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Biomedical subjects

A B Troxel

Publications and source records attributed to A B Troxel.

12 recordsLinked to original sources
PubMed2005

Optimization of oxygen tolerance extension in rats by intermittent exposure.

Optimization of oxygen tolerance extension by intermittent exposure was studied in groups of 20 rats exposed to systematically varied patterns of alternating oxygen and normoxic breathing periods at 4.0, 2.0, and 1.5 ATA. Oxygen periods of 20, 60, and 120 min were alternated with normoxic intervals that provided oxygen-to-normoxia ratios of 4:1, 2:1, 1:1, and 1:3. In general, median survival times had nearly linear relationships to increasing normoxic intervals with oxygen period held constant. Exceptions occurred at 4.0 and 2.0 ATA where a 5-min normoxic interval was too short for adequate recovery even with a 20-min oxygen period, and an oxygen period of 120 min was too long even with a normoxic interval of 30 min. These exceptions did not occur at 1.5 ATA. Survival time for many intermittent exposure patterns was equivalent to that for continuous exposure to an oxygen pressure definable as a time-weighted average of the alternating oxygen and normoxia periods. However, this predictive method underestimated the degree of protection achieved by several of the intermittent exposure patterns, especially those performed at 4.0 ATA. Results provided guidance for selection of intermittent exposure patterns for direct evaluation in humans breathing oxygen at 2.0 ATA. Definition of intermittent exposure patterns and conditions that produced prominent gains in oxygen tolerance can also facilitate the performance of future experiments designed to study potential mechanisms for oxygen tolerance extension by intermittent exposure. Heat shock and oxidation-specific stress proteins that are induced by exposure to oxidant injury are suggested for emphasis in such investigations.

Animals↗
PubMed2005

Glutamine as a neuroprotective agent in high-dose paclitaxel-induced peripheral neuropathy: a clinical and electrophysiologic study.

AIMS: The appearance of peripheral neuropathy is the dose-limiting toxicity in many chemotherapy protocols, and glutamine has been proposed as a potentially neuroprotective agent in patients receiving paclitaxel. MATERIALS AND METHODS: In this non-randomised study, we assessed neurologic signs and symptoms, and changes in nerve-conduction studies in 46 consecutive patients given high-dose paclitaxel either with (n=17) or without (n=29) glutamine. Neurological assessments and electrodiagnostic studies were carried out at baseline and at least 2 weeks (median 32 days) after treatment. RESULTS: Patients who received glutamine developed significantly less weakness (P = 0.02), less loss of vibratory sensation (P = 0.04) and less toe numbness (P = 0.004) than controls. The per cent change in the compound motor action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes after paclitaxel treatment was lower in the glutamine group, but this finding was not statistically significant in these small groups. CONCLUSIONS: In this study, serial neurologic assessment of patient symptoms and signs seemed to be a better indicator of a possible glutamine effect than sensory- or motor-nerve-conduction studies. Prospective randomised trials are needed to clarify the effect of glutamine on paclitaxel and other types of chemotherapy-induced neuropathy.

Action Potentials↗
PubMed2002

Techniques for incorporating longitudinal measurements into analyses of survival data from clinical trials.

This article reviews existing approaches for joint analysis of longitudinal measurements, possibly measured with error or incompletely observed, and event-time data, possibly censored. The models take the form of selection or pattern-mixture models; estimation proceeds via the EM algorithm or Bayesian sampling techniques. The models are compared, their estimation and inferential procedures described, and advantages and disadvantages noted. Examples are discussed from several disease areas, including cancer and AIDS.

Algorithms↗
PubMed2001

Randomized trial of black cohosh for the treatment of hot flashes among women with a history of breast cancer.

PURPOSE: Most breast cancer survivors experience hot flashes; many use complementary or alternative remedies for these symptoms. We undertook a randomized clinical trial of black cohosh, a widely used herbal remedy for menopausal symptoms, among breast cancer patients. PATIENTS AND METHODS: Patients diagnosed with breast cancer who had completed their primary treatment were randomly assigned to black cohosh or placebo, stratified on tamoxifen use. At enrollment, patients completed a questionnaire about demographic factors and menopausal symptoms. Before starting to take the pills and at 30 and 60 days, they completed a 4-day hot flash diary. At the final visit, they completed another menopausal symptom questionnaire. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels were measured in a subset of patients at the first and final visits. RESULTS: Of 85 patients (59 on tamoxifen, 26 not on tamoxifen) enrolled in the study, 42 were assigned to treatment and 43 were assigned to placebo; 69 completed all three hot flash diaries. Both treatment and placebo groups reported declines in number and intensity of hot flashes; the differences between the groups were not statistically significant. Both groups also reported improvements in menopausal symptoms that were, for the most part, not significantly different. Changes in blood levels of FSH and LH also did not differ in the two groups. CONCLUSION: Black cohosh was not significantly more efficacious than placebo against most menopausal symptoms, including number and intensity of hot flashes. Our study illustrates the feasibility and value of standard clinical trial methodology in assessing the efficacy and safety of herbal agents.

Antineoplastic Agents, Hormonal↗
PubMed2001

The pharmacokinetics and pharmacodynamics of high-dose paclitaxel monotherapy (825 mg/m2 continuous infusion over 24 h) with hematopoietic support in women with metastatic breast cancer.

PURPOSE: We evaluated the pharmacokinetics and pharmacodynamics of high-dose paclitaxel (HDP) monotherapy (825 mg/m2 continuous infusion over 24 h) with peripheral blood progenitor cell (PBPC) and G-CSF support in 17 women with metastatic breast cancer. METHODS: Pharmacokinetic and pharmacodynamic data were collected in 17 women entered in a phase II trial of sequential HDP, and high-dose melphalan and cyclophosphamide/thiotepa/carboplatin. RESULTS: The maximal plasma concentration (Cmax), area under the plasma concentration time curve (AUC), apparent clearance (Clapp), duration of plasma concentration above 0.05 microM (t > 0.05 microM) for paclitaxel were (means SD): 9.11 +/- 7.45 microM, 145 +/- 88 microM x h, 8.06 +/- 2.90 l/h per m2 and 82.4 +/- 31.2 h, respectively. There was a significant correlation between the plasma paclitaxel concentration at 1 h (r2 = 0.87), 12 h (r2 = 0.85) and 23 h (r2 =0.92) and the AUC (P < 0.0001). Duration of neutropenia was brief (median 3 days, range 0-5 days) and neutrophil recovery occurred earlier (median 6 days, range 0-7 days) than could be attributed to infused PBPC. Median nadir count for platelets was 66 x 10(9)/l (range 13-160 x 10(9)/l). Pharmacodynamic analysis showed no correlation between pharmacokinetic parameters (Cmax, AUC, t > 0.05 microM) and time to neutropenic nadir, duration of neutropenia, platelet count nadir and grades of neuropathy or mucositis. In ten patients in whom detailed neurologic and nerve conduction studies were performed, linear regression analysis showed a significant correlation between pre- and post-HDP treatment total neuropathy scores (r2 = 0.46, P = 0.03). CONCLUSIONS: HDP (825 mg/m2 continuous infusion over 24 h) did not appear to be myeloablative. The degree of neurotoxicity subsequent to HDP was associated with the degree of baseline neuropathy but was not predictable from pharmacokinetic parameters.

Adult↗
PubMed2001

Genomic characterization of recent human LINE-1 insertions: evidence supporting random insertion.

LINE-1 (L1) elements play an important creative role in genomic evolution by distributing both L1 and non-L1 DNA in a process called retrotransposition. A large percentage of the human genome consists of DNA that has been dispersed by the L1 transposition machinery. L1 elements are not randomly distributed in genomic DNA but are concentrated in regions with lower GC content. In an effort to understand the consequences of L1 insertions, we have begun an investigation of their genomic characteristics and the changes that occur to them over time. We compare human L1 insertions that were created either during recent human evolution or during the primate radiation. We report that L1 insertions are an important source for the creation of new microsatellites. We provide evidence that L1 first strand cDNA synthesis can occur from an internal priming event. We note that in contrast to older L1 insertions, recent L1s are distributed randomly in genomic DNA, and the shift in the L1 genomic distribution occurs relatively rapidly. Taken together, our data indicate that strong forces act on newly inserted L1 retrotransposons to alter their structure and distribution.

3' Flanking Region↗
PubMed1997

Weighted estimating equations with nonignorably missing response data.

We propose weighted estimating equations for data with nonignorable nonresponse in order to reduce the bias that can occur with a complete case analysis. A survey concerning medical practice guidelines, malpractice litigation, and settlement provides the framework. The survey was sent to recipients in two waves: those who responded on the first or second wave are used to estimate a nonignorable nonresponse model, while the fraction of recipients who never responded is used to allow the percentage of missing data to change with each wave. We use the structure of the GEE of Liang and Zeger (1986, Biometrika 73, 13-22), adding weights equal to the inverse probability of being observed. We present simulations demonstrating the bias that can occur with an unweighted analysis and use the survey data to illustrate the methods.

Bias↗
PubMed1993

Phase II study of goserelin for patients with postmenopausal metastatic breast cancer.

PURPOSE: To determine the response rate of postmenopausal breast cancer patients to the gonadotropin-releasing hormone (GN-RH) agonist, Zoladex (goserelin; ICI Pharma, Wilmington, DE). PATIENTS AND METHODS: A multi-institutional single-agent trial in postmenopausal patients was conducted. Serum levels of follicle-stimulating hormone (FSH), testosterone, and estradiol were requested before and after Zoladex treatment. RESULTS: For estrogen receptor-positive (ER+) patients, the response rate was 11%, with one complete response (CR) and three partial responses (PRs) among 36 eligible patients. Responses were of short duration. There were no responses among 16 estrogen receptor-negative (ER-) patients. CONCLUSION: GN-RH agonists have activity in ER+ postmenopausal patients, but response rates are not as high as with other available endocrine therapies and the duration of response is short.

Aged↗
PubMedDate not supplied

Statistical analysis of quality of life with missing data in cancer clinical trials.

We summarize issues that arise when considering quality of life (QOL) data in cancer clinical trials, especially those related to missing data. We describe different types of missing data mechanisms, and discuss ways of assessing and testing missing data mechanisms. A section on presentation of study design and results describes how graphical displays can effectively document the extent of the missing data problem, as well as describe its impact on interpretation of results. Finally, we describe several different statistical methods used to analyse repeated measures, with an emphasis on their properties and their ability to adequately handle different types of missing data mechanisms. We make recommendations as to the most appropriate methods, and suggest important directions for future research.

Data Interpretation, Statistical↗
PubMedDate not supplied

A comparative analysis of quality of life data from a Southwest Oncology Group randomized trial of advanced colorectal cancer.

Longitudinal quality of life measurements from an advanced-stage cancer clinical trial are analysed using a variety of methods, and the results compared. The methods used require different assumptions about the mechanism that produces the missing data. They include analyses that require the data to be missing completely at random; fixed-effects models and weighted generalized estimating equations, which require missing at random data; and a fully parametric approach where the outcomes and the missingness mechanism are jointly modelled, allowing non-ignorable missing data. The data show evidence of non-random missingness, but a formal test of non-ignorable missing data is not significant.

Colorectal Neoplasms↗
PubMedDate not supplied

The quality of life associated with prophylactic treatments for women with BRCA1/2 mutations.

PURPOSE: This study was conducted to obtain and compare the preferences assigned to cancer states and prevention measures by women who had breast cancer, were at high risk for breast cancer, or had neither condition. PATIENTS AND METHODS: We administered a time trade-off questionnaire to 21 breast cancer patients, 28 women with a personal history of multiple breast biopsies or a family history of breast cancer, and 135 women without these conditions (the reference group). We stratified the reference group into two groups aged 20 to 32 years and 33 to 50 years, respectively. RESULTS: All four groups assigned higher preference to breast cancer than to ovarian cancer. Both reference groups preferred using a tamoxifen-like drug to having mastectomy or oophorectomy for cancer prevention; the high-risk and breast cancer groups did not. None of the four groups had a preference between prophylactic mastectomy and breast cancer. All the groups were willing to subtract more years from their life expectancy to protect offspring from genetic risk than to protect themselves. Reference group members in the 33- to 50-year age range had lower mean ratings than the breast cancer group for almost all the health states, and breast cancer patients were less willing than other respondents to trade time for health. Most of these differences were not statistically significant. The high-risk group was similar to the older reference group in time trade-off ratings. DISCUSSION: The time trade-off-based preferences of healthy women may be used to predict the treatment preferences of women with BRCA1/2 mutations. Obtaining healthy women's ratings of treatment outcomes may help health care policy makers envision the consequences of the difficult choices that high-risk women face.

Adult↗