Treatment with a single antimicrobial is sufficient for most infections. The indications for use of two or more antimicrobials are:

• To avoid the development of drug resistance, especially in chronic infections where many bacteria are present (hence the chance of a resistant mutant emerging is high), e.g. tuberculosis.

• To broaden the spectrum of antibacterial activity: (1) in a known mixed infection, e.g. peritonitis following gut perforation or (2) where the infecting organism cannot be predicted but treatment is essential before a diagnosis has been reached, e.g. septicaemia complicating neutropenia or severe community-acquired pneumonia; full doses of each drug are needed.

• To obtain potentiation (or 'synergy'), i.e. an effect unobtainable with either drug alone, e.g. penicillin plus gentamicin for enterococcal endocarditis.

• To enable reduction of the dose of one component and hence reduce the risks of adverse drug reactions, e.g. flucytosine plus amphotericin B for Cryptococcus neoformans meningitis.

Selection of agents. A bacteriostatic drug, by reducing multiplication, may protect the organism from a bactericidal drug (see above, Antagonism). When a combination must be used blind, it is theoretically preferable to use two bacteriostatic or two bactericidal drugs, lest there be antagonism.

Blood Pressure Health

Blood Pressure Health

Your heart pumps blood throughout your body using a network of tubing called arteries and capillaries which return the blood back to your heart via your veins. Blood pressure is the force of the blood pushing against the walls of your arteries as your heart beats.Learn more...

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