What phenomenon can occur in case of using a combination of drugs?

Correct Answer: D

Rationale: The correct answer is D: Synergism. When drugs are used in combination, synergism can occur where the combined effect is greater than the sum of their individual effects. This can lead to enhanced therapeutic benefits or increased adverse effects. Tolerance (A) is the body's reduced response to a drug over time. Tachyphylaxis (B) is a rapid decrease in response to a drug with repeated administration. Accumulation (C) refers to the build-up of a drug in the body due to insufficient elimination. Synergism (D) is the only choice that specifically addresses the interaction between drugs leading to enhanced effects.

Correct Answer: D

Rationale: The correct answer is D: All of the above. Atropine is a non-selective muscarinic antagonist, blocking all muscarinic receptor subtypes (M1, M2, and M3). This is due to its structure and mechanism of action, which allows it to bind and inhibit all types of muscarinic receptors. Atropine's broad action leads to its multiple effects, such as blocking parasympathetic stimulation and increasing heart rate. Choices A, B, and C are incorrect because atropine does not selectively target only one specific muscarinic receptor subtype.

Correct Answer: D

Rationale: Sympathetic stimulation involves the activation of the sympathetic nervous system. Norepinephrine is released from sympathetic nerve terminals, activating adrenoreceptors on postsynaptic sites. Additionally, the adrenal medulla releases epinephrine into the bloodstream. Therefore, all three choices (A, B, and C) are mechanisms through which sympathetic stimulation is mediated. Hence, the correct answer is D. The other choices (A, B, and C) are incorrect as they individually represent different aspects of sympathetic stimulation, but the correct answer encompasses all of them.

Correct Answer: D

Rationale: Step 1: Long-acting decongestants are preferred for sustained relief. Step 2: Xylometazoline has a longer duration of action compared to other choices. Step 3: Epinephrine and norepinephrine are short-acting sympathomimetic agents. Step 4: Phenylephrine is intermediate-acting, not long-acting. Step 5: Therefore, D (Xylometazoline) is the correct choice for long-acting topical decongestant agents.

Correct Answer: C

Rationale: The correct answer is C: Reserpine. Reserpine is a rauwolfia alkaloid acting as an adrenoreceptor antagonist by inhibiting the storage of norepinephrine and serotonin in vesicles. Prazosin (A) is an alpha-1 adrenergic receptor antagonist, Propranolol (B) is a non-selective beta-adre, Phentolamine (D) is a non-selective alpha-adrenergic receptor antagonist, making them all incorrect choices.