Fluticasone furoate

Fluticasone furoate is a synthetic trifluorinated corticosteroid that possesses a very high affinity for the glucocorticoid receptor and has a potent anti-inflammatory action.

Absorption

Fluticasone furoate undergoes incomplete absorption and extensive first-pass metabolism in the liver and gut resulting in negligible systemic exposure. The intranasal dosing of 110 micrograms once daily does not typically result in measurable plasma concentrations (<10 pg/ml). The absolute bioavailability for intranasal fluticasone furoate is 0.50%, such that less than 1 microgram of fluticasone furoate would be systemically available after administration of 110 micrograms.

Distribution

The plasma protein binding of fluticasone furoate is greater than 99%. Fluticasone furoate is widely distributed with volume of distribution at steady-state of, on average, 608 l.

Biotransformation

Fluticasone furoate is rapidly cleared (total plasma clearance of 58.7 l/h) from systemic circulation principally by hepatic metabolism to an inactive 17β-carboxylic metabolite (GW694301X), by the cytochrome P450 enzyme CYP3A4. The principal route of metabolism was hydrolysis of the S-fluoromethyl carbothioate function to form the 17β-carboxylic acid metabolite. In vivo studies have revealed no evidence of cleavage of the furoate moiety to form fluticasone.

Elimination

Elimination was primarily via the faecal route following oral and intravenous administration indicative of excretion of fluticasone furoate and its metabolites via the bile. Following intravenous administration, the elimination phase half-life averaged 15.1 hours. Urinary excretion accounted for approximately 1% and 2% of the orally and intravenously administered dose, respectively.

Paediatric population

In the majority of patients fluticasone furoate is not quantifiable (<10 pg/ml) following intranasal dosing of 110 micrograms once daily. Quantifiable levels were observed in 15.1% of paediatric patients following intranasal dosing of 110 micrograms once daily and only 6.8% of paediatric patients following 55 micrograms once daily. There was no evidence for higher quantifiable levels of fluticasone furoate in younger children (less than 6 years of age). Median fluticasone furoate concentrations in those subjects with quantifiable levels at 55 micrograms were 18.4 pg/ml and 18.9 pg/ml for 2-5 yrs and 6-11 yrs, respectively.

At 110 micrograms, median concentrations in those subjects with quantifiable levels were 14.3 pg/ml and 14.4 pg/ml for 2-5 yrs and 6-11 yrs, respectively. The values are similar to those seen in adults (12+) where median concentrations in those subjects with quantifiable levels were 15.4 pg/ml and 21.8 pg/ml at 55 micrograms and 110 micrograms, respectively.

Elderly

Only a small number of elderly patients (≥65 years, n=23/872; 2.6%) provided pharmacokinetic data. There was no evidence for a higher incidence of patients with quantifiable fluticasone furoate concentrations in the elderly, when compared with the younger patients.

Renal impairment

Fluticasone furoate is not detectable in urine from healthy volunteers after intranasal dosing. Less than 1% of dose-related material is excreted in urine and therefore renal impairment would not be expected to affect the pharmacokinetics of fluticasone furoate.

Hepatic impairment

There are no data with intranasal fluticasone furoate in patients with hepatic impairment. Data are available following inhaled administration of fluticasone furoate (as fluticasone furoate or fluticasone furoate/vilanterol) to subjects with hepatic impairment that are also applicable for intranasal dosing. A study of a single 400 microgram dose of orally inhaled fluticasone furoate in patients with moderate hepatic impairment (Child-Pugh B) resulted in increased C_max (42%) and AUC_(0-∞) (172%) and a modest (on average 23%) decrease in cortisol levels in patients compared to healthy subjects. Following repeat dosing of orally inhaled fluticasone furoate/vilanterol for 7 days, there was an increase in fluticasone furoate systemic exposure (on average two-fold as measured by AUC_(0–24)) in subjects with moderate or severe hepatic impairment (Child-Pugh B or C) compared with healthy subjects. The increase in fluticasone furoate systemic exposure in subjects with moderate hepatic impairment (fluticasone furoate/vilanterol 200/25 micrograms) was associated with an average 34% reduction in serum cortisol compared with healthy subjects. There was no effect on serum cortisol in subjects with severe hepatic impairment (fluticasone furoate/vilanterol 100/12.5 micrograms). Based on these findings the average predicted exposure of 110 micrograms of intranasal fluticasone furoate in this patient population would not be expected to result in suppression of cortisol.

Findings in general toxicology studies were similar to those observed with other glucocorticoids and are associated with exaggerated pharmacological activity. These findings are not likely to be relevant for humans given recommended nasal doses which results in minimal systemic exposure. No genotoxic effects of fluticasone furoate have been observed in conventional genotoxicity tests. Further, there were no treatment-related increases in the incidence of tumours in two year inhalation studies in rats and mice.