Patients should be followed carefully so that any side effects or unusual manifestations of drug idiosyncrasy may be detected. If an allergenic reaction occurs the drug should be discontinued and the patient treated. Prolonged use may result in the overgrowth of non-susceptible organisms. Careful observation of the patient is essential. If superinfection occurs during therapy, appropriate measures should be taken. Positive direct Coomb's tests have been reported during treatment with cephalosporin antibiotics. In haematological studies or in transfusion cross matching procedures when antiglobulin tests are performed on the minor side or in Coomb's testing of newborns whose mothers have received cephalosporins antibiotics before parturition, it should be recognized that a positive Coomb's test may be due to the drug. Cefalexin should be administered with caution in the presence of markedly impaired renal function. Under such conditions, careful clinical observation and laboratory studies should be made because safe dosage may be lower than that usually recommended. Indicate surgical procedures should be performed in conjunction with antibiotic therapy. As a result of administration of cefalexin, a false positive reaction of glucose in the urine may occur. This has been observed with Benedict and Fehlings solutions and also with Clinitest tablets, but not with Test-Tape. The quantitative determination of urinary protein using strong acids is misleading during therapy as precipitation of cefalexin in the urine may occur.