Small Molecule Drug
A low molecular weight compound (typically under 900 daltons) that can often be taken orally and is manufactured through chemical synthesis. Small molecule drugs contrast with peptide and protein drugs in their size, production method, and pharmacokinetic properties. Some GnRH antagonists (relugolix, elagolix) are small molecules rather than peptides.
Technical Context
Small molecules (<900 Da) differ from peptides in key properties: oral bioavailability (typically achievable for small molecules, rarely for peptides), manufacturing (chemical synthesis with exact molecular replication vs biological production with inherent variability), stability (generally more stable than peptides), and regulatory pathway (NDA for small molecules, potentially BLA for biological peptides). Some drugs that target peptide receptors are themselves small molecules rather than peptides: relugolix (oral GnRH antagonist, MW 623 Da) and elagolix (oral GnRH antagonist, MW 631 Da) are non-peptide small molecules designed from the GnRH receptor pharmacophore — they achieve oral bioavailability that peptide GnRH analogues cannot. DPP-4 inhibitors (sitagliptin, saxagliptin) are also small molecules targeting peptide biology. The peptide-to-small-molecule transition represents one endpoint of the peptidomimetic design continuum.