The purpose of a loading dose is to quickly bring the patient's serum concentration of drug up to a desired level. If a drug distributes equally into the entire body mass, the loading dose is simply the desired concentration times the patient's mass. However, drugs distribute in the body to varying extents. The amount of the body mass that the drug distributes into is reflected in its "apparent volume of distribution" (Vd). A Vd of 1.0 indicates that the drug distributes into the entire body mass, but all intravenous anticonvulsants have a Vd less than 1.0.
The loading dose can be calculated as:
D = C * W * Vd , where
C is the desired change in serum concentration (mg/L)
W is the patient's weight (kg), and
Vd is the estimated volume of distribution for the drug (L/kg).
Last revised 9/1/2001
M. Steven Evans [ mail | home page ]