Cis-atracurium is preferred over atracurium due to which of the following advantages?
Q652
Which of the following is NOT a primary function of histamine antagonists as a drug class?
Q653
What is the chemical name for the drug heroin?
Q654
Granisetron is classified as a:
Q655
Which of the following statements about ramelteon is false?
General Pharmacology Indian Medical PG Practice Questions and MCQs
Question 651: Cis-atracurium is preferred over atracurium due to which of the following advantages?
A. Rapid onset
B. No histamine release (Correct Answer)
C. Short duration of action
D. None of the options
Explanation: **No histamine release**
- **Cis-atracurium** is an isomer of atracurium that causes significantly less **histamine release**, reducing the risk of **hypotension**, **tachycardia**, and **bronchospasm**.
- This makes cis-atracurium a safer option, particularly in patients with **cardiovascular instability**, **asthma**, or known **allergies**.
*Rapid onset*
- While both atracurium and cis-atracurium have a relatively **rapid onset** compared to some other neuromuscular blockers, **cis-atracurium**'s onset is generally slightly slower than atracurium.
- Therefore, **rapid onset** is not an advantage of cis-atracurium over atracurium.
*Short duration of action*
- Both atracurium and cis-atracurium have an **intermediate duration of action**, but **cis-atracurium**'s duration is generally slightly longer than atracurium.
- A **shorter duration of action** is not a unique advantage of cis-atracurium over atracurium.
*None of the options*
- This option is incorrect because **cis-atracurium** does offer a significant advantage over atracurium, specifically its reduced potential for **histamine release**.
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.
