Pharmacokinetics and pharmacodynamics of inhaled corticosteroids

There are significant differences in the pharmacokinetic properties of inhaled corticosteroids currently used in medical practice. All are rapidly cleared from the body but they show varying levels of oral bioavailability and more importantly variation in the rate of absorption after inhalation. Oral bioavailability is lowest for fluticasone propionate, indicating a low potential for unwanted systemic corticosteroid effects. Mathematical modeling has shown pulmonary residence times to be longest for fluticasone propionate and triamcinolone acetonide but shortest for budesonide and flunisolide. These properties appear to relate to pulmonary solubility, which appears to be the rate-limiting step in the absorption process.

Pharmacokinetic and pharmacodynamic evaluation of fluticasone propionate after inhaled administration

OBJECTIVE

To evaluate the pharmacokinetic and systemic pharmacodynamic properties of inhaled fluticasone propionate (FP).

METHODS

Single doses of 0.25, 0.5, 1.0 and 3.0 mg FP were administered to groups of six healthy subjects. Serum concentration profiles of FP were monitored over 24 h by means of high-performance liquid chromatography/mass spectrometry (HPLC/MS-MS). Systemic pharmacodynamic effects were evaluated by measuring endogenous serum cortisol and circulating white blood cells, and analyzed with previously developed integrated pharmacokinetic/pharmacodynamic (PK/PD) models.

RESULTS

FP showed a dose-independent terminal half-life with a mean (SD) of 6.0 (0.7) h. Maximum serum concentrations occurred 1.0 (0.5) h after administration, ranging from 90 pg.ml(-1) for the 0.25 mg dose to 400 pg.ml(-1) for the 3.0 mg dose. This, together with an estimated mean absorption time of nearly 5 h and a known oral bioavailability of less than 1%, indicates prolonged residence at and slow absorption from the lungs. In the investigated dose range, the cumulative systemic effect was dose-dependent for both markers of pharmacodynamic activity. For doses of 0.25, 0.50, 1.0 and 3.0 mg FP, the PK/PD-based cumulative systemic-effect parameters were 159, 186, 257 and 372% .h for lymphocyte suppression, 107, 186, 202 and 348% .h for granulocyte induction and 23.6%, 33.8%, 51.0% and 73.6% for cortisol reduction, respectively. The time courses of lymphocytes, granulocytes and endogenous cortisol could be sufficiently characterized with the applied PK/PD models. The measured in vivo EC50 values, 30 pg.ml(-1) and 7.3 pg.ml(-1) for white blood cells and cortisol, respectively, were in good agreement with predictions based on the in vitro relative receptor affinity of FP.

CONCLUSION

After inhalation, FP follows linear pharmacokinetics and exhibits dose-dependent systemic pharmacodynamic effects that can be described by PK/PD modeling.

Clinical PK/PD modelling as a tool in drug development of corticosteroids

Corticosteroids are used for the treatment of a variety of different diseases both locally and systemically. Most therapeutic effects result from glucocorticoid receptor-mediated events, and there seems to be no substance-specific difference in the post-receptor reaction cascade. Therefore, the extent and duration of glucocorticoid effects depend only on the availability of the respective steroid at the receptor site and its affinity to the receptor. This makes glucocorticoids an ideal candidate for PK/PD modelling. Availability at the receptor site is governed by pharmacokinetic parameters such as bioavailability, clearance, protein binding, and volume of distribution. The receptor affinity can easily be measured in vitro. A suitable indirect-response PK/PD model is presented that allows description of the receptor-mediated drug effects such as endogenous cortisol suppression as a function of time. Furthermore, this model allows prediction of the systemic activity of newly developed corticosteroids based on their pharmacokinetics and their respective receptor-binding affinity. The model can also be applied in order to study systemic steroid effects after topical administration or to investigate the effect of the time of dosing on cortisol suppression. Comparison of predictions based on this model and results from large clinical studies are in excellent agreement. Corticosteroids may represent an ideal class of drugs for the successful use of PK/PD modelling during drug development allowing to save time and expenses.

Pharmacokinetic/pharmacodynamic aspects of aerosol therapy using glucocorticoids as a model

Glucocorticoids are predominantly prescribed in asthma therapy as aerosols to achieve high pulmonary effects with reduced systemic spill-over and pronounced pulmonary selectivity. A variety of pharmacokinetic parameters are potentially important for determining pulmonary selectivity. The intent of this article, is to provide a practice-relevant theoretical approach to put the importance of these parameters on pulmonary targeting using pharmacokinetic/pharmacodynamic modeling as a tool in perspective. The applied pulmonary pharmacokinetic/pharmacodynamic model revealed that, in addition to recognized parameters such as systemic clearance, oral bioavailability, and efficiency of pulmonary deposition, other factors, such as the pulmonary release (dissolution) rate and dose, are relevant. However, the volume of distribution (for effect parameters not undergoing a diurnal rhythm) and the receptor affinity of a given glucocorticoid are not important for achieving lung targeting.

Pharmacokinetic/pharmacodynamic evaluation of systemic effects of flunisolide after inhalation

The pharmacokinetics and pharmacodynamics of flunisolide were studied in healthy volunteers after inhalation. In the morning on the day the study began, volunteers inhaled 0.5 mg of flunisolide with and without oral administration of charcoal, or 1 mg, 2 mg, and 3 mg of flunisolide with concomitant administration of charcoal. A placebo group was used to assess the endogenous cortisol, granulocyte, and lymphocyte baseline levels. Flunisolide plasma levels were determined by high-performance liquid chromatography using a tandem mass spectrometer as detector (HPLC/MS/MS). Cortisol plasma levels and differential white blood cell counts were obtained over 12 hours. An integrated pharmacokinetic/pharmacodynamic (PK/PD) model was applied to link the flunisolide plasma concentrations with the effects on lymphocytes, granulocytes, and cortisol. Maximum concentration levels of 3 to 9 ng/mL of flunisolide were observed after 0.2 to 0.3 hours for all of the investigated doses. The terminal half-life ranged from 1.3 to 1.7 hours. There was no statistical difference between treatments in the presence or absence of orally administered charcoal. The pharmacokinetic/pharmacodynamic (PK/PD) models satisfactorily described the time-courses of the effects on granulocytes, lymphocytes, and cortisol suppression. The resulting E50-values (concentrations to induce 50% of the maximum effect) concurred with the reported values of in vitro receptor binding affinities. The duration of the systemic effects were short because of the short half-life of the drug. Cumulative cortisol suppression increased with dose administration and ranged from 20% to 36%. The PK/PD simulations resulted in a smaller degree of cortisol suppression for the drug administered at 10 PM. The cumulative change from baseline was slightly smaller for the effects on granulocytes and lymphocytes than those on cortisol. This information promotes the comparison with other inhaled glucocorticoids.

Pharmacokinetics of methylprednisolone and prednisolone after single and multiple oral administration

The pharmacokinetics of methylprednisolone and prednisolone were evaluated in 24 healthy men after oral administration of single and multiple doses for 3 days. For each drug, 6 different administration regimens with doses ranging from 1 to 80-mg of methylprednisolone and 1.25 to 100-mg of prednisolone, and administration intervals ranging from 3 to 24 hours for both were investigated. Plasma was assayed using a normal phase high-performance liquid chromatography (HPLC) method. Methylprednisolone showed linear pharmacokinetics with no apparent dose or time dependency. Prednisolone showed marked dose dependency with higher clearance and volume of distribution for higher doses. This can be explained by its saturable protein binding of plasma, because unbound clearance and unbound volume of distribution were not dose-dependent. After multiple administration, prednisolone showed significant time-dependent pharmacokinetics with increased unbound clearance and increased unbound volume of distribution. Due to the complicated pharmacokinetic properties of prednisolone, it is extremely difficult to determine the dose needed to obtain a desired target concentration. The pharmacokinetics of methylprednisolone are more predictable because methylprednisolone concentrations are proportional to dose, and no determination of plasma protein binding is needed.

Dependency of cortisol suppression on the administration time of inhaled corticosteroids

Endogenous cortisol suppression is one of the major systemic side effects of inhaled corticosteroids in the treatment of asthma. A previously developed pharmacokinetic/ pharmacodynamic approach was used to evaluate the influence of administration time on the cumulative cortisol suppression (CCS) after single doses of the inhaled corticosteroids flunisolide and fluticasone propionate. Administration time-dependent simulations of CCS were performed with drug-specific pharmacokinetic and pharmacodynamic parameters obtained from previous clinical trials. Both drugs showed similar diurnal variation in CCS, dependent on the administration time, with maximum suppression when administered in the early morning at approximately 3 AM. The optimum administration time for minimized CCS was in the afternoon but was shifted from 3 PM for fluticasone propionate to later time points around 7 PM for flunisolide, probably because of the shorter terminal elimination half-life of flunisolide. Regarding peak to trough fluctuation, however, CCS after fluticasone propionate showed only half the administration time dependency as after flunisolide. Therefore, the ratio between CCS after flunisolide and after fluticasone propionate also followed administration time-dependent variations. This led to the conclusion that administration time has to be considered as a pivotal influential factor in clinical studies comparing CCS among different inhaled corticosteroids.

Dynamic modeling of cortisol reduction after inhaled administration of fluticasone propionate

Fluticasone propionate (FP) is a new corticosteroid that has been developed for the treatment of asthma. The compound has a very high receptor affinity, 18 times that of dexamethasone. After inhalation, FP is systemically available because of inhaled bioavailability. In healthy subjects this may lead to measurable systemic effects, such as cortisol reduction. A clinical study was conducted in 12 healthy volunteers to determine the systemic effects after inhaled administration of single 500-micrograms, 1,000-micrograms, and 2,000-micrograms doses of FP. Blood samples were collected over a 24-hour period after administration. Concentrations of FP and cortisol were measured in plasma by immunoassay. Cortisol reduction was chosen as the pharmacodynamic parameter. A novel linear release rate model was used to parameterize the cortisol data. The pharmacokinetics of FP were linear over the dose range studied. The cortisol release parameters were determined from baseline data (before drug administration). Based on these results, the E50 values for cortisol reduction were then determined for each dose of FP. The average E50 was 0.134 ng/mL for total FP concentrations and 0.013 ng/mL for unbound FP concentrations; these results were not dose dependent. These in vivo pharmacodynamic values measured in healthy subjects are in good agreement with the relatively high receptor affinity of FP.

Pharmacokinetics and pharmacodynamics of cloprednol

The pharmacokinetics and pharmacodynamics of cloprednol after oral administration in doses of 2.5 to 15 mg to healthy volunteers were determined. The half-life of cloprednol ranged from 1.8 h to 2.7 h, the oral clearance (CL/F) was determined to be 15-22 l/h. Since cloprednol shows nonlinear plasma protein binding, the plasma concentrations were converted to their free, unbound concentrations for the PK/PD-analysis. Due to this nonlinearity, the half-life of free, unbound cloprednol was shorter than that of the total drug. For the assessment of pharmacodynamics, differential white blood cell counts were obtained over 24 hours. An integrated pharmacokinetic-pharmacodynamic (PK/PD) approach using a modified Emax-model was applied to link unbound corticosteroid concentrations to the effect on lymphocytes and granulocytes. The E50 value for unbound cloprednol ranged from 3.6 to 4.7 ng/ml and 1.2 to 4.6 ng/ml for granulocytes and lymphocytes, respectively. The PK/PD model allowed a good prediction of the observed effects and was consistent with reported values for glucocorticoid receptor binding affinities for cloprednol.

Pharmacokinetic interaction between endogenous cortisol and exogenous corticosteroids

A problem in the evaluation of pharmacokinetic interactions between prednisolone and cortisol is that both steroids bind to cortisol binding globulin (CBG) and albumin. The binding of both steroids to CBG is saturable in the therapeutic concentration range. General drug binding equations were applied to two drugs and two binding sites and two implicit cubic equations were derived. These equations cannot be solved algebraically. However, the free concentration can be calculated using spreadsheet programs on a personal computer. A spreadsheet for these equations was developed using EXCEL 5.0 and its SOLVER option. Free concentrations of prednisolone and cortisol were determined as a function of total concentrations of both ligands. The simulations show that the protein binding of cortisol remains relatively constant in the physiological range but changes when exogenous corticosteroid is present. However, the degree of protein binding of exogenous corticosteroids that bind to CBG depends on the cortisol concentration which competes for binding sites. At the same time, the exogenous corticosteroid suppresses the release of endogenous cortisol. The presented approach is able to take all of these pharmacokinetic and pharmacodynamic interactions into account leading to a more accurate estimation of active free corticosteroid concentrations.

Pharmacokinetic/pharmacodynamic evaluation of deflazacort in comparison to methylprednisolone and prednisolone

PURPOSE

The pharmacokinetics and pharmacodynamics of deflazacort after oral administration (30 mg) to healthy volunteers were determined and compared with those of 20 mg of methylprednisolone and 25 mg of prednisolone.

METHODS

Methylprednisolone, prednisolone and the active metabolite of deflazacort, 21-desacetyldeflazacort, were measured in plasma using HPLC. For the assessment of pharmacodynamics, differential white blood cell counts were obtained over 24 hours. An integrated pharmacokinetic-pharmacodynamic (PK-PD) model was applied to link corticosteroid concentrations to the effect on lymphocytes and granulocytes.

RESULTS

Deflazacort is an inactive prodrug which is converted rapidly to the active metabolite 21-desacetyldeflazacort. Maximum concentrations of 21-desacetyldeflazacort averaged 116 ng/ml and were observed after 1.3 h. The average area under the curve was 280 ng/ml.h, and the terminal half-life was 1.3 h. 21-Desacetyldeflazacort was cleared significantly faster than both methylprednisolone and prednisolone. The PK-PD-model was suitable to describe time course and magnitude of the observed effects. The results were consistent with reported values for glucocorticoid receptor binding affinities for the investigated compounds.

CONCLUSIONS

Due to the short pharmacokinetic half-life of its active metabolite, pharmacodynamic effects of deflazacort are of shorter duration than those of methylprednisolone and prednisolone. The PK-PD model allows good prediction of pharmacodynamic effects based on pharmacokinetic and receptor binding data.

Pharmacokinetics of triamcinolone acetonide after intravenous, oral, and inhaled administration

The pharmacokinetics of triamcinolone acetonide were studied after intravenous (2 mg), oral (5 mg), and inhaled (2 mg) administration. Triamcinolone acetonide concentrations were measured in plasma by high-performance liquid chromatography/radioimmunoassay. After intravenous administration, triamcinolone acetonide was eliminated with a total body clearance of 37 L/h and a half-life of 2.0 hours. The volume of distribution was 103 L, and oral bioavailability averaged 23%. Absorption was rapid, achieving maximum triamcinolone acetonide levels of 10.5 ng/mL after 1 hour. After inhalation, bioavailability averaged 22% with maximum levels of 2.0 ng/mL observed after 2.1 hours. The resulting systemic levels for all three treatments caused a significant decrease in the number of lymphocytes in blood.

Receptor-based pharmacokinetic-pharmacodynamic analysis of corticosteroids

The pharmacodynamics of three corticosteroids were investigated after intravenous administration of the phosphate esters of methylprednisolone, dexamethasone, and triamcinolone acetonide to healthy subjects at 20, 50, and 80 mg as well as placebo. Twenty-two different pharmacodynamic parameters were followed as a function of time for 48 hours. Statistically significant effects of the glucocorticoids were an increase in blood glucose levels, a decrease in the number of lymphocytes, eosinophils, basophils, and monocytes, and an increase in the number of granulocytes and stab cells. For the most significant pharmacodynamic effects (lymphocytes, granulocytes, and glucose) a previously derived integrated pharmacokinetic/pharmacodynamic model using plasma concentrations, protein-binding data, and in vitro receptor-binding affinities was used to predict the pharmacodynamic effect-time profiles. Good agreement of predicted and measured effects was observed, confirming the validity of the model. The clinical significance of the model was demonstrated by comparison of model-predicted maintenance doses with empirically determined clinical equivalency doses.

A selective HPLC/RIA for dexamethasone and its prodrug dexamethasone-21-sulphobenzoate sodium in biological fluids

A combined high performance liquid chromatography/radioimmunoassay procedure is described for the simultaneous determination of dexamethasone (DEX) and its prodrug dexamethasone-21-sulphobenzoate sodium (DSS) in plasma. After precipitation of the plasma proteins by acetonitrile, the protein-free supernatant was injected onto a C18 reversed phase liquid chromatographic system and DSS- and DEX-containing fractions were collected. Hydrolysis of DSS by 0.01 N NaOH, followed by fractions extraction of both hydrolysed DSS and DEX fractions with ethyl acetate allowed the use of a dexamethasone-specific radioimmunoassay for the selective determination of both compounds. The method is accurate and reproducible (intraday variability for DSS and DEX < 6%, interday variability for DEX 14%), allowing quantification of DEX and DSS as low as 0.3 ng/mL and 0.7 ng/mL, respectively.

Pharmacokinetics and pharmacodynamics of prednisolone after intravenous and oral administration

The pharmacokinetics and pharmacodynamics of prednisolone were investigated according to four different routes of administration: 20 and 40 mg prednisolone orally in the morning, 20 mg prednisolone orally in the evening and 40 mg prednisolone intravenously in form of prednisolone phosphate in the morning. The plasma levels of prednisolone were followed using HPLC. To study the pharmacodynamics of prednisolone, glucose levels and various blood cell parameters such as erythrocytes, leukocytes, segmented neutrophilic granulocytes, eosinophils, basophils, monocytes and lymphocytes were followed. To summarize the data, the area under the effect-time-curve (AUCE) was calculated by the trapezoidal rule. The results show that the pharmacokinetics of prednisolone is dose-dependent (non-linear) and time-dependent. Prednisolone concentrations in plasma after a 20 mg and 40 mg dose are very similar, indicating that the pharmacokinetics of prednisolone are non-linear and dose-dependent with a higher clearance for higher concentrations. The comparison of 20 mg administered in the morning with the same dose given in the evening shows that the pharmacokinetics of prednisolone after oral administration of equal doses changes during the day with higher concentrations in the morning than in the evening. Furthermore, the results of the present study confirm the presence of pharmacodynamic corticosteroid effects on blood cell count and blood glucose. No statistically significant differences were observed for the four different treatments. In summary, it can be concluded that due to the complex pharmacokinetics of prednisolone, it is difficult to make accurate predictions of the expected effect-time relationships.

Pharmacokinetic/pharmacodynamic characteristics of the beta-2-agonists terbutaline, salbutamol and fenoterol

The clinical pharmacokinetics and pharmacokinetic/dynamic properties of the beta-adrenergic drugs fenoterol, salbutamol and terbutaline are reviewed. Sulfate conjugates are the main metabolites in man. The protein binding of these derivatives is rather weak with most pronounced binding observed e.g. fenoterol (40%). Disposition after parenteral administration shows a multi-exponential behavior for all the substances with linear but also stereo-selective pharmacokinetics. After parenteral administration, the drugs are mainly eliminated by renal processes while after oral administration a pronounced metabolic clearance (high first pass effect) is responsible for a low bioavailability, especially for fenoterol (2%). The total clearance for fenoterol is about twice that of salbutamol and terbutaline. Seven to 15% of the delivered aerosol reach typically the systemic circulation. In patients with respiratory disorders, pulmonary absorption is however highly dependent on the disease state. Pharmacokinetics in children do not significantly differ from adults when expressed per kg body weight. Patients with renal failure but not asthmatics show changed pharmacokinetic profiles. Only insignificant interactions with other drugs have been found. Pharmacokinetic/dynamic modeling approaches indicated that fenoterol is 25 times more active at the site of action than salbutamol and terbutaline, but all three drugs show similar bronchopulmonary selectivities. When the overall clinical activity, determined by pharmacokinetic and dynamic properties is compared, the activity gap is reduced: fenoterol (8) greater than salbutamol (2) greater than terbutaline (1). Differences in the first pass effect even inverse the pattern after oral administration. PK/PD modeling quantified the pulmonary effect after inhalation and suggested that the higher incidence of side effects for fenoterol might be linked to an overdosing problem. The application of PK/PD principles may improve the clinical usage and therapy of beta-2-adrenergic drugs.

Simultaneous Measurement of Cortisol in Serum and Saliva After Different Forms of Cortisol Administration

To prove the clinical usefulness of cortisol measurements in saliva for the exact assessment of a patient's corticoid status under therapeutic hormone substitution, we measured simultaneously total cortisol in serum and non-protein-bound cortisol in saliva after administration of different forms of hydrocortisone (cortisol) in eight cortisol-suppressed, healthy male volunteers. The intravenous and oral administration of 20 mg of cortisol exceeds the binding capacity of the corticosteroid-binding globulin (CBG), leading to an increase of the ratio between salivary and serum cortisol at the higher cortisol concentrations in blood. After rectal administration of 100 mg of cortisol acetate, the serum cortisol concentration does not exceed the binding capacity of CBG, so the ratio between salivary and serum cortisol remains nearly constant. However, this ratio was higher after rectal administration than after intravenous and oral administration, probably because of weaker binding of the acetate form of cortisol to CBG. Thus, the salivary measurement of the non-protein-bound (i.e., biologically active) cortisol offers a convenient way to monitor the effectiveness of various forms of systemic corticoid substitution.

Simultaneous measurement of cortisol in serum and saliva after different forms of cortisol administration

To prove the clinical usefulness of cortisol measurements in saliva for the exact assessment of a patient's corticoid status under therapeutic hormone substitution, we measured simultaneously total cortisol in serum and non-protein-bound cortisol in saliva after administration of different forms of hydrocortisone (cortisol) in eight cortisol-suppressed, healthy male volunteers. The intravenous and oral administration of 20 mg of cortisol exceeds the binding capacity of the corticosteroid-binding globulin (CBG), leading to an increase of the ratio between salivary and serum cortisol at the higher cortisol concentrations in blood. After rectal administration of 100 mg of cortisol acetate, the serum cortisol concentration does not exceed the binding capacity of CBG, so the ratio between salivary and serum cortisol remains nearly constant. However, this ratio was higher after rectal administration than after intravenous and oral administration, probably because of weaker binding of the acetate form of cortisol to CBG. Thus, the salivary measurement of the non-protein-bound (i.e., biologically active) cortisol offers a convenient way to monitor the effectiveness of various forms of systemic corticoid substitution.

Pharmacokinetic/dynamic correlation of pulmonary and cardiac effects of fenoterol in asthmatic patients after different routes of administration

Pulmonary and cardiac effects of the beta 2-adrenergic drug fenoterol were studied in 27 asthmatic patients using an integrated pharmacokinetic/dynamic (PK/PD) approach. Airway resistance (Rf), intrathoracic gas volume (IGV), heart rate, and plasma levels were monitored after placebo, injection (12.5 and 25 micrograms), nasal instillation (400 micrograms), inhalation (200 and 400 micrograms), and infusion (200 micrograms/180 min with or without loading dose). The pharmacokinetics were best described by an open three-compartment model with a terminal half-life of 200 min (gamma = 0.23 +/- 0.08 L/hr), a volume of distribution at steady state of 1.9 +/- 0.8 L/kg, and a clearance of 0.86 +/- 0.32 L/hr/kg, with 14 and 9% absorbed after nasal and pulmonary administration, respectively. For the noninhalation regimens, a PK/PD correlation linked the concentration in the shallow pharmacokinetic compartment to the investigated effects via an Emax relationship, resulting in three to five times higher EC50 values (concentration necessary to achieve half-maximal effect) for the heart rate than for the beta 2-mediated effects on IGV and Rf. In contrast, pulmonary effects after inhalation could not be incorporated into the correlation, indicating that these effects are induced locally after inhalation. Intrapatient variability for EC50 and Emax was approximately 90%.

Pharmacokinetics and rectal bioavailability of hydrocortisone acetate

The pharmacokinetics and bioavailability of hydrocortisone after rectal administration of a hydrocortisone acetate foam was determined. Endogenous hydrocortisone was suppressed by dexamethasone administration. Plasma levels were compared with those observed after iv and oral administration. Only a very small part of the rectal dose (100 mg) was absorbed; the mean absolute bioavailability was 2%. There was substantial intersubject variability. Maximum hydrocortisone levels were reached after 2 h and averaged 35 ng/mL. These levels were 10-fold lower than those obtained after oral administration of a fivefold lower dose (20 mg) of hydrocortisone in the same subjects.

Pharmacokinetics and oral bioavailability of hydrocortisone

The pharmacokinetics of 20 mg hydrocortisone were studied after IV and oral administration. Endogenous hydrocortisone was suppressed by dexamethasone administration. Hydrocortisone concentrations were measured in plasma and saliva. After IV administration, hydrocortisone was eliminated with a total body clearance of 18 L/hr and a half-life of 1.7 hr. The volume of distribution was 34 L. Oral bioavailability averaged 96%. Absorption was rapid, achieving maximum hydrocortisone levels of 300 ng/mL after 1 hour. Saliva levels were not proportional to plasma levels, but could be shown to reflect free, non-protein bound hydrocortisone concentrations in plasma.

Pharmacodynamics of methylprednisolone phosphate after single intravenous administration to healthy volunteers

The pharmacokinetics and pharmacodynamics of methylprednisolone were investigated after intravenous administration of methylprednisolone phosphate to healthy subjects at seven different doses (16 to 1000 mg). Forty different pharmacodynamic parameters were followed for 1 week. The pharmacodynamic data were analyzed as a function of time as well as cumulative effects in form of the areas under the effect-time curves. Statistically significant dose-dependent effects of methylprednisolone were observed for 15 pharmacodynamic parameters. Highly significant (P less than or equal to 0.0001) effects were increases in glucose levels, number of white blood cells, and segmented granulocytes as well as a decrease in the number of lymphocytes. For these pharmacodynamic effects an integrated pharmacokinetic/pharmacodynamic model was derived that translates the methylprednisolone plasma concentration-time profiles into effect-time profiles. This model allows prediction of pharmacodynamic effects for any single dose in the range studied at any time point.