Dose dependent pharmacokinetics of prednisone and prednisolone in man

Relative and absolute bioavailability of prednisone and prednisolone after separate oral and intravenous doses

A randomized, four-way cross-over study was conducted in eight healthy male volunteers to determine the relative and absolute bioavailability of prednisone (PN) and prednisolone (PL). PN and PL were administered as single, oral 10-mg tablet doses and as 10-mg zero-order 0.5-hour intravenous infusions. Comparable mean PN and PL maximum plasma concentrations (Cmax), times for Cmax, areas under the plasma concentration-time curves (AUC), and apparent elimination rate constants between tablet treatments demonstrated that PN and PL tablets were bioequivalent. Absolute bioavailability (F) determinations based on plasma PL concentrations were independent of which IV treatment was used as reference and indicated complete systemic availability of PL from both PN and PL tablets. However, F based on plasma PN data was contradictory. Using IV PN as reference, approximately 70% systemic availability was observed from both tablets, whereas using IV PL as reference, systemic availability was greater than unity. PN and PL are model compounds that exemplify the difficulties involved in accurately determining the relative and absolute bioavailability of substances that undergo reversible metabolism.

Corticosteroid therapy in adolescent patients

Since their introduction in the 1950s, corticosteroids have become an important adjunct in the therapy for a wide variety of diseases. Improved guidelines for clinical applications and for reduction in undesirable effects have been achieved through a better understanding of corticosteroid mechanisms of action and pharmacokinetic properties. This discussion will review the indications and adverse effects associated with corticosteroid therapy. Emphasis will be placed on the important aspects of corticosteroid therapy in adolescent patients including recent advances essential to the development of guidelines for dosing and therapeutic monitoring.

The determination of essential clearance, volume, and residence time parameters of recirculating metabolic systems: the reversible metabolism of methylprednisolone and methylprednisone in rabbits

Methods based on moment analysis are described which permit the calculation of the fundamental parameters of reversible drug/metabolite systems. These parameters include the four essential clearances of reversible and irreversible elimination, the central and steady-state distributional volumes, and the sojourn times or turnover rates of the metabolic pair. Additional parameters unique to interconversion systems are developed which describe the properties of metabolic entrapment ("recycled fraction"), conservation ("exposure enhancement"), and equilibrium resulting from reversible metabolism ("Percent parent drug at steady-state"). Parameters obtained by these methods are compared to those generated by conventional mammillary analysis. The influence of perturbation of essential parameters on the response of mammillary descriptors and the state of the interconversion system are simulated. The interconversion analysis is applied to disposition data for methylprednisolone and methylprednisone in the rabbit. Mammillary methods underestimate the metabolic clearance of these two steroids by 30%, while steroid turnover is underestimated by 100%. The steady-state volumes of distribution of the two steroids are overestimated by 10 and 61%. Additional literature data for disposition of several corticosteroids in various species and disease states are reanalyzed. Examination of cortisol/cortisone disposition in thyroid disorders reveals that mammillary methods detect the overall acceleration of steroid elimination in hyperthyroidism, but fail to reveal a 50% reduction in metabolite backconversion and decreased metabolic cycling. These moment analysis methods should facilitate characterization of the pharmacokinetics of the increasing array of reversible drug/metabolite systems.

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.

6 alpha-Methylprednisolone and 6 alpha-methylprednisone plasma protein binding in humans and rabbits

The binding of 6 alpha-methylprednisolone and 6 alpha-methylprednisone to proteins of rabbit and human plasma was studied in vitro by equilibrium dialysis. Steroid binding was determined using radiolabeled compounds and HPLC analysis methods. Both methods produced equivalent results. Plasma protein binding of 6 alpha-methylprednisolone and 6 alpha-methylprednisone averaged 75-82% and was independent of steroid concentration, suggestive of low affinity, nonspecific protein binding. A positive linear correlation of the log octanol-water partition coefficient with the nonspecific binding affinities of a homologous series of steroids, including 6 alpha-methylprednisolone and 6 alpha-methylprednisone, was demonstrated. This correlation suggests that hydrophobic binding is a major determinant of nonspecific steroid-protein interactions.

Effect of liver function on the metabolism of prednisone and prednisolone in humans

The systemic availability of total prednisone and unbound prednisolone, and the urinary excretion of 6 beta-hydroxyprednisolone, were measured after an oral dose of prednisone and an i.v. dose of prednisolone in 22 patients covering a wide range of liver function (galactose elimination capacity ranging from 3.3 mg/min X kg body wt to 9.2 mg/min X kg body wt). The area under the plasma concentration versus time curves of prednisolone and of prednisone decreased with increasing galactose elimination capacity. This dependency of the steroid concentrations on liver function was attributed to a decreased metabolic clearance and not to an increased systemic availability of the steroid given p.o. in patients with impaired liver function. The fractional excretion and the fractional clearance of 6 beta-hydroxyprednisolone declined with decreasing metabolic clearance rate of prednisolone or with decreasing galactose elimination capacity. Thus, the enzymes involved in the 6 beta-hydroxylation are not spared as liver function declines, and the exposure to the biologically active unbound prednisolone is increased in patients with impaired liver function in relation to the amount of prednisone or prednisolone administered.

Pharmacokinetic study in a phase I trial with an alkylating agent, diacetyldianhydrogalactitol (DADAG)

Diacetyldianhydrogalactitol (DADAG), a new alkylating hexitol derivative, was given in 30-min infusions for 5 consecutive days or as a single high-dose administration. The parent drug was eliminated in a biphasic manner, with a terminal half-life of 30-40 h. Dianhydrogalactitol (DAG), the main, pharmacologically active metabolite, appeared after a lag time of about 0.2-0.6 h. Its peak concentration was reached 1-2 h after termination of the infusion. The terminal elimination of DAG followed that of the parent compound. During the 5-day schedule slight accumulation was observed, and the plasma concentrations of both compounds approached the steady state. Over a dose range of 75-1050 mg/m2 the daily mean plasma concentrations of DADAG increased by only about 3-4 times. Dose-dependent expansions of the distribution volumes of the drug (Vc, V lambda, Vss) were observed. The behavior of DADAG and DAG in the body could be adequately described by a three-compartment open model. After equilibration the plasma levels of the parent compound and its metabolite were determined by the rate of return of DADAG from the peripheral compartment and its conversion to DAG.

Methylprednisolone versus prednisolone pharmacokinetics in relation to dose in adults

The disposition and plasma binding of methylprednisolone were examined in seven normal volunteers following the administration of 5, 20 and 40 mg of intravenous methylprednisolone sodium succinate. Methylprednisolone exhibits linear plasma protein binding averaging 77%. The mean plasma methylprednisolone clearance of 337 ml X h-1 X kg-1 was independent of dose. The steroid appears to moderately distribute into tissue spaces with a mean volume of distribution of 1.41 X kg-1. Methylprednisolone disposition parameters were compared with the non-transcortin bound parameters for prednisolone. The prednisolone plasma clearance based on the transcortin free-drug is similar to methylprednisolone total plasma clearance. However, the corrected volume of distribution of prednisolone is only one-half that of methylprednisolone. The disposition rate of these two steroids is thus similar, in spite of their metabolic control by different enzymatic pathways and major influence of saturable transcortin binding on prednisolone elimination.

Fluocortolone: pharmacokinetics and effect on plasma cortisol level

The pharmacokinetics of fluocortolone and its effect on plasma cortisol levels are described after oral administration of 20, 50 and 100 mg to 9 healthy adults. The concentrations of fluocortolone and cortisol in plasma were measured simultaneously by HPLC with UV detection. Fluocortolone was rapidly absorbed after all doses, giving the maximum plasma level after 1.4-2.1 h. After ingestion of 20, 50 and 100 mg, the peak levels were 199, 419 and 812 ng/ml, respectively. The maximum plasma levels and areas under the plasma level-time curves increased in proportion to the dose. Post-maximum plasma levels declined monoexponentially with a half-life of 1.76 h. Plasma half-life (t1/2 = 1.76 h), volume of distribution (1.03 l/kg) and oral clearance (6.9 ml/min/kg) were independent of the dose. The intensity and duration of adrenal suppression was dose dependent. Maximum suppression was observed 8 hours after fluocortolone. Clearcut suppression of cortisol levels after 24 hours was only seen following 100 mg fluocortolone.

The non-linear pharmacokinetics of prednisone and prednisolone. I. Theoretical

Three simple linear and three simple non-linear pharmacokinetic models are presented which incorporate the reversible metabolism that occurs between prednisone and prednisolone. Under steady-state conditions it is possible to not only distinguish between the linear and non-linear models but also to determine which particular model of each group applies to a given set of data. While the non-linear conversion of prednisolone to prednisone is important in explaining the pharmacokinetics of prednisone in all three non-linear models, the same is not true for prednisolone.

Prednisolone excretion in human milk

Six lactating women receiving long-term treatment with prednisolone in doses from 10 to 80 mg/day were studied. Serum and milk samples were assayed for prednisolone and endogenous cortisol by a specific high-performance liquid chromatographic method. The milk and serum concentrations vs time curves for prednisolone were virtually parallel, and the milk concentrations were 5% to 25% of those in serum. The milk/serum concentration ratio increased with increasing serum concentration. At a daily dose of 80 mg prednisolone, the infant would ingest less than 0.1% of that dose; this corresponds to less than 10% of the infant's endogenous cortisol production. Because there is an equilibrium between the concentration of prednisolone in milk and serum, the exposure of the infant is minimized if breast-feeding is avoided during the first 4 hours after the dose. We conclude that from a quantitative point of view the exposure of the infant is minimal, and breast-feeding may be permitted at maternal prednisolone doses of at least 20 mg once or twice daily. At higher doses, exposure may be minimized if nursing is performed greater than 4 hours after the dose.

Prednisolone pharmacokinetics in cushingoid and non-cushingoid kidney transplant patients

Prednisolone pharmacokinetics and protein binding have been compared in 16 cushingoid and 46 non-cushingoid long-term kidney transplant recipients. After oral administration of 10 mg prednisolone, the cushingoid patients had a significantly higher peak prednisolone serum concentration (P less than 0.03), a longer elimination half-time (P less than 0.03), and a larger area under the time-concentration curve of total (P less than 0.01) and free (P less than 0.03) prednisolone. The apparent total body clearance of total and free prednisolone was significantly lower in the cushingoid than in the non-cushingoid patients (P less than 0.02 and less than 0.05, respectively). There was no significant difference in time of peak concentration, apparent volume of distribution or serum protein binding of prednisolone. It is suggested that the development and persistency of some cushingoid features may be related to a decreased total body clearance of prednisolone, which, in turn, may be influenced by impaired renal function.

Nasal bioavailability and systemic effects of the glucocorticoid budesonide in man

Budesonide, a topically potent glucocorticoid, was administered to 4 healthy volunteers by i.v. infusion and by nasal instillation of 100 micrograms tritium-labelled drug. Plasma was analyzed by liquid chromatography plus scintillation counting of collected fractions. After i.v. administration the plasma clearance was 0.921/min and the apparent volume of distribution was 2.81/kg. After nasal administration, the time to reach the peak plasma level was approximately 30 min, and the systemic availability was 102%. Budesonide had marginal effects on plasma cortisol and white blood cell counts either after i.v. or nasal administration. Thus, nasally instilled budesonide in solution is rapidly and completely absorbed from the nasal mucosa. The systemic effects after this clinically recommended nasal dose were negligible.

Effect of dose on the pharmacokinetics of levonorgestrel in the rat during the rapid elimination phase following subcutaneous administration

Adult female rats were given a single, subcutaneous injection of 8, 16 or 32 micrograms of levonorgestrel (LNG). Blood samples were collected at various time intervals and serum concentrations of LNG were determined by radioimmunoassay. The patterns of temporal decline in LNG concentrations in the three dose groups indicated that the pharmacokinetics of LNG during the post-absorptive, rapid-elimination (beta) phase in the rat may be dose-dependent. Half-life, Co and AUC increased with the dose and -beta decreased as the dose increased. Mathematical relationships have been presented which can be used to predict the four parameters as well as concentrations of LNG at any given time after subcutaneous administration during the beta-phase for a given dose in the range of 8-32 micrograms. Significance of dose-dependent pharmacokinetic studies is discussed.

Metabolism of [14C]carbon tetrachloride to exhaled, excreted and bound metabolites. Dose-response, time-course and pharmacokinetics

Fasted male rats were given six doses of 14CCl4 ranging from non-hepatotoxic (0.1 mmole/kg) to severely hepatotoxic (26 mmoles/kg). Time-course and pharmacokinetics of CCl4, 14CO2 and CHCl3 elimination by exhalation were monitored by measuring amounts recovered in breath during discrete 15-min intervals for 8-12 hr. Amounts of 14C-labeled metabolite recovered bound to liver macromolecules at 24 hr and excreted in urine or feces for 24 hr were also determined. Comparison pharmacokinetic studies were done with 14CHCl3 and Na(2)14CO3. After all doses of 14CCl4, the major metabolite was CO2, twenty to thirty times less metabolite was recovered bound to liver macromolecules, and intermediate amounts of metabolite were excreted in urine and feces. CHCl3 was the least abundant metabolite at low CCl4 doses, but the second most abundant at high doses. Stronger associations were found between the magnitude of liver injury at 24 hr (quantitated as serum glutamate-pyruvate transaminase activity) and the extent or rate of CCl4 metabolism by pathways leading to CO2 and CHCl3 than by pathways leading to 14C-metabolites bound in liver or excreted in urine. Time-course and pharmacokinetic data indicated that a major pathway of CCl4 metabolism leading to CO2 became impaired within 2 hr after administration of hepatotoxic doses of CCl4.

Representation and quantitation of the binding interaction between prednisone, prednisolone and corticosteroid binding globulin

The interaction between prednisone and prednisolone (0-500 ng ml-1) for binding sites on corticosteroid binding globulin (CBG) in rabbit plasma has been investigated. The fraction unbound of each steroid rose markedly with increasing concentration at low concentrations (250 ng ml-1), tending to a plateau (0.29 prednisone, 0.15 prednisolone) at the higher concentrations (250-500 ng ml-1), indicating both saturation of CBG and the importance of binding to albumin in higher concentrations. A method is proposed of representing graphically the prednisone-prednisolone-protein interaction in three dimensions.

Plasma protein binding interaction of prednisone and prednisolone

The plasma protein binding interaction of prednisone and prednisolone were characterized by equilibrium dialysis. Prednisone and prednisolone are bound equally but weakly to human albumin (affinity constant, K approximately equal to 1 X 10(3) M-1). Transcortin affinity for prednisolone is 10-fold greater (51.3 X 10(6) M-1) than that for prednisone (4.3 X 10(6) M-1). In competition under pharmacologic conditions, prednisolone inhibits prednisone binding to transcortin producing linear binding averaging 55%. Prednisone does not affect prednisolone binding and does not complicate pharmacokinetic studies of the latter.

Fluid shifts and other factors affecting plasma protein binding of prednisolone by equilibrium dialysis

The effects of drug stability, radioactive tracer purity, buffer composition, protein concentration, and fluid shifts on the nonlinear plasma protein binding of prednisolone were examined by equilibrium dialysis. Prednisolone exhibits a concentration-dependent degradation; however, the limited extent of this does not affect protein binding. Impure tritiated prednisolone used as a tracer produces incorrect, low fractional binding values with the binding parameters generated for transcortin affected more than those for albumin. Isotonic sodium phosphate and Krebs original Ringer phosphate buffers yield similar fractional binding of prednisolone and identical protein binding parameters. Fractional binding of the steroid decreases with total plasma protein concentration, but the association constants remain constant over a twofold dilution of plasma proteins. Further dilution increases these parameters. A time-dependent colloidal osmotic fluid shift during dialysis causes dilution of plasma protein concentrations and diminished drug binding. Theoretical simulations show that the osmotic fluid shifts produce the largest changes in fractional binding for compounds that are bound by low-capacity proteins with low association constants (K less than 10(6) M-1). A mathematical equation was developed to correct bound drug concentrations and fraction bound for protein dilution caused by this effect. The fluid shifts can be prevented by the addition of dextran (mol. wt. 70,000) to the dialysis buffer in a concentration of 55% of the total protein concentration. Multiple factors can diminish the nonlinear prednisolone binding as artifacts during equilibrium dialysis, but the changes are relatively modest.

Alterations in prednisolone disposition as a result of oral contraceptive use and dose

The disposition of total and free prednisolone has been studied in eight female subjects who used combined oestrogen-progestogen oral contraceptives and in eight female subjects who did not, each of whom received separate intravenous doses of 0.1 mg/kg (low) and 1.0 mg/kg (high) of prednisolone. Mean free prednisolone clearance was reduced congruent to 30% in oral contraceptive users compared to control subjects (P less than 0.001), the difference being greater for the low dose (39%) than for the high dose (24%). Pre-dose plasma cortisol concentrations were elevated two-fold (P less than 0.001) in oral contraceptive users compared to control subjects. These effects are consistent with a mechanism in which the competitive inhibition of free prednisolone clearance by cortisol contributes to the reduction of free prednisolone clearance by oral contraceptive use. Mean total prednisolone clearance and steady state distribution volume showed an approximate two-fold dose dependent increase consistent with a similar increase in plasma prednisolone free fraction (P less than 0.001). Free prednisolone clearance showed an 18% dose dependent decrease (P less than 0.001) but free steady-state distribution volume did not change with dose. At plasma prednisolone concentrations less than 400 ng/ml, prednisolone free fractions at any prednisolone concentration were greater after the low, than after the high dose. This effect is consistent with the displacement of prednisolone by cortisol from transcortin but not from albumin.

The absence of effect of azathioprine on prednisolone pharmacokinetics following maintenance prednisone doses in kidney transplant patients

Kidney transplant patients receive chronic prednisone and azathioprine for immunosuppression. However, the effect of azathioprine on prednisolone pharmacokinetics has not been determined in this population. Total and unbound prednisolone concentrations were determined, using high performance liquid chromatography and equilibrium dialysis, in eight kidney transplant patients following their usual oral maintenance dose of prednisone alone and concomitantly with their usual dose of azathioprine. The results showed no significant differences between the two groups in estimates of prednisolone plasma protein binding parameters and peak time, peak concentration, mean input time, clearance/F, volume of distribution/F, or half-life (t 1/2), using total or unbound prednisolone concentrations. Thus, the concomitant administration of azathioprine does not appear to alter the bioavailability or elimination of prednisolone at these doses.

Alterations in prednisolone disposition as a result of time of administration, gender and dose

The disposition of total and free prednisolone has been studied in four male and four female volunteers, each of whom received an intravenous dose of 0.075 mg/kg (low) and 1.5 mg/kg (high) of prednisolone at both 06.00 h and 18.00 h. For the low dose, free prednisolone clearance was 14% lower (P = 0.012) and time-averaged prednisolone free fraction was 22% higher (P less than 0.001) in the morning, there being no circadian difference in total prednisolone clearance. There was no circadian differences in prednisolone disposition at the high dose. These findings are consistent with a mechanism in which cortisol causes a simultaneous competitive inhibition of prednisolone clearance and plasma protein binding at low, but not at high prednisolone doses. Prednisolone clearance was higher in female than in male subjects, the mean increase being 18% (P = 0.022) for total prednisolone and 21% (P = 0.036) for free prednisolone. Mean total prednisolone clearance and steady-state distribution volume were two-fold higher at the high vs the low dose (P less than 0.001), but free prednisolone clearance showed a dose dependent decrease of 11% (P = 0.019). There was no change in free prednisolone steady-state distribution volume.

Quantitative determination of dexamethasone in human plasma by stable isotope dilution mass spectrometry

An analytical method for the quantitation of nanogram to subnanogram amounts of dexamethasone is described. Dexamethasone was isolated from human plasma using a C18-bonded reverse-phase cartridge, purified by subsequent normal-phase HPLC, and the corresponding trimethylsilyl derivative analyzed by gas chromatography-mass spectrometry (GC-MS). The quantitation by isotope-dilution MS was carried out by selected-ion monitoring on the (M + 1)+ ion of the trimethylsilyl derivative of dexamethasone and its stable isotopically labeled diluent, [ 13C6 ,2H3]dexamethasone (681 and 690 m/z, respectively). Methane was used as the GC carrier gas and as the chemical-ionization reagent gas. The sensitivity of the method, judged from the lower limit of detection of the mass spectrometer, was at approximately 100 pg. The inter- and intraassay coefficients of variation (CV) determined at two different concentrations were 3.83 and 3.78% for 2 ng/mL and 2.64 and 1.29% for 5 ng/mL, respectively. Plasma concentration profiles for dexamethasone following a single 1-mg iv and a 2-mg oral dose of dexamethasone administered 24 h apart to two healthy volunteers are presented. The mass fragmentographic method described here is useful for bioavailability and pharmacokinetic studies of the synthetic glucocorticoid.

Altered plasma protein-binding of prednisolone in patients with the nephrotic syndrome

Prednisolone binds in plasma to both albumin and transcortin. Since altered concentrations of plasma proteins change capacity and association constants of the drug-protein complex and thus influence the disposition of the drug, the kinetics of prednisolone following oral prednisone and intravenous (IV) prednisolone were studied in ten nephrotic patients and in 12 healthy volunteers. Compared to normal volunteers, nephrotic patients had significantly higher mean (+/- SD) association constants for the albumin-prednisolone complex (4.20 +/- 2.10 X 10(3) M-1 v 2.26 +/- 0.46 X 10(3) M-1, P less than 0.005) and tended to have higher association constants for the transcortin-prednisolone complex. Following the IV administration of prednisolone and the oral administration of prednisone, nephrotic patients exhibited lower total plasma concentrations of prednisolone than did normal volunteers. The difference was attributable to lower albumin-bound and/or transcortin-bound, but not unbound, concentrations of prednisolone in plasma. The mean prednisolone bioavailability from oral prednisone was not different between nephrotic patients and controls. When calculated with reference to total prednisolone concentrations in plasma, the mean nonrenal clearance rate, but not the mean renal clearance rate, was higher in the nephrotic patients than in the controls (2.63 +/- 0.61 mL/min/kg v 1.85 +/- 0.33 mL/min/kg, P less than 0.005). Compared to normal volunteers, patients with the nephrotic syndrome had lower renal clearance rates of unbound prednisolone when prednisolone was given intravenously (1.58 +/- 0.88 mL/min/kg v 2.89 +/- 0.89 mL/min/kg, P less than 0.005) or when prednisone was given orally (1.18 +/- 0.86 mL/min/kg v 2.80 +/- 1.13 mL/min/kg, P less than 0.005). Nephrotic patients had lower ratios of unbound prednisolone clearance/creatinine clearance (fractional excretion) after IV prednisolone (1.50 +/- 0.81 v 2.27 +/- 0.49, P less than 0.025) or after oral prednisone (1.07 +/- 0.60 v 2.12 +/- 0.77, P less than 0.005) than the controls. Since these fractional excretion values of unbound prednisolone exceeded one, there must be glomerular filtration of prednisolone bound to plasma proteins and/or tubular secretion of prednisolone. This study indicates that the nephrotic dysproteinemia changes the binding of prednisolone to plasma proteins not only in point of quantity, but also in point of quality, and alters the disposition of prednisolone.

Disposition of total and unbound prednisolone in renal transplant patients receiving anticonvulsants

Kidney transplant patients receiving phenytoin or phenobarbital may have decreased graft survival. These drugs have been shown to enhance the metabolism of glucocorticoids. We determined the disposition of total and unbound prednisolone in six stable kidney transplant patients receiving prednisone for immunosuppression and phenytoin or phenobarbital for a seizure disorder. Six similar patients not on anticonvulsants served as controls. A single intravenous dose of prednisolone was administered, and plasma samples were analyzed for prednisolone using a high-performance liquid chromatographic assay. Equilibrium dialysis was used to determine unbound prednisolone concentrations. Pharmacokinetic analysis showed that the half-life of prednisolone was shorter in the anticonvulsant group compared to the controls, based on both total (2.3 +/- 0.4 vs. 3.4 +/- 0.2 hr (SD), P less than 0.01) and unbound (1.7 +/- 0.3 vs. 2.4 +/- 0.2 hr, P less than 0.01) concentrations. Total drug clearance was 10.4 +/- 2.8 liters/hr (0.171 +/- 0.087 liters/hr X kg) in the anticonvulsant group versus 7.2 +/- 1.2 liters/hr (0.100 +/- 0.014 liters/hr X kg) in the controls (P less than 0.05). Unbound prednisolone clearance was 57.2 +/- 12.1 versus 46.4 +/- 8.7 liters/hr (P greater than 0.05) and for weight-corrected estimates 0.886 +/- 0.224 liters/hr X kg versus 0.644 +/- 0.115 liters/hr X kg (P less than 0.05) in the two groups, respectively. Thus, the disposition of prednisolone is altered by anticonvulsants in kidney transplant patients and may require dose alteration.

Relationships between the pharmacokinetics of carbon tetrachloride conversion to carbon dioxide and chloroform and liver injury

Rate and extent of CCl4 metabolism by pathways leading to CO2 and CHCl3 were evaluated by measuring the amounts of these metabolites exhaled during discrete intervals following six different doses of CCl4. Pulmonary pharmacokinetics of 14CO2 and CHCl3 exhalation after CCl4 administration were compared with those after Na214CO3 and 14CHCl3 administration. Exhalation of 14CO2 metabolite declined more rapidly than expected after hepatotoxic doses of CCl4. This decline could be due to injury associated changes in the metabolism of CCl4.

Systemic bioavailability and pharmacokinetics of methylprednisolone in patients with rheumatoid arthritis following 'high-dose' pulse administration

The absolute and relative bioavailability of two methylprednisolone formulations (capsules and suspension) was determined along with its pharmacokinetics in four arthritic female patients, following an unconventional high-dose pulse of 1 g. Plasma concentrations of the drug were measured by a sensitive and specific high-performance liquid chromatographic (HPLC) procedure. The disposition of methylprednisolone from plasma following intravenous (i.v.) infusion of its succinate ester appeared monoexponential with a mean half-life of 2.4 h and an apparent volume of distribution (Vd) of 50 l (0.87 l/kg). The total body clearance (Cl) averaged 15.12 l/h. Absolute bioavailability was assessed by comparing the areas under the plasma concentration time curves (normalized to dose) following oral administration of capsule or suspension with those of intravenous administration. No significant difference (p greater than 0.2) was observed when systemic availability (f, expressed in per cent) following administration of drug in capsule (f = 49.35 per cent) was compared with that obtained following the administration of drug in a suspension (f = 58.26 per cent). The difference in the observed and predicted f may be due to incomplete absorption, hepatic and/or extrahepatic metabolism of methylprednisolone. Subjective evaluation showed no side effects of this high-dose pulse therapy in any of the patients.

Pharmacokinetics and protein binding of prednisolone after oral and intravenous administration

The pharmacokinetics of prednisolone after oral and intravenous administration of 10 and 20 mg have been studied. Serum protein binding of prednisolone was also measured after the i.v. injections. The bioavailability after oral administration was 84.5% after 10 mg and 77.6% after 20 mg (p greater than 0.05). Dose dependent pharmacokinetics were found, the VDss and Clt being significantly larger (p less than 0.01) after 20 mg i.v. than after 10 mg i.v. The protein binding of prednisolone in all subjects was non-linear, and is the most likely cause of the dose dependent pharmacokinetics, as there was no dose dependent variation in elimination half-time.

Prednisone and prednisolone bioavailability in renal transplant patients

Prednisone and prednisolone are drugs with the potential for therapeutic inequivalence due to bioavailability problems. The objective of our study was to compare the systemic bioavailability of prednisolone from oral prednisone and prednisolone. Nine kidney transplant patients receiving prednisone (12.5 to 22.5 mg per day) were administered, in a randomized fashion, the same dose of oral prednisone (Deltasone), oral prednisolone (Delta-cortef) and intravenous prednisolone (Hydeltrasol). Prednisolone and prednisone levels were measured using a specific high-pressure liquid chromatographic assay. Since prednisolone exhibits dose-dependent pharmacokinetics because of nonlinear plasma protein binding, bioavailability from oral prednisone and oral prednisolone, compared to the intravenous dose, was 84.5 +/- 17.8% and 95.5 +/- 17.6% using unbound drug concentrations. These differences were not statistically significant. Furthermore, no significant differences were observed between the two oral formulations in peak prednisolone levels, time of peak levels or half-life using either total or unbound drug concentrations. The results from our study indicate that both of the oral preparations tested provide similar bioavailability of active prednisolone and the conversion of prednisone to prednisolone occurs rapidly.

A single dose of azathioprine does not affect the pharmacokinetics of prednisolone following oral prednisone

Clinical and pharmacokinetic observations suggest that azathioprine may diminish the plasma level of prednisolone. To study the extent of this possible interaction, and to define the underlying mechanism, total and unbound prednisolone and total prednisolone concentrations were assessed in 11 subjects following an oral dose of prednisone once with and once without concomitant oral administration of azathioprine. Azathioprine did not affect the area under the plasma concentration-time curve of total and unbound prednisolone; furthermore, the interconversion of prednisone into prednisolone was not influenced by azathioprine.