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Chapter 12 principles of pharmacology Questions
Question 1 of 5
The following drugs cause their primary pharmacodynamic effect via non-receptor mediated mechanisms:
Correct Answer: B
Rationale: Mannitol (B) acts via osmotic diuresis, increasing urine volume without receptor binding, used in cerebral edema. Magnesium trisilicate (A) neutralizes gastric acid chemically, also correct but B is selected. Methotrexate (C) inhibits DHFR, an enzyme. Dimercaprol (D) chelates metals, non-receptor mediated too. Sumatriptan (original E) is a 5-HTâ‚ agonist. Non-receptor mechanisms, like mannitol's osmotic effect, bypass traditional signaling, critical in emergencies for rapid, physical action, contrasting receptor-based drugs in pharmacology.
Question 2 of 5
The systemic bioavailability of the following oral drugs is increased if taken in the fasting state:
Correct Answer: A
Rationale: Oxytetracycline (A) has increased bioavailability fasting, as food (e.g., calcium) chelates it, reducing absorption. Amoxicillin (B) is unaffected. Levodopa (C) competes with dietary amino acids, correct but A is chosen. Acetylsalicylic acid (D) and fluconazole (original E) are minimally impacted. Fasting enhances tetracycline uptake, critical in antibiotic therapy, avoiding food interactions that lower efficacy, a practical dosing consideration.
Question 3 of 5
The following are substrates for CYP3A:
Correct Answer: A
Rationale: Ciclosporin (A) is a CYP3A substrate, metabolized in the liver, affecting its immunosuppressive levels (e.g., transplant therapy). Clarithromycin (B) is too, also correct but A is chosen. Phenytoin (C) uses CYP2C9. Adrenaline (D) is COMT/MAO-metabolized. Warfarin (original E) is CYP2C9. CYP3A's broad substrate range, critical in drug interactions (e.g., with grapefruit juice), shapes ciclosporin's pharmacokinetics, necessitating monitoring.
Question 4 of 5
In severe renal failure:
Correct Answer: D
Rationale: Smaller digoxin doses are required in severe renal failure (D), as its renal clearance (GFR <10 mL/min) drops, prolonging half-life, risking toxicity. Option A is false (pH may rise). Option B is incorrect (phenytoin range adjusts minimally). Option C lacks evidence. Option E (original) about omeprazole is false. Digoxin's renal dependence, critical in heart failure, necessitates adjustment, a key pharmacokinetic shift in renal impairment.
Question 5 of 5
Important factor/s which may govern diffusion of drugs across cell membranes
Correct Answer: D
Rationale: Diffusion across membranes depends on pKa (ionization state), pH (proportion of non-ionized form via Henderson-Hasselbalch), and lipid solubility (membrane permeability). Molecular weight also influences diffusion but isn't listed. A, B, and C are individually correct, but D (‘All of the above') is the most complete answer, encompassing all key factors. This reflects how physicochemical properties dictate drug movement, critical for pharmacokinetics and drug design.