Antiplatelets, Anticoagulants & Fibrinolytics Flashcards
Which class of haematological drugs inhibits primary haemostasis?
Antiplatelet drugs
What are the processes involving blood cells that occur during primary haemostasis?
Platelet activation and aggregation are the first stages of hemostasis, activated during primary haemostasis. Antiplatelet drugs block this early stage of haemostasis and clot formation.
List FIVE mechanisms or classes of antiplatelet drugs.
(1) Adenosine uptake and PDE3 inhibitors(2) Irreversible cyclooxygenase-1 (COX-1) inhibitors(3) P2Y12 ADP receptor inhibitors(4) Glycoprotein IIb/IIIa receptor inhibitors (also known alpha-IIb/beta-3 integrin inhibitors) (5) Prostacyclin (PGI2) and analogues
Name ONE example of an adenosine uptake and PDE3 inhibitor antiplatelet agent.
Dipyridamole
How fast is the onset of clinically useful antiplatelet actions after administration of dipyridamole?
Fast onset after oral administration (20-30 min) and peak effect (2 to 2.5 hours).
Why is dipyridamole often administered in a modified- or extended-release preparation?
Dipyridamole has a short half-life resulting in a short duration of action of about 3 hours. It is, therefore, often administered in a modified- or extended-release preparation.
What is the clinical mechanism of action of dipyridamole as an antiplatelet agent?
Dipyridamole inhibits platelet activation and aggregation by ↑cAMP within platelets by being a/an:(1) Adenosine reuptake inhibitor → ↑ plasma adenosine activation of A2 receptors on platelets.(2) Phosphodiesterase 3 (PDE3) inhibitor reducing cAMP degradation within platelets.
What is the major dose-limiting side effect of dipyridamole?
By increasing cAMP levels through inhibiting phosphodiesterases (PDEs) and adenosine reuptake, dipyridamole is also a smooth muscle relaxant in vascular smooth muscle. Vasodilation results in dose-limiting side effects. Dipyridamole is therefore usually used as an adjunct or add-on with other antiplatelet agents.
List at least FOUR common adverse effects of dipyridamole when used as an antiplatelet agent.
Headache, hypotension, dizziness, flushing (due to vasodilator effect)Gastrointestinal (GIT) disturbance, diarrhoea, nausea, vomiting (due to effects on GIT smooth muscle).
List TWO cautions over the use of dipyridamole as an antiplatelet agent.
Caution in hypotension or severe coronary artery disease.
List THREE drug-drug interactions of dipyridamole when used as an antiplatelet agent.
(1) Increases levels of adenosine: Increases cardiac adenosine levels and effects.(2) Reduces activity of cholinesterases inhibitors: May aggravate myasthenia gravis.(3) Caution for bleeding when combined with heparin or other anticoagulants and antiplatelets.
Name ONE example of an irreversible cyclooxygenase-1 (COX-1) inhibitor used as an antiplatelet drug.
Aspirin
Explain how aspirin works as an antiplatelet drug.
Aspirin is an irreversible cyclooxygenase-1 (COX-1) inhibitor in platelets. Thus aspirin inhibits the production of thromboxane A2 (TXA2), which promotes platelet aggregation.
Why are the antiplatelet effects of aspirin stronger when it is used at a low dose than when it is used at a high dose?
Aspirin inhibits both COX-1 and COX-2. Aspirin inhibits COX-1 more than COX-2, but as the dose increases, the COX-2 inhibition is sufficient to have clinical consequences. COX-1 is present in platelets, producing thromboxane 2 (TXA2), which promotes platelet aggregation. COX-2 is present in other cells, including the endothelial cells of the blood vessel walls, where it produces prostacyclin (PGI2), which inhibits platelet aggregation. Thus, higher doses of aspirin inhibit COX-2-dependent PGI2 production more, counteracting the antiplatelet effect of inhibiting COX-1-dependent TXA2 production.
Why are the antiplatelet effects of aspirin stronger when it is used once daily than when it is used three to four times daily?
Aspirin irreversibly inhibits both COX-1 and COX-2. COX-1 is present in platelets, producing thromboxane 2 (TXA2), which promotes platelet aggregation. Platelets have no nucleus so when COX-1 is irreversibly inhibited by aspirin, new platelets need to be produced to replace platelets with functional COX-1. It takes from 7 to 14 days to replace platelets. COX-2 is present in other cells, including the endothelial cells of the blood vessel walls, where it produces prostacyclin (PGI2), which inhibits platelet aggregation. These cells have nuclei and can start to make new COX-2 protein within 3 to 4 hours. Thus, once-daily dosing has a stronger antiplatelet effect because it is sufficient for prolonged inhibition of COX-1 in platelets, but allows COX-2-dependent production of antiplatelet PGI2 to recover in other vascular cell types with nuclei.
How fast is the onset of the clinically useful antiplatelet effect of aspirin on once daily dosing?
(1) Onset within 3-4 hours (once COX-2-dependent PGI2 production has recovered).(2) Peak-effect 2 to 3 days as it takes a few days to achieve steady state maximal irreversible inhibition of COX-1 in the population of platelets.
How long does the antiplatelet effect of aspirin last after discontinuation of dosing?
7 to 10 days as aspirin is an irreversible COX-1 inhibitor and it takes time to replace platelets with functional COX-1.
List the TWO adverse effects of aspirin when used as an antiplatelet agent.
(1) Upper gastrointestinal (UGI) events (e.g., gastric ulcers, bleeding) due to inhibition of COX-1 production of protective prostaglandin in the stomach. Even low-dose aspirin for cardioprotective effects is associated with a two- to fourfold increase in UGI events.(2) Increased risk of bruising and bleeding.
What is the major caution over the use of aspirin?
Use with caution in patients with platelet and bleeding disorders (especially active upper gastrointestinal tract bleeding).
What is the major caution over drug-drug interactions for aspirin?
Caution for bleeding when combined with other antiplatelets and anticoagulants.
Name at least TWO examples of ADP P2Y12 receptor inhibitors used as antiplatelet drugs.
ClopidogrelTicagrelor
What is the major pharmacological difference between clopidogrel and ticagrelor?
Clopidogrel is a prodrug with an active metabolite that irreversibly binds to the ADP binding site on the P2Y12 receptor.Ticagrelor and its metabolites bind reversibly at a different site (not the ADP binding site) on the P2Y12 receptor.
How fast is the onset of clinically useful antiplatelet action after administering clopidogrel?
Onset of the clinical effect of clopidogrel takes about 2 to 4 hours as it is a prodrug metabolised to active metabolites. The peak effect takes about 6 to 8 hours.
How long does it take for platelet function to recover after discontinuation of clopidogrel?
About 7 to 10 days. Clopidogrel causes irreversible inhibition of the ADP P2Y12 receptors on platelets. It takes 7 to 10 days to replace new platelets with functional ADP P2Y12 receptors.
How fast is the onset of clinically useful antiplatelet activity after administering ticagrelor?
Approximately 20 to 30 minutes after oral administration with a peak effect after 2 to 3 hours.
How fast does platelet activity recover after discontinuation of ticagrelor?
Approximately 2 to 3 days due to the half-life of ticagrelor and its active metabolites.
List at least THREE contraindications or cautions when using clopidogrel.
(1) Contraindicated in patients with hypersensitivity to the drug(2) Contraindicated in patients with active pathologic bleeding(3) Caution in patients at risk of bleeding (e.g., risk of intracranial haemorrhage, trauma, surgery).(4) Variant alleles of CYP2C19 (4 % to 40 %) are associated with reduced metabolism to active metabolite and diminished antiplatelet response
List examples of drug-drug interactions with clopidogrel that increase the antiplatelet effect and risk of bleeding.
(1) Warfarin, NSAIDs, and salicylates may increase the risk of bleeding (pharmacodynamic interactions)(2) Rifamycins may increase the antiplatelet effect (pharmacokinetic interactions)
List examples of drug-drug interactions with clopidogrel that reduce the antiplatelet effect.
Strong to moderate CYP2C19 inhibitors (e.g., proton pump inhibitors, fluoxetine, ketoconazole, etc.) may reduce the antiplatelet effect by reducing the conversion of clopidogrel to its active metabolite.
List at least THREE contraindications or cautions when using ticagrelor.
(1) Contraindicated in patients with hypersensitivity to the drug, severe hepatic impairment, and in breast-feeding women(2) Contraindicated in patients with a history of intracranial haemorrhage or active pathologic bleeding (e.g., bleeding peptic ulcer)(3) Caution in patients at risk of bleeding (e.g., peptic ulcer, trauma, surgery), elderly, and moderate hepatic failure
List examples of significant drug-drug interactions with ticagrelor.
(1) Anticoagulants, fibrinolytics, & long-term NSAIDs may increase the bleeding risk (pharmacodynamic effects)(2) Aspirin doses >100 mg/day recude the ticagrelor effect but increase the bleeding risk (largely pharmacodynamic interactions)(3) CYP3A inducers (e.g., dexamethasone, phenytoin, etc) may reduce the ticagrelor level and antiplatelet effect (pharmacokinetic interactions)(4) CYP3A strong inhibitors (e.g., clarithromycin, ketoconazole, etc.) may increase the ticagrelor level and risk of adverse reactions (pharmacokinetic interactions).
What class of drugs inhibits secondary haemostasis?
Anticoagulants block secondary haemostasis.
What processes during secondary haemostasis are blocked by anticoagulants?
Anticoagulants block the activation of clotting factors and the resulting activation of fibrin polymerization in secondary haemostasis.
Name THREE classes of oral anticoagulant drugs.
(1) Vitamin K antagonists(2) Direct oral anticoagulant (DOAC) thrombin/factor IIa inhibitors: the “gatrans”.(3) Direct oral anticoagulant (DOAC) factor Xa inhibitors: the “xabans”
Name ONE example of a vitamin K antagonist anticoagulant drug.
Warfarin
Name ONE example of a thrombin/factor IIa inhibitor direct oral anticoagulant drug (DOAC).
Dabigatran (or any other “gatran”)
Name ONE example of a factor Xa inhibitor direct oral anticoagulant drug (DOAC).
Rivaroxaban (or any other “xaban”)
How long is the onset of the anticoagulant action of oral warfarin?
24-72 hours to onset of anticoagulant action and 5-7 days to achieve the peak effect on continuous administration. Although the plasma peak occurs within 2 - 8 hours after oral administration of warfarin, it takes time to deplete reserves of activated vitamin K.
How long does it take to reverse the anticoagulant effect of warfarin on discontinuation of the drug?
Duration of action 2-5 days. Due to the long half-life of some of the coagulation factors. (e.g. Factor II, t1/2 = 50 h) and the long elimination half-life of warfarin (20-60 hours).
List factors contributing to variability in plasma concentrations and anticoagulant actions of warfarin.
Most of the variability in warfarin response is accounted for by:(1) Genetic polymorphisms the genes for CYP2C9, which metabolises warfarin.(2) Genetic polymorphisms the genes for vitamin K reductase complex, subunit 1 (VKORC1), the target for warfarin inhibition of activation of vitamin K.(3) Dietary variation in vitamin K consumption.
List adverse effects of warfarin that are important either because they are common or they are severe.
(1) Haemorrhage / bleeding. Signs include blood in stools or urine, melena, excessive bruising, petechiae, persistent oozing from superficial injuries, excessive menstrual bleeding(2) Hepatitis (0.2% to 0.3%). Greatest risk: >60 years old, male, on warfarin < 1 month(3) Cutaneous necrosis (approx. 1 in 10,000) and infarction of the breast, buttocks and extremities. Probably because of the reduced blood supply to adipose tissue. Typically 3 to 5 days after initiating treatment
Name a drug that can be used to reverse the anticoagulation action of warfarin.
Vitamin K can be used clinically as a reversal agent for warfarin. Dietary consumption of vitamin K can also reduce the effect of warfarin resulting in the risk of drug-food and drug-supplement interactions.
List contraindications and cautions over the use of warfarin.
(1) Contraindicated in patients with- Hypersensitivity to the drug- Active bleeding, risk of pathologic bleeding, after recent major surgery- Severe or malignant hypertension- Severe renal or hepatic disease- Subacute bacterial endocarditis, pericarditis, or pericardial effusion(2) Contraindicated in pregnancy- Teratogen causing severe birth defects in the bone and CNS- Can cause haemorrhagic disorder in the fetus(3) Caution in breast-feeding women(4) Caution in patients with- Diverticulitis, colitis- Mild or moderate hypertension- Mild or moderate renal or hepatic disease- Drainage tubes in any orifice
List examples of significant drug-drug and drug-food interactions with warfarin.
(1) Paracetamol long-term therapy (> 2 weeks) at high doses(> 2g/day) may increase bleeding(2) Numerous drugs (including allopurinol, NSAIDs, salicylates, proton pump inhibitors, metronidazole, etc.) may increase the risk of bleeding(3) Numerous traditional medicines, herbs, supplements, and foods (including ginkgo, ginseng, reishi mushrooms, cranberry juice, etc.) may increase the risk of bleeding(4) Numerous drugs (including barbiturates, corticosteroids, spironolactone, thiazide diuretics, etc.) may reduce the efficacy of warfarin(5) Numerous traditional medicines, herbs, and supplements (including supplements containing vitamin K, green tea, vitamin K-rich foods, etc.) may reduce the efficacy of warfarin
Name a reversal agent for dabigatran.
Idarucizumab. Idarucizumab is a humanized monoclonal antibody fragment that binds dabigatran and its acyl glucuronide metabolites with higher affinity than the binding affinity of dabigatran to thrombin.
Name a reversal agent for rivaroxaban.
Andexanet alfa recombinant modified human factor Xa decoy protein for reversal of “xabans” (and off-label LMWHs).
What is the major pharmacological limitation of heparins compared to warfarin and direct oral anticoagulant drugs (DOACs)?
Heparins cannot be administered orally. They must be administered parenterally.
List the major pharmacological differences between heparin and low molecular weight heparins (LMWHs) that influence their clinical use.
(1) Heparin has a short half-life (about 1 hour) than LMWHs (about 4 hours). (2) Heparin has a higher risk of thrombocytopenia (<5%) than LMWHs (<1%).(3) Heparin complexes with ATIII inhibiting coagulation cascades at many levels, including the contact triggered intrinsic pathway making them good for coating blood collection vessels, while LWMHs are more selective for factor Xa and a lesser extent factor IIa.(4) Good reversal of heparin can be achieved with protamine sulphate while reversal of LMWHs is incomplete.
List THREE major adverse effects of heparins.
(1) Bleeding (in 1-5 % of patients treated with IV heparin). (2) Increased risk of epidural or spinal haematoma and paralysis in patients receiving epidural or spinal anaesthesia or spinal puncture(3) Heparin-induced thrombocytopenia (low platelet count).- Binds to platelet factor 4 (PF4) on activated platelet surface- IgG antibody against the heparin-PF4 complex- Lower risk with LMWHs
List major contraindications and cautions of use of heparins.
(1) Contraindicated in patients with:- Hypersensitive to heparins or pork products- Active major bleeding - Thrombocytopenia or antiplatelet antibodies (2) Caution in:- Elderly patients- Risk of bleeding, including patients with prosthetic heart valves, major surgery, regional or lumbar block anaesthesia, blood dyscrasias, recent childbirth, pericarditis or pericardial effusion, renal insufficiency (for LMWHs)
List major drug-drug interactions of heparins.
(1) Increased risk of bleeding: anitplatelets, anticoagulants, fibrinolytics, NSAIDs, SSRIs(2) Increased risk of bleeding: with various herbs/foods, including chamomile, fenugreek, garlic, ginger, ginkgo, ginseng.
Name an example of a LMWH.
Enoxaparin.
What is another name for the drug class thrombolytics.
Fibrinolytics. Because they breakdown mature fibrin meshworks holding together thrombi.
Name ONE class of fibrinolytics.
Recombinant tissue plasminogen activators.
Name ONE example of a recombinant tissue plasminogen activator.
Alteplase (or any other “teplase”)
At which stage of haemostasis and thrombosis do fibrinolytics work?
Fibrinolytics act against the clot stabilization phase of haemostasis and thrombosis by breaking down fibrin crosslinking to reverse clot stabilization.
List adverse effects of alteplase.
NAME?
List major contraindications and cautions when using alteplase.
(1) Contraindicated in patients with active bleeding, prior intracranial haemorrhage, or recent (within the last 3 months) intracranial or intraspinal surgery, serious head injury, or stroke.(2) Caution in patients with major surgery within 10 days, risk of bleeding (e.g., peptic ulcer), cerebrovascular disease, mitral stenosis, atrial fibrillation, acute pericarditis or subacute bacterial endocarditis
List major drug-drug interactions for alteplase.
(1) Increased risk of bleeding with antiplatelets (especially dipyridamole and aspirin), and anticoagulants (especially warfarin and heparin).(2) Nitroglycerin may reduce alteplase level
What is the route of administration for Ticagrelor?
Oral.
How long does it take for Dipyridamole to reach peak clinical effect?
2-2.5 hours.
What is the duration of clinical effect for drugs that block TXA2 production by platelets?
7-10 days.
Are Antiplatelets targeted towards primary or secondary haemostasis?
Primary haemostasis.
What is the target for Anticoagulants in the haemostasis process?
Secondary haemostasis.
What is the onset of clinical effect for αIIbβ3 integrin inhibitors?
2-4 hours intravenously.
What are the potent anticoagulants that block many factors in extrinsic and intrinsic pathways?
Direct oral anticoagulants (DOACs).
How long does it take for Thrombin (coagulation factor IIa) inhibitors to reach peak action?
About 3 hours.
What are the drug-food & drug-drug interactions for Thrombin inhibitors?
They have notable interactions that need to be considered in clinical decisions.
What are the common adverse effects of Dabigatran?
Bleeding and gastrointestinal symptoms.
What is the bioavailability of Rivaroxaban?
80 - 100%.
What is the mechanism of action of Heparin and LMWHs?
They potentiate the action of antithrombin III
What is the duration of anticoagulant effect after discontinuation of IV heparin?
The effect disappears within hours of discontinuation.
What is used to reverse the effects of heparin?
Protamine sulfate IV infusion.
What is a major adverse effect of heparin-induced thrombocytopenia?
Lower platelet count due to IgG antibody against the heparin-platelet factor 4 complex.
How does Warfarin act as an anticoagulant?
It inhibits the Vitamin K reductase enzyme
What is the onset of action for Warfarin’s anticoagulation effect?
24-72 hours when taken orally.
What are the signs of hemorrhage as an adverse effect of Warfarin?
Blood in stools or urine
What should be monitored regularly when using Warfarin?
International normalized ratio (INR) to ensure appropriate anticoagulant control.
What is the bioavailability of Dabigatran?
3-7%.
What is the half-life of Rivaroxaban?
5-9 hours.
What percentage of Rivaroxaban is excreted through urine?
66%.
What is the main adverse effect of Dabigatran?
Bleeding and gastrointestinal symptoms.
What reduces the level of Dabigatran in the body?
Rifampin.
What is the target of Dabigatran?
Factor IIa.
What is the mechanism of action of Heparin and LMWHs?
They potentiate the action of antithrombin III and inactivate thrombin and other coagulation factors.
What factors are inactivated by the Heparin-AT III complex?
Factors IXa
What is the key difference in the action of LMWHs compared to heparin?
LMWHs are more selective for factor Xa and to a lesser extent for factor IIa.
What are the main adverse effects of Heparin?
Bleeding
What is used to reverse the effects of Heparin?
Protamine sulfate IV infusion.
What is the main adverse effect of LMWHs?
Bleeding.
Are Heparin and LMWHs safe in pregnancy?
Yes
What is the molecular weight of Heparin?
Approximately 15
What is the bioavailability of LMWHs?
86-98%.
What is the half-life of LMWHs?
About 4 hours.
What is the renal excretion percentage for LMWHs?
Less than 1%.
What drugs and substances increase the risk of bleeding when used with heparin?
Antiplatelets
What is the onset of action for the anticoagulation effect of Warfarin?
Oral: 24-72 hours.
How long does it take for Warfarin to reach its peak plasma level?
Oral: 2-8 hours.
