heparin & warfarin Flashcards
6 indications for UFH
acute VTE & PE tx
acute MI and unstable Angina
VTE prophylaxis
cardiopulmonary bypass & vascular surgery
PCI and stent placement
DIC
heparin MOA
both types increase ATIII activity to inhibit thrombin & Xa
LMWH targets Xa more than IIa
aPTT normal vs heparin goal
normal 30-40 secs
heparin is 50-90 secs (1.5-2.5x normal)
4 heparin ADR
1 bleeding
osteoporosis
increased LFT
HIT rxn
4 ways LMWH is diff from UFH (think bioavailability, monitoring, formulations, ADR)
LMWH has better bioavailability and longer half life
LMWH only monitors anti Xa in certain conditions, not routine
LMWH is subQ only?
LMWH has lower risk of HIT, osteoporosis, & is cleared renally
which is ok in pregnancy (heparin or warfarin)
heparin
what causes HIT
heparin binds to PF4 causing Ig to be raised against it causing platelet aggregation (thrombosis)
macrophages from spleen destroys cells (low platelet count)
two features of HIT
thrombosis & low platelets
4 things to monitor with UFH use
aPTT
chromogenic antifactor Xa heparin assay (therapeutic is 0.3-0.7)
activated clotting time (ACT)
CBC & platelets
prophylactic vs therapeutic dosing of UFH
2 lab tests if HIT is suspected
Ag assay for presence of HIT antibodies (P selectin expression assay)
Functional assay for platelet activation in presence of heparin (serotonin release assay)
4 Ts probability score for HIT; high vs low probability score
Thrombocytopenia
Timing of platelet count fall
Thrombosis (or other clinical sequelae)
oTher causes for thrombocytopenia
high is 6+; low is 0-3
prophylactic vs therapeutic dosing of LMWH
prophylactic is based on procedure– 30 to 40mg if enoxaparin; 2500-5000 if dalteparin
therapeutic is wt based—-1to 1.5mg/kg for enoxaparin & 120-200 units/kg in dalteparin
which should you use in renal impairment (UFH or LMWH)
UFH is preferred
5 things to monitor to LMWH
anti-factor Xa if obese, renal insufficiency, pregnancy
platelets
CBC
renal fx (SCr, CrCL)
weight
reversal agent for LMWH
none
protamine only partially reverses it
4 indications for LMWH
VTE prevention post surgery
acute VTE and PE; VTE in cancer
unstable angina or non-Q wave MI
STEMI
2 indications for both UFH and LMWH
tx for acute VTE and unstable angina
VTE prophylaxis
should you increase or decrease UFH doses in pts undergoing PCI and CABG
increase!
4 things that increases bleeding w/ heparin
higher dose
also taking fibrinolytic agents or GIIb/IIIa inhibitors
recent surgery/trauma/invasive procedures
hemostatic defects
two groups with highest risk of HIT
postoperative pts and pts w/ cancer
how do you treat HIT? (include 3 meds)
stop & avoid warfarin
tx w/ argatroban, fondaparinux, lepirudin (direct thrombin inhibitors)
general dosing for protamine sulfate
give smaller doses as time goes on (max of 50mg) & monitor aPTT in reversal
the two ADR of protamine sulfate; 1 contraindication
hypotension & bradycardia
not for ppl w/ fish allergies
MOA for warfarin
blocks synthesis of vitamin K clotting factors by inhibiting vitamin K epoxide
which has no direct effects on established thrombus? (heparin or warfarin)
warfarin
what is the purpose of warfarin? (3 things it prevents)
prevents further clot extension
prevent 2ndary thromboembolic complications
prevents recurrent thromboembolic events
how long does it take warfarin to start working? for full effect?
onset: 1-3 days
full effect: 5-7 days
2 tests to monitor warfarin
PT/INR
CBC every 6 months
normal INR
at or below 1.1
INR goal for afib and VTE treatment w/ warfarin
2-3
INR goal for mechanical heart valve w/ warfarin
can be from 2 to 4
warfarin duration for afib vs VTE tx vs heart valve
indefinite for afib & heart valves
3mo to indefinite for VTE tx
warfarin head related contraindication (2)
recent CNS bleeding or cerebral aneurysm
neurosurgery, cerebrospinal, eye recently or anticipated
vessel related warfarin contraindication (2)
hemorrhagic or blood dyscrasias
malignant HTN
carditis related warfarin contra (2)
pericarditis or pericardial effusion
bacterial endocarditis
abdominal/pelvic region contraindications for warfarin (2)
GI bleeding or pregnancy
physical injury related contraindications for warfarin (2)
trauma or severe bleeding
sig h/o falls or fall risk
pt habit related contraindication for warfarin (2)
non-adherent pts
alcoholic
4 meds that enhance CYP2C9 to LOWER INR <2
griseofulvin
barbiturates
phenytoin
carbamazepine
5 meds/things that inhibit CYP2C9 in raise INR
cimetide
omeprazole
metronidazole
TMP/SMX
amiodarone
alcohol
two things that increase risk of bleeding with warfarin
antiplatelets
NSAIDs
three OTC/herbal products that affect warfarin
NSAIDs
APAP
ginseng, st johns wort
4 ADR of warfarin
bleeding (less severe & more severe)
skin necrosis
purple toes syndrome
teratogenicity
for how long should you overlap warfarin with heparin
until INR>2 for 24hrs at least 5 days of tx
how often do you monitor INR in outpatient person using warfarin
every 2-3days till stable then every 1, 2, 4 wks
you adjust warfarin dosage based on?
INR response
3 causes of supra-therapeutic INR (not comprehensive)
decompensation of cardiac dz
poor nutrition intake
acute illness
by how much should you adjust warfarin dose
10-15% of total weekly dose
how do you adjust dose if the INR is sub-therapeutic
increase weekly dose
consider boost (one time)
how do you adjust dose if the INR is supra-therapeutic
decrease weekly dose
consider one-time dose omission
when you stop warfarin how long does it take for INR to return to baseline
4-5 days
w/ warfarin, what do you do if INR btwn 4.5 to 10 w/o bleeding
omit 1-2 doses
monitor more frequently and resume when INR therapeutic
INR 10+ w/o bleeding. adjust warfarin dose
hold warfarin and give Vit K
resume warfarin when INR therapeutic
serious bleeding at any INR elevation. adjust warfarin
hold warfarin and give vit K via IV
supplement w/ PCC, FFP, or rVIIa
things you can use to reverse warfarin (4)
vit K
FFP
factor VII (rVIIa)
prothrombin complex concentrates (PCC)
