Natural Products as Leads: Neuromuscular blockers and antimalarials MCQs With Answer

Introduction: Natural products have historically provided foundational scaffolds for many clinically important drugs. This quiz focuses on natural-product-derived neuromuscular blockers and antimalarials—key topics in the M.Pharm curriculum. You will encounter questions spanning botanical sources, chemical features, mechanisms of action, resistance mechanisms, pharmacology, adverse effects, and semi-synthetic derivatives. Emphasis is placed on deeper understanding: how unique structural motifs such as the benzylisoquinoline and endoperoxide influence activity, how parasite biology drives drug design, and why natural compounds remain critical leads for new therapeutics. These MCQs will test both factual recall and applied reasoning relevant to drug development and clinical pharmacy.

Q1. Which plant is the primary historical source of d-tubocurarine, the classical neuromuscular blocking alkaloid used as a lead compound?

• Rauvolfia serpentina
• Chondrodendron tomentosum
• Atropa belladonna
• Taxus brevifolia

Correct Answer: Chondrodendron tomentosum

Q2. What is the principal mechanism of action of non-depolarizing neuromuscular blockers like d-tubocurarine at the neuromuscular junction?

• Irreversible inhibition of acetylcholinesterase
• Competitive antagonism of nicotinic acetylcholine receptors
• Activation of presynaptic muscarinic receptors to inhibit ACh release
• Depolarization and sustained opening of nicotinic ion channels

Correct Answer: Competitive antagonism of nicotinic acetylcholine receptors

Q3. Succinylcholine is classified as a depolarizing neuromuscular blocker. Which statement best describes its action?

• It blocks ACh release from motor nerve terminals.
• It binds and permanently inactivates nicotinic receptors.
• It mimics ACh causing prolonged depolarization and receptor desensitization.
• It increases acetylcholinesterase activity, reducing ACh levels.

Correct Answer: It mimics ACh causing prolonged depolarization and receptor desensitization.

Q4. d-Tubocurarine belongs to which alkaloid structural class, important for SAR of neuromuscular blockers?

• Benzylisoquinoline alkaloids
• Tropane alkaloids
• Indole alkaloids
• Quinoline alkaloids

Correct Answer: Benzylisoquinoline alkaloids

Q5. Which drug is commonly used clinically to reverse a non-depolarizing neuromuscular blockade by increasing synaptic acetylcholine?

• Neostigmine
• Succinylcholine
• Pancuronium
• Atropine

Correct Answer: Neostigmine

Q6. Which adverse effect is particularly associated with d-tubocurarine due to non-specific mast cell activation?

• Renal vasoconstriction
• Histamine release causing hypotension and bronchospasm
• Severe cholinergic crisis with salivation
• Prolonged QT interval leading to arrhythmia

Correct Answer: Histamine release causing hypotension and bronchospasm

Q7. Artemisinin, a fast-acting antimalarial, was isolated from which traditional medicinal plant?

• Cinchona officinalis
• Artemisia annua
• Azadirachta indica
• Berberis vulgaris

Correct Answer: Artemisia annua

Q8. What unique chemical moiety in artemisinin is essential for its antimalarial activity?

• A quinoline ring
• An endoperoxide (1,2,4-trioxane) bridge
• A tropane bicyclic core
• An α,β-unsaturated ketone

Correct Answer: An endoperoxide (1,2,4-trioxane) bridge

Q9. How is artemisinin believed to be activated inside Plasmodium-infected red blood cells to exert cytotoxic effects?

• By CYP450-mediated hydroxylation in hepatocytes
• Reductive cleavage by heme iron (Fe2+) releasing free radicals
• Direct inhibition of DNA gyrase
• Competitive inhibition of folate synthesis enzymes

Correct Answer: Reductive cleavage by heme iron (Fe2+) releasing free radicals

Q10. Which antimalarial drug primarily acts by inhibiting heme polymerization (hemozoin formation) in the parasite’s digestive vacuole?

• Mefloquine
• Primaquine
• Chloroquine
• Artesunate

Correct Answer: Chloroquine

Q11. Resistance to chloroquine in Plasmodium falciparum is most commonly associated with mutations in which parasite protein?

• PfMDR1 (multidrug resistance protein 1)
• PfCRT (chloroquine resistance transporter)
• PfKelch13
• PfDHFR (dihydrofolate reductase)

Correct Answer: PfCRT (chloroquine resistance transporter)

Q12. Quinine, an early antimalarial natural product, is obtained from the bark of which genus?

• Salvia
• Cinchona
• Artemisia
• Ginkgo

Correct Answer: Cinchona

Q13. “Cinchonism” associated with quinine/quinidine overdose commonly includes which symptom?

• Severe hyperglycemia
• Tinnitus and hearing impairment
• Renal tubular necrosis
• Excessive salivation and lacrimation

Correct Answer: Tinnitus and hearing impairment

Q14. Why are artemisinin-based combination therapies (ACTs) recommended over artemisinin monotherapy?

• ACTs are less expensive than monotherapy
• Combination therapy extends the half-life of artemisinin by chemical stabilization
• Partner drugs reduce risk of resistance by eliminating residual parasites after artemisinin’s rapid kill
• Artemisinin is inactive unless co-administered with quinoline drugs

Correct Answer: Partner drugs reduce risk of resistance by eliminating residual parasites after artemisinin’s rapid kill

Q15. Which proposed molecular target in Plasmodium has been suggested for artemisinin action by covalent modification following activation?

• PfATP6 (a SERCA-type calcium ATPase)
• DHPS (dihydropteroate synthase)
• 20S proteasome subunit beta
• Ribosomal 30S subunit

Correct Answer: PfATP6 (a SERCA-type calcium ATPase)

Q16. Which of the following is a commonly used semi-synthetic derivative of artemisinin developed for improved solubility and clinical use?

• Artesunate
• Chloroquine phosphate
• Primaquine diphosphate
• Quinacrine

Correct Answer: Artesunate

Q17. Which antimalarial drug is well known to cause hemolysis in patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency?

• Chloroquine
• Primaquine
• Mefloquine
• Artesunate

Correct Answer: Primaquine

Q18. In quinoline antimalarials, which structural feature contributes most to selective accumulation in the acidic digestive vacuole of the parasite?

• Hydrophobic polycyclic core
• Primary alcohol group
• Basic side chain that becomes protonated in acidic environment
• Terminal ester functionality rapidly hydrolyzed by esterases

Correct Answer: Basic side chain that becomes protonated in acidic environment

Q19. Historically, why were natural neuromuscular blockers like curare valuable leads for perioperative medicine?

• They provided reversible inhibition of muscarinic receptors to reduce secretions.
• They produced predictable skeletal muscle relaxation by blocking nicotinic receptors, facilitating intubation and surgery.
• They enhanced opioid analgesia through central nervous system potentiation.
• They acted as local anesthetics when injected peripherally.

Correct Answer: They produced predictable skeletal muscle relaxation by blocking nicotinic receptors, facilitating intubation and surgery.

Q20. What is a key advantage of exploring natural products as leads for drugs such as neuromuscular blockers and antimalarials?

• Natural products are always less toxic than synthetic compounds
• They provide complex, biologically prevalidated scaffolds and unique chemical functionality for optimization
• They eliminate the need for medicinal chemistry optimization
• They always have superior oral bioavailability

Correct Answer: They provide complex, biologically prevalidated scaffolds and unique chemical functionality for optimization

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