Before taking cefalexin Before taking cefalexin make sure your doctor or pharmacist knows: If you are pregnant, trying for a baby or breast-feeding. If you suffer from kidney problems. If you have ever had an allergic reaction to this medicine, a cephalosporin or penicillin antibiotic, or any other medicine. If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines. How to take cefalexin Before beginning treatment, read the manufacturer's printed information leaflet. Take your medication exactly as directed by your doctor. Take cefalexin at regular intervals and complete the prescribed course. It is important to take the full course, even if you feel your infection has cleared up, to prevent the infection coming back. If you forget to take a dose, take one as soon as you remember.