A selective HPLC/RIA for dexamethasone and its prodrug dexamethasone-21-sulphobenzoate sodium in biological fluids

Pharmacokinetics and pharmacodynamics of dexamethasone sodium-m-sulfobenzoate (DS) after intravenous and intramuscular administration: a comparison with dexamethasone phosphate (DP)

The pharmacokinetics (PK) and pharmacodynamics (effects on blood lymphocytes) of dexamethasone (D) after intravenous (i.v.) administration of dexamethasone phosphate (DP, 10 mg, equivalent to 8.3 mg of dexamethasone) and after intravenous and intramuscular (i.m.) administration of dexamethasone sulfobenzoate sodium (DS, 9.15 mg, equivalent to 6 mg of dexamethasone) were assessed. Only 25% of DS was converted into dexamethasone with a half-life for DS of 5.4 hours and 7.4 hours after i.v. and i.m. administration, respectively. Consequently, the mean residence time of D after both i.m. and i.v. administration of DS (10.4-11.6 h) was longer than that after DP administration (6.1 h). The smaller lymphocyte suppression induced by DS (50% of that after DP administration) was shown to be related to differences in the pharmacokinetics. This study revealed significant differences in the pharmacokinetics of D after administration of DS and DP and stresses the importance of the prodrug for the pharmacological response. Because of the slow and incomplete conversion of DS into dexamethasone, its use in emergency medicine situations should be critically evaluated.

A selective HPLC/RIA for the determination of budesonide

A combined HPLC/RIA procedure is described for the selective determination of budesonide (BUD) in plasma. The assay involves the extraction of plasma or serum samples with ethylacetate, consequent HPLC separation of intact budesonide from cross-reacting metabolites on a C8 reversed phase column, collection of the budesonide containing fraction and determination of budesonide immunoreactivity with the budesonide antiserum. The method was accurate, sensitive (IC50 value of 0.9 ng ml-1) and reproducible (intra- and inter-day less than 15%) with a limit of quantification of 0.133 ng ml-1 (RSD < 25%). The evaluation of a limited number of clinical samples after oral administration of budesonide by both the HPLC/RIA procedure and a direct RIA using the same antiserum differed in average by a factor of 2, with the ratio of HPLC/RIA-RIA results declining as a function of time. Thus, this ratio might be a suitable indicator for probing for the ratio of budesonide and overall metabolites on a semi-quantitative level.

Determination of dexamethasone in tears by capillary electrophoresis

A selective capillary zone electrophoresis (CZE) microassay was developed for the simultaneous determination of dexamethasone phosphate and its major metabolite, dexamethasone, in tears. The calibration was carried out in the biological matrix with indoprofen as an internal standard which allowed the separation of dexamethasone phosphate and dexamethasone from the tear constituents. The limits of detection and quantification of the assay were 0.5 and 2.0 microg ml(-1), respectively. This quantification method is essential for the in vivo determination of dexamethasone concentration-time profiles in tears after application of the antiinflammatory drug.

Pharmacokinetics of dexamethasone in premature neonates

OBJECTIVE

Dexamethasone is frequently used in premature neonates with bronchopulmonary dysplasia, however little is known about its disposition in this population.

METHODS

We evaluated the pharmacokinetics of dexamethasone in 9 premature neonates with a mean gestational age of 27.3 weeks and a postnatal age of 21.8 days.

RESULTS

There was a strong relationship between clearance (4.96 ml.min-1.kg-1) and gestational age ( r = 0.884). Pharmacokinetic parameters were grouped based on a gestational age of less than 27 weeks (Group I) and greater than 27 weeks (Group II). Mean clearance in group I and group II was 1.69 and 7,57 ml.min-1.kg-1, respectively. Mean distribution volume in group I and II was 1.26 and 2.19 l.kg-1, respectively. No significant relationships were noted between the disposition of dexamethasone and ventilator requirements or adverse effects.

CONCLUSION

The pharmacokinetics of dexamethasone in premature neonates was related to gestational age.

Determination of dexamethasone in plasma of premature neonates using high-performance liquid chromatography

A high-performance liquid chromatographic assay is described for dexamethasone in neonatal plasma. Samples (100 microliters) were extracted with ethyl acetate (1.0 ml) containing 50 ng of beclomethasone. The mobile phase of acetonitrile-0.01 M phosphate buffer (pH 7.0) (45:55, v/v) was pumped at a flow-rate of 1.0 ml/min through an Ultrasphere ODS column (5.0 microns particles). Detection was by UV absorbance at 240 nm. Calibration plots were linear (r2 > 0.999) from 10-1000 ng/ml. Within-day and between-day precision (C.V.%, coefficient of variation) between 15-900 ng/ml was 1.21-20.6%. Inaccuracy was 7.7%, or less. The minimum quantifiable concentration (C.V. approximately 20%) was 15 ng/ml. Recovery (20-1000 ng/ml) exceeded 75%. Concomitant neonatal medication did not interfere.