A patient has taken an overdose of drug X. Drug X has a volume of distribution of 4L. Their blood concentration of X is 10mg/L. Assuming it has a bioavailiability of 100% by this route of administration, how much of drug X did they consume?
Volume of distribution
The volume of distribution (Vd) is a tricky concept. It is used as an indicator of how a drug distributes in the body. It essentially tells you if it concentrates in the plasma (blood) or spreads out. Some drugs are highly polar and tend to stay in central compartments such as the plasma, these have a low Vd. Others are more lipid soluble and are distributed widely for instance in fat, these have a high Vd. It is calculated by the following formula
Vd = amount of drug in the body/concentration in the plasma
It can be used clinically when trying to determine the loading dose of a drug required for a desired blood concentration and also for estimating blood concentration in the treatment of overdose. Its units are in volume.
