Drug action antibacterial agents

Sulfonamides are antibacterial agents, meaning they are active against bacteria Another term that may be used to describe the general action of these drugs is anti-infective because they are used to treat infections caused by certain bacteria Sulfadiazine, sulfisoxazole, and sulfamethizole are examples of sulfonamide preparations. 

The possession of surface activity per se may be an important faetor in the antibacterial action of a group of drugs, for example the eationie detergents. The addition of low concentrations of surface-active compounds may potentiate the biological effect of an antibacterial agent. Thus, phenols are often more aetive in the presence of soaps. 

Antibacterial drugs are used in veterinary practice for two purposes as therapeutics or prophylactics to control clinical disease, and as feed additives to enhance growth performance of animals. The latter practice presumably depends on the antibacterial action of the drug, even though it is used in low, subtherapeutic doses. The effect thus produced is to be distinguished from the action of a true growth promoter, e.g. monensin (63), and will be discussed in detail later (Section 1.08.6.3). Here we shall consider only the therapeutic/prophylactic properties of antibacterial agents. 

Mechanism of Action. Pyrimethamine blocks the production of folic acid in susceptible protozoa by inhibiting the function of the dihydrofolate reductase enzyme. Folic acid helps catalyze the production of nucleic and amino acids in these parasites. Therefore, this drug ultimately impairs nucleic acid and protein synthesis by interfering with folic acid production. The action of sulfadoxine and other sulfonamide antibacterial agents was discussed in Chapter 33. These agents also inhibit folic acid synthesis in certain bacterial and protozoal cells. 

Throughout this chapter, antibacterial drugs have been grouped based on their mechanism of action. The agents listed in Table 7.9 however, are grouped together based on the pharmacokinetic property of distribution. Each reaches therapeutic concentrations in the urinary tract, but generally fail to reach therapeutic concentrations in serum. Important exceptions are ciprofloxacin and ofloxacin, which can be used for infections outside the urinary tract because they reach therapeutic serum concentrations. 

This emphasis is not based on the fact that the mechanisms of action of these compounds are understood on a more fundamental level than those of other drugs. In fact, less is known, about their modes of action than about the mechanisms of action of many antibacterial agents. On the other hand, acetylcholine seems unique in the diversity of target-receptors to which it can be attached, while unusually good methods are available for measuring both the "affinities" and "efficacies" of members of this class of compounds. 

D. Shinabarger, Mechanism of action of the oxazoUdinone antibacterial agents. Expert Opin. Invesfig. Drugs 8 (1999) 1195-1202. 

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