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Biomedical subjects

W K Cheung

Publications and source records attributed to W K Cheung.

13 recordsLinked to original sources
PubMed1992

Identification of Aeromonas strains to the genospecies level in the clinical laboratory.

One hundred thirty-three strains of Aeromonas (human, n = 102; animal, n = 16; environmental, n = 15) previously identified to the DNA group level by molecular methods were biochemically analyzed for 58 properties. On the basis of the use of between 9 and 16 selected tests, 132 of the 133 strains (99%) could be assigned to their correct hybridization group using this biochemical scheme. The results suggest a feasible approach for identifying aeromonads to genospecies level under appropriate conditions.

Aeromonas↗
PubMed1992

Radiological manifestations of cardiovocal syndrome.

Cardiovocal syndrome is a rare clinical diagnosis that signifies vocal cord palsy associated with various cardiovascular diseases. The radiological manifestations of six cases of clinically diagnosed cardiovocal syndrome are reviewed retrospectively. The common clinical presentation of these six cases was hoarseness that was due to left vocal cord palsy. By means of chest X-rays (CXR) and cardioangiography, four cases were respectively diagnosed to have atrial septal defect (n = 1), ventricular septal defect (n = 1) and mitral stenosis (n = 2), all of which were associated with a common radiological finding of dilatation of pulmonary trunk. The other two cases were separately diagnosed to have proximal descending aortic saccular aneurysm (n = 1) by means of CXR and angiography, and fusiform ascending aortic aneurysm (n = 1) by computed tomography and magnetic resonance image. All these radiological presentations of either aortic aneurysm or dilated pulmonary trunk were associated with encroachment of aorticopulmonary window for which the left recurrent laryngeal nerve was presumably compressed with the result of left vocal cord palsy. Hoarseness that is caused by these underlying cardiovascular diseases is correctable after treatment of the underlying diseases. Hence, clinicians and radiologists should pay attention to the radiological manifestations of patients whose chief complaints are hoarseness and cardiovocal syndrome.

Adult↗
PubMed1991

Pharmacokinetic principles in the design of immediate-release components in sustained-release formulations with zero-order release characteristics.

The potential advantages and disadvantages of incorporating an immediate-release (IR) component in sustained-release formulations with zero-order release characteristics (SR) are discussed. The dose of the IR component for SR doses other than the first one (DIS) should be less than that for the first SR dose (DI). Multiple dosing of an SR formulation with an IR component of dose DI may lead to unnecessary accumulation and fluctuation of plasma drug concentrations. An innovative and practical method for estimating the DI and DIS doses of this IR component is also presented.

Chemistry, Pharmaceutical↗
PubMed1991

Pathogenic properties of Edwardsiella species.

The pathogenic characteristics of 35 Edwardsiella strains from clinical and environmental sources were investigated. Overall, most Edwardsiella tarda strains were invasive in HEp-2 cell monolayers, produced a cell-associated hemolysin and siderophores, and bound Congo red; many strains also expressed mannose-resistant hemagglutination against guinea pig erythrocytes. Edwardsiella hoshinae strains bound Congo red and were variable in their invasive and hemolytic capabilities while Edwardsiella ictaluri strains did not produce either factor; neither E. hoshinae nor E. ictaluri expressed mannose-resistant hemagglutination nor elaborated siderophores under the tested conditions. Selected strains of each species tested for mouse lethality indicated strain variability in pathogenic potential, with E. tarda strains being the most virulent; 50% lethal doses in individual strains did not correlate with plasmid content, chemotactic motility, serum resistance, or expression of selected enzyme activities. The results suggest some potential important differences in pathogenic properties that may help explain their environmental distribution and ability to cause disease in humans.

Animals↗
PubMed1989

Comparative pharmacokinetics of coumarin anticoagulants. XLIX: Nonlinear tissue distribution of S-warfarin in rats.

The serum protein binding of the oral anticoagulant drug warfarin varies widely among rats and largely accounts for corresponding variations in the total serum clearance of the drug. The hepatic uptake of warfarin is concentration dependent despite the concentration independence of the free fraction of warfarin in serum over a wide concentration range. This investigation was designed to determine the distribution of the S enantiomer of warfarin in rats as a function of warfarin concentration, free fraction in serum, dose, and time. Two groups of rats, one with relatively low (0.0043) and the other with relatively high (0.0105) average serum free fraction values, were selected from a large number of adult male Sprague-Dawley rats. All animals received an iv injection of S-warfarin, either 0.25 or 1.0 mg/kg, and were sacrificed at intervals over a period of 10 d. Concentrations of S-warfarin in serum, liver, kidneys, muscle, and fat were determined by HPLC. The tissue:serum concentration ratio (T:S) of the drug was highly concentration dependent, but was independent of dose, time, and (except for fat) free fraction in serum. The T:S for fat was higher in animals with the larger serum free fraction values. The T:S of S-warfarin for the liver was greater than 10 at low concentrations and reached a limiting value of 0.25 at relatively high concentrations of the drug. In general, the T:S versus concentration profiles of S-warfarin are consistent with the presence of two classes of binding sites in the tissues, one with very high affinity and low capacity, the other with lower affinity and apparently unlimited capacity under the experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1988

Importance of oral dosing rate on the hemodynamic and pharmacokinetic profile on nilvadipine.

Nilvadipine was administered as an oral solution formulation to 12 normotensive subjects in a three-way randomized crossover study at a dose of 16 mg as three different dosing regimens: 1) as a single 16 mg dose, 2) as a 1.6 mg dose given hourly for 10 doses, and 3) as an initial dose of 4.8 mg, followed by 1.6 mg doses given every hour for seven additional doses. After each dose, clinical effects, hemodynamic changes and the pharmacokinetic profile of the drug were determined. The mean maximum changes in diastolic (DBP) and systolic (SBP) blood pressure and heart rate (HR) after dosing regimens 1, 2, and 3 were: -33, -13 and +46%; -17, -14 and +38%; and -24, -14 and +36%, respectively. There was a relationship between the changes in DBP and HR and plasma concentrations of nilvadipine only after dosing regimen 1. The effect-concentration relationships were fit to a modified Emax model. There was no relationship between the change in SBP and plasma concentration after any of the dosing regimens. While there were no significant differences in the mean area under the plasma concentration-time curve (AUC0----infinity) between dosing regimens 2 (38.7 ng.hr/mL) and 3 (42.1 ng.hr/mL) (P greater than 0.05), the mean AUC0----infinity after regimen 1 (76.3 ng.hr/mL) was significantly greater than after dosing regimens 2 or 3 (P less than 0.05). The mean maximal plasma concentrations (Cmax) were 31.6, 1.3 and 6.3 ng/mL after dosing regimens 1, 2 and 3, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Pharmacokinetic evaluation of a sustained-release formulation of trihexyphenidyl in healthy volunteers.

Twenty-four male subjects were randomized to receive two oral dosage forms of trihexyphenidyl HCl (alpha-cyclohexyl-alpha-phenyl-1-piperidinepropanol HCl). The dosage regimens were (1) a 5-mg immediate release (IR) tablet given twice daily at time zero and 12 h later, and (2) two 5-mg sustained-release (SR) capsule formulations given daily. The number of adverse experiences following the SR formulation were approximately 50% of those for the IR formulation, the peak concentration (Cmax) after the SR formulation was significantly lower (p less than 0.05) than that after the first dose of the IR formulation, and the time to reach Cmax (tmax) was significantly longer after the SR formulation (p less than 0.05). The SR formulation maintained serum concentrations above 50, 60, and 70% of Cmax values for average time periods of 11.7, 9.4, and 5.9 h, respectively, compared with values of 1.8, 1.2, and 0.9 h after the IR formulation; the differences were all significant (p less than 0.05). The mean elimination half-life (t1/2) was similar (p greater than 0.05) after the SR (10.1 h) and IR (8.7 h) formulations. The statistical power of the study was 98.1% to detect a 20% difference in the area under the curve from time zero to time infinity (AUC0----infinity) between formulations. Although the AUC0----infinity after the SR formulation was statistically smaller (p less than 0.05) than after the IR tablet, the difference was less than 20%. Therefore, the SR formulation was bioequivalent to the IR tablet formulation of trihexyphenidyl.

Adult↗
PubMed1988

Changes in tissue concentrations of 14C-doxorubicin caused by mitoxantrone, mithramycin A and vinblastine in the rat.

The purpose of this study was to determine if mitoxantrone (a new antineoplastic drug) and two other anticancer agents (mithramycin A and vinblastine) could result in changes in the tissue distribution and disposition of doxorubicin in rats. Each of 16 male rats received 1 mg/kg of 14C-labeled doxorubicin on day one and received either saline, or doses of 4 mg/kg of mitoxantrone, 1.7 mg/kg of mithramycin A or 2.9 mg/kg of vinblastine on day three. All rats were sacrificed on day eight. Concentrations of radioactivity in the heart, lung, kidney and muscle were higher in the mitoxantrone treated rats than in the controls. Mithramycin A decreased the concentrations of radioactivity in liver, kidney and fatty tissues, while vinblastine increased the concentrations in heart, liver, lung, muscle and skin. In summary, mithramycin A, vinblastine and mitoxantrone caused a change in tissue concentrations of radioactivity of doxorubicin and/or its metabolites following a single I.V. dose of 14C-labeled doxorubicin in rats. This may cause elevated plasma concentrations of doxorubicin. These findings in the rat could theoretically have implications regarding doxorubicin therapy in man.

Animals↗
PubMed1988

Pharmacokinetics of nilvadipine after single oral doses in healthy volunteers.

Forty healthy male Caucasian volunteers were randomly assigned to five treatment groups to receive a placebo or a 4, 8, 12, 16 or 20 mg dose of nilvadipine. The drug was well tolerated by the subjects at all dose levels. Pharmacokinetic parameters for nilvadipine were determined using model-independent methods. There were no significant differences (p greater than 0.05) in the time to the maximum plasma concentration (Cmax) (tmax), the elimination half-life or the mean residence time among the five treatment groups. Up to doses of about 12 mg, there was a linear relationship between dose and Cmax or area under the plasma concentration-time curve (AUCO----infinity). At doses of 16 and 20 mg, the relationship between dose and Cmax or AUCO----infinity was no longer linear, suggesting that the pharmacokinetics of the drug after single oral doses greater than about 12 mg may be dose-dependent, probably due to concentration-dependent first-pass hepatic elimination of the drug.

Administration, Oral↗
PubMedDate not supplied

Abortifacient activity in leaves, roots and seeds of Phytolacca acinosa.

Fresh leaves, roots and seeds of Phytolacca acinosa were individually extracted with 0.9% saline and cold acetone was added to the supernatants. The resultant precipitates were dialyzed against distilled water and lyophilized to form acetone powders (AP). The relative potencies of abortifacient activity of the APs were: seed greater than root greater than leaf. The abortifacient activity in these APs was susceptible to destruction by heat and pepsin.

Abortifacient Agents↗