Review of Pharmacology - 9E (2015)

Central Nervous System
39. Ans. (b) Phenothiazine; (c) Haloperidol (Ref: KDT 6/e p431)
40. Ans. (b) Decreases formation of 3-OMD (Ref: KDT 6/e p421)
• Levo-dopa is converted to dopamine by dopa decarboxylase (that cannot cross blood brain barrier).
• Carbidopa is an inhibitor of dopa decarboxylase in the periphery. It therefore increases the amount of l-dopa
that reaches the brain (due to inhibition of peripheral metabolism to dopamine).
• Due to inhibition of l-dopa metabolism (by dopa decarboxylase), an alternative pathway of metabolism by
catechol-o-methyl transferase (COMT) is activated.
• COMT metabolizes l-dopa to 3-o-methyl dopa (3-OMD) that can complete with l-dopa for entry in the brain.
• Entacapone and tolcapone is useful in Parkinsonism by inhibiting COMT.
41. Ans. (a) Involuntary movements (Ref: KDT 6/e p419)
Carbidopa can decrease all the adverse effects of levodopa except
• Involuntary movements
• Behavioural effects
42. Ans. (a) Pramipexole (Ref: KDT 6/e p419, 420)
Directly acting D 2
receptor agonists can be
• Ergot derivatives e.g. bromocriptine and pergolide
• Non-ergot compounds e.g. pramipexole and ropinirole
43. Ans. (c) It is a cerebroselective anticholinesterase that affords symptomatic improvement in Alzheimer’s disease (Ref:
KDT 6/e p472, 473)
44. Ans. (d) All of the above (Ref: KDT 6/e p419, 420)
Pramipexole and ropinirole are newer non-ergot dopamine agonists. Now, these are first choice drugs for the treatment of
Parkinsonism (preferred over levo-dopa).
45. Ans. (d) Catechol-o-methyl transferase inhibition (Ref: KDT 6/e p415)
46. Ans. (d) Reserpine (Ref: KDT 6/e p549)
• Neurotransmitters (like dopamine, serotonin and adrenaline) are stored in the vesicles after their synthesis.
These stores of neurotransmitters are released on stimulation of the neuron. Reserpine inhibits the vesicular
transport of these neurotransmitters resulting in depletion of dopamine, serotonin and adrenaline.
• Severe depression (due to deficiency of serotonin) leading to suicidal tendencies and extrapyramidal symptoms
(due to deficiency of dopamine in the brain) are the adverse effects of this drug.
General Central Nervous Pharmacology System
47. Ans. (b) Vitamin B complex (Ref: KDT 6/e p418, 419)
• Pyridoxine is a component of vitamin B complex.
• Pyridoxine is a cofactor for the enzyme, dopa decarboxylase and therefore, administration of vitamin B complex can
stimulate the activity of this enzyme.
• Dopa decarboxylase converts levo-dopa to dopamine. Increased formation of dopamine in the periphery is undesirable
because it cannot cross blood brain barrier. Therefore, stimulation of dopa decarboxylase decreases the therapeutic
effect of l-dopa.
• If the enzyme, dopa decarboxylase is already inhibited with carbidopa, there will be no interaction with
pyridoxine.
48. Ans. (c) Vitamin B complex (Ref: KDT 6/e p418)
49. Ans. (b) Benzhexol (Ref: KDT 6/e p421)
Central anticholinergics like trihexy phenydyl (Benzhexol) are the only drugs effective in drug induced Parkinsonism.
50. Ans. (c) Pyridoxine (Ref: KDT 6/e p418)
‘Pyridoxine abolishes therapeutic effect of levodopa by enhancing peripheral decarboxylation of levodopa, less is available
to cross to the brain.
51. Ans. (a) Tacrine (Ref: KDT 6/e p472)
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