From the Guidelines
Keflex (cephalexin) can cause several side effects, with the most common being gastrointestinal issues like diarrhea, nausea, vomiting, and stomach pain, as well as allergic reactions, and disruption of normal bacterial flora leading to vaginal yeast infections. These side effects are well-documented in various studies, including a prospective cohort study that reported no benefits of cephalexin treatment in patients with long-term indwelling catheters, and instead found a higher frequency of reinfection with cephalexin-resistant bacteria 1. Other potential side effects of Keflex include headache, dizziness, fatigue, and rarely, more serious effects such as Clostridioides difficile-associated diarrhea, blood disorders, liver or kidney problems.
Common Side Effects
- Gastrointestinal issues: diarrhea, nausea, vomiting, stomach pain
- Allergic reactions: mild rashes to severe reactions like anaphylaxis
- Disruption of normal bacterial flora: vaginal yeast infections
- Headache, dizziness, fatigue
Serious Side Effects
- Clostridioides difficile-associated diarrhea
- Blood disorders
- Liver or kidney problems
It is essential for patients to contact their healthcare provider if they experience severe diarrhea, unusual bleeding or bruising, yellowing of the skin or eyes, dark urine, or severe skin reactions. The evidence from a randomized controlled trial also suggests that cephalexin therapy may reduce exacerbations requiring antibiotics in some patients, but this benefit is not universal and must be weighed against the potential risks 2. Taking Keflex with food can help reduce stomach upset, and completing the full prescribed course is crucial even if symptoms improve before finishing.
From the FDA Drug Label
ADVERSE REACTIONS Gastrointestinal Onset of pseudomembranous colitis may occur during or after antibacterial treatment (see WARNINGS). Nausea and vomiting have been reported rarely. The most frequent side effect has been diarrhea. It was very rarely severe enough to warrant cessation of therapy. Dyspepsia, gastritis, and abdominal pain have also occurred As with some penicillins and some other cephalosporins, transient hepatitis and cholestatic jaundice have been reported rarely. Hypersensitivity AlIergic reactions in the form of rash, urticaria, angioedema, and, rarely, erythema multiforme, Stevens-Johnson syndrome, or toxic epidermal necrolysis have been observed. These reactions usually subsided upon discontinuation of the drug In some of these reactions, supportive therapy may be necessary. Anaphylaxis has also been reported. Other reactions have included genital and anal pruritus, genital moniliasis, vaginitis and vaginal discharge, dizziness, fatigue, headache, agitation, confusion, hallucinations, arthralgia, arthritis, and joint disorder. Reversible interstitial nephritis has been reported rarely Eosinophilia, neutropenia, thrombocytopenia, hemolytic anemia, and slight elevations in AST and ALT have been reported In addition to the adverse reactions listed above that have been observed in patients treated with cephalexin, the following adverse reactions and altered laboratory tests have been reported for cephalosporin class antibiotics: Adverse Reactions Fever, colitis, aplastic anemia, hemorrhage, renal dysfunction, and toxic nephropathy Several cephalosporins have been implicated in triggering seizures, particularly in patients with renal impairment when the dosage was not reduced (see INDICATIONS AND USAGE and PRECAUTIONS, General). If seizures associated with drug therapy should occur, the drug should be discontinued. Anticonvulsant therapy can be given if clinically indicated Altered Laboratory Tests Prolonged prothrombin time, increased BUN, increased creatinine, elevated alkaline phosphatase, elevated bilirubin, elevated LDH, pancytopenia, leukopenia, and agranulocytosis.
The side effects of Cephalexin (Keflex) include:
- Gastrointestinal side effects such as diarrhea, nausea, vomiting, dyspepsia, gastritis, and abdominal pain
- Hypersensitivity reactions such as allergic reactions, rash, urticaria, angioedema, and anaphylaxis
- Other reactions including genital and anal pruritus, genital moniliasis, vaginitis, dizziness, fatigue, headache, and reversible interstitial nephritis
- Hematologic side effects such as eosinophilia, neutropenia, thrombocytopenia, and hemolytic anemia
- Hepatic side effects such as transient hepatitis and cholestatic jaundice
- Renal side effects such as renal dysfunction and toxic nephropathy
- Neurologic side effects such as seizures, particularly in patients with renal impairment
- Laboratory tests alterations such as prolonged prothrombin time, increased BUN, and elevated creatinine 3