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Greek Pharmacist License study materials
Greek Pharmacist License study resources

Greek Pharmacist License: Pharmacology and Toxicology

Greek Pharmacist License · Work through your exam, one topic at a time.

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Pharmacology and Toxicology

Pharmacology and toxicology tests receptor theory, quantitative pharmacokinetics, drug interactions and the recognition and management of poisoning. Numerical items on loading dose, clearance and half-life are common, as are antidote-matching questions.

Receptor pharmacology

  • Kd describes affinity (the concentration occupying half the receptors); EC50 describes potency; Emax describes efficacy.
  • A full agonist produces the maximal response, a partial agonist a submaximal response even at full occupancy, and an inverse agonist reduces constitutive activity.
  • Competitive antagonism shifts the dose-response curve right in parallel with unchanged Emax; non-competitive antagonism depresses Emax.
  • Spare receptors mean that EC50 can be far below Kd; this matters when comparing potency with binding affinity.

Pharmacokinetics

  • First-order elimination: t½ = 0.693 × Vd / CL. Zero-order kinetics occur with phenytoin, ethanol and high-dose salicylates.
  • Vd = dose/C₀ after an IV bolus. Loading dose = (Vd × target concentration)/F; maintenance rate = CL × Css/F.
  • Bioavailability is reduced by first-pass metabolism and by efflux transport (P-glycoprotein).
  • Inducers: rifampicin, carbamazepine, phenytoin, St John's wort, smoking. Inhibitors: ketoconazole, clarithromycin, ritonavir, grapefruit juice, cimetidine.

Toxicology and antidotes

  • Paracetamol: N-acetylcysteine, guided by the Rumack–Matthew nomogram from the 4-hour level.
  • Opioids: naloxone. Benzodiazepines: flumazenil, avoided in mixed overdose with tricyclics or in chronic benzodiazepine use.
  • Organophosphates: atropine for muscarinic effects plus pralidoxime for the enzyme.
  • Methanol and ethylene glycol: fomepizole or ethanol; iron: deferoxamine; warfarin: vitamin K₁ plus prothrombin complex concentrate; digoxin: digoxin-specific Fab fragments; carbon monoxide: 100% oxygen; cyanide: hydroxocobalamin.
  • Narrow therapeutic index drugs: digoxin, lithium, warfarin, phenytoin, theophylline, aminoglycosides, ciclosporin.

Worked example

A 70 kg patient needs a loading dose of a drug with Vd 0.5 L/kg and a target concentration of 4 mg/L; F = 1. Vd = 0.5 × 70 = 35 L. Loading dose = 35 L × 4 mg/L = 140 mg. If clearance is 3 L/h, the maintenance infusion is 3 × 4 = 12 mg/h. Reasoning shown: loading dose fills the volume of distribution, maintenance replaces what clearance removes; the two use different parameters and must not be confused.

Traps that cost marks

Assuming a prolonged half-life always means reduced clearance (it may reflect a larger Vd); using flumazenil in tricyclic co-ingestion; forgetting that activated charcoal is time-limited and contraindicated in unprotected airway or corrosives; confusing potency with efficacy.