Test 2 Study Guide Flashcards
What is the half life of Factor II
65 hours
What is the half life of Factor VII
5 hours
What is the half life of Factor IX
25 hours
What is the half life of Factor X
40 hours
Which factors are not manufactured by the liver?
III - Thromboplastin (vascular walls)
IV - Calcium (diet)
VIII:vWF vonWilibran Factor (vascular endothetlial)
Aprotinin MOA
Aprotinin - Antifibrinolytic Agents
Inhibits plasmin, therefore fibrin breakdown is slowed.
Used during cardiac surgery to decrease intraoperative blood loss
I. Aprotinin MOA (PG 449 4th ed)
a. a naturally occurring serine protease inhibitor hat decreases activation of plasminogen and the activity of plasmin
b. Classified as an anti-fibrinolytic, anticoagulant, platelet protective, and anti-inflammatory drug.
c. Possible anaphylactic and analphylactoid reactions
i. Derived from bovine lungs
ii. Rate of occurrence is 2.8%
Protamine MOA
Protamine used for reversing anticoagulation
Protamine found in salmon sperm
How: + charged alkaline protamine combines with the - charged acid heparin to form a stable complex that is devoid of anticoagulant activity
Dose of protamine required to antagonize heparin is typically 1mg for every 100units of circulating heparin activity
Side effects of Protamine?
Side effects
Hypotension
Rapid IV injection of protamine may be associated with histamine release, causing facial flushing, tachycardia, and hypotension.
Pulmonary hypertension
In rare cases, protamine neutralization of heparin can result in secretion of thromboxane and 5-hydroxy tryptamine (serotonin) manifesting as pulmonary vasoconstriction, Pulmonary hypertension, and bronchoconstriction
Allergic reactions
Pretreatment with histamine-receptor antagonists followed by a slow trial of protamine infusion
MOA for Aspirin?
Blocks production of thromboxane A2
Since platelets do not synthesize new proteins, the action of ASA on platelet cyclooxygenase is permanent lasting the life of the platelet (7-10 days)
Complete inactivation is achieved with 160 mg/day
MOA of Dipridamole?
Cilostazol and several of its metabolites are cyclic AMP (cAMP) phosphodiesterase III inhibitors (PDE III inhibitors), inhibiting phosphodiesterase activity and suppressing cAMP degradation with a resultant increase in cAMP in platelets and blood vessels, leading to inhibition of platelet aggregation and vasodilation.
MOA of Dextran
Dextran - In preclinical studies, the mechanism of action is thought to be related to the blockage of the uptake of tissue plasminogen activator by mannose-binding receptors. This process has a direct effect by enhancing endogenous fibrinolysis.
MOA of thienopyridines
Thienopyridines: Clopidogril, Prasugrel and Ticagrelor
Ticlid (Ticlopidine)
Plavix (Clopidogrel)
Work at the G protein receptors
Inhibits adenylyl cyclase which results in lower levels of cyclic AMP and thereby less platelet activation
Dose
Ticlid loading 500 mg followed by 250 mg/day
Plavix loading 300 mg followed by 75 mg/day
Inhibition of platelets persists for 3-4 days after D/C
Adverse effects
Nausea, vomiting and diarrhea
Neutropenia
MOA of Glycoprotein IIb/IIIa Inhibitors
Glycoprotein IIb/IIIa Inhibitors
Platelet surface integrin
Glycoprotein is a receptor for fibrinogen and von Willebrand factor which anchor platelets to foreign surfaces and to each other, thereby mediating aggregation
The receptor is activated by platelet agonists
Thrombin, collagen, or thromboxane A2
Inhibition of the glycoprotein binding blocks platelet aggregation induced by any of the agonist
Examples Reopro (abciximab), Integrilin (Eptifibatide)
OTC supplements that can cause enzyme induction
St. John’s Wort
Used as an antidepressant and anxiolytic.
extract inhibits reuptake of serotonin, norepinephrine, dopamine, and MAO; acts as a tricyclic.
Increased cytochrome P450 activity
May interfere with digoxin pharmacokinetics
avoid MAOIs, SSRIs, and ephedrine
St John’s: happy pill via NT reuptake inhibition. Can decrease dig, induces CP450.
Drugs that block factor II and X
Heparin
Heparin is a negatively charged Mucopolysacharide
Unfractionated heparin (UFH) is an extract of porcine intestines or bovine lung
Heparin is stored in the mast cells
Does not cross the placenta
Thrombin (IIa) and factor Xa are inhibited
LMWH
Derived from standard grad UFH by chemical to yield a molecular weight of 4,000 to 5,000 daltons
LMWH mainly removed by non-saturable renal excretion
Effect prolonged with renal failure
Protamine does not neutralize LMWH
Fondaparinux
Synthetic anticoagulant
Inhibits factor Xa but no direct activity against thrombin
Administer SQ
Elimination half-life 15 hours
Eliminated by kidneys-use with caution in renal failure
Clinical Use: DVT, PE, Alternative pt. with HIT
Heparin and its LMW derivatives, MOA
Heparin - Heparin acts as an anticoagulant by binding to ATIII enhancing the rate of thrombin AT III complex formation by 1,000 to 10,000 times. Thrombin (IIa) and factor Xa are inhibited
Heparin MOA
Has an anti-activated factor X to anti-activated factor II activity of about 1:1
LMWH MOA
Enoxaparin has a corresponding ratio that varies between 4:1 and 2:l
Care should be taken to delay surgery for 12 hours after the last dose
aPTT
Activated partial thromboplastin time (aPTT)
Intrinsic pathway
Heparin tx is usually monitored to maintain the ratio of the aPTT within a defined rage of approximately 1.5 to 2.5 times normal value*
Typically 30 -35 seconds
Heparin prolongs aPTT
*** easily corrected by omitting a dose due to brief half-life (23 min to 2.48 hr)
NEW some hospitals have changed to anti Xa assay instead of aPTT monitoring because of the variability with low dose regimens
ACT
Activated Clotting Time
At high heparin concentration the ACT is used to monitor anticoagulation
Performed by mixing whole blood with and activating substance that has a large surface area such a celite
Influenced by:
Hypothermia
Thrombocytopenia
Presence of aprotinin
Preexisting coagulation deficiencies (fibrinogen, factor XII and factor VII)
ACT
- ACT may be influenced by hypothermia, thrombocytopenia, presence of contact activation inhibitors (aprotinin), and preexisting coagulation deficiencies (fibrinogen, factor XII, factor VII)
- The control ACT is usually 90 to 120 seconds
- Asequate if the ACT is >300 seconds, questionable with ACT between 180 and 300 seconds, and inadequate at < 180 seconds
PT INR
Prothrombin Time/ International Normalized Ratio
Extrinsic pathway
Treatment with oral anticoagulants is best guided by Prothrombin time (PT)
INR addresses the problem of variability
INR is the ratio of a patients prothrombin time to a normal control
Most indication a moderate anticoagulant effect with a target INR
2.0 to 3.0 is appropriate*
Unexpected fluctuations in the dose respond to warfarin may reflect change in died
Proteins C and S what happens when they are low
Protein C
When activated by thrombin, degrades cofactors Va and VIIIa
Greatly diminishes activation of prothrombin and factor X
Protein S
Cofactor for activated Protein C
Low Protein C and S will result in a hypercoagulability state via future activation of prothrombin and factor X
Protein C is a natural anticoagulant