Warfarin: patient knows best | University of Oxford
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Warfarin: patient knows best

Jonathan Wood

An Oxford-led review published last week in the Cochrane Library  - that gold-standard source for the best evidence-based medical care - showed how empowering people at risk of blood clots to determine their own dose of anti-clotting drugs leads to a large drop in adverse events and deaths.

Carl Heneghan from the Centre for Evidence-Based Medicine [CEBM] at the University of Oxford and colleagues found a 50 per cent drop in the number of blood clots and a 36 per cent reduction in deaths among those patients who were able to monitor their own anti-clotting therapy.

Warfarin (Coumadin) is used in a number of conditions where there is a risk of dangerous blood clots, such as deep-vein thrombosis, abnormal heart rhythms, pulmonary embolism, and in patients with mechanical heart valves. In those at increased risk of stroke, warfarin reduces the likelihood of a stroke but also its severity.

The number of people taking anti-clotting drugs is on the up as they are increasingly used for more diseases and the population ages. But it is important to get the dose absolutely right, as while the drugs can prevent clots they can also go too far and cause major bleeds.

Typically, people have to have blood samples taken at a GP surgery or specialist clinic to determine the correct warfarin dose. Once the right dose has been established initially, patients still need to have blood tests on average around once a month.

But a simple device – like those used by diabetics to monitor their blood sugar level – can be used by people on the anti-clotting drug warfarin to help them determine the correct dose. Patients using the device can then either adjust their own medication using pre-determined guidelines (self-management) or they can call a clinic to be told the appropriate dose adjustment (self-monitoring).

Carl Heneghan and colleagues assembled all the best evidence there is to compare outcomes for patients using these different ways of monitoring warfarin levels. They combined data from 18 trials involving a total of almost 5,000 patients. In a podcast on the website of the Cochrane Collaboration, Carl Heneghan says the conclusion was clear: ‘Compared to standard monitoring, patients who self-monitor or self-manage can improve the quality of their oral anticoagulation therapy.’

However, it is worth pointing out that self-monitoring or self-management of warfarin wasn’t possible for up to half of patients for a variety of reasons. These included inability to complete the necessary training, simple refusal by the patient, or exclusion by their GP.

So there is a need for doctors to be able to identify those patients that would benefit. Still, most would agree that giving patients power over their own treatment where possible is a good thing.

‘Self monitoring has impact beyond just the reduction in adverse events,’ says Carl Heneghan. ‘Issues like freedom to travel and time off work for blood tests are important factors for individuals in determining whether to self-test.’

Another Cochrane review published at the same time may also offer significant relief for a different set of patients. As reported in The Times, Sheena Derry of the Nuffield Department of Anaesthetics at Oxford University and colleagues found that migraine sufferers might get pain relief by taking slightly more aspirin than the recommended dose.

David Rose reports that: ‘Taking up to three tablets – up to 1,000mg – in one go could leave one in four (25 per cent) sufferers pain-free within two hours.’ More than half of patients experienced some relief from their debilitating headaches at this dose. Adults are normally advised to take no more than two aspirin tablets in one go.

The researchers also found that aspirin also helped to prevent nausea, vomiting and sensitivity to light commonly caused by migraines – but sachet formulations combining another anti-sickness drug, metoclopramide, worked best at this.