Flashcards in Le Blanc: Pharm Deck (53):
Under normal physiological conditions, little or no intravascular coagulation occurs. This is primarily due to three effects - what are they?
dilution (of factors)
presence of plasma inhibitors
activated clotting factors are rapidly removed by the liver
When vascular damage occurs, several physiologic reactions participate to control blood loss. What are they?
platelet adhesion reaction
formation of a clot
Briefly describe platelet aggregation and formation of the platelet plug
damage to vessel endothelium exposes collagen - vWF comes in and binds - platelets bind to GPIb (platelet adhesion)- when platelets bind they undergo shape change and degranulate - degranulation releases enzymes like ADP and thromboxane A2 which draw in more platelets (aggregation) to create the platelet plug
**no activation of coag cascade yet, just formation of weak platelet plug
2 contents released by platelets that trigger powerful constrictions of blood vessels (transient reaction)
Coagulation occurs due to trauma originating from the extra-vascular space (formation of a macromolecular complex involving Thromboplastin or Tissue Factor, and Factor VII); the most important in vivo
Coagulation is triggered by trauma to the blood itself (from large glycoprotein complexes released by platelets)
What does plasmin do?
degrades a fibrin clot
**this produces D-dimer
What are the three categories of drugs used to treat coagulation disorders? Give an example of each
1. direct acting anticoagulants: calcium chelatlors like EDTA, heparin, factor IIa and 10a inhibitors)
2. indirect acting anticoagulants: Warfarin (coumadin)
3. antiplatelet agents: aspirin
What is a normal platelet count?
150,000 - 400,000
What does prothrombin time reflect?
reflects alterations in the EXTRINSIC pathway (~12 sec)
What is the INR measuring?
PT of the patient/PT reference
**normal is 1.0
2-3 is therapeutic INR
What does the activated PTT reflect?
reflects alterations in the INTRINSIC pathway (normal 24-34 secs)
Where is heparin derived from? Why is this important to consider?
from bovine lung and porcine intestinal mucosa; important to consider bc some people develop allergy
What does heparin bind to and form a complex with to inhibit blood coagulation? What does this essentially do?
alpha2-globulin (antithrombin III); antithrombin III is a natural anti-coagulant, and when bound by heparin it just accelerates the anti-coag effects by like 100x
At low doses, Heparin primarily neutralize Factor (blank). At high doses, it prevents the thrombin-induced activation of (blank), and activation Factors V and VIII
What is one concern with heparin use?
may cause moderate to severe thrombocytopenia **heparin-induced thrombocytopenia
How is heparin administered?
**not effective orally
Does heparin cross the placenta and pass into the maternal milk?
Contraindications with heparin use?
patients with low platelets or history of heparin-induced thrombocytopenia
patients with severe allergy
older patients, esp women
What to do if there is a heparin overdose?
use Protamine Sulfate to bind heparin and neutralize its effects
What are 4 advantages of using low molecular weight heparin?
1. more predictable outcome, 2x longer half life
2. less frequent dosing requirements
3. increased bioavailability from the subcutaneous site of injection
4. less frequent bleeding
What would you use for any of these?
Disseminated intravascular coagulation (DIC)
Open heart surgery
Venous catheter occlusion
How do thrombin inhibitors work as anticoagulants? How are they administered?
they block the enzyme by binding to the catalytic site; given IV
When would you want to use thrombin inhibitors instead of heparin?
in patients that are susceptible to developing heparin induced thrombocytopenia and in coronary angioplasty or coronary bypass surgery
Another type of anticoagulatant is a factor 10a inhibitor. Name two.
This is the most common oral anticoagulant, only active in vivo after 12-24 hours
How does coumadin work?
it is a structural analog of Vitamin K, so it causes the same effects as Vitamin K depletion
**need Vitamin K for formation of clotting factors
What is Vit K used for in the synthesis of clotting factors?
it causes post-ribosomal carboxylation of specific glutamic acid residues; when carboxylated, these amino acid residues bind Ca++ making it less available for the Coag pathway
Warfarin inhibits blood clotting mechanisms by interfering with the hepatic synthesis of (blank)
vitamin K-dependent clotting factors
**VII, IX, X, prothrombin
Warfarin also down-regulates protein C. What effect does this have? What does protein C normally do?
Protein C promotes the degradation of factors 5a and 8a, rendering them inactive. If this is downregulated, you will have increased 5a and 8a and this explains the pro-coagulant activity of warfarin seen in early stages of therapy
So early on in warfarin treatment, what will you observe in regards to coagulation?
first, increased coagulant activity due to increased levels of factor 5a and 8a
What are two measures used to monitor the anticoagulant effects of warfarin?
What are 3 things you could do if you overdose a patient on warfarin?
1. withdraw the drug
2. give vit K supplements
3. tranfuse with whole blood or plasma if major bleeding noted
When should warfarin NOT be used?
when you need to avoid active bleeding
Vit K deficiency
severe hepatic/renal disease
Does warfarin pass the placental barrier?
YES; don't use in pregnant women!
**may lead to abortion and birth defects
Why are newborns more sensitive to oral anticoagulants than adults?
they have lower vitamin K levels (things like warfarin will decrease vit K) and also they have lower rates of metabolism
What is one drug that is known to increase the response to warfarin?
aspirin **any drug that decreases platelet aggregation
What is desmopressin? What is it used for?
synthetic analogue of ADH; stimulates factor 8; used for hemophilia A or in pts with factor 8 antibodies
**think of this: hemophilia a-ate (8 - factor 8)
How does aspirin inhibit platelet aggregation?
aspirin inhibits platelet release of ADP which prevents aggregation; it also acetylates COX, which prevents the formation of thromboxane A2; thromboxane A2 causes platelet aggregation and is a potent vasoconstrictor
Aspirin inhibits the release of (blank) by platelets and their aggregation by acetylating the enzymes (cyclo-oxygenases or COX) of the platelet that synthesize the precursors of (blank), a labile inducer of platelet aggregation and a potent vasoconstrictor
ADP; thromboxane A2
Is the effect of aspirin reversible?
no; it causes a covalent modification due to acetylation of the enzymes (COX)
How do the antiplatelet drugs Ticlopidine and Clopidogrel bisulfate work? When are they used?
they inhibit ADP-mediated platelet aggregation; prevent aggregation by impairing the GPIIb/IIIa receptor; they are used as an alternative to aspirin for recurrent stroke patients
How does abciximab work? When is it used?
it is a chimeric monoclonal antibody that blocks the glycoprotein IIb/IIIa receptor - prevents platelet aggregation;
used in acute coronary syndromes and percutaneous coronary intervention
The Fibrinolytic System dissolves intravascular clots as a result of the action of (blank), an enzyme that digests Fibrin
Plasminogen, an inactive precursor, is converted to (blank) by cleavage of a single peptide bond. (blank) is a relatively non-specific protease, which digests fibrin clots and other plasma proteins, including several coagulation factors
Therapy with thrombolytic drugs tends to dissolve both pathological thrombi and also fibrin deposits at sites of vascular injury. What can these drugs cause as a result?
What should patients with the following conditions receive?
extensive pulmonary emboli
severe iliofemoral thrombophlebitis
acute coronary occlusion
thrombolytic therapy to break up clots
This is released from endothelial cells in response to various signals, including stasis produced by vascular occlusion
tissue plasminogen activator (t-PA)
What does t-PA bind to? Its binding causing the conversion of what to what?
t-PA binds to FIBRIN and converts plasminogen (also binds to fibrin) to plasmin
What does fibrin bind to in the plasma to inhibit its action?
t-PA is a serine protease. It is a poor Plasminogen activator in the absence of (blank). t-PA binds to (blank) and activates bound Plasminogen several hundred-fold more rapidly than it activates Plasminogen in the circulation.
a protein produced by β-hemolytic streptococci. It has no intrinsic enzymatic activity, but forms a stable non-covalent 1:1 complex with Plasminogen. This produces a conformational change that exposes the active site on Plasminogen that cleaves a peptide bond on free Plasminogen molecules to form free Plasmin
When should you NOT use thrombolytic therapy?
surgery w/i 10 days
serious GI bleeding w/i 3 months
history of HTN
active bleeding or hemorrhagic disorder