Dexamethasone In Urine Research Articles

Lack of gender effect on the pharmacokinetics and pharmacodynamics of dexamethasone in the camel after intravenous administration

The pharmacokinetics and pharmacodynamics of dexamethasone were studied in six male and six female camels after a single intravenous dose (0.05 mg kg −1 body weight) of dexamethasone. The pharmacokinetic parameters of the two-compartment pharmacokinetic model for female and male camels, respectively (mean ± SEM) were as follows: terminal elimination half-lives were 8.02 ± 1.15 and 7.33 ± 0.80 h, total body clearances were 95.5 ± 16.0 and 124.5 ± 11.9 ml h −1 per kg, volumes of distribution at steady state were 0.72 ± 0.08 and 0.87 ± 0.14 litre kg −1, and the volumes of the central compartment were 0.12 ± 0.02 and 0.17 ± 0.02 litre kg −1. There was no significant difference in any pharmacokinetic parameter between female and male camels. Pharmacodynamic effects were evaluated by measuring endogenous plasma cortisol, circulating lymphocytes and neutrophils numbers and were analysed using indirect pharmacokinetic/pharmacodynamic models. The estimated IC 50 of dexamethasone for cortisol and lymphocytes for female and male camels were 3.74 ± 0.99 and 2.28 ± 1.09 and 2.63 ± 0.71 and 2.41 ± 0.79 ng ml −1, respectively. The EC 50 for neutrophils for female and male camels were 24.5 ± 5.83 and 20.2 ± 3.82 ng ml −1, respectively. There was no significant difference in any pharmacodynamic parameter between female and male camels. Dexamethasone in urine could be detected for 4–5 days by enzyme-linked immunosorbent assay and for 3–4 days by liquid chromatography/mass spectrometry after an intravenous dose of 0.05 mg kg −1 body weight.

Determination of dexamethasone in urine by gas chromatography with negative chemical ionization mass spectrometry

Dexamethasone, as some other synthetic corticosteroids, is licensed for therapy in veterinary practice, but its misuse as a growth promotor, often in combination with beta-agonists, is forbidden. In this report an analytical method is described for the detection and confirmation of very low concentrations of dexamethasone in urine. The influence of enzymatic hydrolysis time of samples with glucuronidase was studied. The proposed method consisted of the enzymatic hydrolysis of urine samples, which were then extracted and concentrated using solid-phase cartridges with mixed reversed-phase materials (OASIS). No further clean-up step was found to be necessary. Eluates were derivatized following a previously described method [Analyst 119 (1994) 2557]. Detection, identification and quantification of residues of this compound was carried out by gas chromatography with mass spectrometry in the negative chemical ionization mode. The proposed procedure permits the determination of dexamethasone in urine at levels as low as 0.2 ng ml −1

A rapid on-filter immunoassay screen for dexamethasone in equine urine

A simple on-filter immunoassay screen has been developed for the detection and semi-quantification of dexamethasone in equine urine samples. The assay consists of an indirect competitive ELISA in which dexamethasone in standards or samples competes with an immobilised dexamethasone–protein conjugate for binding to a complex of sheep anti-dexamethasone antibodies complexed with alkaline phosphatase-labelled second antibody. The drug–protein conjugate is immobilised as a spot on the surface of a cellulose nitrate filter and the assay is performed with the filter retained within a filtration port. The assay involves two incubation steps, firstly a ten minute competitive step and secondly a five minute step to generate via an enzyme-catalysed reaction an insoluble coloured dye as a spot on the filter at the site of the immobilised drug–protein conjugate. Rapid washing is achieved through use of the filtration system. The assay has a limit of detection of 10–6 M (390 ng ml–1) for a visual end point in which the colour intensity of spots developed in the presence of samples is compared with those of standards. Twelve filters can be processed in a single batch consisting of two standards and ten samples. The assay has been optimised for equine samples and dexamethasone in the urine of a race horse following injection of 20 mg of drug has been detected for 23 h post administration.