Pharmacology and Pharmacotherapy
Pharmacology here rewards mechanism-to-effect reasoning and dosing arithmetic, weighted toward Mongolia's actual disease burden: hypertension and stroke, ischaemic heart disease, type 2 diabetes, chronic hepatitis B and C, tuberculosis, H. pylori–associated gastric disease, and iron-deficiency anaemia.
Core principles
- Dose–response: potency is the EC50 position, efficacy the plateau; a competitive antagonist shifts the curve right, a partial agonist lowers the plateau.
- Kinetics: first-order elimination, t½, steady state after about 4–5 half-lives; loading dose = (Vd × target concentration)/F; maintenance rate = CL × Css.
- Interactions: CYP3A4 and CYP2C9 inhibition or induction, QT prolongation, additive bleeding or hypotension.
- Antimicrobial therapy: right drug, dose and duration, with de-escalation; adherence is decisive in TB.
Worked example
A 60 kg patient needs a theophylline infusion. Vd = 0.5 L/kg, so Vd = 30 L; target 10 mg/L; F = 1. Loading dose = 30 × 10 = 300 mg. If clearance is 3 L/h, maintenance rate = 3 × 10 = 30 mg/h. Adjust for obesity (use adjusted weight for this drug) and remember smoking induces clearance.
Traps
Confusing half-life with time to steady state; using total body weight for a lipophilic drug in an obese patient; omitting renal dose adjustment; starting warfarin without bridging in acute thrombosis; shortening a TB regimen because the patient feels better.