A selective LC/RIA for dexamethasone and its prodrug dexamethasone-21-isonicotinate in biological fluids

A combined LC/RIA procedure is described for the selective determination of dexamethasone (DEX) and its prodrug dexamethasone-21-isonicotinate (DIN) in plasma. The low affinity of the employed dexamethasone antiserum for DIN (cross-reactivity less than 0.5%) allowed the direct determination of DEX in plasma extracts. For the determination of DIN, both substances of interest were separated by LC, the DIN containing fraction was collected, hydrolysed and the generated DEX was consequently assayed by radioimmunoassay. The assay detection limits were 0.1 ng ml-1 for DEX and 0.75 ng ml-1 for DIN. For both substances, inter- and intra-day variabilities (RSDs) were 6 and 12%, respectively.

Pharmacokinetics of rimexolone after intra-articular administration

The pharmacokinetics of rimexolone were investigated after intra-articular injection into the knee joints of patients with rheumatoid arthritis. After a single dose of 40 mg rimexolone the drug could be detected in plasma over 3 months. The suspension dissolves in the synovia very slowly and provides a sustained release of the steroid in the joint. Pharmacokinetic analysis was performed on the assumption that the disposition of rimexolone after intra-articular administration is absorption limited ("flip-flop-case"). Dose linearity was studied in a range from 40 to 200 mg. Total body clearance averaged 106 L/h and was independent of dose. The mean residence time of rimexolone in the knee joint is very long and averaged 25 days. It could be shown that the mean residence time of different glucocorticoids correlates well with the duration of their clinical effectiveness.

Pharmacokinetics and dose linearity testing of methylprednisolone phosphate

The pharmacokinetics of methylprednisolone and methylprednisolone phosphate were investigated after intravenous administration of methylprednisolone phosphate to six healthy subjects at seven different doses between 16 and 1000 mg. Plasma, urine, and saliva were analyzed for methylprednisolone and methylprednisolone phosphate. Furthermore, endogenous hydrocortisone was measured in plasma. No non-linearity in the total body clearance of methylprednisolone phosphate or methylprednisolone could be detected. The average elimination half-life for the prodrug was 3.7 min indicating rapid hydrolysis. After 15 min more than 90 per cent of the phosphate has been hydrolyzed. No prodrug could be detected in saliva; very little of the ester (average 0.9 per cent of the dose) was excreted unchanged into the urine. Methylprednisolone is formed rapidly. The total body clearance was 21 1h-1, the terminal half-life 2.8 h. In the post-distribution phase methylprednisolone levels in saliva went parallel to plasma levels. The mean saliva/plasma ratio was 0.22. An average of 5.2 per cent of the dose was eliminated into the urine in the form of methylprednisolone. Hydrocortisone suppression was dose-dependent. For doses above 125 mg hydrocortisone levels were significantly lowered after 24 h. For doses above 500 mg the suppression was still significant after 48 h. The results indicate a rapid and predictable in vivo conversion of methylprednisolone phosphate to its active form methylprednisolone.

Glucocorticoid receptors in human synovial tissue and relative receptor affinities of glucocorticoid-21-esters

A dexamethasone binding protein was detected in cytosol of 11 human synovial tissues from patients with chronic polyarthritis. The apparent dissociation constant (KD) ranged from 3.3 to 17.1 (mean, 7.0 +/- 4.3) nmol/liter, and the receptor concentration (Ro) from 17 to 65 (mean, 42 + 15) fmol/mg protein. Results of competition assays with an excess of unlabeled aldosterone, estradiol, pregnenolone, and testosterone confirmed that the binding protein had characteristics of a glucocorticoid receptor. With the use of diisopropylfluorophosphate (DFP) for esterase inhibition, and considering the purity of the starting material and the hydrolysis products, we could determine the relative receptor affinities of glucocorticoid-21-esters. In contrast to the high affinity of the glucocorticoid-17-ester examined, esterification in position 21 abolishes binding affinities. Glucocorticoid-21-esters are true prodrugs for which the glucocorticoid action is caused only by the corresponding glucocorticoid alcohol.

Comparative pharmacokinetics of methylprednisolone phosphate and hemisuccinate in high doses

The pharmacokinetics of methylprednisolone and two methylprednisolone esters, the phosphate and the hemisuccinate, were investigated after intravenous administration of the esters to 12 healthy male subjects in two different doses (250 and 1000 mg). Methylprednisolone was formed more rapidly from phosphate than from hemisuccinate. During the first 30 min methylprednisolone levels were three to four times higher after phosphate administration than after hemisuccinate. The mean residence time of the hemisuccinate was significantly longer and the total-body clearance lower than those of the phosphate. Whereas very little of the phosphate (mean, 1.7%) was eliminated unchanged into the urine, there were significant amounts of hemisuccinate (mean, 14.7%) excreted renally and therefore not bioavailable. Methylprednisolone saliva levels paralleled plasma levels; the average saliva/plasma ratio was 0.22. Neither phosphate nor hemisuccinate could be detected in saliva. An average of 7.2% of the administered dose was eliminated in the form of methylprednisolone in urine. Renal clearance was 24 ml/min and not dose or prodrug dependent. For both doses endogenous hydrocortisone levels were lowered after 24 hr. For the 1000-mg dose the depression was still significant after 48 hr. The results indicate that methylprednisolone phosphate results in a faster and more efficient conversion to its active form, methylprednisolone, than methylprednisolone hemisuccinate.

Pharmacokinetics of dexamethasone and its phosphate ester

Dexamethasone in form of its phosphate was given intravenously in two different doses (1.5 mg kg-1 and 15 mg). Plasma levels of the ester and dexamethasone were measured and pharmacokinetic parameters were calculated. The results indicate no dose-dependency of the pharmacokinetic parameters in the investigated range for dexamethasone. Conversion from the prodrug to the active form was rapid; maximum dexamethasone plasma concentrations were reached after 10 min. The results were verified by dexamethasone level monitoring in patients after chronic dosing. Predicted and achieved steady state levels agreed well.

[Pharmacokinetics and pharmacodynamics of prednisolone following extremely high dosage as prednisolone hemisuccinate]

Plasma levels of prednisolone and prednisolone hemisuccinate of volunteers were measured with HPLC following i.v. injections of 1200 and 75 mg of prednisolone, given as the water-soluble hemisuccinate ester. The hemisuccinate ester is hydrolyzed relatively quickly with a plasma half-life between 18 and 25 min, and the resulting prednisolone has a plasma half-life of 3.5-3.7 h. The dose dependency of the pharmacokinetic parameters indicates a partial saturation of the metabolizing enzymes as consequence of the application of the high dose of prednisolone. In saliva no hemisuccinate could be detected. The prednisolone saliva concentration corresponds with those of non-protein-bound prednisolone in plasma measured at the same time. Only minor quantities of intact ester (1-8%) or intact prednisolone (2-4%) are excreted in urine. Following the application of 1200 mg prednisolone the endogenous cortisol level is partially suppressed only 24 h after the i.v. injection; 48 h later the difference from the basis value is not statistically significant. Leukocytosis and granulocytosis are at maximum 24 h after the injection of the high dose, and after 48 h normal values are observed. Lymphocytes and monocytes fall below normal levels for a longer time after 1200 mg compared to 75 mg, the minimum is between 4 and 8 h. Glucose levels are enhanced dose-dependently. They are normalized even after the extremely high dose at 24 h. Sodium, potassium, calcium, plasma proteins, urea, creatinine, hematocrit and hemoglobin showed no significant differences within 48 h following the injections.

Pharmacokinetics and pharmacodynamics of glucocorticoid suspensions after intra-articular administration

Triamcinolone acetonide, triamcinolone hexacetonide, and a combination of betamethasone phosphate and acetate were given intra-articularly in different doses. Plasma levels of the steroids were measured and pharmacokinetic parameters were calculated. As a pharmacodynamic parameter for systemic steroid activity, plasma hydrocortisone levels were monitored for 3 weeks. Results indicate complete absorption from the site of injection over a period of 2 to 3 weeks. Because of its lower solubility, triamcinolone hexacetonide is absorbed slower than triamcinolone acetonide, thus maintaining synovial levels for a longer time and creating lower systemic corticoid levels. Endogenous hydrocortisone suppression correlated with exogenous steroid levels. Threshold concentrations for maximum suppression were determined.

HPLC determination of glucocorticoid alcohols, their phosphates and hydrocortisone in aqueous solutions and biological fluids

High-performance liquid chromatographic (HPLC) assays are described for the determination of dexamethasone phosphate, dexamethasone and hydrocortisone and for the determination of triamcinolone, triamcinolone acetonide, triamcinolone acetonide phosphate and hydrocortisone in aqueous solutions and biological fluids. These assays allow quantification of the glucocorticoids in plasma down to a concentration of 100 ng ml(-1) (dexamethasone phosphate 300 ng ml(-1), hydrocortisone 40 ng ml(-1)). During the development of optimum extraction procedures the pK(a) values of the esters were determined by extractions performed at different pH values. The stability in vitro of the phosphate esters in ampoules, plasma and blood was studied. The esters are stable in their formulated ampoules after long-term storage, whereas the half-life in vitro of dexamethasone phosphate in plasma at 37 degrees C is 5 h and that of triamcinolone acetonide phosphate is 3.5 h. Determination by HPLC of endogenous hydrocortisone in samples from patients who received either dexamethasone phosphate or triamcinolone acetonide phosphate gave results identical with those obtained by radio-immunoassay (RIA).

Pharmacokinetics of diclofenac sodium after intramuscular administration in combination with triamcinolone acetate

Seventy-five mg diclofenac sodium were given intramuscularly to 15 subjects alone and in combination with 40 mg triamcinolone acetate. Plasma levels of diclofenac were measured and pharmacokinetic parameters were calculated. The results indicate no statistically significant differences for most of the parameters. The maximum plasma concentrations (Cpmax) was increased by about 20% in combination with the glucocorticoid, whereas terminal elimination rate did not change significantly.

Pharmacokinetics of prednisolone after high doses of prednisolone hemisuccinate

Prednisolone in the form of its hemisuccinate was given intravenously in two different doses (1200 mg and 75 mg). Plasma levels of the ester and prednisolone were measured and pharmacokinetic parameters were calculated. The results indicate a dose-dependency in the pharmacokinetics of both hemisuccinate and the free alcohol. For the high dose 8 per cent of the administered ester was found unchanged in the urine indicating incomplete conversion of the pro-drug. Comparison with previous studies leads to the conclusion that prednisolone shows doubled non-linear pharmacokinetics with higher total body clearance in the medium dose range than in the low and high dose range. Volume of distribution changes accordingly, but overall elimination rate remains remarkably constant. Saliva levels of prednisolone were low and agree reasonably well with calculated plasma concentrations of free, non-protein-bound prednisolone. No prednisolone hemisuccinate was found in saliva.

Kinetics of methylprednisolone and its hemisuccinate ester

Methylprednisolone in the form of its hemisuccinate ester was injected intravenously in doses of 10 mg/kg and 63.1 mg. Plasma levels of methylprednisolone and of the ester were measured and their kinetics were calculated. Results indicate dose dependency in the kinetics of both. About 10% of the dose was excreted unchanged as hemisuccinate in the urine, indicating incomplete conversion of the prodrug. When methylprednisolone (80 mg) was also taken by mouth, the relative bioavailability of the tablets was 99%. Saliva levels of methylprednisolone were low but paralleled plasma levels in the postdistribution phase. No methylprednisolone hemisuccinate was found in saliva.

Pharmacokinetics of triamcinolone acetonide and its phosphate ester

Triamcinolone acetonide in the form of its phosphate ester was given intravenously in two different doses (10 mg/kg and 80 mg). Plasma levels of the ester and triamcinolone acetonide were measured and pharmacokinetic parameters were calculated. The pharmacokinetics both of the phosphate and the free alcohol were dose-dependent. No unchanged ester was found in the urine, indicating complete conversion of the pro-drug. Triamcinolone was not a major metabolite of triamcinolone acetonide in humans. Renal clearance was low and independent of the dose. Only about 1% of the dose was found in the urine as triamcinolone acetonide.

Simultaneous determination of glucocorticoid alcohols, their succinates and hydrocortisone in plasma

A reversed-phase high-performance liquid chromatographic (HPLC) assay is described for the simultaneous determination of methylprednisolone, methylprednisolone-21-hemisuccinate and endogenous hydrocortisone in biological fluids. This assay is also applicable to the determination of prednisolone-21-hemisuccinate in the presence of prednisolone and hydrocortisone in biological fluids. Prednisolone and hydrocortisone are determined by normal-phase HPLC. The stability of hemisuccinate esters in ampoules, in saline and in plasma has been studied. Whereas the esters were stable in saline at 37 degrees C, they were considerably hydrolysed in plasma at the same temperature. Comparison of hydrocortisone levels obtained by HPLC and radioimmunoassay (RIA) showed the large influence of the cross-reactivity of methylprednisolone and hydrocortisone in the presence of high serum concentrations of methylprednisolone.

Identification of glucocorticoid receptors in normal and neoplastic adult human lung

A dexamethasone-binding protein was detected in cytosol of five normal and three neoplastic lung tissue samples. The apparent dissociation constant of the dexamethasone protein complex ranged from 5.8 to 21 nM (11.4 +/- 5.7 nM for normal tissue cytosol, 12.1 +/- 7.7 nM for the neoplastic tissue cytosol). The binding protein sedimented at 8 S in sucrose density gradient at low ionic strength and showed a high specificity for glucocorticoids. It was concluded that the dexamethasone-binding protein had the characteristics of a glucocorticoid receptor. The glucocorticoid receptor content was determined to be 12-77 fmol/mg protein (37.1 +/- 18.9 fmol/mg protein for the normal tissue cytosol, 51.9 +/- 23.9 fmol/mg protein for the neoplastic tissue cytosol).

[Age dependence of carbohydrate tolerance and insulin secretion (author's transl)]

In 81 healthy male volunteers with normal blood pressure, normal body weight of different age (18-58 years) an intravenous glucose tolerance test with determination of blood sugar and serum insulin levels was done. Furthermore triglycerids and total cholesterol serum levels were measured. The investigations have shown: 1. With increasing age - independent from relative body weight - a highly significant decrease of glucose tolerance controlled by means of k-value according to Conard is to be measured. 2. With increasing age significant decrease of insulinsecretion after intravenous application of glucose is to be measured. Basal serum insulin levels do not significant change with increasing age. 3. With increasing age significant increase of total cholesterol serum level is to be measured, whereas triglycerid serum levels do not change. 4. Because of the significant negative correlation between k-value and total cholesterol discussion is done, that disturbances in fat metabolism are able to lead to a further deteriosation of glucoseutilisation. The investigations have shown, that the diminished glucose tolerance with increasing age is mainly related to an insufficient function of the beta-cell with increasing age.

[Clinical and pharmacologic aspects of various betamethasone crystalline suspensions]

The commercially available betamethasone suspensions for injection used in this study have clearly shown quantitative differences in the combination of their easily hydrosoluble betamethasone esters and those difficult to dissolve in water, as well as in the shapes and sizes of their crystals. With regard to their influence on the endogenous cortisol production the two preparations have shown a highly deviating pharmaco-dynamic duration of action-corresponding to their different galenic composition (betamethasone phosphate/acetate approx. 7-8 days; betamethasone phosphate/dipropionate approx. 16-18 days). During the phase of suppression the reduced endogenous cortisol is largely compensated by the pharmaco-dynamic activity of the exogenous steroid.

Effect of progesterone on RNA and protein synthesis in the rat uterus

The effect of gestagenic compounds on the oestrogen induced nucleic acid and protein synthesis of the rat uterus after castration was investigated. Progesterone causes an inhibition of 3H-uridine incorporation into uterine RNA. The inhibitory effect is strongest when progesterone is administered within 1 hour before isotope labelling. Evaluation of the free labelled nucleotides shows that this effect is not achieved by a blockade of permeability at the cell membrane or by reduction of the phosphorylation process. As a result of this progesterone-induced inhibition, protein synthesis is also reduced.

These results are discussed with regard to the modifying effect of progesterone on oestrogen dependent functions in the uterus.