Bacteriostatic/bactericidal agent

For some indications combination chemotherapy is indicated however then bacteriostatic or bactericidal agents should not be mixed. Synergism between the actions of different drugs is one of the aims of combination therapy. Other indications are delay of development of resistance or the treatment of mixed infections. 

Mechanism of Action An antibacterial UTI agent that inhibits the synthesis of bacterial DNA, RNA, proteins, and cell walls by altering or inactivating ribosomal proteins. Therapeutic Effect Bacteriostatic (bactericidal at high concentrations). Pharmacokinetics Microcrystalline form rapidly and completely absorbed macrocrystalline form more slowly absorbed. Food increases absorption. Protein binding 40%. Primarily concentrated in urine and kidneys. Metabolized in most body tissues. Primarily excreted in urine. Removed by hemodialysis. Half-life 20-60 min. 

Bacteriostatic and bactericidal agents are equivalent for the treatment of most infectious diseases in immunocompetent hosts. Bactericidal agents should be selected over bacteriostatic ones in circumstances in which local or systemic host defenses are impaired. Bactericidal agents are required for treatment of endocarditis and other endovascular infections, meningitis, and infections in neutropenic cancer patients. 

HOST FACTORS A critical determinant of antibiotic efficacy is the status of the host humoral and cellular defense mechanisms. In the immunocompetent host, merely halting the multiplication of the microorganism with a bacteriostatic agent frequently is sufficient to cure the infection. If host defenses are impaired, bacteriostatic activity may be inadequate and a bactericidal agent is required for cure. Examples where this applies include bacterial endocarditis, bacterial meningitis, and disseminated bacterial infections in nentropenic patients. Patients with HIV-1 infection and acquired immunodeficiency syndrome have impaired cellular immune responses. Therapy for opportunistic infection therefore often is snppressive bnt not cnrative disseminated infections with Salmonella or atypical mycobacteria typically require prolonged antibiotic therapy to prevent relapse. 

Know which drugs kill and which drugs maim (Fig. 7.3) Bactericidal antibiotics kill bacteria (cidal). Bacteriostatic agents only inhibit bacterial proliferation while the host s irmnune system does the killing Bactericidal agents are necessary for infections in patients with defective immune systems (cancer, AIDS, diabetes) and for overwhelming infections. Patients MUST take their full coarse of medication. Patient compliance is often poor because it appears that their infection has subsided when in fact it is only suppressed. 

Bacteriostatic agents inhibit bacterial growth, while bactericidal agents actually kill the organism. This distinction is not usually important clinically, as host-defence mechanisms are involved in the final elimination of bacterial pathogens. An exception is the treatment of infections in immunocompromised patients (AIDS, corticosteroids, aniicancer and immunosuppressant drags i. when a bactericidal agent should be used. 

In many therapeutic situations the drug combinations are completely misused (12). Adding another drug to a combination does not reduce the need for sound clinical judgement in therapy. Although there are many disease situations in which the use of more than one antibacterial agent may be justified, generalizations about various combinations of bactericidal or bacteriostatic antibiotics or admixtures have not proven valid. Basically, antibiotic combinations should be avoided as a common practice unless they have shown a clear increase in effectiveness as reported in the literature. 

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,... 

Pharmacology Linezolid is a synthetic antibacterial agent of oxazolidinones. The results of time-kill studies have shown linezolid to be bacteriostatic against enterococci and staphylococci. For streptococci, linezolid was found to be bactericidal for the majority of strains. 

Methenamine (hexamethylenetetramine) is an aromatic acid that is hydrolyzed at an acid pH (<6) to liberate ammonia and the active alkylating agent formaldehyde, which denatures protein and is bactericidal. Methenamine is usually administered as a salt of either man-delic (Mandelamine) or hippuric Hiprex, Urex) acid. Not only do these acids acidify the urine, which is necessary to generate formaldehyde, but also, the resulting low urine pH is by itself bacteriostatic for some organisms. 

Certain antiseptic and therapeutic agents (such as sodium fluoride, stannous fluoride, strontium chloride, urea, dibasic ammonium phosphate, are used in dentrifrices for their anticarcinogenic, bacteriostatic and bactericidal actions. 

Nitrofurantoin is bacteriostatic and bactericidal for many gram-positive and gram-negative bacteria but P aeruginosa and many strains of proteus are resistant. There is no cross-resistance between nitrofurantoin and other antimicrobial agents and resistance emerges slowly. As Escherichia coli resistant to trimethoprim-sulfamethoxazole and fluoroquinolones has become more common, nitrofurantoin has become an important alternative oral agent for treatment of uncomplicated urinary tract infection. 

Antibacterial agents may be classified as bacteriostatic or bactericidal (Table 51-3). For agents that are primarily bacteriostatic, inhibitory drug concentrations are much lower than bactericidal drug concentrations. In general, cell wall-active agents are bactericidal, and drugs that inhibit protein synthesis are bacteriostatic. 

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. 

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