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Food dye sensitivity is not my friend. Blue #1 in it rendered it pretty much useless for my needs. Imagine the discussion with your doctor when you say, "Hey, I think I'm allergic to this antihistamine..." and get blown off. I also have a good number of allergies in my 30s I didn't have when I was young, so I totally agree with a poster above who mentioned that overflowing bucket.

One other thing I will note here is that Benadryl isn't good for glaucoma (or those with higher than normal eye pressures). I never had high eye pressures until I got all of my allergies and had to take medicine for them.

Always give the allergist a full-health run-down and mention these things I have also been told that certain antihistamines can work on stomach acid (though I think that's more of an off label use).

Thanks for sharing. Actually, my third child (DD) gets random (usually only one or two) hives on her face as well. However, it only happens a few times a year and most of the times we can't tie it to any specific food. Since it is only one or two and goes away the same day, we just keep an eye on it and generally don't give her benadryl for that. Her obvious allergic reactions, which we can generally tied to a specific source, usually include other symptoms as well as more severe hives with swelling.

There are so many possible combinations of symptoms that it can make it confusing to track. I know that I would not have known to connect itchy eyes with a food allergy, but that's because in my DS' case, he usually has other issues causing itchy eyes.

I have also heard that developing new allergies as an adult is not uncommon. Thankfully, those aren't usually as severe. That's an interesting tidbit about stomach acid - maybe I should look into that particular use.

The use of H1 receptor blockers including Zyrtec and Clartyne are first line treatments for allergies including food allergies. They block the histamine mediated effects including the rash, itch and some respiratory effects.

Stomach acid release is mediated by histamine binding to H2 receptors. H2 antagonists (blockers) include ranitidine and famotidine. There is some evidence that H2 antagonists may help with the late, second stage, or relapse effects in severe allergy but they are not recommended as main line treatment for allergy. Similarly corticosteroids are used in anaphylaxis but as a second line measure to prevent late responses.

The problem with the regular use of H1 blockers is the patient may miss the first signs that they have ingested an allergen and consume more of the product so have a higher allergen load on board when symptoms appear. It's just something to be aware of.

Allergies develop at all stages of life. Unfortunately patients can develop allergies to medications which have previously been safely used and respond with anaphylaxis on later doses. Allergy can be severe at any time not just in childhood.

Food allergies can also develop later in life due to cross reactivity in similar shaped molecules in other products. Latex allergy is linked to food allergies due to cross reactivity with food triggers including kiwi fruit, banana, chest nuts and avocado.

First line treatment for all allergy is antihistamines then epinephrine given as soon as severe allergy manifests. Other treatment includes IV fluids and occasionally glucagon if patients are on beta blockers as they block epinephrines effects.

Once histamine is activated the response is generalized so that is why food allergies can also manifest as runny eyes or nose, itchy eyes or nose, rash or hives, itchy skin etc. gastrointestinal symptoms include nausea, vomiting, diarrhoea or abdominal cramps, burning in the chest. Respiratory symptoms of wheeze, shortness of breath, itchy throat etc can occur with any allergy, a bronchodilator such as salbutamol can be used. There are also neurological symptoms and so on.

H1 blockers will act at all sites o histamine action but have limited effectiveness against severe cardio respiratory effects including bronchoconstriction, blood vessel dilation which causes hypotension (low blood pressure) and poor pump function of the heart. These are treated by epinephrine and fluids. Fluids alone are ineffective because blood vessels get leaky and that causes edema or swelling in all kinds of tissues including the airway. Therefore epinephrine first to decrease the permeability of blood vessels which contributes to the swelling.

By the way Benadryl contains the H1 antihistamine diphenhydramine. If that isn't working, adding another proprietary H1 blocker, such as Clartyne or Zyrtec, doesn't work,as those receptors are already being acted on by the diphenhydramine. Zyrtec etc are just longer acting formulations, molecules that do the same job as Benadryl but stick around longer and have the advantage that they cause less drowsiness as they are not as neurologically active.

As Polarbear said, always see your doctor if you have concerns or recurrent symptoms. Allergies are a very tricky beast as Howler karma will remind you. And they can change for better or for worse over time.

Yeah-- older first-gen stuff is both H1/H2 blocking, but shorter acting, and as ndw notes above, the second generation meds are more selective for H1 receptors, which tend to exclude the CNS H2 sites (thus making them "non-drowsy" or at least better for most people). They work FAR better (for most people) on the irritating peripheral symptoms like skin, eyes, nasal congestion. They're also a lot more idiosyncratic in terms of individual action, however. (So if loratidine does nothing, the advice is often for patients to try cetirizine, or fexofenadine, for example...)

One thing which is useful to recall when using first-gen versus second-gen antihistamines is that they do various things selectively, and one may sometimes make use of those properties.

Diphenhydramine is useful for GI reactivity in particular-- to the point that it often works as a mild anti-emetic.

Ranitidine is also a histamine blocker, though it's got nowhere near the efficacy of something that hits systemic H1 and H2 receptors like diphenhydramine.

Just recall that those older generation antihistamines that indiscriminately hit both receptor types can cause drowsiness that masks neurological/cardiovascular effects of a systemic reaction.

All this pharmacology-- better living through chemistry at my house, anyway!

Diphenhydramine also acts as an anticholinergic which slows the gut motility and contributes to antiemesis and drowsiness.

Drowsiness, as HowlerKarma, is also a symptom of severe allergy, anaphylaxis, and masking that is very bad. In mild nausea being able to sleep is nice. The drowsiness component is the reason diphenhydramine was used as a sedative adjunct in some Anaesthesia but it has hangover and other side effects that newer agents don't, so I have never seen that done.

Okay I have a question...someone said taking Benadryl and then taking Zyrtec doesn't really work.

My son takes daily Zyrtec for pollen, seasonal allergies (except it is fl and we don't have seasons it is generally year round)....we go visit grandma and she has a cat...he adds a Benadryl to the Zyrtec for a few days and can function without clawing out his eyes and sneezing constantly.

So b then z does no good but z then b can add to the therapy?

Not really true-- the order doesn't matter all that much, except that the off-rate for diphenhydramine on the H1 and H2 receptors that it hits is much faster-- of course, even with zyrtec, it's not as slowly metabolized as it is in adults, so this is why dosing is often twice daily in children.

Mostly the reason for cetirizine as a primary therapeutic agent (with diphenhydramine added as needed) is that the former doesn't lead to CNS side-effects because of receptor selectivity, and it lasts longer.

A relatively minor reason from a pharmacokinetic standpoint is that diphenhydramine has a shorter effective window and blocks sites that would otherwise be occupied by longer-acting cetirizine, but even so, this isn't really a compelling reason. Taking zyrtec and benadryl simultaneously, for example, just means that circulating zyrtec would (hypothetically) fill histamine receptor sites as the diphenhydramine vacates them. If that makes sense.

We've very definitely used zyrtec as a fast-acting add-on therapeutic-- and come to that, so has our allergist right in front of us. Mostly, we use benadryl that way since we all use cetirizine as our first line agent.


But the dosing window for both is very wide. The safety profile of the first gen antihistamines like benadryl is not as good as it is for zyrtec, though, due to CNS depression.

So that probably goes into a lot more detail than anyone cares about, but my ultimate answer is "why on earth would anyone choose to use diphenhydramine as a FIRST agent when second-gen antihistamines exist?" In other words, I'd expect it to be a rather unusual set of circumstances to begin with, where one would be in a position to do benadryl THEN zyrtec. But there's no compelling pharmacological reason why it's unsafe or ineffective. Well, you might lose a touch of the zyrtec to metabolism as it circulates in the bloodstream doing nothing for a few hours until some H1 sites open up-- but it's not likely to make an appreciable difference.

All of this also ignores the fact that H2 sites are mostly left untouched by zyrtec, which is another reason why adding benadryl can seem "effective" whereas adding zyrtec may seemingly make little difference.

Does that help?