Dear Dr Puff n'Stuff

What are the risk factors involved with continued IV drug use after being prescribed Warfarin for Deep Vein Thrombosis.

Gill, Prestwich

Dear Gill,

Quite a few drug-users undergo treatment with warfarin. This is because injecting drug users are at particular risk of getting clots in their veins. They are even more at risk if they inject in their groin or their neck. When a clot occurs in one of the large veins, it called a deep vein thrombosis. It happens most commonly in the legs, causing sudden pain, increased warmth and swelling in the calf. This is a dangerous situation, because there is a high risk that some of the clot will break off, and get itself lodged in the lungs, causing pulmonary embolism which is often fatal. If you suffer sudden pain and swelling in your calf muscles, you must get medical advice as soon as possible. If the thrombosis is confirmed, you will probably be put on warfarin. Warfarin stops clot forming, and therefore prevents you having further trouble while the thrombosis heals. Treatment is completely safe, provided you pay attention to certain precautions. But it is strong medicine and has to be taken with care.

[#] It takes about five days to start working. It is likely therefore that you will be put on heparin injections at first, until the warfarin kicks in. (Heparin is extracted from leeches.) Similarly, when you stop taking it, it will still be in your system for five days.

[#] Usually, you will be on treatment for about three months. But if you get more clots when you stop warfarin, long-term treatment will be advised.

[#] You need to have regular blood tests, to make sure the blood is not too thick or too thin. The tests check a measure called the INR. The right level is between 2 and 3. If it is lower, doctors will increase your dose. If it is higher, they will ask you to miss out some doses.

[#] If you bleed excessively you must see your doctor. For example, cuts or injection sites may take ages to stop bleeding. If there is blood in the toilet for any reason, or if you cough up blood, seek urgent advice (although this is very rare if you take the right dose and have your blood tests).

[#] Do not take any other medicine without asking the advice of a doctor or chemist. Many medicines interact with warfarin, and alter its effect. For example, aspirin makes bleeding more likely. Some antidepressants increase the effect of warfarin, and others work in the opposite direction.

[#] Be very careful about alcohol. Heavy drinking can precipitate serious bleeding if you are on warfarin.

[#] Do not inject in the muscle while on warfarin. There is a danger of blood release into the tissues, which can then turn into an abscess.

[#] If you inject, think about stopping. If you get one thrombosis, you are much more at risk of further thrombosis in the future. But if injecting is so important to you that you decide to continue even after suffering thrombosis, do what you can to lower the risks of further trouble. Avoid the groin and neck. Use veins in your elbows, hands and feet if possible. Take exercise, and don’t get overweight. Above all, think of giving up smoking, which very much increases the danger of thrombosis. This is easier than it was, thanks to nicotine patches and a new medicine called Zyban. Get in touch with your local anti-smoking service for further advice. Think "Which do I prefer – the fag or the needle?" Doing both may be one indulgence too far.

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