Half life (t ½) is the time required to:

Correct Answer: A

Rationale: The correct answer is A because half-life represents the time taken for the concentration of a drug in the plasma to reduce by 50%. This is crucial during the elimination phase when the drug is being cleared from the body. Choice B is incorrect as half-life does not specifically relate to drug metabolism into active metabolites. Choice C is incorrect as half-life is not about drug absorption but elimination. Choice D is incorrect as half-life does not pertain to drug binding to plasma proteins but rather the rate of elimination from the body.

Correct Answer: C

Rationale: Parasympathomimetic drugs mimic the effects of the parasympathetic nervous system. Stimulation of the parasympathetic system leads to a decrease in heart rate (bradycardia). This is why choice C is correct. Bronchodilation (A) is caused by sympathetic stimulation, mydriasis (B) is caused by sympathetic stimulation, and constipation (D) can be caused by anticholinergic drugs, which have the opposite effect of parasympathomimetic drugs.

Correct Answer: B

Rationale: Step-by-step rationale: 1. Ipratropium is a bronchodilator used in asthma. 2. It works by blocking muscarinic receptors, reducing bronchoconstriction. 3. Atropine and Homatropine are anticholinergic drugs but not commonly used in asthma. 4. Lobeline is a respiratory stimulant, not used for bronchodilation in asthma. Summary: Ipratropium is the correct choice as it specifically targets bronchodilation in asthma by blocking muscarinic receptors. Atropine, Homatropine, and Lobeline are not commonly used for this purpose in asthma treatment.

Correct Answer: A

Rationale: The correct answer is A because alpha agonists cause mydriasis (pupil dilation), not miosis (pupil constriction). Alpha agonists like phenylephrine work by stimulating alpha receptors in the iris dilator muscle, leading to pupil dilation. Therefore, choice A is incorrect. Choices B, C, and D are incorrect because alpha agonists do cause mydriasis, beta antagonists do decrease the production of aqueous humor, and alpha agonists do increase the outflow of aqueous humor from the eye, respectively.

Correct Answer: C

Rationale: Rationale: 1. Pindolol is a non-selective beta-blocker with intrinsic sympathomimetic activity (partial beta-agonist). 2. It competes with catecholamines for beta-adrenergic receptors, reducing heart rate and blood pressure. 3. Propranolol (A) and metoprolol (B) are non-selective beta-blockers without partial agonist activity. 4. Betaxolol (D) is a selective beta-1 blocker without partial agonist activity. Summary: Pindolol (C) is the correct choice due to its partial beta-agonist activity, which distinguishes it from the other options that lack this property.