Perflenapent (EchoGen, Sonus Pharmaceuticals, Bothel, WA, USA) is a transpulmonary echocardiographic contrast agent for use in patients with suspected or established cardiovascular disease to provide opacification of cardiac chambers, enhance left ventricular border delineation with resulting improvement in wall motion visualisation. EchoGen comprises liquid droplets of dodecafluoropentane stabilised by polyfluoroalkyl(polyoxyethylene) ethanol and dispersed in an aqueous formulation containing sucrose. Dodecafluoropentane is the chemical name used to reflect the perflenapent/perflisopent mixture. Following activation and administration of EchoGen, dodecafluoropentane microbubbles are formed. EchoGen should only be used in patients where the study without contrast enhancement is inconclusive. The European Commission has approved SONUS Pharmaceuticals' EchoGen (perflenapent emulsion) in all 15 countries of the European Union. EchoGen is a fluorocarbon-based ultrasound contrast agent which has been approved as a transpulmonary echocardiographic contrast agent for use in patients with suspected or established cardiovascular disease who have had previous inconclusive non-contrast studies. Additional approved labeling in the EU states that the use of EchoGen in spectral and color Doppler studies was shown to enhance the visualization of blood flow across mitral, aortic and tricuspid valves in a subset of patients. In 2000 SONUS Pharmaceuticals withdrew the NDA for EchoGen in the USA.

Thymidine is a water-soluble pyrimidine deoxynucleoside and potent thymidine kinase substrate. Thymidine is known to be converted to dTTP and utilized for DNA synthesis. It is also known that thymidine is converted by catabolic enzymes to several end products. Excess thymidine results in high levels of dTTP, which exerts a regulatory feedback inhibition in the nucleotide biosynthesis pathways leading to DNA synthesis. This property of thymidine is used when it is given in high doses to patients with solid tumors. Thymidine is being tested in Phase II of clinical trials for the treatment of cancer and 5'-Nucleotidase Syndrome.