When prescribing a loading dose of a new medication, there are many factors that a clinician has to consider. Clearance can ultimately be determined through:ĬL=(0.693 X Vd)/ Half-life Issues of Concern MD=(Concentration Steady State X Clearance X Dosing Interval)/BioavailabilityĬlearance can be determined using the known half-life of a medication, which is the length of time required for a dose to reach 50% of its initial plasma concentration. The calculation of loading dose should not be confused with maintenance dose, which is the dose required to maintain steady-state concentration. Vd=Dose of medication given/Concentration in the Plasma The volume of distribution is typically calculated as follows: LD=(Volume of Distribution X Concentration Steady State)/Bioavailabilityįor this formula, concentration steady-state is defined as the therapeutic concentration of medication in the body, while bioavailability is the fraction of an administered dose that reaches systemic circulation.

Ī loading dose is typically calculated through the following formula: For instances where a therapeutic steady-state concentration is needed immediately, loading doses can be utilized to more rapidly achieve this therapeutic concentration. Reaching this concentration is typically not an issue for drugs with short half-lives however, other medications or conditions may require more rapid therapeutic onset. Typically, for any medication, five to seven half-lives are required for this to be achieved. The characteristics that define an individual medication’s PK can help determine the loading dose. While a patient is taking a specific drug to achieve the therapeutic benefit, the drug must reach a certain steady-state concentration. An individual medication’s PK is governed by how it moves within the body through absorption, bioavailability, distribution, metabolism, and excretion. PK is the relationship between an administered dose of a drug and its measured concentration within the body.

For each of these individual medications, the route of administration, appropriate dosage, and frequency of use are determined by the medication’s pharmacokinetics (PK).

In the field of medicine, the treatment for most conditions uses various pharmacological medications.

Loading dose