A loading dose is a short term, higher concentration dose of a drug that may be initially given to a patient. For example, let's say that the normal dose of an antibiotic is one pill a day. This dose is called the "maintenance dose", the dose required to maintain an efficient concentration of the drug in the patient's blood stream. However, the doctor instructs the patient to take two pills on the first day only and then finish off the rest of the prescription at one pill a day. This initial two-pill dose is the loading dose. The purpose of the loading dose is to help the patient attain the efficient concetration of the drug in their blood stream much faster than if they were taking just the maintenance dose.

All kinds of drugs, from antibiotics to painkillers, can have a loading dose. This dose can also be given by all common methods of administration, including orally, intravenously, and sublingually. However, several factors need to be considered when determining if the patient should get a loading dose and what concentration it should be. These factors include the patient's:

  • age
  • weight
  • overall health
  • tolerance to the drug in question

A loading dose is generally given for only a short period of time, from hours to days at most. Long term use of the drug at loading dose concentrations is generally toxic and not advised.

Rang's Pharmacology, Fourth edition, 1999