Part 1 obgyn notes Sri Lanka
    NOTES for part 1
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    100 Bio available drugs Warfarin

    100 Bio available drugs Warfarin

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    📊 TABLE 1 — Drugs with VERY HIGH Oral Bioavailability (≈90–100%)

    (Minimal first-pass effect + near-complete absorption)

    Category
    Drugs
    Antibiotics
    Metronidazole, Linezolid, Chloramphenicol, Doxycycline, Minocycline, Clindamycin
    Antifungals
    Fluconazole, Voriconazole
    CNS – Benzodiazepines
    Diazepam, Lorazepam, Alprazolam, Clonazepam
    Antiepileptics
    Levetiracetam, Valproate, Lamotrigine
    Anticoagulant
    Warfarin
    Analgesic
    Paracetamol
    Respiratory
    Theophylline, Montelukast
    Miscellaneous (High-yield)
    Allopurinol, Pregabalin, Gabapentin, Methyldopa, Clonidine

    🔒 Exam note: These have high / near-complete oral bioavailability, but examiners usually avoid saying “absolute 100%”.

    📉 TABLE 2 — Drugs with <100% Oral Bioavailability (EXAM TRAPS)

    Reason
    Drug examples
    Key exam logic
    Extensive first-pass hepatic metabolism
    Propranolol, Metoprolol, Verapamil, Morphine, Lidocaine
    Large fraction metabolised before reaching systemic circulation
    Incomplete / variable absorption
    Digoxin, Furosemide, Acyclovir
    Poor solubility or permeability
    P-glycoprotein efflux
    Digoxin, Cyclosporine, Rivaroxaban
    Drug pumped back into gut lumen
    Degradation in stomach / intestine
    Penicillin G, Erythromycin (base), Insulin
    Acid or enzymatic destruction
    Food interaction reduces absorption
    Levothyroxine, Alendronate, Tetracyclines
    Chelation or binding with food
    Presystemic gut wall metabolism (CYP3A4)
    Midazolam, Cyclosporine
    Intestinal metabolism before liver
    High polarity / large molecule
    Heparin, LMWH
    Cannot cross intestinal epithelium
    Chemical instability
    Nitroglycerin
    Rapid degradation → very low oral BA