## Classification of Anticholinergic Drugs by Structure **Key Point:** Anticholinergic drugs are classified as tertiary amines (lipophilic, cross BBB) or quaternary ammonium compounds (hydrophilic, do not cross BBB). ### Tertiary Amines vs. Quaternary Ammonium Compounds | Property | Tertiary Amines | Quaternary Ammonium | |----------|-----------------|--------------------| | **Lipophilicity** | Lipophilic | Hydrophilic | | **BBB Penetration** | Yes, crosses BBB | No, does not cross BBB | | **CNS Effects** | Atropine toxicity, mydriasis, cycloplegia | Minimal CNS effects | | **Examples** | Atropine, scopolamine | Ipratropium, glycopyrrolate, methscopolamine | | **GI Absorption** | Well absorbed orally | Poor oral absorption | | **Clinical Use** | Systemic effects (mydriasis, cycloplegia, antiemetic) | Inhaled/topical (bronchospasm, COPD) | **High-Yield:** Atropine is the prototypical tertiary amine anticholinergic. Its lipophilic nature allows CNS penetration, causing atropine toxicity (confusion, agitation, hallucinations, hyperthermia) at overdose. ### Why This Matters Clinically **Clinical Pearl:** Quaternary ammonium anticholinergics (ipratropium, glycopyrrolate) are preferred for inhaled/topical use because they lack CNS penetration and systemic absorption, making them safer for respiratory and ophthalmic applications. **Mnemonic:** **TAM** = **T**ertiary **A**mines cross the **M**embrane (BBB). Atropine, scopolamine are the classic examples.
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