This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Pharmacology, Subject name: Pharmacology
Loading of dose of a drug primarily depends on: 
Select and explain. 
A. Volume of distribution, B. Clearance, C. Rate of administration, D. Half life
A: Volume of distribution
Answer: A: Volume of distribution 
Explanation: Ans. A. Volume of distributionLoading dose is dependent on volume of distribution; whereas maintenance dose depends on the clearance.Loading doseMaintenance dose* It is the initial high dose which is given to achieve the desired plasma concentration after saturating (loading) the tissue binding sites.* Just enough drug is given in each dose to replace the drug eliminated* When time to reach steady state is long, as it is for drugs with long half-lives, it is desirable to give a loading dose that promptly raises the concentration of drug in plasma * LD=Vdx Desired plasma concentration (mg/L)* MD = Clearance x Desired plasma concentration (mg/L)