What is the most successful treatment option for poison sumac?

Cold milk compress. Depending on the severity mild cases can be treated with cold milk compresses, easing off the plant material. And shake lotion. Over the counter poison ivy products to neutralize the chemical are available. For more severe extensive cases oral steroids can relieve and resolve the case. Use ivy shield as a preventive in suspect areas.
See below. Topical steroids for mild cases; systemic steroids for more severe cases.