Cephalexin 500mg Tablets
It is used to treat bacterial infections.
Drug Class
Antibiotic
Pharmacologic Class
First-generation cephalosporin
Pregnancy Category
B
FDA Approved
Jan 1971
DEA Schedule
Not Controlled
Overview
What is this medicine?
Cephalexin is an antibiotic used to treat various bacterial infections, such as those of the skin, ears, throat, bones, and urinary tract. It works by stopping the growth of bacteria. It is important to take the full course of medication as prescribed, even if you feel better, to prevent the infection from returning.
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 place, avoiding the bathroom. Keep all medications in a safe location, 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 place, avoiding the bathroom. Keep all medications in a safe location, 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 with food or milk if stomach upset occurs.
- Drink plenty of fluids to help prevent kidney stones (rare side effect).
- Avoid alcohol if experiencing gastrointestinal side effects, as it may worsen them.
Available Forms & Alternatives
Available Strengths:
- Cephalexin 250mg/5ml Susp 100ml
- Cephalexin 250mg/5ml Susp 200ml
- Cephalexin 125mg/5ml Susp 100ml
- Cephalexin 125mg/5ml Susp 200ml
- Cephalexin 250mg Capsules
- Cephalexin 500mg Capsules
- Cephalexin 250mg Tablets
- Cephalexin 500mg Tablets
- Cephalexin 750mg Capsules
- Cephalexin 125mg/5ml Susp 100ml
- Cephalexin 500mg Tablets
- Cephalexin 250mg Tablets
Dosing & Administration
Adult Dosing
Standard Dose:
250 mg to 1 g every 6 to 12 hours, depending on infection severity and type. For 500mg tablets, common is 500 mg every 6 or 12 hours.
Dose Range:
250 - 1000 mg
Condition-Specific Dosing:
mildToModerateInfections:
250 mg every 6 hours or 500 mg every 12 hours
skinAndSkinStructureInfections:
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
boneAndJointInfections:
250 mg to 500 mg every 6 hours
Pediatric Dosing
Neonatal:
Not established (use with caution, consult specific guidelines)
Infant:
25 to 50 mg/kg/day in divided doses every 6 or 8 hours; for severe infections, up to 100 mg/kg/day
Child:
25 to 50 mg/kg/day in divided doses every 6 or 8 hours; for severe infections, up to 100 mg/kg/day (max 4 g/day)
Adolescent:
Adult dosing (250 mg to 1 g every 6 to 12 hours)
Dose Adjustments
Renal Impairment:
Mild:
CrCl 30-59 mL/min: No adjustment needed for standard doses, consider extending interval for higher doses.
Moderate:
CrCl 15-29 mL/min: 250 mg to 500 mg every 8 to 12 hours.
Severe:
CrCl < 15 mL/min: 250 mg to 500 mg every 12 to 24 hours.
Dialysis:
Hemodialysis: 250 mg to 500 mg after each dialysis session. Peritoneal Dialysis: 250 mg to 500 mg every 12 hours.
Hepatic Impairment:
Mild:
No adjustment
Moderate:
No adjustment
Severe:
No adjustment
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), 2 hours (suspension)
FoodEffect:
Food may delay absorption and peak concentrations but does not significantly affect the total amount absorbed.
Distribution:
Vd:
0.26 L/kg
ProteinBinding:
10-15%
CnssPenetration:
Limited (does not achieve therapeutic concentrations in CSF unless meninges are inflamed)
Elimination:
HalfLife:
0.5 to 1.2 hours (normal renal function)
Clearance:
Not available (primarily renal excretion)
ExcretionRoute:
Renal (glomerular filtration and tubular secretion)
Unchanged:
>90%
Pharmacodynamics
OnsetOfAction:
Rapid
PeakEffect:
1-2 hours (plasma concentration)
DurationOfAction:
6-12 hours (based on dosing interval)
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor immediately or seek emergency medical attention:
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, which can lead to life-threatening bowel problems. 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 taking this medication do not experience severe side effects, and some may not have any side effects at all. However, if you notice any of the following side effects or any other unusual symptoms, contact your doctor:
Stomach pain or diarrhea
Upset stomach or vomiting
This is not an exhaustive list of possible side effects. If you have concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor immediately or seek emergency medical attention:
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, which can lead to life-threatening bowel problems. 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 taking this medication do not experience severe side effects, and some may not have any side effects at all. However, if you notice any of the following side effects or any other unusual symptoms, contact your doctor:
Stomach pain or diarrhea
Upset stomach or vomiting
This is not an exhaustive list of possible side effects. If you have concerns about side effects, consult 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:
- Severe, watery, or bloody diarrhea (may occur up to 2 months after stopping medication)
- Rash, hives, itching, or peeling skin
- Swelling of the face, throat, tongue, lips, or eyes
- Difficulty breathing or swallowing
- Wheezing
- Fever, sore throat, or chills (signs of new infection)
- Unusual bleeding or bruising
- Yellowing of skin or eyes (jaundice)
- Dark urine
- Severe stomach pain
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.
If you are currently taking probenecid, as this may interact with the medication.
Additionally, to ensure safe use, 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 if it is safe for you to take this medication with your other drugs and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor to confirm 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.
If you are currently taking probenecid, as this may interact with the medication.
Additionally, to ensure safe use, 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 if it is safe for you to take this medication with your other drugs and health conditions. Never start, stop, or change the dose of any medication without first consulting your doctor to confirm 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 can increase the risk of developing a second infection. If you are pregnant, planning to become pregnant, or are breastfeeding, discuss the potential benefits and risks of this medication with your doctor to make an informed decision about your treatment.
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 can increase the risk of developing a second infection. If you are pregnant, planning to become pregnant, or are breastfeeding, discuss the potential benefits and risks of this medication with your doctor to make an informed decision about your treatment.
Overdose Information
Overdose Symptoms:
- Nausea
- Vomiting
- Epigastric distress
- Diarrhea
- Hematuria (rare)
- Convulsions (rare, especially in renal impairment)
What to Do:
Call 1-800-222-1222 (Poison Control) immediately or seek emergency medical attention. Treatment is primarily supportive; hemodialysis may be useful in severe cases of renal impairment.
Drug Interactions
Moderate Interactions
- Metformin (increased metformin plasma concentrations)
- Probenecid (decreased renal excretion of cephalexin, leading to increased and prolonged plasma levels)
Monitoring
Baseline Monitoring
Renal function (CrCl)
Rationale: Cephalexin is primarily renally eliminated; dose adjustment is required in renal impairment.
Timing: Prior to initiation, especially in elderly or patients with known renal issues.
Routine Monitoring
Signs and symptoms of infection resolution
Frequency: Daily
Target: Resolution of fever, pain, inflammation
Action Threshold: Lack of improvement or worsening symptoms after 2-3 days may indicate treatment failure or resistant organism.
Signs of superinfection (e.g., oral thrush, vaginal yeast infection, severe diarrhea)
Frequency: Daily throughout treatment and shortly after
Target: Absence of new infections
Action Threshold: Development of new symptoms requires evaluation and potential treatment discontinuation.
Renal function (CrCl)
Frequency: Periodically, especially in prolonged therapy or patients with fluctuating renal function
Target: Stable CrCl
Action Threshold: Significant decline in CrCl may necessitate dose adjustment.
Symptom Monitoring
- Rash
- Hives
- Itching
- Swelling (face, lips, tongue, throat)
- Difficulty breathing or swallowing
- Severe diarrhea (especially watery or bloody)
- 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). Studies in animals have shown no evidence of harm to the fetus, and there are no adequate and well-controlled studies in pregnant women, but extensive clinical experience suggests low risk.
Trimester-Specific Risks:
First Trimester:
Generally considered low risk.
Second Trimester:
Generally considered low risk.
Third Trimester:
Generally considered low risk.
Lactation
Cephalexin is excreted in low concentrations in human milk. It is generally considered compatible with breastfeeding (Lactation Risk L2). Monitor breastfed infant for potential adverse effects such as diarrhea, candidiasis (thrush, diaper rash), or allergic reaction (rash).
Infant Risk:
Low risk of adverse effects; potential for alteration of gut flora, candidiasis, or allergic sensitization.
Pediatric Use
Dosing is weight-based. Safety and efficacy are established for pediatric patients. Neonates require careful consideration due to immature renal function.
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. Dose adjustment is necessary in elderly patients with impaired 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 not effective against MRSA, Pseudomonas aeruginosa, or most anaerobic bacteria.
- Often used for skin and soft tissue infections, uncomplicated urinary tract infections, and streptococcal pharyngitis.
- Advise patients to complete the entire course of therapy, even if symptoms improve, to prevent the development of antibiotic resistance.
- Can cause false-positive results for urine glucose tests using Benedict's solution or Fehling's solution, but not with enzyme-based tests.
- May cause Clostridioides difficile-associated diarrhea (CDAD), ranging from mild diarrhea to fatal colitis. Consider CDAD in patients presenting with diarrhea after antibiotic use.
Alternative Therapies
- Other first-generation cephalosporins (e.g., Cefazolin - IV)
- Penicillins (e.g., Amoxicillin, Dicloxacillin)
- Macrolides (e.g., Azithromycin, Clarithromycin - for penicillin-allergic patients)
- Clindamycin
- Trimethoprim/Sulfamethoxazole (for UTIs)
- Doxycycline (for skin infections, some UTIs)
Cost & Coverage
Average Cost:
Varies widely, typically low per 30 tablets
Generic Available:
Yes
Insurance Coverage:
Tier 1 (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 consult with your pharmacist. If you have any questions or concerns about this 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 reporting the incident, be prepared to provide detailed information, including the name of the medication taken, the amount, and the time it occurred.