Eli5: How do antihistamines work and what is the difference between first generation and second?
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Receptors are present on our cell surface. These are naturally used to regulate normal functions.
Histamine (naturally uccoring chemical) binds to these receptors to start inflammation (swelling)
There are 3 receptors
H1. Present in smooth muscles (promotes tightening of muscle)
H2. In the stomach (increase acid production)
H3. In the brain (increases activity)
H4. Immune cells (results in inflammation)
Anti histamines block these receptors either selectively or individually. This blockade results in the opposite effect because the rest of the body’s systems are normal.
The difference between 1st and 2nd is that
1st are able to move into the brain through a barrier called blood brain barrier. Because of this they cause drowsiness while 2nd don’t.
Another fun fact is that we have H2 blockers. They are technically antihistamines but are called H2RA’s or H2 receptor antagonists (another name for blockers)
Sauce: I’m a Pharmacist.
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