Kinetics of methylprednisolone and its hemisuccinate ester

Design, Synthesis, and Evaluation of a Set of Carboxylic Acid and Phosphate Prodrugs Derived from HBV Capsid Protein Allosteric Modulator NVR 3-778

Hepatitis B virus (HBV) capsid protein (Cp) is necessary for viral replication and the maintenance of viral persistence, having become an attractive target of anti-HBV drugs. To improve the water solubility of HBV capsid protein allosteric modulator (CpAM) NVR 3-778, a series of novel carboxylic acid and phosphate prodrugs were designed and synthesized using a prodrug strategy. In vitro HBV replication assay showed that these prodrugs maintained favorable antiviral potency (EC50 = 0.28−0.42 µM), which was comparable to that of NVR 3-778 (EC50 = 0.38 µM). More importantly, the cytotoxicity of prodrug N8 (CC50 > 256 µM) was significantly reduced compared to NVR 3-778 (CC50 = 13.65 ± 0.21 µM). In addition, the water solubility of prodrug N6 was hundreds of times better than that of NVR 3-778 in three phosphate buffers with various pH levels (2.0, 7.0, 7.4). In addition, N6 demonstrated excellent plasma and blood stability in vitro and good pharmacokinetic properties in rats. Finally, the hemisuccinate prodrug N6 significantly improved the candidate drug NVR 3-778’s water solubility and increased metabolic stability while maintaining its antiviral efficacy.

Recent advances in prodrug-based nanoparticle therapeutics

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Treatment of Inflammatory Bowel Disease

According to recent clinical consensus, pharmacotherapy of inflammatory bowel disease (IBD) is, or should be, personalized medicine. IBD treatment is complex, with highly different treatment classes and relatively few data on treatment strategy. Although thorough evidence-based international IBD guidelines currently exist, appropriate drug and dose choice remains challenging as many disease (disease type, location of disease, disease activity and course, extraintestinal manifestations, complications) and patient characteristics [(pharmaco-)genetic predisposition, response to previous medications, side-effect profile, necessary onset of response, convenience, concurrent therapy, adherence to (maintenance) therapy] are involved. Detailed pharmacological knowledge of the IBD drug arsenal is essential for choosing the right drug, in the right dose, in the right administration form, at the right time, for each individual patient. In this in-depth review, clinical pharmacodynamic and pharmacokinetic considerations are provided for tailoring treatment with the most common IBD drugs. Development (with consequent prospective validation) of easy-to-use treatment algorithms based on these considerations and new pharmacological data may facilitate optimal and effective IBD treatment, preferably corroborated by effectiveness and safety registries.

Signed, Sealed, Delivered: Conjugate and Prodrug Strategies as Targeted Delivery Vectors for Antibiotics

Innate and developed resistance mechanisms of bacteria to antibiotics are obstacles in the design of novel drugs. However, antibacterial prodrugs and conjugates have shown promise in circumventing resistance and tolerance mechanisms via directed delivery of antibiotics to the site of infection or to specific species or strains of bacteria. The selective targeting and increased permeability and accumulation of these prodrugs not only improves efficacy over unmodified drugs but also reduces off-target effects, toxicity, and development of resistance. Herein, we discuss some of these methods, including sideromycins, antibody-directed prodrugs, cell penetrating peptide conjugates, and codrugs.

Modeling Corticosteroid Pharmacokinetics and Pharmacodynamics, Part I: Determination and Prediction of Dexamethasone and Methylprednisolone Tissue Binding in the Rat

The plasma and tissue binding properties of two corticosteroids, dexamethasone (DEX) and methylprednisolone (MPL), were assessed in the rat in anticipation of developing physiologically based pharmacokinetic and pharmacokinetic/pharmacodynamic models. The tissue-to-plasma partition coefficients (K _P) of DEX and MPL were measured in liver, muscle, and lung in vivo after steady-state infusion and bolus injection in rats. Since K _P is often governed by reversible binding to macromolecules in blood and tissue, an attempt was made to assess K _P values of DEX and MPL by in vitro binding studies using rat tissue homogenates and to compare these estimates to those obtained from in vivo kinetics after dosing. The K _P values of both steroids were also calculated in rat tissues using mechanistic tissue composition-based equations. The plasma binding of DEX and MPL was linear with moderate binding (60.5% and 82.5%) in male and female rats. In vivo estimates of steroid uptake appeared linear across the tested concentrations and K _P was highest in liver and lowest in muscle for both steroids. Assessment of hepatic binding of MPL in vitro was severely affected by drug loss at 37°C in male liver homogenates, whereas DEX was stable in both male and female liver homogenates. With the exception of MPL in liver, in vitro-derived K _P estimates reasonably agreed with in vivo values. The mechanistic equations modestly underpredicted K _P for both drugs. Tissue metabolism, saturable tissue binding, and active uptake are possible factors that can complicate assessments of in vivo tissue binding of steroids when using tissue homogenates. SIGNIFICANCE STATEMENT: Assuming the free hormone hypothesis, the ratio of the unbound drug fraction in plasma and in tissues defines the tissue-to-plasma partition coefficient (K _P), an important parameter in physiologically based pharmacokinetic modeling that determines total drug concentrations within tissues and the steady-state volume of distribution. This study assessed the plasma and tissue binding properties of the synthetic corticosteroids, dexamethasone and methylprednisolone, in rats using ultrafiltration and tissue homogenate techniques. In vitro-in vivo and in silico-in vivo extrapolation of K _P was assessed for both drugs in liver, muscle, and lung. Although the extrapolation was fairly successful across the tissues, in vitro homogenate studies severely underpredicted the K _P of methylprednisolone in liver, partly attributable to the extensive hepatic metabolism.

A benzothiadiazine derivative and methylprednisolone are novel and selective activators of transient receptor potential canonical 5 (TRPC5) channels

The transient receptor potential canonical channel 5 (TRPC5) is a Ca²⁺-permeable ion channel, which is predominantly expressed in the brain. TRPC5-deficient mice exhibit a reduced innate fear response and impaired motor control. In addition, outgrowth of hippocampal and cerebellar neurons is retarded by TRPC5. However, pharmacological evidence of TRPC5 function on cellular or organismic levels is sparse. Thus, there is still a need for identifying novel and efficient TRPC5 channel modulators. We, therefore, screened compound libraries and identified the glucocorticoid methylprednisolone and N-[3-(adamantan-2-yloxy)propyl]-3-(6-methyl-1,1-dioxo-2H-1λ⁶,2,4-benzothiadiazin-3-yl)propanamide (BTD) as novel TRPC5 activators. Comparisons with closely related chemical structures from the same libraries indicate important substructures for compound efficacy. Methylprednisolone activates TRPC5 heterologously expressed in HEK293 cells with an EC₅₀ of 12μM, while BTD-induced half-maximal activation is achieved with 5-fold lower concentrations, both in Ca²⁺ assays (EC₅₀=1.4μM) and in electrophysiological whole cell patch clamp recordings (EC₅₀=1.3 μM). The activation resulting from both compounds is long lasting, reversible and sensitive to clemizole, a recently established TRPC5 inhibitor. No influence of BTD on homotetrameric members of the remaining TRPC family was observed. On the main sensory TRP channels (TRPA1, TRPV1, TRPM3, TRPM8) BTD exerts only minor activity. Furthermore, BTD can activate heteromeric channel complexes consisting of TRPC5 and its closest relatives TRPC1 or TRPC4, suggesting a high selectivity of BTD for channel complexes bearing at least one TRPC5 subunit.

Glucocorticoid administration in athletes: Performance, metabolism and detection

It is generally acknowledged in the sporting world that glucocorticoid (GC) use enhances physical performance. This pharmacological class is therefore banned by the World Anti-Doping Agency (WADA) in in-competition samples after systemic but not local (defined as any route other than oral, intravenous, intramuscular or rectal) administration, which thus allows athletes to use GCs for therapeutic purposes. According to the 2016 WADA list, the urine reporting level for all GCs is set at 30ng/ml to distinguish between the authorized and banned routes of administration. The actual data on the ergogenic effects of GC intake are nevertheless fairly recent, with the first study showing improved physical performance with systemic GC administration dating back only to 2007. Moreover, the studies over the last decade coupling ergogenic and metabolic investigations in humans during and after GC intake have shown discrepant results. Similarly, urine discrimination between banned and authorized GC use remains complex, but it seems likely to be improved thanks to new analytical studies and the inclusion of the authorized GC uses (local routes of administration and out-of-competition samples) in the WADA monitoring program. In this review, we first summarize the current knowledge on the ergogenic and metabolic GC effects in humans during various types of exercise. We then present the antidoping legislation and methods of analysis currently used to detect GC abuse and conclude with some practical considerations and perspectives.

Review article: The pharmacokinetics and pharmacodynamics of drugs used in inflammatory bowel disease treatment

BACKGROUND

The following review is a compilation of the recent advances and knowledge on the behaviour of the most frequently used compounds to treat inflammatory bowel disease in an organism.

RESULTS

It considers clinical aspects of each entity and the pharmacokinetic/pharmacodynamic relationship supported by the use of plasma monitoring, tissue concentrations, and certain aspects derived from pharmacogenetics.

The role of human carboxylesterases in drug metabolism: have we overlooked their importance?

Carboxylesterases are a multigene family of mammalian enzymes widely distributed throughout the body that catalyze the hydrolysis of esters, amides, thioesters, and carbamates. In humans, two carboxylesterases, hCE1 and hCE2, are important mediators of drug metabolism. Both are expressed in the liver, but hCE1 greatly exceeds hCE2. In the intestine, only hCE2 is present and highly expressed. The most common drug substrates of these enzymes are ester prodrugs specifically designed to enhance oral bioavailability by hydrolysis to the active carboxylic acid after absorption from the gastrointestinal tract. Carboxylesterases also play an important role in the hydrolysis of some drugs to inactive metabolites. It has been widely believed that drugs undergoing hydrolysis by hCE1 and hCE2 are not subject to clinically significant alterations in their disposition, but evidence exists that genetic polymorphisms, drug-drug interactions, drug-disease interactions and other factors are important determinants of the variability in the therapeutic response to carboxylesterase-substrate drugs. The implications for drug therapy are far-reaching, as substrate drugs include numerous examples from widely prescribed therapeutic classes. Representative drugs include angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, antiplatelet drugs, statins, antivirals, and central nervous system agents. As research interest increases in the carboxylesterases, evidence is accumulating of their important role in drug metabolism and, therefore, the outcomes of pharmacotherapy.

Dose-ranging pharmacokinetics of colistin methanesulphonate (CMS) and colistin in rats following single intravenous CMS doses

OBJECTIVES

The aim of this study was to evaluate the effect of colistin methanesulphonate (CMS) dose on CMS and colistin pharmacokinetics in rats.

METHODS

Three rats per group received an intravenous bolus of CMS at a dose of 5, 15, 30, 60 or 120 mg/kg. Arterial blood samples were drawn at 0, 5, 15, 30, 60, 90, 120, 150 and 180 min. CMS and colistin plasma concentrations were determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS). The pharmacokinetic parameters of CMS and colistin were calculated by non-compartmental analysis.

RESULTS

Linear relationships were observed between CMS and colistin AUCs to infinity and CMS doses, as well as between CMS and colistin C(max) and CMS doses.

CONCLUSIONS

CMS and colistin pharmacokinetics were linear for a range of colistin concentrations covering the range of values encountered and recommended in patients even during treatment with higher doses.

Prodrug strategies to overcome poor water solubility

Drug design in recent years has attempted to explore new chemical spaces resulting in more complex, larger molecular weight molecules, often with limited water solubility. To deliver molecules with these properties, pharmaceutical scientists have explored many different techniques. An older but time-tested strategy is the design of bioreversible, more water-soluble derivatives of the problematic molecule, or prodrugs. This review explores the use of prodrugs to effect improved oral and parenteral delivery of poorly water-soluble problematic drugs, using both marketed as well as investigational prodrugs as examples. Prodrug interventions should be considered early in the drug discovery paradigm rather than as a technique of last resort. Their importance is supported by the increasing percentage of approved new drug entities that are, in fact, prodrugs.

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.

Methylprednisolone sodium succinate in pediatric parenteral nutrition: influence of vehicle injection

Many drugs can be administered in parenteral nutrient mixtures, but no work on the delivery of corticoids by such means is reported. We studied the influence of pediatric parenteral nutrient mixtures on the kinetic parameters of the corticoid methylprednisolone injected in an intravenous bolus in rabbits as its sodium succinate ester. Four groups of six male New Zealand rabbits were used. After extraction, the plasma drug concentrations were measured by high performance liquid chromatography. The distribution volume of the ester and the clearance rates of the two entities (ester and methylprednisolone) were lowered in the presence of a lipid emulsion. The description of these pharmacokinetic parameters provides a basis for a preclinical study of 24h administration of methylprednisolone in a parenteral nutrient mixture.

Pharmacokinetic considerations in the treatment of inflammatory bowel disease

This review describes the pharmacokinetics of the major drugs used for the treatment of inflammatory bowel disease. This information can be helpful for the selection of a particular agent and offers guidance for effective and well tolerated regimens. The corticosteroids have a short elimination half-life (t1/2beta) of 1.5 to 4 hours, but their biological half-lives are much longer (12 to 36 hours). Most are moderate or high clearance drugs that are hepatically eliminated, primarily by cytochrome P450 (CYP) 3A4-mediated metabolism. Prednisone and budesonide undergo presystemic elimination. Any disease state or comedication affecting CYP3A4 activity should be taken into account when prescribing corticosteroids. Depending on the preparation used, 10 to 50% of an oral or rectal dose of mesalazine is absorbed. Rapid acetylation in the intestinal wall and liver (t1/2beta 0.5 to 2 hours) and transport probably by P-glycoprotein affect mucosal concentrations of mesalazine, which apparently determine clinical response. Any clinical condition influencing the release and topical availability of mesalazine might modify its therapeutic potential. Metronidazole has high (approximately 90%) oral bioavailability, with hepatic elimination characterised by a t1/2beta of 6 to 10 hours and a total clearance of about 4 L/h/kg. Ciprofloxacin is largely excreted unchanged both renally (about 45% of dose) and extrarenally (25%), with a relatively short t1/2beta (3.5 to 7 hours). Thus, renal function affects the systemic availability of ciprofloxacin. Both mercaptopurine and its prodrug azathioprine are metabolised to active compounds (6-thioguanine nucleotides; 6-TGN) by hypoxanthine-guanine phosphoribosyltransferase and to inactive metabolites by the polymorphically expressed thiopurine S-methyltransferase (TPMT) and xanthine oxidase. Patients with low TPMT activity have a higher risk of developing haemopoietic toxicity. Both mercaptopurine and azathioprine have a short t1/2beta (1 to 2 hours), but the t1/2beta of 6-TGN ranges from 3 to 13 days. Therapeutic response seems to be related to 6-TGN concentration. Almost complete bioavailability has been observed after intramuscular and subcutaneous administration of methotrexate, which is predominantly (85%) excreted as unchanged drug with a t1/2beta of up to 50 hours. Thus, renal function is the major determinant for disposition of methotrexate. Cyclosporin is slowly and incompletely absorbed. It is extensively metabolised by CYP3A4/5 in the liver and intestine (median t1/2beta and clearance 7.9 hours and 0.46 L/h/kg, respectively), and inhibitors and inducers of CYP3A4 can modify response and toxicity. Infliximab is predominantly distributed to the vascular compartment and eliminated with a t1/2beta between 10 and 14 days. No accumulation was observed when it was administered at intervals of 4 or 8 weeks. Methotrexate may reduce the clearance of infliximab from serum.

Methylprednisolone concentrations in the vitreous and the serum after pulse therapy

PURPOSE

Intravenous (i.v.) pulse of corticosteroids has been used to treat severe eye inflammation from different origins. Whether such large doses result in vitreous levels that differ either in magnitude or duration from more conventional corticotherapy remain unsolved issues. The authors therefore determined levels of methylprednisolone hemisuccinate and methylprednisolone in the vitreous and serum of patients at different times after a single i.v. perfusion of methylprednisolone hemisuccinate.

METHODS

Fifty patients scheduled for a first vitrectomy received an i.v. injection of 500 mg hemisuccinate methylprednisolone at different times before surgery (from 15-24 hours). Patients were divided into two groups: those with (n = 21) and without (n = 29) retinal detachment (RD). Pure vitreous samples were analyzed by high-pressure liquid chromatography.

RESULTS

Both the ester and the nonester methylprednisolone forms were sampled in the vitreous, showing a slower rate of hydrolysis compared to the serum. On average, the highest concentration of total methylprednisolone in the vitreous was found at 2.5 hours and rapidly decreased for the group of patients with RD. In the group of patients without RD, the highest concentration was reached at 6 hours and then slowly decreased. The antiinflammatory potency in the nondetached retina eyes was approximately 500 times more than in the physiologic vitreous, but despite the route of administration (i.v. or oral), only 1/10 of the corticosteroid serum concentration was measured in the vitreous.

CONCLUSION

High concentration of methylprednisolone is achieved by i.v. pulse therapy without changing the kinetic of entry in the vitreous of nondetached retina eyes when compared to conventional oral corticotherapy. Hydrolysis occurs in the vitreous resulting in high rate of active form. Pulse therapy could be considered in cases of severe ocular inflammation involving the posterior segment of the eye.

Time-variant increase in methylprednisolone clearance in patients with acute respiratory distress syndrome: a population pharmacokinetic study

Methylprednisolone (MP) disposition was evaluated in 20 individuals who participated in an ongoing randomized, double-blind, placebo-controlled study designed to evaluate the efficacy of MP in the treatment of acute respiratory distress syndrome (ARDS). MP (1 mg/kg) was given as a loading infusion over 30 minutes followed by a 1 mg/kg/day continuous i.v. infusion. Patients were switched to oral MP upon restoration of oral intake. MP plasma concentrations (n = 110) were determined using a specific HPLC method. Population pharmacokinetic analysis was performed using nonlinear mixed-effects models, implemented in NONMEM, version V. MP plasma concentration data were described by a one-compartment open model with a time-dependent, non-linear increase in the clearance (CL) of MP during the course of therapy. Initial clearance of MP (CLo) in ARDS patients at the start of therapy increased to a maximal value (CLmax) after approximately 7 days. The estimate of CLmax was similar to the CL of MP in healthy individuals reported previously. Population mean estimates (+/- SE) of parameters in the model were as follows: CLo = 13.2 +/- 2.4 L/h, CLmax = 25.0 +/- 3.6 L/h, time of half-maximal increase in CL (T50) = 41.1 +/- 8.2 h, gamma (Hill coefficient) = 3.8 +/- 0.6, and volume of distribution (Vd) = 137 +/- 30.2 L. Disease progression indices and patient demographics were evaluated as covariates, and no significant correlation was found. Means (+/- SD) of plasma protein binding differed between healthy individuals (72% +/- 4%) and ARDS patients (46% +/- 11%) (p < 0.001). The pharmacokinetics of MP in ARDS patients has not been described previously.

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

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

Pharmacokinetics of methylprednisolone and prednisolone after single and multiple oral administration

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

Methylprednisolone inhibits uptake of Ca2+ and Na+ ions into concanavalin A-stimulated thymocytes

The glucocorticoid drug methylprednisolone inhibits respiration in concanavalin A-stimulated rat thymocytes at concentrations that are relevant to its acute clinical efficacy against autoimmune diseases and spinal cord injury. Methylprednisolone affects several processes, including ion cycling, substrate oxidation reactions and RNA/DNA synthesis. The inhibition of respiration used to drive ATP-consuming cycles of Ca2+ and Na+ ions across the plasma membrane has been proposed to be either primary or secondary to restriction of cellular ATP supply. By comparing the effects of methylprednisolone with those of myxothiazol, an inhibitor of the mitochondrial electron transport chain, we show that the effects of methylprednisolone on Ca2+ and Na+ cycling are primary. We propose that methylprednisolone acts by affecting membrane properties to inhibit Ca2+ and Na+ uptake across the plasma membrane and to increase H+ uptake across the mitochondrial membrane, and that other effects are secondary.

Steroid therapy in obstructive airway diseases

Asthma and chronic obstructive pulmonary disease (COPD) are two common illnesses that cause significant morbidity and mortality. Steroids are widely used in both conditions. They act through steroid or glucocorticoid receptors (GR) causing up or down regulation of protein synthesis resulting in an increase in lipocortin 1 and beta 2 adrenergic receptors, and decreased levels and activities of cytokines or cytokine receptors, which reduces the inflammatory process in the airways and decreases bronchial hyperreactivity. Consequently symptoms of airway obstruction are alleviated and lung function is improved. In asthma, steroids have been convincingly shown to be effective in the treatment of both acute exacerbations and chronic condition. In COPD, however, only a subset of patients seem to respond favourably to steroid therapy. Therapeutic trials are therefore recommended before committing to a long-term treatment in order to determine this subset of patients, as no markers of steroid responsiveness can be identified. The inhaled steroids currently available have a good safety profile with significant side effects occurring only occasionally. Such side effects are usually confined to the oropharynx, causing local irritation, candidiasis and dysphonia, which can be easily overcome. Biochemical abnormalities involving bone, adrenal, carbohydrate and lipid profiles have been noted with high doses of inhaled steroids; however, these have no significant clinical effects.

Effects of methylprednisolone on lesioned and uninjured mammalian spinal neurons: viability, ultrastructure, and network electrophysiology

An in vitro investigation was undertaken to provide information regarding the effectiveness of methylprednisolone sodium succinate (MPSS) as a treatment for the primary mechanical injury of spinal cord (SC) trauma. Exposure of uninjured mouse SC cells to MPSS for 24 h caused neuronal stress when the concentration exceeded 150 micrograms/mL; neuronal death occurred at concentrations above 600 micrograms/mL. The concentration range for MPSS protection of SC neurons subjected to a defined physical injury (laser microbeam transection of a primary dendrite 100 microns from the perikaryon) was very narrow: survival in the 30 micrograms/mL group differed significantly from the untreated control group (68.5% +/- 14.1 vs. 47.1% +/- 14.1), treatment with 20 or 60 micrograms/mL MPSS did not increase survival, and treatment with 100 micrograms/mL MPSS accelerated ultrastructural deterioration and increased the likelihood of death. Enhanced survival of lesioned neurons was observed when 30 micrograms/mL MPSS was applied within 15 min of dendrotomy but not when MPSS was administered 2 h after lesioning. Multimicroelectrode plate (MMEP) studies of SC network electrical activity indicated that MPSS associated readily with neuronal membranes. This finding was consistent with the hypothesis that MPSS may protect lesioned neurons by stabilizing damaged membranes, enhancing lesion resealing, and limiting the spread of ion-mediated damage. However, comparisons of neurite die-back 24 h after dendrotomy found no significant difference between MPSS-treated and control neurons. Application of 30 or 100 micrograms/mL MPSS increased the spontaneous burst activity of SC networks grown on MMEPs, however, there was no evidence that the increased excitability at these concentrations was the result of specific actions of MPSS on GABA or NMDA synapses.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Pilot study of the pharmacokinetics of methylprednisolone after single and multiple intravenous doses of methylprednisolone sodium succinate and methylprednisolone suleptanate to healthy volunteers

The pharmacokinetics of methylprednisolone were evaluated in 29 healthy volunteers after multiple intravenous doses of methylprednisolone sodium succinate or the novel prodrug, methylprednisolone suleptanate. Subjects were assigned randomly to one of four treatment groups (40, 100, 250, or 500 mg) and then randomly assigned to receive either the sodium succinate or suleptanate prodrugs. Doses were administered every 6 hours for 48 hours. Plasma and urine were assayed for methylprednisolone and unchanged prodrug using HPLC methods. Methylprednisolone pharmacokinetics exhibited both a dose and time dependency, which was similar for administration of both prodrugs. After first-dose administration, mean clearance increased from 19.5 L/hr for 40-mg doses to 27.7 L/hr after 500-mg doses of the sodium succinate ester, and from 20.1 to 31.7 L/hr after the suleptanate ester. After multiple dosing, mean clearance values increased from 31.1 to 44.7 L/hr for sodium succinate dosing, and from 31.5 to 46.0 L/hr for suleptanate dosing. Apparent systemic clearance values determined after multiple dosing were 1.5- to 1.8-fold greater than corresponding first-dose values. No dependence on time was apparent for any prodrug pharmacokinetic parameter. These data suggest that the dose dependency of methylprednisolone pharmacokinetics is related to dose-dependent prodrug hydrolysis, whereas the time dependence possibly reflects auto-induction of methylprednisolone metabolism. Based on comparison of methylprednisolone pharmacokinetic parameters derived for each prodrug, methylprednisolone suleptanate resulted in a faster and slightly more efficient conversion to methylprednisolone than methylprednisolone sodium succinate.

Inhaled corticosteroids in asthma: a dose-proportionality study with triamcinolone acetonide aerosol

The systemic exposure to triamcinolone acetonide (TAA) after inhalation of aerosolized drug has not been examined previously. This study evaluates the plasma concentrations, pharmacokinetics and dose proportionality of TAA after single oral inhalations at doses of 400, 800, and 1600 mcg. Nine moderately asthmatic male patients received each of the doses in a randomized crossover manner using a 1-week washout period between dosing. Serial blood samples were collected for 10 hours postdosing for the determination of plasma TAA concentrations by using a specific radioimmunoassay. The pharmacokinetic profiles that were obtained showed slow and limited absorption over the first 4 hours after dosing followed by rapid elimination with a half-life of approximately 2 hours (range: 1.8-2.3 hr). Comparison of pharmacokinetic parameters from each dose group showed excellent proportionality and consistent absorption for all patients. Mean Cmax values ranged from 0.51 ng/mL after the 400 mcg dose to 1.01 ng/mL and 1.97 ng/mL after the 800 and 1600 mcg doses, respectively. Mean AUC0-10 values for these same doses were 2.6 ng x hr/mL, 5.3 ng x hr/mL and 10.5 ng x hr/mL, respectively. The results suggest that systemic exposure to TAA is minimal after oral inhalation, occurs in a dose proportional fashion, and produces circulating plasma concentrations which are unlikely to have significant adverse systemic effects.

High dose oral methylprednisolone in patients with rheumatoid arthritis: pharmacokinetics and clinical response

A commercially available 1.0 g intravenous (i.v.) dosage formulation of methylprednisolone, as the sodium hemisuccinate salt (Solu Medrol, Upjohn) was administered both parenterally and orally (pulse steroid therapy) on separate occasions, to eight elderly (mean 65 y) patients with active rheumatoid arthritis. The relative oral bioavailability of the sterol was 69.2%. Elimination of methylprednisolone was prolonged when given orally; the mean residence times were 7.23 h and 3.94 h for oral and i.v. administrations, respectively. Clinical response to pulse steroid therapy was no different with respect to route of administration. There were no significant differences in standard clinical and laboratory assessments of disease activity when the two therapies were compared. Oral administration of methylprednisolone in patients requiring high-dose pulse steroid therapy is convenient and avoids the discomfort and inconvenience associated with i.v. administration.

Disposition of methylprednisolone and its sodium succinate prodrug in vivo and in perfused liver of rats: nonlinear and sequential first-pass elimination

The disposition of methylprednisolone (MP) and its prodrug succinate ester, methylprednisolone sodium succinate (MS), were examined both in vivo and in situ (perfused livers) in rats. In vivo studies included iv and oral dosing of 10 or 50 mg/kg of MP in both forms, while liver perfusion involved initial perfusate concentrations of 5 and 25 micrograms/mL of either compound. Steroid concentrations were measured by HPLC. In the intact rat, clearance (CL) values of both compounds were high, twice the hepatic plasma flow, and decreased by one-half after the high dose, indicating nonlinear kinetics. The volumes of distribution of MS and MP were essentially constant with dose. Incomplete availability of MP from iv MS (52-55%) and from the oral dose (10%) was found. Sequential first-pass metabolism was investigated in situ. Extensive hepatic extraction of MP (84%) occurred at the low dose, but decreased to 48% at the high dose, supporting in vivo observations of high CL and nonlinearity. Extraction of MS was also high (83%), but MP availability was slight (8%). The MS and MP data were fitted to a sequential first-pass model yielding an average fraction of MS metabolized-to-MP value of 0.22. The prodrug MS and the active metabolite MP thus demonstrate both systemic and hepatic nonlinearity in rats, and the low availability of MP from iv MS was due, in part, to sequential first-pass elimination. This factor is more extensive in rats than in other species.

In vitro hydrolysis of steroid acid ester derivatives of prednisolone in plasma of different species

The in vitro hydrolysis of two new classes of steroid acid esters synthesized from prednisolone as local anti-inflammatory steroids was investigated in rat, rabbit, and human plasma. One class was synthesized by incorporating methoxycarbonyl groups at the 16 position of prednisolone to produce 16 alpha-methoxycarbonyl prednisolone (P16CM) and its 17-deoxy analogue (DP16CM). The other class was synthesized by modifying the ketol side chain of prednisolone to produce methyl 20 alpha- and methyl beta-dihydroprednisolonate (P4 alpha and P4 beta). The P16CM and P4 beta were rapidly and completely hydrolyzed within 1 h of incubation in rat and rabbit plasma and within 4 h in human plasma. There was a marked species difference in the hydrolysis of DP16CM which occurred in the following order: rat greater than human greater than rabbit. The in vitro hydrolysis of P4 alpha was much slower than that of P4 beta; the process continued over 24 h in rat plasma. As expected, no change in the initial concentration of prednisolone was found over 120 h of incubation in rat plasma. This marked species difference in the hydrolysis of these steroid acid esters is probably related to the differences in the amounts, types, and activities of the hydrolyzing enzymes (e.g., esterases) in the plasma of the three species. From this study it can be concluded that the existence of an hydroxyl group at C-17 and the orientation of hydroxyl groups at C-20 play an important role in the systemic hydrolysis rate of the carboxy ester group on the steroid nucleus.

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

Pharmacodynamic models for "directly suppressive" effects of methylprednisolone are based on the premise that receptor interactions of steroids are followed by immediate suppression of either the circadian secretion of cortisol or the constant rate recirculation of histamine-containing basophils that persists until inhibitory concentrations of methylprednisolone disappear. Methylprednisolone doses of 0, 10, 20, and 40 mg were given as the 21-succinate sodium salt in a balanced crossover study to six normal men. Plasma steroid concentrations and blood histamine were measured simultaneously. Both forms of methylprednisolone exhibited linear kinetic parameters. One dynamic model quantitates the baseline circadian pattern and the decline and return of cortisol with similar parameter estimates for all three dose levels. A similar model describes the monoexponential decline and the log-linear return to steady-state baseline of blood histamine. Similar inhibitory concentration values for both effects approximated the equilibrium dissociation constant of in vitro steroid receptor binding. The new models are more physiologically appropriate for these steroid effects than three other models that are commonly employed in pharmacodynamics. Steroid effects generally appear to be receptor mediated with either nongene immediate responses or gene-mediated delayed effects. These models allow quantitation of the rapid effects of steroids with simple equations and common fitted parameters for all steroid dose levels.

Urinary excretion of prednisolone following intravenous administration in humans

The urinary excretion of prednisolone was studied in eight normal human volunteers (two women and six men) following intravenous (16, 32, 48 and 64 mg) doses. Urine prednisolone concentrations were determined by a high performance thin layer chromatographic method (HPTLC). The overall mean prednisolone elimination half life in urine following all the intravenous doses as determined by the rate and sigma minus plots was 1.13 +/- 0.25 hour. This was independent of dose and shorter than that found in plasma (4.10 +/- 1.00 s.d. hour). The overall mean percentage of dose excreted unchanged in urine was 16.7 +/- 5.8% following all intravenous and oral doses respectively. About 80% of this amount was excreted within the first 4 hours of the intravenous administration. Renal clearance of prednisolone decreased with time by the first order kinetic (r = 0.790) and its overall value following all IV doses was 0.0183 +/- 0.0103 (s.d.) l/h/kg. The metabolic clearance remained constant with increasing doses from 16 to 64 mg (0.0883 +/- 0.0306 s.d. l/h/kg). From this study it was concluded that a definitive account of the renal elimination of prednisolone and its possible metabolites warrant further investigation. The fraction of the dose excreted unchanged was relatively small and variable suggesting that prednisolone elimination occurs mainly by metabolism.

Pharmacokinetics and dose linearity testing of methylprednisolone phosphate

The pharmacokinetics of methylprednisolone and methylprednisolone phosphate were investigated after intravenous administration of methylprednisolone phosphate to six healthy subjects at seven different doses between 16 and 1000 mg. Plasma, urine, and saliva were analyzed for methylprednisolone and methylprednisolone phosphate. Furthermore, endogenous hydrocortisone was measured in plasma. No non-linearity in the total body clearance of methylprednisolone phosphate or methylprednisolone could be detected. The average elimination half-life for the prodrug was 3.7 min indicating rapid hydrolysis. After 15 min more than 90 per cent of the phosphate has been hydrolyzed. No prodrug could be detected in saliva; very little of the ester (average 0.9 per cent of the dose) was excreted unchanged into the urine. Methylprednisolone is formed rapidly. The total body clearance was 21 1h-1, the terminal half-life 2.8 h. In the post-distribution phase methylprednisolone levels in saliva went parallel to plasma levels. The mean saliva/plasma ratio was 0.22. An average of 5.2 per cent of the dose was eliminated into the urine in the form of methylprednisolone. Hydrocortisone suppression was dose-dependent. For doses above 125 mg hydrocortisone levels were significantly lowered after 24 h. For doses above 500 mg the suppression was still significant after 48 h. The results indicate a rapid and predictable in vivo conversion of methylprednisolone phosphate to its active form methylprednisolone.

Methylprednisolone pharmacokinetics after intravenous and oral administration

1. The pharmacokinetics of methylprednisolone (MP) were studied in five normal subjects following intravenous doses of 20, 40 and 80 mg methylprednisolone sodium succinate (MPSS) and an oral dose of 20 mg methylprednisolone as 4 x 5 mg tablets. Plasma concentrations of MP and MPSS were measured by both high performance thin layer (h.p.t.l.c.) and high pressure liquid chromatography (h.p.l.c.). 2. The mean values (+/- s.d.) of half-life, mean residence time (MRT), systemic clearance (CL) and volume of distribution at steady state (Vss) of MP following intravenous administration were 1.93 +/- 0.35 h, 3.50 +/- 1.01 h, 0.45 +/- 0.12 lh-1 kg-1 and 1.5 +/- 0.63 1 kg-1, respectively. There was no evidence of dose-related changes in these values. The plasma MP concentration-time curves were superimposable when normalized for dose. 3. The bioavailability of methylprednisolone from the 20 mg tablet was 0.82 +/- 0.11 (s.d.). 4. In vivo hydrolysis of MPSS was rapid with a half-life of 4.14 +/- 1.62 (s.d.) min, and was independent of dose. In contrast, in vitro hydrolysis in plasma, whole blood and red blood cells was slow; the process continuing for more than 7 days. Sodium fluoride did not prevent the hydrolysis of MPSS.

Comparative pharmacokinetics of methylprednisolone phosphate and hemisuccinate in high doses

The pharmacokinetics of methylprednisolone and two methylprednisolone esters, the phosphate and the hemisuccinate, were investigated after intravenous administration of the esters to 12 healthy male subjects in two different doses (250 and 1000 mg). Methylprednisolone was formed more rapidly from phosphate than from hemisuccinate. During the first 30 min methylprednisolone levels were three to four times higher after phosphate administration than after hemisuccinate. The mean residence time of the hemisuccinate was significantly longer and the total-body clearance lower than those of the phosphate. Whereas very little of the phosphate (mean, 1.7%) was eliminated unchanged into the urine, there were significant amounts of hemisuccinate (mean, 14.7%) excreted renally and therefore not bioavailable. Methylprednisolone saliva levels paralleled plasma levels; the average saliva/plasma ratio was 0.22. Neither phosphate nor hemisuccinate could be detected in saliva. An average of 7.2% of the administered dose was eliminated in the form of methylprednisolone in urine. Renal clearance was 24 ml/min and not dose or prodrug dependent. For both doses endogenous hydrocortisone levels were lowered after 24 hr. For the 1000-mg dose the depression was still significant after 48 hr. The results indicate that methylprednisolone phosphate results in a faster and more efficient conversion to its active form, methylprednisolone, than methylprednisolone hemisuccinate.

Pharmacokinetics of methylprednisolone succinate, methylprednisolone, and lidocaine in the normal dog and during hemorrhagic shock

Pharmacokinetics of methylprednisolone succinate and methylprednisolone following methylprednisolone sodium succinate administration were studied in five dogs under normal conditions and then during a severe hemorrhagic shock. In order to evaluate hepatic blood flow, lidocaine clearance was simultaneously measured. In the normal state, the clearance of methylprednisolone succinate was 1.64 +/- 0.499 L/h/kg and its half-life was 15.33 +/- 3.84 min. The systemic availability of methylprednisolone from methylprednisolone succinate was 59.9 +/- 8.3%, and the maximal methylprednisolone concentration was observed after a delay of 7.68 +/- 6.31 min. Using a reservoir technique in anesthetized dogs, severe hemorrhagic shock was obtained. Changes in lidocaine clearance indicated a subsequent reduction of hepatic blood flow. The clearance of methylprednisolone succinate decreased to 0.488 +/- 0.240 L/kg/h, and the half-life increased to 40.66 +/- 23.48 min. The exact availability of methylprednisolone from methylprednisolone succinate during shock was not calculable because methylprednisolone kinetics were time dependent. The plasma methylprednisolone concentration was relatively high and persistent during the shock. It was concluded that methylprednisolone sodium succinate is a prodrug which can be released in sufficient quantities as its active moiety (i.e., methylprednisolone) during severe hemorrhagic shock in the dog. In addition, after a single intravenous administration, the slow process of methylprednisolone elimination may give sustained methylprednisolone concentrations for several hours.

Pharmacokinetics of dexamethasone and its phosphate ester

Dexamethasone in form of its phosphate was given intravenously in two different doses (1.5 mg kg-1 and 15 mg). Plasma levels of the ester and dexamethasone were measured and pharmacokinetic parameters were calculated. The results indicate no dose-dependency of the pharmacokinetic parameters in the investigated range for dexamethasone. Conversion from the prodrug to the active form was rapid; maximum dexamethasone plasma concentrations were reached after 10 min. The results were verified by dexamethasone level monitoring in patients after chronic dosing. Predicted and achieved steady state levels agreed well.

Determination of methylprednisolone in rat tissue by high-performance liquid chromatography

Methylprednisolone was determined in various types of rat tissue following an intravenous injection of methylprednisolone sodium succinate. Two modes of tissue work-up were investigated: digestion with subtilisin Carlsberg, a proteolytic enzyme, and homogenization with methanol. The final determination was by reversed-phase high-performance liquid chromatography with dexamethasone as internal standard. The extraction yields of methylprednisolone and dexamethasone from tissue homogenate and the extraction yield of methylprednisolone after incubation with viable tissue were determined. The experiments show that methylprednisolone and the internal standard are extracted in similar yields from tissue homogenates and that methylprednisolone can be recovered in a good yield after incubation with viable tissue, provided that the tissue does not have a high metabolic activity. There was a good agreement between the analytical results from the two different types of tissue work-up. The method of analysis proved feasible for pharmacokinetic work.

Dose-dependent pharmacokinetics of prednisolone in normal and adrenalectomized rats

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

Oral absorption of 21-corticosteroid esters: a function of aqueous stability and intestinal enzyme activity and distribution

The intestinal absorption of hydrocortisone and prednisolone are compared with three water-soluble derivatives (succinate, phosphate, and lysinate) in experiments at two levels of biological system complexity. Rates of absorption are compared by measuring permeabilities from rat intestinal perfusions of drugs and derivatives in solution. Extents of absorption are compared over a 10-fold dose range of parent steroid and with the steroid derivatives by measuring plasma levels from solid oral dosage in dogs. While the parent steroids are well absorbed over the entire length of the intestinal tract, variability in plasma levels is observed at higher doses. Limited solubility and resultant dissolution rate variability are likely to be playing a role in the early erratic blood level profiles found at higher doses. While the soluble prodrugs have a dissolution rate advantage which results in a greater concentration gradient, their absorption is limited by their aqueous luminal stability, their polarity and resultant passive membrane permeability, and the distribution and activity of enzyme reconversion sites in the intestinal tract. The unstable lysinate ester, targeted for aminopeptidase, has an absorption profile and permeability similar to that of the parent steroid. The absorption of the moderately stable succinate ester is limited by its polarity and the activity of intestinal esterases. The stable phosphate derivative is well absorbed in the upper intestine, where high levels of alkaline phosphatase exist, while the prodrug polarity and drop-off of enzyme activity limit its absorption from the lower gastrointestinal (GI) tract.

Pharmacokinetics of methylprednisolone, methylprednisolone sodium succinate, and methylprednisolone acetate in dogs

The absolute bioavailability and pharmacokinetic parameters of two methylprednisolone formulations (methylprednisolone sodium succinate and methylprednisolone acetate) were determined in five dogs. Plasma concentrations of methylprednisolone, methylprednisolone sodium succinate, and methylprednisolone acetate were measured by sensitive and specific high-performance liquid chromatographic methods. After intravenous methylprednisolone sodium succinate administration, methylprednisolone was released rapidly but the extent of availability was rather low (43.6%). This has been tentatively explained in terms of its subsequent single-pass metabolism in the liver, i.e., hepatic hydrolysis of methylprednisolone sodium succinate followed by immediate hepatic elimination of the released methylprednisolone. After intramuscular administration of methylprednisolone acetate, its absorption was slow (half-time of absorption, 69.04 h) and the availability of the released methylprednisolone was low (42.7%). Therapeutic implications of these results are discussed, especially those which are relevant to shock therapy.

Pharmacokinetics of prednisolone after high doses of prednisolone hemisuccinate

Prednisolone in the form of its hemisuccinate was given intravenously in two different doses (1200 mg and 75 mg). Plasma levels of the ester and prednisolone were measured and pharmacokinetic parameters were calculated. The results indicate a dose-dependency in the pharmacokinetics of both hemisuccinate and the free alcohol. For the high dose 8 per cent of the administered ester was found unchanged in the urine indicating incomplete conversion of the pro-drug. Comparison with previous studies leads to the conclusion that prednisolone shows doubled non-linear pharmacokinetics with higher total body clearance in the medium dose range than in the low and high dose range. Volume of distribution changes accordingly, but overall elimination rate remains remarkably constant. Saliva levels of prednisolone were low and agree reasonably well with calculated plasma concentrations of free, non-protein-bound prednisolone. No prednisolone hemisuccinate was found in saliva.

Pharmacokinetics of triamcinolone acetonide and its phosphate ester

Triamcinolone acetonide in the form of its phosphate ester was given intravenously in two different doses (10 mg/kg and 80 mg). Plasma levels of the ester and triamcinolone acetonide were measured and pharmacokinetic parameters were calculated. The pharmacokinetics both of the phosphate and the free alcohol were dose-dependent. No unchanged ester was found in the urine, indicating complete conversion of the pro-drug. Triamcinolone was not a major metabolite of triamcinolone acetonide in humans. Renal clearance was low and independent of the dose. Only about 1% of the dose was found in the urine as triamcinolone acetonide.