Pharmacology: Aspirin is a cyclooxygenase inhibitor and decreases the capacity of platelets to synthesize thromboxane. The half-life of aspirin is only 20 min; however its COX-inhibitory effect on platelets is permanent. Its clinical effect will therefore last for the life span of platelets, which is 7–10 days.

Clinical indications: The benefit of aspirin for protection against cardiovascular disease is well known. Aspirin given long-term can reduce the risk of both vascular events and vascular-related mortality. In addition, timely use of aspirin reduces the acute myocardial infarction-related mortality and also decreases the chances of myocardial infarction in patients with unstable coronary syndromes. Aspirin also has a proven role in the secondary prevention of stroke and reduction of mortality in patients with acute cerebrovascular ischemic events.

Risk of hemorrhage: Several studies have investigated the effect of aspirin on post-polypectomy bleeding . They are all retrospective case-control studies. A recent meta-analysis demonstrated that taking Aspirin or NSAIDs does not increase the risk of post-polypectomy bleeding . There is no need for interruption of these prior to the procedure [4]. This is in line with the current recommendation by ASGE [5].

Pharmacology: In addition to aspirin , several new antiplatelet drugs have been in clinical use. Based on their mechanism of action, they are generally classified into three groups: inhibitors of ADP-induced platelet aggregation such as clopidogrel, ticlopidine; glycoprotein IIb/IIIa receptor blockers such as abciximab, tirofiban, and eptifibatide, other antiplatelet drugs such as dipyridamole and cilostazol (Fig. 6.1).

Inhibitors of ADP-induced platelet aggregation (clopidogrel and ticlopidine): These drugs are derivatives of thienopyridine and irreversibly block the ADP receptor on platelets. They are effective in the prevention of future vascular events in patients with transient ischemic event or strokes. They are also commonly used in patients after placement of coronary artery stents. Clopidogrel has a better side effect profile compared to ticlopidine. Antiplatelet effect of clopidogrel and ticlopidine takes several days to develop, reaching a maximum of 40–60% inhibition in 3–5 days. The duration of the antiplatelet affect lasts 7–10 days.

Glycoprotein IIb/IIIa receptor blockers (abciximab , tirofiban , and eptifibatide ): Activation of platelet IIb/IIIa receptor complex is the final common pathway for platelet aggregation. The main clinical use of this class of antiplatelet agents is in patients with acute coronary syndrome. These drugs are administered parentally. Based on their molecular weight, they are classified into two groups. Abciximab is of larger size and is a monoclonal antibody. Its antiplatelet action lasts up to 24 h after stopping intravenous infusion. Tirofiban and eptifibatide are smaller in size and are non-peptide and peptide of GP IIb/IIIa receptor antagonists, respectively. They have a short duration of action and their effect lasts only 4 h after stopping the infusion.

The main clinical indication of GP IIb/IIIa inhibitors is in patients with acute coronary syndrome who are undergoing primary coronary intervention.

Other antiplatelets (dipyridamole and cilostazol ): Dipyridamole antiplatelet activity is by inhibition of adenosine uptake and cGMP phosphodiesterase activity. Its main clinical use is in the prevention of cerebrovascular events in combination with aspirin .

Cilostazol is another phosphodiesterase inhibitor that has both vasodilatory and antiplatelet effects. It is mainly used in patients with peripheral vascular disease to treat intermittent claudication.

There is little data on the effect of antiplatelet drugs on post-polypectomy bleeding . Studies are restricted to case-control studies. A recent review showed that the risk of immediate and delayed post-polypectomy bleeding increases in patients taking clopidogrel alone or in combination with aspirin or NSAIDs [4].

High-risk procedures: There is very limited data to provide any evidence-based recommendation. In consideration of pharmacology and the bleeding risk associated with antiplatelet agents, it is recommended to discontinue non-aspirin antiplatelet agents 7–10 days prior to the procedure. As the onset of action of these medications is relatively slow, they can be restarted on the day after the procedure.

It is very rare for patients undergoing colonoscopy to be on these medications. Nevertheless, GP IIb/IIIa infusion should be stopped in patients undergoing high-risk procedure or those with active GI bleeding. Platelet transfusion and/or use of DDAVP may have a role in reversing the effect of these medications.

Dipyridamole : Dipyridamole does not appear to increase the risk of bleeding when it is used alone or in combination with aspirin [6]. Low-risk procedures can be safely performed while taking dipyridamole. The safety of high-risk procedures in this group is unknown.

Although the evidence behind this guideline is limited, temporary cessation of antiplatelet agents and maintaining patients on aspirin as long as agreed by cardiologist is recommended.

Pharmacology: Warfarin is a coumadin derivative that inhibits the synthesis of vitamin K dependent factors, i.e., factors II, VII, IX, and X and also protein C and S. Its mechanism of action is through inhibition of intrahepatic activation of vitamin K. It has a rapid bioavailability with a half-life of 40 h. Its effect can be easily monitored using INR.

Clinical indication: Warfarin is one of the most used anticoagulants . It is effective in prevention and treatment of venous thromboembolic events . In addition, it protects against thromboembolism in the setting of atrial fibrillation and prosthetic heart valves. Increased risk of bleeding is an inherent side effect of warfarin .

Warfarin does not increase the risk of bleeding in patients undergoing low-risk procedures, as long as the INR is not beyond the therapeutic range. Simple mucosal biopsies can be safely performed in patients on warfarin ; however, there is no trial data to fully support this.

Data on the risk of bleeding after high-risk procedures in patients on warfarin are very limited. One study of 1657 polypectomies showed that warfarin is an independent risk factor for bleeding [7]. It is also not entirely clear what level of anticoagulation is safe for high-risk procedures. It is accepted that the INR level below 1.5 is safe. There is very limited data for high-risk colonoscopic procedures; however, this level can be extrapolated from other procedures such as liver or renal biopsies. A randomized study of 70 patients on warfarin undergoing polypectomy for colonic polyps of less than 10 mm in size demonstrated a post-polypectomy bleeding rate of 23% and 6% for conventional and cold snare polypectomy, respectively [8]. This trial supports the use of cold snare for polypectomy pf small polyps in patients on warfarin .