1. In this classification, the drugs are grouped based on the biological system that they target in the recepient. For example, the antibiotics streptomycin and erthyromycin inhibit the protein synthesis in bacteria and are classified in the same group.
2. However their mode of action is different. Streptomycin inhibits the initiation of protein synthesis, while erythromycin prevents the incorporation of new amino acids to the protein.