General Pharmacology — MCQs

General Pharmacology Indian Medical PG Practice Questions and MCQs

Question 651: Therapeutic index of a drug is an indicator of its:

A. Effectiveness
B. Adverse Effects
C. Therapeutic Effect
D. Safety Profile (Correct Answer)

Explanation: ***Safety Profile*** - The **therapeutic index (TI)** is a ratio that compares the dose of a drug that produces a **toxic effect** to the dose that produces a **therapeutically desired effect**. - A higher therapeutic index generally indicates a **safer drug**, as it means a larger dose is required to cause toxic effects compared to the therapeutic dose. *Effectiveness* - While related to efficacy, effectiveness usually refers to how well a drug works in **real-world clinical practice**, not directly measured by the therapeutic index. - The therapeutic index focuses on the **margin between efficacy and toxicity**, rather than just the degree of positive response. *Adverse Effects* - The **therapeutic index** considers the toxic dose, which leads to adverse effects, but it's a measure of the **margin of safety**, not just the presence or absence of adverse effects. - It quantifies the **risk of adverse effects** relative to the therapeutic benefit, rather than simply listing or describing them. *Therapeutic Effect* - The **therapeutic index** incorporates the dose required for a therapeutic effect, but its primary purpose is to assess the **risk of toxicity** in relation to that therapeutic effect. - It's a measure of the **balance between benefit and harm**, not solely the therapeutic benefit itself.

Question 652: Which of the following is NOT a primary function of histamine antagonists as a drug class?

A. Antipruritic
B. Sedation
C. Inhibition of gastric acid secretion
D. Antivertigo (Correct Answer)

Explanation: ***Antivertigo*** - While some first-generation **H1-antihistamines** like dimenhydrinate and meclizine have **antivertigo** properties due to their anticholinergic and sedative effects, this is a specific *effect* of certain histamine antagonists, not a general *function* that all antagonists exhibit. - The question asks for an exception to the *general functions* of histamine antagonists. **Antivertigo** is not a primary, universal effect of histamine antagonism in the way the other options describe. *Antipruritic* - **H1-antihistamines** block the action of **histamine** on **H1 receptors**, which are involved in mediating itching (**pruritus**). - This is a common and primary function of **H1-antagonists** in treating allergic reactions and skin conditions. *Sedation* - First-generation **H1-antihistamines** readily cross the **blood-brain barrier** and block **H1 receptors** in the brain, leading to drowsiness and **sedation**. - This is a well-known side effect and, in some cases, a therapeutic use of these drugs. *Inhibition of gastric acid secretion* - **H2-antihistamines** (e.g., ranitidine, cimetidine) specifically block **histamine H2 receptors** on **parietal cells** in the stomach, thereby reducing **gastric acid secretion**. - This is a primary function of a distinct class of histamine antagonists used to treat acid-related disorders.

Question 653: What is the chemical name for the drug heroin?

A. Morphine
B. Codeine
C. Opium
D. Diacetylmorphine (Correct Answer)

Explanation: ***Diacetylmorphine*** - **Diacetylmorphine** is the chemical name for **heroin**, synthesized by acetylating **morphine**. - This chemical alteration makes it more **lipophilic**, allowing it to cross the **blood-brain barrier** more quickly and produce a more intense effect. *Morphine* - **Morphine** is a naturally occurring **opioid alkaloid** found in the **opium poppy**. - While heroin is derived from morphine, it is a chemically altered substance, not simply morphine itself. *Codeine* - **Codeine** is another naturally occurring **opioid alkaloid** in the opium poppy, but it is less potent than morphine. - It is often used as a **cough suppressant** and for mild to moderate pain relief. *Opium* - **Opium** is the dried latex obtained from the opium poppy (**Papaver somniferum**), containing various alkaloids, including **morphine** and **codeine**. - It is not a single chemical compound but a mixture of substances from which opioids are derived.

Question 654: Granisetron is classified as a:

A. Dopamine antagonist
B. 5HT3 antagonist (Correct Answer)
C. 5HT2 antagonist
D. 5HT3 receptor agonist

Explanation: ***5HT3 antagonist*** - **Granisetron** is a highly selective **5-hydroxytryptamine type 3 (5HT3) receptor antagonist**. - It is primarily used to prevent and treat **chemotherapy-induced nausea and vomiting (CINV)** and **postoperative nausea and vomiting (PONV)**. *5HT2 antagonist* - While 5HT2 receptors are involved in various physiological processes, granisetron does not primarily act on these receptors. - Examples of **5HT2 antagonists** include agents like mirtazapine, which has antidepressant and antiemetic properties via other mechanisms. *Dopamine antagonist* - **Dopamine antagonists** (e.g., metoclopramide) primarily block dopamine D2 receptors and are also used as antiemetics. - Granisetron's primary mechanism of action is distinct from dopamine receptor blockade. *5HT3 receptor agonist* - An **agonist** would activate the 5HT3 receptor, which would likely *promote* nausea and vomiting, counteracting the intended therapeutic effect of granisetron. - Granisetron's antiemetic action is due to its ability to *block* these receptors.

Question 655: Which of the following statements about ramelteon is false?

A. Is a substrate of CYP1A2
B. Approved for treatment of insomnia
C. Has high addiction liability (Correct Answer)
D. Agonist at MT1 and MT2 receptors

Explanation: ***Has high addiction liability*** - Ramelteon is a **melatonin receptor agonist** that does not bind to GABA receptors, distinguishing it from benzodiazepines and Z-drugs (zolpidem, eszopiclone, zaleplon). - Its mechanism of action leads to a **very low risk of abuse and dependence**, contrary to the statement. *Is a substrate of CYP1A2* - Ramelteon is extensively metabolized in the liver, primarily by **CYP1A2**, which is accurate. - This metabolic pathway can lead to drug interactions if co-administered with **CYP1A2 inhibitors** (e.g., fluvoxamine), which can significantly increase ramelteon concentrations. *Approved for treatment of insomnia* - Ramelteon is indeed indicated for the **treatment of insomnia**, particularly for difficulties with **sleep onset**. - It works by mimicking the action of **melatonin**, promoting the regulation of the sleep-wake cycle. *Agonist at MT1 and MT2 receptors* - Ramelteon acts as a **selective agonist** at the **melatonin MT1 and MT2 receptors** in the suprachiasmatic nucleus. - Activation of these receptors helps to modulate the **circadian rhythm**, thereby promoting sleep.

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