Of all drug classes, antibiotics are one of the most common causes of allergic reactions. The reactions can range from skin rash to severe life-threatening side effects. Ampicillin is a member of a group of drugs called penicillins. All of the penicillins contain a similar chemical structure with some minor modifications. So someone who has a rash with ampicillin is likely to have a rash when they take any penicillin.

Ceftin (also known as cefuroxime) is a member of a group of antibiotics called cephalosporins. This group of antibiotics is very closely related to the penicillins. Some people are allergic to both groups of drugs. Neither the penicillins nor cephalosporin antibiotics contain "sulfa." It is important for people who have had skin rash or other kinds of drug side effects to make certain that they remind their health care professionals. If the reactions have been severe, a medication alert bracelet is a good thing to consider. Although there are several companies that can supply bracelets and other forms of alerts, Medic Alert, a nonprofit foundation, is the oldest and best known.