If the inside of a blood-vessel wall is damaged at any point a clot of blood - a thrombosis - may form at this site; the clot may stay where it is, impeding the blood-flow, or move on around the body to cause what is called an embolism. Coronary thrombosis is the result of an unwanted aggregation of clotted blood. Drugs designed to interfere with, and sometimes prevent, clotting are called 'anticoagulants'.

These drugs fall into two main groups. First come substances such as heparin which directly assist in preventing blood from clotting; these are administered by injection into the bloodstream. Second are the oral anticoagulants, such as nicoumalone and warfarin, which are taken in tablet form and act indirectly by stopping the body from producing one of its numerous 'clotting factors'.

Anticoagulants like heparin slow down the process of clotting. Heparin can be highly effective, but again it is not without side-effects: bleeding from the nose, bruising, and sometimes fever and allergy. Doctors like to monitor the progress of the clotting times in a patient very closely, both to adjust the dosage if required and, on occasions, to try to discontinue treatment altogether.

The indirect anticoagulants are mainly derivatives of a substance called coumarin. Their action is a good deal slower than that of the direct-action drugs, perhaps taking several days to be effective; for this reason, if there is any sense of urgency in the case, heparin is frequently prescribed initially. Again careful checks on how long clotting is taking are necessary, and adverse effects, mainly bleeding, are not unknown.

In short, anticoagulants should be taken with extreme caution, and strictly in accordance with your physician's advice. There are a number of reasons why you might not be able to take the drugs - impaired kidney function, having just had a baby, recovering from surgery, taking other drugs and so on. In fact, patients on anti-coagulant therapy are usually given a warning card to carry so that doctors can take this into account when prescribing "further drug treatments.

If a blood clot has formed there are drug available to help dissolve it. One of these is streptokinase, which is an enzyme, or biological catalyst. The drug is administered either by an intravenous injection or by means of a catheter snaked directly into the coronary artery where the clot has formed. This is, of course, a delicate business, and to be effective the procedure has to be carried out very soon after a warning sign has indicated that coronary thrombosis is the problem. Conversely, the risks are comparatively small and the advantages for people with a high risk of acute heart attack are undeniable. Streptokinase, although still experimental, has reduced the likelihood of death resulting from a first or second heart attack.

Anticoagulants are essential drugs for people who have been fitted with mechanical heat-valve replacements.




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