Pharmacokinetics and protein binding of prednisolone after oral and intravenous administration

Clinical Pharmacokinetic and Pharmacodynamic Considerations in the Treatment of Ulcerative Colitis

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) of unknown etiology, probably caused by a combination of genetic and environmental factors. The treatment of patients with active UC depends on the severity, localization and history of IBD medication. According to the classic step-up approach, treatment with 5-aminosalicylic acid compounds is the first step in the treatment of mild to moderately active UC. Corticosteroids, such as prednisolone are used in UC patients with moderate to severe disease activity, but only for remission induction therapy because of side effects associated with long-term use. Thiopurines are the next step in the treatment of active UC but monotherapy during induction therapy in UC patients is not preferred because of their slow onset. Therapeutic drug monitoring (TDM) of the pharmacologically active metabolites of thiopurines, 6-thioguanine nucleotide (6-TGN), has proven to be beneficial. Thiopurine S-methyltransferase (TMPT) plays a role in the metabolic conversion pathway of thiopurines and exhibits genetic polymorphism; however, the clinical benefit and relevance of TPMT genotyping is not well established. In patients with severely active UC refractory to corticosteroids, calcineurin inhibitors such as ciclosporin A (CsA) and tacrolimus are potential therapeutic options. These agents usually have a rather rapid onset of action. Monoclonal antibodies (anti-tumor necrosis factor [TNF] agents, vedolizumab) are the last pharmacotherapeutic option for UC patients before surgery becomes inevitable. Body weight, albumin status and antidrug antibodies contribute to the variability in the pharmacokinetics of anti-TNF agents. Additionally, the use of concomitant immunomodulators (thiopurines/methotrexate) lowers the rate of immunogenicity, and therefore the concomitant use of anti-TNF therapy with an immunomodulator may confer some advantage compared with monotherapy in certain patients. TDM of anti-TNF agents could be beneficial in patients with primary nonresponse and secondary loss of response. The potential benefit of applying TDM during vedolizumab treatment has yet to be determined.

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.

Pharmacokinetics and Bioavailability Study of a Prednisolone Tablet as a Single Oral Dose in Bangladeshi Healthy Volunteers

The aim of the study was to assess the pharmacokinetic and bioavailability of 2 formulations of 5-mg prednisolone tablets, reference product (Teva UK Limited) and Pred (Eskayef Bangladesh Ltd) as test product. The open-label, randomized, 2-way crossover studies were conducted on 14 healthy subjects. Participants were assigned to receive both products as a single dose (20 mg formulations, 4 × 5 mg tablets) followed by a 2 weeks’ washout period. Following oral administration, samples were obtained at various time intervals and analyzed for prednisolone concentrations using a validated high-performance liquid chromatography assay method with ultraviolet detection. The obtained values for test and reference products were 683.00 ± 94.54 ng/mL and 635.16 ± 125.57 ng/mL for C_max; 2716.54 ± 196.28 ng·h/mL and 2780.5 ± 119.73 ng·h/mL for AUC_0-12; 3284.36 ± 138.12 ng·h/mL and 3317.96 ± 133.95 ng·h/mL for AUC_0-∞, respectively. From the paired Student t test, no significant differences between 2 formulations were observed (P > .05). The 90% confidence intervals of C_max, AUC_0-12, and AUC_0-∞ were found to be 99.0% to 100.9%, 99.4% to 100.5%, and 99.9% to 101.3%, respectively. Finally, it can be concluded that Pred (Test) of Eskayef Bangladesh Ltd and prednisolone (Reference) of Teva UK Limited are bioequivalent and interchangeable.

Evaluation of a Sustained-Release Prednisolone Acetate Biodegradable Subconjunctival Implant in a Non-Human Primate Model

PURPOSE

We evaluate the toxicity and plasma toxicokinetic (TK) profile of a biodegradable subconjunctival microrod for sustained prednisolone acetate (PA) release over 12 weeks in a non-human primate model.

METHODS

The biodegradable copolymer poly(l-lactide-co-ε-caprolactone) (PLC) and 40-wt% PA microrods were used and fashioned into 8 and 16 mm lengths. Twelve monkeys were divided into two treatment groups of PA-loaded and blank microrods, with six monkeys each receiving either 8- or 16-mm microrods subconjunctively implanted into both eyes. TK and hematology parameters were analyzed. Ophthalmic clinical evaluation, including slit-lamp and ophthalmoscopy examinations, was performed.

RESULTS

Over the study period of 12 weeks, the mean area under the plasma concentration-time curve was 45.7% higher, and the maximum plasma concentration was 17.2% lower for the animals treated with 40-wt% PA 16-mm microrods compared to 8-mm microrods (251.44 versus 172.54 hours × nanograms per milliliter and 8.53 versus 10.30 ng/mL, respectively). The PA release was significantly below the levels of assumed toxicity. There was no significant difference in the time to reach maximum concentration between the 8- and 16-mm microrod groups (7.33 and 8 hours; P = 0.421). Findings from clinical evaluation, hematology, and histopathology showed no ocular side effects and no significant adverse systemic effects.

CONCLUSION

The PA biodegradable microrods demonstrated safe toxicokinetics even with the larger size implant containing a higher amount of drug. The PA implant may be considered as a safe alternative to the application of topical PA eyedrops.

TRANSLATIONAL RELEVANCE

The results provide the evidence of the safety of implanting a steroid delivery system subconjunctively, offering an alternative to topical PA eyedrops.

Population Pharmacokinetics of Prednisolone in Relation to Clinical Outcome in Children With Nephrotic Syndrome

BACKGROUND

The relapse frequency in children with nephrotic syndrome (NS) is highly variable despite standardized prednisolone treatment regimens. Existing evidence on the relationship between prednisolone pharmacokinetics (PK) and clinical response in children with NS is scarce and limited. The aim of this study was to develop a pediatric popPK model for prednisolone based on our previous model based on healthy adults using salivary measurements in children with NS and to correlate clinical outcome with between-subject variability in prednisolone exposure.

METHODS

The pharmacokinetics of prednisolone in a well-defined, prospective cohort consisting of 104 children with NS while in remission was determined. Pharmacokinetic parameters were analyzed in relation to relapse patterns and side effects. Noninvasive salivary prednisolone measurements were performed using a sparse sampling strategy. A population pharmacokinetic approach was used to derive individual estimates of apparent clearance (CL/F) and apparent volume of distribution (V/F) from the salivary concentration-time curve, followed by calculation of the area under the curve (AUC) of free prednisolone. The individual free serum prednisolone exposure from prednisolone in saliva was derived from the salivary concentration-time curves. Genetic polymorphisms of CYP3A4, CYP3A5, ABCB1, NR1L2, and POR were explored in relation to between-subject variability of CL/F.

RESULTS

Moderate interindividual variability was found for CL/F (CV, 44.7%). Unexplained random between-subject variability (eta) of CL/F was lower in patients carrying 1 or 2 ABCB1 3435C>T alleles compared to wild type: median -0.04 (interquartile range, -0.17 to 0.21) and 0.00 (-0.11 to 0.16) versus 0.17 (-0.08 to 0.47), P = 0.046. Exposure to free prednisolone was not associated with frequent relapses or adverse effects.

CONCLUSIONS

This study provides evidence for the possibility of prednisolone drug monitoring through salivary measurements and this may be of particular usefulness in pediatric patients. However, the observed variability in prednisolone exposure, in the therapeutic dose range studied, is not considered to be a major determinant of clinical outcome in children with NS.

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.

Buccal films of prednisolone with enhanced bioavailability

The conventional formulation of prednisolone is considered to be low in efficacy, primarily on account of their failure in providing and maintaining effective therapeutic drug levels. This study aims to focus on development of a mucoadhesive buccal delivery system with a twofold objective of offering a rapid as well as a prolonged delivery of prednisolone coupled with enhanced therapeutic efficacy. Buccoadhesive films of prednisolone were prepared by solvent-casting method using hydroxyl propyl methyl cellulose (K100), Carbopol 940 and/or Eudragit NE 40 D. Placebo films possessing the most desirable physicomechanical properties were selected for drug loading. The effect of polymer and its content on film properties, i.e. mucoadhesive strength, swelling and hydration, in vitro drug release was studied. Based on these studies, film F7D was selected for ex vivo permeation across porcine cheek mucosa. The steady state flux of prednisolone across the buccal mucosa was found to be 105.33 ± 32.07 µg/cm(2)/h. A comparative pharmacokinetic study of prepared film (F7D) and oral suspension of prednisolone was conducted. In vivo data of buccal film show greater bioavailability (AUC0-α: 24.26 ± 4.06 µg.h/ml versus 10.65 ± 2.15 µg.h/ml) and higher Cmax (2.70 ± 0.38 µg/ml versus 2.29 ± 0.32 µg/ml) value when compared to oral suspension. The data observed from this study highlight the feasibility of the buccal route as a viable option for delivery of prednisolone.

Correction for Volume Shift during Equilibrium Dialysis by Measurement of Protein Concentration

Volume shift during equilibrium dialysis produces errors in estimating the fraction of drug unbound. This study describes a method in which protein concentration in the plasma is used to correct binding data for volume shifts. Data are presented for phenytoin, a drug that does not bind to the dialysis system, and for verapamil, a drug that does. The conventional method of not correcting for volume shift, the method described previously by one of us (TNT) for a drug that does not bind to the dialysis system, and the proposed method of determining fraction unbound are compared and discussed. It is concluded that the second method is simple and can be used to determine the unbound fraction for a drug, such as phenytoin, which does not bind to the dialysis system. If a drug binds to the dialysis system, as does verapamil, the proposed method of measuring protein concentration before and after dialysis can be reliably used to correct for volume shift.

Trigger values for investigation of hormonal activity in drinking water and its sources using CALUX bioassays

To screen for hormonal activity in water samples, highly sensitive in vitro CALUX bioassays are available which allow detection of estrogenic (ERα), androgenic (AR), progestagenic (PR), and glucocorticoid (GR) activities. This paper presents trigger values for the ERα, AR, PR, and GR CALUX bioassays for agonistic hormonal activities in (drinking) water, which define a level above which human health risk cannot be waived a priori and additional examination of specific endocrine activity may be warranted. The trigger values are based on 1) acceptable or tolerable daily intake (ADI/TDI) values of specific compounds, 2) pharmacokinetic factors defining their bioavailability, 3) estimations of the bioavailability of unknown compounds with equivalent hormonal activity, 4) relative endocrine potencies, and 5) physiological, and drinking water allocation factors. As a result, trigger values of 3.8ng 17β-estradiol (E2)-equivalents (eq)/L, 11ng dihydrotestosterone (DHT)-eq/L, 21ng dexamethasone (DEX)-eq/L, and 333ng Org2058-eq/L were derived. Benchmark Quotient (BQ) values were derived by dividing hormonal activity in water samples by the derived trigger using the highest concentrations detected in a recent, limited screening of Dutch water samples, and were in the order of (value) AR (0.41)>ERα (0.13)>GR (0.06)>PR (0.04). The application of trigger values derived in the present study can help to judge measured agonistic hormonal activities in water samples using the CALUX bioassays and help to decide whether further examination of specific endocrine activity followed by a subsequent safety evaluation may be warranted, or whether concentrations of such activity are of low priority with respect to health concerns in the human population. For instance, at one specific drinking water production site ERα and AR (but no GR and PR) activities were detected in drinking water, however, these levels are at least a factor 83 smaller than the respective trigger values, and therefore no human health risks are to be expected from hormonal activity in Dutch drinking water from this site.

The influence of uremia on pharmacokinetics and protein binding of prednisolone

The pharmacokinetics and protein binding of prednisolone have been compared in 6 uremic patients and 6 healthy controls after intravenous injection of 20 mg prednisolone. The uremic patients had a 53% longer elimination half-time (p less than 0.01) and a 34% larger area under the time-concentration curve (AUC) (p less than 0.05) of total prednisolone than the controls. The total body clearance of total prednisolone was 26% lower and of free prednisolone 40% lower in the uremic patients than in the controls (p less than 0.01). The volume of distribution at steady state was 17% larger in the patients than in the controls, but the difference was not statistically significant. The protein binding of prednisolone was decreased in the patients, the proportion of free prednisolone being 26% higher than in the controls (p less than 0.05). The amount of free prednisolone, expressed as the AUC of free prednisolone, was 67% larger in the patients than in the controls (p less than 0.01). These results indicate that uremic patients taking prednisolone may be more prone to develop glucocorticoid side-effects because of higher concentration of free, biologically active prednisolone, secondary to a reduced rate of elimination and a decreased serum protein binding of prednisolone.

Altered prednisolone pharmacokinetics in patients treated with rifampicin

The pharmacokinetics and protein binding of prednisolone were studied in 7 patients before and after 3 weeks of rifampicin therapy. The elimination half-time for prednisolone decreased by 45 +/- 8.1% (p less than 0.01), and the total body clearance of prednisolone increased by 91 +/- 26% (p less than 0.01). The area under the time-concentration curve (AUC) of total (free plus protein-bound) prednisolone decreased by 48 +/- 7.3% (p less than 0.01) and of free, unbound prednisolone by 57 +/- 9.8% (p less than 0.01). The reduction in AUC was greater for free than for total prednisolone (p less than 0.05) mainly due to the non-linear nature of prednisolone protein binding. There was no significant change in the volume of distribution. Because of the marked reduction in total and especially free prednisolone, the dosage should be adjusted accordingly if prednisolone and rifampicin are prescribed concomitantly.

Application of gastrointestinal simulation for extensions for biowaivers of highly permeable compounds

The goal of this study was to apply gastrointestinal simulation technology and integration of physiological parameters to predict biopharmaceutical drug classification. GastroPlus was used with experimentally determined physicochemical and pharmacokinetic drug properties to simulate the absorption of several weak acid and weak base BCS class II compounds. Simulation of oral drug absorption given physicochemical drug properties and physicochemical parameters will aid justification of biowaivers for selected BCS class II compounds.

Biowaiver monographs for immediate release solid oral dosage forms: prednisolone

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing for the approval of immediate release (IR) solid oral dosage forms containing prednisolone are reviewed. Data on its solubility, oral absorption, and permeability are not totally conclusive, but strongly suggest a BCS Class 1 classification. Prednisolone's therapeutic indications and therapeutic index, pharmacokinetics, and the possibility of excipient interactions were also taken into consideration. Available evidence indicates that a biowaiver for IR solid oral dosage forms formulated with the excipients tabulated in this article would be unlikely to expose patients to undue risks.

Classification of orally administered drugs on the World Health Organization Model list of Essential Medicines according to the biopharmaceutics classification system

Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).

Management of acute severe asthma

Asthma is a chronic inflammatory disorder that results in recurrent episodes of reversible airflow obstruction. Lung hyperinflation results from obstruction or dynamic airway collapse during exhalation. Obstruction and dynamic hyperinflation both play a deleterious role in asthma. Patients who present with asthma have increased inspiratory work of breathing due to lung hyperinflation and auto-positive end-expiratory pressure (auto-PEEP). The goal of acute care treatment is to reverse bronchoconstriction and inflammation, thus reducing dynamic hyperinflation, so that breathing is restored to baseline, unlabored, quiet breathing.

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.

Treatment of acute asthma. A new look at the old and at the new

beta-Agonists remain the mainstay of therapy for acute asthma and, for most patients, standard doses are acceptable. Although the onset of action of systemic steroids is still not clear, steroids promote recovery and should be given to patients with acute illness. Intravenous magnesium sulfate appears to improve pulmonary function in the most severely ill patients but is not useful in patients with more moderate episodes. Ipratropium bromide is a weak bronchodilator that still needs to be tested as an adjunct to standard treatment regimens before its role in adults with asthma can be determined; given its ease of use and favorable safety profile it could be considered for patients with more severe acute illness. Aminophylline has not been found by most studies to improve outcomes and the narrow therapeutic range and unfavorable safety profile relegate it to a last-line agent or no use at all. Helium-oxygen mixtures currently have no role in moderately ill patients but have a theoretical advantage as a temporizing measure in severely ill patients. Drugs used in the management of chronic asthma, such as inhaled steroids and leukotriene-modifying agents, are making their way into the acute treatment arena, and other newly developed specific mediator inhibitors or blockers deserve attention. The use of isomers of beta-agonists is another area that is attracting attention and study. Systemic steroids are used to prevent relapse after emergency department discharge and the addition of other agents such as leukotriene-modifying agents or inhaled steroids may further prevent the need for urgent visits or hospitalization. The search for optimal treatment strategies for acutely ill patients is challenging and exciting and, with more attention and resources being devoted to this area, newer treatments will be found that will eventually have a greater impact on the high morbidity associated with acute asthma.

Ketoprofen and prednisolone do not modulate neutrophil CR1, CR3 and Fc gamma RIII expression in healthy volunteers

We assessed the effect of ketoprofen and prednisolone on the complement receptors (CR1 and CR3) and Fc gamma RIII expression on polymorphonuclears in an ex vivo study, using a randomized, single-blind, placebo-controlled, parallel design. Twenty-four healthy, male, Caucasian volunteers received either oral ketoprofen 100 mg twice daily, or prednisolone 5 mg twice daily, or placebo twice daily for 7.5 days. CR1, CR3 and Fc gamma RIII on unstimulated and FMLP-, C5a-, LTB4-, and GM-CSF-stimulated neutrophils were assessed using specific monoclonal antibodies and flow cytometry. No statistically significant drug effect was found for CR1, CR3, and Fc gamma RIII expression on polymorphonuclears. An in vitro study also yielded negative results. These findings do not support the hypothesis that the effect of non-steroidal antiinflammatory drugs on neutrophils is due to CR1, CR3, or Fc gamma RIII modulation.

Pharmacology of 11 beta-hydroxysteroid dehydrogenase

In clinical practice synthetic glucocorticoids are mainly used as therapy for inflammatory disorders and in suppressing immunological responses to transplanted allografts. The presence of an 11 beta-hydroxyl (11 beta-OH) group is mandatory for the antiinflammatory effects of glucocorticosteroids. The interconversion of the 11 beta-OH into the corresponding 11-keto group and vice versa by 11 beta-OH-steroid dehydrogenase might thus play a pivotal role for the efficacy of these steroids. Estimates of the apparent capacity to interconvert these steroids have been derived from plasma and tissue concentration measurements. Such estimates reveal that the interconversion process is concentration dependent and tissue specific. It remains to be established whether modulating that process might allow the immunosuppressive effect to be targeted within certain organs, thereby increasing the ratio between therapeutic and side effects of glucocorticoid administration.

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.

Prednisone and prednisolone interconversion in the rabbit utilizing unbound concentrations

Prednisolone (POH) and prednisone (PO) were both administered via seven different intravenous infusions (three POH and four PO) in each of six rabbits to obtain steady state. Bolus doses of POH and PO were also administered to four of the rabbits. Plasma samples of POH and PO were analyzed by normal phase HPLC. Unbound concentrations of both compounds were estimated in each rabbit using equilibrium dialysis and computer fit of the nonlinear or linear binding. The unbound fraction of POH ranged between 3 and 15 per cent from tracer to total concentrations of 2000 micrograms-1. The unbound fraction of PO ranged between 23 and 34 per cent and appeared nonlinear for four of the rabbits. The mean apparent unbound clearances of POH ranged from 4.4 to 6.1 lh-1kg-1 and from 4.1 to 5.9 lh-1kg-1 for PO, and were dose-independent for both compounds. The available fraction of POH from PO was 50 to 70 per cent and independent of dose. The available fraction of PO from POH averaged 44 per cent at the low infusion rate decreasing to 16 and 20 per cent at the medium and high infusion rates. Although saturability in the formation of PO from POH was noted, this nonlinear step is apparently not large enough to induce observable changes from linearity in the overall disposition of unbound POH.

Clinical pharmacokinetics of prednisone and prednisolone

The growth of knowledge in the field of the pharmacokinetics of prednisolone/prednisone has been slow for several reasons. First, convenient and specific methods for measuring these steroids only became available with the development of high performance liquid chromatographic methods. Secondly, prednisolone is nonlinearly bound to transcortin and albumin: since the unbound concentrations of prednisolone are biologically relevant, it was necessary to determine the free fraction in each plasma sample. Thirdly, due to the short half-life of prednisolone no steady-state is achieved, and therefore area under the concentration-time curve needed to be determined in all studies. Fourthly, prednisolone and prednisone are interconvertible and prednisolone is given intravenously as an ester prodrug, features which created controversies about the correct interpretation of pharmacokinetic results. Finally, the total body clearances of total and (to a lesser degree) of unbound prednisolone increase with increasing concentrations of prednisolone. Therefore, in order to compare pharmacokinetic results between different subjects, standardised doses had to be administered. The investigations performed so far have revealed that: (1) the dose-dependent pharmacokinetics partly explain the clinical observation that an alternate-day regimen with prednisone yields fewer biological effects; (2) the interconversion of prednisone into prednisolone is not a limiting factor, even in patients with severely impaired liver function; (3) hypoproteinaemia per se does not cause increased unbound concentrations of prednisolone in vivo; (4) patients with liver failure, renal failure or a renal transplant, subjects older than 65 years, women on estrogen-containing oral contraceptive steroids or subjects taking ketoconazole have increased unbound concentrations of prednisolone-whereas hyperthyroid patients, some patients with Crohn's disease, subjects taking microsomal liver enzyme-inducing agents or patients on intravenous prednisolone phthalate (instead of prednisolone phosphate) or on some brands of enteric coated prednisolone tablets have decreased concentrations of prednisolone. The biological relevance of the altered pharmacokinetics is supported in part by altered clinical effects and altered effects on cellular immunofunctions.

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

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

Effect of betamethasone on airway obstruction and bronchial response to salbutamol in prednisolone resistant asthma

Twelve patients with chronic severe asthma, having previously shown an FEV1 increase of less than 20% of the predicted value with prednisolone treatment (20-60 mg daily for 10 days), took part in a double blind crossover comparison of equipotent anti-inflammatory doses of betamethasone and prednisolone. Betamethasone (8 mg) and prednisolone (40 mg) were administered daily for 10 days with a washout period of 10 days between. In this first part of the study betamethasone was administered intramuscularly and prednisolone orally. Placebo injections and tablets were used. Mean FEV1 was not significantly different before each period. There was a significant increase in FEV1 while they were taking betamethasone but not prednisolone. Individual analysis of the data showed that FEV1 increased with betamethasone in nine patients and remained stable or decreased in three. During treatment with prednisolone baseline FEV1 increased moderately in three patients (FEV1 0.3, 0.5 and 0.6 l) and remained stable or decreased in nine. There was no significant difference between the bronchodilator responses to cumulative doses of inhaled salbutamol when they were measured immediately before, on the last day of treatment with each steroid, and between steroid treatment periods. The same protocol was followed four months later in five of the 12 patients but both drugs were administered orally on this occasion. Similar results were obtained. The greater effect of betamethasone on bronchial obstruction may be due to its longer biological half life or to some unidentified property of its metabolites. The bronchial response to inhaled beta 2 agonist appears not to be influenced by either steroid in these patients.

Effect of structural alterations on the biotransformation rate of glucocorticosteroids in rat and human liver

The effect of structural alterations on the biotransformation rate of glucocorticosteroids (GCS) by rat- and human-liver 9000 g supernatant fraction was studied. Insertion of a 16 alpha-hydroxy group in the prednisolone molecule (16 alpha-hydroxyprednisolone) was found to decrease the rate of biotransformation. Substitution of the 16 alpha,17 alpha-hydroxy groups with a symmetric acetal (in, for example, desonide) or especially a non-symmetric acetal (in, for example, budesonide), enhanced the biotransformation rate several-fold, particularly in human liver. Differences in the rates of metabolism in rat and human liver were observed. Hydrogenation of the 1,2-double bond in prednisolone and budesonide (hydrocortisone and 1,2-dihydrobudesonide) enhanced the biotransformation rate nine-fold in rat liver but only two-fold in human liver. Fluorination of the steroid nucleus in 6 alpha- and 9 alpha-positions enhanced the biotransformation rate several-fold in human liver, but in rat liver fluorination marginally decreased the rate of biotransformation. These in vitro results correlate well with available data on the first-pass liver metabolism of the studied GCS. This indicates that in vitro data can be useful in predicting oral bioavailability of GCS.

The dose-dependent systemic availability of prednisone: one reason for the reduced biological effect of alternate-day prednisone

An analysis of the literature was performed, revealing that in many studies both the desired and the undesired effects are decreased in alternate-day prednisone regimens as compared with the daily regimens. In the present report evidence is given that part of the diminished biological effect of dose-spacing regimens is attributable to a decreased total exposure to prednisolone. Following a high dose of 0.8 mg kg-1 of oral prednisone or prednisolone the plasma concentration vs time curves of total prednisolone, unbound prednisolone and prednisolone bound to albumin or transcortin were always less than four times higher than following a low dose of 0.2 mg kg-1 of prednisone or prednisolone. This dose-dependent systemic availability of prednisolone explains partly the diminished biological effect when the same total amount of prednisone or prednisolone is divided into several small doses as opposed to a single oral dose.

Fluocortolone: pharmacokinetics and effect on plasma cortisol level

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

Drug level monitoring of antiasthmatic drugs

In general assays pertaining to drug level monitoring (DLM) of antiasthmatic agents (except theophylline), published during the period 1978-1983, used mostly high-performance liquid chromatographic (HPLC) methodology (approximately 45%) with mass spectrometric (MS) based assays in second place (approximately 30%) followed by immunochemical techniques (approximately 25%). Whenever nanogram or subnanogram antiasthmatic drug concentrations had to be measured such as for the adrenergic stimulants or for the prophylactic agents, then both HPLC-and MS-based methodologies were employed with about equal frequency. The trend in DLM for the phosphodiesterase inhibitor class (theophyllines) seemed to be shifting towards the HPLC methodologies. In part, this was justified by the need for improved selectivity. This criterion appears to have been better satisfied by HPLC, but for all practical purposes the immunochemical methods are and will probably continue to prevail in the clinical laboratory setting until HPLC procedures become truly automated. In the case of DLM of corticosteroids used for the asthmatic, the situation is in our opinion still unclear. This is caused by the presence of endogenous corticosteroids and metabolites, the levels of which in man are known to vary. The current immunochemical procedures offer a facile but less selective option. The future for selective routine corticosteroid assays may well be in HPLC or gas chromatography coupled with MS.

Prednisolone pharmacokinetics in cushingoid and non-cushingoid kidney transplant patients

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

Nasal bioavailability and systemic effects of the glucocorticoid budesonide in man

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

Intra-individual consistency of prednisolone kinetics during long-term prednisone treatment

Eleven patients on long-term prednisone treatment were studied on two occasions separated by 45 to 325 days. In 10 patients the total body clearance of prednisolone only changed about 10%. In one case a 78.5% decrease was observed after stopping treatment with rifampicin and isoniazide. No association was found between the prednisone dose rate (mg/kg per month), patient age or mean endogenous plasma hydrocortisone level and prednisolone clearance/kg. The results indicate considerable intra-individual consistency of prednisolone kinetics if other conditions are not changed.