Understanding Drug Action, Interaction and Reaction

Monitoring of physical, cellular, biochemical, immunological and psychological parameter during the course of any drug therapy imparts us valuable information regarding drug action (expected relief), interaction (action in association dietary items and other drugs) and reaction (adverse effect of the drug or adverse drug reaction or ADR). Let us take the treatment of psoriasis, a chronic, immunological and inflammatory disease of skin for understanding drug, action, interaction and reaction. Psoriasis presents with erythematous, scaly (pustular) or indurated plaques over the extensor aspects of limbs, trunk, head and face and is widely treated with acitretin (synthetic aromatic analogue of retinoic acid).

Action of acitretin:

Systemic treatment with acitretin promotes cellular differentiation of epidermis and decrease proliferation rate in psoriatic plaques. It also exerts anti-inflammatory effect by modulating lymphocyte functions and inhibition of neutrophil migration. Psoriatic inflammation generally subsides within 6-12 weeks' period of treatment with acitretin. It is indicated for the treatment of moderate to severe psoriasis in adult patients. Pregnancy should be ruled out in female patients and they should be advised to use effective contraception at least for a period of three years to avoid pregnancy.

Interactions of acitretin:

• Acitretin interferes with the contraceptive action of minipill contraceptives and may result in failure of contraception.


• Use of alcohol during acitretin treatment should be avoided as ethanol converts acitretin to etretinate and thus prolongs clearance of acitretin.


• There is a risk of hypervitaminosis-A if acitretin is given along with vitamin-A.


• Risk of hepatitis increases if acitretin is administered in combination with methotrexate.


• Use of tetracyclines or its derivatives should be avoided in patients on acitretin therapy as there are chances of development of pseudotumor cerebri.


• Acitretin may decrease night vision, so patients should be advised to avoid driving at night.


• Acitretin should not be used in lactating mothers as it is excreted in the breast milk and may harm the baby as the drug is teratogenic.


• Acitretin sensitizes the skin to UV light so patient should be advised to avoid excessive exposure to sunlight.

Adverse drug reactions:

• Use of acitretin is contraindicated in pregnancy and during lactation. Fetal deformities like dysmorphia and cardiovascular malformations have been reported with the use of acitretin and/or etretinate.


• The drug has teratogenic.


• Commonly encountered adverse effects with acitretin are mucocutaneous effects like chelitis, xerosis, rhinitis, skin peeling over palms & soles, nail dystrophy, and hair loss.


• Dryness and irritation of eyes.


• Use of tetracycline or minocycline along with acitretin may lead to the development of pseudotumor cerebri.