This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pharmacokinetics, Subject name: Pharmacology
[{'content': 'Arrange the following drugs according to increasing volume of distribution. 1. Haloperidol 2. Gentamicin 3. Heparin 4. Chloroquine \nSelect and explain. \nA. 3-2-4-1, B. 3-2-1-4, C. 2-3-4-1, D. 2-1-3-4', 'role': 'user'}, {'content': 'Answer: B \nExplanation: * Chloroquine has highest volume of distribution. It is concentrated in liver and retina. * Heparin is high molecular weight compound and thus not able to cross most membranes. It has low Vd. * Gentamicin again cannot cross many membranes because of polar nature and thus has low Vd. * Haloperidol is a drug working in CNS. So, it must be able to cross other membranes also resulting in high Vd. Thus the sequence is Chloroquine > Haloperidol > Gentamicin > Heparin', 'role': 'assistant'}]