Some drugs, such as analgesics, hypnotics and antiemetics, may be used effectively when administered as a single dose. More frequently, however, drugs are administered on a continual basis. In addition, most drugs are administered with sufficient frequency that measurable and, often, pharmacologically significant concentrations of drug remain in the body when a subsequent dose is administered. For drugs administered in a fixed dose and at a constant dosing interval (e.g. 250 mg every 6 h), the peak plasma concentration following the second and succeeding doses of a drug is higher than the peak concentration following the administration of the first dose. This results in an accumulation of drug in the body relative to the first dose. Additionally, at steady state, the plasma concentration of drug during a dosing interval at any given time since the dose was administered will be identical.