Answer: A. Stibogluconate

Explanation: Stibogluconate is the drug of choice in the treatment of kala azar (visceral leishmaniasis). It belongs to the antimonial group of compounds and has been used for decades in endemic regions despite its toxicity concerns.

Answer: A. Rifampicin

Explanation: Rifampicin is known to cause thrombocytopenia as an adverse effect in some patients. This side effect involves a reduced platelet count, which can increase the risk of bleeding and requires monitoring during therapy.

Answer: C. Nevirapine

Explanation: Nevirapine is not a nucleoside analog; it is a non-nucleoside reverse transcriptase inhibitor. In contrast, lamivudine, zidovudine, and acyclovir are examples of nucleoside analogs used in antiviral therapies.

Answer: C. Antisense oligonucleotide

Explanation: Nusinersen is an antisense oligonucleotide that modulates gene expression. It was approved by the USFDA in 2016 for the treatment of spinal muscular atrophy, marking a breakthrough in genetic therapy.

Answer: B. Antisense nucleic acids

Explanation: Antisense nucleic acids inhibit protein synthesis by binding specifically to mRNA, thereby preventing the translation process. This mechanism offers a targeted approach for antimicrobial therapy and gene regulation.

Answer: B. Carbidopa

Explanation: Carbidopa is used in combination with levodopa to inhibit its peripheral metabolism. This allows more levodopa to cross the blood–brain barrier, thereby increasing its efficacy in the treatment of Parkinson’s disease.

Answer: B. H⁺/K⁺ ATPase

Explanation: Proton pump inhibitors (PPIs) target the H⁺/K⁺ ATPase enzyme in the gastric parietal cells, reducing stomach acid secretion by blocking the final step of acid production in the stomach.

Answer: A. Ergosterol

Explanation: Amphotericin B binds to ergosterol, a component of fungal cell membranes, creating pores that lead to cell death. This mechanism underlies its potent antifungal activity and is critical in treating systemic mycoses.

Answer: A. Linezolid

Explanation: Linezolid exhibits nearly 100% oral bioavailability, meaning that its absorption from the gastrointestinal tract is almost complete. This property makes it highly effective when administered orally for treating infections.

Answer: C. The lethal dose for 50% of animals to the effective dose for 50% of animals

Explanation: The therapeutic index is defined as the ratio between the lethal dose (LD₅₀) and the effective dose (ED₅₀). A higher index indicates a greater margin of safety for a drug.

Answer: B. Insulin

Explanation: Ligand-gated ion channels are typically modulated by neurotransmitters and certain drugs such as benzodiazepines. Insulin, however, does not interact with these channels and works through receptor tyrosine kinases.

Answer: B. Drug toxicity

Explanation: Pharmacovigilance involves the continuous monitoring of drug safety, particularly focusing on adverse drug reactions and toxicity. This process is essential for ensuring the ongoing safety of pharmaceuticals in the market.

Answer: C. Antiarrhythmic class III

Explanation: Antiarrhythmic drugs of class III are known to cause QT prolongation by affecting cardiac ion channels, which can lead to potentially life-threatening arrhythmias. Their use requires careful monitoring of the heart rhythm.

Answer: C. Diltiazem

Explanation: Diltiazem is a calcium channel blocker that contains a benzothiazepine moiety. It is used in the treatment of hypertension and angina, and its unique structure contributes to its pharmacological profile.

Answer: A. DNA dependent RNA polymerase

Explanation: Rifampicin specifically binds to and inhibits the bacterial DNA-dependent RNA polymerase, thereby blocking RNA synthesis. This action is central to its antibacterial activity, especially against Mycobacterium tuberculosis.

Answer: B. GPCR

Explanation: G protein-coupled receptors (GPCRs) are characterized by their seven transmembrane domains. They play key roles in cell signaling and are targets for a large number of drugs.

Answer: D. All of the above

Explanation: Non-linear pharmacokinetics may result from saturation of multiple processes, including protein binding, hepatic metabolism, and active renal transport. These saturable processes can lead to disproportionate increases in drug concentration with increasing doses.

Answer: A. Aspirin

Explanation: Aspirin acetylates specific serine residues on both COX-1 and COX-2 enzymes, leading to irreversible inhibition. This action reduces the production of prostaglandins, which are involved in inflammation and pain.

Answer: B. Terbutaline

Explanation: Bambuterol is an inactive prodrug that is metabolized into terbutaline, a beta-2 agonist. Terbutaline then exerts its bronchodilator effects, making it useful in treating respiratory conditions such as asthma.

Answer: C. Both absorption and elimination

Explanation: The elimination rate constant (Kₑ) is calculated during both the absorption and elimination phases of pharmacokinetic studies, as it reflects the rate at which a drug is cleared from the body over time.