Dosage

Dosage designates the peptide quantity administered or used in an experimental protocol, expressed in mass (mg, µg, ng), concentration (mg/mL, µM, nM) or biological activity units (IU) according to context. Mastering dosage is one of the most critical methodological skills in peptide research: poorly calibrated concentrations directly compromise reproducibility and scientific validity of results.

Several calculation levels must be distinguished. (1) Gross mass: total quantity indicated on the vial (e.g. 5 mg). (2) Net peptide mass: corrected for HPLC purity and net peptide content (a 5 mg vial at 98% HPLC and 80% net content actually contains 5 × 0.98 × 0.80 = 3.92 mg of active peptide). (3) Working concentration: after reconstitution in a precise solvent volume. (4) Final concentration: after dilution in the experimental medium (cell culture, assay buffer, animal volume).

In in vitro research, typical concentrations vary enormously by peptide activity: nM for high-affinity hormonal peptides (semaglutide, GLP-1, oxytocin), µM for less potent growth factors (GHK-Cu, certain thymosin fragments), mM for low-affinity antimicrobial peptides. Dose-response curves (8 to 12 points over 4 to 6 decades of concentration) are the gold standard to characterize EC₅₀, IC₅₀ and Emax.

In RUO in vivo research (exclusively animal models with ethics authorization), dosages are typically expressed in µg/kg or mg/kg, with adjustment by administration route (subcutaneous, intraperitoneal, intravenous) and frequency (single dose, chronic daily, weekly). Inter-species allometries (mouse, rat, rabbit, dog) follow empirical rules from classical pharmacology but remain subject to experimental validation.

Absolute RUO rule: no dosage information on a research peptide commercial site can be interpreted as human use advice. The "Research Use Only" mention prohibits any clinical extrapolation. Dosages documented in scientific literature are exclusively experimental and not transposable to therapeutic use without full regulatory clinical validation.