1. Clinical Overview
A topical combination product used primarily in dermatology for the treatment of chronic, scaling, and inflammatory skin conditions. Coal Tar acts as an anti-inflammatory, antipruritic, and keratoplastic agent, while Salicylic Acid provides keratolytic, comedolytic, and mild anti-inflammatory effects. This combination is a cornerstone of therapy for psoriasis and seborrheic dermatitis in the Indian context, valued for its efficacy and cost-effectiveness.
| Onset | Duration | Bioavailability |
|---|---|---|
| Therapeutic effects on scaling and erythema are typically observed within 1-2 weeks of consistent use. Immediate antipruritic effects may be noted sooner. | Effects are not systemic; local action persists as long as the medication remains on the skin. Regular application (once or twice daily) is required to maintain therapeutic benefit. | Topical bioavailability is negligible for systemic absorption when used on intact skin as directed. Minimal percutaneous absorption occurs. |
2. Mechanism of Action
The combination works synergistically. Coal Tar reduces epidermal hyperproliferation and dermal inflammation by inhibiting DNA synthesis and modulating interleukin-6. It also has antipruritic and vasoconstrictive effects. Salicylic Acid facilitates the penetration of Coal Tar by breaking down intercellular keratinocyte adhesions (desmosomes) through dissolution of the intracellular cement. It also promotes shedding of scales and unblocks pores.
3. Indications & Uses
- Chronic Plaque Psoriasis (Scalp and Body)
- Scalp Seborrheic Dermatitis (Dandruff)
- Chronic Eczema with Lichenification and Scaling
4. Dosage & Administration
Adult Dosage: Apply a thin layer to the affected area once or twice daily, or as directed by the physician. For scalp: Apply, 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 in gently. 3. Avoid contact with eyes, mucous membranes, and genital areas. 4. For scalp use, protect the forehead with petroleum jelly to prevent staining. 5. Can be used with occlusion (plastic wrap) for thick plaques under medical guidance. 6. Wash hands after application.
5. Side Effects
Common side effects may include:
- Local Skin Irritation (burning, stinging)
- Staining of skin, hair, and clothing (brownish-yellow)
- Unpleasant Odor
- Temporary Hair Discoloration
- Dryness
- Folliculitis
6. Drug Interactions
| Drug | Effect | Severity |
|---|---|---|
| Warfarin and other Oral Anticoagulants | Increased risk of bleeding due to potential systemic absorption of salicylic acid displacing warfarin from protein binding sites and affecting platelet function. | Major |
| Methotrexate | Increased risk of methotrexate toxicity due to displacement from plasma protein binding by salicylic acid. | Major |
| Other Topical Medications (e.g., Tretinoin, Benzoyl Peroxide, strong acids) | Increased risk of severe local irritation and dryness. | Moderate |
| Photosensitizing Drugs (e.g., Doxycycline, Fluoroquinolones) | Additive risk of photosensitivity reactions with Coal Tar. | Moderate |
| Topical Corticosteroids | Often used sequentially (not simultaneously) in a rotational regimen. No direct pharmacokinetic interaction. | Minor |
7. Patient Counselling
- DO apply a thin layer only to affected areas.
- DO wash hands thoroughly after application.
- DO use sun protection (sunscreen, clothing) as Coal Tar can cause photosensitivity.
- DO test on a small area first to check for irritation.
- DON'T apply to broken, raw, or infected skin.
- DON'T use on the face, groin, or axillae unless directed by a doctor.
- DON'T cover with tight bandages or occlusive dressings unless advised.
- DON'T use with other topical medicines without consulting your doctor.
8. Toxicology & Storage
Overdose: Topical overdose (excessive application over large areas): Symptoms of salicylate toxicity (Salicylism) - tinnitus, vertigo, headache, confusion, hyperventilation, nausea, vomiting, metabolic acidosis. Severe: seizures, coma, respiratory failure. Chronic overuse can lead to local skin atrophy, striae, and telangiectasia.
Storage: Store at room temperature (15-25°C) in a cool, dry place. Protect from light. Keep the container tightly closed. Keep out of reach of children. Do not freeze.