Compare Keflex vs. Penicillin

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

Keflex
(cephalexin)

Penicillin Vk
(penicillin)

Treats bacterial infections. Keflex (cephalexin) is good for treating many bacterial infections, and is available as a generic.Kills bacteria. Penicillin Vk (Penicillin) is good for treating many bacterial infections and is available as a generic. You may need to use another form of birth control along with your birth control pills. It's also best taken on an empty stomach but it can cause an upset stomach.
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
Reviews for Penicillin
71%
-7% worse vs. Keflex
52%
-4% worse vs. Keflex
12%
-2% worse vs. Keflex
1297 reviews
Have you used Penicillin Vk (penicillin)?
Worth itNot sureNot worth it
Side effects
KeflexPenicillin

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

More about Keflex side effects »

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

More about Penicillin side effects »
How it works
KeflexPenicillin
Keflex (cephalexin) is an antibiotic. It kills bacteria by preventing them from making their own protective covering.Penicillin Vk (Penicillin) is an antibiotic. It kills bacteria by preventing them from making their own protective covering.
Type of medication
KeflexPenicillin
Prescription onlyPrescription only
Available as
KeflexPenicillin
  • Pill
  • Liquid
  • Pill
Used for
KeflexPenicillin
Risk factors for serious side effects
KeflexPenicillin
  • Weakened immune system
  • Not taking Keflex (cephalexin) correctly
  • History of penicillin or cephalosporin allergies
Detailed Keflex (cephalexin) risks & warnings »
  • Prior severe allergic reaction to Penicillin Vk (Penicillin)
Detailed Penicillin Vk (penicillin) risks & warnings »
Pregnancy

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

The FDA hasn’t classified this medicine’s effects on unborn babies. Talk with your doctor about this medicine if you’re pregnant or planning on it.

Food
KeflexPenicillin
  • Can take with or without food.
  • Can be taken with or without food.
No food related info.
Upsides and benefits
KeflexPenicillin
  • 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.
  • Available in generic.
  • Available in different forms: tablet, capsule and suspension.
  • Used to treat many types of bacterial infections.
Downsides and risks
KeflexPenicillin
  • 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.
  • Many bacteria have developed resistance. Your doctor may run tests to see if Penicillin will work on your infection.
  • Can make birth control pills less effective.
  • Best taken on an empty stomach, but can cause stomach upset and diarrhea.
Tips from our pharmacists for people taking the medication
KeflexPenicillin
  • 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.
  • Take this medication exactly how your doctor tells you to.
  • If you're taking birth control pills, this medication can make them less effective.
  • Try to take it on an empty stomach. If this gives you an upset stomach, take it with food.
  • Can cause diarrhea, nausea or vomiting.
Learn more
More about KeflexSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Keflex (cephalexin)?
Worth itNot sureNot worth it
More about PenicillinSide effectsReviews & ratingsAlternativesFDA package insert
Have you used Penicillin Vk (penicillin)?
Worth itNot sureNot worth it