Carbon 13 Urea

http://classyfire.wishartlab.com/tax_nodes/C0000000
http://classyfire.wishartlab.com/tax_nodes/C0000264
http://classyfire.wishartlab.com/tax_nodes/C0000364
http://classyfire.wishartlab.com/tax_nodes/C0000517
http://classyfire.wishartlab.com/tax_nodes/C0000517
http://classyfire.wishartlab.com/tax_nodes/C0004557
http://classyfire.wishartlab.com/tax_nodes/C0000278
http://classyfire.wishartlab.com/tax_nodes/C0003940
http://classyfire.wishartlab.com/tax_nodes/C0004150
http://classyfire.wishartlab.com/tax_nodes/C0001831
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=CHEBI:32285
http://www.genome.jp/dbget-bin/www_bget?drug:D01749
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=636363
https://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?sid=347827869
https://www.chemspider.com/Chemical-Structure.552162.html
https://mor.nlm.nih.gov/RxNav/search?searchBy=RXCUI&searchTerm=226724
https://www.ebi.ac.uk/chebi/searchId.do?chebiId=32285
https://www.ebi.ac.uk/chembldb/index.php/compound/inspect/CHEMBL2096648
https://www.drugs.com/pro/pranactin-citric.html
https://en.wikipedia.org/wiki/Urea_breath_test