Two chromatographic methods for the determination of corticosteroids in human biological fluids: pharmacokinetic applications

Efficient dispersive solid-phase extraction of methylprednisolone from exhaled breath of COVID-19 patients

In the current study, bismuth ferrite nano-sorbent was synthesized and utilized as a sorbent for the dispersive solid-phase extraction of methylprednisolone from exhaled breath samples. The size and morphology of the nano-sorbent were characterized by X-ray diffraction analysis and scanning electron microscopy. Following its desorption with acetonitrile, methylprednisolone was quantified by a high-performance liquid chromatography-ultraviolet detector. Factors affecting the extraction of methylprednisolone were optimized. Under optimized experimental conditions, a linear relationship between the analytical signals and methylprednisolone concentration was obtained in the range of 0.001-0.2 μg mL^-1 for exhaled breath condensate samples and 0.002-0.4 μg per filter for filter samples. A pre-concentration factor of 6.4-fold, corresponding to an extraction recovery of 96.0%, was achieved. The validated method was applied for the determination of methylprednisolone in real samples taken from the exhaled breath of COVID-19 patients under mechanical ventilation.

Analysis of corticosteroids by high performance liquid chromatography–electrospray mass spectrometry

A high performance liquid chromatography electrospray mass spectrometry (HPLC-ESI-MS) method, for the detection of corticosteroids in cosmetics has been developed. A water-acetonitrile linear gradient on a C-18 reversed-phase column was found to be suitable in separating triamcinolone and its main derivatives, which greatly differ in lipophilicity. Detection was performed in negative electrospray ionisation mode. Good correlation between peaks areas and solutions concentration was found in the range 0.05-10.0 micro g ml(-1) and the detection limits resulted in the range of 20-45 pg injected. The method was successfully applied to the analysis of real samples of shampoo.

Solvent and solid-phase extraction of natural and synthetic corticoids in human urine

Optimization of the main variables that affect solvent and solid-phase extraction processes, using disposable C18 cartridges and the non-ionic polymeric resin Serdolit AD-2, of human urine containing natural and synthetic corticoids is described. The data were obtained from different HPLC separations of these compounds using calibration graphs obtained before and after extraction of these compounds. The procedures, including sample preconcentration, showed efficiencies over 90%. NaCl was used to avoid emulsion formation in solvent extraction. The results achieved using solvent and solid-phase extraction are discussed.

Optimization of the high-performance liquid chromatrographic separation of a mixture of natural and synthetic corticosteroids

Systematic optimization of the HPLC separation of a mixture of natural and synthetic corticosteroids was carried out for screening purposes. The method involves binary, ternary or quaternary mixtures containing water, methanol, acetonitrile and tetrahydrofuran. It was possible to separate thirteen out of fourteen corticosteroids contained in a sample in about 26 min, with a 5-microns Hypersil-C18 (250 mm x 4.6 mm I.D.) column thermostated at 30 degrees C, using a mobile phase composed of water-tetrahydrofuran (72:28, v/v). This separation was not improved using other C8 or C18 columns. The effect of temperature on the separation of these compounds was also studied. Calibration graphs were established for each corticosteroid up to 8 micrograms/ml using indapamide as internal standard. The detection limits were in the range 0.02-0.14 ng. The optimized method was applied to urine samples spiked with corticosteroids and showed potential for future applications.

Immunoaffinity chromatography combined with gas chromatography-negative ion chemical ionisation mass spectrometry for the confirmation of flumethasone abuse in the equine

Immunoaffinity chromatography using a synthesised immunosorbent was used to extract tritiated dexamethasone (with dexamethasone carrier) from equine urine at a recovery of 81.7 +/- 8.4% (mean +/- S.D.). A method utilising this procedure coupled to cool on-column injection gas chromatography-negative ion chemical ionisation mass spectrometry is also described for the confirmation of low levels of flumethasone in equine urine samples.

Routine screening and quantitation of urinary corticosteroids using bench-top gas chromatography-mass-selective detection

A method was developed for the routine screening, confirmation and quantitation of corticosteroids in human urine using bench top capillary gas chromatography (GC)-mass-selective detection. The free and conjugated corticosteroid fractions were isolated by liquid-liquid partition. After evaporation to dryness under vacuum the corticosteroid residues were derivatized to form the methyloxime trimethylsilyl ether derivatives. Both GC retention data and characteristic spectral data based on authentic reference standards were used for the identification and quantitation of cortisol, cortisone, tetrahydrocortisol and tetrahydrocortisone in the ppb (ng/ml) concentration range. The method is simpler and more efficient than the other GC-mass spectrometric (MS) techniques. It is also more sensitive than the liquid chromatographic-MS method.

In vitro hydrolysis of steroid acid ester derivatives of prednisolone in plasma of different species

The in vitro hydrolysis of two new classes of steroid acid esters synthesized from prednisolone as local anti-inflammatory steroids was investigated in rat, rabbit, and human plasma. One class was synthesized by incorporating methoxycarbonyl groups at the 16 position of prednisolone to produce 16 alpha-methoxycarbonyl prednisolone (P16CM) and its 17-deoxy analogue (DP16CM). The other class was synthesized by modifying the ketol side chain of prednisolone to produce methyl 20 alpha- and methyl beta-dihydroprednisolonate (P4 alpha and P4 beta). The P16CM and P4 beta were rapidly and completely hydrolyzed within 1 h of incubation in rat and rabbit plasma and within 4 h in human plasma. There was a marked species difference in the hydrolysis of DP16CM which occurred in the following order: rat greater than human greater than rabbit. The in vitro hydrolysis of P4 alpha was much slower than that of P4 beta; the process continued over 24 h in rat plasma. As expected, no change in the initial concentration of prednisolone was found over 120 h of incubation in rat plasma. This marked species difference in the hydrolysis of these steroid acid esters is probably related to the differences in the amounts, types, and activities of the hydrolyzing enzymes (e.g., esterases) in the plasma of the three species. From this study it can be concluded that the existence of an hydroxyl group at C-17 and the orientation of hydroxyl groups at C-20 play an important role in the systemic hydrolysis rate of the carboxy ester group on the steroid nucleus.

Urinary excretion of prednisolone following intravenous administration in humans

The urinary excretion of prednisolone was studied in eight normal human volunteers (two women and six men) following intravenous (16, 32, 48 and 64 mg) doses. Urine prednisolone concentrations were determined by a high performance thin layer chromatographic method (HPTLC). The overall mean prednisolone elimination half life in urine following all the intravenous doses as determined by the rate and sigma minus plots was 1.13 +/- 0.25 hour. This was independent of dose and shorter than that found in plasma (4.10 +/- 1.00 s.d. hour). The overall mean percentage of dose excreted unchanged in urine was 16.7 +/- 5.8% following all intravenous and oral doses respectively. About 80% of this amount was excreted within the first 4 hours of the intravenous administration. Renal clearance of prednisolone decreased with time by the first order kinetic (r = 0.790) and its overall value following all IV doses was 0.0183 +/- 0.0103 (s.d.) l/h/kg. The metabolic clearance remained constant with increasing doses from 16 to 64 mg (0.0883 +/- 0.0306 s.d. l/h/kg). From this study it was concluded that a definitive account of the renal elimination of prednisolone and its possible metabolites warrant further investigation. The fraction of the dose excreted unchanged was relatively small and variable suggesting that prednisolone elimination occurs mainly by metabolism.

Effect of food on the absorption and pharmacokinetics of prednisolone from enteric-coated tablets

Prednisolone absorption and bioavailability of 10 mg enteric-coated (EC) and plain (uncoated) tablets were investigated after fasting and heavy meals (EC only) consumed to satiety in normal healthy volunteers. The same volunteers had also received 16 mg of prednisolone intravenously. In fasted subjects, the absolute bioavailability fraction, as normalised for intravenous doses, of prednisolone from plain tablets was 1.055 and from EC tablets was 0.996. The peak concentrations after plain and EC tablets were 309 and 249 ng/ml attained at 0.98 and 5.14 h, respectively. The means plasma elimination half-lives following the plain, EC tablets and intravenous administration in fasting conditions were 3.73, 3.89 and 3.78 h, respectively. Food interfered with both the absorption and the pharmacokinetics of prednisolone after EC tablets resulting in variability in its plasma levels. In some cases absorption of prednisolone was delayed for 12 h and remained at a measurable level for 24 h. In other cases, a normal absorption pattern was observed. This inter- and intrasubject variability of the effect of food appears to be related to its quantity, constituents and also the subjects physiological characteristics. It is concluded that enteric-coated prednisolone tablets should be administered at least 2 h between meals. However, for more predictable corticosteroid absorption (perhaps thus avoiding the therapeutic failure), plain prednisolone tablets are preferable.