BCSE Pharmacology and Toxicology 4 — Questions and Answers
Question 1: Fluoroquinolones exert their bactericidal effect by inhibiting which bacterial enzyme?
- DNA gyrase (topoisomerase II) and topoisomerase IV (Correct answer)
- RNA polymerase beta subunit
- Dihydropteroate synthase
- Penicillin-binding proteins
Correct answer: DNA gyrase (topoisomerase II) and topoisomerase IV
Fluoroquinolones inhibit bacterial DNA gyrase and topoisomerase IV, enzymes necessary for DNA supercoiling and decatenation, halting DNA replication and causing bacterial cell death.
Question 2: A patient on chemotherapy develops peripheral neuropathy and the Vinca alkaloid vincristine is suspected. What is the mechanism of this toxicity?
- Binding beta-tubulin and inhibiting microtubule polymerization (Correct answer)
- Alkylating DNA and preventing strand separation
- Inhibiting topoisomerase II and causing double-strand breaks
- Intercalating into DNA and blocking RNA synthesis
Correct answer: Binding beta-tubulin and inhibiting microtubule polymerization
Vincristine binds beta-tubulin dimers and prevents microtubule assembly, disrupting axonal transport in peripheral neurons, which leads to sensorimotor neuropathy.
Question 3: Which first-line drug for type 2 diabetes primarily reduces hepatic glucose production?
- Metformin (Correct answer)
- Glipizide
- Pioglitazone
- Sitagliptin
Correct answer: Metformin
Metformin activates AMP-activated protein kinase (AMPK), suppressing hepatic gluconeogenesis and glycogenolysis, thereby reducing fasting plasma glucose without causing hypoglycemia.
Question 4: Lead poisoning in children is most associated with which neurological sequela?
- Cognitive impairment and reduced IQ (Correct answer)
- Acute hemorrhagic encephalitis
- Spastic diplegia of lower extremities
- Sensorineural hearing loss
Correct answer: Cognitive impairment and reduced IQ
Chronic low-level lead exposure in children disrupts synaptic development and calcium-mediated neurotransmitter release, causing irreversible cognitive deficits and reduced IQ.
Question 5: Which antiepileptic drug acts primarily by prolonging sodium channel inactivation?
- Phenytoin (Correct answer)
- Ethosuximide
- Vigabatrin
- Gabapentin
Correct answer: Phenytoin
Phenytoin stabilizes the inactive state of voltage-gated sodium channels, reducing repetitive high-frequency neuronal firing without affecting normal baseline neuronal activity.
Question 6: A patient develops blue-gray skin discoloration, thyroid dysfunction, and pulmonary toxicity after years of antiarrhythmic therapy. Which drug is responsible?
- Amiodarone (Correct answer)
- Sotalol
- Flecainide
- Adenosine
Correct answer: Amiodarone
Amiodarone, a class III antiarrhythmic that also has class I, II, and IV properties, accumulates in tissues due to its extreme lipophilicity, causing multi-organ toxicity including thyroid, lung, liver, and skin.
Question 7: The therapeutic effect of benzodiazepines in anxiety disorders is mediated by:
- Potentiating GABA-A receptor chloride ion channel opening frequency (Correct answer)
- Directly activating GABA-B receptors and inhibiting calcium channels
- Blocking NMDA glutamate receptors
- Inhibiting serotonin reuptake at presynaptic terminals
Correct answer: Potentiating GABA-A receptor chloride ion channel opening frequency
Benzodiazepines bind allosterically to GABA-A receptors, increasing the frequency of chloride channel opening in response to GABA and enhancing inhibitory neurotransmission.
BCSE Pharmacology and Toxicology 4
Fluoroquinolones exert their bactericidal effect by inhibiting which bacterial enzyme?