Keflex (Generic Cephalexin): Complete Medication Guide
Key Takeaways
Cephalexin is a first-generation cephalosporin antibiotic used to treat bacterial infections like skin infections, strep throat, and urinary tract infections.
It works by killing bacteria and stopping their growth to help your body fight infection.
Common side effects include nausea, diarrhea, and stomach upset, which are usually mild.
Serious allergies are rare but require immediate medical attention, especially if you have a history of penicillin allergies.
Take the full course of medication as prescribed, even if you feel better, to prevent antibiotic resistance.
Keflex (Cephalexin) Overview
Cephalexin, commonly sold under the brand name Keflex, is a first-generation cephalosporin antibiotic. This medication belongs to a class of antibiotics that work by disrupting the cell walls of bacteria, effectively killing them and stopping their growth. Cephalexin treats a wide range of bacterial infections, including skin and soft tissue infections, urinary tract infections, respiratory infections like strep throat, and bone infections.
Generic cephalexin is the same medication as the brand name Keflex—it contains the identical active ingredient and works the same way in your body. The main difference is cost. Generic vs Brand Name Drugs are equally effective, and choosing generic cephalexin can save you significant money on your prescription. This medication is available in capsule, tablet, and liquid suspension forms, making it easy to take by mouth.
Cephalexin is commonly prescribed because it's effective, generally well-tolerated, and affordable. It works best when taken as directed, and it's important to complete the entire course even if you start feeling better. This helps prevent antibiotic resistance, which occurs when bacteria survive treatment and become harder to kill with future antibiotics.
Side Effects
Most people tolerate cephalexin well, but like all medications, it can cause side effects. Many are mild and go away as your body adjusts to the drug.
Common Side Effects
Nausea and vomiting — Your stomach may feel upset, especially when taking the medication on an empty stomach. Taking cephalexin with food may help reduce this.
Diarrhea — Cephalexin can disrupt the balance of good bacteria in your digestive system, leading to loose stools. This is usually mild and temporary.
Stomach pain or cramping — You may experience mild abdominal discomfort or cramping while taking this antibiotic.
Headache — Some people report mild to moderate headaches during treatment.
Vaginal yeast infection — Antibiotics can kill good bacteria that normally prevent yeast overgrowth, leading to infection, especially in women.
Dizziness — A small number of people feel lightheaded or dizzy while taking cephalexin.
Serious Side Effects
Severe allergic reaction (anaphylaxis) — Though rare, cephalexin can trigger a life-threatening allergic reaction with difficulty breathing, swelling of the face or throat, and loss of consciousness. This requires immediate emergency care.
Severe diarrhea (C. difficile infection) — In rare cases, cephalexin can lead to serious diarrhea caused by Clostridioides difficile, a harmful bacterium. Contact your doctor if diarrhea is severe, watery, or lasts more than a few days.
Liver problems — Rarely, this medication can affect liver function, causing yellowing of skin or eyes, dark urine, or pale stools.
Kidney problems — People with existing kidney disease may have trouble clearing this drug from their body, potentially leading to buildup and toxicity.
Hemolytic anemia — Very rarely, cephalexin can destroy red blood cells, causing fatigue, shortness of breath, or pale skin.
When to Seek Medical Attention
Contact your healthcare provider if common side effects persist or worsen after a few days of treatment. If you experience signs of a serious allergic reaction—such as hives, difficulty breathing, or facial swelling—seek emergency medical care immediately. Additionally, if you develop severe diarrhea that lasts more than a few days, abdominal pain that worsens, or signs of liver or kidney problems like yellowing skin or dark urine, reach out to your doctor right away.
This information is educational and does not replace advice from your healthcare provider.
Dosage
Infection Type |
Typical Dose |
Frequency |
Skin and soft tissue infections |
500 mg |
Every 6 hours for 7–14 days |
Strep throat and respiratory infections |
250–500 mg |
Every 6 hours for 10 days |
Urinary tract infections |
500 mg |
Every 6 hours for 7–14 days |
Bone infections |
500 mg |
Every 6 hours for 4–6 weeks |
Children's dosage |
12.5–25 mg per kg |
Every 6 hours (varies by weight) |
Important: If you miss a dose, take it as soon as you remember, but don't double up on doses. Never stop taking cephalexin without talking to your doctor, even if you feel better. Stopping early can allow bacteria to survive and cause the infection to return, potentially stronger than before.
Drug Interactions
Cephalexin may interact with other medications, supplements, or foods. These interactions can reduce how well cephalexin works or increase your risk of side effects. Always tell your healthcare provider about all medications, vitamins, and supplements you're taking.
Probenecid
Probenecid (a medication for gout) can reduce how quickly your body removes cephalexin, potentially raising antibiotic levels in your bloodstream. Your doctor may adjust your cephalexin dose if you take both medications together.
Metformin
Cephalexin may slightly increase metformin levels in your body, potentially raising the risk of side effects. Your doctor may monitor your blood sugar more closely if you take both drugs, especially if you have kidney problems.
Birth Control Pills
Antibiotics like cephalexin may reduce the effectiveness of oral contraceptives by disrupting gut bacteria that help absorb hormones. Use backup contraception during treatment and for 7 days after finishing cephalexin.
Warfarin (Blood Thinner)
Cephalexin may increase the effect of warfarin, a medication that prevents blood clots. This could raise your bleeding risk. Your doctor may monitor your blood clotting time more closely and adjust your warfarin dose.
Alcohol
While moderate alcohol consumption is generally safe with cephalexin, heavy drinking may slow your recovery and increase stomach upset. It's best to limit or avoid alcohol while taking this antibiotic.
Antacids Containing Aluminum or Magnesium
These can slow how quickly your body absorbs cephalexin, potentially reducing its effectiveness. Take antacids at least 2 hours before or after cephalexin.
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Pros and Cons
Pros
Effective against common infections — Cephalexin treats a wide range of bacterial infections, including skin, respiratory, and urinary tract infections.
Generally well-tolerated — Most people experience mild side effects or none at all, making it a safe choice for many patients.
Affordable generic option — Generic medications a cost-effective alternative to brand-name drugs can save you money while providing the same benefits as brand name Keflex.
Multiple dosage forms — Available as capsules, tablets, and liquid suspension, making it easy to take for different ages and preferences.
Fast-acting — You may start feeling better within 24–48 hours of starting treatment.
Cons
Allergic reactions possible — People with penicillin or cephalosporin allergies may experience allergic reactions, ranging from mild rashes to severe anaphylaxis.
Antibiotic resistance risk — Overuse or incomplete courses of cephalexin contribute to antibiotic resistance, making future infections harder to treat.
Gastrointestinal side effects — Nausea, diarrhea, and stomach upset are common, especially when taking the medication on an empty stomach.
Requires multiple daily doses — Most infections require taking cephalexin four times daily, which can be inconvenient for some people.
May interact with other medications — Cephalexin can interact with birth control, blood thinners, and other drugs, requiring careful monitoring.
Frequently Asked Questions
Get answers to common questions about Keflex (generic cephalexin).
Most people start feeling better within 24–48 hours of beginning cephalexin, though this varies depending on the infection type and severity. However, you should complete the entire prescribed course (usually 7–14 days) even if symptoms disappear. Stopping early can allow bacteria to survive and return, potentially stronger than before.
Yes, you can take cephalexin with or without food. Taking it with food may actually help reduce stomach upset and nausea, which are common side effects. If your stomach is sensitive, consider taking doses with a light meal or snack.
Take the missed dose as soon as you remember, unless it's almost time for your next dose. In that case, skip the missed dose and take your next dose on schedule. Never double up on doses to make up for a missed one, as this increases the risk of side effects.
Yes, generic cephalexin is just as effective as brand name Keflex. Generic vs. Brand-Name Drugs contain the same active ingredient and work identically in your body. The FDA requires generic drugs to meet the same strict safety and quality standards as brand names, so you get the same benefits at a lower cost.
Yes, cephalexin can disrupt the balance of good bacteria in your body, potentially leading to yeast infections, especially in women. If you develop signs of a yeast infection—such as unusual vaginal discharge, itching, or burning—contact your doctor. They may prescribe an antifungal medication to treat it alongside continuing your antibiotic.
The Bottom Line
Cephalexin (generic Keflex) is a reliable, affordable antibiotic used to treat bacterial infections affecting the skin, respiratory system, urinary tract, and bones. It works by killing bacteria and stopping their growth, helping your body fight infection. Most people tolerate it well, with side effects ranging from mild stomach upset to rare allergic reactions. The key to success is taking the full course as prescribed, even when you feel better, to prevent antibiotic resistance and ensure the infection doesn't return.
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