Dithranol: Efficacy in Psoriasis
Dithranol (also known as cignolin or anthralin, brand names Micanol, Psoradexan, and magistral formulations from pharmacies) is a classic topical antipsoriatic agent that has been used in dermatology for nearly a century. In Germany, dithranol remains an established option for plaque psoriasis, especially in specialized skin clinics and day clinics. The substance is prescribed in various strengths (between 0.1 and 3 percent) as an ointment, cream, or stick and is individually tailored to the patient's skin.
Compared to modern biologic therapies such as TNF inhibitors, IL 17 antagonists, or IL 23 inhibitors, dithranol is inexpensive, easily manageable, and without systemic effects. However, the application is demanding and leaves typical skin discoloration. In modern psoriasis therapy, dithranol is often chosen as an option for stable plaques, in pediatric treatment, or in patients who wish to avoid systemic therapies or cannot receive them for safety reasons.
Mechanism of Action
The exact mechanism of action of dithranol is not fully understood. Several parallel effects are discussed: inhibition of epidermal hyperproliferation through reduction of mitochondrial function in keratinocytes, anti-inflammatory effect through reduction of neutrophil chemotaxis and proinflammatory cytokines, and direct inhibition of DNA replication in proliferative cells.
Clinically, this effect manifests in normalization of epidermal differentiation, reduction of characteristic plaque scaling, and slow healing of psoriatic lesions over several weeks. The effect is slow but sustained: with short-term treatment success (minute therapy over 30 minutes), first visible changes are often seen after two to four weeks, and complete plaque healing after six to eight weeks.
Systemic absorption through the skin is minimal, so systemic side effects are practically non-existent even with large-area application. The typical local irritative effect is part of the therapeutic effect and is deliberately employed in appropriate regimens.
Indications
- Chronic plaque psoriasis, especially with stable, well-demarcated plaques on trunk and extremities
- Pediatric psoriasis, because systemic therapies are used restrictively in children
- Psoriasis in day clinic setting with minute therapy followed by UV therapy
- Adjuvant to other therapies for treatment-resistant plaques, supplementary to glucocorticoids, calcipotriol, or UV therapy
- Off-label for alopecia areata in the past, rarely used today
Dithranol is not suitable for application on the face, mucous membranes, genital region, or intertriginous areas because the thin skin there leads to severe irritation. In pustular psoriasis, acutely inflamed psoriasis, or erythroderma, dithranol is contraindicated because it worsens the course.
Dosage and Administration
Classical therapy: Start with low concentration 0.1 to 0.25 percent, increase weekly to irritation threshold. Apply once daily to plaques, leave on for several hours or overnight.
Minute therapy (Short Contact Therapy): Apply 1 to 3 percent dithranol for 10 to 30 minutes daily, then wash off with water and mild soap. This modern variant is better tolerated and most frequently used in outpatient practice.
Inpatient or day clinic: Combination with UV therapy following Ingram protocol, with daily increase in concentration and UV dose.
Application technique: Apply only to plaques themselves, protect surrounding healthy skin with vaseline or zinc paste. Wash hands thoroughly after application, clothing can become stained (wear old clothes for this reason). Strictly avoid eye contact.
Duration of therapy: usually 4 to 8 weeks, with individual adjustment of concentration according to skin tolerance. Maintenance therapy is rare because dithranol is paused in stable psoriasis.
Renal insufficiency and hepatic insufficiency: no adjustment usually required with topical application.
Side Effects
Very common: Skin redness, burning, irritation at the application site, especially in the initial phase. Skin discoloration from dark red to brownish, which subsides slowly after treatment ends.
Common: Contact dermatitis, pruritus, dryness, discoloration of hair, nails, clothing, laundry, furniture, and tiles. Discoloration on skin and nails is reversible, but often permanent on textiles.
Occasional: Bullous reactions at very high concentrations, allergic skin reactions, worsening of psoriasis with too rapid concentration increase.
Rare: Pronounced skin irritation with weeping erosions, worsening of adjacent healthy skin, secondary bacterial infection.
Note: the typical skin redness around the treated area is part of the mechanism of action and not a treatment error. However, excessive irritation requires concentration reduction or treatment pause.
Drug Interactions
- Other topical antipsoriatics such as calcipotriol or glucocorticoids: sequential application possible, simultaneous application to the same skin area can affect the efficacy of both. Calcipotriol is oxidatively inactivated by dithranol, so temporal separation is advisable.
- UV therapy: desired synergy in Ingram protocol, but stronger irritative effect. Cautious UV dose increase and skin monitoring.
- Topical retinoids such as tazarotene or adapalene: additional skin irritation, combination with caution.
- Topical calcineurin inhibitors such as tacrolimus, pimecrolimus: combination possible, but skin irritation can be additive.
- Methotrexate or biologics systemically: no direct interactions because dithranol is not systemically absorbed. Sequential application possible in therapy planning.
Special Precautions
Pregnancy: limited data. Short-term use on a small area after individual counseling possible when clearly indicated. Breastfeeding: do not apply on breast and near nipple, otherwise usually acceptable.
Children: Dithranol is an established option for childhood psoriasis from school age onwards because systemic therapies are used restrictively there. Medical supervision is advisable.
Skin cleaning after application: with water and mild soap. Stubborn discoloration can be removed with special solutions but usually cannot be completely eliminated immediately.
Environmental protection: wear old dark clothing, cover bed sheets with protective covering, clean bathtub immediately after application because discoloration otherwise becomes permanent.
Eye protection: when applying on head or forehead area, protect eyes with vaseline and protective covering. In case of accidental eye contact, rinse immediately and seek medical evaluation.
Lifestyle in psoriasis: light therapy, stress management, avoidance of triggers such as alcohol, nicotine, and infections, skin care with fat-rich emollients between treatment periods, psychological support if needed due to burden from visible plaques.
Fitness to drive: not impaired by topical application.
You might also be interested in
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- Betamethasone valerate, another topical glucocorticoid
- Methotrexate, classic systemic antipsoriatic
- Secukinumab, IL 17 antagonist as modern biologic
- Ustekinumab, IL 12 IL 23 antagonist as biologic
Frequently Asked Questions
Why does dithranol discolor my skin?
Dithranol oxidizes in the presence of oxygen and light to form colored breakdown products. These discolorations are a typical sign of efficacy and are not harmful. On the skin they are reversible and fade over weeks after treatment ends. On textiles and some surfaces they can be permanent.
How does dithranol differ from biologic therapies?
Dithranol is a topical, classic antipsoriatic with locally limited effect and no systemic effects. Biologics such as TNF inhibitors or IL 23 antagonists are systemic therapies for moderate to severe psoriasis with high efficacy, higher costs, and more potential risks. For stable plaque psoriasis, dithranol can be a cost-effective and easily manageable option.
What is minute therapy?
Minute therapy (Short Contact Therapy) is a modern application form in which higher dithranol concentrations (1 to 3 percent) are applied to plaques for only 10 to 30 minutes and then washed off. It is better tolerated than classic overnight application and most frequently used in outpatient practice.
What to do if skin irritation is too severe?
Reduce concentration, pause therapy, apply mild emollient care, if needed use topical glucocorticoid briefly. Moderate redness is desired, severe weeping irritation requires therapy adjustment. With very pronounced reaction, medical evaluation is advisable.
Sources
- Gelbe Liste, Dithranol Active Ingredient Profile
- BfArM, Federal Institute for Drugs and Medical Devices
- AWMF, Guidelines for Psoriasis Vulgaris
- German Dermatological Society
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