Half life (t ½) doesn’t depend on:

Correct Answer: B

Rationale: The correct answer is B: Time of drug absorption. Half-life is a pharmacokinetic parameter that represents the time required for the concentration of a drug in the body to decrease by half. The half-life of a drug is not influenced by the time it takes for the drug to be absorbed into the bloodstream. Factors such as biotransformation, concentration in plasma, and the rate of drug elimination affect the half-life of a drug. Biotransformation can alter the drug's chemical structure, affecting its elimination rate. Higher plasma concentrations can lead to a longer half-life, while a faster rate of drug elimination results in a shorter half-life.

Correct Answer: A

Rationale: Bethanechol is the correct answer as it is mainly muscarinic in action. Bethanechol is a selective muscarinic receptor agonist with minimal nicotinic receptor activity. It is used to stimulate the bladder and gastrointestinal smooth muscle. Carbachol, while also a direct-acting cholinomimetic, has both muscarinic and nicotinic actions. Acetylcholine, the natural neurotransmitter, acts on both muscarinic and nicotinic receptors. "None of the above" is incorrect as Bethanechol is mainly muscarinic in action.

Correct Answer: B

Rationale: The correct answer is B: Pralidoxime. Pralidoxime is an antidote used to regenerate cholinesterase inhibited by organophosphate poisoning, which affects skeletal muscle neuromuscular junctions. It works by reactivating the cholinesterase enzyme, restoring its function. Succinylcholine (A) is a muscle relaxant, not an agent for regenerating cholinesterase. Pirenzepine (C) is a muscarinic receptor antagonist used for gastric ulcers. Propiverine (D) is a bladder antimuscarinic. So, the most effective agent for regenerating cholinesterase at the neuromuscular junction is Pralidoxime.

Correct Answer: D

Rationale: The correct answer is D: Beta 2 receptor. Bronchial smooth muscle relaxation is mainly mediated by Beta 2 adrenergic receptors when activated by agonists like salbutamol. These receptors stimulate adenylate cyclase leading to increased cAMP levels, which in turn promotes muscle relaxation. Alpha 1 receptors (Choice A) and Alpha 2 receptors (Choice B) are associated with vasoconstriction and decreased sympathetic outflow, respectively, not bronchial smooth muscle relaxation. Beta 1 receptors (Choice C) are primarily found in the heart and play a role in cardiac function, not bronchial smooth muscle relaxation.

Correct Answer: A

Rationale: Rationale: Labetalol is a reversible nonselective alpha-beta antagonist. It blocks both alpha and beta receptors. It is reversible due to its competitive binding, making it effective in managing hypertension. Phentolamine is an alpha blocker, not affecting beta receptors. Metoprolol and Propranolol are both beta blockers, targeting beta receptors only, making them selective and not reversible nonselective alpha-beta antagonists.