Antibacterial agent, selection

Although the antibacterial spectmm is similar for many of the sulfas, chemical modifications of the parent molecule have produced compounds with a variety of absorption, metaboHsm, tissue distribution, and excretion characteristics. Administration is typically oral or by injection. When absorbed, they tend to distribute widely in the body, be metabolized by the Hver, and excreted in the urine. Toxic reactions or untoward side effects have been characterized as blood dyscrasias crystal deposition in the kidneys, especially with insufficient urinary output and allergic sensitization. Selection of organisms resistant to the sulfonamides has been observed, but has not been correlated with cross-resistance to other antibiotic families (see Antibacterial AGENTS, synthetic-sulfonamides). 

The proteins of the outer membrane, many of which traverse the whole structure, are currently the subject of active study. Some of the proteins consist of three subunits, and these units with a central space or pore running through them are known as porrns. They are thought to act as a mechanism of selectivity for the ingress or exclusion of metabolites and antibacterial agents (see Chapter 8). 

The management of a patient with a UTI includes initial evaluation, selection of an antibacterial agent and duration of therapy, and follow-up evaluation. 

There are four general properties for a good antibacterial agent. It must be selective. Eliminating all species of bacteria from the body may leave the patient prone to superinfection. It should kill bacteria rather than just prevent their multiplication it should be bactericidal rather than bacteriostatic. Bacteria should not develop resistance to the drug. Lastly,... 

The classification of antibacterial agents as bactericidal or bacteriostatic has limitations. Some agents that are considered to be bacteriostatic may be bactericidal against selected organisms. On the other hand, enterococci are inhibited but not killed by vancomycin, penicillin, or ampicillin used as single agents. 

Consequently, drugs that cause inadequate production of peptidoglycans or other structural components within the cell wall may produce a selective bactericidal effect. Also, a limited number of antibacterial agents directly punch holes in the bacterial cell membrane, destroying the selective permeability and separation of internal from external environment,... 

Isoniazid, isonicotinic acid hydrazide, is the most potent and selective of the tuberculostatic antibacterial agents. 

A recent review covers the nonclassical polycyclic /3-lactams synthesized with the aim of discovering new lead compounds in the field of antibacterial agents <2000T5743>. Selected compounds 122-127 related to penam or penem structures are shown in Figure 12. 

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