First-Pass Metabolism
Definition
The phenomenon where a drug is metabolized by the liver before reaching systemic circulation, significantly reducing bioavailability. This is a primary reason most peptides are administered by injection rather than orally.
What this means for research sourcing
Mechanistic terms like this describe how research compounds behave in vitro. See the mechanism overviews for compounds Volta stocks.
Related Terms in Pharmacology
Bioavailability
The proportion of a substance that enters the circulation when introduced into the body and is able to have an active effect. Different administration routes affect bioavailability.
Half-Life
The time required for the concentration of a substance in the body to decrease by half. Determines dosing frequency and accumulation patterns.
Pharmacokinetics
The study of how a drug moves through the body — absorption, distribution, metabolism, and excretion (ADME).
Pharmacodynamics
The study of what a drug does to the body — its mechanism of action, therapeutic effects, and dose-response relationships. Complementary to pharmacokinetics.
Receptor Agonist
A substance that binds to a receptor and activates it, mimicking the action of a naturally occurring substance. Many therapeutic peptides are receptor agonists.
Receptor Antagonist
A substance that binds to a receptor and blocks its activation, preventing the natural ligand from exerting its effect.
Desensitization
A reduction in receptor response after prolonged or repeated exposure to an agonist. Can lead to reduced effectiveness of some peptides over time.
Tachyphylaxis
A rapid and acute decrease in response to a drug after repeated doses in a short time period. Distinct from slower desensitization, tachyphylaxis can occur after just a few doses. Melanotan II and some GHRPs are susceptible to tachyphylaxis without proper cycling.