CLINICAL PHARMACOLOGY
Mechanism of Action
Flunisolide has demonstrated marked anti-inflammatory activity in classical test systems. It is a corticosteroid that is several hundred times more potent than cortisol in animal anti-inflammatory assays, and several hundred times more potent than dexamethasone in anti-inflammatory effect as determined by the McKenzie skin blanching test. The clinical significance of these findings is unknown.
The precise mechanism of corticosteroid action is unknown. Airway inflammation is an important component in the pathogenesis of asthma. Corticosteroids have been shown to have a wide range of anti-inflammatory effects, inhibiting both inflammatory cells (e.g. mast cells, eosinophils, neutrophils, macrophages, and lymphocytes) and release of inflammatory mediators (e.g., histamine, eicosanoids, leukotrienes, and cytokines) involved in allergic and non-allergic-mediated inflammation. These anti-inflammatory actions of corticosteroids may contribute to their efficacy in asthma.
Pharmacodynamics
Dose finding for AEROSPAN Inhalation Aerosol was based on comparability of systemic exposure to flunisolide CFC inhalation aerosol. The effect of flunisolide CFC inhalation aerosol and AEROSPAN Inhalation Aerosol on pharmacokinetics and 12-hour plasma cortisol levels was investigated in two studies. In both studies, the Cmax and AUC of flunisolide, 6β-OH flunisolide, and 12-hour plasma cortisol measurements were comparable for 1000 mcg of flunisolide CFC inhalation aerosol and 320 mcg of AEROSPAN Inhalation Aerosol. The first was a parallel arm study in 31 subjects. Pharmacokinetics and plasma cortisol levels were determined after single and multiple doses of flunisolide CFC inhalation aerosol 1000 µg and AEROSPAN Inhalation Aerosol 160 µg or 320 µg administered twice daily for 13.5 days. At steady state, flunisolide mean peak plasma concentrations from flunisolide CFC inhalation aerosol 1000 mcg and AEROSPAN Inhalation Aerosol 320 mcg were found to be 2.6 ng/mL and 3.4 ng/mL, respectively. The corresponding mean AUC values for the 12-hr dosing interval were 5.7 ng.hr/mL and 4.7 ng.hr/mL, respectively. At steady state, the mean peak plasma concentrations of 6β-OH flunisolide from flunisolide CFC inhalation aerosol 1000 mcg and AEROSPAN Inhalation Aerosol 320 mcg were found to be 0.9 ng/mL and 0.3 ng/mL, respectively. The corresponding mean AUC values for the 12-hr dosing interval were 3.8 ng.hr/mL and 1.1 ng.hr/mL, respectively. The second was a crossover study in 11 subjects after single doses of flunisolide CFC inhalation aerosol 1000 mcg or AEROSPAN Inhalation Aerosol 320 mcg. The mean peak plasma concentrations of flunisolide from the flunisolide CFC inhalation aerosol 1000 mcg and AEROSPAN Inhalation Aerosol 320 mcg were found to be 2.5 ng/mL and 3.3 ng/mL, respectively. The corresponding mean AUC values were 5.1 ng.hr/mL and 5.8 ng.hr/mL, respectively. The mean peak plasma concentrations of 6 β -OH flunisolide from flunisolide CFC inhalation aerosol 1000 mcg and AEROSPAN Inhalation Aerosol 320 mcg were found to be 0.8 ng/mL and 0.3 ng/mL, respectively. The corresponding mean AUC values were 3.8 ng.hr/mL and 2.3 ng.hr/mL, respectively.
Controlled clinical studies with flunisolide CFC inhalation aerosol included over 500 treated asthma patients, among them 150 children aged 6 years and older. Open label studies of two years or more duration included more than 120 treated patients. No significant adrenal suppression attributed to flunisolide was seen in these studies.
The potential effects of AEROSPAN Inhalation Aerosol and flunisolide CFC inhalation aerosol on the hypothalamic-pituitary-adrenal (HPA) axis were studied in 2 placebo- and active- controlled studies and 2 active-controlled, open label, long-term studies [see
Clinical Studies
]. In the placebo-controlled studies, the ability to increase cortisol production in response to stress was assessed by the 60 minute cosyntropin (ACTH) stimulation test. For adult and adolescent patients treated with AEROSPAN Inhalation Aerosol 80 mcg, 160 mcg, 320 mcg, or placebo twice daily for 12 weeks, 92% (22/24), 93% (26/28), 93% (26/28), and 92% (22/24) of patients, normal at baseline, respectively, continued to have a normal stimulated cortisol response (peak cortisol ≥18 mcg/dL and an increase in plasma cortisol ≥7 mcg/dL within 60 minutes after cosyntropin injection) at trial's end. All patients had peak cortisol levels ≥ 18mcg/dL. There was no significant suppression of 24 hour urinary cortisol, and 100% (96/96) of patients treated with AEROSPAN Inhalation Aerosol had normal morning serum cortisol levels at the end of study. For pediatric patients treated with the AEROSPAN Inhalation Aerosol, 80 mcg and 160 mcg or placebo twice daily for 12 weeks, 91% (31/34), 97% (28/29), and 89% (24/27) of patients, respectively, continued to have a normal stimulated cortisol response (as defined above) at trial's end. No suppression of 24-hour urinary cortisol was noted. In these studies, comparable results were obtained in patients treated with flunisolide CFC inhalation aerosol.
In the active-controlled, open label, long-term studies, 99.4% (161/162) of adult and adolescent patients and 98.4% (126/128) pediatric patients treated with AEROSPAN Inhalation Aerosol had normal morning serum cortisol levels (≥ 5 mcg/dL) after 12 or 52 weeks of treatment, respectively. For patients treated with AEROSPAN Inhalation Aerosol, 92.5% (99/107) continued to have a normal stimulated plasma cortisol response to cosyntropin at trial's end with all having peak cortisol levels ≥ 18mcg/dL. In these studies, no suppression of 24-hour urinary cortisol was noted, and comparable results were obtained in patients treated with flunisolide CFC inhalation aerosol.
Pharmacokinetics
All the data described below is based on studies conducted in subjects 18 to 51 years of age.
Absorption
Flunisolide is rapidly absorbed after oral inhalation. Mean values for the time to maximum concentration, Tmax, of flunisolide range from 0.09 to 0.17 hr after a single 320 mcg dose of AEROSPAN Inhalation Aerosol. The corresponding mean values for the maximum concentration, Cmax, of flunisolide vary from 1.9 to 3.3 ng/mL. Oral bioavailability is less than 7%. Over the dose range of 80 mcg to 320 mcg of AEROSPAN Inhalation Aerosol, values for Cmax increase proportionately with dose after single as well as multiple dose administration.
Distribution
Flunisolide is extensively distributed in the body, with mean values for apparent volume of distribution ranging from 170 to 350 L after a single 320 mcg dose of AEROSPAN Inhalation Aerosol.
Metabolism
Flunisolide is rapidly and extensively converted to 6ß-OH flunisolide and to water-soluble conjugates during the first pass through the liver. Conversion to 6ß-OH flunisolide, the only circulating metabolite detected in man, is thought to occur via the cytochrome P450 enzyme system, particularly the enzyme CYP3A4. 6ß-OH flunisolide has a low corticosteroid potency (ten times less potent than cortisol and more than 200 times less potent than flunisolide). Maximum levels of 6ß-OH flunisolide were 0.66 mcg/mL after a single 320 mcg dose of AEROSPAN Inhalation Aerosol, and 0.71 mcg/mL after multiple doses of AEROSPAN Inhalation Aerosol.
Excretion
Urinary excretion of flunisolide is low. Less than 1% of the administered dose of flunisolide is recovered in urine after inhalation. The half-life values for 6ß-OH flunisolide range from 3.1 to 5.1 hrs after administration of AEROSPAN Inhalation Aerosol in the dose range of 160 mcg to 320 mcg.
Disposition and Elimination
Twice daily inhalation administration of flunisolide for up to 14 days did not result in appreciable accumulation of flunisolide. Upon multiple dosing with 160 mcg and 320 mcg, the Cmax values were 1.0 ng/mL and 2.1 ng/mL, respectively. The corresponding AUC0-12hr values were 1.2 ng.hr/mL and 2.5 ng.hr/mL.
Flunisolide is rapidly cleared from the body, independent of route of administration or dose administered. Flunisolide is not detectable in plasma twelve hours post-dose. After administration of 320 mcg of AEROSPAN Inhalation Aerosol the elimination half-life ranges from 1.3 to 1.7 hours. After a single 320 mcg dose, mean oral clearance values, not adjusted for bioavailability, range from 83 to 167 L/hr.
Special Populations
There were no gender differences for flunisolide after single and multiple dose administration of the AEROSPAN Inhalation Aerosol. Formal pharmacokinetic studies using flunisolide were not carried out in any other special populations.
NONCLINICAL TOXICOLOGY
Carcinogenesis, Mutagenesis, Impairment of Fertility
In a 22 month study in Swiss mice, flunisolide at oral doses up to 500 mcg/kg/day (approximately 3 and 4 times the maximum recommended daily inhalation dose [MRDID] in adults and children on a mg/m2 basis) did not demonstrate any carcinogenic effects.
In a two year study in Sprague Dawley rats, administration of flunisolide in the diet at a dose of 2.5 mcg/kg/day (less than MRDID in adults or children on a mg/m2 basis) resulted in an increased incidence of mammary gland adenomas and islet cell adenomas of the pancreas in females. The significance of these findings for humans is unknown. There were no significant increases in the incidence of any tumor type in female rats at a dose of 1.0 mcg/kg/day (less than MRDID in adults or children on a mg/m2 basis), or in male rats at a dose of 2.5 mcg/kg/day (less than MRDID in adults or children on a mg/m2 basis).
Flunisolide showed no mutagenic activity when tested in in vitro bacterial assay systems (Ames Assay and the Rec-assay) and no clastogenic activity when tested in the in vitro chromosomal aberration assay using Chinese Hamster CHL cells and in the in vivo mouse bone marrow chromosomal aberration assay.
Studies on the effects of flunisolide on fertility in female rats showed that flunisolide, at an oral dose of 200 mcg/kg/day (approximately 3 times MRDID on a mg/m2 basis) impaired fertility, but was devoid of such effects at doses up to 40 mcg/kg/day (less than MRDID on a mg/m2 basis).
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