each structural unit of enalaprilat, substituting various amino acids. Adding lysine at one end of the drug turned out to have strong activity and had adequate bioavailability when given orally; analogs of that compound resulted in lisinopril, which takes its name from the discovery with lysine. Merck conducted clinical trials, and the drug was approved for hypertension in 1987 and congestive heart failure in 1993. The discovery posed a problem, since sales of enalapril were strong for Merck, and the company did not want to diminish those sales. Merck ended up entering into an agreement with Zeneca under which Zeneca received the right to co-market lisinopril, and Merck received the exclusive rights to an earlier stage aldose reductase inhibitor drug candidate, a potential treatment for diabetes. Zeneca's marketing and brand name, "Zestril", turned out to be stronger than Merck's effort. The drug became a blockbuster for AstraZeneca (formed in 1998), with annual sales in 1999 of $1.2B. The US patents expired in 2002. Since then, lisinopril has been available under many brand names worldwide; some formulations include the diuretic hydrochlorothiazide. References Further reading External links ACE inhibitors Amino acid derivatives AstraZeneca brands Carboxamides Carboxylic acids Embryotoxicants Enantiopure drugs Merck & Co. brands Pyrrolidines Teratogens Wikipedia medicine articles ready to translate