Therapeutic index (TI) is:

Correct Answer: A

Rationale: The correct answer is A because the therapeutic index (TI) is a ratio that measures the safety of a drug by comparing the dose that produces therapeutic effects to the dose that causes toxicity. This ratio helps determine the margin of safety of a drug for a specific indication. Choice B is incorrect because TI does not directly measure effectiveness. Choice C is incorrect as bioavailability is a different concept related to drug absorption. Choice D is incorrect because TI focuses on safety and not drug elimination. Therefore, A is the correct answer as it accurately reflects the purpose of the therapeutic index.

Correct Answer: C

Rationale: The correct answer is C: Atropine. Atropine is useful in the treatment of uterine spasms because it acts as an antispasmodic agent by blocking the action of acetylcholine on smooth muscle, including the uterus. Carbachol (A) is a cholinergic agonist that would exacerbate spasms. Vecuronium (B) is a neuromuscular blocking agent used for muscle relaxation during surgery. Edrophonium (D) is a cholinesterase inhibitor used for diagnosing myasthenia gravis. In summary, Atropine is the correct choice due to its antispasmodic properties, while the other options would not be effective or appropriate for treating uterine spasms.

Correct Answer: A

Rationale: The correct answer is A: Heart. Alpha adrenoreceptor subtypes are mainly associated with smooth muscle tissues, not cardiac muscle like the heart. Alpha-1 receptors are present in blood vessels, prostate, and pupillary dilator muscle, helping in vasoconstriction, ejaculation, and pupil dilation respectively. Alpha-2 receptors are also found in these tissues, modulating neurotransmitter release and smooth muscle contraction. The heart primarily contains beta adrenoreceptor subtypes, which regulate heart rate and contractility. Therefore, the distribution of alpha adrenoreceptor subtypes is not associated with the heart.

Correct Answer: C

Rationale: Rationale: 1. Prazosin is an alpha1-selective antagonist used to treat hypertension by blocking alpha1 receptors in blood vessels. 2. Phentolamine (A) is a non-selective alpha-blocker. 3. Dihydroergotamine (B) is a 5-HT1 receptor agonist used for migraine. 4. Labetalol (D) is a non-selective alpha and beta blocker. Therefore, C (Prazosin) is the correct answer as it is a selective alpha1 blocker.

Correct Answer: B

Rationale: The correct answer is B: Flurazepam. Flurazepam is a benzodiazepine derivative because it contains a benzodiazepine ring structure in its chemical composition. Benzodiazepines are a class of drugs commonly used as hypnotics due to their sedative and hypnotic effects. Zolpidem (A) is a non-benzodiazepine hypnotic drug, while Secobarbital (C) and Phenobarbitone (D) are barbiturates, not benzodiazepines. Benzodiazepines are preferred over barbiturates for hypnotic use due to their lower risk of respiratory depression and overdose.