Metabolism of psychotropic drugs include phase 1 and phase 2 reactions. All of the following are phase 2 reactions except:
C. Oxidation is not a phase 2 reaction—it is a phase 1 reaction. Various types of phase 2 reactions include glucuronidation, acetylation, sulfation, and glutathione conjugation. Hydrolysis and hydroxylation are considered to be other phase 1 reactions.
Reference:
Breastfeeding is contraindicated when certain psychotropics are administered. The characteristic features of such psychotropics that are secreted in breast milk include all except:
B. Most prescribed drugs transfer into breast milk except very large molecules such as heparin and insulin, but the amount transferred is negligent for most drugs. The mechanism of transfer is passive diffusion through the lipid cell membrane of the lactating glands. Factors such as low plasma protein binding and high lipid solubility aid a drug in reaching high concentrations in breast milk. As milk is slightly more acidic than plasma, weakly basic drugs transfer more readily into breast milk, become ionized in the acid medium, and so get ‘trapped’. Unionized molecules cross biological membranes more easily than charged particles (ions). If a breastfeeding mother must take psychotropics and the drug is a relatively safe one, it is recommended that the drug is taken 30–60 minutes after nursing and 3–4 hours before the next feed, if possible.
A 25-year-old postgraduate student is suffering from initial insomnia during his fi nal year of study. He is asking for a hypnotic that will cause least disturbance to his sleep architecture. The best choice is:
C. Zolpidem is a non-benzodiazepine hypnotic of the imidazopyridine class. It is rapidly absorbed and has a short elimination half-life (mean 2.5 hours). It decreases sleep-onset latency, reduces disruptive midnight awakenings but has less consistent effects on total sleep time. It does not affect the REM distribution and unlike benzodiazepines, which increase stage 2 NREM at the expense of deep sleep NREM, zolpidem does not increase stage 2. It is unclear if zolpidem produces clinically significant rebound as yet but dependence is thought to be low compared to other hypnotics.
Selegiline is used as an antiparkinsonian agent. Its mechanism of action is:
E. Two types of monoamine oxidase have been recognized: monoamine oxidase A predominantly metabolizes norepinephrine and serotonin; monoamine oxidase B predominantly metabolizes dopamine. Selegiline is a selective inhibitor of monoamine oxidase B that retards the breakdown of dopamine and so it prolongs the anti-parkinsonism effect of levodopa as an adjunctive therapy for patients with fluctuating response to levodopa. Some studies have found it to be effective for treating depression but only at very high doses at which selective MAO-B inhibition effect is taken over by non-specific inhibition.
Which of the following antidepressants is most selectively serotonergic?
C. Citalopram (and escitalopram) is the most selective inhibitor of serotonin reuptake, with negligible effects on the reuptake of other monoamines such as norepinephrine or dopamine. It does not have any clinically significant effect on histaminergic, GABAergic, or acetylcholinergic transmission. Paroxetine has clinically significant anticholinergic activity. Fluoxetine weakly inhibits norepinephrine reuptake and binds to 5-HT2C receptors. Sertraline weakly inhibits both norepinephrine and dopamine reuptake, without any additional clinical advantage.
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