Methyl nicotinate is the methyl ester of that is used as an active ingredient as a rubefacient in over-the-counter topical preparations indicated for muscle and joint pain.?The action of methyl nicotinate as a rubefacient is thought to involve peripheral vasodilation.

The glycine amide of 4-aminobenzoic acid. Its sodium salt is used as a diagnostic aid to measure effective renal plasma flow (ERPF) and excretory capacity.

D-proline is an isomer of the naturally occurring amino acid L-Proline. D-amino acids have been found in relatively high abundance in human plasma and saliva. These amino acids may be of bacterial origin but there is also evidence that they are endogenously produced through amino acid racemase activity.