Dose-dependent pharmacokinetics of prednisolone in normal and adrenalectomized rats

The pharmacokinetics of prednisolone after 5- and 50-mg/kg doses given as the sodium succinate salt was examined in normal and adrenalectomized rats. Prednisolone, prednisone, and corticosterone concentrations in plasma were determined by HPLC and free prednisolone measured by equilibrium dialysis. Prednisolone sodium succinate was rapidly and completely hydrolyzed to prednisolone as indicated by the absence of the ester from plasma within 5 min after intravenous injection. Prednisolone was rapidly metabolized to prednisone, while corticosterone concentrations in normal rats declined rapidly and were undetectable by 1 hr. Adrenalectomy had no effect on the disposition and protein binding of prednisolone. Dose, however, had a marked effect on prednisolone pharmacokinetics, with mean plasma clearance decreasing from 6.18 to 3.07 L/h per kg and mean steady-state volume of distribution decreasing from 2.14 to 1.05 L/kg from the lower to higher steroid dose. Half-life (0.50 hr) and mean residence time (0.35 hr) were unaffected by dose. Prednisolone plasma protein binding was nonlinear due to saturation of transcortin binding. Changes in pharmacokinetic parameters were not related to the nonlinear plasma binding, but were more likely caused by saturation of elimination pathways and tissue binding sites.     

A Pharmacokinetic/Pharmacodynamic Approach to Predict Total Prednisolone Concentrations in Human Plasma

Prednisolone and prednisone are two widely used corticosteroids for various inflammatory and immune diseases. Prednisolone is the active form of prednisone in vivo. Total prednisolone in plasma exhibits nonlinear pharmacokinetics mainly due to its nonlinear protein binding. Other factors such as reversible metabolism (or interconversion between prednisolone and prednisone), competitive protein binding from endogenous cortisol, cortisol circadian rhythm, and prednisolone mediated cortisol suppression complicate prednisolone pharmacokinetics. This study was aimed to develop a new approach to describe the nonlinear pharmacokinetics of total prednisolone and predict total prednisolone concentrations in plasma. Based on literature datasets, a linear two-compartment pharmacokinetic model was developed to adequately describe the reversible metabolism between free prednisone and prednisolone. Cortisol and prednisolone protein binding were described via the sum of a Langmuir and linear type binding. The endogenous cortisol circadian rhythm and cortisol suppression during prednisone or prednisolone exposure were described with a previously reported linear release rate pharmacokinetic/pharmacodynamic (PK/PD) model. By combining the pharmacokinetic models for free prednisone and prednisolone, the linear release rate model for cortisol suppression, and competitive protein binding between cortisol and prednisolone, we were able to predict total prednisolone concentrations in plasma. The predicted total prednisolone concentrations in plasma were in good agreement with the literature reported data. Thus, this PK/PD approach shows that the combination of nonlinear protein binding, cortisol circadian rhythm, and cortisol suppression could account for the nonlinearity of total prednisolone. In addition, it also allows a valid prediction of total prednisolone in plasma after either prednisone or prednisolone administration.     

The nonlinear pharmacokinetics of prednisone and prednisolone. II. Plasma protein binding of prednisone and prednisolone in rabbit and human plasma

The protein binding characteristics of prednisone and prednisolone were determined in human and rabbit plasma and in a 4.7 per cent human serum albumin (HSA) solution. The influence of prednisolone on prednisone binding in human plasma was also examined. Prednisolone exhibited nonlinear binding and prednisone linear binding characteristics in both human and rabbit plasma. Prednisone binding was not influenced by the presence of prednisolone. Prednisone binding to HSA was linear but to a degree substantially lower than observed in human plasma, suggesting the possibility that prednisone binds to other proteins in human plasma. The results support the hypothesis that the protein binding characteristics of prednisone and prednisolone do not explain the reported nonlinear pharmacokinetics of prednisone.     

Dose dependent pharmacokinetics of prednisone and prednisolone in man

Six healthy male volunteers were given 5, 20, and 50 mg of oral prednisone and 5, 20, and 40 mg doses of intravenous prednisolone. Plasma and urine concentrations of prednisone and prednisolone were determined by HPLC, and the binding of prednisolone to plasma proteins was measured by radioisotopic and equilibrium dialysis techniques. The pharmacokinetics of both oral prednisone and intravenous prednisolone were dose-dependent. The mean oral dose plasma clearances of prednisone ranged from 572 ml/min/ 1.73 m ² for the 5mg dose to 2271 ml/min/1.73 m ² for the 50 mg dose. Changes in prednisone half-life were insignificant, but increases in the half-life of its metabolite were dose-dependent. The systemic plasma clearance of i.v. prednisolone was dose-dependent and increased from 111 to 194 ml/min/1.73 m ² over the 5 to 40 mg i.v. dosage range. The steady-state volume of distribution also increased, but little change in mean transit time and half-life was found. The binding of prednisolone to plasma proteins was markedly concentration-dependent, and a two compartment, nonlinear equation was used to characterize the effective binding of prednisolone to transcortin and albumin. The apparent pharmacokinetic parameters of protein-free and transcortin-free prednisolone were relatively constant with dose. The interconversion of prednisone and prednisolone varied with time and dose, although prednisolone concentrations dominated by 4-to 10-fold over prednisone. In urine, 2–5% of either administered drug was excreted as prednisone and 11–24% as prednisolone. The apparent renal clearances of both steroids were also nonlinear and unrelated to protein binding. These studies indicate that the pharmacokinetics of prednisone and prednisolone are dose-dependent and that protein binding does not fully explain their apparent nonlinear distribution and disposition.This work was supported in part by Grant 24211 from the National Institutes of General Medical Sciences, National Institutes of Health.     

Pharmacokinetic and pharmacodynamic interactions between dehydroepiandrosterone and prednisolone in the rat

The effects of multiple-dosing with dehydroepiandrosterone sulfate (DHEA-SO4) on the pharmacokinetics and pharmacodynamics of prednisolone were examined. Prednisolone (25 mg/kg i.v.) was administered to male and female Sprague-Dawley rats (250-350 g) alone and following DHEA-SO4 (4 mg/kg i.v., every 8 h for 4 days). Male control rats cleared prednisolone faster [3.68 +/- 1.30 (males) vs 1.01 +/- 0.7 l/h/kg; p < 0.05] and had larger Vss (1.38 +/- 0.459 vs 0.394 +/- 0.500 l/kg; p < 0.05) than females both due largely to lesser plasma protein binding. Prednisolone clearance and Vss were not altered by DHEA-SO4 in males or females. The net effect of prednisolone on basophils and plasma corticosterone did not differ with gender. DHEA-SO4 had no effect on plasma corticosterone and did not alter prednisolone action. DHEA-SO4 inhibited basophil trafficking in males, but to a lesser extent than prednisolone, and antagonized the effect of prednisolone on basophil trafficking in both sexes. The steroid-sparing effect observed with DHEA clinically may not be due to an alteration of corticosteroid pharmacokinetics but partly to its ability to affect immune functions.     

Nonlinear pharmacokinetics and interconversion of prednisolone and prednisone in rats

The pharmacokinetics of prednisolone and prednisone were examined in 32 rats at four intravenous doses (5, 10, 25, and 50 mg/kg). Each rat was given one dose of either intravenous prednisolone or prednisone, and plasma concentrations of both compounds were measured by HPLC. Mammillary moment analysis showed the apparent clearance and volume of distribution of prednisolone and the apparent clearance of prednisone to be dose-dependent. Further diagnostic analysis using a linear interconversion model revealed modest interconversion between the two steroids and at least two saturable clearance processes: the conversion of prednisolone to prednisone and the irreversible elimination of prednisone. A comprehensive model which incorporates the nonlinear clearances of prednisolone and prednisone plus the additional feature of nonlinear tissue distribution of prednisolone was then constructed. Four differential equations describing the rate of change of each steroid in each compartment were used to numerically fit by nonlinear least squares analysis all plasma concentration-time profiles simultaneously. The final estimates from the full model only partly agreed with the results from the two moment analyses but confirmed the general structure of the model. The nonlinear tissue distribution of prednisolone was reinforced by assay of muscle tissue. This study demonstrates the utility of the model-building process where simpler models yield insights into more elaborate schemes with complex nonlinear features.     

High-pressure liquid chromatographic evaluation of aqueous vehicles for preparation of prednisolone and prednisone liquid dosage forms.

A high-pressure liquid chromatographic method was developed that separates prednisolone from prednisone, prednisone from methylprednisolone succinate sodium, and hydrocortisone from hydrocortisone acetate or cortisone acetate. The common liquid dosage preservatives methylparaben, propylparaben, and sodium benzoate do not interfere with quantitative prednisolone, prednisone, and hydrocortisone determinations. The method was used to study prednisolone and prednisone stability in five aqueous vehicles (water, citrate buffer USP, 50% glycerin, 50% sorbitol, and 50% sucrose) containing 10% (v/v) ethanol. Prednisone crystallized out in all vehicles except glycerin, in which it appeared to be stable for at least 92 days. Prednisolone did not crystallize in any vehicle but decomposed quickly in citrate buffer. Sorbitol and glycerin appeared to be the best vehicles for prednisolone. The developed method was applied successfully to the quantitative determinations of prednisolone, prednisone, and hydrocortisone in commercial tablets.     

Nonlinear pharmacokinetics and interconversion of prednisolone and prednisone in rats

The pharmacokinetics of prednisolone and prednisone were examined in 32 rats at four intravenous doses (5, 10, 25, and 50 mg/kg). Each rat was given one dose of either intravenous prednisolone or prednisone, and plasma concentrations of both compounds were measured by HPLC. Mammillary moment analysis showed the apparent clearance and volume of distribution of prednisolone and the apparent clearance of prednisone to be dose-dependent. Further diagnostic analysis using a linear interconversion model revealed modest interconversion between the two steroids and at least two saturable clearance processes: the conversion of prednisolone to prednisone and the irreversible elimination of prednisone. A comprehensive model which incorporates the nonlinear clearances of prednisolone and prednisone plus the additional feature of nonlinear tissue distribution of prednisolone was then constructed. Four differential equations describing the rate of change of each steroid in each compartment were used to numerically fit by nonlinear least squares analysis all plasma concentration-time profiles simultaneously. The final estimates from the full model only partly agreed with the results from the two moment analyses but confirmed the general structure of the model. The nonlinear tissue distribution of prednisolone was reinforced by assay of muscle tissue. This study demonstrates the utility of the model-building process where simpler models yield insights into more elaborate schemes with complex nonlinear features.Supported in part by grant No. 41037 from the National Institute of General Medical Sciences, National Institutes of Health and by a fellowship for M.-L. H. from Smith Kline & French Laboratories.     

A Pharmacokinetic Comparison of Two Oral Liquid Glucocorticoid Formulations

To compare pharmacokinetics of liquid prednisolone and prednisone solutions and to assess relative bioavailability, six healthy adult men were administered 15 mg of each formulation. Blood samples were obtained and assayed for plasma prednisolone concentrations by high-performance liquid chromatography. Peak concentration was significantly higher with liquid prednisolone (mean ± SD 430.3 ± 62.5 vs 333.0 ± 27.8 ng/ml, p=0.013), with similar times to peak concentration. Prednisolone liquid gave higher concentrations at every time point (statistically significant for all except 0.25 hrs after the dose), resulting in a significantly greater total area under the curve (2029.8 ± 246.9 vs 1633.3 ± 221.1 ng/ml•hour, respectively, p=0.002). Clearance was slower for prednisolone (128.3 ± 15.1 vs 149.1 ± 17.6 ml/min/1.73 m², p=0.01), and the relative bioavailability of the prednisolone liquid using prednisone liquid as the reference standard was 116 ± 14%. Thus, prednisolone liquid has similar pharmacokinetic characteristics as prednisone liquid, with improved bioavailability.     

Effect of smoking on prednisone,prednisolone, and dexamethasone pharmacokinetics

The pharmacokinetics of oral prednisone and oral dexamethasone were examined in 18 healthy male adults. Eight subjects also received intravenous prednisolone and intravenous dexamethasone. Half of each group were cigarette smokers as confirmed by plasma thiocyanate concentrations. Plasma and urine concentrations of prednisone and prednisolone were assayed by high performance liquid chromatography, while plasma dexamethasone was measured by radioimmunoassay. There were no statistically significant differences between smokers and nonsmokers in the systemic availability of prednisolone (75 versus 84%), oral dose clearance of prednisone (29 versus 27 ml/min/kg), systemic prednisolone clearance (2.8 versus 2.9 ml/min/kg), or in the interconversion rates, volumes of distribution, or urinary recoveries of prednisone and prednisolone. Similarly, the pharmacokinetics of dexamethasone were unaffected by smoking. A limited correlation (r=0.55) was found between the high oral dose clearances of prednisone and the lower values of dexamethasone (6.73 and 5.71 ml/min/kg in smokers and nonsmokers). A two- to threefold variability occurred in oral dose clearances of each steroid with partial intrasubject covariance. Unlike the anticonvulsants, which markedly induce corticosteroid metabolism, smoking has no effect on their pharmacokinetics and should not complicate therapy with these drugs.This work was supported in part by Grant 1079 from The Council for Tobacco Research and by Grant 24211 from The National Institutes of General Medical Sciences. National Institutes of Health.     

Plasma protein binding of prednisolone in normal volunteers and arthritic patients

Summary The plasma binding of prednisolone was studied in twenty normal volunteers and twenty rheumatoid arthritis patients. An in vitro assessment of the binding following the addition of prednisolone, prednisone, and hydrocortisone to the plasmas obtained from the subjects showed significant differences in the percentage of prednisolone bound. However, the differences observed were regarded as clinically insignificant. The plasma protein binding was determined by an in vitro equilibrium dialysis of the individual plasma samples at 37° C. Prednisolone levels on both sides of the dialysis membrane were determined using radioactivity and HPLC analytical methodologies. The percentages of prednisolone bound calculated from the analytical results of either the radiochemical or HPLC method were not significantly different. The change in the percentage of prednisolone bound to plasma proteins was studied as a function of the total prednisolone plasma concentration in a normal volunteer and in a systemic lupus erythematosis patient. As a result of prednisolone binding to both transcortin and albumin, the binding of prednisolone changes as a function of prednisolone concentration. The binding data were fitted using nonlinear least squares regression, and the affinity constants for the binding of prednisolone to transcortin and albumin were estimated.     

Pharmacokinetics of prednisone and prednisolone at steady state in the rabbit

A range (approximately 0.2-2.0 micrograms/min/kg) of constant rate iv infusions of prednisolone (as the phosphate ester) was administered to five rabbits either singly or as two consecutive infusions, and then again at about the same rates of infusion as part of multiple infusion studies. Prednisone (as the succinate) was also infused at three different infusion rates (range, 1.5-15 micrograms/min/kg) to four of the five rabbits. Plasma concentrations of prednisolone and prednisone at steady state were measured by HPLC. The binding of prednisone and prednisolone in plasma was measured by equilibrium dialysis. The multiple infusion studies demonstrated that the nonlinearity in plasma clearance of prednisolone could not be attributed to any time-dependent effect. The average plasma clearance of prednisolone increased by 250% when its rate of infusion was increased 10-fold. The ranges of clearance values at low and high rates of infusion were 2.51-4.08 and 6.08-10.98 ml/min/kg, respectively. The binding of prednisolone in plasma was found to be concentration dependent. At the lower rates of infusions, the clearance of unbound prednisolone appeared to increase on increasing its rate of infusion but remained relatively constant thereafter (greater than 1.0 microgram/min/kg). The ranges of unbound plasma prednisolone clearance at low and high rates of infusions were 30.3-67.7 and 50.6-110.2 ml/min/kg, respectively. The percentage of unbound prednisone increased on increasing the total plasma prednisone concentration (ranges at low and high concentrations of prednisone were 15.5-33.7 and 32.3-47.6%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Receptor-mediated prednisolone pharmacodynamics in rats: model verification using a dose-sparing regimen

Our receptor/gene-mediated model of corticosteroid action was tested and extended by examining the pharmacokinetics/dynamics of multiple low doses vs. a single higher dose of intravenously administered prednisolone in adrenalectomized male Wistar rats. Low-dose rats received 3 bolus doses (5 mg/kg) of prednisolone at 0, 0.5 and 1.0 hr. High-dose animals were given a single 25 mg/kg dose of prednisolone. Both regimens were expected to produce equivalent net responses based on model predictions. Control rats were not dosed. The profiles of free hepatic cytosolic glucocorticoid receptors and the hepatic tyrosine aminotransferase (TAT) enzyme were examined. Plasma prednisolone concentrations showed bi-exponential decline for both doses using pooled animal data. Clearance of total plasma prednisolone was 4.16 and 3.21 L/hr per kg in low- and high-dose groups. Volume of distribution at steady state (approximately 1.50 L/kg) and central volume (approximately 0.6 L/kg) were similar for both groups. Receptor levels from 5-16 hr stabilized at 64% of the 0-hr control value. Receptor and TAT profiles were essentially superimposable for both dosing groups. Our previous model was used to simultaneously describe prednisolone plasma concentrations, hepatic receptors, and TAT activity. The ability of total plasma prednisolone (Cp), corticosteroid binding globulin (CBG)-free plasma prednisolone (CCBG), and free plasma prednisolone (CF) to describe the kinetics/dynamics were examined. The CF values produced optimum fitting of all receptor data. The similarity of the two dosing groups supports the view that appropriately timed doses of a steroid can be used in an optimally efficacious manner by first filling all receptor sites and then replacing steroid as receptors are expected to recycle from nuclear/DNA binding sites as the steroid is eliminated.     

Effect of the anti-inflammatory agent tenidap on the pharmacokinetics and pharmacodynamics of prednisolone.

The effect of tenidap, a new nonsteroidal anti-inflammatory agent, on the pharmacokinetics and pharmacodynamics of prednisolone was studied in healthy male subjects. In a randomized crossover study, 12 subjects received either tenidap sodium 120 mg daily or placebo orally for 28 days. On day 21, each subject received a single dose of either 0.8 mg/kg oral prednisone or 0.66 mg/kg intravenous prednisolone followed by the other steroid on day 28. Blood and urine samples were collected, and the pharmacokinetic parameters of prednisone and prednisolone were determined in each treatment period. Pretreatment with tenidap did not cause any significant changes in the overall disposition of prednisone or prednisolone. For example, for free prednisolone, the intravenous area under concentration was 1,144 +/- 195 ng.h/mL and 1,244 +/- 140 ng.h/mL, and the systemic availability after oral prednisone was 53 +/- 10% and 51 +/- 12% with placebo and tenidap, respectively. The renal clearance of prednisolone was significantly reduced after tenidap pretreatment, however (from 143 to 77 mL/min/1.73 m2). The suppression of plasma cortisol and whole blood histamine levels were analyzed to evaluate the potential pharmacodynamic interactions between tenidap and prednisolone. There were no significant changes in the pharmacodynamic parameters between placebo and tenidap groups. The excretion of less than 20% of the dose of prednisolone in urine makes the overall effects of tenidap on prednisolone kinetics and dynamics of inconsequential clinical importance.     

Bioavailability and disposition of prednisone and prednisolone from prednisone tablets

The relative bioavailability of two 50 mg prednisone tablet formulations was determined in 18 healthy male volunteers who were not pretreated with dexamethasone. Plasma and urine samples were collected over a 24-h period and their concentrations of prednisone and prednisolone were assayed by a specific and sensitive high pressure liquid chromatography (HPLC) method. Bioavailability was assessed by comparing the areas under the plasma concentration-time curves and by the relative amounts of prednisone and prednisolone in urine. There were no significant differences between the bioavailability of the film-coated and standard 50 mg tablets. Eight subjects subsequently received a 40 mg equivalent intravenous dose of prednisolone as prednisolone succinate to provide plasma concentrations of prednisolone similar to concentrations found after oral doses of prednisone. The systemic bioavailability of prednisolone, the active metabolite generated from film-coated and standard prednisone tablets, was estimated to be 0·77±0·15 and 0·80±0·11, respectively. The nonlinear distribution, the interconversion, and the simultaneous elimination of these drugs, however, complicate any assessment of their relative and absolute bioavailability.     

Removal of prednisone and prednisolone by plasma exchange

The effect of plasma exchange on the pharmacokinetics of prednisone and prednisolone was studied. Two patients undergoing plasma exchange while receiving oral prednisone therapy were studied. Patient 1 received prednisone 50 mg daily; patient 2 received 60 mg daily. On a day when the patients were to undergo plasma exchange, blood samples for determination of prednisone and prednisolone concentrations were obtained just before the daily prednisone dose and at various times before, during, and after plasma exchange. The amount of both drugs in plasma removed by plasma exchange was also determined. On a day when the patients were not receiving plasma exchange therapy, additional blood samples were obtained just before the daily prednisone dose and at 0.5, 1, 2, 4, 6, and 8 hours after the dose. Values for elimination rate constant, half-life, area under the curve, clearance, and volume of distribution on and off plasma exchange were calculated from serum concentration-time curves for prednisone and prednisolone. Only prednisolone data proved adequate for pharmacokinetic calculations. Values of pharmacokinetic variables for prednisolone on and off plasma exchange did not differ substantially in either patient. The amount of combined prednisone and prednisolone removed by plasma exchange in each patient was less than 1% of the administered prednisone dose. In the two patients studied, changes in pharmacokinetic values for prednisolone attributable to plasma exchange and the amount of combined prednisone and prednisolone removed by plasma exchange were minimal. Supplemental dosing of prednisone following plasma exchange appears unnecessary.     

Endogenous and exogenous glucocorticoids in cushingoid patients

The pharmacokinetics of prednisone/prednisolone and the time-course of endogenous hydrocortisone were investigated in 15 stable renal transplant patients and 12 patients with oral mucocutaneous vesiculoerosive diseases. All 27 patients were given their usual prednisone dose orally on one occasion, and 24 were given an equivalent amount of prednisolone intravenously on another occasion. After dosing, 8-14 plasma samples were obtained for the determination of total prednisolone, prednisone, and hydrocortisone concentrations by high performance liquid chromatography and unbound prednisolone concentrations by equilibrium dialysis. The bioavailability of prednisone, the interconversion of prednisone into prednisolone, the total and unbound prednisolone clearances, the prednisolone binding capacity of albumin and transcortin, and the affinity of albumin for prednisolone were not different when the 14 patients without cushingoid side effects were compared with the 13 cushingoid patients. Patients with cushingoid side effects had a higher affinity constant for prednisolone binding to transcortin, more frequently exhibited peak hydrocortisone levels within the normal range, and more often had measurable (greater than 10 ng/ml) hydrocortisone in the plasma samples collected during the kinetic studies, as compared with those not showing side effects. The data suggest that endogenous hydrocortisone production is not as suppressed in patients with visible cushingoid signs as in noncushingoid patients and that no significant difference in the pharmacokinetics of exogenous glucocorticoids exists between patients with and without cushingoid side effects.     

Dose ranging pharmacokinetics and brain distribution of norfloxacin using microdialysis in rats

The purpose of this study was to investigate the effect of dose on norfloxacin pharmacokinetics and distribution into the brain extracellular fluid (ECF), in freely moving rats. Unbound concentrations of norfloxacin in hippocampus were determined by microdialysis after an i.v. bolus dose of 12.5, 25, 50, 100, or 150 mg/kg in rats. In vivo recovery of norfloxacin was determined by retrodialysis by calibrator. Among three fluoroquinolones (enoxacin, pefloxacin, and ciprofloxacin) selected as potential calibrators, ciprofloxacin was selected as the best one. Maximum ECF brain norfloxacin concentrations are rapidly obtained but the ECFbrain/plasma areas under curves (AUC) ratios are low and independent of dose with a mean value of 8.2 +/- 5.8%. By contrast, norfloxacin systemic pharmacokinetics was nonlinear, with total plasma clearance decreasing significantly from 23.0 +/- 3.4 to 14.4 +/- 3.8 mL/min/kg when dose increased from 12.5 to 150 mg/kg.     

Comparison of suppressive potency between prednisolone and prednisolone sodium succinate against mitogen-induced blastogenesis of human peripheral blood mononuclear cells in-vitro

Clinically, both prednisolone and prednisolone sodium succinate are widely used as immunosuppressive agents for the treatment of various allergic disorders. However, whether prednisolone sodium succinate itself has immunosuppressive or anti-inflammatory effects is unclear, and prednisolone sodium succinate may exhibit its efficacy only after hydrolytic conversion to prednisolone in-vivo. If this is the case, the impairment of prednisolone sodium succinate conversion to prednisolone in some clinical conditions may attenuate the efficacy of prednisolone sodium succinate. We therefore compared the pharmacological efficacy of prednisolone with that of prednisolone sodium succinate in-vitro using human peripheral blood mononuclear cells (PBMCs). PBMCs were obtained from 5 healthy subjects and 1 patient with pneumonia. The cells were incubated in the presence of concanavalin A and the cell growth was estimated by 3-(4,5-dimethyl thiazo-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Both prednisolone and prednisolone sodium succinate dose-dependently suppressed PBMC blastogenesis. Mean (s.d.) prednisolone and prednisolone sodium succinate IC50 (concentration of drug that gave 50% inhibition of cell growth) values were 580.0 (1037.9) and 3237.1 (4627.3) nM, respectively. The ratio of prednisolone IC50/prednisolone sodium succinate IC50 ranged from 0.005 to 0.230. Thus, prednisolone sodium succinate potency was markedly lower than that of prednisolone. After incubation of PBMCs with 100 microM prednisolone sodium succinate, 22.7-42.9 microM prednisolone was liberated into the culture medium, as determined by HPLC. The ratio of prednisolone liberation from prednisolone sodium succinate was not affected by the presence of fetal bovine serum or PBMC, or both, in the culture medium. These results suggested that the PBMC-suppressive effects of prednisolone sodium succinate might be due, at least partially, to prednisolone liberated from prednisolone sodium succinate into the culture medium. Prednisolone sodium succinate can be converted to prednisolone in the absence of serum or PBMCs, but the ratio of this conversion was very slow (t(1/2) > 4 days). Therefore, impairment of the enzymatic conversion of prednisolone sodium succinate to prednisolone in some pathological conditions such as liver diseases may result in attenuation of the clinical efficacy of prednisolone sodium succinate.     

The macromolecular binding of prednisone in plasma of healthy volunteers including pregnant women and oral contraceptive users

The macromolecular binding of prednisone has been studied in the plasma of eight healthy human volunteers. The subjects included two control males, two control females, two females taking estrogen-containing oral contraceptives, and two females in the third trimester of pregnancy. All volunteers exhibited the expected nonlinear plasma binding of prednisolone with free fraction increasing as the total prednisolone concentration was increased. Both the oral contraceptive and pregnant subjects had increased transcortin binding capacity over the control volunteers as evidenced by their increased binding of prednisolone. Prednisone macromolecular binding, however, was not altered by either changing total prednisone concentration or transcortin binding capacity. The mean prednisone free fraction was 0.250 +/- 0.027 in the eight subjects over the concentration range 0-2500 ng/ml. The addition of prednisolone in up to a 25-fold excess did not alter prednisone's free fraction. Prednisone apparently does not bind to transcortin with the same strong affinity that characterizes prednisolone's binding, and due to albumin's extensive binding capacity, prednisone macromolecular binding is not saturable over the pharmacological drug concentration range.