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Flashcards in Anticoagulants Deck (60)
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Blood coagulation consists of how many factors? Pathways?

13 clotting factors (factor XIII crosslinks fibrin to make a more stable clot), 2 pathways (Intrinsic system and Extrinsic system)


What is factor IV?



What is factor VI?

Factor V activated


What is factor V?

Part of the Xa complex


What is the Extrinsic Pathway?

Tissue Factor Pathway
(1) Operates during tissue injury
(2) Bypasses several steps
(3) Occurs in seconds


What test will you use to evaluate the extrinsic system? What factor is dependent upon this process? What drug is it used to monitor?

PT test; normal value ~13 seconds; Depends on factor VII levels; used to monitor Coumadin levels


What is the Intrinsic Pathway?

Contact activation pathway
(1) requires almost all the factors
(2) is relatively slow


What test will you use to evaluate the intrinsic system? What drug is it used to monitor?

PTT test, normal value is ~30 seconds; used to monitor Heparin levels (hemophilia) (Heparin is also monitored by "heparin levels" now)


What is the Common Pathway? What is important about this pathway?

The pathway in which both Extrinsic and Intrinsic meet; Thrombin, the last enzyme, converts soluble fibrinogen to insoluble fibrin mesh in which blood cells are trapped, forming a clot.


What factors are vitamin K dependent?

IX, VII, X, II (Prothrombin)


T/F vitamin K dependent factors are only within the intrinsic and common pathways.

FALSE, all the pathways!


Heparin: Mechanism of Action

(1) Activates antithrombin III in the plasma
(2) Antithrombin inhibits thrombin (IIa), IXa, Xa


How is Heparin given?

- Given S.C. or I.V. (not effective orally)
- Has rapid onset of action when given parenterally


Heparin: Uses

(1) immediate anticoagulation (i.e. in M.I.)
(2) Venous thrombosis
(3) Pulmonary embolism
(4) Thrombosis prophylaxis


What is the general usage of Heparin in the hospital?

Used for the first 7-10 days followed by warfarin with a 3-5 day overlap (have to overlap warfarin and heparin until the warfarin takes therapeutic effect)


T/F Heparin is used both in vivo and in vitro



Heparin: Overdose/Adverse Effects

- Causes increased bleeding (internally or externally)
- Is of animal origin, may produce allergic reactions in some patients
- Causes transient thrombocytopenia in ~25% of cases (10% drop in platelet count)
- Can cause Heparin Induced Thrombocytopenia (HIT) in ~1-4% of patients (immune response against heparin and factor IV;7-10 days after- 50% drop in platelet count)


What is the antidote for HIT?

Protamine (a basic protein) neutralizes acidic heparin


What is the difference between unfractioned and low molecular weight heparins?

- Low molecular weight heparins are smaller forms of heparin with better bioavailability and longer half lives
- Unfractioned heparin has antithrombin activity by a long arm wrapped around ATIII and thrombin
- LMWH doesn't have the long arm so has more anti Xa activity (how it is measured in the lab)


How is LMWH given?

SQ injection


LMWH: Contraindications

Renal disease


How can you follow levels of LMWH?

By following levels of anti-Xa activity


What are names of LMWH?

(1) Enoxaparin
(2) Deltaparin
(3) Fondaparinux


Warfarin: Mechanism of Action

- Inhibits the proper synthesis of vitamin K- dependent factors (II, VII, IX, X)
~Vit K is needed for gamma carboxylation of glutamic acid residues in these factors
- Has a delayed onset of action: time required to decrease the plasma levels of preformed clotting factors


T/F Warfarin acts as an anticoagulant directly

FALSE; indirectly


How long does it take to produce the effect of Warfarin? Why?

~72 hours; delay is related to half lives of these clotting factors (II-60hr, VII-6hr, IX-24hr, X-40hr)


How is Warfarin used?

- Orally; effective in vivo only because of its indirect effect
- Long-term therapy (6 weeks to 6 months or longer)


T/F Warfarin is highly bound to albumin (plasma proteins).



What are the high drug interactions with warfarin?

because of the displacement of warfarin from plasma albumin by other drugs (too much warfarin in the blood)


Warfarin- Uses

(1) Venous thrombosis
(2) Pulmonary Embolism
(3) Atrial fibrillation
(4) Mechanical heart valves
(5) MI after starting heparin