Half-Life (Pharmacological)
Pharmacological half-life is the time for plasma drug concentration to decrease by 50%. It determines dosing frequency: CJC-1295 DAC has a half-life of 6–8 days; Ipamorelin has a half-life of approximately 2 hours.
Overview
Half-life (t½) is one of the most fundamental pharmacokinetic parameters. It is determined by the volume of distribution and clearance rate of a compound: t½ = 0.693 × (Vd / CL). After one half-life, 50% remains; after two, 25%; after five half-lives, less than 3.2% of the original dose remains (effectively eliminated). Conversely, with repeated dosing, steady-state concentration is reached after approximately five half-lives. Peptide engineering often aims to extend half-life — achieved by albumin binding (DAC attachment, fatty acid modification), PEGylation, or amino acid substitutions that resist enzymatic degradation. Knowing a peptide's half-life is essential for designing research protocols: a compound with a 2-hour half-life requires multiple daily doses for continuous receptor occupancy, while a 7-day half-life supports weekly dosing.
Related Terms
Frequently asked questions
How many half-lives until a peptide is fully cleared?+
Approximately five half-lives eliminates ~97% of a dose. For Ipamorelin (2-hour half-life), ~10 hours for clearance; for Semaglutide (7-day half-life), ~5 weeks.
What is steady-state concentration?+
Steady state is reached after approximately five half-lives of regular dosing, when the amount of drug administered per dose equals the amount cleared. Concentration fluctuates between peak and trough but averages consistently.
Why do some peptide analogues have much longer half-lives than the natural hormone?+
Synthetic analogues are engineered with structural modifications — fatty acid chains, albumin-binding moieties, amino acid substitutions, or PEG groups — that protect against enzymatic degradation and prolong their presence in circulation.