Which of the following medications is NOT associated with zero-order kinetics?
E. Zero-order kinetics occurs when the body metabolizes a constant amount of the drug. The metabolic pathway is rapidly saturated, leading to a limit being set for drug elimination. So only a constant amount of drug is eliminated irrespective of plasma levels, for example our body can metabolize around 1 unit of alcohol per hour; if you have taken 4 units, it will take 4 hours for the alcohol to get out of your system. So the time taken is directly proportional to the amount consumed, unlike in first-order kinetics where it takes four to fi ve half-lives for the drug to get out of the system, irrespective of the dose consumed. The most important difference to remember is that a constant fraction (percentage) is eliminated in first-order kinetics while a constant amount is eliminated in zero-order kinetics.
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In which of the following situations is a measurement of plasma concentration of a drug the least valuable?
A. Measurement of plasma level is not routinely done for most of the available psychotropic medications. But it is useful, and often indicated, when there is a therapeutic window, suspected drug interactions, unusual toxic reaction at therapeutic doses, and non-response to treatment in spite of administering adequate dose. Therapeutic window is a range of plasma concentration within which a drug produces the therapeutic response. If the level of drug is outside the defined ‘window’, the therapeutic response is inadequate. Therapeutic index is a ratio of median toxic dose to median effective dose of a drug. Failure to respond to treatment may be due to noncompliance, which can be detected in some cases by measuring the plasma levels.
The most probable diagnosis in a clozapine-treated patient who has persistent tachycardia, fatigue, fever, and eosinophilia is:
D. Myocarditis is a fatal complication of clozapine use. It can occur very subtly with observable signs developing well after cardiac failure sets in. This is an idiosyncratic, eosinophilic inflammation of the myocardium. Persistent tachycardia, fever (flu like), chest pain, palpitations, dependent oedema, and signs of heart failure must prompt a detailed investigation, including cardiac enzymes (elevated), ECG (ST elevation), ESR (elevated), WBC (eosinophilia), and echocardiogram. With a good monitoring system in place for agranulocytosis, myocarditis is becoming a leading cause of clozapine-related fatalities.
Which of the following patients is at a higher risk of developing lithium-induced hypothyroidism?
C. It is well established that the risk of hypothyroidism related to lithium use varies widely across the population. Middle-aged women, who probably have a higher risk of having asymptomatic antithyroid antibodies before initiation of lithium, are at the maximum risk of clinical hypothyroidism (up to 20% prevalence). Importantly, this hypothyroidism does not correlate with the dose of lithium prescribed.
Which one of the following regarding mirtazapine is true? It is:
A. Mirtazapine is called a noradrenergic and specific serotonergic antidepressant (NaSSA). The therapeutic action of mirtazapine is due to central alpha 2 antagonist action, thus cutting the brakes for the release of norepinephrine (alpha 2 inhibitory autoreceptors) and serotonin (alpha 2 heteroreceptors constantly inhibit serotonin release too). Mirtazapine also acts as an antagonist at 5HT2A, 5HT2C, and 5HT3 receptors, which may contribute to the favourable side-effect profile compared to SSRIs. Mianserin acts in a similar way. Mirtazapine does not block the reuptake pump.
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