Topiramate is an anti-epileptic drug used for

Correct Answer: A

Rationale: Step-by-step rationale for why the correct answer is A: Topiramate is primarily used for migraine prophylaxis due to its ability to reduce the frequency and severity of migraines. It works by stabilizing electrical activity in the brain. The other choices are incorrect because topiramate is not typically used for acute seizures, mood stabilization, or pain management. It is important to differentiate between the specific indications for each medication to ensure appropriate treatment.

Correct Answer: B

Rationale: The correct answer is B: Fraction of an unchanged drug reaching the systemic circulation following any route of administration. Bioavailability refers to the proportion of an administered dose of unchanged drug that reaches the systemic circulation. This is crucial in determining the effectiveness of a drug. Option A is incorrect because bioavailability is not specifically related to the amount excreted in urine. Option C is incorrect as it refers to permeability through the blood-brain barrier, which is a different concept. Option D is incorrect as it pertains to plasma protein binding, which is not the same as bioavailability. In summary, bioavailability is about the amount of a drug that reaches systemic circulation intact, making option B the correct choice.

Correct Answer: A

Rationale: The correct answer is A because half-life is the time taken for the concentration of a drug in the plasma to decrease by 50%. This is a measure of the rate of elimination of a drug from the body. Choice B is incorrect because half-life does not specifically refer to metabolism. Choice C is incorrect because absorption is not related to half-life. Choice D is incorrect because half-life is not about binding to plasma proteins but about elimination from the body.

Correct Answer: D

Rationale: The correct answer is D because bound drug is not the pharmacologically active part of the drug. The active form of a drug is the unbound fraction that can exert its pharmacological effects. When a drug is bound to plasma proteins, it is unable to exert its pharmacological action until it becomes unbound. Choice A is true because bound drug cannot diffuse into tissues. Choice B is correct because binding to plasma proteins decreases the apparent volume of distribution. Choice C is also true as displacement of bound drug can lead to increased effects of the drug due to increased free drug concentration.

Correct Answer: B

Rationale: First-order kinetics means the rate of drug elimination is proportional to the drug concentration. Clearance (choice B) represents the volume of plasma cleared of the drug per unit time, which remains constant in first-order kinetics. The other choices are incorrect because: A: In first-order kinetics, the amount of drug eliminated per unit time decreases as drug concentration decreases. C: The elimination half-life is independent of dose in first-order kinetics. D: Complete elimination within two half-lives is a general rule but not specific to first-order kinetics.