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

A pharmacokinetic simulation tool for inhaled corticosteroids

The pharmacokinetic (PK) behavior of inhaled drugs is more complicated than that of other forms of administration. In particular, the effects of certain physiological (mucociliary clearance and differences in membrane properties in central and peripheral (C/P) areas of the lung), formulation (as it relates to drug deposition and particle dissolution rate), and patient-related factors (lung function; effects on C/P deposition ratio) affect the systemic PKs of inhaled drugs. The objectives of this project were (1) to describe a compartmental model that adequately describes the fate of inhaled corticosteroids (ICS) after administration while incorporating variability between and within subjects and (2) based upon the model, to provide a freely available tool for simulation of PK trials after ICS administration. This compartment model allows for mucociliary removal of undissolved particles from the lung, distinguishes between central and peripheral regions of the lung, and models drug entering the systemic circulation via the lung and the gastrointestinal tract. The PK simulation tool is provided as an extension package to the statistical software R ('ICSpkTS'). It allows simulation of PK trials for hypothetical ICS and of four commercially available ICS (budesonide, flunisolide, fluticasone propionate, and triamcinolone acetonide) in a parallel study design. Simulated PK data and parameters agreed well with literature data for all four ICS. The ICSpkTS package is especially suitable to explore the effect of changes in model parameters on PK behavior and can be easily adjusted for other inhaled drugs.

A mass balance study to evaluate the biotransformation and excretion of [14C]-triamcinolone acetonide following oral administration

The principle objective of this study was to characterize the absorption, metabolism, and disposition of orally administered [14C]-triamcinolone acetonide. Six healthy male subjects each received a single 100 microCi (approximately 800 micrograms) oral dose of [14C]-triamcinolone acetonide. Plasma, urine, and fecal samples were collected at selected times and analyzed for triamcinolone acetonide and [14C]-derived radioactivity. Plasma protein binding of triamcinolone acetonide was also determined. Metabolite profiling and identification were carried out in plasma and excreta. Principle metabolites were assessed for activity with in vitro anti-inflammatory models. [14C]-triamcinolone acetonide was found to be systemically absorbed following oral administration. The presystemic metabolism and clearance of triamcinolone acetonide were extensive, with only a small fraction of the total plasma radioactivity being made up of triamcinolone acetonide. Little to no parent compound was detected in the plasma 24 hours after administration. Most of the urinary and fecally [14C]-derived radioactivity was also excreted within 24 and 72 hours postdose, respectively. Mean plasma protein binding of triamcinolone acetonide was constant, predictable, and a relatively low 68% over a 24-fold range of plasma concentrations. Three principle metabolites of triamcinolone acetonide were profiled in plasma, urine, and feces. These metabolites were identified as 6 beta-hydroxy triamcinolone, 21-carboxylic acid triamcinolone acetonide, and 6 beta-hydroxy-21-oic triamcinolone acetonide. All three metabolites failed to show any concentration-dependent effects in anti-inflammatory models evaluating IL-5-sustained eosinophil viability and IgE-induced basophil histamine release.

A study comparing the clinical pharmacokinetics, pharmacodynamics, and tolerability of triamcinolone acetonide HFA-134a metered-dose inhaler and budesonide dry-powder inhaler following inhalation administration

The impending phaseout of chlorofluorocarbons as propellants in pressurized metered-dose inhalers used in the treatment of asthma has resulted in the development of alternative devices to deliver drug to the pulmonary airways. These alternative devices include metered-dose inhalers using environmentally friendly hydroflurocarbon propellants and breath-actuated dry-powder inhalers. The purpose of this study was to compare the single- and multiple-dose pharmacokinetics, pharmacodynamics, and tolerability of a newly developed hydroflurocarbon formulation of triamcinolone acetonide (Azmacort HFA 225 mcg Inhalation Aerosol) to that of the dry-powder formulation of budesonide (Pulmicort Turbuhaler 200 mcg). This three-way crossover study used 18 normal healthy subjects each receiving a 675 mcg dose of triamcinolone acetonide, 600 mcg dose of budesonide, or placebo twice a day for 5 days. Serial plasma samples were collected after the first and last dose of test medication for pharmacokinetic analysis. Pharmacodynamics were assessed by changes in hypothalamic-pituitary-adrenal axis function as measured by 8 a.m. serum cortisol, 24-hour overnight serum cortisol AUC(0-24), and 24-hour urinary-free cortisol after the last evening dose of test drug. Tolerability was assessed through physical examinations, vital signs, 12-lead ECG, routine clinical labs, and adverse events recording. Both compounds were systemically absorbed. However, no significant drug accumulation was noted with chronic dosing. Chronic dosing did result in a statistically significant 20% reduction in basal 24-hour serum cortisol AUC(0-24) for both compounds. There were no clinically significant abnormalities in physical examination, vital signs, 12-lead ECG, or routine clinical labs noted during the study. Overall, the study drugs were well tolerated, with adverse events characterized as mild to moderate in severity.

A pharmacokinetic study to evaluate the absolute bioavailability of triamcinolone acetonide following inhalation administration

Triamcinolone acetonide is a glucocorticoid administered by oral inhalation in the management of asthma. With oral inhalation of glucocorticoids, systemic absorption can come from oropharyngeal, gastrointestinal, or airway deposition of the drug. The objectives of this study were to determine the absolute bioavailability of triamcinolone acetonide following inhalation administration and to delineate the airway contribution of triamcinolone acetonide absorption relative to the absolute bioavailability. All subjects received a 5-minute 400 mcg intravenous infusion of triamcinolone acetonide and a single 800 mcg dose of inhaled triamcinolone acetonide with and without oral charcoal administration in a randomized three-way crossover fashion. The oral charcoal allowed for isolating the pulmonary component of absorption by adsorbing the oropharyngeal and gastrointestinal deposited drug. The mean (+/- SD) absolute bioavailability value for inhaled triamcinolone acetonide was 25% (8.75%). Delineation of the airway contribution of triamcinolone acetonide absorption showed that 10.4% of an inhaled dose is absorbed as triamcinolone acetonide from the lungs. Mean (+/- SD) total body clearance was rapid at 0.57 (0.12) L/hr/kg. The mean (+/- SD) apparent volume of distribution following the intravenous dose was a low 1.96 (0.31) L/kg. No significant differences were noted in the apparent terminal elimination half-life of triamcinolone acetonide (approximately 2.4 hr) between treatments.

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

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

Pharmacokinetic/pharmacodynamic evaluation of systemic effects of flunisolide after inhalation

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

Pharmacologic therapy of asthma during pregnancy

Asthma is a common, potentially serious medical complication during pregnancy. Optimal clinical and pharmacologic management is necessary to mitigate maternal and fetal complications. Mild asthma may be managed in most cases with inhaled beta 2-mimetics. Anti-inflammatory therapy is recommended for the treatment of moderate and severe asthma. Based on limited human experience, beclomethasone is currently the recommended inhaled corticosteroid during pregnancy. However, other inhaled corticosteroids may have advantages compared to beclomethasone because of reduced systemic absorption, which may adversely affect intrauterine growth. Based upon theoretic considerations, theophylline is now considered a secondary therapy, but data demonstrating the superiority of inhaled corticosteroids versus theophylline during pregnancy are lacking.

Simultaneous determination of triamcinolone acetonide and hydrocortisone in human plasma by high-performance liquid chromatography

A validated HPLC method for the simultaneous determination of triamcinolone acetonide and hydrocortisone has been established to monitor the plasma levels of the compounds in healthy volunteers following intramuscular (i.m.) administration of triamcinolone acetonide. Plasma (1.0 ml) was extracted with dichloromethane after addition of the internal standard, fluocortolone. The compounds were separated using a LiChrospher RP 18 column and detected by UV absorbance. Specificity, linearity, as well as the repeatability, intermediate precision and accuracy of the method were established. The limit of quantification was 0.6 ng/ml for triamcinolone acetonide (C.V. = 8.7%, R.E. = 2.6%, n = 6) and 2.0 ng/ml for hydrocortisone (C.V. = 8.3%, R.E. = 2.8%, n = 6). Data on the stability of triamcinolone acetonide in human plasma are presented. Recovery of the compounds and the internal standard have been studied. The results of quality control samples (n = 126) determined during routine analysis of volunteer samples are described. Plasma levels of triamcinolone acetonide after i.m. administration of 40 mg of triamcinolone acetonide are presented.

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

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

Nasal mucosal inflammation has no effect on the absorption of intranasal triamcinolone acetonide

The potential for enhanced systemic absorption of intranasal triamcinolone acetonide was explored in patients with inflamed nasal mucosa. Twelve allergic rhinitis patients with documented nasal inflammation, and 12 healthy volunteers, each received a single, therapeutic, 400-micrograms dose of triamcinolone acetonide in each nostril. Blood was obtained at fixed time points after the dose, and plasma concentrations of triamcinolone acetonide were determined by radioimmunoassay. There were no statistically significant differences in any of the derived pharmacokinetic parameters (maximum plasma triamcinolone acetonide concentrations [Cmax], time to maximum plasma triamcinolone concentrations [Tmax], elimination half-life [t1/2], and area under the plasma concentration-time curve [AUC0-12] from 0 to 12 hours) between treatment groups. A once-a-day, chronic regimen (6 weeks) of triamcinolone acetonide was also administered to five patients with allergic rhinitis. Pharmacokinetic parameters were similar to the parameters derived from healthy volunteers after acute administration. There was no evidence of drug accumulation. The results of this study indicate that acute and chronic intranasal administration. The results of this study indicate that acute and chronic intranasal administration of therapeutic doses of triamcinolone acetonide to patients with inflamed nasal mucosa does not result in enhanced systemic drug absorption or accumulation.