Fluticasone propionate is a synthetic, fluorinated corticosteroid. Like other
topical corticosteroids, fluticasone propionate has anti-inflammatory, anti-pruritic,
and vasoconstrictive properties.The mechanism of the anti-inflammatory activity
of the topical steroids, in general, is unclear. However, corticosteroids are
thought to act by the induction of phospholipase A2 inhibitory proteins,
collectively called lipocortins. It is postulated that these proteins control
the biosynthesis of potent mediators of inflammation such as prostaglandins
and leukotrienes by inhibiting the release of their common precursor, arachidonic
acid, which is released from membrane phospholipids by phospholipase A2.
The extent of percutaneous absorption of topical corticosteroids is determined by many factors, including the vehicle and the integrity of the epidermal barrier. Occlusive dressing with hydrocortisone for up to 24 hours has not been demonstrated to increase penetration: however, occlusion of hydrocortisone for 96 hours markedly enhances penetration. Topical corticosteroids can be absorbed from normal intact skin, while inflammation and/or other disease processes in the skin increase percutaneous absorption.
Fluticasone propionate is lipophilic and has a strong affinity for the glucocorticoid receptor. It has weak affinity to the progesterone receptor, and virtually no affinity for the mineralocorticoid, estrogen, or androgen receptors.The therapeutic potency of glucocorticoids is related to the half-life of the glucocorticoid-receptor complex. Fluticasone propionate binding to the glucocorticoid receptor is rapid.
The half life of the fluticasone propionate-glucocorticoid receptor complex is approximately 10 hours.
Fluticasone propionate absorbed systemically is rapidly metabolized in the liver by esterase -catalyzed hydrolysis to the 17-beta-carboxylic acid which has no significant glucocorticoid or anti-inflammatory activity.
Pharmacology
Animals
Fluticasone propionate was shown to be approximately twice as potent in topical
activity as beclomethasone according to the McKenzie vasoconstrictor assay.
Although relative vasoconstrictor activity does not necessarily imply similar
relative therapeutic efficacy, evidence for local anti-inflammatory action without
systemic effects has been demonstrated by studies in laboratory animals and
confirmed in human clinical pharmacology studies.
Animal studies of the relative anti-inflammatory and hypothalamic-pituitary-adrenal (HPA) axis inhibitory potencies of topically applied drug demonstrated that fluticasone propionate has an advantageous therapeutic index ( > 200 times that of beclomethasone dipropionate).
Studies in rodents were conducted to quantitate and compare anti-inflammatory activity after topical administration of fluticasone propionate and the ability to produce specific systemic steroid-related effects after topical, oral or parenteral administration.
Topical anti-inflammatory activity was measured in rats and mice using the inflammatory response to croton oil applied topically to the ear. Results showed that fluticasone propionate was essentially equipotent with fluocinolone acetonide in both rats and mice.
Systemic responses to repeated topical applications of fluticasone propionate were assessed by measurement of thymus involution and reduction in stress-induced plasma corticosterone (HPA axis suppression) in rats and mice, and adrenal atrophy in the rat. In these tests, fluticasone propionate was 50-100-fold less potent than fluocinolone acetonide in the rat (56-fold greater therapeutic index) and 100 times less potent than fluocinolone acetonide in mice (relative therapeutic index 91). Therefore, in both species, the separation between topical anti-inflammatory and systemic activity after topical application, was highly favourable to fluticasone propionate.
Comparison of systemic activity after topical and subcutaneous dosing of flutica-sone propionate showed that, in both rats and particularly in mice, fluticasone propionate is more potent when given subcutaneously.
In rats, fluticasone propionate given subcutaneously was compared with betamethasone alcohol and fluocinolone acetonide using thymus involution, adrenal atrophy, and inhibition of carrageenin granuloma formulation as assessments of systemic activity. Fluticasone propionate was equipotent with betametha-sone alcohol and between 13 and 38 times less potent than fluocinolone acetonide.
In mice, using thymus involution and HPA axis suppression, fluticasone propionate given subcutaneously, was approximately equipotent with betamethasone alcohol and approximately 4 times less potent than fluocinolone acetonide.
After oral dosing in the rat, fluticasone propionate caused some thymus involution, adrenal atrophy and HPA axis suppression but was 6 to 38 times less potent than betamethasone alcohol. In the mouse, oral fluticasone propionate is 60 to 200 times less potent than betamethasone alcohol.
Fluticasone propionate was screened for a wide range of steroid hormonal or anti-hormonal activity.To ensure significant systemic exposure fluticasone propionate was administered subcutaneously to rats and mice, and was found to be devoid of androgenic, anabolic, oestrogenic, and anti-gonadotrophic activity. Fluticasone propionate had some progestational activity in oestrogen-primed weanling rabbits, and also showed some anti-androgenic and anti-oestrogenic activity. Weak anti-anabolic activity, another characteristic of potent glucocorticoids, was observed in the castrated rat. Fluticasone propionate lacked mineralocorticoid activity but caused significant diuresis and urinary excretion of sodium and potassium.
Pharmacokinetics
Pharmacokinetic data from rat, dog and man indicate that clearance is high relative to hepatic blood flow. Consequently, first-pass metabolism is extensive and oral bioavailability is negligible.
Studies examining the distribution of radio labelled fluticasone propionate in the rat have shown that orally-administered drug is absorbed and then excreted in the bile on first-pass through the liver. Thus, only minute traces of radioactivity pass into the systemic circulation.
The vast majority of a radio labelled dose following intravenous (rat and dog), oral and subcutaneous (mouse, rat and dog) administration is excreted via the faeces, and evidence from bile duct-cannulated animals indicates that the major route of excretion is via the bile. Renal excretion is of minor importance, as urinary excretion accounts for less than 5% of a parenteral dose. No unchanged drug is excreted in the bile of rats or dogs, but a significant amount, (up to 40%) of unchanged compound was found in the faeces of dogs dosed orally with flutica-sone propionate.
Thus, the low oral bioavailability of fluticasone propionate expected due to extensive first-pass metabolism is compounded by incomplete absorption from the gastrointestinal tract particularly in the dog. The major route of metabolism in rat, dog and humans is the hydrolysis of the fluorinated carbothioate group to yield the inactive carboxylic acid.
When administered orally to pregnant rats (100 µg/kg) or rabbits (300 µg/kg), a very small fraction of the dose ( < 0.005%) passes across the placenta.
Studies performed in rats following topical administration of radio labelled
flutica-sone propionate cream or ointment have shown that only about 5% of the
dose is absorbed through the skin, the majority of which is excreted in the
faeces. The majority of the dose (73%) is recovered from the surface of the
application site. Fluticasone propionate is stable and is not metabolized by
dermal enzymes when incubated with human skin homogenates in vitro or
when applied dermally to rats.
Human
In human volunteers, fluticasone propionate was 9.5 times more potent than fluoci-nolone acetonide and intermediate in potency between betamethasone-17-valerate (less potent) and clobetasol- 17-propionate (more potent).
No evidence of HPA axis suppression was seen in 45 healthy volunteers who repeatedly
applied large amounts (between 30 g and 50 g per day) of fluticasone propionate
ointment or cream formulations with or without occlusion. This was despite the
fact that 15 of the 45 volunteers had applied 0.05% fluticasone propionate ointment
(a ten-fold higher concentration of ointment than that currently marketed).
The minimal effects on the HPA axis probably result from the relatively poor
penetration of fluticasone propionate through the various layers of the skin.
Specialized studies have shown fluticasone propionate to have no potential
to cause irritancy, contact sensitization, photo toxicity or photo contact allergenicity,
despite the aggressive nature of the dosing schedules employed. Fluticasone
propionate ointment (0.05%) and cream (0.005% and 0.05%) preparations were applied
in volumes of 0.1 mL for up to 26 days in these specialised studies.
Pharmacokinetics
The pharmacokinetic characteristics following administration of fluticasone propionate in man are similar to those of other glucocorticoids, except that oral bioavailability is extremely low. This low oral bioavailability, coupled with high plasma clearance and efficient biliary excretion of metabolites, enhances the topical versus systemic effects. Studies with radio labelled and unlabelled flutica-sone propionate administered orally to human volunteers indicate that the majority of the dose (87%-100%) is excreted in the faeces, with up to 75% as unchanged drug, depending on the dose administered. Between 1% and 5% of the dose is excreted as metabolites in urine.
Single intravenous doses of 2 mg in healthy volunteers revealed that the clearance
of fluticasone propionate approximates liver blood flow, with renal clearance
accounting for less than 1%.These results indicate that hepatic extraction is
almost complete and that oral bioavailability is close to zero. The plasma elimination
half-life is approximately 3 hours, and the volume of distribution is approximately
260 L.
The poor penetration of fluticasone propionate, suggested from the minimal
effects on the HPA axis, was also evidenced by low plasma concentrations after
dermal application. The application of 12.5 g of 0.05% fluticasone propionate
cream twice daily for 21 days without occlusion to healthy male volunteers resulted
in trough plasma concentrations generally below the limit of detection (0.05
ng/mL) throughout the study.
Maximum trough levels of 0.069 to 0.39 ng fluticasone propionate/mL were observed following the twice daily application of 50 g of 0.05% fluticasone propionate cream under occlusion for 5 days.
The twice daily application of 25 g of 0.005% fluticasone propionate ointment under occlusion for 5 days to healthy male volunteers resulted in maximum trough levels in the range of 0.22 to 0.77 ng/mL.
Toxicology
Acute Toxicity
Pharmacokinetic studies in the rat have shown that only 5% of the dermal dose is absorbed through the skin.
However, intravenous and subcutaneous dosing allows toxicity to be fully charac-terised after maximal systemic exposure.
The results of the acute toxicity studies with fluticasone propionate administered
by inhalation, orally, subcutaneously and intravenously, demonstrated a large
margin of safety over the anticipated exposure of humans following the dermal
application of cream preparations containing 0.05% fluticasone propionate. Systemic
exposure following the dermal application of 0.05% cream would be 45 µg/kg,
assuming human percutaneous absorption of approximately 5% and the use in a
50 kg person of 90 g of cream in one day.The approximate LD50 values
are shown in the following table:
| Species |
Route |
Approx. LD50 (mg/kg) |
| Mouse |
Oral |
>1000 |
| Rat |
Oral |
>1000 |
| Mouse |
Subcutaneous |
>1000 |
| Rat |
Subcutaneous |
>1000 |
| Rat |
Intravenous |
>2 |
| Rat |
Inhalation |
>1.66 |
| Dog |
Inhalation |
>0.82 |
High oral doses of 1 g/kg were well tolerated in both the mouse and rat. The
only (reversible) changes observed were a slowing in growth rate and microscopically-evident
cortical depletion of the thymus of animals killed 3 days after dosing.
Subcutaneous doses of fluticasone propionate at 1 g/kg were administered to
mice and rats. Animals progressively lost condition and body weight and the
effects seen were thymic depletion and various lesions associated with a compromised
immune system. In addition, gastric steroid ulcers were seen.These observed
changes are the expected response to glucocorticoid therapy. The lack of reversible
thymic effects in subcutaneously-dosed animals is almost certainly due to the
deposition and leaching of insoluble steroid from the injection site.
When given intravenously to rats at a dose of 2 mg/kg, the only changes seen were slightly subdued behaviour immediately after treatment and reversible thymic involution.
Chronic Toxicity
Subacute toxicity studies were conducted in adult and juvenile rats for periods
up to 35 days and in Beagle dogs for periods up to 44 days. Fluticasone propionate
was administered as follows:
| Species |
Route |
Doses* |
Dosing Period |
| Rat |
Oral (gavage) |
1000 µg/kg/day |
15 days |
| Dog |
Oral (gavage) |
3000 µg/kg/day |
7 days |
| Rat |
Subcutaneous |
250/90 µg/kg/day |
36 days |
| 10 µg/kg/day |
35 days |
| Dog |
Subcutaneous |
160 µg/kg/day |
36 days |
| Rat |
Inhalation |
60 µg/L/day |
7 days |
| 18.2 µg/L/day |
14 days |
| 475 µg/L/day |
30 days |
| Dog |
Inhalation |
20 mg/animal/day |
10 days |
| 9 mg/animal/day |
44 days |
| Key: * - maximumdose of fluticasone propionate administered. |
Clinical observations were similar for all routes of administration in both species. These consisted of reduced weight gain and general loss of condition. Inhalation studies in the dog resulted in clinical signs associated with the administration of a potent glucocorticoid and were consistent with the symptoms of Canine CushingsÕ Syndrome.
Changes typical of glucocorticoid overdosage were seen in both haematological and clinical chemistry parameters. Effects were seen on the red cell parameters and a characteristic leukopenia resulting from a lymphopenia accompanied by a neutrophilia. Endogenous cortisol and corticosterone were depressed in dogs and rats respectively.
Microscopic pathology was again consistent with the administration of a potent glucocorticoid showing thymic and adrenal atrophy, lymphoid depletion in rats and dogs and glycogenic vacuolation of the liver in dogs.
There were no specific effects on the maturation of juvenile rats after subcutaneous dosing.
The application of a cream formulation containing 0.05% fluticasone propionate and an ointment containing 0.05, 0.10 or 0.20% w/w fluticasone propionate to the abraded skin of rats for up to 35 days did not compromise the healing of damaged areas of skin. Some skin thinning was observed at the site of application. Expected glucocorticoid effects, namely reduced body weight gain and slight changes in hematology and clinical chemistry, were observed. However, absorption of flutica-sone propionate was of a low order as no significant differences were observed in the corticosterone levels between treated and control animals.
Fluticasone propionate ointment was well tolerated following daily applications to the skin of the rat at dose levels of 0.05, 0.10 and 0.20% w/w for 26 weeks. Thinning of the skin at the application sites, due to slight to moderate thinning of the dermal collagen, together with loss of fat was observed.
Daily dermal administration of 0.8% w/w of fluticasone propionate ointment under occlusion for up to 6.5 hours per day to Beagle dogs for 26 weeks was also well tolerated. A single papilloma was observed at the treatment site in each of 2 dogs at the high dose level. This may have been a consequence of local immunosup-pression. Three dogs at the high dose level showed moderate to large diffuse corneal opacities at the end of treatment. These animals had intercurrent ocular infections during the study. Increased susceptibility to ocular infection in these dogs may have occurred in part as a result of the recognised immunosuppressive effect of corticosteroids.
Mutagenicity
Fluticasone propionate did not induce gene-mutation in prokaryotic microbial
cells and there was no evidence of toxicity or gene-mutational activity in eukaryotic
Chinese hamster cells in vitro. The compound did not induce point-mutation
in the Fluctuation assay, and did not demonstrate gene-convertogenic activity
in yeast cells. No significant clastogenic effect was seen in cultured human
peripheral lymphocytes in vitro and fluticasone propionate was not demonstrably
clastogenic in the mouse micronucleus test when administered at high doses by
oral or subcutaneous routes. Furthermore, the compound did not delay erythroblast
division in bone marrow.
Reproduction and Teratology
Subcutaneous studies in the mouse and rat at 150 and 100 µg/kg/day respectively, revealed maternal and foetal toxicity characteristic of potent glucocorticoid compounds, including reduction in maternal weight gain, embryonic growth retardation, increased incidences of retarded cranial ossification, and of omphalo-coele and cleft palate in rats and mice, respectively. In the rabbit, subcutaneous doses of 30 µg/kg/day and above were incompatible with sustained pregnancy. This is not unexpected since rabbits are known to be particularly sensitive to glucocorticoid treatment.
Following oral administration of fluticasone propionate up to 300 µg/kg to the rabbit, there were no maternal effects nor increased incidence of external, visceral, or skeletal foetal defects. A very small fraction ( < 0.005%) of the dose crossed the placenta following oral administration to rats (100 µg/kg /day) and rabbits (300 µg/kg/day).
Carcinogenicity
No treatment related effects were observed on the type or incidence of neoplasia in an 80 week dermal oncogenicity study in mice treated with a 0.05% fluticasone propionate ointment, in an 18 month oral (gavage) study in mice administered fluticasone propionate at dose levels of up to 1 mg/kg/day. In a lifetime (2 years) snout-only inhalation study in rats, at dose levels of up to 57 µg/kg/day, there was an increase in the incidence of tumours in the mammary gland, liver and pancreas. These were not considered as evidence of tumorogenic effect of fluticasone propionate based on the absence of statistical support of an increase in incidence and the historical tumour data.
Local Tolerance
Little or no irritancy was observed following the application of ointment formulations containing up to 0.1% fluticasone propionate either as daily doses for 35 days to the skin of the rat or as single dose, non-occluded or occluded tests on intact or abraded guinea pig skin. Negligible irritancy was produced following the application of fluticasone propionate cream or ointment (containing up to 0.05% w/w flutica-sone propionate) formulations as single occluded doses on intact and abraded skin and as a series of 4 daily repeated non-occluded doses on the intact skin of the guinea pig.
A single application of 0.05% w/w fluticasone propionate ointment or cream to abraded skin sites on rats did not affect the normal wound healing process. Micronised fluticasone propionate was considered to be non-irritating in the rabbit eye when assessed using a modified Draize test and in the guinea pig split adjuvant test for evaluating contact sensitivity, results were completely negative.
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