A "loading dose" refers to a higher initial amount of medication given to quickly reach a desired level in the body. It helps to achieve the therapeutic effect faster than the regular dose would. Full definition
The initial loading dose protocol is one injection every 4 days for a total of 8 injections. (pettao.com)
It's crucial that the full loading dose, following the directions in the package insert, be given. (caberfeidh.com)
In more severe cases of seizures dogs are often hospitalized to receive intravenous loading doses of phenobarbital since it otherwise may take up to 2 weeks to reach a steady concentration in the bloodstream. (tampabayvets.net)