Formulary Monographs [ANTIINFECTIVES, 0800]

Drug Selection - General Principles

Choice of antibiotic for the treatment of bactericidal infections must be made with two factors in mind:

(i) The known or likely organism involved:

(ii) Patient factors.

(1) Rational treatment re-quires a diagnosis. In many cases there is only one microbic cause and antibiotic choice is easy. Many other diseases, e.g. pneumonia or urinary tract infection, are caused by any of a number of different bacteria and laboratory help is required.

In mild illness and where laboratory facilities are out of reach, treatment may be justifiably begun without such help. In severe illnesses e.g. meningitis, septicaemia, a bacteriologic diagnosis is mandatory.

The blind prescribing of antibiotics for unexpected fevers usually leads to greater difficulty in establishing a diagnosis and must be avoided. The casual prescribing of antibiotics for “flu-like” illness remains, as always, bad medical practice.

(2) The Patient

The patient’s history must be meticulously taken for drug allergies. The presence of liver or renal disease, age and immuno compromised status must be considered. Rational therapy may be illustrated by the case of a woman with dysuria and nausea in early pregnancy. The causative organism is reported to be resistant to ampicillin but sensitive to nitrofurantoin (high risk of nausea), gentamicin (given i.m. and should be avoided in pregnancy), tetracycline and Co-trimoxamole (both should be avoided in pregnancy) and cephalexin. The Penicillins and cepha-losporins are safest in pregnancy so cephalexin, although costly, is clearly the drug of choice in this case.

The following principles or rules should be observed when antibiotics are considered.
Viral infections, in general, should not be treated with antibiotics.

Local sensitivities of com-mon pathogens should be ascertained from the hospital microbiologist.

The dose must be tailored to the patient, as in (1) above.

The route and times in relation to meals must be considered.

Broad Spectrum Antibiotics should not, in general, be used if a narrow spectrum drug will do.

Costly antibiotic should not be used if an inexpensive one is equally suitable.