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Doctor insights on: First Generation Antihistamine

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Are first generation antihistamines more effective than second generation? I always wonder why some are still on drugstore shelves, like chlorpheniram

Are first generation antihistamines more effective than second generation? I always wonder why some are still on drugstore shelves, like chlorpheniram

Less side effects: There are many medications that remain on shelves for over-the-counter use that probably should be removed. New generation antihistamines are as effective as old ones. Of interest is that some individuals respond favorably to one over the other. The side effect profile and frequency of dosing is what really separates the new from the old antihistamines. In this case, newer is better. ...Read more

Dr. Paul Carter
601 doctors shared insights

Antihistamine (Definition)

Sedating and non-sedating antihistamines prevent and treat allergic reactions, and are ...Read more


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Whats the difference between a first generation antihistamine like chlorpheniramine and second generation antihistamines like allegra (fexofenadine)?

Whats the difference between a first generation antihistamine like chlorpheniramine and second generation antihistamines like allegra (fexofenadine)?

1st and second: First generation antihistamines are sedating and short acting and have usually other properties such as anticholinergic or drying properties. Second generation antihistamines are long aciting, usually dosed once a day, and are less or non sedating and selective antihistamines with less active properties on other receptors. ...Read more

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What is the difference between first and second-generation antihistamines?

What is the difference between first and second-generation antihistamines?

Side effects: The second generation antihistamines were developed to try and decrease the side effects of the first generations. Many are "purified" first generation antihistamines so they have the active effects without the side effects of drowsiness, sedation, dry mouth etc. They also tend to have longer half lives, meaning they can be taken once or twice a day not every 4 hours. ...Read more

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Difference between first and second generation antihistamines? Why are 1st generation considered nonsedating?

Difference between first and second generation antihistamines? Why are 1st generation considered nonsedating?

Sedation: 1st generation are sedating because many people, up to 40%, get sleepy when taking them. 2nd generation antihistamines are chemically modified and are less likely to cause sedation. The generics of the less sedating are cetirizine, fexafenadine, and loratidine. They cause sedation in some people, up to 11%, but much less than the older drugs. ...Read more

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Doctors, what is the difference between first and second generation antihistamines?

CNS: The 1st generation AH gets into the brain area thereby blocking the stimulatory effect on alertness from histamine. The 2nd generations ones do not get into the brain and thus do not usually induce drowsiness. 1st gen- more drying and better for runny nose , the sedating effect also better for itching than 2nd gen. ...Read more

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Is antihistamines first generation effective drug for common cold and does vitamin c important during common cold?

Probably not: Antihistamines are effective for sneezing and runny nose due to allergies, by blocking histamine receptors,. but can over dry nasal passages during colds. Atrovent nasal spray helps runny nose and decongestants (use Short term only) help congestion. Vitamin C may help prevent colds, but not as effective once you have one. Rest, fluids, chicken soup, zinc, humidifier, and netipot help. ...Read more

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I am about to take an antihistamine for the first time but my friends tell me to use it before bedtime. Will I still feel the effects the next day?

Depends on the med: Some antihistamines are more sedating than others. Medications like Benadryl (diphenhydramine) can definitely cause sedation. Newer antihistamines like Allegra and Claritin are non-sedating and Zyrtec is sedating in roughly 10-20% of patients. ...Read more

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What if I am concerned my hives are caused by an antihistamine in the first place? I.E. Zyrtec and allegra (fexofenadine)

Go to allergy dr: Go to an allergy doctor and get tested. Usually if you take antihistamine and break out more you might suspect a reaction to antihistamine, but you won't know for sure unless it happens every time you take it, or you get an allergy testing. ...Read more

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Can a pregnant woman take desloratidine tablets as antihistamine medication during the first month of pregnancy or is it a contraindication?

Can a pregnant woman take desloratidine tablets as antihistamine medication during the first month of pregnancy or is it a contraindication?

Probably not: This drug is classified as category c in pregnancy and thus you should consider taking those with category b classification with pregnancy. In fairness, I have not seen much data linking fetal anomalies to any of the approved antihistamines. However it is better to be safe than sorry. ...Read more

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For educational purposes, i look up any meds i take. Which cytochrome p450 enzymes metabolize the first-gen antihistamine periactin (cyproheptadine hydrochloride)? Or are effected?

Cyproheptadine: Aromatic ring hydroxylation ( followed by glucuronide conjugation), and n-demethylation, end heterocyclic ring oxidation were shown to occur in man. The principal metabolite, however, was identified tentatively as a quaternary ammonium. Glucuronide-like conjugate of cyproheptadine. The exact mechanisms for the glucuronidation are not entirely clear. ...Read more