation patients, 29 (1.4%) developed PTLD after a median period of 0.5 years (range 0.1 to 23.3 years). PTLD patients were more likely to have received cyclosporine (76% versus 62%, P<0.05), tacrolimus (10% versus 2%, P<0.05) and OKT3 (28% versus 10%, P<0.01). As the burden of immunosuppression increased from dual, to triple, to OKT3 therapy, the risks of early onset, extensive-stage, polymorphic, Epstein-Barr virus (EBV)-associated and fatal PTLD progressively increased. The majority of patients presented with an extra-nodal mass (45%), were afebrile (76%), and had stage-IV disease (60%). EBER-ISH was positive in 58%. Actuarial 5-year disease-free survival was 53.7%. The independent predictors of mortality on multivariate Cox regression were polymorphic histology (HR 7.4, 95% CI 1.5-37) and an international prognostic index (IPI) >1 (HR 2.7, 95% CI 1.1-6.8). Compared with other treatments, chemotherapy was associated with higher survival rates (100% versus 18% at 3 years, P=0.0001). In conclusion, PTLD is more likely, occurs earlier, and is more often fatal, in the setting of intensive immunosuppression. Nevertheless, excellent long-term outcomes are achievable with early recognition and institution of appropriate treatment.

Humans↗
PubMed2003

Overdose advice.

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Drug Industry↗