What is the recommended treatment for a patient with poison ivy (Toxicodendron dermatitis)?

Treatment of Poison Ivy Dermatitis

For mild to moderate poison ivy, apply prescription-strength topical corticosteroids (mometasone furoate 0.1% or betamethasone valerate 0.1% ointment) twice daily to affected areas, and for severe cases involving >30% body surface area or limiting self-care, immediately start systemic prednisone 0.5-1 mg/kg daily for 7 days followed by a 4-6 week taper. 1, 2

Immediate Post-Exposure Decontamination

If you catch the patient within hours of exposure, aggressive decontamination can prevent or reduce severity:

• Remove contaminated clothing and jewelry first, then brush off any dry plant material before washing 2
• Wash with soap and water immediately for maximum benefit: 100% urushiol removal if done instantly, but this drops to 50% at 10 minutes, 25% at 15 minutes, and only 10% at 30 minutes 1, 2
• Commercial decontamination products, hand cleaners, or even dishwashing soap used within 2 hours still provide 55-70% symptom reduction with no significant difference between products 1, 2, 3

Treatment Algorithm by Severity

Mild to Moderate Cases

Apply moderate-to-high potency topical corticosteroids twice daily - specifically mometasone furoate 0.1% ointment or betamethasone valerate 0.1% ointment 1, 2. Note that over-the-counter hydrocortisone preparations have NOT been shown to improve symptoms in randomized trials, despite FDA approval for poison ivy 1, 2, 4.

Add oral antihistamines for pruritus control:

• Non-sedating second-generation antihistamines (loratadine 10 mg daily) during daytime 1, 2
• First-generation antihistamines (diphenhydramine 25-50 mg or hydroxyzine 25-50 mg) at bedtime for their sedative properties 1, 2
• Be aware that evidence for antihistamines relieving local itching is uncertain; they may primarily help with sleep rather than itch relief 2

Reassess after 2 weeks - if reactions worsen or do not improve, escalate to the next treatment level 5

Moderate Cases (Persistent or Worsening)

Continue the above regimen but consider adding:

GABA agonists as second-line therapy if antihistamines fail:

• Pregabalin 25-150 mg daily OR gabapentin 900-3600 mg daily 5, 1
• These work by reducing peripheral calcitonin gene-related peptide release and modulating central μ-opioid receptors 5

Severe Cases

Initiate systemic corticosteroids immediately when:

• 30% body surface area is involved 1

• Self-care activities are limited 1
• Facial, genital, or widespread involvement is present 2

Prednisone dosing:

• 0.5-1 mg/kg body weight daily for 7 days 1, 2
• Critical: Follow with a weaning dose over 4-6 weeks to prevent rebound flare 1, 2
• Short tapers are a common pitfall that leads to recurrence 1

Continue topical corticosteroids to affected areas and oral antihistamines for symptomatic relief 1, 2

Supportive Care Measures

Skin care:

• Apply alcohol-free moisturizing creams or ointments twice daily, preferably urea-containing (5-10%) moisturizers 1, 2
• Avoid frequent washing with hot water 1, 2
• Avoid skin irritants including over-the-counter anti-acne medications, solvents, or disinfectants 1, 2

Symptomatic relief:

• Cool compresses for localized symptoms 2
• Oatmeal baths for widespread pruritus (though evidence is limited) 2

Sun protection:

• Apply sunscreen SPF 15 to exposed areas every 2 hours when outside 1, 2

Critical Warning Signs Requiring Antibiotics

Check for secondary bacterial infection at every visit:

• Increased warmth, tenderness, or pain 1, 2
• Purulent drainage 1, 2
• Honey-colored crusting 1, 2
• Cellulitis (spreading erythema with induration) 1, 2

Any of these signs require antibiotic therapy in addition to the dermatitis treatment 1, 2

Common Pitfalls to Avoid

• Do not use over-the-counter hydrocortisone as monotherapy - it lacks efficacy in randomized trials despite being FDA-approved for this indication 1, 2, 4
• Do not prescribe short systemic steroid courses - tapers must be 4-6 weeks to prevent rebound 1, 2
• Do not delay systemic steroids in severe cases - waiting increases morbidity and duration of symptoms 1, 2
• Do not forget to educate about decontamination timing - patients often don't realize the narrow window for effective washing 1, 2

Expected Course

The dermatitis typically begins within days of exposure and lasts up to 3 weeks with appropriate treatment 2, 6, 7. Approximately 50-75% of individuals react to urushiol 2.