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Cephalexin capsules photographed on a matte clinical surface
DoseRoutine Cephalexin — Cephalexin capsules photographed on a matte clinical surface. Original DoseRoutine photography.
medicationPrescription only (US)Approved by the FDA as a first-generation oral cephalosporin antibiotic for a range of bacterial infectionsContraindicated in patients with a documented severe hypersensitivity to cephalosporins

CephalexinBenefits, Dosage & Interactions

Also known as: Keflex

Cephalexin, also known by the brand name Keflex, is an antibiotic belonging to the class of drugs called cephalosporins. It is commonly prescribed to treat a variety of bacterial infections, including those affecting the respiratory tract, skin and soft tissue, bones, joints, urinary tract, and middle ear.

How much Cephalexin do people take?

Trials in these cohorts used cephalexin doses ranging from 500 mg twice daily (post-cesarean prophylaxis) up to 1 g four times daily (high-dose cellulitis pilot trial). Route reported: Oral capsule or suspension. Frequency reported: Studied two to four times per day depending on indication and dose. These are amounts documented in the cited studies and labels for Cephalexin — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.

See the full reported protocol and its sources

Researched by DoseRoutine Research TeamReviewed for accuracy by Nicholas Alexander, RSE, SO, PMPLast updated Educational reference only — not medical advice. Always confirm dosing and safety decisions with a licensed clinician.

Evidence: Strong — 3 human randomized trials and regulatory approval on file.
Evidence strengthStrong · 4/4
PreclinicalStrong human evidence

3 human randomized trials and regulatory approval on file.

Chemical structure of Cephalexin (PubChem CID 27447)
Structure via PubChem
Plasma half-life
Reported as approximately 1 hour in adults with normal renal function
Typical timing
with a meal
Default unit
mg

What published protocols report

Ranges documented in the literature, shown for reference. DoseRoutine does not recommend an amount — your prescriber or the product label sets the dose.

Reported amounts
Trials in these cohorts used cephalexin doses ranging from 500 mg twice daily (post-cesarean prophylaxis) up to 1 g four times daily (high-dose cellulitis pilot trial)[1][2][3]
Route studied
Oral capsule or suspension[1][2][3]
Frequency
Studied two to four times per day depending on indication and dose[1][2][3]
Cycle length
Short courses of about 3–14 days across the cited trials[1][2][3]
Half-life
Reported as approximately 1 hour in adults with normal renal function[1][2][3]

Reported for Cephalexin in the cited sources. Published ranges are not dosing advice.

References & evidence

Documents the Cephalexin entry is written from. Each number matches an inline marker above.

  1. [1]Effect of Post-Cesarean Delivery Oral Cephalexin and Metronidazole on Surgical Site Infection Among Obese Women: A Randomized Clinical TrialValent AM, DeArmond C, Houston JM, Reddy S, Masters HR, Gold A · JAMA · 2017 · Peer-reviewed · PMID 28975304
  2. [2]High-dose cephalexin for cellulitis: a pilot randomized controlled trialYadav K, Eagles D, Perry JJ, Taljaard M, Sandino-Gold G, Nemnom MJ · CJEM · 2023 · Peer-reviewed · PMID 36592299
  3. [3]Randomized controlled trial of cephalexin versus clindamycin for uncomplicated pediatric skin infectionsChen AE, Carroll KC, Diener-West M, Ross T, Ordun J, Goldstein MA · Pediatrics · 2011 · Peer-reviewed · PMID 21339275

References & Evidence

Sources on this page that document Cephalexin dosing, timing and safety.

  1. [1]U.S. National Library of Medicine View source
  2. [2]National Center for Biotechnology Information View source

Educational information only — not medical advice. Dose ranges vary by person, indication and prescriber.

What is Cephalexin?Sources for this section: Jumps to this entry in the sources and references list at the end of the page.

Cephalexin, also known by the brand name Keflex, is an antibiotic belonging to the class of drugs called cephalosporins. It is commonly prescribed to treat a variety of bacterial infections, including those affecting the respiratory tract, skin and soft tissue, bones, joints, urinary tract, and middle ear. Cephalexin is effective against a broad spectrum of Gram-positive bacteria and some Gram-negative bacteria. It works by interfering with the formation of the bacterial cell wall, which is essential for the survival of the bacteria. Cephalexin is available in oral forms, including capsules, tablets, and an oral suspension. It is not an injectable medication. The dosage and duration of treatment with Cephalexin are user-directed and must be set by a licensed clinician based on the type and severity of the infection, as well as the patient's individual factors. As an antibiotic, it is crucial to complete the full course of treatment as prescribed, even if symptoms improve, to prevent the development of antibiotic resistance. (MedlinePlus)

What does the research say about Cephalexin?

Tap a section to expand.

Cephalexin exerts its antibacterial effect by inhibiting bacterial cell wall synthesis. It is a beta-lactam antibiotic, meaning its structure contains a beta-lactam ring. This ring is crucial for its activity. Cephalexin acts by binding to and inactivating penicillin-binding proteins (PBPs) located on the inner bacterial cell membrane. PBPs are enzymes (transpeptidases) that are vital for the cross-linking of peptidoglycan chains, which form the rigid structure of the bacterial cell wall. By inhibiting these enzymes, Cephalexin prevents the formation of a strong, stable cell wall, leading to weakened cell walls, increased permeability, and ultimately, bacterial cell lysis and death. This mechanism of action is bactericidal, meaning it kills bacteria rather than just inhibiting their growth. (DrugBank)

Source for this section: Sources for How does Cephalexin work?: Jumps to this entry in the sources and references list at the end of the page.

Cephalexin is a widely used antibiotic that offers several benefits in treating bacterial infections: * **Broad-spectrum activity:** It is effective against a range of common bacterial pathogens, including *Staphylococcus aureus* (excluding methicillin-resistant strains), *Streptococcus pneumoniae*, *Streptococcus pyogenes*, *Escherichia coli*, *Klebsiella pneumoniae*, and *Proteus mirabilis*. This broad coverage makes it useful for various infections. * **Treatment of various infections:** Cephalexin is commonly prescribed for: * **Respiratory tract infections:** Such as pharyngitis (strep throat) and tonsillitis. * **Skin and soft tissue infections:** Including impetigo, cellulitis, and furunculosis. * **Urinary tract infections (UTIs):** Including cystitis. * **Bone and joint infections:** Such as osteomyelitis. * **Otitis media:** Middle ear infections. * **Oral administration:** Its availability in oral forms makes it convenient for outpatient treatment, avoiding the need for injections in many cases. (MedlinePlus, DrugBank)

The efficacy of Cephalexin has been established through numerous clinical studies and extensive clinical use since its introduction. For example, a review of clinical trials published in various medical journals supports its use in skin and soft tissue infections, demonstrating high cure rates. Similarly, its effectiveness in treating uncomplicated urinary tract infections is well-documented in clinical guidelines. (Cochrane reviews on antibiotics for specific infections often include cephalosporins like cephalexin; FDA drug labels provide summaries of clinical evidence for approval). The FDA label for Cephalexin provides detailed information on its approved indications and the clinical data supporting its use in treating susceptible bacterial infections. (FDA label for Cephalexin)

Like all medications, Cephalexin can cause side effects, although not everyone experiences them. Common side effects often include: * Diarrhea * Nausea * Vomiting * Indigestion or stomach pain * Dizziness * Headache More serious, but less common, side effects can include: * Allergic reactions (rash, itching, hives, swelling of the face/lips/tongue, difficulty breathing) - this requires immediate medical attention. * *Clostridioides difficile*-associated diarrhea (CDAD), which can range from mild diarrhea to severe colitis. This can occur even several months after stopping the antibiotic. * Liver problems (rare, but symptoms like yellowing skin/eyes, dark urine, severe stomach pain should be reported). * Kidney problems (rare). * Vaginal yeast infection in females. Patients should report any persistent or worsening side effects to their healthcare provider. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.

Source for this section: Sources for What are the side effects of Cephalexin?: Jumps to this entry in the sources and references list at the end of the page.

Before taking Cephalexin, patients should be aware of several warnings: * **Allergic Reactions:** Inform your doctor if you have ever had an allergic reaction to Cephalexin, other cephalosporin antibiotics (e.g., Cefazolin, Cefuroxime), or penicillin antibiotics. Cross-reactivity between penicillins and cephalosporins can occur, although it is rare. If you develop a rash, itching, swelling, or difficulty breathing, seek immediate medical attention. * **Pseudomembranous Colitis:** Cephalexin, like nearly all antibiotics, can cause *Clostridioides difficile*-associated diarrhea (CDAD), which can range from mild to life-threatening. If you develop severe or persistent diarrhea, abdominal pain, or fever during or after treatment, contact your doctor immediately. * **Renal Impairment:** Patients with kidney disease may require a reduced dosage of Cephalexin. Your doctor will adjust the dose based on your kidney function. * **Fungal Infections:** Prolonged use of antibiotics can sometimes lead to an overgrowth of non-susceptible organisms, including fungi, which may result in new infections. * **Pregnancy and Breastfeeding:** Consult your doctor if you are pregnant, planning to become pregnant, or breastfeeding. While Cephalexin is generally considered safe during pregnancy, and only small amounts pass into breast milk, its use should be carefully evaluated. (FDA label for Cephalexin, MedlinePlus) This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.

Source for this section: Sources for Who should avoid Cephalexin?: Jumps to this entry in the sources and references list at the end of the page.

Cephalexin is generally contraindicated in individuals with a known hypersensitivity or allergic reaction to cephalexin or any other cephalosporin antibiotic. A history of severe hypersensitivity (e.g., anaphylaxis, severe skin reactions) to penicillin antibiotics should also be carefully evaluated, as there is a potential, albeit small, for cross-reactivity. Patients with kidney impairment require dose adjustments rather than a complete contraindication, but severe renal failure might necessitate alternative treatments. (FDA label for Cephalexin) This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.

Source for this section: Sources for When should Cephalexin not be taken?: Jumps to this entry in the sources and references list at the end of the page.

While Cephalexin has relatively few major drug-drug interactions compared to some other antibiotics, certain combinations should be approached with caution or avoided: * **Metformin:** Concurrent use of Cephalexin with metformin (a medication for diabetes) can increase the levels of metformin in the body, potentially leading to an increased risk of side effects like lactic acidosis. Monitoring blood glucose levels and adjusting metformin dosage may be necessary. (DrugBank) * **Probenecid:** Probenecid, a medication used to treat gout, can decrease the renal excretion of Cephalexin, leading to higher and more prolonged concentrations of Cephalexin in the blood. This interaction is sometimes utilized therapeutically but requires careful monitoring. * **Other Antibiotics:** Combining Cephalexin with bacteriostatic antibiotics (e.g., tetracyclines, macrolides) may theoretically interfere with Cephalexin's bactericidal action; however, this interaction is generally not considered clinically significant for common therapeutic regimens. Always inform your doctor about all other medications you are taking. Always discuss your full medication list, including over-the-counter drugs, herbal supplements, and vitamins, with your healthcare provider to identify any potential interactions. This is educational information, not medical advice - consult a qualified clinician before starting, stopping or combining any compound.

Source for this section: Sources for What should you not mix with Cephalexin?: Jumps to this entry in the sources and references list at the end of the page.

Cephalexin can typically be taken "with meal", meaning it can be taken with or without food. Some individuals may find that taking it with food helps reduce stomach upset, nausea, or vomiting. The specific dosing schedule (e.g., two, three, or four times a day) and duration will be determined by your licensed clinician based on the infection being treated. It is crucial to space doses evenly throughout the day and to complete the full course of treatment as prescribed, even if you start feeling better, to ensure the infection is fully eradicated and to prevent the development of antibiotic resistance. (MedlinePlus)

Source for this section: Sources for When should you take Cephalexin?: Jumps to this entry in the sources and references list at the end of the page.

Put it into practice

Reading about Cephalexin is the first step — DoseRoutine helps you act on it. These free tools turn what you just learned into a routine.

What interacts with Cephalexin?

Documented interactions for Cephalexin: the other compound, the severity and confidence of the interaction, what happens, and what to do.
Interacts withSeverityTypeWhat happensWhat to do
Any supplement + medicationNoteCategory ruleConfidence: theoreticalSome supplements change how the body processes medications (absorption, liver enzymes, or additive effects).Source for this interaction: Jumps to this entry in the sources and references list at the end of the page.Specific pairs are checked against a licensed drug database and shown with their own severity. Always confirm with your provider or pharmacist.
Any vitamin + medicationNoteCategory ruleConfidence: theoreticalCertain vitamins interact with specific medications (e.g., vitamin K with blood thinners).Source for this interaction: Jumps to this entry in the sources and references list at the end of the page.Specific pairs are checked against a licensed source; confirm with your provider.

Frequently asked questions about Cephalexin

Cephalexin treats bacterial infections, including those affecting the respiratory tract (like strep throat), skin and soft tissues (like cellulitis), urinary tract (like UTIs), bones, joints, and middle ear. It is not effective against viral infections like the common cold or flu.

You may start to feel better within a few days of starting Cephalexin. However, it is very important to continue taking the medication for the entire duration prescribed by your doctor, even if your symptoms improve, to ensure the infection is completely cleared and to prevent resistance.

While there isn't a direct interaction between Cephalexin and alcohol, alcohol consumption can sometimes worsen side effects like stomach upset, nausea, or dizziness. It's generally advisable to limit or avoid alcohol while taking antibiotics to allow your body to heal and to minimize potential discomfort.

If you miss a dose, take it as soon as you remember, unless it is almost time for your next dose. In that case, skip the missed dose and resume your regular dosing schedule. Do not take a double dose to make up for a missed one. Contact your doctor or pharmacist if you are unsure.

Yes, Cephalexin is commonly prescribed for children, particularly in liquid suspension form. Dosage for children is typically based on their weight and the severity of the infection. A licensed clinician must determine the appropriate dose and duration for pediatric patients.

As a medication, Cephalexin can overlap with other supplements, prescription medicines, hormones and peptides. Because Cephalexin is usually taken with a meal, most avoidable conflicts come from what else lands in that same window. Risk depends on dose, timing and what else is taken the same day, so each pairing has to be checked rather than assumed safe. The free checker at https://doseroutine.com/interaction-checker covers Cephalexin with no sign-up.

Whether Cephalexin fits alongside testosterone replacement therapy depends on the protocol — dose, ester and ancillaries such as HCG or anastrozole — and on current bloodwork. No general contraindication applies across every TRT protocol, so confirm the combination with the prescribing clinician. See the free TRT interaction reference: https://doseroutine.com/trt-supplement-interactions

"Peptides" is not one category — healing peptides, GLP-1 agonists, growth-hormone secretagogues and melanocortins each behave differently next to Cephalexin. Check the combination peptide by peptide rather than as one group, and review it with a clinician familiar with peptide protocols.

Published frequency for Cephalexin varies by protocol and formulation, so the label or prescription is what sets it. It is typically taken with a meal. Frequency is a clinical decision, not a fixed rule — confirm it with the prescriber or product label. Comparison of apps that keep a schedule like this: https://doseroutine.com/best-dose-tracking-apps

For Cephalexin the useful record is the dose, the time it was actually taken, and what else was taken in the same window. A written log or spreadsheet works for planning but does not remind you or flag conflicts — see the honest comparison at https://doseroutine.com/vs/spreadsheet and the wider roundup at https://doseroutine.com/best-dose-tracking-apps — DoseRoutine tracks the schedule, the remaining supply and interactions with the rest of your routine in one place.

Trials in these cohorts used cephalexin doses ranging from 500 mg twice daily (post-cesarean prophylaxis) up to 1 g four times daily (high-dose cellulitis pilot trial). Route reported: Oral capsule or suspension. Frequency reported: Studied two to four times per day depending on indication and dose. These are amounts documented in the cited studies and labels for Cephalexin — they are reported for reference, not a recommendation. Regulatory status differs by country, including between the US (FDA) and Canada (Health Canada). Confirm any amount with a licensed clinician before you take it.

Sources cited on this page

Specific documents referenced by the numbered markers above. Each number matches the marker in the text.

  1. MedlinePlus(opens in a new tab)U.S. National Library of Medicine · medlineplus.gov/druginfo/meds/a682733.html
  2. PubChem CID 27447(opens in a new tab)National Center for Biotechnology Information · pubchem.ncbi.nlm.nih.gov/compound/27447

Verify at

Publisher search links for Cephalexin. These are places to check the information — they are not citations, so they are not numbered.

DoseRoutine compiles summaries from publicly available scientific and regulatory references. Always verify important decisions with a licensed clinician. How we source and review this information.

What is the short answer on Cephalexin?

Plain-text summary, safe to quote verbatim:

Cephalexin, also known by the brand name Keflex, is an antibiotic belonging to the class of drugs called cephalosporins. It is commonly prescribed to treat a variety of bacterial infections, including those affecting the respiratory tract, skin and soft tissue, bones, joints, urinary tract, and middle ear.
Source: DoseRoutine — https://doseroutine.com/library/cephalexin

Cephalexin cheat sheet

DoseRoutine cheat sheet · Medication

Cephalexin

Cephalexin, also known by the brand name Keflex, is an antibiotic belonging to the class of drugs called cephalosporins. It is commonly prescribed to treat a variety of bacterial infections, including those affecting the respiratory tract, skin and soft tissue, bones, joints, urinary tract, and middle ear.

Evidence

Strong

3 human randomized trials and regulatory approval on file.

Studied range

Trials in these cohorts used cephalexin doses ranging from 500 mg twice daily (post-cesarean prophylaxis) up to 1 g four times daily (high-dose cellulitis pilot trial)

Route

Oral capsule or suspension

Frequency studied

Studied two to four times per day depending on indication and dose

Half-life

Reported as approximately 1 hour in adults with normal renal function

Timing

with a meal

Prescription only (US)Approved by the FDA as a first-generation oral cephalosporin antibiotic for a range of bacterial infectionsContraindicated in patients with a documented severe hypersensitivity to cephalosporins

Key references

  1. Effect of Post-Cesarean Delivery Oral Cephalexin and Metronidazole on Surgical Site Infection Among Obese Women: A Randomized Clinical Trial (2017)
  2. High-dose cephalexin for cellulitis: a pilot randomized controlled trial (2023)
  3. Randomized controlled trial of cephalexin versus clindamycin for uncomplicated pediatric skin infections (2011)

Studied ranges, not dosing advice. Not medical advice — talk to a clinician. doseroutine.com/library/cephalexin

Cite this page

Using this in an article, AI answer, or research note? Please attribute:

DoseRoutine. (2026). Cephalexin — Overview, Benefits & Side Effects. Retrieved from https://doseroutine.com/library/cephalexin
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