Allergic reactions to the antibiotic penicillin are common. Meropenem is an antibiotic that fights many of the same infections as penicillin. Meropenem may be an option for patients who are allergic to penicillin. However, meropenem and penicillins have similar chemical structures; therefore, doctors often avoid using meropenem in patients who are allergic to penicillin. Information about the frequency of meropenem allergy in patients with penicillin allergy is limited. With some drugs, such as penicillin and meropenem, doctors can perform a “skin test” for allergic reactions by administering small amounts of the drug under the skin. It is important to know about antibiotic options for patients who cannot take penicillin because of allergy.