1. Clinical Overview
A topical combination preparation used primarily in the management of chronic plaque psoriasis, seborrheic dermatitis, and other hyperkeratotic or scaling dermatoses. Coal Tar (1% w/v) acts as an antipsoriatic and antipruritic agent by reducing epidermal proliferation and inflammation. Salicylic Acid (3% w/v) is a keratolytic agent that promotes desquamation of hyperkeratotic skin, enhances penetration of coal tar, and has mild anti-inflammatory properties. This combination is a cornerstone of topical therapy in India due to its efficacy, low cost, and long-standing safety profile.
| Onset | Duration | Bioavailability |
|---|---|---|
| Keratolytic effects of salicylic acid may be seen within 3-5 days. Antipsoriatic and anti-inflammatory effects of coal tar typically become noticeable after 1-2 weeks of regular application. | Therapeutic effects persist for 24-48 hours after application, necessitating daily or alternate-day use for maintenance. | Topical bioavailability is low and variable. Systemic absorption of coal tar is minimal (<1%). Salicylic acid percutaneous absorption ranges from 1-25%, depending on vehicle, skin condition, and surface area treated. |
2. Mechanism of Action
The combination works synergistically. Salicylic Acid disrupts intercellular keratinocyte cohesion in the stratum corneum by dissolving the intercellular cement, leading to desquamation of scales. This keratolytic action allows for better penetration of Coal Tar into the psoriatic plaque. Coal Tar exerts antiproliferative effects by inhibiting DNA synthesis and reducing mitotic activity in the basal layer of the epidermis. It also has anti-inflammatory properties (reduces dermal infiltrate and epidermal neutrophils) and antipruritic effects, possibly via local vasoconstriction and a mild anesthetic action.
3. Indications & Uses
- Chronic Plaque Psoriasis (Stable Plaques)
- Scalp Psoriasis
- Seborrheic Dermatitis of Scalp and Body
- Hyperkeratotic Skin Disorders (e.g., Lichen Simplex Chronicus, Ichthyosis Vulgaris)
4. Dosage & Administration
Adult Dosage: Apply a thin layer to affected areas once or twice daily, or as directed by physician. For scalp: Apply to wet scalp, massage gently, leave on for 5-10 minutes, then rinse thoroughly.
Administration: 1. Wash and dry the affected area. 2. Apply a thin film and rub gently until absorbed. 3. Avoid contact with eyes, mucous membranes, and genital areas. 4. For scalp use, part hair and apply directly to lesions. 5. Can be used under occlusion (e.g., plastic wrap) only under medical supervision for short periods to enhance efficacy on thick plaques. 6. Wash hands thoroughly after application.
5. Side Effects
Common side effects may include:
- Local Skin Irritation (burning, stinging)
- Staining of Skin, Hair, and Clothing/Fabrics
- Unpleasant Odor
- Dryness of Skin
- Folliculitis
- Temporary Hair Discoloration (blond hair may turn orange-brown)
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Other Topical Salicylates or Keratolytics (e.g., Lactic Acid, Urea) | Increased risk of skin irritation and systemic absorption of salicylates. | Moderate |
| Topical Corticosteroids | Salicylic acid may enhance penetration of steroids, increasing potency and potential for side effects. | Moderate |
| Topical Tretinoin or Retinoids | Concomitant use can cause severe local irritation and dryness. | Major |
| Photosensitizing Drugs (e.g., Tetracyclines, Fluoroquinolones, Thiazides) | Coal tar is photosensitizing; additive risk of severe sunburn/phototoxicity. | Major |
| Oral Anticoagulants (e.g., Warfarin) | Absorbed salicylic acid may potentiate anticoagulant effect by displacing warfarin from protein binding sites and inhibiting platelet function. | Major (with large surface area application) |
| Oral Hypoglycemics (e.g., Sulfonylureas) | Salicylates may potentiate hypoglycemic effect. | Moderate (with large surface area application) |
| Methotrexate | Salicylates can reduce renal clearance of methotrexate, increasing risk of toxicity. | Major (with large surface area application) |
7. Patient Counselling
- DO apply a thin layer only to affected areas.
- DO wash hands thoroughly after application.
- DO use old towels and bed sheets as staining is likely.
- DO test on a small area first to check for irritation.
- DO use sun protection (SPF 30+) on treated areas when going outdoors.
- DON'T apply to face, eyes, mucous membranes, or genital areas unless directed.
- DON'T use on broken, raw, or infected skin.
- DON'T cover large areas of the body without doctor's advice.
- DON'T use tight occlusive dressings unless prescribed.
- DON'T use in children without pediatrician/dermatologist advice.
8. Toxicology & Storage
Overdose: Topical Overdose (Excessive Application): Severe local irritation, chemical burns, intense stinging. Systemic Salicylate Toxicity (Salicylism): Tinnitus, hearing loss, vertigo, hyperventilation, respiratory alkalosis progressing to metabolic acidosis, nausea, vomiting, hyperthermia, lethargy, confusion, coma. Severe toxicity includes pulmonary edema, cerebral edema, and renal failure.
Storage: Store in a cool, dry place, away from direct sunlight and heat. Ideal storage temperature: below 30°C. Keep the container tightly closed. Keep out of reach of children and pets. Do not freeze. Do not use if the solution has changed color or shows signs of separation (unless it is a suspension that requires shaking).