ABSTRACT
Viruses cause gastroenteritis much more often than food poisoning; rotavirus and adenovirus are common in children, norovirus in adults. Diarrhoea is the main symptom. A bacterial infection of the kidney, usually caused by infection spreading up the ureters. It is commoner in children who have vesico-ureteric reflux and in pregnancy, when the ureters are dilated. Balanitis occurs at all ages and may be due to dermatitis, fungal or bacterial infection. Nitrofurantoin is not suitable for treating pyelonephritis because it does not achieve adequate concentration of the antibiotic in the blood or the tissue of the kidney. Trimethoprim has serious interactions with methotrexate, azathioprine, ciclosporin, mercaptopurine and tacrolimus, so be aware when prescribing for a patient with a long-term inflammatory condition such as rheumatoid arthritis. Trimethoprim interacts significantly with phenytoin. A split or an ulcer in the anal skin, previously thought to be caused by passing a large, hard stool but considered to be an ischaemic ulcer.
