INTRODUCTION

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Inhaled corticosteroids have now gained widespread acceptance as first-line anti-inflammatory therapy for the treatment of asthma both in Europe and the United States. It is well recognized that all inhaled corticosteroids are associated with dose-related systemic adverse effects (1). Adrenal suppression is well recognized to be a sensitive and reproducible marker of systemic bioactivity (2).

Previous steady-state dose-ranging studies in healthy volunteers (3) and asthmatics (4) have shown that fluticasone propionate (FP) produces greater adrenal suppression than budesonide when both are given by pressurized metered-dose inhalers (pMDI). This can be explained in terms of the longer elimination half-life and longer receptor residency half-time, along with greater lipophilicity and systemic tissue retention for FP compared with budesonide (5). From first principles the pharmacological and pharmacokinetic properties of triamcinolone acetonide (TAA) are such that differences in steady-state systemic bioactivity would also be predicted when comparing TAA and FP (7, 9, 10).

We have therefore performed a repeated dosing study in asthmatic patients already receiving inhaled corticosteroids in order to evaluate the dose-response relationship for adrenal suppression at steady state with FP and TAA both given by pMDI.

	METHODS

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Patients

Twelve stable mild-to-moderate asthmatic patients (six female) of mean age (SEM): 34.3 (2.9) yr, mean FEV₁: 82.1 (2.0) % predicted, and FEF_25-75%: 53.6 (5.5) % predicted, completed the study. All patients were receiving less than or equal to 400 µg/d of inhaled cortico-steroid (median dose: 250 µg/d; range: 100 to 400 µg/d). No patient had received oral steroids within the previous 3 mo. All subjects had normal full blood count and biochemical profile (including urea and electrolytes, liver function tests, and bone markers) and normal urinalysis. All gave written informed consent.

Approval for the study was obtained from the Tayside Medical Ethics Committee. It was considered unethical and unsafe to perform repeated corticotrophin (ACTH) (tetracosactrin) stimulation tests as this is now contraindicated in the UK data sheet (Synacthen; CIBA Laboratories, Horsham, UK) because of reports of hypersensitivity and anaphylactic reactions in asthmatic subjects.

Study Design

A single-blind (investigator-blind) placebo-controlled randomized crossover design was used. Subjects attended for initial screening where FEV₁ and FEV_25-75% were measured using a Vitalograph Compact spirometer (Vitalograph Ltd, Buckingham, UK) and were included in the trial if their FEV₁ was greater than 70% predicted and FEF_25-75% less than 70% predicted. Spirometry was also measured at each visit to ensure the FEV₁ did not vary by more than 15% between treatments. Patients were randomized to receive either TAA 100 µg per actuation (dose delivered to patient as Azmacort oral inhaler with integrated space device; Rhone-Poulenc Rorer Pharmaceuticals Inc., Research Triangle Park, NC) or fluticasone propionate 110 µg per actuation (dose delivered to patient as Flovent metered-dose inhaler; Glaxo-Wellcome Inc., Collegville, PA).

Six patients received FP first in sequence and the other six patients received TAA first in sequence. Each drug sequence was given over a total of 9 d in twice daily divided doses at 8:00 A.M. and 10:00 P.M. The doses were as follows, given sequentially each for 3 d: TAA: 2 puffs b.i.d., 4 puffs b.i.d., and 8 puffs b.i.d., (i.e., total daily dose of 400 µg, 800 µg, 1,600 µg, respectively); FP: 2 puffs, A.M./1 puff P.M., 4 puffs A.M./3 puffs P.M., 7 puffs b.i.d. (i.e., total daily dose of 330 µg, 770 µg, 1,540 µg, respectively). Prior to each 9-d drug sequence (i.e., either FP or TAA), patients received the respective matching placebo inhaler (pMDI or oral inhaler) 2 puffs b.i.d., also for 3 d. The patients' usual inhaled corticosteroid therapy was discontinued during the placebo and treatment periods. There was also a 12-d, washout between each of the 9-d treatment sequences where patients received their usual maintenance inhaled corticosteroid therapy. Each inhaler was discharged twice prior to inhalation, and each inhalation was followed by mouth rinsing.

The inhalers were masked and sealed in envelopes by a pharmacist along with instruction sheets at the beginning of the trial in order to make it investigator blind. None of the subjects had previously used Flovent or Azmacort. Prior to the study and at each visit, subjects were given detailed tuition, by a third party, in how to use their inhaler, according to the manufacturer's package insert instructions, along with the use of a Vitalograph aerosol inhalation monitor device (Vitalograph, Bucks, UK). Each subject received a written instruction sheet to follow while taking their inhaler at home and a simple tick chart was used as an aid to compliance.

Measurements

All assays were performed in duplicate and in a blinded fashion by a separate technician. The subjects attended the laboratory at 7:30 A.M., 9 ¹/₂ h after taking the sixth dose (at 10:00 P.M.) of each drug dose level or placebo. A cannula was inserted into an antecubital fossa vein to permit blood sampling, and subjects then rested supine for 30 min. After the rest period, blood samples were taken for measurement of serum cortisol at 8:00 A.M. Subjects also emptied their bladder soon after taking the sixth dose (10:00 P.M.) of study drug and collected all voided urine until 8:00 A.M. the following morning. The total volume of the overnight 10-h urine specimen was measured. Aliquots were kept for assay of cortisol and creatinine levels.

Assays

All assays were performed in duplicate in a blinded fashion. Serum and urinary cortisol was measured using a commercial radioimmunoassay (ria) kit (Immunodiagnostic Systems Ltd, Boldon, Tyne & Wear, UK). The coefficient of variability (cv) for analytical imprecision for urinary cortisol within the assay was 10% and between the assay was 7.2%. Corresponding cv values for serum cortisol were 7.1% for within assay and 7.2% for between assay. Urinary creatinine was measured on a Cobas-Bio autoanalyzer (Roche Products Ltd, Welwyn Garden City, Herts, UK). The coefficient of variability intra-assay was 3.9%, and inter-assay was 0.63%.

Statistical Analysis

The study was designed with a sample size of 12 with 80% power (beta error = 0.2) to detect a 20% difference in 8:00 A.M. cortisol (the primary endpoint) between treatments with the alpha error set at 0.05 (two-tailed). All data were analyzed using a Statgraphics software package (STSC Software Group, Rockville, MD). The presence of dose-related suppression was determined using least-squares regression analysis to evaluate the overall effects of all three dose levels for each drug.

Comparisons between treatments were made by an overall multifactorial analysis of variance (MANOVA), followed by Duncan's multiple-range testing. All data were log transformed prior to analysis to normalize their distribution. For doses < 1,000 µg/d, individual values for low overnight urinary cortisol excretion < 10 nmol/10 h were analyzed using the chi-square test.

	RESULTS

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There were no significant carryover effects between the first and second placebo using either of the parameters measured: 8:00 A.M. serum cortisol 574.4 versus 539.1 nmol/L and overnight corrected urinary cortisol/creatinine ratio 5.0 versus 5.3 nmol/mmol. There were no significant differences between the FEV₁ values (as % predicted) comparing placebo (PL) with low (L), medium (M), and high (H) doses of each drug: PL (92.3); TAA (L: 96.6, M: 94.9, H: 94.5); FP (L: 96.6, M: 92.3, H: 95.0).

8:00 A.M. Serum Cortisol

Regression analysis showed there was significant dose-related suppression with FP (p < 0.001) but not with TAA (Figure 1). At the highest dose there was a 2.33-fold ratio between FP and PL (p < 0.05), and a 2.03-fold ratio between TAA and FP (p < 0.05). There was no significant difference between TAA and PL at any dose. Compared with PL there were significant (p < 0.05) differences with medium and high doses of FP but at no dose of TAA. Geometric means (SEM) were as follows (nmol/L): PL: 574.4 (33.1); FP: L: 501.1 (28.9), M: 419.1 (41.8), H: 246.8 (44.4); TAA: L: 554.9 (32.0), M: 538.0 (53.6), H: 500.8 (90.0).

View larger version (17K): [in this window] [in a new window]   Figure 1.   Geometric means with standard error of mean for placebo (PL); triamcinolone acetonide (TAA) at 400 µg/d, 800 µg/d, and 1,600 µg/d; and fluticasone propionate (FP) at 330 µg/d, 770 µg/d, 1,540 µg/d for 8:00 A.M. serum cortisol (top) and overnight corrected urinary cortisol/creatinine excretion (bottom). Regression analysis showed significant dose-related suppression for FP (*p < 0.001) for serum cortisol and (*p < 0.005) for urinary cortisol/creatinine excretion, but not a significant effect for TAA.

Overnight Urinary Cortisol

Regression analysis for overnight corrected urinary cortisol/ creatinine excretion showed FP to cause significant (p < 0.005) dose-related suppression, whereas this was not significant with TAA (Figure 1). At the high dose there was a significant (p < 0.05) 2.69-fold ratio between FP and PL and a 1.9-fold ratio between FP and TAA. There were significant (p < 0.05) differences from placebo for medium and high doses of FP and for the medium dose of TAA. Geometric means (SEM) were as follows (nmol/mmol): PL: 5.0 (0.7); FP: L: 4.2 (0.6), M: 2.2 (0.3), H: 1.9 (0.5); TAA: L: 4.3 (0.6), M: 3.3 (0.4), H: 3.5 (1.0). For doses < 1,000 µg/d the number of individual results with an abnormal low value for urinary cortisol excretion (< 10 nmol/10 h) were 10/24 (42%) for FP and 3/24 (13%) for TAA (p < 0.005) (Figure 2).

View larger version (17K): [in this window] [in a new window]   Figure 2.   Individual values for uncorrected overnight urinary cortisol excretion for all three dose levels of each drug. For doses < 1,000 µg/d, individual abnormal low levels (< 10 nmol/10 h) were: 10/24 (42%) for fluticasone propionate (FP) versus 3/24 (13%) for triamcinolone acetonide (TAA) (p < 0.005).

	DISCUSSION

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We have shown that for effects on 8:00 A.M. serum cortisol and overnight corrected urinary cortisol/creatinine excretion, inhaled FP produced significant dose-related suppression, whereas inhaled TAA did not. We compared microgram-equivalent doses of FP and TAA on the basis that they are most likely to be prescribed in this fashion in everyday clinical practice. Further dose-response studies are required to assess their relative potencies on the steep part of the airway dose-response curve for antiasthmatic efficacy. In this way it would be possible to evaluate the relative therapeutic index for both drugs.

The greater systemic effects of repeated drug dosing at steady state for FP compared with TAA are due to the longer plasma elimination half-time (FP, 14.4 h versus 3.6 h) (5, 9) and longer receptor residency half-time (FP, 11.5 h versus TAA 3.9 h) (7), along with greater systemic tissue retention due to a fivefold difference in lipophilicity (8). Our results for adrenal suppression with FP versus TAA at steady state are similar to those found with budesonide versus FP at steady state, also in asthmatics (4). This is perhaps not surprising given the similar pharmacologic and pharmacokinetic properties of TAA and budesonide.

We looked at two main endpoints for adrenocortical activity, namely 8:00 A.M. serum cortisol and overnight urinary corrected cortisol/creatinine. Previous studies with beclomethasone dipropionate and FP have shown that overnight urinary-corrected cortisol/creatinine excretion is more sensitive at detecting effects on adrenocortical activity than 8:00 A.M. plasma cortisol (4, 11). Indeed, a fractionated overnight collection for corrected urinary cortisol/creatinine excretion is as sensitive as a full 24-h measurement of uncorrected urinary cortisol excretion (11).

The above results look at mean figures, but it is probably more clinically relevant to look at the individual systemic response to inhalation of corticosteroid. When looking at clinically relevant treatment doses < 1,000 µg/d, it can be seen that there were three times as many individual results with an abnormal low value for overnight urinary cortisol excretion with FP than TAA. This is important to the physician when prescribing inhaled corticosteroids to individual patients, since there is no simple way of distinguishing which patients will or will not have abnormal urinary cortisol levels at a given dose. In this respect, it is known that there is good correlation between urinary cortisol excretion and serum cortisol response to ACTH stimulation in patients receiving inhaled corticosteroid therapy (12). We were unable to evaluate ACTH stimulation response in our study because it is contraindicated on the UK data sheet (Synacthen, CIBA Laboratories) for use in asthmatic or atopic subjects because of potential anaphylactic reactions.

As both FP and TAA have a high degree of first-pass hepatic metabolism, the swallowed fraction of the inhaled dose will only contribute a small component to the overall systemic bioactivity of the unchanged active drug. The first-pass metabolism has been calculated to be 99% for FP (13) and 89% for TAA (10). Thus, the amount of systemically bioavailable drug will predominantly depend on absorption from the lung (14). We are unaware of any direct comparative in vitro data examining the inhaler devices used to deliver FP and TAA although it is likely that the spacer attachment would enhance the respirable fraction of TAA.

In conclusion, we have shown at steady state in asthmatic patients that FP delivered by pressurized metered-dose inhaler (as Flovent) produced significant dose-related adrenal suppression in terms of 8:00 A.M. serum cortisol and overnight corrected urinary cortisol/creatinine excretion, whereas TAA (as Azmacort) did not. Further studies are required in asthmatic patients using similar drug delivery systems, for example, comparing Azmacort and Flovent both given via a spacer in order to compare the relative airway and systemic bioactivity at an equivalent respirable fraction.