The reasons determing bioavailability are:

Correct Answer: C

Rationale: The correct answer is C because bioavailability is determined by the extent of absorption and hepatic first-pass effect. Absorption refers to how much of a substance is taken up by the body, while the hepatic first-pass effect is the initial metabolism of a drug in the liver before it reaches systemic circulation. These factors directly impact the amount of a substance that is available to produce its desired effect. Rheological parameters of blood (A) are unrelated to bioavailability. The amount of a substance obtained orally and quantity of intakes (B) may affect bioavailability indirectly but do not determine it. Glomerular filtration rate (D) is related to renal excretion, not bioavailability.

Correct Answer: A

Rationale: The correct answer is A: Procaine. It is a short-acting drug due to its rapid metabolism by plasma esterases, resulting in a shorter duration of action compared to the other choices. Procaine's quick onset and short duration make it suitable for minor procedures. Tetracaine, Bupivacaine, and Ropivacaine are all long-acting local anesthetics with slower metabolism and longer durations of action, making them more suitable for prolonged surgeries or chronic pain management.

Correct Answer: A

Rationale: The correct answer is A: Hypotension and bradycardia. Nicotine is a stimulant that typically causes hypertension and tachycardia due to its effects on the sympathetic nervous system. Therefore, hypotension and bradycardia are not consistent with the toxic effects of nicotine. Choices B, C, and D are incorrect because convulsions, coma, respiratory arrest, skeletal muscle depolarization blockade, respiratory paralysis, hypertension, and cardiac arrhythmias are all potential toxic effects of a large dose of nicotine due to its impact on various physiological systems.

Correct Answer: D

Rationale: The correct answer is D (Both B and C). Succinylcholine and mivacurium are metabolized by plasma cholinesterase. An abnormal variant of plasma cholinesterase (B) can lead to prolonged neuromuscular blockade. Additionally, hepatic disease (C) can impair the metabolism of these drugs, further prolonging their effects. Therefore, in patients with both abnormal plasma cholinesterase and hepatic disease, the neuromuscular blockade can be significantly prolonged. Renal failure (A) does not directly impact the metabolism of succinylcholine and mivacurium, so it is not a significant factor in this context.

Correct Answer: A

Rationale: The correct answer is A: Xylometazoline. Xylometazoline is an alpha2-selective agonist, which means it specifically targets alpha2-adrenergic receptors. By activating these receptors, xylometazoline promotes constriction of the nasal mucosa, leading to reduced swelling and congestion. Phenylephrine (B) and methoxamine (C) are alpha1-selective agonists, not alpha2-selective, so they would not promote constriction of nasal mucosa. Epinephrine (D) is a non-selective agonist that acts on both alpha and beta receptors, leading to a broader range of effects, not specifically nasal constriction.