A Comprehensive Guide to Cephalexin Side Effects and Risks

According to the Centers for Disease Control and Prevention (CDC), using population data obtained from the 2022 U.S. Census, 21 million cephalexin outpatient prescriptions were written in 2022.

Cephalexin is an antibiotic frequently used to treat bacterial infections, such as respiratory, skin, and urinary tract infections. Its efficacy and broad-spectrum activity make it a go-to option, but its widespread use necessitates understanding its side effects and risks.

[signup]

What Is Cephalexin?

Cephalexin is a first-generation cephalosporin antibiotic. 

Mechanism of Action

Cephalosporins are a subset of the broader beta-lactam antibiotic family, which also includes penicillins. These antibiotics are widely used due to their effectiveness against a variety of bacterial infections and their generally favorable safety profiles.

Cephalosporins kill bacteria by disrupting the formation of their cell walls. They achieve this by binding to specific enzymes called penicillin-binding proteins (PBPs) in the bacterial cell membrane. This binding blocks the action of the transpeptidase enzyme, which is responsible for creating cross-links between peptidoglycan strands that provide strength and rigidity to the cell wall. Without a properly formed cell wall, the bacteria cannot maintain their structure and ultimately die. (7) 

This effect is particularly effective against gram-positive bacteria, which have a thicker peptidoglycan layer in their cell walls, making them more susceptible to cephalosporins (7, 24).  

Common Uses

Cephalexin is prescribed to treat certain types of infections caused by bacteria, including Staphylococcus and Streptococcus species, Escherichia coli, Proteus mirabilis, and Klebsiella pneumoniae. 

These infections include: 

• Respiratory tract infections (e.g., pneumonia)
• Middle ear infections (otitis media)
• Skin infections (e.g., impetigo)
• Bone infections (e.g., osteomyelitis)
• Genitourinary tract infections (e.g., urinary tract infection)

Dosage Guidelines

Cephalexin dosing will depend on age, the condition being treated, and comorbid conditions. Always take this medication as your doctor prescribes to ensure efficacy and prevent unwanted complications.

Children at Least 15 Years and Adults

• The usual dose is 250 mg every 6 hours for 7 to 14 days, but a dose of 500 mg every 12 hours may be prescribed.
• For more severe infections, larger doses of up to 4 grams daily, taken in divided doses, may be needed.
• Dose adjustments are required for patients with impaired kidney function. 

Pediatrics (Over 1 Year) 

• The usual dose is 25-50 mg/kg body weight in equally divided doses for 7 to 14 days.
• A total daily dose of 50-100 mg/kg body weight in equally divided doses may be prescribed to treat severe infections. 
• The recommended dose for treating otitis media is 75-100 mg/kg body weight in equally divided doses.

Common Side Effects of Cephalexin

The most common side effects reported with cephalexin are related to digestive upset, including:

• Diarrhea (the most frequently observed side effect in clinical trials)
• Indigestion
• Irritation of the stomach lining 
• Abdominal pain
• Nausea
• Vomiting

Other mild side effects may include: 

• Headache
• Fatigue
• Vaginal yeast infections

These side effects usually don't require medical attention. They may go away within a couple of days. Talk with your doctor if they are severe, bothersome, or don't go away. (10, 32)

Serious Side Effects and Reactions

Though rare, cephalexin can cause serious side effects that require immediate medical attention. Rare but serious side effects include (19, 20): 

• Allergic reaction
• Clostridioides difficile (C. diff) infection
• Blood-related side effects, such as low red blood cell count (anemia), low white blood cell count (neutropenia), low platelet count (thrombocytopenia), and prolonged prothrombin time
• Neurotoxicity

Call your doctor right away if you experience any of the following symptoms (2, 29):

• Rash
• Itching
• Swelling of the face, tongue, or throat
• Trouble breathing
• Dizziness
• Severe, watery diarrhea
• Fever
• Increased bleeding and bruising
• Altered mental state or level of consciousness
• Seizures

Cephalexin Interactions With Other Medications

Cephalexin can interact with other medications, potentially altering their effects. This list is not all-inclusive, but examples of drugs that can interact with cephalexin include:

• Live Vaccines: Antibiotics can interfere with the immunological response to live vaccines, reducing their efficacy.
• Cholestyramine: Cholestyramine reduces cephalexin absorption and should be administered one hour after or six hours before cephalexin (27). 
• Dofetilide: Cephalexin can interfere with the renal elimination of dofetilide, increasing the risk of cardiac arrhythmias (17). 
• Lixisenatide: Lixisenatide may slow the absorption of cephalexin. If concomitant use is required, administer cephalexin at least one hour before lixisenatide. (1) 
• Probenecid: Probenecid inhibits the renal elimination of cephalexin, increasing its plasma concentrations and the risk of adverse reactions (20). 
• Metformin: Cephalexin may reduce renal elimination of metformin, resulting in increased plasma concentrations and an increased risk of hypoglycemia (low blood sugar). Patients should monitor blood sugar regularly, and adjustments to the metformin dose may be necessary if these two medications are administered together. (19) 
• Warfarin: Cephalexin may increase the effects of warfarin, causing you to bleed more easily. Patients may need to monitor INR more frequently after starting cephalexin, and adjustments to the warfarin dose may be necessary if these two medications are administered together. (11) 

Risk Factors and Populations at Higher Risk for Side Effects

Certain populations may be more vulnerable to cephalexin's side effects. 

Pregnancy and Breastfeeding

Cephalexin is classified as a pregnancy category B medication. This means that there are no adequate studies that have been conducted specifically on pregnant women, but animal studies have not shown any evidence of fertility impairment or risk to the fetus. (20) 

Cephalexin is excreted into human breast milk in small amounts. When prescribing cephalexin to someone who is breastfeeding, healthcare providers should carefully evaluate the benefits of breastfeeding against the necessity of antibiotic treatment and the potential risks to the breastfed infant. (20)

Allergies

Cephalexin is contraindicated in patients with a history of allergy to cephalosporin antibiotics.

Cephalexin may be prescribed as an alternative antibiotic for patients with a penicillin allergy. However, there is a risk of cross-hypersensitivity – 10% of individuals with a history of penicillin allergy may also react to other beta-lactam antibiotics like cephalexin. Monitor these patients closely for any signs of an allergic reaction and discontinue the antibiotic if any allergy symptoms occur. (23) 

Renal Impairment

The kidneys primarily excrete cephalexin. Patients with kidney (renal) impairment are at a higher risk of toxicity due to impaired drug elimination. Dosing regimens should be modified for patients with renal impairment:

• Creatinine Clearance > 60 mL/min: No dose adjustment
• Creatinine Clearance 30-59 mL/min: No dose adjustment; do not exceed a maximum dose of 1 gram/day
• Creatinine Clearance 15-29 mL/min: 250 mg every 8 or 12 hours
• Creatinine Clearance 5-14 mL/min (not yet on dialysis): 250 mg every 24 hours
• Creatinine Clearance 1-4 mL/min (not yet on dialysis): 250 mg every 48 or 60 hours

Older Adults

Clinical studies have not demonstrated geriatric-specific problems that would limit the use of cephalxin in older adults. However, because older adults are more likely to have age-related kidney problems, dose adjustments as outlined above may be required. (9)

Managing Side Effects: Practical Tips for Patients

To reduce the risk of side effects, tell your doctor if you have any of these conditions before taking cephalexin: 

• Bleeding disorders
• Kidney disease
• Liver disease
• Seizures
• Allergy to cephalosporin or penicillin antibiotics
• Pregnant or breastfeeding

Strategies to Minimize Discomfort

To manage common side effects while taking cephalexin, follow these tips:

• Take With Food: Taking cephalexin with meals can reduce gastrointestinal discomfort.
• Stay Hydrated: Drinking plenty of fluids with electrolytes helps manage diarrhea and prevents dehydration (3). 
• Dietary Adjustments: Eating bland foods can help minimize nausea and vomiting.

Over-the-Counter Relief Options

• Probiotics, such as Saccharomyces boulardii, can help restore gut flora disrupted by antibiotics, preventing antibiotic-associated diarrhea.
• Ginger: Taken in tea or capsule form, ginger can treat symptoms of digestive upset, including nausea, indigestion, and abdominal pain. 
• Pain Relievers: Acetaminophen or ibuprofen can reduce headache pain. It is always advised to consult a healthcare professional before adding any over-the-counter medications to your regimen.

FAQs on Cephalexin Side Effects

What to Do If I Miss a Dose?

If you miss a cephalexin dose, take it as soon as you remember. If it's near the time of the next dose, skip the missed dose and resume your regular schedule. Do not double up to make up for a missed dose. (10) 

Can Cephalexin Cause Allergies or Rash?

Cephalexin can cause allergic reactions, the most common symptom being a rash. If you experience a rash, itching, swelling, or difficulty breathing while taking cephalexin, seek medical attention immediately.

How Long Do Side Effects Last After Stopping Cephalexin?

Most side effects resolve shortly after discontinuing cephalexin. However, severe side effects, such as allergic reactions or C. diff infections, can last longer and may require additional treatment.

Can Cephalexin Cause Diarrhea or Stomach Issues?

Cephalexin can cause digestive upset, including diarrhea, stomach pain, and nausea (18).  

Talk to your doctor if you have severe abdominal pain, watery diarrhea, and fever. These are symptoms of a serious C. diff infection that can appear while taking cephalexin and up to two months after you've finished it. (18) 

When Should I Contact My Healthcare Provider?

Contact your healthcare provider if you experience severe or persistent side effects, signs of an allergic reaction, unusual bleeding or bruising, or any other symptoms that concern you while taking cephalexin.

[signup]

Key Takeaways

• Cephalexin is a widely used antibiotic effective against various bacterial infections. While generally safe, there is a risk of mild and more severe side effects. 
• Safe and effective cephalexin use depends on understanding these risks, recognizing symptoms, and knowing when to seek medical help.
• Open communication between patients and healthcare providers can minimize the risk of severe adverse reactions. Always discuss any concerns or side effects you experience with your healthcare team to ensure the best possible outcomes and maintain the effectiveness of your treatment regimen.