Trimethoprim

Trimethoprim is still the antibiotic of choice, but may not be for much longer. It is cheap and effective. It is just as effective as co-trimoxazole but has fewer side effects. In the UK, 78% of community-acquired E. coli infections will be sensitive to it. This does not mean, however, that 22% of patients will not be sensitive, when treated empirically because resistance detected in the laboratory is not always reflected in clinical failure. It should also be remembered that population-based data generated from urine specimens sent to laboratories should be interpreted with extreme caution since many simple urinary tract infections are treated successfully without recourse to an mid-stream sample of urine. Those specimens analysed by laboratories may represent a more complicated patient group, with a higher incidence of resistant flora. Data on antibiotic resistance patterns should be generated from populations appropriate to the patient being treated.

Nitrofurantoin

This is returning to popularity as a first-line treatment for urinary tract infections as 88% of community-acquired urinary tract infections are sensitive to it. It is also useful for long-term prophylaxis. A further advantage is that it can be safely given to pregnant women, although it may cause neonatal haemolysis if used at term. It does not induce bacterial resistance in the bowel. The major problem with nitrofurantoin is compliance, since it can cause nausea and vomiting (which of course is worse in pregnancy). Nitrofurantoin should not be used for pyelonephritis. This is because it does not achieve cidal levels in the blood or kidney substance. It should only be used to treat lower urinary tract infections. It is an excellent agent for prophylaxis, like trimethoprim.

Cephalosporins

Most community-acquired infections are still sensitive to the cephalosporins. However, they are more expensive than trimethoprim and also disrupt the major gut flora more, thus giving potentially more side effects to the woman (vaginal thrush, etc). Cephalosporins are the empirical drug treatment of choice in pregnancy and whilst breast-feeding, because of the excellent safety profile.

Ampicillin/amoxicillin

Unfortunately, because 40% of E. coli are now resistant to these drugs, they are no longer recommended for treatment of acute urinary tract infection unless the bacterial sensitivities are known. Amoxicillin is safe in pregnancy, and whilst breast-feeding.

Co-amoxiclav

The addition of the ОІ-lactamase inhibitor clavulanic acid to amoxicillin has improved its effectiveness against E. coli. At present, bacteriologists prefer this drug to be left as a second-line agent when the sensitivities are known, or in complicated urinary tract infections. There is no evidence of teratogenicity, but manufacturers advise avoiding co-amoxiclav in pregnancy unless essential.

The quinolones

These new agents can be used, as a second-line treatment, if trimethoprim has failed or in complicated urinary tract infections. Unfortunately, no quinolone can be used in pregnancy (arthropathy in animal studies). 4-Quinolones should be used with caution in patients with epilepsy or a history of fits, in hepatic or renal impairment, diabetics, and patients taking theophylline or non-steroidal anti-inflammatary drugs (see BNF). The cost for a course of a 4-quinolone is approximately ten times that for trimethoprim.

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