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Dithranol Anthralin

Dithranol (Anthralin)

Introduction

Dithranol, also known by its alternative name Anthralin, is a topical medication primarily used in the treatment of psoriasis, a chronic autoimmune skin disorder characterized by red, scaly patches. It has been a mainstay in dermatological practice for over a century and remains relevant today despite the advent of modern immunomodulators and biologics. Its unique mechanism of action and cost-effectiveness make it a viable option, especially in resource-limited settings.

Historical Background

Dithranol was first synthesized in the early 20th century, though its therapeutic potential was not realized until the mid-20th century when it began to be widely used for treating psoriasis. Initially, crude forms derived from natural sources like Goa powder were employed before the development of purified synthetic versions. Over time, formulations have improved to reduce irritation and enhance efficacy.

Chemical Composition and Properties

Dithranol is an anthracene derivative with the molecular formula C14H10O3. It appears as a yellowish-brown powder and is highly lipophilic, allowing it to penetrate the skin layers effectively. It is unstable in the presence of light and oxygen, requiring it to be stored in tightly sealed containers and applied for short durations.

Mechanism of Action

Dithranol exerts its therapeutic effect through multiple mechanisms:

  1. Anti-proliferative Action: It inhibits DNA synthesis in keratinocytes, thereby slowing down the rapid skin cell turnover seen in psoriasis.

  2. Anti-inflammatory Effects: It reduces the infiltration of inflammatory cells by modulating cytokine release.

  3. Oxidative Stress Induction: The drug generates reactive oxygen species (ROS) within skin cells, which contributes to the normalization of epidermal differentiation.

These combined effects help to reduce the thickness and scaling of psoriatic plaques. While its primary indication is chronic plaque psoriasis, dithranol may occasionally be used in other hyperproliferative skin conditions. However, psoriasis remains its most validated and accepted use.

Formulations and Application

Dithranol is available in various concentrations ranging from 0.1% to 2%. It is typically formulated in ointments or creams and used in one of two regimens:

  1. Short-contact therapy: The preparation is applied for 10 to 30 minutes and then washed off. This reduces the risk of irritation and staining.

  2. In-patient Ingram regimen: A traditional method involving tar baths, dithranol application, and ultraviolet light therapy under supervision.

Modern formulations often include additives like salicylic acid or coal tar to enhance efficacy and reduce irritation.

Usage Guidelines

  • Begin with the lowest concentration to assess skin tolerance.

  • Gradually increase the concentration as tolerated.

  • Avoid application on sensitive areas like the face or genitals.

  • Use gloves during application to avoid staining.

Efficacy

Numerous studies have demonstrated the effectiveness of dithranol in reducing psoriatic plaque thickness, scaling, and erythema. Its efficacy is comparable to some topical corticosteroids, although it may take longer to show results. When used consistently, remission periods can be prolonged.

Side Effects

Though effective, dithranol is associated with several side effects:

  • Skin Irritation: Erythema and burning are common, especially at higher concentrations.

  • Staining: It stains the skin, clothes, and bathroom fixtures, which may discourage patient compliance.

  • Photosensitivity: Increased sensitivity to sunlight can occur, necessitating protective measures.

To mitigate these, short-contact therapy and combined regimens are often preferred.

Contraindications

  • Hypersensitivity to dithranol or any formulation components

  • Acute, inflamed psoriasis (e.g., erythrodermic or pustular types)

  • Use on face or mucous membranes

Special Populations

  • Children: Use with caution and under medical supervision.

  • Pregnancy and Lactation: There is limited data; use only if clearly needed.

Comparisons with Other Treatments

Compared to newer biologic treatments, dithranol is less effective in severe cases but has fewer systemic side effects and is significantly more affordable. It holds a unique niche in topical psoriasis therapy, especially for patients who prefer non-steroidal options or those in developing countries.

Patient Education

Effective patient education is critical for successful dithranol therapy. Patients should be informed about:

  • Proper application technique

  • Expected side effects and how to manage them

  • Importance of adherence to treatment schedules

  • Strategies to prevent staining

Visual aids and demonstration can be especially helpful.

Research and Developments

Recent research has focused on improving dithranol formulations to enhance skin penetration and reduce side effects. Encapsulation in liposomes and nanoparticles is under investigation, as are combination therapies with corticosteroids or vitamin D analogs.

Clinical Guidelines and Recommendations

Leading dermatological associations like the American Academy of Dermatology (AAD) and the British Association of Dermatologists (BAD) include dithranol in their treatment algorithms for psoriasis, particularly for mild-to-moderate cases.

Practical Tips for Clinicians

  • Perform a patch test before initiating therapy.

  • Recommend dark-colored clothing and towels during use.

  • Advise use in well-ventilated areas due to strong odor.

  • Monitor for signs of excessive irritation.

Economic Considerations

Dithranol is one of the most cost-effective therapies for psoriasis, especially in countries with limited access to biologics. Its low cost makes it accessible to a wide patient population, although its aesthetic drawbacks remain a limiting factor.

Conclusion

Dithranol (Anthralin) continues to be a valuable therapeutic agent for psoriasis despite the emergence of newer drugs. Its efficacy, affordability, and non-steroidal nature make it a cornerstone in dermatologic care for selected patients. With ongoing research and development, there is potential for further innovation that could improve its usability and patient acceptability. For both patients and clinicians seeking an alternative or adjunct to modern therapies, dithranol remains a worthwhile consideration.