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Biomedical subjects

J S Markowitz

Publications and source records attributed to J S Markowitz.

At least 73 records · Page 4Linked to original sources
PubMed1996

Unopposed positive selection and autoreactivity in mice expressing class II MHC only on thymic cortex.

The normal development of T cells in the thymus requires both positive and negative selection. During positive selection, thymocytes mature only if their T-cell receptors react with some specificity to host major histocompatibility complex (MHC) and host peptides. During negative selection, thymocytes die if their T-cell receptors react with too high an affinity to the presenting cell, self MHC, and peptides to which they are exposed. These two processes are important for the development of the T-cell repertoire and the acquisition of self-tolerance, but their precise location and temporal relationship are not known. We have used the keratin 14 (K14) promoter to re-express a class II MHC antigen (I-Ab) in class II-negative mice. The transgenic I-A molecule is expressed only on thymic cortical epithelium; thymic medullary epithelium and bone-marrow-derived cells are I-A negative. CD4+ cells are positively selected in K14 mice, but clonal deletion does not ocur in K14 mice or in relB-negative mice, which lack a thymic medulla. The K14 CD4 cells are autoreactive, as they proliferate extensively to and specifically lyse I-Ab-positive target cells. These autoreactive cells make up 5% of the peripheral CD4 T cells, providing and estimate of the minimal frequency of positively selected cells that must subsequently undergo negative selection for self-tolerance to be preserved. Thus positive and negative selection occur in anatomically distinct sites.

Animals↗
PubMed1996

A prospective study on the reliability and cost effectiveness of preoperative ultrasound screening of the "marginal" liver donor.

With the growing shortage of available liver donors, many donors with risk factors that would have traditionally precluded liver procurement are now being considered. In this prospective study, we evaluated 50 "marginal" liver donors with pre-procurement abdominal ultrasounds and correlated results with findings at procurement and with subsequent allograft function. The results show that the ultrasounds have a specificity of 96% and a sensitivity of 68% in predicting abnormalities in donor livers that precluded transplantation. In addition, using ultrasound to screen marginal donors would result in significant savings in manpower and hospital resource utilization without "missing" any normal liver organs. Our results also show that, when properly selected, livers from donors with one or more high-risk factors function well with acceptable primary nonfunction rates.

Costs and Cost Analysis↗
PubMed1996

Orthotopic liver transplantation for congenital biliary atresia. An 11-year, single-center experience.

OBJECTIVE: The authors analyze a single center's 11-year experience with 190 orthotopic liver transplants for congenital biliary atresia. SUMMARY BACKGROUND DATA: Hepatic portoenterostomy generally is the initial treatment for children with congenital biliary atresia. Despite multiple modifications of the hepatic portoenterostomy, two thirds of treated patients still develop recurrent cholestasis, portal hypertension, cholangitis, and cirrhosis. Therefore, the only hope of long-term survival in the majority of children with congenital biliary atresia is definitive correction with orthotopic liver transplantation. METHODS: The medical records of 190 consecutive patients undergoing orthotopic liver transplantation for congenital biliary atresia from July 1, 1984 to February 29, 1996 were reviewed. Results were analyzed via Cox multivariate regression analysis to determine the statistical strength of independent associations between pretransplant covariates and patient and graft survival. Actuarial patient and graft survival was determined at 1, 2, and 5 years. The type and incidence of post-transplant complications were determined, as was the quality of long-term graft function. The median follow-up period was 3.21 years. RESULTS: The liver grafts were comprised on 155 whole-organ, 24 reduced-size, and 11 living donor organs. Median pretransplant values for recipient age, weight, and total bilirubin were 1.4 years, 12.3 kg, and 13.8 mg/dL, respectively. One hundred sixty-four patients (86%) had undergone prior hepatic portoenterostomy. Eighty-seven patients (46%) were United Network for Organ Sharing (UNOS) status 1 or 2 at the time of liver transplantation. The majority (15/24, 62%) of reduced-size graft recipients were UNOS status I at the time of transplantation. One hundred fifty-nine patients (84%) received a single graft, whereas 31 patients required 37 retransplants. The 1, 2, and 5 year actuarial patient survival rates were 83%, 80% and 78% respectively, whereas graft survival rates were 81%, 77%, and 76%, respectively. Cox multivariate regression analysis demonstrated that pretransplant total bilirubin, UNOS status, and graft type significantly predicted patient survival, whereas recipient age, weight, and previous hepatic portoenterostomy did not. Current median follow-up values for total bilirubin and aspartate aminotransferase levels in the 154 surviving patients were 0.5 mg/dL and 34 international units/L, respectively. CONCLUSION: Long-term patient survival after orthotopic liver transplantation for congenital biliary atresia is excellent and is independent of recipient age, weight, or previous hepatic portoenterostomy. Optimal results are obtained in this patient population when liver transplantation is performed before marked hyperbilirubinemia, and when possible, using a living-donor graft.

Actuarial Analysis↗
PubMed1996

Death rates among patients hospitalized with community-acquired pneumonia: a reexamination with data from three states.

OBJECTIVES: Death rates for community-acquired pneumonia based on relatively small-scale, published studies tend to exceed 15% to 20%. This study reexamined these estimates by using very large, population-based databases. METHODS: Death rates from 1993 associated with community-acquired pneumonia were reexamined with hospital discharge data from all of Washington, Illinois, and Florida. RESULTS: These death rates were substantially lower (7.0%, 8.1%, and 9.7%, respectively) than what appears in the literature. Significant risk factors for dying were being 65 years of age or older (odds ratio [OR] = 2.9), being positive for human immunodeficiency virus (OR = 2.9), and having a high severity of illness (OR = 7.1). CONCLUSION: Sampling bias associated with selection for hospital admissions explain the discrepancy between previous and this study's results.

AIDS-Related Opportunistic Infections↗
PubMed1996

Zolpidem-induced psychosis.

Zolpidem is reported to be a safe and effective hypnotic agent for the short-term treatment of insomnia. There are several case reports of zolpidem causing psychotic reactions in patients with no history of psychosis. We report two additional cases in which zolpidem was implicated in psychotic reactions characterized by auditory and visual hallucinations as well as delusional thinking. Both patient's symptoms resolved with the discontinuation of zolpidem use. It appears that our cases share several features in common with the other reported cases. All were female, there appeared to be some dose dependency involved, and the adverse event resolved fairly quickly upon zolpidem discontinuation. Zolpidem should be used at the lowest effective dose for the least amount of time as necessary. Female patients may possibly require smaller doses. In patients manifesting new-onset or unexplained psychotic symptoms, zolpidem use should be considered in the differential diagnosis.

Adult↗
PubMed1996

"Smart drugs"?

Explore the source record for details and available documents.

Drug Interactions↗
PubMed1995

Thermal degradation of clozapine-N-oxide to clozapine during gas chromatographic analysis.

Studies were undertaken to determine if clozapine-N-oxide, the principal urinary metabolite of the antipsychotic agent clozapine, may interfere with the gas chromatographic-mass spectrometric bioanalysis of clozapine. Following injection of clozapine-N-oxide onto a (5% phenyl)methylpolysiloxane capillary column operated at 250 degrees C, significant on-column reduction of clozapine-N-oxide to the parent drug occurred. Accordingly, preparation of biological samples for clozapine determination by gas chromatography should avoid conditions which reportedly co-extract the N-oxide to assure no artifactual contribution of this metabolite in the detection of clozapine.

Clozapine↗
PubMed1995

Class II major histocompatibility complex-deficient mice initially control an infection with Leishmania major but succumb to the disease.

Class II major histocompatibility complex (MHC)-deficient (H-2b) mice do not express I-A or I-E molecules and, as a result, do not develop CD4 cells. Thus, they represent the ideal model for examining the importance of CD4 cells and MHC class II molecules in resistance to infection with Leishmania major and the capacity of MHC class I-restricted T cells to mediate resistance to L. major. Class II MHC-deficient mice and control (C57BL/6, normal and nude) mice were infected with L. major. Although MHC class II-deficient mice were able to control infection more effectively than nude mice, cutaneous lesions on the mice eventually progressed, and parasite replication became uncontrolled. These results suggest that CD4 cells and MHC class II molecules are essential for resistance to L. major and that in the absence of these cells and molecules, such mice can transiently control infection with L. major but are unable to resolve such infections.

Animals↗
PubMed1995

Interactions between antipsychotic and antihypertensive drugs.

OBJECTIVE: To provide a comprehensive review of the pharmacokinetic and pharmacodynamic interactions between antipsychotics and antihypertensive and to provide recommendations for the selection of antihypertensive in patients receiving antipsychotic therapy. DATA SOURCES: A MEDLINE search of the English-language literature was used to identify pertinent human and animal studies, reviews, and case reports. STUDY SELECTION: All available sources were reviewed. DATA EXTRACTION: Background information was obtained from comprehensive reviews. Individual case reports were assimilated, and pertinent data were extracted. DATA SYNTHESIS: Because hypertension is common in patients with psychiatric illness and antihypertensive agents are used for a multiplicity of indications, significant numbers of patients receive concurrent therapy with antihypertensives and antipsychotics. Many antipsychotics may block the antihypertensive efficacy of guanethidine and related drugs. The interaction between clonidine and antipsychotics is defined less clearly. Limited data suggest possible additive hypotensive effects when chlorpromazine and methyldopa are given in combination. Increased plasma concentrations of thioridazine with a resultant increase in adverse effects have been reported when propranolol or pindolol are added to the regimen. A similar increase in chlorpromazine concentrations has been reported when propranolol was added. Although there are no reports documenting an interaction between a calcium-channel antagonist and an antipsychotic, the possible inhibition of oxidative metabolism of antipsychotics, additive calcium-blocking activity, and additive pharmacodynamic effects are theorized. Hypotension and postural syncope were reported in a patient given therapeutic dosages of chlorpromazine and captopril, and in 2 patients when clozapine was added to enalapril therapy. CONCLUSIONS: No antipsychotic-antihypertensive combination is absolutely contraindicated, but no combination should be considered to be completely without risk. Antihypertensives with no centrally acting activity, such as diuretics, may be the least likely to result in adverse reactions. The combination of the beta-antagonists propranolol or pindolol with thioridazine or chlorpromazine should be avoided if possible. Scrupulous patient monitoring for attenuated or enhanced activity of either agent is essential whenever antipsychotics and antihypertensives are given concurrently.

Adrenergic alpha-Agonists↗