Cephalexin is one of the most commonly prescribed antibiotics in the United States, used to treat a wide variety of bacterial infections. If you’ve been prescribed cephalexin — often sold under the brand name Keflex — you may be wondering exactly what it treats, how it works, and what to expect while taking it. Here’s a complete overview, along with important safety information to keep in mind. This is educational information only and isn’t a substitute for guidance from your prescribing doctor or pharmacist.
Key Takeaways
- Cephalexin is a cephalosporin antibiotic used to treat a range of bacterial infections.
- It’s commonly prescribed for skin, respiratory, ear, bone, and urinary tract infections.
- Cephalexin does not treat viral infections such as colds or the flu.
- Common side effects include nausea, diarrhea, and stomach upset.
- Always complete the full prescribed course, even if symptoms improve early.
What Is Cephalexin?
Cephalexin is a prescription antibiotic that belongs to a class of drugs called cephalosporins, which are chemically related to penicillin. It’s available in capsule, tablet, and liquid form and is typically taken by mouth. Like other antibiotics, cephalexin only works against bacterial infections — it has no effect on viruses.
What Is Cephalexin Used For?
Doctors prescribe cephalexin for a variety of bacterial infections affecting different parts of the body. It’s a versatile antibiotic that’s been used safely for decades, making it one of the more familiar options for common infections that respond well to this class of medication.
| Condition | Body System Affected |
|---|---|
| Skin and soft tissue infections | Skin |
| Upper respiratory infections | Respiratory tract |
| Ear infections (otitis media) | Ear |
| Urinary tract infections | Urinary system |
| Bone and joint infections | Musculoskeletal system |
| Strep throat | Throat |
How Does Cephalexin Work?
Cephalexin works by interfering with bacteria’s ability to build their protective cell walls. Without a functional cell wall, bacteria become unstable and are eventually destroyed by the body’s immune system. This mechanism makes cephalexin effective against many common, susceptible strains of bacteria, though it doesn’t work against every type of bacterial infection.
How Is Cephalexin Typically Taken?
Cephalexin is usually taken by mouth, with or without food, at intervals your doctor specifies based on your particular infection. The exact dose and length of treatment depend on factors like the type and severity of infection, your age, weight, and kidney function. It’s important to take cephalexin exactly as prescribed and to complete the entire course, even if you start feeling better after a few days — stopping early can allow the infection to return or contribute to antibiotic resistance.
What Are the Common Side Effects of Cephalexin?
- Nausea or stomach upset
- Diarrhea
- Headache
- Dizziness
- Vaginal itching or discharge (yeast infection)
What Are the Serious Side Effects or Warnings to Know?
- Signs of an allergic reaction, such as rash, hives, swelling, or difficulty breathing
- Severe or watery diarrhea, which could signal a serious intestinal condition
- Signs of liver problems, such as yellowing skin or eyes
- A small risk of cross-reactivity in people with a severe penicillin allergy
Who Should Avoid Cephalexin or Use It With Caution?
- Anyone with a known allergy to cephalosporin antibiotics
- People with a history of severe penicillin allergy
- Those with kidney disease, who may need a dose adjustment
- Pregnant or breastfeeding individuals, who should discuss risks and benefits with a doctor
What Should You Know Before Taking Cephalexin?
- Tell your doctor about all medications, supplements, and allergies before starting
- Take doses at evenly spaced intervals as directed
- Don’t share your prescription with anyone else
- Finish the entire course, even if symptoms resolve early
- Ask your doctor whether a probiotic might help offset digestive side effects
Frequently Asked Questions
Is cephalexin a penicillin? No. Cephalexin is a cephalosporin, a related but distinct class of antibiotic. People with mild penicillin allergies are sometimes still able to take cephalosporins, but this should always be confirmed with a doctor first.
Can cephalexin treat a cold or the flu? No. Colds and the flu are caused by viruses, and antibiotics like cephalexin have no effect on viral infections.
How long does cephalexin take to work? Many people notice improvement within two to three days, though it’s important to finish the full prescribed course even after symptoms improve.
Can you drink alcohol while taking cephalexin? There’s no major known interaction, but alcohol can worsen some side effects like stomach upset and is generally best limited while recovering from an infection.
What should you do if you miss a dose? Take the missed dose as soon as you remember, unless it’s almost time for your next dose — in that case, skip it and continue your regular schedule rather than doubling up.
Cephalexin remains a widely used, well-studied antibiotic for treating a range of common bacterial infections. Understanding what it treats, how to take it correctly, and what side effects to watch for can help you use it safely and effectively — always in partnership with your prescribing doctor.
