Keflex 250mg Capsules
It is used to treat bacterial infections.
Drug Class
Antibiotic
Pharmacologic Class
First-generation Cephalosporin
Pregnancy Category
Category B
FDA Approved
Jan 1971
DEA Schedule
Not Controlled
Overview
What is this medicine?
Cephalexin is an antibiotic medication used to treat various bacterial infections. It works by stopping the growth of bacteria. It is commonly used for skin infections, urinary tract infections, and certain respiratory infections.
How to Use This Medicine
Taking Your Medication
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help. Continue using the medication even if your symptoms improve.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry location, avoiding bathrooms. Keep all medications in a safe place, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so. If you have questions about disposal, consult your pharmacist. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses.
To use this medication correctly, follow your doctor's instructions and read all the information provided. Take your medication as directed, with or without food. If you experience stomach upset, taking it with food may help. Continue using the medication even if your symptoms improve.
Storing and Disposing of Your Medication
Store your medication at room temperature in a dry location, avoiding bathrooms. Keep all medications in a safe place, out of the reach of children and pets. Dispose of unused or expired medications properly. Do not flush them down the toilet or pour them down the drain unless instructed to do so. If you have questions about disposal, consult your pharmacist. You may also have access to drug take-back programs in your area.
Missing a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next dose, skip the missed dose and resume your regular schedule. Do not take two doses at the same time or take extra doses.
Lifestyle & Tips
- Take the medication exactly as prescribed by your doctor, even if you start to feel better. Do not skip doses or stop taking it early, as this can lead to antibiotic resistance and recurrence of infection.
- You can take cephalexin with or without food. If it causes stomach upset, try taking it with food or milk.
- Drink plenty of fluids while taking this medication.
- Do not share this medication with others, even if they have similar symptoms.
Available Forms & Alternatives
Available Strengths:
Generic Alternatives:
Dosing & Administration
Adult Dosing
Standard Dose:
250 mg to 1 g every 6 or 12 hours, depending on infection severity
Dose Range:
250 - 1000 mg
Condition-Specific Dosing:
mildToModerateInfections:
250 mg every 6 hours or 500 mg every 12 hours
severeInfections:
500 mg every 6 hours or 1 g every 12 hours
skinAndSoftTissueInfections:
500 mg every 12 hours
streptococcalPharyngitis:
250 mg every 6 hours or 500 mg every 12 hours for 10 days
urinaryTractInfections:
250 mg every 6 hours or 500 mg every 12 hours
Pediatric Dosing
Neonatal:
Not established (use with caution, consult specific guidelines)
Infant:
25-50 mg/kg/day in divided doses (every 6 or 12 hours)
Child:
25-50 mg/kg/day in divided doses (every 6 or 12 hours), up to 100 mg/kg/day for severe infections
Adolescent:
25-50 mg/kg/day in divided doses (every 6 or 12 hours), up to 100 mg/kg/day for severe infections (max 4 g/day)
Dose Adjustments
Renal Impairment:
Mild:
CrCl 30-59 mL/min: No adjustment needed for standard doses, consider extending interval to q8-12h for higher doses.
Moderate:
CrCl 15-29 mL/min: 250-500 mg every 12 hours.
Severe:
CrCl < 15 mL/min: 250-500 mg every 24 hours.
Dialysis:
Hemodialysis: 250-500 mg after each dialysis session. Peritoneal Dialysis: 250 mg every 12 hours.
Hepatic Impairment:
Mild:
No adjustment needed
Moderate:
No adjustment needed
Severe:
No adjustment needed
Pharmacology
Mechanism of Action
Cephalexin is a bactericidal antibiotic that inhibits bacterial cell wall synthesis by binding to one or more of the penicillin-binding proteins (PBPs). This inhibits the final transpeptidation step of peptidoglycan synthesis in the bacterial cell wall, leading to cell lysis and death.
Pharmacokinetics
Absorption:
Bioavailability:
>90%
Tmax:
1 hour (capsules/tablets)
FoodEffect:
Food may delay absorption but does not affect the total amount absorbed. Taking with food may reduce gastrointestinal upset.
Distribution:
Vd:
0.26 L/kg
ProteinBinding:
10-15%
CnssPenetration:
Limited (does not achieve therapeutic concentrations in CSF for meningitis)
Elimination:
HalfLife:
0.5-1.2 hours (normal renal function)
Clearance:
Not available (primarily renal excretion)
ExcretionRoute:
Renal (glomerular filtration and tubular secretion)
Unchanged:
>90%
Pharmacodynamics
OnsetOfAction:
Rapid (within 1 hour)
PeakEffect:
1 hour (plasma concentration)
DurationOfAction:
6-12 hours (based on dosing frequency and half-life)
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin (with or without fever)
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of a severe skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis), such as:
+ Red, swollen, blistered, or peeling skin (with or without fever)
+ Red or irritated eyes
+ Sores in the mouth, throat, nose, or eyes
Signs of liver problems, including:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Fever, chills, or sore throat
Unexplained bruising or bleeding
Feeling extremely tired or weak
Confusion
Hallucinations (seeing or hearing things that are not there)
Difficulty urinating or changes in urine output
Seizures
Severe dizziness
Severe headache
Severe joint pain
Vaginal itching or discharge
Important Note: Diarrhea is a common side effect of antibiotics. However, in rare cases, a severe form of diarrhea called C. diff-associated diarrhea (CDAD) may occur. This can lead to a life-threatening bowel problem. If you experience stomach pain, cramps, or loose, watery, or bloody stools, contact your doctor immediately. Before treating diarrhea, consult with your doctor.
Other Possible Side Effects
Most people do not experience significant side effects or only have minor ones. However, if you notice any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Stomach pain or diarrhea
Upset stomach or vomiting
Reporting Side Effects
This is not an exhaustive list of possible side effects. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin (with or without fever)
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Signs of a severe skin reaction (Stevens-Johnson syndrome/toxic epidermal necrolysis), such as:
+ Red, swollen, blistered, or peeling skin (with or without fever)
+ Red or irritated eyes
+ Sores in the mouth, throat, nose, or eyes
Signs of liver problems, including:
+ Dark urine
+ Tiredness
+ Decreased appetite
+ Upset stomach or stomach pain
+ Light-colored stools
+ Vomiting
+ Yellow skin or eyes
Fever, chills, or sore throat
Unexplained bruising or bleeding
Feeling extremely tired or weak
Confusion
Hallucinations (seeing or hearing things that are not there)
Difficulty urinating or changes in urine output
Seizures
Severe dizziness
Severe headache
Severe joint pain
Vaginal itching or discharge
Important Note: Diarrhea is a common side effect of antibiotics. However, in rare cases, a severe form of diarrhea called C. diff-associated diarrhea (CDAD) may occur. This can lead to a life-threatening bowel problem. If you experience stomach pain, cramps, or loose, watery, or bloody stools, contact your doctor immediately. Before treating diarrhea, consult with your doctor.
Other Possible Side Effects
Most people do not experience significant side effects or only have minor ones. However, if you notice any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Stomach pain or diarrhea
Upset stomach or vomiting
Reporting Side Effects
This is not an exhaustive list of possible side effects. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Signs of a severe allergic reaction: rash, hives, itching, swelling of the face, lips, tongue, or throat, difficulty breathing or swallowing. Seek immediate medical attention.
- Severe or watery diarrhea, especially if it contains blood or mucus, which may occur during or up to several months after treatment. This could be a sign of Clostridioides difficile-associated diarrhea (CDAD). Contact your doctor immediately.
- Unusual bruising or bleeding.
- Yellowing of the skin or eyes (jaundice).
- Dark urine.
- Persistent nausea or vomiting.
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you are currently taking probenecid, as this may interact with the medication.
Additionally, to ensure safe treatment, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
* Your existing health problems
This information will help your doctor determine whether it is safe for you to take this medication in conjunction with your other medications and health conditions. Never start, stop, or adjust the dosage of any medication without first consulting your doctor to confirm that it is safe to do so.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
If you are currently taking probenecid, as this may interact with the medication.
Additionally, to ensure safe treatment, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
* Your existing health problems
This information will help your doctor determine whether it is safe for you to take this medication in conjunction with your other medications and health conditions. Never start, stop, or adjust the dosage of any medication without first consulting your doctor to confirm that it is safe to do so.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication. If you are taking this drug for an extended period, your doctor may recommend regular blood tests to monitor your condition.
If you have diabetes and regularly test your urine for glucose, consult with your doctor to determine the most suitable testing method for you, as this medication may affect the accuracy of certain tests. Additionally, be sure to notify all your healthcare providers and laboratory personnel that you are taking this medication, as it may impact the results of certain lab tests.
Do not take this medication for longer than prescribed, as this may increase the risk of developing a secondary infection.
If you are pregnant, planning to become pregnant, or are breastfeeding, it is crucial to discuss the potential benefits and risks of this medication with your doctor to ensure the best possible outcome for you and your baby.
If you have diabetes and regularly test your urine for glucose, consult with your doctor to determine the most suitable testing method for you, as this medication may affect the accuracy of certain tests. Additionally, be sure to notify all your healthcare providers and laboratory personnel that you are taking this medication, as it may impact the results of certain lab tests.
Do not take this medication for longer than prescribed, as this may increase the risk of developing a secondary infection.
If you are pregnant, planning to become pregnant, or are breastfeeding, it is crucial to discuss the potential benefits and risks of this medication with your doctor to ensure the best possible outcome for you and your baby.
Overdose Information
Overdose Symptoms:
- Nausea
- Vomiting
- Epigastric distress
- Diarrhea
- Hematuria (blood in urine)
- In rare cases, seizures (especially in patients with renal impairment)
What to Do:
In case of suspected overdose, contact a poison control center immediately. In the U.S., you can call 1-800-222-1222. Medical attention may be required, including supportive care and, if necessary, hemodialysis to remove the drug from the body.
Drug Interactions
Major Interactions
- Metformin (increased metformin levels, monitor for lactic acidosis)
- Live bacterial vaccines (e.g., typhoid vaccine, may reduce vaccine efficacy)
Moderate Interactions
- Probenecid (decreases renal excretion of cephalexin, increasing cephalexin levels)
- Oral anticoagulants (e.g., warfarin, may enhance anticoagulant effect due to alteration of gut flora, monitor INR)
- Other nephrotoxic drugs (e.g., aminoglycosides, furosemide; theoretical increased risk of nephrotoxicity, monitor renal function)
Monitoring
Baseline Monitoring
Renal function (serum creatinine, BUN, CrCl)
Rationale: Cephalexin is primarily renally eliminated; dose adjustment is necessary in renal impairment.
Timing: Prior to initiation, especially in elderly or patients with known renal dysfunction.
Routine Monitoring
Clinical response to therapy (resolution of infection symptoms)
Frequency: Daily
Target: Improvement of symptoms (e.g., fever reduction, wound healing)
Action Threshold: Lack of improvement or worsening symptoms may indicate treatment failure or resistant organism.
Signs of superinfection (e.g., oral thrush, vaginal candidiasis, severe diarrhea)
Frequency: Daily throughout therapy and for several weeks post-therapy
Target: Absence of new infections
Action Threshold: Development of new symptoms, especially severe or persistent diarrhea (consider C. difficile infection).
Renal function (serum creatinine, BUN)
Frequency: Periodically, especially during prolonged therapy or in patients with pre-existing renal impairment or concurrent nephrotoxic drugs.
Target: Stable renal function
Action Threshold: Significant increase in creatinine/BUN may require dose adjustment or discontinuation.
Symptom Monitoring
- Rash
- Hives
- Itching
- Swelling (face, lips, tongue, throat)
- Difficulty breathing or swallowing (signs of allergic reaction)
- Severe or watery diarrhea
- Abdominal pain or cramps
- Nausea
- Vomiting
- Headache
- Dizziness
- Vaginal itching or discharge
- Oral thrush (white patches in mouth)
Special Patient Groups
Pregnancy
Cephalexin is generally considered safe for use during pregnancy (Pregnancy Category B). Animal reproduction studies have not demonstrated a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. It should be used during pregnancy only if clearly needed.
Trimester-Specific Risks:
First Trimester:
No increased risk of major birth defects observed.
Second Trimester:
No increased risk of adverse outcomes observed.
Third Trimester:
No increased risk of adverse outcomes observed.
Lactation
Cephalexin is excreted in small amounts into breast milk. It is generally considered compatible with breastfeeding (Lactation Risk L1). Monitor breastfed infants for potential adverse effects such as diarrhea, candidiasis (thrush, diaper rash), or allergic reactions (rash).
Infant Risk:
Low
Pediatric Use
Cephalexin is safe and effective for use in pediatric patients, including infants, children, and adolescents, for indicated infections. Dosing is typically weight-based. Close monitoring for adverse effects, especially gastrointestinal upset and rash, is recommended.
Geriatric Use
No overall differences in safety or effectiveness have been observed between elderly and younger patients, but greater sensitivity of some older individuals cannot be ruled out. As cephalexin is substantially excreted by the kidney, the risk of toxic reactions to this drug may be greater in patients with impaired renal function. Because elderly patients are more likely to have decreased renal function, care should be taken in dose selection, and it may be useful to monitor renal function.
Clinical Information
Clinical Pearls
- Cephalexin is a first-generation cephalosporin, primarily active against Gram-positive bacteria (e.g., Staphylococcus aureus, Streptococcus pyogenes) and some Gram-negative bacteria (e.g., E. coli, Klebsiella pneumoniae, Proteus mirabilis).
- It is a common choice for skin and soft tissue infections (e.g., cellulitis, impetigo), uncomplicated urinary tract infections, and streptococcal pharyngitis.
- Patients should be advised to complete the full course of therapy to prevent the development of antibiotic resistance.
- Can cause gastrointestinal upset; taking with food may help alleviate this.
- Not effective against MRSA (Methicillin-resistant Staphylococcus aureus) or Pseudomonas aeruginosa.
Alternative Therapies
- Amoxicillin (for susceptible infections)
- Dicloxacillin (for staphylococcal skin infections)
- Clindamycin (for skin and soft tissue infections, especially if penicillin allergy or MRSA concern)
- Trimethoprim/sulfamethoxazole (for UTIs)
- Nitrofurantoin (for UTIs)
- Other first-generation cephalosporins (e.g., Cefazolin IV)
Cost & Coverage
Average Cost:
$10 - $30 per 30 capsules (250mg generic)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Preferred Generic)
General Drug Facts
If your symptoms or health issues persist or worsen, it is essential to contact your doctor promptly. To ensure safe and effective treatment, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so it is a good idea to check with your pharmacist for more information. If you have any questions or concerns about your medication, do not hesitate to discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek emergency medical attention. When seeking help, be prepared to provide detailed information about the overdose, including the medication taken, the amount, and the time it occurred.