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Doctor insights on: I'm Allergic To Penicillin Can I Take Cephalexin 500mg

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I'm allergic to penicillin, can I take keflex?

I'm allergic to penicillin, can I take keflex?

Maybe: Penicillins (like amoxil) & cephalosporins (like keflex) are both beta-lactam antibiotics named because of their ringed chemical structure. Allergy to penicillins is sometimes directed against this ring, and an allergic reaction may also occur if a similar antibiotic is taken. It is estimated that about 10% of penicillin-allergic patients are also allergic to cephalosporins like keflex. ...Read more

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Dr. William Singer
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Keftabs (Definition)

Keftabs is a first generation cephalosporin which is a kind of cephalosporin type drug (anti-bacterial ...Read more


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What to do if I have strept throat, and I'm allergic to penicillin, can take amoxicillin or keflex instead?

What to do if I have strept throat, and I'm allergic to penicillin, can take amoxicillin or keflex instead?

No to Amoxicillin: You shouldn't take Amoxicillin and there is a 1 in 10 chance that you'll have a reaction to Keflex. If your allergic reaction to penicillin wasn't severe, (anaphylaxis or other), then it would be reasonable to try Keflex ...Read more

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Dr. Crystal Twynham
Board Certified
27 years in practice
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Allergic to penicillin can I take keflex?

Likely, not certain: The majority of people who are told they are allergic to penicillin are not actually so (they get rashes for other reasons, e.g.). Of those that are allergic, about 70% or more will lose the allergy after about 10 years. If you are still allergic, there is about a 10% chance of cross-reaction to 1st-gen cephalosporins like keflex. An allergist can perform testing to judge your risk for a reaction. ...Read more

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If i'm allergic to penicillin is it safe to take keflex pulvales?

No: If you are truly allergic to penicillin, you should avoid all penicillin derivatives and the first generation cephalosporins. Keflex is a first gen. Cephalosporin and may cross react with penicillin. See a board certified allergist to help you determine if penicillin is a true allergy for you. ...Read more

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Dr. Crystal Twynham
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27 years in practice
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I m allergic to penicillin keflex azithromiacin my daughter has scarlet fever and i m worried about what i can take if i get it ?

I m allergic to penicillin keflex azithromiacin my daughter has scarlet fever and i m worried about what i can take if i get it ?

Don't panic: Scarlet fever is an acute febrile illness, primarily affecting children, caused by group a beta-hemolytic streptococci. Clinical manifestations include fever, sore throat, and fine sand-paper like rash caused by a toxin produced by the strep. Although penicillins are antibiotics of choice, there are other antibiotics that are effective. Your doctor will know. A throat culture is helpful. ...Read more

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What to do if I have strept throat, and im allergic to penicillin, can take amoxicillin or keflex instead?

What to do if I have strept throat, and im allergic to penicillin, can take amoxicillin or keflex instead?

No : Amoxicillin is within penicillin class and the risk of having a reaction is significant so it should be avoided. There is controversy about the risk of cross reaction between class of antibiotics penicillin and cephalosporin (keflex). It appears the risk is low (but not 0). If penicillin allergy was years ago, skin testing for penicillin can help know if it is still there. Allergist can help. ...Read more

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Is it possible for you to take cephalexin if you r allergic to penicillins?

Is it possible for you to take cephalexin if you r allergic to penicillins?

Yes: Cross reactivity between the two classes are low so Cephalexin is not contraindicated in penicillin allergy patients. You should have your prescribing physician to follow you for any signs of reactions and get proper treatment. ...Read more

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Can I take cephalexin if I am highly allergic to penicillin? I have not taken penicillin since I was very young. Reaction of hives convulsions

Can I take cephalexin if I am highly allergic to penicillin? I have not taken penicillin since I was very young.  Reaction of hives convulsions

Penicillin allergy: You have what is known as an immediate hypersensitivity reaction to penicillin derivatives and should never be given one, since this is life-threatening. There is said to be cross-hypersensitivity reactions to cephalosporins in 5% of pen allergic persons, and 0.1% of these have a severe reaction. My advice would be not to take a cephalosporin antibiotic unless there was no alternative. ...Read more

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I am allergic to penicillin is it safe to take cephalexin for infection in the urine.

Yes: Unless you had an anaphylactic reaction to penicillin (major breathing problems) there is little risk to trying cephalexin. ...Read more

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Is it a bad idea for someone allergic to penicillin safely take keflex, a cephalosporin?

Yes: Cephalexin (keflex) is a first generation cephalosporin and a very close cousin to penicillin. Though it is not 100% true that all penicillin allergic individuals are also allergic to cephalexin, there is a high likelihood of that happening. ...Read more

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Dr. Crystal Twynham
Board Certified, General Surgery
27 years in practice
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