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Biomedical subjects

J T Barr

Publications and source records attributed to J T Barr.

At least 19 recordsLinked to original sources
PubMed1991

Use of a clinical data registry to evaluate medical technologies. Experience from the International Bone Marrow Transplant Registry.

We reviewed the 18 disease-specific evaluations that used the data base of the International Bone Marrow Transplant Registry to determine the effectiveness of alternative strategies for bone marrow transplant. We identify 17 treatment variables that physicians can control and report the associations between these variables and five clinical endpoints: stable engraftment, graft-versus-host disease, development of interstitial pneumonia, relapse, and disease-free survival. We also suggest policies to promote active participation in establishing and operating a registry.

Bone Marrow Transplantation↗
PubMed1991

Test performance characteristics of the serum phenytoin concentration (SPC): the relationship between SPC and patient response. The Veterans Administration Epilepsy Cooperative Study Group.

A retrospective analysis of Veterans Administration (VA) Cooperative Study No. 118 was conducted to examine the relationship between serum phenytoin concentration (SPC) and various measures of patient response in 111 patients on monotherapy, mostly after 12 months of treatment. Using patient response rating scales specifically developed and validated for the VA study, we plotted SPC vs overall composite score as well as vs each of the three component ratings of neurotoxicity, systemic toxicity, and seizure type and frequency. No statistically significant association was noted between SPC and any of the response measures. We also calculated test performance characteristics for using SPC and a therapeutic range of 10-22 micrograms/ml to categorize patient status with regard to overall response, toxicity, and seizure frequency. Test sensitivities (0.13-0.53), specificities (0.62-0.81), and positive predictive values (0.08-0.44) were much lower than desirable. This results in a large proportion of false-positive and false-negative errors associated with the use of SPC as a test. Our retrospective evaluation suggests that the range of SPC values in successfully treated patients is quite broad; the value of the commonly accepted SPC therapeutic range in predicting various measures of patient response is quite limited; and patient response, therefore, should be the ultimate end point in monitoring patients on phenytoin. Prospective studies of the relationship between SPC and response should be conducted.

Double-Blind Method↗
PubMed1990

Using population-based serum drug concentration cutoff values to predict toxicity: test performance and limitations compared with Bayesian interpretation.

The use of population-based serum drug concentration cutoff values for several commonly monitored drugs as tests to distinguish toxicity from nontoxicity was studied. Serum drug concentration and response data published in studies of theophylline, digoxin, aminoglycosides, vancomycin, and procainamide were analyzed to determine the prevalence of toxicity in each group of patients. Serum drug concentration cutoff values were then varied, and the following performance characteristics of the cutoffs as tests for predicting toxicity were calculated for each value: sensitivity, specificity, likelihood ratio, predictive value, and ratio of net consequences. At commonly accepted cutoff values, sensitivity was lower than desirable, positive predictive values were less than negative values, and the ratio of net consequences indicated that false-negative errors are implicitly weighted as more risky than false-positive errors. As the cutoff for each drug was increased, specificity increased but sensitivity decreased, positive predictive values increased but negative predictive values decreased, and the ratio of net consequences increased. Therapeutic drug monitoring would improve if practitioners and laboratorians collaborated to (1) conduct prospective studies of the test performance characteristics of drug concentrations, (2) estimate the pretest probability of toxicity for each patient, (3) combine the pretest estimate with the test characteristics to make a posttest estimate, and (4) develop a more patient-specific, Bayesian approach.

Aminoglycosides↗
PubMed1989

Protein and elemental analysis of contact lenses of patients with superior limbic keratoconjunctivitis or giant papillary conjunctivitis.

Soft contact lenses worn by six patients (12 eyes) diagnosed as having contact lens-induced superior limbic keratoconjunctivitis (SLK) and from four patients (5 eyes) with giant papillary conjunctivitis (GPC) were analyzed for protein concentration and for elemental content. Fifty-five percent water content, ionic lenses containing methacrylic acid had high protein concentration. Calcium was not a common element found on protein-coated lenses. Sulfur and iron were found on used and new lenses. An elevated level of mercury was detected in one gray lens that had been disinfected in thimerosal-preserved saline with a high heat disinfection unit by a patient with SLK.

Age Factors↗
PubMed1989

Increasing severity of illness among patients undergoing phase 1 trials. Implications for nursing resources.

To determine whether the severity of illness of hospitalized patients participating in Phase 1 trials has changed, a modified APACHE II (MA II) index was used to evaluate retrospectively each Phase 1 patient admitted during September through December 1983 and the same 4-month span in 1987. During the 1983 period, 28 patients were enrolled in 13 Phase 1 protocols. Their average length of stay (LOS) was 12.6 days (+/- 12.3 SD) with a mean MA II of 3.44 (+/- 2.69 SD). During the same 4 months in 1987, there were 37 patients enrolled in 18 Phase 1 trials with a mean LOS of 13.5 days (+/- 13.4 SD) and a mean MA II of 6.08 (+/- 3.33). As indicated by MA II scores, 1987 hospitalized patients enrolled in Phase 1 trials had a higher severity of illness than did 1983 Phase 1 patients (p = 0.01). The implications of an oncology patient population with an increasing severity of illness are examined in relation to nursing staff forecasting, resource allocation, and productivity.

Drug Evaluation↗
PubMed1989

Aspheric rigid gas permeable contact lenses: practitioner discrimination of base curve increments using fluorescein pattern evaluation.

Evaluation of the fluorescein pattern is the main clinical indicator of the fit of a rigid gas permeable (RGP) contact lens to the cornea. Traditionally, manufacturers inventory RGP lenses in 0.05-mm base curve increments. The objective of this study was to test the hypothesis that experienced practitioners are not able to discern base curve/cornea relations of aspheric design lenses correctly to within +/- 0.05 mm. Eleven clinicians with expertise in fitting rigid lenses were asked to interpret fluorescein patterns and lens fittings of the Bausch & Lomb Quantum aspheric RGP lens on five adapted rigid lens wearers. The results showed that the experienced practitioners used in this study were not able to discriminate cornea/base curve relations of Quantum aspheric lenses within +/- 0.05 mm more than 67% of the time (p less than 0.05). There were no patient-to-patient differences based on type of lens fit (interpalpebral or lid attachment) or degree of corneal toricity. Lenses fitted in 0.10-mm base curve steps were judged as being as acceptable as lenses fitted in 0.05 mm steps (p less than 0.05). It was concluded that Quantum aspheric design lenses need only be trial fitted in 0.10-mm base curve steps.

Computers↗
PubMed1988

Evaluation of contact lenses by microbial enumeration and protein determination.

Contact lenses worn for varying periods of time (from 1 to 48 months) were subjected to microbiological examination by plate counts and protein determination. Seventy percent of the lenses displayed bacterial colony counts below 120 colony-forming units (CFU)/lens, 28 percent were in the range of 140 to 9060 CFU/lens, and one lens was contaminated with greater than 6 x 10(4) CFU/lens. Fungal contaminants were detected in three lens specimens in the range of 220 to 760 CFU/lens. Protein accumulation showed wide variation of up to 1.2 mg of protein per lens. Statistical analysis indicated highly significant associations (p less than 0.001) between the bacterial colony counts obtained with three different media. Some significant associations were found between the protein concentration and bacterial counts. The data did not indicate statistically significant relations between the above variables and either the water content or the length of wear of the contact lenses.

Adolescent↗
PubMed1987

Design and interpretation of bioassays for carcinogenicity.

A description is presented of the difficulties often met in developing meaningful scientific discussions regarding regulatory policy, with examples. In particular, the design and interpretation of rodent bioassays evoke strong emotional responses in many areas. It is suggested that interested parties engage in a scientific debate on some of the more important issues in the appropriate journals, with the purpose of seeking consensus whenever that may be found.

Animals↗
PubMed1986

Applying decision analysis in therapeutic drug monitoring: using receiver-operating characteristic curves in comparative evaluations.

In the first of a three-part series, decision-analysis techniques were applied to the evaluation, comparison, and selection of analytic systems for the purpose of improving the information content of serum drug concentration determinations. Receiver-operating characteristic (ROC) curves that graphically compare true-positive and false-positive rates at selected drug concentrations were developed and used to evaluate the clinical performance of analytic systems. Decision matrices were constructed using simulated toxicity and serum-concentration data from 150 subjects. These decision matrices were used to construct ROC curves and the curves were compared with prototype curves representing ideal, useful, useless, and hazardous test systems. The ROC curves were used to determine the analytic method (e.g., enzyme-multiplied immunoassay technique versus nephelometric assay) and analyte (e.g., free versus total drug concentration) that conveyed the most information and yielded the fewest errors in classifying patients as toxic or nontoxic. The use of ROC curves to compare new or modified analytic test systems, to monitor use of a given analytic method within an institution over time, and to compare the clinical performance of a given assay method in the therapeutic drug monitoring practices of various institutions is discussed. Decision-analysis techniques can assist practitioners in selecting the optimal analytic test system for reducing analytic variation as well as improving the quality and predictive ability of the serum drug concentration.

Decision Theory↗
PubMed1986

Applying decision analysis in therapeutic drug monitoring: using decision trees to interpret serum theophylline concentrations.

In the second of a three-part series, decision analysis is applied to therapeutic drug monitoring decisions that affect individual patients, using theophylline concentration and toxicity data to illustrate general concepts. Likelihood ratios and conditional probability curves were developed. The curves were used to determine the probability of toxicity based on the clinician's assessment of patient status and a measured serum theophylline concentration. A decision tree to "rule in" or "rule out" toxicity was constructed. Selection of a serum concentration cutoff level for classifying patients as toxic or nontoxic depends on the probabilities of the possible outcomes of the decision process and the clinician's assessment of the value of each possible outcome; therefore, no single concentration value is best for classifying patients. A decision tree was also constructed for evaluating therapeutic options when the clinician is confronted with adverse effects that may be drug related. In three prototype cases, the expected utility for discontinuing theophylline, continuing the drug at the same dosage, or lowering the dosage was determined and used to evaluate the relative worth of each therapeutic option. A more comprehensive interpretation of the serum theophylline concentration is provided by decision-analysis techniques than by observation of pharmacologic effect alone, because other factors such as merit, risk, and consequences of alternative decisions are considered.

Decision Theory↗
PubMed1985

The calculation and use of carcinogenic potency: a review.

Six methods of estimating carcinogenic potency now in use to some extent by regulatory agencies are examined. It is concluded that none of these methods is adequate for regulatory decision making when used alone, as is usually the case, but that all are useful as a contribution to the whole risk assessment process. The needs for further development and improvement of these methods, where appropriate to human risk, are identified and discussed in view of the growing use of potency estimates in regulatory decision making.

Animals↗
PubMed1979

Evaluation of blood culture procedures in a pediatric hospital.

To determine optimal clinical laboratory techniques for detecting pediatric bacteremia, we studied 7,768 consecutive blood cultures in a 1-year period. Blood was inoculated into one vented 50-ml bottle of brucella broth with 0.05% sodium polyanetholsulfonate and one unvented 50-ml bottle of Columbia broth with 0.05% sodium polyanetholsulfonate and 0.05% cysteine. Bottles were visually examined for growth on days 1 through 7 and blindly subcultured aerobically and anaerobically on days 1, 2, and 7. There were 724 (9.3%) positive cultures, and 484 (6.2%) were clinically significant. The most frequent isolates from bacteremic patients were Haemophilus influenzae (24%) and Streptococcus pneumoniae (17%). Growth was noted in only one bottle in 25% of clinically significant isolates. Bottles inoculated with greater than or equal to 1 ml of blood became positive earlier than bottles inoculated with less than 1 ml. After 1 day of incubation, 48% of the clinically significant cultures showed growth on visual examination, whereas 85% showed growth on subculture. Only 19% of Haemophilus isolates were detected visually on day 1, whereas 88% were recovered on subculture. By day 7, 3.5% of all isolates (including 18% of pneumococcal isolates and 1% of Haemophilus isolates) could no longer be recovered on subculture. We conclude that a two-bottle blood culture system and blind subculture within 24 h will optimize detection of pediatric bacteremia.

Bacteria↗
PubMed1979

A ladder curriculum in clinical microbiology.

A continuum of four microbiology courses for medical technology majors has been developed by the Medical Laboratory Science Program at Northeastern University. Using a system approach to curriculum design, the academic and clinical faculty identified career-entry capabilities, delineated appropriate subject content, and developed an instructional system which placed individual topics into one of four courses in the ladder curriculum: a basic, second-year, university-based clinical microbiology course stressing microbial technique and common organism identification; third-year microbiology and cellular physiology courses developing theoretical aspects; a fourth-year, hospital-based clinical microbiology rotation emphasizing isolation and identification techniques for significant pathogens; and a fourth-year, university-based, didactic course covering host defense-organism virulence interactions, infectious disease principles, and new techniques and unusual isolates as reported in the recent journal literature. Based on four years of experience with this system and in light of the publication of the 1978 American Society for Medical Technology (ASMT) Competency Statements, the Northeastern Medical Laboratory Science Program faculty is currently reexamining the continuum to insure completeness and appropriateness of overall subject content, to provide reinforcement, and to remove unnecessary duplication among the courses in the curriculum.

Certification↗