Pharmacotherapy of poison ivy/oak dermatitis

May 2001

With spring upon us and summer not far off, it is timely to discuss the pharmacotherapy of a common summertime inflammatory condition. Numerous products and ingredients are available over-the-counter (OTC) for pediatric clinicians to consider when recommending therapy to their patients with poison ivy/oak.

Rhus plants

The genus Rhus includes the plants poison ivy and oak as common causes of allergic contact dermatitis in the United States. Poison sumac, also a member of the genus Toxicodendron, can also result in contact dermatitis. However, poison sumac is not as geographically widespread as poison ivy and oak. These plants produce a chemical substance, urushiol, which is responsible for the allergic response that often occurs when contact is made with them.

The process of how urushiol results in dermatitis is interesting, for it is present only within the plant internally, and is not present directly on the plant surface. Damage to any part of the plant can result in release of the urushiol resin. This may occur by stepping upon or brushing up against it. Additionally, urushiol can be released by natural damage to the plant, such as from wind or animals. Urushiol is not spread by wind or air. In those very sensitive to urushiol only a small amount (several micrograms) is needed to result in noticeable symptoms. It is even possible to contract a dermatitis from poison ivy/oak and sumac from dead plants, as the resin is still present and capable of producing an inflammatory response. When these plants are burned, it is also possible for urushiol to be present in airborne particulate matter that may come in contact with skin over widespread parts of the body.

Reports have also shown urushiol to remain antigenically viable for extended periods on inanimate objects, such as clothing. Poison ivy/oak dermatitis results from a type IV immunologic (cell-mediated) reaction. Sensitized T-lymphocytes in the skin result in an intensely pruritic vesiculopapular rash which can vary in severity, from mild, locally affected areas to an extensive presence of significant edema and swelling. Bullae and weeping may also occur.

SOURCE: EDWARD A. BELL, PHARMC, BCPS

Goals of treating poison ivy/oak include mainly symptom relief and prevention of secondary problems, such as bacterial infection from scratching. Systemic corticosteroids (eg, 1-2 mg/kg/day of prednisone for 10-14 days) are often used and are effective. Higher potency topical corticosteroids (by prescription) can also be effective. While OTC products specific for the treatment of poison ivy/oak may not be necessary in all patients, their availability and commonality of use warrants discussion of appropriate application.

General considerations for OTC product use include information that some ingredients can be irritating and worsen the dermatitis, such as alcohol, topical antihistamines, and topical anesthetics (especially benzocaine). Topical antihistamines (eg, diphenhydramine) and topical anesthetics can be sensitizing and may worsen lesions, and products containing them generally should be avoided.

Some products are available in ointment formulations, and their use can result in increased maceration when used in patients with weeping lesions or in intertriginous areas. Cream-based products may be more appropriate as they are less likely to retain and trap moisture as ointments. Some OTC products are available as gel or spray formulations, and often contain alcohol, which can be irritating to open, tender lesions.

Several classes of ingredients are available in OTC products, such as local anesthetics, corticosteroids (hydrocortisone), antipruritics, antihistamines or astringents. Most products contain more than one active ingredient. In addition to specific ingredients, consider what pharmaceutical form of preparation may be most beneficial to the patient, such as lotion, ointment or cream.

Commonly available antipruritics include calamine, phenol, menthol and camphor. Calamine also possesses astringent properties, and camphor, menthol and phenol may also be considered to have antiseptic properties. Although some choose topical products containing diphenhydramine for its antihistaminic and antipruritic properties, histamine is not significantly responsible for the typical symptoms of poison ivy/oak, and as mentioned above, topical antihistamines can be sensitizing. Systemic antihistamines may be used, primarily for their sedative effects. Oral diphenhydramine is a highly sedating antihistamine that can be used for this purpose. Colloidal oatmeal bath products can additionally be used to relieve itching. When added to bath water, the tub can become quite slippery and patients should be cautioned about this. When the bath is completed the skin should be pat dried (vs. wiping), so as to leave a soothing film of colloidal oatmeal on the skin. It has also been recommended to use cold or tepid showers (without soap), or cold water compresses, for antipruritic effects.

Astringents promote drying of oozing lesions and additionally provide a protective film over inflamed skin. Calamine and aluminum acetate (Burow’s Solution) are commonly used astringents. Burow’s Solution also softens affected skin and removes crusted tissue. If hydrocortisone is used it is helpful to apply the cream formulation, applying it after use of Burow’s Solution, in order to provide an emollient effect. Calamine often leaves a tan-colored film, which some patients may consider cosmetically unappealing, especially if applied to the face.

Hydrocortisone, a low potency corticosteroid, is widely available OTC (in concentrations of 0.05%-1%) and is additionally present in many combination OTC products marketed for the treatment of poison ivy/oak. Hydrocortisone effectively reduces inflammation and is also an antipruritic. Higher potency topical corticosteroids may be necessary in patients with more severe dermatitis.

Prophylactic products

The best method to avoid contracting poison ivy/oak dermatitis is simple avoidance of the plant. Familiarity with the appearance of the ivy, oak and sumac plants is helpful. Washing with water and soap immediately (within 15 minutes) after contact with the plant can prevent dermatitis, although this is often impractical. Clothes and other contaminated objects should also be cleaned. A few products are available OTC that are labeled as preventative products. Tecnu Outdoor Skin Cleanser (Tec Labs) can be applied after exposure (as soon as possible) and rubbed into the affected area. Water is not necessary to remove the applied solution, but it should be wiped off with a cloth after at least 2 minutes of application. Stokogard Outdoor Cream (Stockhausen) is a barrier cream that can be effective at preventing dermatitis if applied prior to exposure to poison ivy, oak or sumac. IvyBlock Lotion has also shown to be effective in blocking urushiol from causing a dermatitis if applied at least 15 minutes prior to exposure. Further application every 4 hours during periods of potential exposure is also necessary.

For more information:

• Grevelink SA, et al. Effectiveness of various barrier preparations in preventing and/or ameliorating experimentally produced Toxicodendron dermatitis. J Am Acad Dermatol. 1992;27(2 Pt 1):182-188.
• Marks JG Jr, et al. Prevention of poison ivy and poison oak allergic contact dermatitis by quaternium-18 bentonite. J Am Acad Dermatol. 1995;33(2 Pt 1):212-216.
• Keefner KR. Poison ivy/oak/sumac dermatitis. In: Handbook of Nonprescription Drugs. Washington, D.C: American Pharmaecutical Association; 2000:647-63.
• Epstein E. Poison ivy and poison oak (Rhus allergy). In: Common Skin Disorders. Philadelphia: WB Saunders; 1994:143-146.