The structure of penicillins is characterized by the presence of a β-lactam ring. The basic structures of penicillins all contain a parent nucleus (6-aminopenicillanic acid, 6-APA) and a side chain (CO-R). The parent nucleus is the main antimicrobial component, synthesized from the thiazole ring and the β-lactam ring, and if the β-lactam ring is destroyed, its antimicrobial activity disappears. The side chain, on the other hand, is mainly related to its antimicrobial spectrum, whether it is acid-resistant, whether it is enzyme-resistant and other pharmacological properties. Among penicillins, except for penicillin G, which is a natural penicillin, the rest are semi-synthetic penicillins. The side chain of penicillin G is benzyl, and other penicillin antibiotics, such as ampicillin, are obtained by replacing the hydrogen on the benzyl group of penicillin with an amino group. Amoxicillin, or hydroxyamphetamine penicillin, is para-hydroxyamphetamine. The use of penicillins should be under the guidance of a medical professional.