amoxicillin /əmok′səsil″in/ , a beta-lactam semisynthetic oral penicillin antibiotic. ▪ INDICATIONS: It is prescribed in the treatment of infections caused by a susceptible gram-negative or gram-positive bacteria. ▪ CONTRAINDICATIONS: Known hypersensitivity to any penicillin prohibits its use. ▪ ADVERSE EFFECTS: Among the most serious adverse reactions are anaphylaxis, nausea, and diarrhea. Allergic reactions and rashes are common.