CONTRAINDICATIONS
Cephalexin is contraindicated in patients with known allergy to the cephalosporin group of
antibiotics.
WARNINGS
BEFORE CEPHALEXIN THERAPY IS INSTITUTED, CAREFUL INQUIRY SHOULD BE
MADE CONCERNING PREVIOUS HYPERSENSITIVITY REACTIONS TO
CEPHALOSPORINS AND PENICILLIN. CEPHALOSPORIN C DERIVATIVES SHOULD
BE GIVEN CAUTIOUSLY TO PENICILLIN-SENSITIVE PATIENTS.
SERIOUS ACUTE HYPERSENSITIVITY REACTIONS MAY REQUIRE EPINEPHRINE
AND OTHER EMERGENCY MEASURES.
There is some clinical and laboratory evidence of partial cross-allergenicity of the penicillins and the
cephalosporins. Patients have been reported to have had severe reactions (including anaphylaxis) to
both drugs.
Any patient who has demonstrated some form of allergy, particularly to drugs, should receive
antibiotics cautiously. No exception should be made with regard to cephalexin.
Pseudomembranous colitis has been reported with nearly all antibacterial agents,
including cephalexin, and may range from mild to life threatening. Therefore, it is
important to consider this diagnosis in patients with diarrhea subsequent to the
administration of antibacterial agents.
Treatment with antibacterial agents alters the normal flora of the colon and may permit overgrowth
of clostridia. Studies indicate that a toxin produced by Clostridium difficile is a primary cause of
antibiotic-associated colitis.
After the diagnosis of pseudomembranous colitis has been established, appropriate therapeutic
measures should be initiated. Mild cases of pseudomembranous colitis usually respond to drug
discontinuation alone. In moderate to severe cases, consideration should be given to management
with fluids and electrolytes, protein supplementation, and treatment with an antibacterial drug
clinically effective against Clostridium difficile colitis.
PRECAUTIONS
General: Patients should be followed carefully so that any side effects or unusual manifestations of
drug idiosyncrasy may be detected. If an allergic reaction to cephalexin occurs, the drug should be
discontinued and the patient treated with the usual agents (e.g., epinephrine or other pressor
amines, antihistamines, or corticosteroids).
Prolonged use of cephalexin may result in the overgrowth of nonsusceptible organisms. Careful
observation of the patient is essential. If superinfection occurs during therapy, appropriate measures
should be taken.
Positive direct Coombs' tests have been reported during treatment with the cephalosporin
antibiotics. In hematologic studies or in transfusion cross-matching procedures when antiglobulin
tests are performed on the minor side or in Coombs' testing of newborns whose mothers have
received cephalosporin antibiotics before parturition, it should be recognized that a positive Coombs'
test may be due to the drug.
Cephalexin 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.
Indicated surgical procedures should be performed in conjunction with antibiotic therapy.
As a result of administration of cephalexin, a false-positive reaction for glucose in the urine may
occur. This has been observed with Benedict's and Fehling's solutions and also with Clinitest tablets.
As with other b-lactams, the renal excretion of cephalexin is inhibited by probenecid.
Broad-spectrum antibiotics should be prescribed with caution in individuals with a history of
gastrointestinal disease, particularly colitis.
Pregnancy Category B: The daily oral administration of cephalexin to rats in doses of 250 or 500
mg/kg prior to and during pregnancy, or to rats and mice during the period of organogenesis only,
had no adverse effect on fertility, fetal viability, fetal weight, or litter size. Note that the safety of
cephalexin during pregnancy in humans has not been established.
Cephalexin showed no enhanced toxicity in weanling and newborn rats as compared with adult
animals. Nevertheless, because the studies in humans cannot rule out the possibility of harm,
cephalexin should be used during pregnancy only if clearly needed.
Nursing Mothers: The excretion of cephalexin in the milk increased up to 4 hours after a 500-mg
dose; the drug reached a maximum level of 4 mcg/ml, then decreased gradually, and had
disappeared 8 hours after administration. Caution should be exercised when cephalexin is
administered to a nursing woman.