Anti-Angina, Anti-thrombolytics & Thrombolytics Flashcards
Hemostasis steps
1st:
cessation of bleeding from an injured blood vessel
Reflex Vasospasm
-slow down the bleeding
Exposure of TF
-platelet adhesion and activation (TXA2, ADP & 5-TH)
Platelet plug
- platelet are connected to each other by fibrinogen
-role of tPA, NO and PGs
Hemostasis steps
2nd:
Fibrin clot
- conversion of prothrombin (II) to thrombin (IIa). Thrombin converts of fibrogen (I) to fibrin (Ia; mesh)
Dissolution of the clot (fibrinolysis)
-plasminogen is converted to plasmin, the enzyme that dissolves the fibrin
Fibrin Clot
involve a number of precursor proteins and active proteases
components at each stage:
- TF, Phospholipids & Ca++
- organizing surface (platelets)
- precursor protein (zymogen –> active protease)
- protease from the preceding stage –> activate next process
- non enzymatic protein cofactors (active enhance activity of other enzymes)
What 3 things need to happen in order for the clotting formation to happen?
- ADP binding to P2Y12–>Gi–> decrease cAMP
- ADP binding to P2Y1–> Gq–> increase Ca++
- TxA2 binding to TxA2 receptor–> Gi–> increase Ca++
What is the extrinsic pathway?
VII–>VIIa–>X–>Xa
What is the intrinsic pathway?
Phospholipids and # of factors XII–>XIIa–>XI–>XIa–>IX–>IXa–>X–>Xa
What is the common pathway?
Xa–>II (prothrombin)–> IIa (thrombin) –> I (fibrinogen) –> Ia (fibrin) –> red clot
Thrombin (IIa)
converts fibrinogen to fibrin monomers by cleaving fibrinopeptides A & B. this allows fibrin to form a gel
Cofactor Va
V: present freely in the plasma & as a component of platelets. it is coverted to Va by thrombin, which increase by 50x’s the coagulation activity of Xa
Xa
common pathway
Tissue Factors (TF)
non-enzymatic lipoprotein cofactor that greatly increases the proteolytic efficiency of VIIa. VIIa activates X.
present in the surface of cells that do not normally contact plasma
Antithrombin
a plasma protein that inhibits aggregation factors Xa and IIa.
heparan sulfate is a proteoglycan synthesized by the endothelium cells and stimulate the activity of antithrombin.
Protein C & S
degrades cofactors Va and VIIIa, which leads to the decrease in prothrombin and factor X activation.
prostaglandins (PGI2) & NO inhibit platelet aggregation.
Prevent clotting
antiplatelet agents: Aspirin, dipyridamole, ticlopidine, abcximab, eptifibatide & prasugrel
clotting cascade modulators: heparin, lepirudin, warfarin, dabigatran, rivaroxaban
Promote clot breakdown
tissue plasminogen activator (t-PA): alteplase, strepto & urokinase
Activated partial thr omboplastin time (aPTT)
add Ca++, phospholipids, and a particular substance. analyze for clotting time.
measure intrinsic pathway by factor XII
Prothrombin time (PT)
add thromboplastin (TF+phospholipids) & analyze for clotting time. measure of the extrinsic/common pathway decrease in PT time= more bleeding less coagulation increase in PT time= less bleeding more coagulation
Heparin Na+ & Ca++
heterogeneity in composition, but similar biological activity (150 USP units/mg).
naturally occurring mixture of sulfated muccopolysaccharides produced by mast cells and basophils.
Heparin MOA
increases the rate of thrombin-antithrombin reactions by making the reactive site more accessible to the protease. thrombin inactivation
Heparin Uses
prevention and treatment of embolism (post-op), deep vein thrombosis, pulmonary embolism, initial management of unstable angina or acute MI.
Heparin Information
Immediate onset (30-60 mins): heparin acts on ACTIVATED factors that are already circulating in the blood.
OD: protamine sulfate (+ charges that binds ionically to heparin)
DDI: any drug that may increase the risk of bleeding (salicylates). recent trauma, peptic ulcer, etc.
AE: bleeding
heparin associated thrombocytopenia (HAT): unknown MOA, but not immune mediated
heparin induced thrombocytopenia (HIT): immune mediated
Parental Heparin
Pharmacokinetics: administration can be IV or SQ outpatient basis for DVT patients. has an immediate onset; hepatic elimination and excretion, with some excreted unchanged in urine
SE: thrombocytopenia (early/late) hemorrhage
Contraindications: existing bleeding conditions or bleeding tendency
OD: administer protamine sulfate (+ binds to heparin)
LMW Heparins
inhibits factor Xa, very little effect on factor IIa. less incidence of thrombocytopenia and hemorrhage. more predictable PK
Anixtra (fondaparinux)
synthetic heparin that binds only to Xa
-less likely to produce HIT
used for thromboprophylaxis of pts undergoing hip or knee surgery, pulmonary embolism and deep venous thrombosis.