Cephalexin is a first-generation cephalosporin antibiotic widely used to treat bacterial infections in humans and animals. Developed in the 1960s, it was designed as a safer and more effective alternative to earlier penicillin antibiotics, offering broad-spectrum activity against Gram-positive bacteria and some Gram-negative strains. Cephalexin works by inhibiting bacterial cell wall synthesis, making it bactericidal, and it quickly became a mainstay therapy for respiratory tract infections, skin and soft tissue infections, urinary tract infections, and bone infections. Its oral formulation, good absorption, and favorable safety profile contributed to its widespread adoption in both outpatient and inpatient settings, remaining one of the most commonly prescribed antibiotics today.
BRAND NAMES
The most common and widely recognized brand name is Keflex.
Other brand names for cephalexin include:
Biocef
Keftab
Daxbia
Rilexine (also a veterinary brand name)
Keflet
Panixine (also known as Panixine Disperdose)
Zartan
MECHANISM OF ACTION
Cephalexin is a first-generation cephalosporin antibiotic that exerts bactericidal activity by inhibiting bacterial cell wall synthesis. It binds to penicillin-binding proteins (PBPs) on the bacterial cell membrane, interfering with the cross-linking of peptidoglycan, which is essential for cell wall strength and rigidity. This disruption weakens the bacterial cell wall, ultimately causing cell lysis and death. Cephalexin is particularly effective against Gram-positive bacteria such as Staphylococcus and Streptococcus species, while retaining some activity against certain Gram-negative organisms.
PHARMACOKINETICS
Absorption
Cephalexin is rapidly and efficiently absorbed from the gastrointestinal tract, mainly in the upper intestine, following oral administration. Being acid-stable, its absorption is not significantly influenced by food intake.
Distribution
The volume of distribution (Vd) of cephalexin in humans is roughly 0.23 L/kg, which corresponds to a total body distribution of about 15 liters.
Metabolism
Cephalexin undergoes minimal metabolism in the body. The majority of the drug remains unchanged, which contributes to its predictable pharmacokinetics and allows effective elimination primarily via the kidneys.
Excretion
Cephalexin is mainly eliminated by the kidneys through glomerular filtration and active tubular secretion. In healthy individuals, more than 90% of the drug is excreted unchanged in the urine within eight hours of administration.
PHARMACODYNAMICS
Cephalexin is a bactericidal, time-dependent antibiotic that inhibits bacterial cell wall synthesis. Its pharmacodynamic effectiveness is primarily determined by the duration that the free drug concentration remains above the pathogen’s minimum inhibitory concentration (fT>MIC).
DOSAGE AND ADMINISTRATION
Route: Oral (capsules, tablets, or suspension).
Typical adult dose: 250–500 mg every 6–12 hours, depending on infection severity.
Pediatric dose: 25–50 mg/kg/day divided every 6–12 hours.
Duration: Usually 7–14 days, based on infection type and clinical response.
Administration Tips:
Can be taken with or without food.
Complete the full course to prevent bacterial resistance.
Shake well if using the liquid suspension.
DRUG INTERACTIONS
Cephalexin can interact with several medications, including metformin, anticoagulants (e.g., warfarin), loop diuretics, probenecid, certain live vaccines, and zinc supplements. These interactions may affect drug levels, increase the risk of side effects, or reduce the effectiveness of cephalexin or the co-administered medication.
FOOD INTERACTIONS
Cephalexin generally has no significant food interactions and can be taken with or without food. Taking it with food may help reduce potential gastrointestinal side effects such as nausea or diarrhea.
CONTRAINDICATIONS
Cephalexin is primarily contraindicated in patients with a known allergy or hypersensitivity to cephalexin or other cephalosporins. Because of potential cross-reactivity, it should also be avoided or used with extreme caution in individuals who have experienced severe allergic reactions (such as anaphylaxis) to penicillin or other beta-lactam antibiotics.
SIDE EFFECTS
Diarrhea.
Nausea or vomiting.
Stomach pain or upset stomach.
Indigestion or heartburn.
Headache.
Dizziness.
Fatigue or general weakness.
Rash or itching.
Genital or anal itching/vaginal discharge.
OVERDOSE
Nausea and vomiting.
Stomach (abdominal) pain or epigastric distress.
Diarrhea (potentially severe or bloody).
Blood in the urine (hematuria), which may appear pink, red, or dark brown.
Seizures or convulsions.
Agitation, confusion, or hallucinations.
Reactions secondary to an allergic response, such as difficulty breathing or swelling of the face/throat.
TOXICITY
Cephalexin is generally safe and well-tolerated when used as prescribed, with low toxicity in healthy individuals. Toxic effects are mainly a concern in cases of overdose, pre-existing kidney or liver impairment, or severe adverse reactions.
