Compare Keflex vs. Flagyl

Head-to-head comparisons of medication uses, side effects, ratings, and more.

Keflex
(cephalexin)

Flagyl
(metronidazole)

Treats bacterial infections. Keflex (cephalexin) is good for treating many bacterial infections, and is available as a generic.Treats and prevents bacterial infections. Flagyl (metronidazole) is very good at treating certain bacterial infections, but you can't have any alcohol while on it since it'll make you throw up a lot.
Reviews & ratings
Filter group. All currently selected
Filter group. All currently selected
5.08Keflex
Reviews for Keflex
64%
of people (All ages) say Keflex is worth it
48%
say it works well
14%
say it's a big hassle
686 reviews
Have you used Keflex (cephalexin)?
Worth itNot sureNot worth it

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Have you used Flagyl (metronidazole)?
Worth itNot sureNot worth it
Side effects
KeflexFlagyl

The Keflex FDA package insert doesn’t have numbers about how common side effects are.

More about Keflex side effects »
  • Headache 18%
  • Nausea 10%
  • Metallic taste 9%
  • Genital itching 5%
  • Diarrhea 4%
  • Stomach problems 4%
  • Dizziness 4%
  • Stuffy nose 3%
  • Abnormal urine 3%
  • Menstrual cramps 3%
More Flagyl side effects »
How it works
KeflexFlagyl
Keflex (cephalexin) is an antibiotic. It kills bacteria by preventing them from making their own protective covering.Flagyl (metronidazole) is an antibiotic that kills bacteria by interacting with their DNA and preventing proteins from being made.
Type of medication
KeflexFlagyl
Prescription onlyPrescription only
Available as
KeflexFlagyl
  • Pill
  • Liquid
  • Pill
  • Extended-release pill
  • Injection
Used for
KeflexFlagyl
Risk factors for serious side effects
KeflexFlagyl
  • Weakened immune system
  • Not taking Keflex (cephalexin) correctly
  • History of penicillin or cephalosporin allergies
Detailed Keflex (cephalexin) risks & warnings »
  • Taking high doses of Flagyl (metronidazole)
  • Taking Flagyl (metronidazole) for a long time
  • Taking Flagyl (metronidazole) incorrectly
Detailed Flagyl (metronidazole) risks & warnings »
Pregnancy

Research studies with animals haven’t found a risk to unborn babies, but it hasn’t been properly studied in humans.

Research studies with animals haven’t found a risk to unborn babies, but it hasn’t been properly studied in humans.

Interactions
KeflexFlagyl
No interactions related info.
  • Alcohol interacts with Flagyl (metronidazole) to cause a serious reaction in people that includes stomach upset, throwing up, feeling sick, or turning red. Avoid alcohol while you're taking Flagyl (metronidazole), and for 3 days after you're done taking it.
Alcohol
KeflexFlagyl
No alcohol related info.
  • Don't drink any alcohol (don't even use mouthwash with alcohol in it) while taking Flagyl (metronidazole) and for at least 3 days after using it, because it can cause a serious reaction in your stomach and make you throw up.
  • You can't drink alcohol while on Flagyl (metronidazole), and for at least 3 days after you finish it.
Food
KeflexFlagyl
  • Can take with or without food.
  • Can be taken with or without food.
  • If you're on blood thinners, let your doctor know. Flagyl (metronidazole) can interact with your medicines and make you more likely to bleed.
Upsides and benefits
KeflexFlagyl
  • Available in generic.
  • Available in different forms: tablet, capsule, and suspension.
  • Used to treat many types of bacterial infections.
  • Can be taken with or without food.
  • Generally few side effects compared with other antibiotics.
  • Flagyl (metronidazole) is good at killing a variety of bacteria.
  • Unlike many other antibiotics, Flagyl (metronidazole) is less likely to make bacteria resistant to it.
  • Most forms are available as a generic, so it's relatively cheap.
Downsides and risks
KeflexFlagyl
  • Can cause diarrhea.
  • You may need to take Keflex (cephalexin) 2 to 4 times a day, which can be hard to remember.
  • If you're allergic to penicillins or other antibiotics, you might not be able to take this medicine.
  • You can't drink alcohol while on Flagyl (metronidazole), and for at least 3 days after you finish it.
  • Side effects can include nausea, headache, stomach upset, and a metallic taste in your mouth.
  • If you're taking Flagyl (metronidazole) for a long time, there's a risk of more side effects, such as nerve damage.
  • If you're on blood thinners, let your doctor know. Flagyl (metronidazole) can interact with your medicines and make you more likely to bleed.
Tips from our pharmacists for people taking the medication
KeflexFlagyl
  • Finish all of the medicine your doctor gives you, even if you start to feel better. Stopping it early can cause the bacteria to develop resistance.
  • Store the suspension in the refrigerator. Shake well before using, and discard the bottle after 14 days.
  • Can take with or without food.
  • Don't drink any alcohol (don't even use mouthwash with alcohol in it) while taking Flagyl (metronidazole) and for at least 3 days after using it, because it can cause a serious reaction in your stomach and make you throw up.
  • Take this medicine exactly as your doctor or pharmacist tells you. Don't stop taking it early, or the bacteria left in your body could become resistant.
  • If you're taking the extended-release (ER) form, take it 1 hour before, or 2 hours after you eat.
Learn more
More about KeflexSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Keflex (cephalexin)?
Worth itNot sureNot worth it
More about FlagylSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Flagyl (metronidazole)?
Worth itNot sureNot worth it