Foundational Biomedical Sciences Knowledge Base
Foundational Biomedical Sciences Knowledge Base tests the physiology, pathophysiology, pharmacology, microbiology, biochemistry, genetics, and anatomy that explain management rather than stand alone. Level 3 items embed a basic science fact inside a clinical stem, so the science must be usable at the bedside.
Pharmacokinetics and interactions
- First-order elimination removes a constant fraction per unit time; half-life is 0.693 times volume of distribution divided by clearance, and steady state is reached after four to five half-lives.
- Zero-order drugs (phenytoin, ethanol, high-dose salicylate) eliminate a constant amount, so small dose increases raise levels disproportionately.
- CYP inducers: rifampin, carbamazepine, phenytoin, phenobarbital, St John's wort. Inhibitors: macrolides, azole antifungals, cimetidine, grapefruit, valproate, ritonavir.
- Prodrugs needing activation: clopidogrel via CYP2C19, codeine via CYP2D6.
Acid-base
Anion gap equals sodium minus chloride plus bicarbonate, normal 8-12. Winter's formula: expected pCO2 equals 1.5 times bicarbonate plus 8, plus or minus 2. Delta-delta is (anion gap minus 12) divided by (24 minus bicarbonate): about 1 indicates a pure high-gap acidosis, below 1 a coexisting non-gap acidosis, and above 2 a coexisting metabolic alkalosis.
Microbiology
Staphylococcus aureus is catalase and coagulase positive in clusters; Streptococcus pyogenes is bacitracin sensitive and beta-hemolytic; pneumococcus is a lancet-shaped diplococcus that is optochin sensitive. Gram-negative endotoxin (lipid A) drives the cytokine cascade of septic shock.
Physiology and genetics
Oxygen delivery equals cardiac output times 1.34 times hemoglobin times arterial saturation; the Fick principle relates consumption to arteriovenous difference. Autosomal dominant disease carries 50% recurrence risk, autosomal recessive 25%, X-linked shows no male-to-male transmission, and mitochondrial disease is maternally inherited.
Worked example
pH 7.30, pCO2 30, bicarbonate 14, sodium 138, chloride 100. The anion gap is 24, so this is a high-gap metabolic acidosis. Winter's formula predicts a pCO2 of 29 plus or minus 2, so 30 represents appropriate respiratory compensation. Delta-delta is 12/10, or 1.2, consistent with a pure high-gap acidosis. The differential includes ketones, lactate, uremia, and toxins.
Traps
Assuming a normal pH excludes serious acid-base disease. Forgetting that the anion gap must be corrected for hypoalbuminemia (add 2.5 per 1 g/dL below 4). Confusing clearance with half-life, and missing enzyme induction that lowers drug levels.