Pharmacokinetics and pharmacodynamic modeling of direct suppression effects of methylprednisolone on serum cortisol and blood histamine in human subjects

Fifty Years of Unraveling the Clinical Pharmacology of Corticosteroids

This review will highlight portions of Dr. William Jusko's and colleagues' work that affected the clinical use and study of corticosteroids in acute and chronic disease management. Selected publications related to corticosteroid pharmacokinetics and pharmacodynamics from the 1970s through today were included in this review, with a focus on the foundational human-based studies conducted in the 1970s-1990s. Dr. Jusko contributed significantly to early corticosteroid pharmacology across several domains including: 1) foundational corticosteroid pharmacokinetic methods and parameter development, 2) disease state-variation in corticosteroid pharmacokinetics, 3) drug interaction effects on corticosteroid pharmacokinetics, and 4) early corticosteroid pharmacodynamic studies. In an era where little was known about the pharmacokinetics and pharmacodynamics of corticosteroids, Dr. Jusko's work opened the eyes of researchers and clinicians to the potential for disease and drug interactions that could reduce or enhance the effects of corticosteroids. This significant body of work paved the way for alternative routes of administration that would be useful in concentrating the activity at the site of action and markedly reduced systemic drug exposure, minimizing the risk of adverse effects through application of the dose-sparing pharmacokinetic and pharmacodynamic principles.

Treating the Side Effects of Exogenous Glucocorticoids; Can We Separate the Good From the Bad?

It is estimated that 2% to 3% of the population are currently prescribed systemic or topical glucocorticoid treatment. The potent anti-inflammatory action of glucocorticoids to deliver therapeutic benefit is not in doubt. However, the side effects associated with their use, including central weight gain, hypertension, insulin resistance, type 2 diabetes (T2D), and osteoporosis, often collectively termed iatrogenic Cushing's syndrome, are associated with a significant health and economic burden. The precise cellular mechanisms underpinning the differential action of glucocorticoids to drive the desirable and undesirable effects are still not completely understood. Faced with the unmet clinical need to limit glucocorticoid-induced adverse effects alongside ensuring the preservation of anti-inflammatory actions, several strategies have been pursued. The coprescription of existing licensed drugs to treat incident adverse effects can be effective, but data examining the prevention of adverse effects are limited. Novel selective glucocorticoid receptor agonists and selective glucocorticoid receptor modulators have been designed that aim to specifically and selectively activate anti-inflammatory responses based upon their interaction with the glucocorticoid receptor. Several of these compounds are currently in clinical trials to evaluate their efficacy. More recently, strategies exploiting tissue-specific glucocorticoid metabolism through the isoforms of 11β-hydroxysteroid dehydrogenase has shown early potential, although data from clinical trials are limited. The aim of any treatment is to maximize benefit while minimizing risk, and within this review we define the adverse effect profile associated with glucocorticoid use and evaluate current and developing strategies that aim to limit side effects but preserve desirable therapeutic efficacy.

Harnessing Clinical Trial and Real-World Data Towards an Understanding of Sex Effects on Drug Pharmacokinetics, Pharmacodynamics and Efficacy

Increasing clinical data on sex-related differences in drug efficacy and toxicity has highlighted the importance of understanding the impact of sex on drug pharmacokinetics and pharmacodynamics. Intrinsic differences between males and females, such as different CYP enzyme activity, drug transporter expression or levels of sex hormones can all contribute to different responses to medications. However, most studies do not include sex-specific investigations, leading to lack of sex-disaggregated pharmacokinetic and pharmacodynamic data. Based available literature, the potential influence of sex on exposure-response relationship has not been fully explored for many drugs used in clinical practice, though population-based pharmacokinetic/pharmacodynamic modelling is well-placed to explore this effect. The aim of this review is to highlight existing knowledge gaps regarding the effect of sex on clinical outcomes, thereby proposing future research direction for the drugs with significant sex differences. Based on evaluated drugs encompassing all therapeutic areas, 25 drugs demonstrated a clinically meaningful sex differences in drug exposure (characterised by ≥ 50% change in drug exposure) and this altered PK was correlated with differential response.

Population pharmacodynamic modeling of intramuscular and oral dexamethasone and betamethasone effects on six biomarkers with circadian complexities in Indian women

Population pharmacokinetic/pharmacodynamic (PK/PD) analysis was performed for extensive data for differing dosage forms and routes for dexamethasone (DEX) and betamethasone (BET) in 48 healthy nonpregnant Indian women in a partial and complex cross-over design. Single doses of 6 mg dexamethasone phosphate (DEX-P), betamethasone phosphate (BET-P), or 1:1 mixture of betamethasone phosphate and acetate (BET-PA) were administered orally (PO) or intramuscularly (IM) where each woman enrolled in a two-period cross-over study. Plasma concentrations collected over 96 h were described with a two-compartment model with differing PO and IM first-order absorption inputs. Overall, BET exhibited slower clearance, similar volume of distribution, faster absorption, and longer persistence than DEX with BET acetate producing extremely slow absorption but full bioavailability of BET. Six biomarkers were assessed over a 24-h baseline period with four showing circadian rhythms with complex baselines. These baselines and the strong responses seen after drug dosing were fitted with various indirect response models using the Laplace estimation methods in NONMEM 7.4. Both the PK and six biomarker responses were well-described with modest variability likely due to the homogeneous ages, weights, and ethnicities of the women. The drugs either inhibited or stimulated the influx processes with some models requiring joint inclusion of drug effects on circadian cortisol suppression. The biomarkers and order of sensitivity (lowest IC₅₀/SC₅₀ to highest) were: cortisol, T-helper cells, basophils, glucose, neutrophils, and T-cytotoxic cells. DEX sensitivities were generally greater than BET with corresponding mean ratios for these biomarkers of 2.86, 1.27, 1.72, 1.27, 2.69, and 1.06. Overall, the longer PK (e.g. half-life) of BET, but lesser PD activity (e.g. higher IC₅₀), produces single-dose response profiles that appear quite similar, except for the extended effects from BET-PA. This comprehensive population modeling effort provides the first detailed comparison of the PK profiles and six biomarker responses of five commonly used dosage forms of DEX and BET in healthy women.

Transitioning from Basic toward Systems Pharmacodynamic Models: Lessons from Corticosteroids

Technology in bioanalysis, -omics, and computation have evolved over the past half century to allow for comprehensive assessments of the molecular to whole body pharmacology of diverse corticosteroids. Such studies have advanced pharmacokinetic and pharmacodynamic (PK/PD) concepts and models that often generalize across various classes of drugs. These models encompass the "pillars" of pharmacology, namely PK and target drug exposure, the mass-law interactions of drugs with receptors/targets, and the consequent turnover and homeostatic control of genes, biomarkers, physiologic responses, and disease symptoms. Pharmacokinetic methodology utilizes noncompartmental, compartmental, reversible, physiologic [full physiologically based pharmacokinetic (PBPK) and minimal PBPK], and target-mediated drug disposition models using a growing array of pharmacometric considerations and software. Basic PK/PD models have emerged (simple direct, biophase, slow receptor binding, indirect response, irreversible, turnover with inactivation, and transduction models) that place emphasis on parsimony, are mechanistic in nature, and serve as highly useful "top-down" methods of quantitating the actions of diverse drugs. These are often components of more complex quantitative systems pharmacology (QSP) models that explain the array of responses to various drugs, including corticosteroids. Progressively deeper mechanistic appreciation of PBPK, drug-target interactions, and systems physiology from the molecular (genomic, proteomic, metabolomic) to cellular to whole body levels provides the foundation for enhanced PK/PD to comprehensive QSP models. Our research based on cell, animal, clinical, and theoretical studies with corticosteroids have provided ideas and quantitative methods that have broadly advanced the fields of PK/PD and QSP modeling and illustrates the transition toward a global, systems understanding of actions of diverse drugs. SIGNIFICANCE STATEMENT: Over the past half century, pharmacokinetics (PK) and pharmacokinetics/pharmacodynamics (PK/PD) have evolved to provide an array of mechanism-based models that help quantitate the disposition and actions of most drugs. We describe how many basic PK and PK/PD model components were identified and often applied to the diverse properties of corticosteroids (CS). The CS have complications in disposition and a wide array of simple receptor-to complex gene-mediated actions in multiple organs. Continued assessments of such complexities have offered opportunities to develop models ranging from simple PK to enhanced PK/PD to quantitative systems pharmacology (QSP) that help explain therapeutic and adverse CS effects. Concurrent development of state-of-the-art PK, PK/PD, and QSP models are described alongside experimental studies that revealed diverse CS actions.

Population Pharmacokinetic/Pharmacodynamic Modeling of Methylprednisolone in Neonates Undergoing Cardiopulmonary Bypass

Methylprednisolone is used in neonates to modulate cardiopulmonary bypass (CPB)–induced inflammation, but optimal dosing and exposure are unknown. We used plasma methylprednisolone and interleukin (IL)‐6 and IL‐10 concentrations from neonates enrolled in a randomized trial comparing one vs. two doses of methylprednisolone to develop indirect response population pharmacokinetic/pharmacodynamic models characterizing the exposure–response relationships. We applied the models to simulate methylprednisolone dosages resulting in the desired IL‐6 and ‐10 exposures, known mediators of CPB‐induced inflammation. A total of 64 neonates (median weight 3.2 kg, range 2.2–4.3) contributed 290 plasma methylprednisolone concentrations (range 1.07–12,700 ng/mL) and IL‐6 (0–681 pg/mL) and IL‐10 (0.1–1125 pg/mL). Methylprednisolone plasma exposure following a single 10 mg/kg intravenous dose inhibited IL‐6 and stimulated IL‐10 production when compared with placebo. Higher (30 mg/kg) or more frequent (twice) dosing did not confer additional benefit. Clinical efficacy studies are needed to evaluate the effect of optimized dosing on outcomes.

Glucocorticoids dosing in obese subjects: A systematic review

Glucocorticoids (GCs) are amongst the most widely used and effective treatments to control inflammatory and autoimmune diseases. In obese subjects, drug dosing adjusted by body weight is problematic, all the more so as patients are at higher risk of GC metabolic side effects. We propose here to describe the determinants of drug pharmacokinetics (PK) in obese subjects and GC pharmacology, and to identify the existing PK studies that may help discussing the best size descriptor for GC dosing in obese subjects. A clinician and a pharmacist screened PubMed using the MeSH Terms: "glucocorticoids" OR "steroidal agents" AND "pharmacokinetics" AND "obesity" OR "overweight". The search was limited to the publications written in English language and to those performed in humans. A systematic search using the MeSH terms was performed until August 31st, 2017. Only three such PK studies have been published so far that compare dexamethasone, prednisolone and methylprednisolone in obese and normal weight subjects. The studies concur that GC partially distribute in the excess of body weight and that adjustment by total body weight (TBW) or by body weight (BW) excess would increase the initial plasma GC concentration after a loading dose and would thus be inappropriate. Contradictory results are observed regarding GC exposure or clearance according to the GC studied. Behind this overwhelming lack of conclusive evidence for adjusting GC by body weight, further PK studies are clearly needed for guiding their dosing. Furthermore, studies demonstrated an increased sensibility to GC, even when GC exposure was reduced, suggesting that adjustment by body weight may not only be unnecessary but also dangerous.

Population pharmacokinetic/pharmacodynamic modeling of histamine response measured by histamine iontophoresis laser Doppler

The epicutaneous histamine (EH) test is the current gold standard method for the clinical evaluation of allergic conditions. However, the EH method is limited in providing an objective and qualitative assessment of histamine pharmacodynamic response. The histamine iontophoresis with laser Doppler (HILD) monitoring method, an alternative method, allows a fixed dose of histamine to be delivered and provides an objective, continuous, and dynamic measurement of histamine epicutaneous response in children and adults. However, due to the high sampling frequency (up to 40 Hz), the output files are usually too cumbersome to be directly used for further analysis. In this study, we developed an averaging algorithm that efficiently reduces the HILD data in size. The reduced data was further analyzed and a population linked effect pharmacokinetic/pharmacodynamic (PK/PD) model was developed to describe the local histamine response. The model consisted of a one-compartment PK model and a direct-response fractional maximum effect (Emax) model. The parameter estimates were obtained as follows: absorption rate constant (ka), 0.094/min; absorption lag time (Tlag), 2.72 min; partitioning clearance from local depot to systemic circulation (CLpar), 0.0006 L/min; baseline effect (E0), 13.1 flux unit; Emax, 13.4; concentration at half maximum effect (EC50) 31.1 mg/L. Covariate analysis indicated that age and race had significant influence on Tlag and EC50, respectively.

A quantitative approach to analysing cortisol response in the horse

The cortisol response to glucocorticoid intervention has, in spite of several studies in horses, not been fully characterized with regard to the determinants of onset, intensity and duration of response. Therefore, dexamethasone and cortisol response data were collected in a study applying a constant rate infusion regimen of dexamethasone (0.17, 1.7 and 17 μg/kg) to six Standardbreds. Plasma was analysed for dexamethasone and cortisol concentrations using UHPLC-MS/MS. Dexamethasone displayed linear kinetics within the concentration range studied. A turnover model of oscillatory behaviour accurately mimicked cortisol data. The mean baseline concentration range was 34-57 μg/L, the fractional turnover rate 0.47-1.5 1/h, the amplitude parameter 6.8-24 μg/L, the maximum inhibitory capacity 0.77-0.97, the drug potency 6-65 ng/L and the sigmoidicity factor 0.7-30. This analysis provided a better understanding of the time course of the cortisol response in horses. This includes baseline variability within and between horses and determinants of the equilibrium concentration-response relationship. The analysis also challenged a protocol for a dexamethasone suppression test design and indicated future improvement to increase the predictability of the test.

Pharmacodynamics and tolerability of repository corticotropin injection in healthy human subjects: A comparison with intravenous methylprednisolone

Repository corticotropin injection (porcine adrenocorticotropic hormone [ACTH] analog) and intravenous methylprednisolone (IVMP) are used to treat inflammatory conditions such as multiple sclerosis (MS) exacerbations and rheumatoid arthritis. This multiple‐dose, randomized, crossover, open‐label study evaluated and compared pharmacodynamic outcomes in subjects who received ACTH analog (80 U subcutaneously) or IVMP (1 g) daily for 5 days. Specific outcome measures included IVMP and cortisol concentrations, total cortisol‐equivalent exposure, immune cell population changes, and tolerability. IVMP and ACTH analog increased granulocyte numbers and decreased lymphocyte counts; effects on both were significantly less pronounced with ACTH analog. Based on total cortisol‐equivalent exposure (assuming linearity), administration of 80 U of ACTH analog equates to 30 mg IVMP. Because IVMP doses significantly higher than 30 mg are usually required to treat MS exacerbations, the lower cortisol‐equivalent exposure of 80 U ACTH analog supports the hypothesis that efficacy of ACTH analog results from both steroid‐dependent and ‐independent properties. Adverse events were mild in severity; subject incidence for adverse‐event reporting was similar following both regimens. The clinical relevance of these findings in autoimmune disease populations is unknown and requires further evaluation.

Attenuation of acute plasma cortisol response in calves following intravenous sodium salicylate administration prior to castration

Pain associated with castration in cattle is an animal welfare concern in beef production. This study examined the effect of oral aspirin and intravenous (i.v.) sodium salicylate on acute plasma cortisol response following surgical castration. Twenty bulls, randomly assigned to the following groups, (i) uncastrated, untreated controls, (ii) castrated, untreated controls, (iii) 50 mg/kg sodium salicylate i.v. precastration and (iv) 50 mg/kg aspirin (acetylsalicylic acid) per os precastration, were blood sampled at 3, 10, 20, 30, 40, 50 min and 1, 1.5, 2, 4, 6, 8, 10 and 12 h postcastration. Samples were analyzed by competitive chemiluminescent immunoassay and fluorescence polarization immunoassay for cortisol and salicylate, respectively. Data were analyzed using noncompartmental analysis, a simple cosine model, anova and t-tests. Intravenous salicylate V(d(ss)) was 0.18 L/kg, Cl(B) was 3.36 mL/min/kg and t(1/2 lambda) was 0.63 h. Plasma salicylate concentrations above 25 microg/mL coincided with significant attenuation in peak cortisol concentrations (P = 0.029). Peak salicylate concentrations following oral aspirin administration was <10 microg/mL and failed to attenuate cortisol response. Once salicylate concentrations decreased below 5 microg/mL, cortisol response in the castrated groups was significantly higher than uncastrated controls (P = 0.018). These findings have implications for designing drug regimens to provide analgesia during routine animal husbandry procedures.

Reduced methylprednisolone clearance causing prolonged pharmacodynamics in a healthy subject was not associated with CYP3A5*3 allele or a change in diet composition

The influence of diet and genetics was investigated in a healthy white person who had distinctly low methylprednisolone clearance. Pharmacokinetic and pharmacodynamic parameter values were similar on 2 occasions during the consumption of a low-carbohydrate diet and a Weight Watchers diet, indicating that the decreased clearance was unlikely attributable to a change in diet composition. Although the subject was found to be homozygous for CYP3A5*3, genetic findings were not significant for a number of other CYP3A4 and CYP3A5 allelic variants. Because of the high prevalence of CYP3A5*3/*3 in whites and because 5 of 7 white control subjects are also homozygous for CYP3A5*3, this genotype cannot fully explain the reduced metabolism of the drug. Other genetic or contributing factors might have been involved. New polymerase chain reaction-based genotyping methods for functionally defective CYP3A5*6, *8, *9, and *10 alleles were developed in this study. These assays will be useful for CYP3A5 genotype analysis in future clinical studies.

Altered methylprednisolone pharmacodynamics in healthy subjects with histamine N-methyltransferase C314T genetic polymorphism

This study investigated the potential differences in methylprednisolone pharmacodynamics between healthy subjects with different histamine N-methyltransferase (HNMT) C314T genotypes. Six individuals with C/C genotype and 4 with C/T genotype were administered a single intravenous dose of methylprednisolone 0.6 mg/kg ideal body weight in a randomized 2-period manner. Methylprednisolone plasma concentrations were fitted with a 1-compartment model. Cortisol and whole blood histamine suppression were assessed by indirect response models, with circadian baseline cortisol analyzed by Fourier analysis. The area between the baseline and effect curve and the area under the effect versus time curve suppression ratio were used to characterize plasma histamine suppression. Methylprednisolone pharmacokinetics and plasma and whole blood histamine suppression were similar between the 2 genotype groups. Median nadir of cortisol and the 50% inhibitory concentration for cortisol were significantly higher in subjects with C/T genotype than those with C/C genotype (P=.031 and .033, respectively, Wilcoxon rank sum test). Subjects who are heterozygous for the T314 variant allele thus appeared less sensitive to the suppressive effects of methylprednisolone on cortisol secretion.

Pharmacokinetic-pharmacodynamic modelling: history and perspectives

A major goal in clinical pharmacology is the quantitative prediction of drug effects. The field of pharmacokinetic-pharmacodynamic (PK/PD) modelling has made many advances from the basic concept of the dose-response relationship to extended mechanism-based models. The purpose of this article is to review, from a historical perspective, the progression of the modelling of the concentration-response relationship from the first classic models developed in the mid-1960s to some of the more sophisticated current approaches. The emphasis is on general models describing key PD relationships, such as: simple models relating drug dose or concentration in plasma to effect, biophase distribution models and in particular effect compartment models, models for indirect mechanism of action that involve primarily the modulation of endogenous factors, models for cell trafficking and transduction systems. We show the evolution of tolerance and time-variant models, non- and semi-parametric models, and briefly discuss population PK/PD modelling, together with some example of more recent and complex pharmacodynamic models for control system and nonlinear HIV-1 dynamics. We also discuss some future possible directions for PK/PD modelling, report equations for general classes of novel semi-parametric models, as well as describing two new classes, additive or set-point, of regulatory, additive feedback models in their direct and indirect action variants.

Pharmacokinetics and pharmacodynamics of systemically administered glucocorticoids

Glucocorticoids have pleiotropic effects that are used to treat diverse diseases such as asthma, rheumatoid arthritis, systemic lupus erythematosus and acute kidney transplant rejection. The most commonly used systemic glucocorticoids are hydrocortisone, prednisolone, methylprednisolone and dexamethasone. These glucocorticoids have good oral bioavailability and are eliminated mainly by hepatic metabolism and renal excretion of the metabolites. Plasma concentrations follow a biexponential pattern. Two-compartment models are used after intravenous administration, but one-compartment models are sufficient after oral administration.The effects of glucocorticoids are mediated by genomic and possibly nongenomic mechanisms. Genomic mechanisms include activation of the cytosolic glucocorticoid receptor that leads to activation or repression of protein synthesis, including cytokines, chemokines, inflammatory enzymes and adhesion molecules. Thus, inflammation and immune response mechanisms may be modified. Nongenomic mechanisms might play an additional role in glucocorticoid pulse therapy. Clinical efficacy depends on glucocorticoid pharmacokinetics and pharmacodynamics. Pharmacokinetic parameters such as the elimination half-life, and pharmacodynamic parameters such as the concentration producing the half-maximal effect, determine the duration and intensity of glucocorticoid effects. The special contribution of either of these can be distinguished with pharmacokinetic/pharmacodynamic analysis. We performed simulations with a pharmacokinetic/pharmacodynamic model using T helper cell counts and endogenous cortisol as biomarkers for the effects of methylprednisolone. These simulations suggest that the clinical efficacy of low-dose glucocorticoid regimens might be increased with twice-daily glucocorticoid administration.

Population pharmacokinetics and pharmacodynamics of ciclesonide

Ciclesonide is a novel glucocorticoid that is converted into ciclesonide--active principle (CIC-AP) in the lung. The study objectives were to identify a structural model for population pharmacokinetic (PK) analysis of CIC-AP using nonlinear mixed-effects modeling, assess the influence of select covariates on PK and/or pharmacodynamic (PD) parameters, and investigate the effects of CIC-AP on endogenous cortisol. Pooled concentration data from nine phase I studies (dose: 400-3600 micrograms) involving healthy and asthmatic patients were included in the PK analysis. There were 151 subjects (3300 observations) for the CIC-AP population PK analysis. Various models examined inter- and intrasubject variability for the PK parameters. Population estimates of the PK parameters of clearance and volume of distribution were 396 L/h (64.8% co-efficient of variation [CV]) and 1190 L (41.2% CV), respectively. Pharmacodynamic population estimates included maximum cortisol release rate, 3140 ng/h (5.4% CV). The EC50 of CIC-AP was 0.88 ng/mL. Ciclesonide is a safe corticosteroid that causes negligible cortisol suppression. The disposition and effect of CIC-AP can be described using mixed-effect modeling. The estimated EC50 is similar to mean Cmax from an 800-micrograms dose, further suggesting CIC-AP has little effect on cortisol suppression.

Heparin and low molecular weight heparin: background and pharmacology

The various LMWHs available for therapeutic use have multiple mechanisms of action, most of which are similar to the mechanisms of UH. The relative potencies of expression of the mechanisms differ between LMWH and UH and among specific LMWHs. The pharmacokinetics of LMWHs and UH are often measured according to the results of anti-Xa assays, although the correlation between anti-Xa levels and the antithrombotic activities of the drugs is questionable. Animal models of thrombosis give some information regarding the antithrombotic efficacy of different LMWHs when compared with UH and with other LMWHs, but the results are not directly applicable to human thrombosis. Unfortunately, no single measure of antithrombosis has been developed in humans whereby the potencies of LMWHs, UH, and other new anticoagulants can be directly compared. Large clinical outcome studies are expensive and difficult to carry out. Perhaps for this reason, different subcutaneous LMWHs have not been compared with each other in this format. Various LMWHs have demonstrated equivalent efficacy and safety when compared with intravenous UH and high-dose subcutaneous UH, and it is reasonable to assume that there would not be large differences in efficacy and safety among different agents. The superiority of one subcutaneous regimen over another can be confirmed (or refuted) only by the performance of well-planned clinical studies.

Prednisolone pharmacokinetics and pharmacodynamics in relation to sex and race

Prednisolone pharmacokinetics (PK) and pharmacodynamics (PD) were investigated in relation to sex and race in white males, black males, white females, and black females (n = 8/group) after a single oral dose (0.27 mg/kg) of prednisone. The study consisted of baseline and prednisone phases with 32-hour sampling in each phase. Women were studied during the luteal phase of their menstrual cycle. Total and free plasma prednisolone concentrations were assayed by HPLC and ultrafiltration, and pharmacokinetic data were analyzed by compartmental fitting using WinNonlin. Plasma cortisol concentrations were assayed by HPLC; T-helper, T-suppressor lymphocyte, and neutrophil cell counts were determined by FACS and hemocytometry, and these pharmacodynamic data were evaluated by basic and extended indirect response models using ADAPT II. Total body weight-normalized free prednisolone oral clearance and apparent volume of distribution were higher in men compared with women, regardless of race (by 22% in whites and 40% in blacks for oral clearance, p < 0.01; by32% in whites and 38% in blacks for apparent volume of distribution, p < 0.01). The 50% inhibitory concentration (IC50) values for T-suppressor cell-trafficking inhibition were higher in whites than in blacks, regardless of sex (by 125% in men and 208% in women, p < 0.01). The IC50 or SC50 values for effects of prednisolone on cortisol secretion and T-helper lymphocyte or neutrophil trafficking were not statistically different between men and women, blacks and whites. The findings of this study suggest that there are some prednisolone PK/PD differences related to sex and race. However, these differences do not suggest the need for dosage adjustments, and additional experiments with repeat dosing are needed to fully evaluate the clinical implication of these findings.

Role of dosage regimen in controlling indirect pharmacodynamic responses

The role of drug delivery in controlling indirect pharmacodynamic responses was assessed via computer simulations and literature review. Simulations of responses related to basic indirect response mechanisms were performed for various drug input rates which allowed the importance of drug delivery rate on the overall pharmacodynamic response to be evaluated. Response versus time profiles of integrated or net responses and efficiency were examined. Rate of drug input has the greatest influence on the area under the effect curve when doses are larger and target drug concentrations are above the IC(50)/SC(50). The pharmacodynamics of drugs which elicit indirect pharmacologic responses such as corticosteroids, diuretics, growth hormone, erythropoietin and insulin indicate that sustained drug delivery enhances the therapeutic efficiency and pharmacodynamic availability.

Indirect pharmacodynamic models for responses with multicompartmental distribution or polyexponential disposition

Basic indirect response models where drug alters the production (kin) of the response variable (R) based on the Hill function previously assumed one-compartment distribution of the response variable and simple first-order loss (kout) of R. These models were extended using convolution theory to consideration of two-compartment distribution of R and/or polyexponential loss of R. Theoretical equations and methods of data analysis were developed and simulations are provided to demonstrate expected response behavior based on biexponential response dissipation. The inhibition model was applied to our previous data for inhibition of circadian cortisol secretion by prednisolone. The presence of multicompartment response variables and/or polyexponential loss complicates the response patterns and resolution of pharmacologic parameters of indirect response models and requires careful experimental and data analysis approaches in order to properly evaluate such pharmacodynamic responses. The occurrence of these alternative distribution or disposition components does not alter the area under the effect curve (AUCE) which remains identical to the basic models. Model misselection was addressed by testing fittings comparing the basic and new models. Use of the former for these more complex models does not severely perturb the calculated cardinal dynamic parameters. These models may provide improved insights into indirect responses with complexities in distribution or disposition.

Randomized trial of blood eosinophil count monitoring as a guide to corticosteroid dosage adjustment after heart transplantation

BACKGROUND

Increases in blood eosinophil counts (EOS) beyond 0.06 x 10(9)/liter precede treated heart allograft rejection. An oral prednisolone dose of 0.35 mg/kg/day usually suppresses EOS below this threshold.

METHODS

We designed a randomized trial to compare our empirical protocol for steroid dose adjustment with a novel protocol guided by EOS monitoring during the first 3 months after heart transplantation. Eighty patients were randomized to either have their EOS reported and used for steroid dose adjustment (RG; n=40), or not reported (NG; n=40). RG patients had their steroid dosage increased if EOS exceeded 0.06 x 10(9)/liter.

RESULTS

RG patients had an 83% lower risk of treated rejection (P=0.035) and lower median intravenous dose of methyl-prednisolone (P=0.017) than NG during the first 6 postoperative weeks. The proportion of diagnostic increases in EOS that were followed within 2 weeks by treated rejection was 42% greater in NG than RG (P=0.0001), compatible with a direct impact of EOS-guided prednisolone dose adjustment on the risk of subsequent rejection. Overall, RG had less than half the risk of rejection of any grade (P<0.001) and significantly more rejection-free biopsies than NG (P=0.001). The mean oral prednisolone dosage was significantly greater in RG than NG during the first (P=0.014) and second (P=0.001) 6 weeks of follow-up. This did not increase the incidence of serious steroid-related side effects.

CONCLUSIONS

EOS monitoring is a simple, cheap, and effective means of optimizing steroid immunosuppression. Restriction of the EOS-guided steroid dosing protocol to periods of prolonged hospitalisation during the first 3 postoperative months should limit the requirement for higher prednisolone dosage without affecting immunosuppressive efficacy.

An interactive algorithm for the assessment of cumulative cortisol suppression during inhaled corticosteroid therapy

The objective of the study was to develop an algorithm based on a pharmacokinetic-pharmacodynamic (PK/PD) modeling approach to quantify and predict cumulative cortisol suppression (CCS) as a surrogate marker for the systemic activity of inhaled corticosteroid therapy. Two Excel spreadsheets, one for single dose and another for steady-state multiple doses of inhaled steroids, were developed for predicting CCS. Four of the commonly used inhaled steroids were chosen for the purposes of simulation: fluticasone propionate (FP), budesonide (BUD), flunisolide (FLU), and triamcinolone acetonide (TAA). Drug-specific PK and PD parameters were obtained from previous single- and multiple-dose studies. In cases in which multiple-dose data were not available, the single-dose data were extrapolated. The algorithm was designed to calculate CCS based on 5 input parameters: name of drug, dose, dosing interval, time(s) of dosing, and type of inhaler device. In addition, a generalized algorithm was set up to calculate CCS based on clearance, volume of distribution, absorption rate, protein binding, pulmonary deposition, oral bioavailability, and unbound EC50 of the corticosteroid of interest. The spreadsheet allowed predictions of CCS for single doses as well as steady-state conditions. A simple method has been developed that facilitates comparisons between various drugs and dosing regimens and has the potential to significantly reduce the number of comparative clinical trials to be performed for evaluating the short-term systemic activity of inhaled corticosteroids.

Modeling interactions between adrenal suppression and T-helper lymphocyte trafficking during multiple dosing of methylprednisolone

A physiologic pharmacodynamic model was developed to jointly characterize the effects of corticosteroid treatment on adrenal suppression and T-helper cell trafficking during single and multiple dosing in asthmatic patients. Methylprednisolone (MP), cortisol, and T-helper cell concentrations obtained from a previously published study during single day and 6 days of multiple dosing MP treatment were examined. The formation and disposition kinetics of MP were described with a compartmental model. The biorhythmic profile of basal cortisol secretion rate was analyzed using a recent Fourier approach based on circadian harmonics. A three-compartment loop model was proposed to represent three major T-helper cell pools: blood, extravascular site, and lymph nodes. T-helper cell synthesis and degradation rate constants were obtained from the literature. The suppressive effects of cortisol and MP on T-helper cell concentrations were described with a joint additive inhibition function altering the cell migration rate from lymph nodes to blood. The model adequately described both plasma cortisol profiles and T-helper cells in blood after single and multiple doses of MP. The potency of MP for suppression of cortisol secretion was estimated as IC50 = 0.8 ng/ml. The biorhythmic nature of the basal T-helper cells in blood was well described as under the influence of basal circadian cortisol concentrations with IC50 = 79 ng/ml. The model fitted potency of MP for suppression of T-helper cells was IC50 = 4.6 ng/ml. The observed rebound of T-helper cells in blood can also be described by the proposed model. The rhythm and suppression of plasma cortisol and T-helper cells before and during single and multiple dose MP treatment were adequately described by these extended indirect response models.

A pharmacokinetic/pharmacodynamic approach to predict the cumulative cortisol suppression of inhaled corticosteroids

The suppression of endogenous cortisol release is one of the major systemic side effects of inhaled corticosteroids in the treatment of asthma. The circadian rhythm of the endogenous cortisol release and the resulting plasma concentrations as well as the release suppression during corticosteroid therapy could previously be described with an integrated PK/PD model. Based on this model, a PK/PD approach was developed to quantify and predict the cumulative cortisol suppression (CCS) as a surrogate marker for the systemic activity of inhaled corticosteroid therapy. The presented method was applied to predict CCS after single doses and during short-term multiple dosing of the inhaled corticosteroids flunisolide (FLU), fluticasone propionate (FP), and triamcinolone acetonide (TCA), and after oral methylprednisolone as systemic reference therapy. Drug-specific PK and PD parameters were obtained from previous single-dose studies and extrapolated to the multiple-dose situation. For single dosing, a similar CCS within the range of 16-21% was predicted for FP 250 micrograms, FLU 500 micrograms, and TCA 1000 micrograms. For multiple dosing, a respective CCS of 28-33% was calculated for FLU 500 micrograms bid, FP 250 micrograms, bid, and TCA 1000 micrograms bid. Higher cortisol suppression compared to these single and multiple dosing regimens of the inhaled corticosteroids was predicted after oral doses of only 1 mg and 2 mg methylprednisolone, respectively. The predictive power of the approach was evaluated by comparing the PK/PD-based simulations with data reported previously in clinical studies. The predicted CCS values were in good correlation with the clinically observed results. Hence, the presented PK/PD approach allows valid predictions of CCS for single and short-term multiple dosing of inhaled corticosteroids and facilitates comparisons between different dosing regimens and steroids.

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.

Note: caution in use of empirical equations for pharmacodynamic indirect response models

An empirical equation was recently proposed and used to characterize inhibitory drug effects on production of an endogenous substance. The limitations of this empirical equation are described utilizing mathematical equations and simulations based on the exact differential equation for Indirect Response Model I. The latter is preferable for fitting data using indirect response models.

Absence of seasonal variation in the phase of the endogenous circadian rhythm in humans

Humans may be subject to seasonal variations, as evidenced by the existence of seasonal affective disorder (SAD) and midwinter insomnia. However, some recent studies have shown that the seasonal variation in the phase of the circadian rhythm is relatively weak in healthy humans. In the present study, evidence is found that there is no seasonal variation in the phase of the endogenous circadian rhythm at all. Body temperature, cortisol excretion, and subjective alertness of six subjects recorded under constant routine conditions showed no systematic seasonal variation in circadian phases. This finding indicates that secondary zeitgebers blocked or counterbalanced the seasonal variation in the entrainment effect of the natural photoperiod. The human being may live in an environment in which the photoperiod has lost its status of primary zeitgeber.

Indirect-response model for the time course of leukopenia with anticancer drugs

BACKGROUND

Because both the nadir count and the duration of leukopenia after chemotherapy with anticancer drugs are important, a pharmacodynamic model describing the entire time course of leukopenia is valuable. In this study, a pharmacodynamic model was developed to simulate leukopenia.

METHODS

The model was developed with the 3-hour infusion data of paclitaxel. A concentration-time curve of paclitaxel for each patient estimated by a 3-compartment pharmacokinetic model was used as input to the model, which had 2 compartments corresponding to leukocytes in bone marrow and peripheral blood, respectively. Differentiation stages of myeloid cells sensitive to anticancer drugs were assumed, and exposure to a drug during their sensitive period as a function of time was used to inhibit the production of leukocytes in bone marrow. The model was validated by fitting the data of 24-hour infusion of paclitaxel or 14-day infusion of etoposide.

RESULTS

Successful fitting of the leukopenia after a 3-hour infusion of paclitaxel was achieved. The following parameters were estimated: lag-time, 58 +/- 38 (mean +/- SD) hours before the leukocyte count started to decline; exposure giving 50% inhibition of leukocyte production (IC), 12.1 +/- 6.1 microg x h/mL; and sensitive period, 288 +/- 64 hours. These estimations were within physiologic ranges. In validation, leukopenia after 24-hour infusion of paclitaxel or 14-day infusion of etoposide was also explained by the model. Age was significantly negatively correlated with IC of paclitaxel (P = .039).

CONCLUSIONS

This mechanistic model describes the time course of leukopenia and may provide a platform for pharmacodynamic analysis of anticancer drugs.

Expanding clinical applications of population pharmacodynamic modelling

Population pharmacokinetics or pharmacodynamics is the study of the variability in drug concentration or pharmacological effect between individuals when standard dosage regimens are administered. We provide an overview of pharmacokinetic models, pharmacodynamic models, population models and residual error models. We outline how population modelling approaches seek to explain interpatient variability with covariate analysis, and, in some approaches, to characterize the unexplained interindividual variability. The interpretation of the results of population modelling approaches is facilitated by shifting the emphasis from the perspective of the modeller to the perspective of the clinician. Both the explained and unexplained interpatient variability should be presented in terms of their impact on the dose-response relationship. Clinically relevant questions relating to the explained and unexplained variability in the population can be posed to the model, and confidence intervals can be obtained for the fraction of the population that is estimated to fall within a specific therapeutic range given a certain dosing regimen. Such forecasting can be used to develop optimal initial dosing guidelines. The development of population models (with random effects) permits the application of Bayes's formula to obtain improved estimates of an individual's pharmacokinetic and pharmacodynamic parameters in the light of observed responses. An important challenge to clinical pharmacology is to identify the drugs that might benefit from such adaptive-control-with-feedback dosing strategies. Drugs used for life threatening diseases with a proven pharmacokinetic-pharmacodynamic relationship, a small therapeutic range, large interindividual variability, small interoccasion variability and severe adverse effects are likely to be good candidates. Rapidly evolving changes in health care economics and consumer expectations make it unlikely that traditional drug development approaches will succeed in the future. A shift away from the narrow focus on rejecting the null hypothesis towards a broader focus on seeking to understand the factors that influence the dose-response relationship--together with the development of the next generation of software based on population models--should permit a more efficient and rational drug development programme.

Pharmacokinetics and receptor-mediated pharmacodynamics of corticosteroids

The corticosteroids, such as prednisolone and methylprednisolone, provide diverse antiinflammatory and immunosuppressive effects which typically show responses with slow onset and prolonged duration. This report summarizes modeling efforts which are successful in describing such steroid effects. Clinical effects with such a pattern, including adrenal suppression and altered trafficking of basophils and helper T-cells, can be related to plasma drug concentrations by models containing an inhibition function and differential equations for controlling input and disposition of the response variable. Some responses have circadian-controlled inputs which add time-dependent complexities to the models. Kinetic/dynamic data for several corticosteroid effects yield IC50 values which agree well with receptor KD values. A relationship of linear AUC of effect versus log AUC of steroid in plasma is found with these models over a large range of doses. Gene-mediated effects of corticosteroids are initiated by receptor-binding which causes a cascade effect altering DNA transcription, RNA, mRNA and proteins or enzymes accounting for drug effects. Models for such behavior have been developed in animals for hepatic tyrosine aminotransferase (TAT) enzyme activity. Studies with methylprednisolone formulated in liposomes show tissue sequestration of steroid, prolonged receptor-binding and extended inhibition of splenocyte proliferation. The data and models usually show good correspondence of the AUC of receptor occupancy with the AUC of pharmacologic response.

Repeated assessment of methylprednisolone pharmacokinetics during chronic immunosuppression in renal transplant recipients

OBJECTIVE

To compare the pharmacokinetics of methylprednisolone in renal transplant recipients on 2 occasions separated by at least 1 month during chronic immunosuppression.

DESIGN

A prospective unblinded trial.

PATIENTS

Ten renal transplant recipients (aged 25-62 years) evaluated in a public university-affiliated hospital clinic.

INTERVENTIONS

All patients received their chronic oral dose of methylprednisolone as a 10-20-minute intravenous infusion during the 2 study periods.

MAIN OUTCOME MEASURES

Serum methylprednisolone concentrations were determined by HPLC and were used to generate the pharmacokinetic parameters of the drug.

RESULTS

During study 1, which ranged from 1.2 to 24 months posttransplant, the mean +/- SD methylprednisolone dose was 13.2 +/- 6.4 mg. In study 2 (2.5-38.5 mo posttransplant), the mean dose was 10.6 +/- 3 mg. During both study periods, methylprednisolone concentrations exhibited a monoexponential decline. Considerable variability in methylprednisolone clearance was observed between periods in certain patients. Four of the 10 patients demonstrated a reduction in clearance from study 1 to study 2, which ranged from a 28% to a 53% decrease. Two patients exhibited an increase in clearance of 40% and 49%. The mean +/- SD total body clearance in study 1 was 363 +/- 330 mL/min/kg, whereas the mean volume of distribution was 1.18 +/- 0.53 L/kg. The mean elimination rate constant was 0.29 +/- 0.14 h-1, with a mean serum half-life of 2.87 +/- 1.15 h during the first phase. In study 2, the mean methylprednisolone clearance was 261 +/- 150 mL/min/kg (p > 0.05) and the mean volume of distribution was 0.89 +/- 0.31 L/kg (p > 0.05). The mean serum half-life of methylprednisolone was 2.91 +/- 0.60 h (p > 0.05), with the mean elimination rate constant of 0.25 +/- 0.06 h-1 (p > 0.05).

CONCLUSIONS

These data demonstrate that intrapatient variability in methylprednisolone clearance exists among certain renal allograft recipients. As a result of the observed variability, patients who are continued on the same dose of methylprednisolone during the posttransplant period of chronic immunosuppression will be subjected to a changing pattern of exogenous glucocorticoid exposure. The impact of these changing patterns requires further prospective evaluation.

Pharmacokinetics of methylprednisolone in elderly and young healthy males

OBJECTIVE

To characterize and compare the pharmacokinetics of a single intravenous dose of methylprednisolone in elderly and young healthy males.

DESIGN

A randomized, parallel pharmacokinetic trial.

SETTING

A public university-affiliated hospital.

SUBJECTS

Seven healthy, elderly white males (aged 69 to 82 years) and five healthy, young white males (aged 24 to 37 years) who gave informed consent and fulfilled all screening criteria.

MEASUREMENTS

Serial blood samples were obtained over a 24-hour study period after intravenous administration of a 10-mg dose of methylprednisolone. Serum methylprednisolone concentrations were determined by high performance liquid chromatography and utilized to determine the pharmacokinetic parameters.

RESULTS

Methylprednisolone serum concentrations declined in a linear manner in both groups. However, 4 hours after the dose, the mean serum concentration of methylprednisolone was 50.9 +/- 15.1 ng/mL in the elderly group and 37.6 +/- 7.5 (P = 0.07) ng/mL in the young group. The clearance of methylprednisolone was 237 +/- 62 mL/h/kg, with a volume of distribution of 1.10 +/- 0.07 L/kg, for the elderly group, whereas the young males had a mean drug clearance of 359 +/- 90 mL/h/kg (P < 0.05) and a mean volume of distribution of 1.28 +/- 0.34 L/kg. The half-life of methylprednisolone ranged from 1.90 to 5.40 hours in the elderly group; the range was 1.99 to 3.31 hour (P = 0.016) in the young group.

CONCLUSION

A slower methylprednisolone clearance was noted in the elderly group compared with the young counterparts. This pharmacokinetic alteration seen in healthy elderly subjects may contribute to the increased incidence of adverse effects from chronic glucocorticoid therapy that has been observed among elderly patients.

Inhibition of rat splenocyte proliferation with methylprednisolone: in vivo effect of liposomal formulation

The effect of a liposomal formulation of methylprednisolone (MPL) on the inhibition of lymphocyte proliferation in spleen cells was investigated following IV dosing in rats. Liposomes do not alter the suppressive action of MPL when placed in lymphocyte culture. Rat splenocytes were found to have greater sensitivity to MPL (EC50 = 7.9 nM) than do human peripheral blood lymphocytes (EC50 = 28 nM). In vivo studies in rats utilized 2 mg/kg IV bolus doses of liposomal MPL compared to drug in solution. Animals were sacrificed at various times post-dosing until 120 h, spleen was excised and, after incubation of lymphocytes with PHA, splenocyte blastogenic responses were assessed by measuring cellular incorporation of 3H-thymidine. The suppressive effect of liposomal MPL in comparison with free drug was significantly prolonged (> 120 h vs < 18 h). Inhibition effects versus time were described by a pharmacodynamic model using MPL concentrations in plasma as an input function. A nonlinear relationship was found between suppression of splenocyte proliferation and the concentration of bound glucocorticoid receptors in spleen. Only partial receptor occupancy accompanied complete lymphocyte suppression. The suppression of endogenous corticosterone in plasma for both treatments was similar with values from L-MPL rats returning to baseline after 24 h. These results demonstrate enhanced efficacy of local immunosuppression by targeting spleen with liposomal MPL.

Cortisol pharmacodynamic response to long-term methylprednisolone in renal transplant recipients

STUDY OBJECTIVE

To examine the pharmacodynamic patterns of cortisol and pharmacokinetic values of long-term methylprednisolone in renal transplant recipients.

DESIGN

Twenty-four-hour pharmacokinetic and pharmacodynamic evaluation of patients who participated in a glucocorticoid-monitoring program.

SETTING

University-based renal transplant clinic.

PATIENTS

Fourteen renal transplant recipients studied during a clinically stable period.

INTERVENTIONS

The daily oral methylprednisolone dose for each patient was administered intravenously, and serial plasma cortisol and methylprednisolone samples were obtained over 24 hours.

MEASUREMENTS AND MAIN RESULTS

Methylprednisolone was analyzed by high-performance liquid chromatography. The baseline morning cortisol serum concentrations ranged from 9.8-210.7 ng/ml. After the drug was administered, cortisol declined in a linear fashion with a mean suppression half-life of 2.4 +/- 0.9 hours. The cortisol nadir was reached at 12-16 hours in 11 of 14 patients. The return cortisol area under the curve (AUC-Cret) was noted in all patients and ranged from 57-987 ng.hr/ml. The total cortisol area under the curve was greater in patients who had been transplanted for longer than 2 years (1676 +/- 252 vs 836 +/- 405 ng.hr/ml; p < 0.05) compared with more recently transplanted patients. Methylprednisolone clearance ranged from 100-1181 ml/hr/kg with a mean volume of distribution of 1.3 +/- 0.6 L/kg. The methylprednisolone half-life ranged from 1.2-4.7 hours. The correlation between AUC-Cret and methylprednisolone AUC was -0.64 (p < 0.05).

CONCLUSIONS

The pharmacodynamic response of cortisol in renal transplant recipients may be associated in part with long-term steroid exposure. However, the interrelationship between the endocrine and immune system may also affect cortisol's disposition and subsequent recovery patterns in this population. Considerable interpatient variability was apparent in both the cortisol pharmacodynamic response as well as the pharmacokinetics of methylprednisolone. These findings suggest a more individualized dosing method may be necessary to optimize the immunosuppressive effect of glucocorticoids and minimize clinical toxicity.

Pharmacodynamic modeling of cortisol suppression from fluocortolone

The effect of fluocortolone on cortisol suppression was characterized using a 'direct suppression pharmacodynamic model'. The model incorporates the physiologic circadian secretion of cortisol under normal and treatment conditions, together with pharmacokinetic data from single fluocortolone doses of 20, 50, and 100 mg. A mean IC50 value (fluocortolone plasma concentration at which the circadian secretion of cortisol is inhibited by 50%) of 15.5 ng.ml-1 was found. This analysis shows how use of pharmacodynamic modeling can characterize dose-proportionality data to provide an in vivo measure of drug potency.

Gender-based effects on methylprednisolone pharmacokinetics and pharmacodynamics

The pharmacokinetics and selected pharmacodynamic responses to methylprednisolone were investigated in six men and six premenopausal women after a dose of 0.6 mg/kg ideal body weight. Women (luteal phase) exhibited a greater methylprednisolone clearance (0.45 versus 0.29 L/hr/kg) and shorter elimination half-life (1.7 versus 2.6 hours) than men. The volume of distribution of methylprednisolone was similar when normalized for ideal body weight. Pharmacodynamic models were used to examine the methylprednisolone suppressive effects on cortisol secretion and basophil and helper T lymphocyte trafficking. A significantly smaller 50% inhibitory concentration (IC50) value (0.1 versus 1.7 ng/ml) was seen in the women for suppression of cortisol secretion, indicating increased sensitivity. However, the area under the concentration-time curve of effect was similar for both groups. The IC50 values for effects of methylprednisolone on basophil trafficking related to estradiol concentrations in a log-linear fashion in women, with increased sensitivity found at higher estradiol concentrations. Men displayed a greater 24-hour net suppression in blood basophil numbers, but no difference was observed in net cortisol and helper T lymphocyte suppression between the sexes. These findings suggest that methylprednisolone dosages should be based on ideal body weight. Although women are more sensitive to methylprednisolone as measured by cortisol suppression, they eliminate the drug more quickly, generally producing a similar net response.

Pharmacokinetics of methylprednisolone hemisuccinate and methylprednisolone in chronic liver disease

The disposition of methylprednisolone (MP) and its prodrug hemisuccinate (MPHS) was assessed in six middle-aged patients with chronic liver disease (CLD) and compared with six younger, healthy subjects after a single IV dose of 25.4 mg of MPHS. Blood and urine samples were collected over 12 hours. Plasma and urine concentrations of MPHS and MP and plasma cortisol were measured by HPLC. MPHS clearance (CL) was significantly reduced in the CLD group (495 vs. 1389 mL/hr/kg) whereas volume of distribution (Vss) of MPHS (about 0.35 1/kg) did not differ. The elimination half-life, t1/2 beta, was significantly longer in CLD (0.61 vs. 0.32 hr). The percent recovery of unchanged MPHS in urine was similar (about 9%) in both groups. The kinetic parameters of MP did not differ between the two groups for: clearance (about 370 L/hr/kg IBW), Vss (about 1.3 L/kg), and t1/2 beta (about 3.0 hr). The suppression t1/2 of cortisol after MPHS was longer (3.9 vs. 1.9 hr) indicating metabolic pathways for cortisol and MP are affected differently in CLD. Reduction in MPHS CL may reflect altered hepatic blood flow due to both cirrhosis and age effects. However, good availability of MP from MPHS and lack of perturbation of MP pharmacokinetics in CLD patients may provide therapeutic advantages in selection of this glucocorticoid. This is the first study that characterizes the disposition of the prodrug MPHS and the formation of MP simultaneously in CLD patients.

Comparison of four basic models of indirect pharmacodynamic responses

Four basic models for characterizing indirect pharmacodynamic responses after drug administration have been developed and compared. The models are based on drug effects (inhibition or stimulation) on the factors controlling either the input or the dissipation of drug response. Pharmacokinetic parameters of methylprednisolone were used to generate plasma concentration and response-time profiles using computer simulations. It was found that the responses produced showed a slow onset and a slow return to baseline. The time of maximal response was dependent on the model and dose. In each case, hysteresis plots showed that drug concentrations preceded the response. When the responses were fitted with pharmacodynamic models based on distribution to a hypothetical effect compartment, the resulting parameters were dose-dependent and inferred biological implausibility. Indirect response models must be treated as distinct from conventional pharmacodynamic models which assume direct action of drugs. The assumptions, equations, and data patterns for the four basic indirect response models provide a starting point for evaluation of pharmacologic effects where the site of action precedes or follows the measured response variable.

Comparative methylprednisolone pharmacokinetics in renal transplant patients receiving double- or triple-drug immunosuppression

OBJECTIVE

To assess the pharmacokinetics of chronic methylprednisolone therapy in renal transplant patients receiving double-drug (methylprednisolone and azathioprine) and triple-drug (methylprednisolone, azathioprine, and cyclosporine) immunosuppression.

DESIGN

Parallel, randomized trial.

PATIENTS

Fourteen renal transplant recipients (aged 29-65 y) evaluated in a public, university-affiliated hospital clinic.

INTERVENTIONS

All patients received their chronic oral dose of methylprednisolone via a 10-20-minute intravenous infusion.

MAIN OUTCOME MEASURES

Serum methylprednisolone concentrations were determined by HPLC and were used to generate pharmacokinetic parameters for this drug.

RESULTS

The mean daily methylprednisolone dosage was 19 +/- 19 mg in the double-drug group and 9 +/- 2 mg in the triple-drug group. Mean serum creatinine concentrations were 124 +/- 44 and 124 +/- 27 mumol/L, respectively. Mean methylprednisolone clearances were similar in both groups: 405 +/- 205 (double-drug) and 373 +/- 365 mL/h/kg (triple-drug) (p > 0.05). Mean steady-state volume of distribution was 1.5 +/- 0.8 L/kg in the double-drug group and 1.3 +/- 0.8 L/kg in the triple-drug group (p > 0.05). Plasma half-life ranged from 1.7 to 4.3 h (mean 2.7) in the double-drug group versus 1.4 to 3.4 h (mean 2.6) in the triple-drug group (p > 0.05).

CONCLUSIONS

These data indicate that cyclosporine had no definitive influence on methylprednisolone disposition. The results reveal a wide variation in methylprednisolone metabolism in renal transplant recipients receiving either a double- or triple-drug immunosuppressive regimen. Typically, methylprednisolone is prescribed according to a standardized dosing protocol that assumes minimal interpatient variation. Therefore, the pharmacokinetic variability noted in this study may have important clinical implications regarding the development of chronic toxicity (e.g., osteoporosis, hypothalamic-pituitary-adrenal suppression) and the attainment of successful immunosuppression.

Evaluation of dose-related pharmacokinetics and pharmacodynamics of prednisolone in man

The pharmacokinetics and pharmacodynamics of prednisolone were evaluated in normal male volunteers. Seven subjects completed 3 phases: 16.4- and 49.2-mg iv prednisolone, and a phase with no drug to assess baseline responses. Plasma concentrations of prednisolone and urine concentrations of prednisolone and 5 metabolites were assayed by HPLC. Protein binding of prednisolone was measured by ultrafiltration. The polyexponential disposition of free and total plasma prednisolone were evaluated and apparent parameters were compared between doses. Suppression of plasma cortisol and alterations in blood basophil and helper-T cell trafficking were used as pharmacodynamic indices. Pharmacodynamic models were used to relate total or free plasma prednisolone concentrations to each of these effects generating response parameters and IC50 (50% inhibitory) concentrations common to both doses. The pharmacokinetics of total drug were comparable to previous findings with CL and Vss increasing with dose. Free prednisolone exhibited slight capacity-limited elimination and distribution as CL and Vss decreased with the larger dose. Pharmacodynamic models jointly fitting all three phases characterized the suppression/trafficking phenomena equally well with use of total or free drug concentrations. In each case the models provided realistic values of parameters relating to steroid sensitivity--in particular IC50--and to the underlying physiology of the affected systems. This study comprehensively elucidates the complexities of prednisolone pharmacokinetics and demonstrates how plasma concentration--time profiles of total or free prednisolone can be utilized for evaluation of prednisolone pharmacodynamics.

Pharmacoimmunodynamics of methylprednisolone: trafficking of helper T lymphocytes

A two-compartment closed model was used to characterize the cell trafficking behavior of helper T cells in response to various single doses of methylprednisolone. Steroids are assumed to inhibit the circadian-determined cell return from extravascular sites to blood in a classic inhibitory pattern reflected by an IC50. The rate of cell efflux from tissues is modeled with a cosine function having a period of 24 hr and a maximum at about 1 AM. Nonlinear least-squares regression employing differential equations was used to analyze helper T-cell data from three human studies from our laboratory. The IC50 value of methylprednisolone of 12-19 ng/ml approximates receptor KD values. Simulations were performed to demonstrate the log-linear role of steroid dose or AUC on the integral of effect of helper T cells over a wide range of methylprednisolone doses. This pharmacodynamic model allows flexibility for characterizing any type of steroid dosing regimen and is relevant in describing complex response data for corticosteroid immunosuppressive effects in man.

Pharmacokinetics and pharmacodynamics of methylprednisolone when administered at 8 am versus 4 pm

The temporal variations in the pharmacokinetics and pharmacodynamics of methylprednisolone at 8 AM versus 4 PM were investigated in six healthy male volunteers. Subjects completed three phases: no drug administration, 20 mg intravenous methylprednisolone at 8 AM, and the same dose at 4 PM. Methylprednisolone clearance was 28% greater in the afternoon. The suppressive effects of methylprednisolone on basophils (measured as whole blood histamine), helper T lymphocytes, and cortisol concentrations, assessed by the ratio of the area under the curve (AUC) after methylprednisolone to the baseline AUC, were not different between the phases. The 50% inhibitory concentration values for methylprednisolone derived from pharmacodynamic models were also similar, indicating no difference in intrinsic responsiveness. However, cortisol concentrations returned to baseline about 4 hours earlier after the 4 PM compared with the 8 AM dose because of the enhanced afternoon methylprednisolone clearance. These findings are in agreement with other studies that suggest adequate clinical effects and less disturbance of cortisol circadian behavior when methylprednisolone is administered as a single dose in the morning.

A pharmacokinetic and pharmacodynamic comparison of plain and enteric-coated prednisolone tablets

1. Eight healthy volunteers and eight patients suffering from chronic obstructive pulmonary disease (COPD) received 30 mg prednisolone as plain (P) and enteric-coated tablets (EP) in a randomised, cross-over manner. Plasma prednisolone and cortisol and blood glucose were measured over 24 h. 2. Although absorption of prednisolone was considerably slower when administered as the enteric-coated form, peak plasma drug concentrations and total AUC (0,24 h) were equivalent for the two formulations. Malabsorption of prednisolone was not observed. 3. The administration of EP was associated with significantly less adrenal suppression in volunteers than P as judged by measurement of AUC (0,24 h) values for endogenous cortisol. However, this difference did not reach statistical significance in the patient group. 4. Plasma cortisol concentrations declined more slowly following administration of the enteric-coated form to both groups. The difference in time taken (median and range) to maximum suppression of cortisol was statistically significant (P less than 0.05) between P (2.5 h; 2-4 h) and EP (4 h; 3-12 h) preparations administered to volunteers. There was a similar significant difference (P less than 0.05) between P (2.5 h; 1-4 h) and EP (7 h; 2-12 h) in the patients. 5. Plasma cortisol concentrations were significantly lower at 24 h in patients receiving the enteric-coated product in association with higher terminal prednisolone concentrations. 6. Blood glucose concentrations increased over an 8 h period in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)

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.