Antibacterial drugs bacteriostatic effect

Antibiotics possess antibacterial activity and are used in the treatment of eye infections. Sulfonamides possess a bacteriostatic effect against a wide range of gram-positive and gram-negative microorganisms. They are used in the treatment of conjunctivitis, comeal ulcer, and other superficial infections of the eye. See the Summary Drug Table Select Ophthalmic Preparations and Chapter 6 for additional information on the sulfonamides. 

The effect of antibacterial drugs can be observed in vitro (3). Bacteria multiply in a growth medium under control conditions. If the medium contains an antibacterial drug, two results can be discerned 1. bacteria are killed—bactericidal effect 2. bacteria survive, but do not multiply-bacteriostatic effect Although variations may occur under therapeutic conditions, different drugs Lullmann, Color Atlas of Pharmacology... 

Antibacterial drugs can be either bactericidal or bacteriostatic The effectiveness of bacteriostatic drugs depends on an intact host immune system. Antimicrobial agents may be administered singly or in combination. Some combinations induce synergy and/or delay emergence of resistance. 

Due to their excellent bactericidal and bacteriostatic properties and their general lack of serious side-effects (ref. 16) the B-lactam antibiotics still belong to the most favoured antibacterial drugs that are avaible. The research activities in the field of 6-lactam antibiotics including the chemical synthesis of 6-lactam antibiotics and related compounds, have increased up to now (ref. 16). 

Lincomycins bacteriostatic activity is based on the inhibition of the bacterial proteic synthesis. Lincomycin A in particular have been largely employed in clinical therapy of infections caused by micoplasmas, Gram-positive bacteria, and cocci but it presents a lot of side effects overcome by 7-clindamycin (Fig. 21), a semi-synthetic drug with larger spectrum of action and major antibacterial activity. 

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. 

Although lipid solubility at physiological pH enhances a drug s penetrability of a membrane, too much may not necessarily result in increased activity. Many antibacterial sulfonamides exhibit their peak effectiveness at pH values at which they are only approximately half-ionized. These sulfonamides have pKa values in the 6-8 range. The apparent reason is that even though the molecular form can readily penetrate the bacterial membrane, only the anionic form is bacteriostatic once inside. Thus approximately 50% ionization appears to be optimal. Nevertheless, several highly active sulfonamides exist with a pKa considerably outside of this optimal range. Other factors are also presumably involved. 

---