Drugs for Psoriasis

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Chapter: Essential pharmacology : Drugs Acting On Skin And Mucous Membranes

Psoriasis is an immunological disorder manifesting as localized or widespread erythematous scaling lesions or plaques. There is excessive epidermal proliferation attended by dermal inflammation. Periodic flareups are common.


DRUGS FOR PSORIASIS

 

Psoriasis is an immunological disorder manifesting as localized or widespread erythematous scaling lesions or plaques. There is excessive epidermal proliferation attended by dermal inflammation. Periodic flareups are common. Drugs can diminish the lesions, but cannot cure the disease. Therapy has to be prolonged and adjusted to the severity of disease. Topically applied emollients, keratolytics, antifungals afford variable symptomatic relief, but topical corticosteroids are the primary drugs used. They are very effective in mild-to-moderate disease, and initially even in severe cases. Most patients respond within 3 weeks, and the response may be hastened by applying the steroid under occlusion. Therapy is started with a potent steroid which is substituted after improvement by either weekly application or by a milder preparation. However, they carry their own local and systemic adverse effects, and lesions may progressively become refractory. Systemic therapy with corticosteroids and/or immunosuppressants is reserved for severe and refractory cases. Other topically used drugs are:

 

Calcipotriol

 

It is a synthetic non-hypercalcaemic vit D analogue effective topically in plaque type psoriasis. It binds to the intracellular vit D receptor in epidermal keratinocytes and suppresses their proliferation while enhancing differentiation. On absorption through the skin, it is inactivated rapidly by metabolism so that little systemic effect on calcium metabolism is exerted. Benefit in psoriasis is slow; but most cases respond in 4–8 weeks. Response is maintained till treatment is continued. Efficacy of calcipotriol in psoriasis is rated comparable to a moderate potency topical steroid. Combination with a steroid is more effective than either drug alone. Side effects are skin irritation, erythema and scaling. Hypercalcaemia is rare. It is a safe and effective alternative to steroids, but expensive.

 

DAIVONEX 0.005% oint; apply over psoriatic lesions twice daily.


Tazarotene

 

This synthetic retinoid applied as a topical gel (0.05–0.1%) is moderately effective in psoriasis. It is a prodrug which is hydrolysed in the skin to tezarotenic acid that exerts antiproliferative and anti-inflammatory action by binding to the intracellular retinoic acid receptor and modification of gene function. Combination with a topical steroid/calcipotriol may benefit refractory cases. Skin irritation, burning sensation, peeling are common. These can be minimized by careful application to the plaques only. It is teratogenic.

 

Coaltar

 

This crude preparation containing many phenolic compounds exerts a phototoxic action on the skin when exposed to light, especially UVA, and retards epidermal turnover. Applied as ointment or alcoholic solution on psoriatic plaques (generally with salicylic acid) and exposed to sunlight daily, it induces resolution of psoriatic lesions in majority of cases, but relapses are common. Its use has declined now because of strong smell, cosmetic unacceptability, skin irritation, allergy, and potential for photosensitivity and carcinogenicity.

 

EXETAR: coaltar 6%, salicylic acid 3%, sulfur ppt. 3%, oint.

 

TARSYL: coaltar 1%, salicylic acid 3% lotion.

 

IONAXT: coaltar 4.25%, salicylic acid 2% scalp lotion.

 

Photochemotherapy (PUVA: Psoralen ultraviolet A)

 

Photoactivated psoralen undergoes O2 independent as well as O2 dependent reactions and binds to pyrimidine bases— interferes with DNA synthesis and epithelial cell turnover. PUVA therapy has produced gratifying results in severely debilitating psoriasis, but relapses occur when treatment is stopped. Oral methoxasalen is followed 1–2 hours later by UVA exposure on alternate days. There are serious concerns regarding potential of PUVA to cause skin cancer, cataracts and immunological damage. Being inconvenient and carrying risks, it is reserved for severe cases of psoriasis only.

 

Psoralens have also been used to accelerate tanning—a maximum of 2 weeks treatment has been advised for this purpose. Other applications of PUVA are in lichen planus, urticaria pigmentosa, atopic dermatitis and cutaneous T cell lymphoma.

 

Adverse Effects: Mottling, erythema, burns, blistering, premature ageing of skin, gastric discomfort, nervousness and insomnia.

 

Acitretin

 

It is a synthetic retinoid for oral use in psoriasis, lichen planus, severe ichthyosis, etc. It acts by binding to ‘retinoic acid receptor’ in epidermal cells and regulating their proliferation and maturation. Inflammation is suppressed. Because of frequent and potentially serious adverse effects, use of acitretin is restricted to recalcitrant, pustular and other forms of severe psoriasis. Combination with topical antipsoriatic drugs is advised.

 

Dose: 0.5–0.75 mg/kg/day oral;

 

ACITRIN 10, 25 mg tab.

 

Dryness of skin and eyes, gingivitis, erythema and scaling of skin, alopecia, arthralgia, myalgia, lipid abnormalities and liver damage are the important adverse effects. Elimination of acitretin is very slow (taking months) because of accumulation in body fat. It is highly teratogenic. Women taking acitretin must not conceive during and till 3 years after stopping it. Drinking alcohol should be prohibited during and till 3 months after acitretin use.

 

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