Prescription medication · First-Generation Cephalosporin
cephalexin
Also sold as Keflex. Cephalexin treats infections caused by bacteria.
Data updated 2026-05-15
- 20,636
- FDA reportsModerately reported
- 2
- InteractionsFew interactions
- 4
- Recall records
What the data shows
cephalexin (Keflex) is a prescription First-Generation Cephalosporin, reported at a middle-of-the-pack volume (20,636 FDA reports), with 2 documented drug interactions.
Reporting volume reflects how widely a drug is used and studied, not how dangerous it is, a FAERS report documents a temporal association, never proof of cause.
cephalexin (Keflex) is a prescription First-Generation Cephalosporin. Cephalexin treats infections caused by bacteria.
Cephalexin is an antibiotic medicine. It fights bacterial infections in your body.
Verify with FDA → · CMS NADAC pricing →
Drug Pricing (NADAC)
Generic Price
$0.05/unit
Generic Available
Yes (13 manufacturers)
Pricing data from NADAC (CMS), effective December 18, 2024. Compare all drug costs →
What it does
Cephalexin treats infections caused by bacteria.
Common side effects
Diarrhea, Nausea, Vomiting
Key warnings
Cephalexin can cause severe allergic reactions.
The sections below are summarized in plain English from cephalexin's FDA-approved prescribing information. They describe what the official label says, and are not personal medical advice.
How It Works
Cephalexin belongs to a class of drugs called cephalosporins. It works by stopping the growth of bacteria. This helps your body fight off the infection.
Side Effects (from patient reports)
Based on 20,636 FDA adverse event reports.
Most-reported reactions
Adverse reactions in FAERS for cephalexin, by number of reports
- Chronic Kidney Disease
Chronic Kidney Disease
2,155 reports
- Renal Failure
Renal Failure
1,554 reports
- Acute Kidney Injury
Acute Kidney Injury
1,538 reports
- Pain
Pain
1,365 reports
- Diarrhoea
Diarrhoea
1,350 reports
- Fatigue
Fatigue
1,239 reports
- Nausea
Nausea
1,220 reports
- Dyspnoea
Dyspnoea
1,164 reports
- Anxiety
Anxiety
1,132 reports
- Rash
Rash
1,093 reports
What this shows Bars show how often each reaction was reported, not how likely it is to happen, a report records a temporal association, never proof that the drug caused it.
Reports over time
Adverse-event reports filed for cephalexin each year to the FDA Adverse Event Reporting System (FAERS).
Year-to-year volume tracks usage, prescribing, and scrutiny, not a change in per-patient risk. Source: FDA FAERS.
Where cephalexin sits
cephalexin has more FDA adverse-event reports than 56% of the drugs FAERS tracks. A high position reflects how widely a drug is used and watched, not how dangerous it is.
Percentile across all drugs PlainMeds tracks by FAERS report volume. The dot is cephalexin; the line is the median (50th percentile).
FDA Adverse Event Report Analysis
Detailed analysis of 20,636 reports from the FDA Adverse Event Reporting System (FAERS). Reports span 2003–2025.
Total Reports
20,636
Reports Mentioning Death
1,749
8.5% of reports — not proof of cause
Hospitalization Reports
7,230
Top Indication
Product Used For Unknown Indication
Gender Distribution
Age Distribution
Most Reported Adverse Reactions (FAERS)
| # | Reaction | Reports |
|---|---|---|
| 1 | CHRONIC KIDNEY DISEASE | 2,155 |
| 2 | RENAL FAILURE | 1,554 |
| 3 | ACUTE KIDNEY INJURY | 1,538 |
| 4 | PAIN | 1,365 |
| 5 | DIARRHOEA | 1,350 |
| 6 | FATIGUE | 1,239 |
| 7 | NAUSEA | 1,220 |
| 8 | DYSPNOEA | 1,164 |
| 9 | ANXIETY | 1,132 |
| 10 | RASH | 1,093 |
| 11 | HEADACHE | 1,089 |
| 14 | VOMITING | 837 |
| 15 | DIZZINESS | 828 |
| 16 | URINARY TRACT INFECTION | 804 |
| 17 | PAIN IN EXTREMITY | 797 |
Reactions in Death Reports
Reactions in Hospitalization Reports
Source: FDA FAERS (Adverse Event Reporting System) Reports are voluntary and do not establish causation
Serious Warnings
Cephalexin can cause severe allergic reactions. Tell your doctor if you are allergic to penicillin or other cephalosporin antibiotics. This medicine can also cause severe diarrhea. If you get diarrhea, tell your doctor right away. People with kidney problems may need a lower dose to prevent seizures.
Known Drug Interactions
( 7.1 ) Probenecid-The renal excretion of cephalexin is inhibited by probenecid. Co-administration of probenecid with cephalexin is not recommended. 7.2 Probenecid The renal excretion of cephalexin is inhibited by probenecid.
Mechanism: Probenecid blocks your kidneys from removing cephalexin from your body. This causes the antibiotic to build up to higher levels than intended.
7 DRUG INTERACTIONS Metformin: increased metformin concentrations. ( 7.3 ) 7.1 Metformin Administration of cephalexin with metformin results in increased plasma metformin concentrations and decreased renal clearance of metformin. Careful patient monitoring and dose adjustment of metformin is recommended in patients concomitantly taking cephalexin and metformin [see Clinical Pharmacology (12.3) ].
Mechanism: Cephalexin makes it harder for your kidneys to remove metformin from your body. This causes the metformin to stay in your blood longer and reach higher levels than usual.
This is a plain-language summary of FDA-label interaction records and does not provide individual medication-combination directions.
Common Questions
Can I take cephalexin if I'm allergic to penicillin?
Can cephalexin cause diarrhea?
How long should I take cephalexin?
What should I do if I miss a dose?
Can I take cephalexin with food?
Does cephalexin interact with other medicines?
Can cephalexin affect my blood sugar?
Can cephalexin cause a false positive urine glucose test?
What if I still feel sick after taking cephalexin for a few days?
Can I drink alcohol while taking cephalexin?
What are the common side effects of cephalexin?
Does cephalexin interact with other medications?
What drug class is cephalexin?
What pregnancy or breastfeeding source fields are listed for cephalexin?
Has cephalexin been recalled?
Active Recalls
Failed Impurities/Degradation Specifications An out-of-specification result was observed in the related substance test at the sixth month of stability analysis. The individual impurity was identified to be Cephalexin Glucose Adduct.
Ascend Laboratories, LLC
Labeling: Not Elsewhere Classified: Back label states Each contains: cephalexin monohydrate, USP equivalent to 2.5g' instead of Each Bottle contains: cephalexin monohydrate, USP equivalent to 5g
Bryant Ranch Prepack, Inc.
Labeling: Not Elsewhere Classified: Back Label states Each contains: cephalexin monohydrate, USP equivalent to 5g' on the back label instead of Each Bottle contains: cephalexin monohydrate, USP equivalent to 5g'
Bryant Ranch Prepack, Inc.
Failed Impurities/degradation specifications: Repackager recall due to Out of Specification detected by manufacturer for Individual Unidentified Impurity found during related substance test analysis of Cephalexin
Preferred Pharmaceuticals, Inc.
Related Medications in First-Generation Cephalosporin
Other drugs grouped near cephalexin - same-class peers and common alternatives.
amikacin
Amikin
Amikacin is an antibiotic medicine.
Compare with cephalexin →
amoxicillin
Amoxil
Amoxicillin and Clavulanate Potassium is a combination medicine used to fight bacterial infections.
Compare with cephalexin →
amoxicillin/clavulanate
Augmentin
Augmentin is a combination of two medicines, amoxicillin and clavulanate.
Compare with cephalexin →
ampicillin/sulbactam
Unasyn
Unasyn is a combination of two antibiotics that fights bacteria in your body.
Compare with cephalexin →
azithromycin
Zithromax, Z-Pack
Azithromycin is an antibiotic that fights bacteria.
Compare with cephalexin →
Compare beyond drug class
Nationwide peers by FAERS volume & death-report share
Two PlainMeds-derived comparison paths for cephalexin: nearest FDA FAERS report volume and nearest death-report share among drugs with at least 1,000 logged reports, excluding same-class neighbors listed above. Counts reflect reporting volume, not proven individual harm.
Similar FAERS report volume
Nearest drugs by total FAERS reports. This record: 20,636.
Similar death-report share
Nearest drugs by FAERS death-report share. This record: 8.48%.
- ofloxacin Δ 0.02 pts · 7,063 reports · Fluoroquinolone Antibiotic 8.45%death share
- atenolol Δ 0.03 pts · 130,943 reports · Beta-1 Selective Blocker 8.51%death share
- carbamazepine Δ 0.04 pts · 65,260 reports · Anticonvulsant 8.43%death share
- albuterol Δ 0.05 pts · 113,967 reports · Short-Acting Beta-2 Agonist 8.43%death share
Medication Guides
Understanding Drug Interactions
How CYP450 enzymes, inhibitors, and inducers affect your medications
Generic vs Brand Name Drugs
FDA requirements, cost savings, and when the difference matters
Narrow Therapeutic Index Drugs
FDA bioequivalence and label-record context for narrow therapeutic index medicines
Common Drug Interactions
Dangerous medication combinations and how to protect yourself
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What the FDA Data Shows for cephalexin
The FDA label for cephalexin (sold under brand names such as Keflex) classifies it as a prescription-only medication in the First-Generation Cephalosporin class. Cephalexin treats infections caused by bacteria. Official labeling lists 5 commonly reported side effects, including Diarrhea, Nausea, Vomiting.
Post-market surveillance from the FDA Adverse Event Reporting System (FAERS) captures real-world experience. For this drug, FAERS contains 20,636 voluntary reports. The database also lists 2 documented drug interactions derived from FDA labeling, with the top-flagged interaction rated moderate severity. NADAC pricing from CMS shows a generic unit cost of $0.05.
Report counts do not establish causation, a FAERS entry documents a temporal association, not proof that the drug produced the outcome. Widely prescribed medications naturally accumulate more reports than niche therapies, so raw totals must be interpreted alongside total exposure. Shortage status, recall history (currently 4 recall records on file), and patent information are separate source-record fields. This page is a public FDA/CMS registry and does not provide medical, treatment, substitution, or medication-change directions.
Data Sources
Drug labeling: FDA Drug Labels (SPL/DailyMed). Adverse events: FDA Adverse Event Reporting System (FAERS). Pricing: CMS National Average Drug Acquisition Cost (NADAC).
FAERS reports are voluntary and do not establish causation. Drug interactions are derived from FDA labeling and clinical references. This registry does not provide medication decisions.
Last updated: February 11, 2025
PlainMeds is rendered directly from FDA openFDA/FAERS extracts, DailyMed labels, and CMS drug-pricing files, no number is typed in by an editor. FAERS counts, recalls, shortages, and price figures on this page are queried live from those federal extracts. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2026-05-15. Primary sources: openFDA / FAERS, DailyMed and CMS Part B ASP.
Read our methodology - how this data is sourced, computed, and verified.
Data currency: FDA FAERS adverse-event reports through 2025, CMS NADAC acquisition-cost pricing effective December 2024, compiled from the source snapshot dated . See our methodology for per-source dates and refresh cadence. Spot a figure that looks wrong? Report a data issue.
All federal data sources used on this page
- FDA Orange Book - approved drug products with therapeutic equivalence. accessdata.fda.gov/cder/ob
- FDA DailyMed - NIH-hosted drug labeling for FDA-approved meds. dailymed.nlm.nih.gov
- FDA Adverse Event Reporting System (FAERS) - post-marketing safety surveillance. fda.gov/drugs/faers
- NLM RxNorm - standardized clinical drug nomenclature. nlm.nih.gov/research/umls/rxnorm
- CMS Medicare Part B Drug Average Sales Price Files - federal drug pricing data. cms.gov/medicare/part-b-drugs/asp
- FDA Drug Shortages Database - current and resolved drug shortage tracking. accessdata.fda.gov/drugshortages