Ampicillin-specific rashes.

Ampicillin is one of the most common drugs to elicit a rash, with an overall incidence of 3% to 8%. "Ampicillin-specific" rashes are thought to be nonhypersensitivity reactions and cause maculopapular erythema with minimal irritation or pruritus. If the rash is indeed an ampicillin-specific one, then discontinuation of ampicillin is not mandatory, and subsequent use of ampicillin or other beta-lactam antibiotics is tolerated. On the other hand, true hypersensitivity reactions with urticarial and anaphylactic properties demand prompt discontinuation of the drug and warrant supportive care. Unfortunately, there is no immediate definitive scientific method to differentiate between the two.