Direct anticoagulants and their targets
Direct-acting anticoagulants work directly in the blood plasma, neutralizing already activated coagulation factors at the final stages of fibrin formation (predominantly factors IIa and Xa).
Based on the mode of interaction with targets, they are classified into:
- Antithrombin-dependent agents (heparin and analogues): they do not block enzymes on their own, but significantly enhance the protective action of the endogenous anticoagulant — antithrombin III.
- Direct active-site inhibitors: bind directly to the active site of thrombin or factor Xa. These include hirudin, dabigatran, and rivaroxaban.
Lipid-lowering agents and enzymes
The regulation of lipid metabolism is based on suppressing the synthesis and absorption of cholesterol:
- HMG-CoA reductase inhibitors (statins): simvastatin, atorvastatin, and rosuvastatin block the main liver enzyme responsible for cholesterol synthesis.
- Absorption inhibitors (ezetimibe): inhibit a specific sterol transporter in the intestine, reducing the incorporation of cholesterol into chylomicrons (can be used in combination with simvastatin).
- Other groups: fibrates (gemfibrozil), bile acid sequestrants (cholestyramine), nicotinic acid (niacin), and eicosanol.
Dual action of vasopeptidase inhibitors
An innovative class of drugs, exemplified by omapatrilat, demonstrates a combined effect on vascular tone through a dual mechanism:
- Suppression of angiotensin-converting enzyme (ACE) activity, which reduces the vasopressor effect of the renin-angiotensin system.
- Blockade of neutral endopeptidase — an enzyme that degrades endogenous vasodilator peptides.
This results in a potent reduction in blood pressure through the simultaneous elimination of vasoconstriction and enhancement of vasodilation. However, the drug did not enter medical practice due to a high risk of angioedema.
Sartans as an alternative to ACE inhibitors
Angiotensin II receptor type 1 blockers (sartans), such as losartan, irbesartan, valsartan, and eprosartan, address the issue of incomplete suppression of the renin-angiotensin system.
Traditional ACE inhibitors block only the main vascular pathway of angiotensin II formation, leaving its tissue synthesis active. Sartans act differently: they provide direct blockade of $AT_1$ receptors and eliminate the effects of angiotensin II regardless of its origin pathway, providing more reliable cardiovascular protection.
Inhibitors are the "brakes" of biochemical reactions: they either enhance natural defenders (like heparin with antithrombin III) or take the "driver's seat" themselves (the active site of an enzyme or receptor), blocking the pathway of a pathological signal.
Class and exam questions
What is the main difference between heparin and direct active-site inhibitors?
Heparin belongs to antithrombin-dependent agents and does not block factors by itself, but rather significantly enhances the action of endogenous antithrombin III. Direct inhibitors bind directly to the active site of the enzyme.
Why are sartans considered more effective compared to ACE inhibitors?
ACE inhibitors block only the systemic pathway of angiotensin II synthesis, leaving tissue synthesis active. Sartans block receptors directly, eliminating the effects of angiotensin II regardless of its pathway of formation.
What mechanism underlies the action of statins?
Statins (e.g., simvastatin, atorvastatin) block HMG-CoA reductase, a key enzyme responsible for cholesterol synthesis in the liver.
What else to study on this topic
- Pharmacokinetics of omapatrilat and reasons for its withdrawal
- Comparison of tissue and systemic synthesis of angiotensin II
- The role of intestinal sterol transporters during ezetimibe administration
- Features of the action of fibrates and bile acid sequestrants
- Differences between antithrombin-dependent drugs and direct thrombin inhibitors
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