Pharmacokinetics and the "Pro-drug" Evolution
The evolution of ACE inhibitors from the early days of Captopril to modern agents has been defined by improvements in how the body processes the medication. Most modern versions are classified as "pro-drugs." This means that when the patient swallows the tablet, the chemical is in an inactive state. It must first pass through the liver, where enzymes convert it into the active form that actually blocks the angiotensin-converting enzyme.
For example, Enalapril is converted into Enalaprilat, and Ramipril becomes Ramiprilat. This design allows the medication to be absorbed more efficiently from the digestive tract and provides a longer-lasting effect. Consequently, while the very first ACE inhibitors required three doses a day, the modern pro-drug versions usually only require a single daily dose to maintain stable blood pressure and heart protection for a full twenty-four hours.