Nonlinear pharmacokinetics and interconversion of prednisolone and prednisone in rats

Food effects and pharmacokinetic evaluation of oral single-dose prednisone acetate and prednisolone in healthy Chinese subjects

BACKGROUND

To assess the food effects and pharmacokinetic profile of oral prednisone (test preparation,5 mg) and prednisolone tablets (reference preparation,5 mg) using a randomized, two-period, two crossover, single-dose, fast and fed trial in 48 (24 in fast, 24 in fed) healthy Chinese adult subjects.

MATERIALS AND METHODS

In the trial, the plasma concentrations were determined at different time points up to 24 h and the pharmacokinetic parameters were analyzed according to the concentration data by non-compartmental analysis using WinNonlin software. All laboratory parameters, vital signs and adverse events (AEs) were monitored and recorded under the supervision of the clinicians throughout the whole process of the study.

RESULTS

Prednisone and prednisolone undergo interconversion in liver. On average, the bioavailability of prednisolone after oral prednisone is approximately 80% of that after prednisolone. And about 20% of prednisolone is converted to prednisone after administration of equivalent oral of prednisolone tablet. Food taken with prednisone or prednisolone tablets delays the time reach the peak prednisone or prednisolone concentration (Tmax) by approximately 0.5 h but does not affect systemic exposure. Prednisone and prednisolone tablets were well tolerated, and there were no serious adverse events reported in the study.

CONCLUSIONS

For there was no information about the pharmacokinetic profile and food effects of oral prednisone and prednisolone tablets, the result of this research would be a clinical medication for doctors especially dealing patients with varying degrees of liver diseases.

CLINICAL TRIAL REGISTRATION

CTR20200093; registered in http://www.chinadrugtrials.org.cn/ at 11 March 2020.

The Physiological and Pharmacological Significance of the Circadian Timing of the HPA Axis: A Mathematical Modeling Approach

As a potent endogenous regulator of homeostasis, the circadian time-keeping system synchronizes internal physiology to periodic changes in the external environment to enhance survival. Adapting endogenous rhythms to the external time is accomplished hierarchically with the central pacemaker located in the suprachiasmatic nucleus (SCN) signaling the hypothalamus-pituitary-adrenal (HPA) axis to release hormones, notably cortisol, which help maintain the body's circadian rhythm. Given the essential role of HPA-releasing hormones in regulating physiological functions, including immune response, cell cycle, and energy metabolism, their daily variation is critical for the proper function of the circadian timing system. In this review, we focus on cortisol and key fundamental properties of the HPA axis and highlight their importance in controlling circadian dynamics. We demonstrate how systems-driven, mathematical modeling of the HPA axis complements experimental findings, enhances our understanding of complex physiological systems, helps predict potential mechanisms of action, and elucidates the consequences of circadian disruption. Finally, we outline the implications of circadian regulation in the context of personalized chronotherapy. Focusing on the chrono-pharmacology of synthetic glucocorticoids, we review the challenges and opportunities associated with moving toward personalized therapies that capitalize on circadian rhythms.

Physiologically Based Pharmacokinetic Modeling Involving Nonlinear Plasma and Tissue Binding: Application to Prednisolone and Prednisone in Rats

The pharmacokinetics (PK) of prednisolone (PNL) exhibit nonlinearity related to plasma protein binding, tissue binding, metabolic interconversion with prednisone (PN), and renal elimination. Blood and 11 tissues were collected from male Wistar rats after steady-state (SS) infusion and after subcutaneous boluses of 50 mg/kg of PNL. Concentrations of PNL and PN were measured by liquid chromatography-tandem mass spectrometry. Plasma and tissue profiles were described using a complex physiologically based pharmacokinetics (PBPK) model. Concentrations of PN and PNL were in rapid equilibrium in plasma and tissues. The tissue partition coefficients (K p ) of PNL calculated from most subcutaneously dosed tissue and plasma areas were similar to SS infusion and in silico values. The blood-to-plasma ratio of PNL was 0.71 with similar red blood cell and unbound-plasma concentrations. Plasma protein binding (60%-90%) was related to corticosteroid-binding globulin (CBG) saturation. Tissue distribution was nonlinear. The equilibrium dissociation constant (K d ) of PNL shared by all tissues was 3.01 ng/ml, with the highest binding in muscle, followed by liver, heart, intestine, and bone and the lowest binding in skin, spleen, fat, kidney, lung, and brain. Fat and bone distribution assumed access only to interstitial space. Brain PNL concentrations (K p = 0.05) were low owing to presumed P-glycoprotein-mediated efflux. Clearances of CBG-free PNL were 1789 from liver and 191.2 ml/h from kidney. The PN/PNL ratio was nonlinear for plasma, spleen, heart, intestine, bone, fat, and linear for the remaining tissues. Our PBPK model with multiple complexities well described the PK profiles of PNL and PN in blood, plasma, and diverse tissues. SIGNIFICANCE STATEMENT: Because steroids, such as prednisolone and prednisone, have similar and complex pharmacokinetics properties in various species, receptors in most tissues, and multiple therapeutic and adverse actions, this physiologically based pharmacokinetics (PBPK) model may provide greater insights into the pharmacodynamic complexities of corticosteroids. The complex properties of these compounds require innovative PBPK modeling approaches that may be instructive for other therapeutic agents.

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.

Pharmacokinetics and anti-inflammatory pharmacodynamics of prednisolone in cynomolgus monkey

The purpose was to investigate whether the pharmacokinetics and pharmacodynamics of prednisolone in the non-human primate was an appropriate surrogate for man. After single intravenous doses of 0.03, 0.3, and 3 mg kg(-1), prednisolone demonstrated a dose-dependent clearance and volume of distribution. When corrected for concentration-dependent protein binding, the free clearance was linear at the tested dose levels. The protein binding-corrected volume of distribution was similar across doses. The serum half-life was estimated as being between 2 and 4 h. Prednisolone exhibits near complete inhibition of the cytokines TNF-alpha, IL-1beta, IL-6 and IL-8 with very similar IC50 estimates from 0.09 to 0.16 microg ml(-1) (from 0.24 to 0.44 microM). The monkey demonstrated a similar pharmacokinetics-pharmacodynamics profile of prednisolone when compared with man (from the literature).

Assessment of the impact of dosing time on the pharmacokinetics/pharmacodynamics of prednisolone

Prednisolone is widely used for the treatment of inflammation and auto-immune diseases. It exhibits nonlinear pharmacokinetics (PK); and its induced systemic effects (pharmacodynamics (PD)) are commonly evaluated with two biomarkers, cortisol and blood lymphocytes in plasma. Circadian patterns are observed in both biomarkers. Furthermore, the disease itself may show a circadian pattern. For example, in rheumatoid arthritis patients, better therapeutic outcomes have been reported when prednisolone was administered in the very early morning. The aim of this study is to evaluate the impact of dosing time on the PK/PD of prednisolone with a simulation approach using an interactive algorithm. A series of simulations were performed with either intravenous or oral administration of prednisolone or prednisone. The results showed that the initial or maximum concentration and trough concentration of total prednisolone were lower when the drug was administered in the early morning around 6 AM: . Oscillation patterns were observed in cumulative cortisol suppression (CCS) and alteration of total lymphocyte trafficking in blood. When the drug was given in the morning within the therapeutic dose range, or around 6 PM: for a small dose amount (<1 mg), the minimum CCS and maximum effect on lymphocytes were observed. These results indicated that the PK/PD of prednisolone are time- and dose-dependent, and suggested that it is necessary to consider the application of chronotherapy to achieve better clinical outcomes with fewer side effects of prednisolone, and a PK/PD simulation approach could provide a valuable tool to evaluate and predict time-dependency in the system.

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

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

Pharmacokinetic principles of immunosuppressive drugs

A basic tenet of clinical pharmacology is that the pharmacologic activity of an exogenously administered agent is related to the free drug concentration available at its receptor or ligand-binding site. The discipline of pharmacokinetics can be defined as the study of the processes that lead to the availability of an agent to its site of action. In this review we will discuss basic principles of pharmacokinetics that govern the absorption, distribution, metabolism, elimination and binding of immunosuppressive drugs commonly utilized in whole organ transplantation. In a discipline such as organ transplantation, where the agents utilized carry significant toxicity and where failure of efficacy can have dire consequences, knowledge of the pharmacokinetics of the agents utilized has become a basic skill for all transplant professionals. In this review we describe some of the underlying principles that govern the disposition of the agents commonly utilized in solid organ transplantation. In addition, we hope this review will help in understanding some of the basic drug interactions encountered in transplant practice.

Reversible metabolism of drugs

Many drugs undergo reversible metabolism. The basis of our understanding of this process is the reversible metabolism of prednisone (PD)-prednisolone (PL). The pharmacokinetics of reversible metabolism requires the use of four area under the curve values integrated into four equations for clearance (CL). Other variables, such as linear versus non-linear disposition, can play important roles in reversible metabolism. Of recent interest is the reversible metabolism of haloperidol which consists of an interconversion process between the parent drug haloperidol (HL) and its reduced metabolite (RH). However, the interconversion of HL-RH differs from the PD-PL model in that, whereas PD and PL are both active, RH is considered to be a therapeutically inactive, possibly toxic, metabolite. This article reviews the pharmacodynamic and pharmacokinetic properties of HL and RH and the possible clinical effects that can result from this reversible metabolism.

Effect of corticosteroid binding globulin on the pharmacokinetics of prednisolone in rats

PURPOSE

The effect of exogenous corticosteroid binding globulin (CBG) on the pharmacokinetics of intravenous prednisolone was determined in rats to test the "free hormone hypothesis."

METHODS

A dose of CBG to yield 95% binding with 1000 ng/ml of prednisolone in vitro in rat plasma or saline was administered before dosing 2 mg/kg of prednisolone hemisuccinate or methylprednisolone intravenously. Drug concentrations in plasma samples were assayed by HPLC.

RESULTS

Single administration of CBG decreased apparent prednisolone clearance by 56% (155 to 66 ml/min/kg) and reduced apparent VSS by 35% (4.1 to 2.7 L/kg) (p < 0.001). Methylprednisolone pharmacokinetics, studied as a negative control because the drug does not bind to CBG, did not change.

CONCLUSIONS

The corticosteroid bound to CBG does not appear to be available for removal by clearance organs.

Intra- and interethnic variability in reduced haloperidol to haloperidol ratios

Steady-state haloperidol and reduced haloperidol concentrations were measured in 250 schizophrenic patients from 4 ethnic groups: 39 Blacks, 66 Caucasians, 82 Chinese, and 63 Mexican Americans. The distribution of the reduced haloperidol to haloperidol concentration (RH/HL) ratios was bimodal in all ethnic groups, with the antimode determined by probit plot as 0.46, 0.51, 0.36, and 0.76, respectively. With these antimodes, the proportion of patients with low RH/HL ratios were 41%, 42%, 73%, and 57% in the four ethnic groups, respectively. Compared with the other three ethnic groups, in the Chinese patients the ratio was lower. The mean RH/HL ratio in the Chinese was 0.34 compared with 0.81 to 0.87 in the non-Chinese groups. In 53 patients who were treated with two or more haloperidol dosage regimens, steady-state haloperidol and reduced haloperidol drug concentrations obtained from the different regimens were positively correlated with the haloperidol dose (R = .79 and R = .62, respectively). Our data suggest not only the existence of a bimodal distribution in the RH/HL ratio, but also that the antimode separating the low and high ratio subgroups is different among the various ethnic groups.

Effects of indomethacin on the pharmacokinetics and pharmacodynamics of prednisolone in rats

The effect of indomethacin on the disposition of prednisolone and the induction of tyrosine aminotransferase (TAT) was examined in male Sprague-Dawley rats. Rats were pretreated with either indomethacin (5 mg/kg, intraperitoneally) or phosphate buffered saline (control) twice daily for 6 days followed by a single dose of prednisolone. Blood samples were collected after prednisolone administration. In separate animals, hepatic TAT activity (pharmacologic effect) was measured 4 h after the prednisolone dose. In addition, the effect of indomethacin on the in vitro protein binding of prednisolone was examined in pooled rat and human plasma. The clearance and apparent volume of distribution of prednisolone in the control and indomethacin-treated animals were similar, averaging 4.71 versus 4.05 L/h/kg and 1.37 versus 1.33 L/kg, respectively. The elimination half-life was 0.48 h in both groups. Indomethacin also did not affect the protein binding of prednisolone in rat or human plasma. However, indomethacin pretreatment increased the hepatic TAT activity induced by prednisolone. These studies indicate that indomethacin may affect the pharmacological effects of prednisolone without influencing its pharmacokinetics.

Bioavailability and reversible metabolism of prednisone and prednisolone in man

The pharmacokinetics of prednisone and prednisolone was examined in 12 healthy male subjects to assess the bioavailability and the parameters of reversible metabolism between the two steroids. After an oral prednisone dose of 0.8 mg kg-1 and an intravenous prednisolone dose of 0.66 mg kg-1, the bioavailability was found to be about 62%. The fraction of the dose recovered in the urine as the hydroxylated metabolites of prednisone and prednisolone was lower after the oral prednisone dose, suggesting that poor absorption of prednisone was the main cause of the low bioavailability. There was a high degree of interconversion between prednisone and prednisolone with 76% of the dose being recycled. The formation clearance of prednisolone from prednisone is much greater than the formation clearance of prednisone from prednisolone or the irreversible elimination clearances of the two steroids. The possible dose dependences of bioavailability and interconversion may be important factors in prednisolone therapy.