Review of Pharmacology - 9E (2015)

Review of Pharmacology
9. Ans. (a) Barbiturates (Ref: KDT 7/e p29)
For acidic drug poisonings (like barbiturates, salicylates and methotrexate), urinary alkalinizing agents are prescribed
whereas for basic drug poisonings, (morphine, amphetamine, atropine etc.) urinary acidifying agents are administered.
10. Ans. (c) Cytochrome oxidase (Ref: Katzung 11/e p55)
• Drugs can be metabolized by cytochrome P450 dependent oxidations and cytochrome P450 independent
oxidations (i.e., by monooxygenases)
• NADPH cytochrome P450 reductase is same as flavin monooxygenase
• Cytochrome oxidase is involved in respiratory chain and not in drug metabolism.
• CYP3A4 is responsible for the metabolism of 50% of prescription drugs metabolised by the liver.
11. Ans. (a) Clopidogrel (Ref: KDT 6/e p609, 610)
• ADP receptor antagonists, ticlopidine and clopidogrel are prodrugs.
12. Ans. (a) Is excreted mainly by the kidneys (Ref: KDT 7/e p29)
Ionized molecules cannot cross the biological membranes. Therefore, these are less likely to be absorbed. Entry of these
molecules through blood brain barrier and blood placental barrier is also restricted. These drugs cannot be reabsorbed in
the nephron, thus are excreted by the kidneys.
13. Ans. (b) Small changes of pH near the pKa of a weak acidic drug will not affect its degree of ionization
(Ref: Katzung 11/e p9, 11)
General Pharmacology
• pKa is the pH at which half of the drug is in the ionized form. There is maximum variation
in the ionization of a drug at pH near its pKa value.
• Phenobarbitone is an acidic drug having pKa of 7.2. Therefore, at pH = 7.2, 50% of drug
is ionized and 50% un-ionized. In acidic medium, more of it will be unionized (because
it is acidic in nature). In plasma (pH = 7.4), more will be ionized (60%) and less (40%)
un-ionized.
14. Ans. (c) Low oral bioavailability always and necessarily mean poor absorption (Ref: Katzung 11/e p43-44; KDT 6/e p17)
• Low oral bioavailability can also be due to high first pass metabolism. For detail see text.
15. Ans. (b) Salicylates (Ref: Katzung 11/e p1019)
Salicylates stay in the blood whereas digoxin, diazepam and organophosphates are distributed widely.
16. Ans. (d) Binding sites are non specific and one drug can displace the other (Ref: Katzung 10/e p47, 48)
• Acidic drugs bind to albumin whereas basic drugs bind to α 1
acid glycoprotein.
• It is the free form of the drug that is metabolized or excreted. Bound form is not available for either metabolism
or excretion.
• Many drugs can bind to the same plasma protein binding site resulting in the displacement reactions.
• When plasma concentration increases, both free as well as bound drug will increase in plasma.
17. Ans. (b) Morphine (Ref: Katzung 12/e p39-40)
All drugs listed in the options are highly plasma protein bound (>90%) whereas morphine has only 35% binding to plasma
proteins.
18. Ans. (a) Active transport; (b) Passive transport (Ref: KDT 7/e p11-13)
Drugs are transported across the membranes by:
(a) Passive diffusion and filtration
(b) Specialized transport
Specialized transports are of two types:
1. Active transport
2. Facilitated diffusion
19. Ans. All (Ref: KDT 7/e p20, 30-33)
• High protein binding of a drug make it restricted to vascular compartment and thus has tendency to lower volume of
distribution. It behaves as a long acting drug as bound fraction is not available for metabolism or excretion.
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