Acitretin 25 mg · Hard-gelatin capsules

Absorption: — Oral absorption of acitretin is optimal when given with food. For this reason, acitretin was given with food in all of the following trials. After administration of a single 50-mg oral dose of acitretin to 18 healthy subjects, maximum plasma concentrations ranged from 196 to 728 ng per mL (mean: 416 ng per mL) and were achieved in 2 to 5 hours (mean: 2.7 hours). The oral absorption of acitretin is linear and proportional with increasing doses from 25 to 100 mg. Approximately 72% (range: 47% to 109%) of the administered dose was absorbed after a single 50-mg dose of acitretin was given to 12 healthy subjects.

Distribution: — Acitretin is more than 99.9% bound to plasma proteins, primarily albumin.

Metabolism: ( See Pharmacokinetic Drug Interactions: Ethanol. ) — Following oral absorption, acitretin undergoes extensive metabolism and interconversion by simple isomerization to its 13-cis form (cis-acitretin). The formation of cis-acitretin relative to parent compound is not altered by dose or fed/fast conditions of oral administration of acitretin. Both parent compound and isomer are further metabolized into chain-shortened breakdown products and conjugates, which are excreted. Following multiple-dose administration of acitretin, steady-state concentrations of acitretin and cis-acitretin in plasma are achieved within approximately 3 weeks.

Elimination: — The chain-shortened metabolites and conjugates of acitretin and cis-acitretin are ultimately excreted in the feces (34% to 54%) and urine (16% to 53%). The terminal elimination half-life of acitretin following multiple-dose administration is 49 hours (range: 33 to 96 hours), and that of cis-acitretin under the same conditions is 63 hours (range: 28 to 157 hours). The accumulation ratio of the parent compound is 1.2; that of cis-acitretin is 6.6.

Psoriasis: — In an 8-week trial of acitretin pharmacokinetics in subjects with psoriasis, mean steady-state trough concentrations of acitretin increased in a dose-proportional manner with dosages ranging from 10 to 50 mg daily. Acitretin plasma concentrations were nonmeasurable (<4 ng per mL) in all subjects 3 weeks after cessation of therapy.

Elderly: — In a multiple-dose trial in healthy young (n = 6) and elderly (n = 8) subjects, a 2-fold increase in acitretin plasma concentrations were seen in elderly subjects, although the elimination half-life did not change.

Renal Failure: — Plasma concentrations of acitretin were significantly (59.3%) lower in subjects with end-stage renal failure (n = 6) when compared with age-matched controls, following single 50-mg oral doses. Acitretin was not removed by hemodialysis in these subjects.

Pharmacokinetic Drug Interactions — (see also boxed CONTRAINDICATIONS AND WARNINGSand PRECAUTIONS: Drug Interactions):

In studies of in vivo pharmacokinetic drug interactions, no interaction was seen between acitretin and cimetidine, digoxin, phenprocoumon, or glyburide.

Ethanol: — Clinical evidence has shown that etretinate (a retinoid with a much longer half-life, see below) can be formed with concurrent ingestion of acitretin and ethanol. In a 2-way crossover trial, all 10 subjects formed etretinate with concurrent ingestion of a single 100-mg oral dose of acitretin during a 3-hour period of ethanol ingestion (total ethanol, approximately 1.4 g per kg body weight). A mean peak etretinate concentration of 59 ng per mL (range: 22 to 105 ng per mL) was observed, and extrapolation of AUC values indicated that the formation of etretinate in this trial was comparable to a single 5-mg oral dose of etretinate. There was no detectable formation of etretinate when a single 100-mg oral dose of acitretin was administered without concurrent ethanol ingestion, although the formation of etretinate without concurrent ethanol ingestion cannot be excluded (see boxed CONTRAINDICATIONS AND WARNINGS). Of 93 evaluable psoriatic subjects on acitretin therapy in several foreign trials (10 to 80 mg per day), 16% had measurable etretinate levels (>5 ng per mL).

Etretinate has a much longer elimination half-life compared with that of acitretin. In one trial the apparent mean terminal half-life after 6 months of therapy was approximately 120 days (range: 84 to 168 days). In another trial of 47 subjects treated chronically with etretinate, 5 had detectable serum drug levels (in the range of 0.5 to 12 ng per mL) 2.1 to 2.9 years after therapy was discontinued. The long half-life appears to be due to storage of etretinate in adipose tissue.

Progestin-only Contraceptives: — It has not been established if there is a pharmacokinetic interaction between acitretin and combined oral contraceptives. However, it has been established that acitretin interferes with the contraceptive effect of microdosed progestin preparations. 1Microdosed “minipill” progestin preparations are notrecommended for use with acitretin. It is not known whether other progestin-only contraceptives, such as implants and injectables, are adequate methods of contraception during acitretin therapy.

In 2 double-blind, placebo-controlled trials, acitretin was administered once daily to subjects with severe psoriasis (e.g., covering at least 10% to 20% of the body surface area). At 8 weeks (see Table 1) subjects treated in Trial A with 50 mg of acitretin per day showed significant improvements ( P≤0.05) relative to baseline and to placebo in the physician’s global evaluation and in the mean ratings of severity of psoriasis (scaling, thickness, and erythema). In Trial B, differences from baseline and from placebo were statistically significant ( P≤0.05) for all variables at both the 25-mg and 50-mg doses; it should be noted for Trial B that no statistical adjustment for multiplicity was carried out.