Final answer:
Penicillins are classified based on antimicrobial spectrum into natural penicillins, aminopenicillins, penicillinase-resistant penicillins, and antipseudomonal penicillins, each with varying structure, spectrum of activity, and resistance to degradation.
Step-by-step explanation:
The four names used to classify penicillins based on their antimicrobial spectrum are natural penicillins, aminopenicillins, penicillinase-resistant penicillins, and antipseudomonal penicillins.
- Natural penicillins: Includes Penicillin G and V, primarily active against gram-positive bacteria.
- Aminopenicillins: Introduced by adding an amino group, such as ampicillin and amoxicillin, these penicillins have expanded coverage against gram-negative bacteria.
- Penicillinase-resistant penicillins: Created to resist enzymatic degradation by penicillinase; an example is methicillin, which has a bulky R group that protects the beta-lactam ring.
- Antipseudomonal penicillins: Designed to combat Pseudomonas infections, these have a broader gram-negative coverage.
All these penicillins contain a four-member cyclic amide called a lactam. The beta-lactam ring is essential for their antibacterial activity, which involves inhibition of cell wall synthesis in bacteria. Strategic chemical modifications to the R group attached to this ring have led to the development of semisynthetic penicillins with varied characteristics like increased spectrum of activity, acid stability, and resistance to degradation by lactamase enzymes.