## Distinguishing Propranolol from Atenolol ### Lipophilicity: The Key Discriminator **Key Point:** Propranolol is highly lipophilic (fat-soluble), whereas atenolol is hydrophilic (water-soluble). This structural difference has profound clinical consequences. ### Clinical Implications of Lipophilicity | Property | Propranolol | Atenolol | |----------|-------------|----------| | **Lipophilicity** | High | Low | | **CNS penetration** | Crosses BBB readily | Minimal BBB crossing | | **CNS side effects** | Nightmares, depression, fatigue | Rare | | **Metabolism** | Hepatic (first-pass) | Renal excretion | | **Cardioselectivity** | Non-selective (β1 + β2) | Selective (β1) | | **IAS** | None | None | **High-Yield:** Propranolol's lipophilicity causes it to accumulate in the brain, leading to CNS adverse effects (insomnia, vivid nightmares, depression, cognitive impairment). This is the most clinically relevant distinguishing feature and a common NEET PG trap. ### Clinical Pearl **Clinical Pearl:** Patients on propranolol frequently report neuropsychiatric symptoms (nightmares, mood changes, fatigue) due to central β-adrenergic blockade. Atenolol, being hydrophilic, does not cross the blood–brain barrier significantly and thus avoids these CNS effects — making it preferred in patients with depression or sleep disorders. ### Why Lipophilicity Matters 1. **CNS penetration** → propranolol reaches brain tissue; atenolol does not 2. **Neuropsychiatric toxicity** → propranolol causes nightmares, depression; atenolol does not 3. **Drug interactions** → propranolol undergoes hepatic metabolism (CYP450); atenolol is renally excreted 4. **Patient tolerance** → lipophilicity is the primary reason some patients switch from propranolol to atenolol [cite:KD Tripathi 8e Ch 12]
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