Dexamethasone residues

Supercritical fluid extraction, offers also some desirable advantages including processing at low temperature, recovery of a solvent-free extract, and rapid extraction. However, very limited studies have been published on the use of supercritical fluids for the isolation of corticosteroids from biological samples. A combination of supercritical fluid extraction and liquid chromatography has been employed for the detection of dexamethasone residues in bovine tissues (448). 

Figure 4.4. The chemical synthesis of dexamethaso-ne-HSA. Dexamethasone hemisuccinate is first converted to a reactive intermediate with isobutylchlorocarbonate and is then coupled to the free E-NH2 of the lysine residues in human serum albumin (HSA).

Residue depletion studies indicated that different formulations led to different dexamethasone depletion rates. Studies in cattle and pigs indicated that dexa-methasone residues were quickly eliminated from muscle and milk of cows. Residues did not occur in the free form in fat, whereas the depletion rate in liver was the slowest. Following intramuscular administration of 60 g/kg bw to cows, mean dexamethasone levels in milk declined from 8.4 ppb at the first milking after treatment to below 1 ppb at the sixth milking after treatment (52). 

Following dexamethasone tteatment of heifers and young bulls with 60 g/ kg bw, mean dexamethasone levels in liver declined from 127 ppb at 1 day after treatment to 16 ppb at 2 days after treatment to below 2.6 ppb at 4 days after treatment. Over the same time period, mean residues in kidney declined from 78 ppb to 13 ppb and finally to less than 0.9 ppb, respectively. Residues in muscle declined from 3.3 ppb to 0.75 ppb and finally to less than 0.5 ppb, respectively. Residues at the injection site declined from 8 ppb to 3.7 ppb and finally to 2.2 ppb, respectively. However, residues could not be detected in fat. Unlike with cattle, residues could not be detected in pigs given 60 g dexamethasone/kg bw intramuscularly. 

Milk from a lactating cow treated with 200 mg trichlormethiazide and 5 mg dexamethasone for 3 days was found to contain 6 ppb trichlormethiazide residues at 8 h after the last dose, and no detectable residues at the 24 h milking... 

Corticosteroids potentially used in food-producing animals include a variety of compounds such as cortisone, cortisol, prednisone, prednisolone, methylpredniso-lone, betamethasone, dexamethasone, flumethasone, fluoroprednisolone, isoflu-predone, and triamcinolone. Corticosteroid administration to feedlots as growth-promoting agents has been recently introduced illicitly in animal production because of their ability to promote water retention in the body. This use has been strongly enhanced for commercial reasons, in order to produce meat more appealing to consumers, due to the juicy and lean look. It is therefore crucial to rely on accurate, sensitive and specific analytical methods to measure residues in biological samples. 

As an example, evaporated extracts with residues of methylprednisolone can be cleaned up by partitioning between hexane and acetonitrile, and then between hexane and water saturated with sodium sulfate, and finally into dichloromethane (532). Evaporated extracts with residues of fiuoroprednisolone can be cleaned up by partitioning between acetonitrile and hexane, then between hexane and water, and finally into dichloromethane (533). Ethyl acetate extracts with residues of prednisolone, fiuoroprednisolone, triamcinolone, and betamethasone can be cleaned up by successive washing with aqueous acid and base to remove impurities (531). Ethyl acetate extracts containing residues of dexamethasone can be efficiently cleaned up by washing with aqueous sodium hydroxide (535). 

Sample preparation Condition a Bond-Elut C18 SPE cartridge by washing with 2 mL MeCN, 2 mL acetone water 2 98, and 4 mL water. Do not allow cartridge to run dry. 2 mL Plasma -I- 40 pL 5 pg/mL dexamethasone in MeOH, add to the SPE cartridge, allow to sit for 15 min, wash twice with 2 mL water, wash twice with 2 mL acetone water 2 98, pull a vacuum on the column for 15 min, elute with 1 mL MeCN under vacuum. Evaporate the eluate to dryness under a stream of nitrogen at 40°, dissolve the residue in 150 pL dichloromethane, inject a 100 pL aliquot. 

Sample preparation Dilute 0.1-1 mL urine to 1 mL with water if necessary, add 50 p,L 10 iJ,g/mL dexamethasone in MeOH, vortex, add to a Chem-Elut cartridge (cat. no. 1003), allow to stand for 5 min, elute twice with 5 mL portions of ethyl acetate (which are first used to rinse the sample tube) at 5 min intervals, wash eluate twice with 1 mL 200 mM NaOH, add 1 g anhydrous sodium sulfate, let stand for 30 min. Evaporate the organic phase at 30°under a stream of nitrogen. Reconstitute the residue in 250 xL mobile phase, inject a 50 p,L aliquot. 

Dexamethasone 21-acetate (9-a-fluoro-16-a-methylprednisolone-21-acetate, prednisolone F acetate) [1177-87-3] M 434.5, m 215-225°, 229-231°, [a] +77.6° (c 1, dioxane), +73° (c 1, CHCI3). Dexamethasone 21-acetate is purified on neutral AI2O3 using CHCI3 as eluent, the fractions are evaporated, and the residue is recrystallised from CHCI3. Store it below 8°. It has 239nm (s 14,900) in EtOH. It is a glucocorticoid... 

Sample preparation One tablet (0.25 mg digoxin) + 5 mL acetone ethanol 9 1 containing 0.11826 mg dexamethasone, sonicate 5 min, centrifuge at 1400 g for 5 min, evaporate supernatant under vacuum, dissolve residue in 100 pL MeOH, ii ject 0.2 pL aliquots. 

Sample preparation 750 xL Serum -<- 75 p.L MeOH 100 p.L 1.5 pgfmL dexamethasone in MeOH + 2 mL ethyl acetate, shake for 10 min, centriflige at 2500 g for 10 min. Remove 1.9 mL of the organic layer and evaporate it to dryness under a stream of nitrogen at 45°, reconstitute the residue in 100 p.L ethyl acetate, inject a 17 pXi aliquot. 

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