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Doctor insights on: Allergic Reaction To Antibiotic Keflex Cephalexin

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My 2 1/2 year has an allergic reaction to keflex has hives all over body how much Benedryl can I give her she is 28 lbs ?

My 2 1/2 year has an allergic reaction to keflex has hives all over body how much Benedryl can I give her she is 28 lbs ?

Benadryl (diphenhydramine) dosing: Benadryl (diphenhydramine) is effective between 0.5 to 1.0 mg/kg per dose every 8-12 hrs. Based on pt being 28 lbs then a tspn of benadryl (diphenhydramine) 12.5mg/5ml will give pt 12.5 mg which is about 1 mg/kg. ...Read more

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Dr. John Chiu
2,491 doctors shared insights

Allergies (Definition)

Allergies occur when your immune system is triggered by envirionmental factors it should ignore--for example, pollen in the air, or dander on a cat or dog--and creates cells to fight against them. An allergic reaction typically causes itching, congestion, or drainage, and ...Read more


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I was given Keflex around 3 months ago for Hidradenitis. I had an allergic reaction and stopped taking it . I've had hives ever since. Why is that?

I was given Keflex around 3 months ago for Hidradenitis. I had an allergic reaction and stopped taking it . I've had hives ever since. Why is that?

Not Keflex: HIves is a particular kind of rash, and rarely lasts more than a few days. And any rash due to cephalexin (Keflex) allergy would not last more than 1-2 weeks after stopping the drug. So whatever the cause of your current rash, it probably isn't hives and cephalexin isn't the cause. If you're taking any other medications, you might be allergic to one of them. Discuss with your doctor. ...Read more

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Always fine w penicillin, but had extreme allergic reaction reaction to keflex! does that mean I am now also allergic to penicillin for sure?

Always fine w penicillin, but had extreme allergic reaction reaction to keflex! does that mean I am now also allergic to penicillin for sure?

Not necessarily: While penicillin and Cephalexin (keflex) share some features, allergy to one does not necessarily to one mean that you are allergic to the other. See a board-certified allergist/immunologist to sort things out. ...Read more

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I had a severe allergic reaction to keflex. Can i trust taking other antiobios in the future without being pre-tested? How to know if allergic again?

I had a severe allergic reaction to keflex. Can i trust taking other antiobios in the future without being pre-tested? How to know if allergic again?

Many options: Antibiotics are in a number of chemical classes. With a severe reaction to Keflex (also called cefazolin), you should avoid antibiotics in the cephalosporin and probably the penicillin class, as there is a higher chance of cross reactivity. Typically, we will give antibiotics in a different chemical class rather than testing. For you, examples may be clindamycin, Ciprofloxacin or vancomycin. ...Read more

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I read that the flu shot is made from antibiotics. Safe for people allergic to keflex and penicillin?

I read that the flu shot is made from antibiotics. Safe for people allergic to keflex and penicillin?

No/ Yes: Influenza vaccines are made with dead viral antigens or inactivated live virus. They are not made with antibiotics and can be given to anyone who is allergic to antibiotics. ...Read more

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Why would i suddenly have so many med allergies (hives, etc?) allergic to nsaids, opiates, keflex, and more. All within a couple yrs. Why?

Why would i suddenly have so many med allergies (hives, etc?) allergic to nsaids, opiates, keflex, and more. All within a couple yrs. Why?

It is uncommon: First you need to describe what kinds of problem you have had with each of the drugs since some may not really be from an allergy. Becoming "allergic" to drugs with unrelated chemical structure in 2 years is also rare. You need to consult an allergist to help you sort this out. ...Read more

Dr. John Chiu
1,005 doctors shared insights

Allergic Reaction (Definition)

Allergic reactions are sensitivities to substances, called allergens, that come into contact with the skin, nose, eyes, respiratory tract, and gastrointestinal tract. They can be inhaled into the ...Read more


Dr. John Leander Po
1,117 doctors shared insights

Antibiotic (Definition)

An antibiotic is a medicine that slows, stops, or kills germs. The germs are usually bacteria causing an infection in a person, so the person uses antibiotics to help his body get ...Read more