What is the recommended treatment for mechlorethamine extravasation?

• A. Inject 2 mL of sodium thiosulfate per mg of mechlorethamine extravasated.
• B. Apply cold compress only and observe.
• C. Inject hyaluronidase into the site.
• D. Do not intervene; monitor for systemic symptoms.

Answer: (A)

Mechlorethamine acts as a vesicant, so prompt antidotal therapy around the extravasation site is essential to limit tissue injury. The best approach is to inject sodium thiosulfate peripherally around the leaked area, typically using a dose of about 2 mL for each milligram of mechlorethamine extravasated, and dilute it in saline or sterile water with injections at multiple nearby sites. This antidote helps neutralize the reactive alkylating agent and reduces the risk of necrosis when given as soon as possible, ideally within about 6 hours of exposure. After administering the antidote, continue local care, monitor for evolving tissue damage, and avoid relying on simple cold compresses or observation alone, which do not address the injury. Hyaluronidase is not the standard treatment for mechlorethamine extravasation, since the goal here is neutralization of the drug rather than enhancing diffusion.