Patients should be counseled that antibacterial drugs including Keflex should only be used to treat bacterial infections. They do not treat viral infections (e.g., the common cold). When Keflex is prescribed to treat a bacterial infection, patients should be told that although it is common to feel better early in the course of therapy, the medication should be taken exactly as directed. Skipping doses or not completing the full course of therapy may (1) decrease the effectiveness of the immediate treatment and (2) increase the likelihood that bacteria will develop resistance and will not be treatable by Keflex or other antibacterial drugs in the future.
Metformin In healthy subjects given single 500 mg doses of cephalexin and metformin, plasma metformin mean cmax and AUC increased by an average of 34% and 24%, respectively, and metformin mean renal clearance decreased by 14%. No information is available about the interaction of cephalexin and metformin following multiple doses of either drug.
Although not observed in this study, adverse effects could potentially arise from co-administration of cephalexin and metformin by inhibition of tubular secretion via organic cationic transporter systems. Accordingly, careful patient monitoring and dose adjustment of metformin is recommended in patients concomitantly taking cephalexin and metformin.
Probenecid As with other b-lactams, the renal excretion of cephalexin is inhibited by probenecid.
Drug / Laboratory Test Interactions
As a result of administration of Keflex, a false-positive reaction for glucose in the urine may occur. This has been observed with Benedictís and Fehlingís solutions and also with Clinitest® tablets.
Keflex is contraindicated in patients with known allergy to the cephalosporin group of antibiotics.