Anticoagulants Flashcards
Warfarin inducers? (less drug)
CRAP gpS
C arbamazepine
R ifampicin
A lcohol - chronic
P henytoin
(griseolfin)
(phenobarbitone)
St John’s Wort & Sulfonylurea
Warfarin inhibitors? (more drug)
SiCkfAcE.com + grapefruit juice
S imvastatin
(isoniazid)
C iprofloxacin - tendonitis/rupture
(ketconazole/antifungals)
(fluoxetine)
A lcohol acute
(cardiac/LF)
E rythromycin
(sulphonamides & Na+ Valproate)
(cimetidine)
(omeprazole)
(metronidazole)
what is never prescribed w/ warfarin?
DOAC
prophylactic LMWH
therapeutic LMWH (unless “bridging”)
normal INR?
0.8 - 1.2
target INR in AF?
2 - 3
target INR in metallic valve?
2.5-3.5 / 3-4
if raised INR, but NOT bleeding, Tx for INR:
- <6
- 6 - 8
- > 8
- minor bleeding + INR>5?
- reduce dose
- omit dose for 2 days, then reduce
- oral Vit K 1-5mg
- IV Vit K 1-3mg
(restart doses when INR <5)
Tx for bleeding, with any raised INR:
- minor
- major
- life threatening
- oral Vit K
- 5-10mg IV Vit K
- prothrombin complex concentrate (Beriplex)
drugs that increase risk of bleeding even if INR in range?
NSAIDs
steroids
aspirin
clopidogrel
how does warfarin work?
Vit K reductase inhibitor
- less reduced Vit K
- less 1972 factor production
- less of clotting cascade
how does heparin or LMWH work?
activates antithrombin III & inhibits thrombin
- therefore less clotting cascade
how do DOACs work?
inhibit factor Xa
- less prothrombin to thrombin
- less fibrin, less clots
what drugs to STOP if Sx of bleeding/ tarry stools/ haemoptysis/ haemaemesis?
warfarin
DOAC
LMWH
antiplatelet
what kind of thrombophrophylaxis is given on admission to hospital?
prophylactic LMWH (dalteparin 5000 U daily S/C)
compression stockings
when would you not give compression stockings?
in PAD
(absent foot pulses)
may cause acute limb ischaemia
monitoring when starting someone on warfarin?
INR daily, or alternate days, until 2-3 on two consecutive occasions
(a meaningful INR can only be obtained 3–4 days after starting Tx)
Then, twice weekly for 1–2 weeks (this should be continued if HT, RF or bleed risk)
Then, weekly measurements until > two INR measurements are 2-3
Thereafter, longer intervals (for example, < 12 weeks, if agreed locally)
Once stable, changes seldom required.
painkiller to avoid prescribing with warfarin?
NSAID (stomach ulcers will be at risk of bleed)
if INR is >1.5 perioperatively?
give 5mg oral Vit K
when to stop warfarin before surgery?
when resumed?
5 days before (converted to tinzaparin/LMWH)
evening of surgery/next day
what INR for surgery to go ahead?
<1.5
is warfarin okay to take in pregnancy?
is warfarin safe in breastfeeding?
No! teratogenic
BF - yes
what if rapid anticoagulation with warfarin is required?
Give 5 mg or 10 mg
once a day
for 2 days
remeasure INR on day three
when an immediate effect is required from warfarin? (for example DVT, PE)
heparin/LMWH is given concomitantly for first 2 days, due to initial pro-coagulant affect of warfarin
(this is done in secondary care)
examples of LMWHs?
dalteparin sodium
enoxaparin sodium
tinzaparin sodium
what to prescribe as prophylaxis of DVT in medical patients?
what if thy’re on COCP?
when to be cautious?
what to avoid prescribing alongside?
dalteparin sodium 5000 units S/C every 24 hours (LMWH)
stop COCP!
bleeding risk - recent stroke
DOACs
which drugs are Xa inhibitors?
DOACs
-Xa-ban
how to Tx VTE (DVT/PE)?
1) LMWH S/C
dalteparin sodium approx 15,000 units
(200 units/kg daily + max. per dose 18 000 units)
2) OR fondaparinux S/C
(if body-weight 50–100 kg)
7.5 mg every 24 hours, usually warfarin started at the same time
either should be continued for at least 5 days and until INR ≥ 2 for at least 24 hours
how to Tx massive PE (haemodynamic instability)?
unfractioned heparin (UFH) + thrombolytic therapy (US‑enhanced, catheter‑directed thrombolysis)
if life threatening, occasionally surgical thrombectomy
how to give VTE prophylaxis if patient has a phobia to needles?
apixaban PO 2.5 mg twice daily
what to consider before prescribing NOACs?
eGFR
Tx acute stroke?
CT <1 hr
if no haemorrhage:
<80 years and onset <4.5 hours ago consider thrombolysis (alteplase)
Aspirin 300mg oral
if INR > 1.5 on the day before surgery?
phytomenadione (vitamin K) 1–5 mg PO, using the IV preparation, is indicated
if a pt on warfarin with INR in range is being Tx with clarithromycin?
continue warfarin at normal dose and re-check INR in 48 hours
role of LMWH?
- LMWH is used SC for Tx PE/DVT and ACS (i.e. unstable angina and MI)
- it is also used (at a much lower dose) for DVT prophylaxis in a signifcant proportion of inpatient
- 3 LMWH: enoxaparin, dalteparin and tinzaparin
- you can prescribe LMWH in units or
mg - unfractionated heparin is used IV when tighter control is needed (i.e. much less commonly)
when to prescribe a lower dose of LMWH?
patients with low body weight or severe renal failure
name of Vit K drug?
phytomenadione
what to search for INR tables/warfarin?
“oral anticoagulants”
Pt with DVT, weight 60 kg, INR 1.0 (<1.4), Tx?
- 1st: LMWH or fondaparinux to patients with confirmed proximal DVT (in/above popliteal) or PE
- dalteparin sodium 25 000 units/mL injection
- tinzaparin 175 units/kg SC daily
- enoxaparin sodium 100 mg/mL injection
OR - fondaparinux sodium 12.5 mg/mL injection
Enoxaparin/dalteparin/tinzaparin are contraindicated in?
- with current (or history of) heparin-induced thrombocytopenia
- high risk of bleeding (e.g. acute gastroduodenal ulcer, cerebral haemorrhage, conditions causing a predisposition to bleed, serious coagulation disorders)
- within 3 months stroke (unless due to emboli)
LMWHs generally preferred over UF in DVT/PE - EXCEPT when?
- in the case of significant renal impairment
- UF effects are easier to reverse
dose of tinzaparin for 60kg patient in DVT Tx?
- tinzaparin sodium 20 000 units/mL injection
- 175 units/kg SC daily
- 60*175 = 10500
- but can only be given in increments of 0.05ml which is 1000 units
- therefore 11 000 units is practical for administration
dose of dalteparin for 60kg patient for DVT Tx?
- dalteparin sodium 25 000 units/mL injection
- 12 500 units for a patient weighing 57-68 kg SC daily (0.5 mL) using the 25 000 units/mL strength
fondaparinux dose for 60kg patient in DVT Tx?
- fondaparinux sodium 12.5 mg/mL injection
- body weight 50–100 kg — 7.5 mg every 24 hours
- 7.5 mg SC daily (0.6 mL) using the 12.5 mg/mL preparation
how does fondaparinux work?
synthetic pentasaccharide that inhibits activated factor X
it is given S/C in a dose based on weight
enoxaparin dose for 60kg adult in DVT Tx?
- enoxaparin sodium 100 mg/mL injection
- 1.5 mg/kg SC daily
- 60*1.5 = 90 mg
- 0.9 mL of the 100 mg/mL injection
Tx heparin OD?
Protamine sulphate
