As an anticoagulant, clopidogrel is used, inter alia, for the prevention of myocardial infarction, stroke, stent implantation and for the treatment of peripheral occlusive disease, in the presence of certain conditions in competition with the much cheaper conventional anticoagulants such as ASA (acetylsalicylic acid, aspirin). Clopidogrel acts principally as ADP receptor blocker, so that the ADP-dependent platelet activation and thus the platelet aggregation is inhibited.
What is clopidogrel?Clopidogrel is a relatively new drug that acts as an anti-platelet agent on blood clotting.
Platelets, also referred to as platelets, are equipped with adenosine diphosphate receptors, on which, if necessary, the platelet aggregation is controlled to z. B. to close injured blood vessels.
The drug clopidogrel inhibits the platelet receptors so that no or limited platelet aggregation can occur. Clopidogrel is a thienopyridine derivative and, in its role as anticoagulant, belongs to the group of antiplatelet agents. The drug is administered in a metabolically inactive form and after oral ingestion must first be converted into the bioactive form by oxidation and hydrolysis over several stages.
The bioavailability after absorption in the digestive tract is about 50%. About 30% of Central Europeans carry a mutant gene that reduces or completely prevents the conversion of the active ingredient into the bioactive form. Inactivation of platelet adenosine diphosphate receptors is irreversible, so the effect of clopidogrel persists for a few days even after discontinuation of the drug until the "old" platelets are replaced with newly formed platelets which is the case after about a week.
In the presence of certain conditions or diseases such as stroke, myocardial infarction, constriction of the coronary arteries or peripheral arterial occlusive disease (PAD), the resulting repair mechanism in the form of platelet aggregation can lead to occlusion of the blood vessels with sometimes serious consequences.
In these cases, anticoagulants - also known as anticoagulants or blood thinners - reduce the tendency of platelets to coagulate to prevent the formation of so-called thrombi (aggregation clumps) in the veins or to resolve existing thrombi again. Since the aggregation of platelets is controlled by adenosine diphosphate receptors (ADP receptors), there is a possibility of intervention here. The clopidogrel converted into the bioactive form makes the ADP receptor P2Y12 inactive by inhibition. The goal is to reduce the tendency for the formation of some life-threatening thrombi, is achieved. It must be remembered that the process of inactivation or inhibition of P2Y12 receptors is irreversible.
This means that platelets can not regain their ability to aggregate even after the drug clopidogrel has broken down in the liver. The ability to coagulate is only restored through the process of natural renewal of platelets. The life cycle of the platelets in humans is about 7 to 10 days, so that 10 days after degradation of clopidogrel a complete renewal of the platelets has taken place and the coagulation ability is fully restored, which z. B. may be important in upcoming operations.
Medical application & use
Clopidogrel is processed in a variety of drugs from different manufacturers - including generic drugs - in the form of certain salts. Monopreparations containing exclusively clopidogrel as active ingredients as well as combination preparations with at least one further active ingredient are offered. Combination preparations contain as the second active ingredient usually aspirin (aspirin), which also contributes to the coagulation inhibition, but attacks at another point in the coagulation process.
To achieve a rapid anticoagulant effect, a so-called loading dose of once 300 to 600 milligrams is required, while the normal daily maintenance dose is 75 milligrams. Taking full account of the loading dose, the full effect is achieved within two to six hours, while full anticoagulation protection is achieved only after five to seven days without taking the loading dose. As a special feature interactions with other anticoagulants, with certain analgesics and with so-called proton inhibitors to reduce gastric acidity must be considered.
Risks & Side Effects
On the one hand, the greatest dangers associated with the use of drugs containing the active substance clopidogrel lie in the fact that the active ingredient in non-responders due to a known gene mutation is not or only insufficiently converted into the bioactive form.
As a result, the intended anticoagulation is not or not fully achieved. If it is not known if the patient belongs to the non-responder group, regular use of clopidogrel may be almost ineffective. After all, in Central Europe, about 30% of people are affected by the mutation. Also interactions with other medicines must be considered. If additional anticoagulants are also taken, the anticoagulant effect is usually enhanced. Interactions with antidepressants and proton inhibitors for the treatment of reflux consist in a reduction of anticoagulation.
The other extreme is an overdose of the drug. There is no known antidote that could reverse or reduce the effects of clopidogrel in case of accidental overdose. The only option is to infuse platelet-containing fluids, but care should be taken that the platelets are also changed as long as clopidogrel is present in the blood. The half-life for the degradation of clopidogrel is 7 to 8 hours. As adverse effects during the treatment period, gastrointestinal bleeding, increased nosebleeds, hematomas, diarrhea and rash may occur.
In the event of accidental injury or emergency surgery, the problem may arise that clopidogrel's anticoagulant effect can not be reversed in the short term and may cause bleeding that is difficult to arrest.