Dose-related adverse effect caused by phenytoin is:

Correct Answer: C

Rationale: Step-by-step rationale: 1. Phenytoin is known to cause gingival hyperplasia. 2. This adverse effect is dose-related, meaning it occurs more frequently with higher doses. 3. Gingival hyperplasia is characterized by overgrowth of gum tissue. 4. It is not associated with physical or psychological dependence, exacerbated seizures, or extrapyramidal symptoms. Summary: Choice A is incorrect as phenytoin does not cause dependence. Choice B is incorrect as phenytoin does not worsen seizures. Choice D is incorrect as extrapyramidal symptoms are not typically caused by phenytoin.

Correct Answer: B

Rationale: The correct answer is B: Coma, depressed respiration, and miosis. In opioid overdosage, coma occurs due to central nervous system depression, depressed respiration is a result of respiratory center suppression, and miosis is a classic sign of opioid toxicity due to the activation of the parasympathetic nervous system. Mydriasis (pupil dilation) is not a common feature in opioid overdosage. Chills and abdominal cramps are more indicative of opioid withdrawal rather than overdose. Tremor and vomiting are not typically part of the diagnostic triad of opioid overdosage.

Correct Answer: A

Rationale: The correct answer is A: The nigrostriatal system. Parkinsonian symptoms and tardive dyskinesia are caused by dopamine blockade in the nigrostriatal system, which is responsible for motor control. Dopamine blockade here leads to movement disorders. Choices B, C, and D are incorrect because tardive dyskinesia and Parkinsonian symptoms are not primarily related to dopamine blockade in the mesolimbic and mesofrontal systems (B), chemoreceptor trigger zone of the medulla (C), or the tuberoinfundibular system (D). These systems are associated with other functions such as reward processing, nausea/vomiting regulation, and hormone release, respectively.

Correct Answer: B

Rationale: The correct answer is B (2-3 weeks) because antidepressants typically require time to build up in the body and affect neurotransmitter levels. It takes time for the brain to adapt to the medication and for changes in mood to become noticeable. A: 2-3 days is too short for significant effects. C: 24 hours is not enough time for the medication to take full effect. D: 2-3 months is too long for most individuals to wait for improvement.

Correct Answer: D

Rationale: The correct answer is D: It has a high potential of toxicity. Piracetam is known for its low toxicity and safety profile, making it a popular nootropic. A: It is not a GABA derivative, but it does modulate some GABA receptors. B: It does influence neuro-vegetative functions positively. C: Improvement with piracetam typically starts earlier, around the 2nd week, rather than the 3rd week as mentioned in the incorrect choice.