Half-life
The time required for the concentration of a peptide in the body to decrease by half. Determines dosing frequency — short half-life peptides (minutes) need daily dosing, while long half-life peptides (days) can be dosed weekly.
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Related Terms
The time required for the blood concentration of a peptide to decrease by 50% during the elimination phase. Determines how long a peptide remains active and how frequently it must be dosed.
Distribution half-lifeThe time required for a peptide to distribute from the bloodstream into tissues during the initial distribution phase. Typically much shorter than the elimination half-life.
BioavailabilityThe fraction of an administered dose that reaches systemic circulation unchanged. Subcutaneous injection provides 65–95% bioavailability for most peptides; oral bioavailability is typically below 1% without absorption enhancers.
Clearance rateThe volume of blood from which a peptide is completely removed per unit time, expressed in mL/min or L/hr. Clearance determines dosing frequency along with half-life.
Steady stateThe condition where the rate of peptide administration equals the rate of elimination, resulting in consistent plasma levels. Typically reached after 4–5 half-lives of regular dosing.