Acitretin

MECHANISM OF ACTION

Acitretin acts as a systemic retinoid by regulating the growth and differentiation of skin cells. It binds to nuclear retinoic acid receptors (RARs), which modulate the transcription of genes involved in keratinocyte proliferation and differentiation. By normalizing the production and shedding of skin cells, acitretin reduces the excessive scaling, thickening, and inflammation seen in severe psoriasis. Unlike topical treatments, its effects are systemic, influencing multiple layers of the skin and, in some cases, other epithelial tissues. Clinical improvements are typically seen over several weeks of therapy, and the drug’s use is carefully monitored due to potential teratogenicity, liver toxicity, and alterations in lipid metabolism.

PHARMACOKINETICS

Absorption

Acitretin is well absorbed from the gastrointestinal tract following oral administration, with an estimated bioavailability of approximately 60–70%. Peak plasma concentrations are generally reached within 1 to 4 hours after dosing, although food can influence the rate and extent of absorption.

Distribution

The volume of distribution of Acitretin is approximately 0.4 to 0.7 L/kg. Acitretin is highly bound to plasma proteins, primarily albumin, which influences its distribution throughout the body, including the skin and other epithelial tissues.

Metabolism

Acitretin is primarily metabolized in the liver through oxidation and conjugation pathways, forming inactive metabolites. Some of these metabolites can undergo reversible conversion to etretinate, especially in the presence of alcohol. The metabolism of acitretin is influenced by liver function, and its metabolites are mainly excreted via the urine and, to a lesser extent, in the feces.

Excretion

Acitretin is eliminated from the body mainly as metabolites. Following hepatic metabolism, these metabolites are primarily excreted in the urine, with a smaller portion excreted in the feces. Only minimal amounts of unchanged acitretin are eliminated, reflecting its extensive metabolism and conversion to inactive compounds, including the potential formation of etretinate in certain conditions.

PHARMACODYNAMICS

Acitretin is a systemic retinoid that exerts its therapeutic effect by binding to nuclear retinoic acid receptors (RARs), which regulate the transcription of genes involved in keratinocyte proliferation and differentiation. By normalizing skin cell growth and turnover, acitretin reduces scaling, thickening, and inflammation in severe psoriasis. Its effects are dose-dependent, gradual in onset, and require careful monitoring due to potential teratogenicity, hepatotoxicity, and lipid abnormalities.

DOSAGE AND ADMINISTRATION

• Route: Oral administration 

• Initial dose: Usually 25–50 mg once daily 

• Maintenance dose: Typically 10–50 mg per day, individualized based on clinical response and tolerability 

• Monitoring: Regular liver function tests, lipid profiles, and pregnancy status are essential due to the risk of hepatotoxicity, hyperlipidemia, and teratogenicity 

• Timing: It may be taken with or without food, but should preferably be taken at the same time every day 

• Dose adjustment: Required for patients with liver impairment, elderly patients, or those at high risk of adverse effects; strict pregnancy prevention measures must be followed.

DRUG INTERACTIONS

Acitretin can interact with hepatotoxic drugs, alcohol, and vitamin A supplements, increasing the risk of liver toxicity, hyperlipidemia, and teratogenicity. Its absorption may be reduced by bile acid–binding agents, and alcohol can convert it to the long-acting metabolite etretinate. Careful monitoring of liver function, lipids, and strict pregnancy prevention is essential during therapy.

FOOD INTERACTIONS

Acitretin absorption can be influenced by high-fat meals, and alcohol must be avoided because it can convert the drug to the long-acting teratogenic metabolite etretinate. Vitamin A supplements and certain herbal products may increase toxicity, so patients should maintain a consistent diet and consult their doctor before taking any supplements.

CONTRAINDICATIONS

Acitretin is contraindicated in patients with known hypersensitivity to acitretin or other retinoids. It should not be used during pregnancy or in women planning to become pregnant due to a high risk of severe fetal malformations. The drug is also contraindicated in patients with severe liver disease, uncontrolled hyperlipidemia, or chronic alcohol use. Caution is required in individuals with renal impairment or other conditions that may increase the risk of toxicity.

SIDE EFFECTS

• Dryness of skin, lips (cheilitis), and mucous membranes 

• Peeling or itching of the skin 

• Hair thinning or hair loss (alopecia) 

• Headache 

• Dizziness 

• Nausea 

• Elevated liver enzymes 

• Increased blood lipids (hypertriglyceridemia) 

• Joint or muscle pain 

• Sensitivity to sunlight (photosensitivity)

TOXICITY

Acitretin toxicity, typically caused by excessive dosing or prolonged use, mainly results in symptoms of hypervitaminosis A due to its retinoid activity. This can lead to severe dryness of the skin and mucous membranes, liver toxicity, elevated lipid levels, and, most importantly, a high risk of teratogenic effects.