#7524 - Anticoagulation - Medical Finals & OSCEs Notes

Anticoagulation

Warfarin

Contraindications:

• Haemorrhagic stroke

• Potential bleeding lesions (ulcers, varices)

• Uncorrected major bleeding

• Pregnancy (teratogenic)

• Uncorrected bleeding disorders such as CRF, thrombophilia, thrombocytopaenia, liver failure

• Uncontrolled hypertension such as SBP>200mmHg

• Bleeds: intracranial/spinal, postpartum, trauma, surgery

Cautions: high risk of falls and NSAIDs due to ulcer risk

Administration

Standard: 5mg OD for two days and check INR on day three

Immediate: use heparin

Slow-loading (safe in AF): 1mg/2mg OD to be therapeutic in three or four week

Maintenance: usually 3-9mg OD at the *same time each day* usually in the evening so that they can adjust after taking an INR in the morning

Targets

Mechanical aortic valves: 3

Mechanical mitral valves: 3.5

Recurrent VTEs on anticoagulation: 3.5

Most scenarios are 2.5: AF, VTE, antiphospholipid syndrome, cardioversion preparation, bioprosthesis, post-MI, arterial embolisation, dilated cardiomyopathy, mitral stenosis or regurgitation with a history of thrombus.

Duration

• 6 weeks distal DVT

• 3 months proximal DVT or PE

• Long-term if recurrent DVT or AF or mechanical heart valves

• A month before cardioversion and three months after if sinus rhythm is maintained

• It can be stopped abruptly without harm when the course is finished

Monitor

Daily or alternate daily INR until the INR is within the therapeutic range on two consecutive tests. Then test INR twice weekly then weekly then longer i.e. up to every three months. Do higher frequency monitoring if there is a higher risk of bleeding (CKD, severe HTN, liver disease). In general, a 15% change in dose is equivalent to an INR change of 1.

Stopping warfarin

IV vitamin K. Oral vitamin K takes longer. Vitamin K as administered drug, PO or IV = phytomenadione. PCC also=prothrombin complex concentrate. Trade name Beriplex. Rapid treatment=combination of PCC and IV vit K. Use fresh frozen plasma (FPP) if there is no PCC but in emergencies PCC is more effective and in non-emergencies vitamin K is sufficient.

• Major bleeding, regardless of what the INR is: stop warfarin and reverse with PCC and 5mg (or 10mg) of IV vitamin K.

• INR >5 with minor bleeding: stop warfarin and also give oral vitamin K 1-3mg

• INR <5 with minor bleeding: stop warfarin and consider oral vitamin K 1-3mg and consider modifying the dose

• INR >12 with no bleeding: omit warfarin and reverse with oral 5mg vitamin K

• INR 8-12 with no bleeding: omit warfarin and reverse with oral 2mg vitamin K

• INR 5-9 with no bleeding: omit warfarin and restart with a modified dose when INR<5, no need for reversal

Also Stop 5 days before surgery as INR must be <1.5 for surgery

Side effects

2-4% risk of bleeding per annum that requires transfusion. 0.2% risk per annum of a fatal haemorrhage

Also: n+v, purpura, alopecia, pancreatitis, hepatotoxicity

Interactions

TCAs, SSRIs, NSAIDs, antibiotics, alcohol, carbamazepine, phenytoin, St John’s Wort, amiodarone, steroids, aspirin, cranberry juice, tamoxifen, thyroxine. Refer to PCBRAS and ODEVICES acronyms.

Rivaroxaban

A director inhibitor of Factor X that does not require monitoring

SEs: nausea, haemorrhage. Stop immediately if major haemorrhage occurs.

Used as VTE prophylaxis after TKR/THR 10mg OD for 2-5 weeks, starting 6 hours after surgery.

Dabigatran

A direct inhibitor of thrombin with rapid onset and...