Notes on specific antimicrobials

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Some organisms are becoming ineffective because micro-organisms are resistant to them hence antimicrobial susceptibility testing should be sought where possible. Patients should be counselled to complete courses even when they feel better. 

Oral amoxicillin should be used in preference to oral ampicillin because of it's better absorption, efficacy and cost effectiveness. However, the same is not true of the injectable preparations because they have similar efficacy. 

Chloramphenicol must be limited to serious infections such as Klebsiella pneumonia, Haemophilus influenzae infections, difficult to treat pelvic inflammatory disease and brain abscesses and not used indiscriminately in the treatment of fever. An exception to this is when there is need for a broad spectrum antibiotic and it is unavailable. Furthermore, the oral preparation should be used judiciously as it is more prone to cause aplastic anaemia than the injectable formulation. 

Dosage of gentamicin, streptomycin and kanamycin (aminoglycosides) must be carefully adjusted for weight and renal function. Careful monitoring of serum urea and/or creatinine and checking for complaints of auditory or vestibular symptoms (adverse effects) is necessary. An exception exists for duration less than 3 days use or when lower doses are used. 

Patients with penicillin allergy (that is, a pruritic rash, angioedema or anaphylaxis) must not be given penicillin. Rashes occurring after 48 hours are rarely due to allergy and are not a contraindication to further use. Note that penicillins have cross-reactivities with other medicines including cephalosporins and carbapenems. In such instances macrolides are suitable alternatives. Patients with a history of co-trimoxazole allergy may be offered desensitisation (see section on HIV related diseases)