What are the indications for coal tar in dermatology?

Indications for Coal Tar in Dermatology

Coal tar is a traditional topical treatment that has been used for over 100 years in dermatology with specific therapeutic applications. Coal tar is primarily indicated for the treatment of psoriasis, atopic dermatitis, and seborrheic dermatitis as an antiproliferative and anti-inflammatory agent 1.

Primary Indications

Psoriasis

• First-line indication: Coal tar is effective for treating mild to moderate plaque psoriasis 1
• Formulations: Available as shampoos (for scalp psoriasis), bath solutions (for soaking affected areas), and combined with topical corticosteroids 1
• Combination therapy: Most effectively used in combination with phototherapy (Goeckerman treatment) for enhanced efficacy 1, 2
  • Studies show significant improvement in patients with recalcitrant psoriasis treated with combination tar and phototherapy, with 85% experiencing prolonged remission (average 2.6 years) 1
  • Modified Goeckerman technique (crude coal tar 2.5% plus UVA) has shown >75% PASI reduction in 27.3% of patients with moderate to severe psoriasis 2

Seborrheic Dermatitis

• Effective for treating scalp seborrheic dermatitis 1, 3
• Coal tar shampoos (2-10% solution) are particularly useful for long-term maintenance of remission 4

Atopic Dermatitis

• Used as an anti-inflammatory agent in the treatment of atopic dermatitis 1

Other Dermatological Conditions

• Less common applications include treatment of folliculitis, eczema, and vitiligo 3

Formulations and Administration

Available Forms

• Multiple formulations exist including:
  • Shampoos (particularly for scalp involvement)
  • Bath solutions (for soaking affected areas)
  • Lotions and creams (for localized application)
  • Combined preparations with corticosteroids 1

Dosing Considerations

• Concentration: A randomized controlled trial of 324 patients with mild to moderate psoriasis showed better improvement with 1% coal tar lotion compared to 5% coal tar extract 1
• For scalp psoriasis: Coal tar shampoos are recommended for maintenance therapy after initial treatment with more potent agents 4

Mechanism of Action

Coal tar works through multiple mechanisms:

• Antiproliferative effects on keratinocytes
• Anti-inflammatory properties
• Functions as an aryl hydrocarbon receptor agonist 1

Efficacy and Evidence

• For pediatric psoriasis: Combination of coal tar and phototherapy showed lesion clearance in 64% of patients, with 83% maintaining clearance at 4 months 1
• For moderate to severe psoriasis: Modified Goeckerman technique demonstrated >50% PASI reduction in 63.6% of patients 2
• Efficacy is supported by decades of clinical use, though fewer modern controlled trials exist compared to newer agents 1, 5

Adverse Effects and Limitations

Common Side Effects

• Folliculitis
• Irritant contact dermatitis
• Contact sensitivity
• Photosensitivity/phototoxicity
• Staining of skin, clothing, and bathing facilities 1

Patient Tolerability Issues

• Often poorly tolerated due to cosmetic concerns:
  • Strong tar odor
  • Staining of clothes and skin
  • Messy application 1

Safety Concerns

• Carcinogenic in animal studies but epidemiologic studies in humans fail to show increased risk of skin cancer with therapeutic use 1, 5, 6
• Theoretical increased risk of carcinogenicity with prolonged use in combination with phototherapy 1
• Studies have shown urinary excretion of coal tar metabolites and chromosomal aberrations of lymphocytes in children treated with combination coal tar and phototherapy 1

Special Populations

Pregnancy

• Risk of topical coal tar used for brief periods during pregnancy is likely to be small 1

Pediatric Use

• Should be used with caution in children 1
• For pediatric psoriasis, coal tar preparations can be used as monotherapy or combined with other topical therapies (Strength of recommendation: C) 1
• Coal tar preparations in combination with phototherapy are effective for pediatric psoriasis but may be limited by theoretical long-term risk of carcinogenesis (Strength of recommendation: B) 1

Practical Considerations

• When using coal tar for psoriasis treatment, consider alternating with other treatment modalities to decrease potential long-term risks 1
• For scalp application, solutions, foams, and gels are preferred over creams and ointments 4
• Although the use of tar products for localized psoriasis has decreased over time in the U.S., they are still often used in other countries 1

Treatment Algorithm for Coal Tar Use

1. For scalp psoriasis:

   • If predominant scaling: First use salicylic acid shampoo to remove scales, then apply coal tar shampoo
   • For maintenance: Use coal tar shampoo 2-3 times weekly 4

2. For plaque psoriasis:

   • Consider as monotherapy for mild cases
   • For moderate to severe cases: Use in combination with phototherapy (Goeckerman treatment) 1, 2

3. For seborrheic dermatitis:

   • Apply coal tar shampoo to affected areas
   • Can be used for long-term maintenance therapy 4