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. Zenecas marketing and brand name, "Zestril", turned out to be stronger than Mercks 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
"Lisinopril". Drug Information Portal. U.S. National Library of Medicine.
Enalaprilat, however, had a problem of its own in that it had poor oral availability. This was overcome by the researchers at Merck by the esterification of enalaprilat with ethanol to produce enalapril. : 13 Merck introduced enalapril to market in 1981; it became Mercks first billion dollar-selling drug in 1988.: 13  The patent expired in 2000, opening the way for generics. References
External links
"Enalapril". Drug Information Portal. U.S. National Library of Medicine.