Which of the following agents is a full antagonist of opioid receptors?

Correct Answer: C

Rationale: The correct answer is C: Naloxone. Naloxone is a full antagonist of opioid receptors because it binds strongly to these receptors, blocking their activation by opioids. This competitive inhibition prevents opioid drugs from exerting their effects, making naloxone an effective overdose reversal agent. Meperidine (A) is a partial agonist, buprenorphine (B) is a partial agonist with mixed antagonist activity, and butorphanol (D) is a mixed agonist-antagonist. Therefore, they do not fully block opioid receptors like naloxone does.

Correct Answer: C

Rationale: The correct answer is C: Nefazodone. Third-generation heterocyclic antidepressants are newer antidepressants with improved side effect profiles compared to older generations. Nefazodone falls under this category due to its unique mechanism of action involving serotonin and norepinephrine reuptake inhibition. It is also known for its lower risk of causing weight gain and sexual dysfunction compared to older antidepressants. Amitriptyline (A) and Maprotiline (B) are first-generation tricyclic antidepressants, known for their anticholinergic side effects. Tranylcypromine (D) is a monoamine oxidase inhibitor (MAOI), which is a different class of antidepressants with its own set of side effects and interactions.

Correct Answer: A

Rationale: The correct answer is A: Caffeine. Caffeine is a methylxanthine derivative known for its psychostimulant effects on the central nervous system. Methylxanthines are a class of compounds that include caffeine, theophylline, and theobromine, all of which act as stimulants. Sydnocarb (B) is a psychostimulant but not a methylxanthine derivative. Amphetamine (C) is a different class of psychostimulant compounds, and Meridil (D) is not a psychostimulant. Therefore, caffeine is the correct choice as the methylxanthine derivative with psychostimulant properties.

Correct Answer: D

Rationale: Addiction involves both psychological and physiological components. Psychological dependence refers to the emotional reliance on a substance or behavior, while physiological dependence involves changes in the body that lead to withdrawal symptoms. Tolerance is a phenomenon where more of a substance is needed to achieve the same effects. Therefore, all of the above options are associated with addiction, making choice D the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Flumazenil. Flumazenil is a specific benzodiazepine receptor antagonist that competitively inhibits the effects of benzodiazepines like midazolam, accelerating recovery from sedative actions. Naloxone (A) is used to reverse opioid effects, not benzodiazepines. Ketamine (C) is a dissociative anesthetic and not used to reverse benzodiazepine sedation. Fomepizole (D) is used in methanol or ethylene glycol toxicity, not for benzodiazepine reversal. Flumazenil is the specific antidote for benzodiazepine overdose.