Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2018 Publisher: Allergan Pharmaceuticals Ireland, Castlebar Road, Westport, County Mayo, Ireland
Pharmacotherapeutic group: TOPICAL ANTIPSORIATIC AGENT
ATC-code: D05AX05
Both gels have demonstrated therapeutic effects as early as 1 week after commencement of a course of treatment. A good clinical response was seen in up to 65% of the patients after 12 weeks of treatment.
The therapeutic effect of the higher concentration gel is more rapidly apparent and the efficacy more marked.
In various studies in which patients were also evaluated for 12 weeks following cessation of therapy, it was found that patients continued to show a certain clinical benefit, however, no difference between the higher and lower concentrations with regard to this effect was observed.
Tazarotene, a member of the acetylenic class of retinoids, is a prodrug which is converted to its active free form, tazarotenic acid, by de-esterification in the skin area.
Tazarotenic acid is the only known metabolite of tazarotene to have retinoid activity.
The active metabolite specifically regulates gene expression, thus modulating cell proliferation, hyperplasia, and differentiation in a wide range of tissues, as has been demonstrated in in vitro and in vivo trials.
The exact mechanism of action of tazarotene in psoriasis is, as yet, unknown. Improvement in psoriatic patients occurs in association with restoration of normal cutaneous morphology, and reduction of the inflammatory markers ICAM-1 and HLA-DR, and of markers of epidermal hyperplasia and abnormal differentiation, such as elevated keratinocyte transglutaminase, involucrin, and keratin 16.
Results of a pharmacokinetic study of single topical application of 0.1% 14C-tazarotene gel show that approximately 5% is absorbed when applied to normal skin under occlusion.
After a single topical application of tazarotene gel to 20% body surface area for 10 hours in healthy volunteers, tazarotene was not detectable in the plasma. Maximum plasma levels for the active metabolite tazarotenic acid of 0.3 ± 0.2 ng/ml (for the 0.05% strength) and 0.5 ± 0.3 ng/ml (0.1% gel) were measured after approximately 15 hours. The AUC was 40% higher for the 0.1% gel compared with the 0.05% gel. Thus, the two strengths of the gel are not strictly dose proportional with respect to systemic absorption.
Repeated topical application of the 0.1% gel over 7 days led to maximum plasma levels for tazarotenic acid of 0.7 ± 0.6 ng/ml after 9 hours.
After dermal application, tazarotene undergoes esterase hydrolysis to form its free acid, tazarotenic acid, and oxidative metabolism to form inactive sulphoxide and sulphone derivatives.
Secondary metabolites of tazarotenic acid (the sulphoxide, the sulphone and an oxygenated derivative of tazarotenic acid) have been detected in human urine and faeces. The elimination half-life of tazarotenic acid after dermal application of tazarotene is approximately 18 hours in normal and psoriatic subjects.
After intravenous administration, the half-life of tazarotene was approximately 6 hours and that of tazarotenic acid 14 hours.
After single topical application of 0.1% 14C-tazarotene gel for 10 hours to psoriatic lesions (without occlusion), 4.5% of the dose was recovered in the stratum corneum and 2.4% in the epidermal/dermal layers. Less than 1% of the dose was absorbed systemically. More than 75% of drug elimination was completed within 72 hours.
In a small five patient study, repeated topical application of tazarotene 0.1% gel over 13 days results in a mean peak plasma level of tazarotenic acid of 12 ± 8 ng/ml. These patients had psoriatic lesions on 8-18% of body surface area. In a larger 24 psoriatic patient study, tazarotene 0.05% and 0.1% gels were applied for 3 months and yielded a Cmax of 0.45 ± 0.78 ng/ml and 0.83 ± 1.22 ng/ml, respectively.
In a 1 year clinical study with 0.05% and 0.1% tazarotene gel, tazarotene was detected in 3 out of 112 patients at plasma concentrations below 1 ng/ml, while its active metabolite tazarotenic acid was found in 31 patients. Only four patients had plasma concentrations of tazarotenic acid greater than or equal to 1 ng/ml (maximum 2.8 ng/ml).
The safety of daily dermal application of tazarotene gel was tested in mouse, rat and mini-pig over periods of up to one year. The main observation was reversible skin irritation. In the case of the mini-pig, an incomplete healing of the dermal irritation was observed after an 8 week recovery period. The rat appears to be the most sensitive species to tazarotene, as is the case with other retinoids. Here, dermal application induced severe skin reactions and clinically significant retinoid-like systemic effects. No adverse systemic effects were observed in the other species.
After oral administration of 0.025 mg/kg/day for 1 year in the cynomolgus monkey, no toxic effects were observed. At higher doses, typical symptoms of retinoid toxicity were seen.
Safety of use during pregnancy has not been established. Teratogenic and embryotoxic effects were observed after oral administration in the rat and rabbit. In dermal application studies during foetal development, skeletal alterations and decreased pup weight at birth and at the end of the lactation period were observed.
Animal tests suggest that tazarotene or its active metabolite is excreted in breast milk and passes the placenta barrier.
No effects on fertility are reported after topical application in the male and female rat.
No evidence of a mutagenic potential of tazarotene has been reported in in vitro and in vivo trials.
In long term investigations of the effects of dermal and oral administration in animals, no carcinogenic effects were observed.
There was an increased incidence of photocarcinogenic effects in the hairless mouse when exposed to UV light after topical application of tazarotene.
Tazarotene gel has a considerable irritative potential on skin in all animal species investigated.
Instillation of tazarotene gel in the eye of the rabbit resulted in irritation with marked hyperaemia of the conjunctiva, but there was no corneal damage.
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