Review of Pharmacology - 9E (2015)

Autacoids
56. Ans. (c) Cyclooxygenase (Ref: Katzung 10/e p554; KDT 6/e p185)
• Aspirin is an NSAID and acts by irreversible inhibition of cyclooxygenase enzyme that decreases the formation of
prostaglandins.
57. Ans. (a) Bleeding time (Ref: Harrison’s 16/e p341 and KDT 6/e p609)
• Antiplatelet drugs (like aspirin and clopidogrel) prolong the bleeding time.
• Anticoagulant drugs prolong the clotting time.
• Drugs interfering with intrinsic pathway (like heparin) prolong the aPTT.
• Drugs interfering with extrinsic pathway (like warfarin) prolong the PT.
• Thrombin time is prolonged in cases of afibrinogenemia and dysfibrinogenemia.
58. Ans. (a) Prostaglandin E 1
analogue (Ref: KDT 6/e p181)
Natural prostaglandin in body is PGE 2
whereas misoprostol and alprostadil are synthetic PGs which are PGE 1
analogs.
59. Ans. (c) COX-1 is an inducible enzyme (Ref: KDT 6/e p185)
COX-2 is inducible whereas cox-1 is a constitutional (house keeping) enzyme.
60. Ans. (d) Piroxicam (Ref: KDT, 6/e p194)
Piroxicam is a long acting analgesic due to enterohepatic circulation. Single daily dose is usually sufficient.
61. Ans. (d) Hepatotoxicity is likely to occur (Ref: KDT 6/e p198, 199)
Ingestion of 10g (ten gram) of paracetamol will result in acute poisoning. Chances of death and fulminant hepatic failure
are high if the plasma levels are above the line joining 200 µg/ml at 4 hours and 30µg/ml at 15 hours. Gastric lavage and
activated charcoal at 6 hours will not be effective because most of the drug would have been absorbed by this time.
62. Ans. (c) PGE 2
has marked oxytocic action while PGF 2a
has tocolytic action (Ref: KDT 6/e p181)
• PGE 2
mainly causes softening of cervix and is utilized for cervical ripening whereas PGF 2a
is an oxytocic agent and
can be utilized for the induction of abortion.
63. Ans. (c) Primary pulmonary hypertension (Ref: KDT 6/e p180, 182)
PGI 2
analogs (like epoprostenol and treprostinil) are used for treatment of pulmonary hypertension. PGE 1
analogs are
used for first trimester abortion (misoprostol), impotence (alprostadil) and maintenance of the patency of ductus arteriosus
(alprostadil).
64. Ans. (a) It is formed in platelets; (b) It is formed from PGG 2
/H 2;
(c) It is prothrombotic; (e) Aspirin can inhibit its production
(Ref: KDT 6/e p174)
• TXA 2
is produced inside the platelets with the help of TXA 2
synthetase.
• It is formed from cyclic endoperoxides (PGG 2
/H 2
) with the help of an enzyme, cyclooxygenase.
• Aspirin inhibits its production by irreversible inhibition of cyclooxygenase enzyme.
• TXA 2
causes aggregation of platelets, therefore is prothrombotic.
65. Ans. (a) Tinnitus is an early symptom; (b) 10-30 g causes poisoning (Ref: KDT 6/e p189-190; Washington Mannual of Medical
Therapeutics, 31/e p586)
General Autacoids Pharmacology
• Symptoms of aspirin poisoning
––
At anti-inflammatory dose (3-6 gm/day) produces the syndrome called Salicylism comprising of dizziness, tinnitus,
vertigo, excitement, mental confusion, reversible impairment of hearing.
––
The dose has to be titrated to one which is just below that produces these symptoms, tinnitus is a good
guide.
––
Metabolic acidosis, hyperthermia and acidotic breathing are seen in severe poisoning
––
Aspirin causes platelet dysfunction by inhibiting cyclooxygenase pathway.
––
Fatal dose in adult is 15-30 g but considerably lower in children.
66. Ans. (a) Aspirin; (b) Indomethacin; (e) Diclofenac (Ref: KDT 6/e p187, 193, 195)
• Aspirin inhibits COX irreversibly by acetylating one of its serine residues; return of COX activity depends on synthesis
of fresh enzyme. Other NSAIDS like indomethacin, diclofenac etc are competitive and reversible inhibitors of
COX, return of activity depends on their dissociation from the enzyme which is turn is governed by the pharmacokinetic
characteristics of the compound.
• Corticosteroids like betamethasone act by inhibiting phospholipase A 2
.
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