A patient has been prescribed warfarin (Coumadin) in addition to a heparin infusion. The patient asks the nurse why he has to be on two medications. The nurse’s response is based on which rationale?

Correct Answer: D

Rationale: The correct answer is D because heparin is a fast-acting anticoagulant that is used initially to rapidly thin the blood while warfarin takes time to reach therapeutic levels. By using both medications together, the patient is protected against blood clots during this transition period. Choices A and B are incorrect because there is no evidence that the oral and injection forms work synergistically or result in fewer adverse effects when used together. Choice C is incorrect because heparin alone can achieve adequate anticoagulation levels, but the combination is more about the timing of onset of action for each medication.

Correct Answer: A

Rationale: The correct answer is A because the volume of distribution (Vd) is a pharmacokinetic parameter that describes the extent of drug distribution in the body. It is calculated by dividing the total amount of drug in the body by the concentration of the drug in the plasma. Therefore, the concentration of a substance in plasma is essential for determining Vd. Choice B (Concentration of substance in urine) is incorrect because Vd is not calculated based on urine concentration but rather on plasma concentration. Choice C (Therapeutical width of drug action) is unrelated to Vd calculation as it refers to the range of drug concentrations in the body that produce the desired therapeutic effect. Choice D (A daily dose of drug) is also incorrect as Vd is not directly calculated from the daily dose but rather from the concentration of the drug in the plasma.

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: A

Rationale: Prilocaine is the correct answer as it can cause methemoglobinemia due to its metabolite o-toluidine. This metabolite oxidizes hemoglobin to methemoglobin, leading to reduced oxygen-carrying capacity. Procaine, lidocaine, and ropivacaine do not typically cause methemoglobinemia as they lack the metabolites responsible for this condition. So, prilocaine is the only local anesthetic among the choices that can lead to methemoglobinemia.

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.