Cephalexin: Uses, Dosage, Side Effects, and More

Introduction

Cephalexin is a commonly prescribed antibiotic that belongs to the class of cephalosporins. First introduced in the 1960s, it has since become a staple in treating a wide range of bacterial infections. It is well-tolerated, effective, and available in both generic and brand-name forms (e.g., Keflex). Despite its long history, many patients and even healthcare professionals seek clear and concise information about its mechanism, applications, and precautions.

In this article, we explore everything you need to know about Cephalexin—how it works, what it’s used for, possible side effects, proper usage, and frequently asked questions.

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What is Cephalexin?

Cephalexin is a first-generation cephalosporin antibiotic. Like other beta-lactam antibiotics (such as penicillins), it works by interfering with the bacterial cell wall synthesis, ultimately leading to cell death. It is effective against many Gram-positive bacteria and some Gram-negative bacteria.

Brand Names

• Keflex

• Keftab

• Daxbia (U.S.)

• Rilexine (veterinary use)

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Mechanism of Action

Cephalexin inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs) located inside the bacterial cell wall. This binding disrupts the final transpeptidation step of peptidoglycan synthesis, a critical component of the bacterial wall. Without a properly formed cell wall, the bacteria are unable to survive, particularly during cell division, leading to their death.

It is classified as a bactericidal antibiotic, meaning it kills bacteria rather than merely inhibiting their growth.

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What Infections Does Cephalexin Treat?

Cephalexin is approved to treat a variety of infections caused by susceptible strains of bacteria. Common indications include:

1. Respiratory Tract Infections

• Streptococcal pharyngitis (strep throat)

• Tonsillitis

• Bronchitis (when caused by susceptible organisms)

2. Skin and Soft Tissue Infections

• Cellulitis

• Impetigo

• Wound infections

• Abscesses

3. Urinary Tract Infections (UTIs)

• Cystitis

• Pyelonephritis (mild cases)

4. Bone Infections (Osteomyelitis)

• Especially caused by Staphylococcus aureus

5. Ear Infections (Otitis Media)

• Particularly in children

Off-Label Uses:

• Dental prophylaxis for patients with penicillin allergy

• Animal bites (alternative to amoxicillin-clavulanate in some cases)

• Uncomplicated pneumonia (when caused by susceptible organisms)

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Who Can Take Cephalexin?

Cephalexin is generally safe for adults and children, including infants older than 1 year. However, its use should be guided by a healthcare provider.

Special Populations:

• Pregnancy: Generally considered safe (Pregnancy Category B)

• Breastfeeding: Low risk, but some cephalexin may be excreted in breast milk

• Elderly: Use with caution; dosage adjustment may be required due to kidney function decline

• Renal Impairment: Dosage adjustment is essential as the drug is excreted primarily through the kidneys

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Dosage and Administration

Dosage depends on the type and severity of the infection, the patient’s age, and renal function.

Typical Adult Dosage:

• 250–500 mg every 6 hours or 500 mg–1 g every 12 hours

• Maximum daily dose: 4 grams

Children (over 1 year):

• 25–50 mg/kg/day in divided doses

• For severe infections, up to 100 mg/kg/day may be used

Note: Cephalexin is available in capsule, tablet, and liquid suspension forms.

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How to Take Cephalexin

• Take with or without food. However, taking it with food may reduce stomach upset.

• Complete the full course, even if symptoms improve earlier.

• Shake the oral suspension well before each use and store it in the refrigerator.

• Never double up on doses if a dose is missed; take the next dose as scheduled.

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Common Side Effects of Cephalexin

Most people tolerate cephalexin well, but like all medications, it can cause side effects.

Common Side Effects:

• Nausea

• Diarrhea

• Vomiting

• Stomach pain

• Headache

• Fatigue

Less Common but Serious Side Effects:

• Allergic reactions: rash, itching, swelling, severe dizziness, trouble breathing

• Clostridioides difficile-associated diarrhea (CDAD): Can occur during or after treatment

• Liver dysfunction: Elevated liver enzymes

• Seizures (in rare cases, especially with kidney disease)

If any severe or persistent symptoms occur, consult a healthcare provider immediately.

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Cephalexin Allergies

Patients with a history of allergy to penicillins or other cephalosporins should be cautious. About 10% of people allergic to penicillin may also react to cephalosporins like cephalexin (cross-reactivity).

Symptoms of an Allergic Reaction:

• Hives

• Swelling (face, lips, throat)

• Difficulty breathing

• Anaphylaxis (a medical emergency)

If any allergic symptoms appear, discontinue the medication and seek emergency care.

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Drug Interactions

Cephalexin generally has a low potential for drug interactions. However, some medications may interact:

Notable Interactions:

• Metformin: Cephalexin may increase metformin levels, increasing the risk of lactic acidosis

• Probenecid: May increase blood levels of cephalexin by decreasing renal clearance

• Anticoagulants (e.g., warfarin): Rarely, cephalexin can enhance the effects and increase bleeding risk

• Live vaccines: May reduce vaccine efficacy; check with a provider if recently vaccinated

Always inform your healthcare provider about all medications and supplements you’re taking.

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Cephalexin and Antibiotic Resistance

As with all antibiotics, misuse of cephalexin can lead to antibiotic resistance, a growing global concern. Resistance occurs when bacteria adapt and become less susceptible to antibiotics.

Tips to Avoid Resistance:

• Only take antibiotics when prescribed

• Complete the entire course as directed

• Don’t use leftover antibiotics for new infections

• Avoid pressuring doctors for antibiotics unnecessarily

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Cephalexin vs. Other Antibiotics

Cephalexin is often preferred when penicillin cannot be used or in cases where a mild, first-line agent is needed.

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Cephalexin in Veterinary Use

Cephalexin is also widely used in veterinary medicine, especially for dogs and cats. It treats skin infections, abscesses, and UTIs. However, human formulations should never be given to pets without veterinary guidance, as dosing differs.

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Storage and Shelf Life

• Capsules/Tablets: Store at room temperature away from moisture and heat

• Liquid suspension: Store in the refrigerator; discard after 14 days

• Keep out of reach of children and do not freeze the liquid form

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Frequently Asked Questions (FAQs)

1. How long does cephalexin take to work?

Symptoms often begin to improve within 24–48 hours of starting treatment, but full resolution may take several days depending on the infection.

2. Can you drink alcohol while taking cephalexin?

Moderate alcohol consumption is not known to interfere with cephalexin, but it’s best to avoid alcohol to ensure optimal recovery.

3. Can cephalexin be used for COVID-19?

No. Cephalexin is not effective against viral infections like COVID-19. It should only be used to treat or prevent bacterial infections.

4. Is cephalexin a strong antibiotic?

It’s considered moderately strong and is effective for many common bacterial infections. It’s typically a first-line agent for uncomplicated cases.

5. What if I miss a dose?

Take it as soon as you remember. If it’s almost time for your next dose, skip the missed dose—do not double up.

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Conclusion

Cephalexin is a time-tested, reliable antibiotic that plays a vital role in treating various bacterial infections. It is particularly effective against Gram-positive organisms and is often chosen for skin infections, UTIs, and respiratory tract infections. Like all medications, it must be used responsibly under medical supervision to minimize the risk of side effects and antibiotic resistance.

If you have any questions about your prescription or how to take cephalexin, always consult with a qualified healthcare provider or pharmacist.