Avoidance: Practitioners should become familiar with the species of toxicodendron found in their geographic area and instruct patients with handouts and photographs showing the appearance of the plant and the most likely exposure sites. With the exception of poison sumac, the saying "Leaves of three, let them be!" conveys the basic message. An excellent article by Guin et al. (see ref. 27) contains superb color photographs and comprehensive information about the characteristics and regional distribution of each major species.

Barriers: Several effective barrier products are available OTC: Ivy Block® (EnviroDerm), Stocko Gard® (Stockhausen Inc.), Hollister Moisture Barrier® (Hollister Inc.), Hydropel® (C&M Pharmacal), Poison Oak-N-Ivy Armor® (Tec Labs) and Tecnu Poison Oak-N-Ivy Armor® (Tec Labs). When applied prior to exposure and according to the package instructions, up to 90% of a reaction can be prevented if exposure occurs.

Removal of the antigen: If exposure to an offending toxicodendron is recognized, immediate washing with mild soap and water may totally prevent the reaction. The antigen penetrates the epidermis rapidly and after 10 minutes some penetration may occur. There is agreement that washing within the first hour of exposure will mitigate the severity of the reaction, and any exposed person should cleanse thoroughly at the first opportunity to limit transfer of the resin to other skin areas. Exposure to this type of contact antigen can occur indirectly from the fur of pets wandering through the brush or from camping equipment that has come in contact with the resin. This may be the surreptitious cause of unexplained or persistent cases. Pets should be shampooed; camping equipment should be washed with detergent.

Hyposensitization: Two extracts of urushiol are commercially available for the purpose of hyposensitization. Successful treatment will result in milder and shorter reactions; however, the results are transient and do not afford complete prevention. This procedure should be undertaken only by a dermatologist or allergist familiar with the process. Because of the limited results, subjects should be carefully chosen and should be fully aware of the limited results and potential side effects.

Topical Therapy

Proprietary lotions: An array of OTC products is available at any pharmacy. These contain different combinations of ingredients that relieve the itching, dry the exudate from the vesicles, and prevent secondary infection. They may, in fact, be modestly effective in mild cases. As noted earlier, several products contain benzocaine and diphenhydramine, which are both highly sensitizing when applied to dermatitic skin. These products are not effective in cases of severe or widespread exposure except for the local drying and antimicrobial effect. A prescription cream containing 5% doxepin HCl is an effective antipru-ritic, but caution must be taken to avoid systemic side effects and drug interactions.

Topical steroids: Despite some claims to the contrary, topical steroid creams are of considerable value provided they are used appropriately. These products are effective in mild to moderate cases applied to the sites of active dermatitis that are not overtly blistered. In some cases, they are sufficient as monotherapy. In more severe cases, they can be used in conjunction with systemic medication on the areas of acute erythema. Once an area is overtly blistered, these medications cannot penetrate and are ineffective. Potency should be a group IV steroid or stronger.

Antihistamines: An antihistamine may be occasionally useful in an agitated patient with intense itching. In adult patients, 25 to 50 mg hydroxyzine QID or 10 mg doxepin QID can be used. In children, hydroxyzine or cyproheptadine in appropriate dosage for weight or age is recommended.

Systemic steroids: Severe reactions can be incapacitating and result in time lost from work or vacation. If a reaction is progressing rapidly, and especially if there is extensive facial or genital involvement with edema, systemic steroids should be considered. Treatment for adults should start with 30 to 40 mg prednisone STAT dose, then 30 to 40 mg in a single morning dose for the next 14 days. The prednisone can then be rapidly tapered over the ensuing week. This 3-week regimen will usually avoid late flare-ups.

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