Antiplatelet drugs such as aspirin, dipyridamole (Persantine), and sulfinpyra-
zone (Anturane) are prescribed for the prevention and formation of blood clots
(platelet aggregation).
Patients who have chronic or acute atrial fibrillation are also given anticoag-
ulants to prevent the formation of mural thrombi (blood clots in the heart).
Anticoagulants can be administered orally (coumadin) or parenterally
(heparin) to combine with antithrombin III, thus inactivating thrombin and other
clotting factors. This prevents the formation of a fibrin clot.
Anticoagulants are poorly absorbed through the GI mucosa and destroyed by
liver enzymes so it is given subcutaneously or intravenously. Anticoagulants can
be given as an IV bolus or infusion. Clotting time is prolonged and partial throm-
boplastin time (PTT) and activated partial thromboplastin time (aPTT) are mon-
itored during therapy.
Anticoagulants decrease platelet count causing thrombocytopenia. The anti-
dote for heparin is protamine sulfate, which is given intravenously.
When IV therapy is to be discontinued, oral warfarin (Coumadin) or
dicumarol is administered simultaneously. However, you must monitor lab values
as heparin is gradually stopped and coumadin is added. The dose of Coumadin
is adjusted based on PT values.
The International Normalized Ratio (INR) is the laboratory test used to mon-
itor patients on anticoagulant therapy. Normal INR is 1.3 to 2.0 and patients on
warfarin therapy are maintained at an INR of 2.0 to 3.0. Monitoring the lab val-
ues at regular intervals is required for the duration of drug therapy.
Patients should also be observed for petechiae and ecchymosis, tarry stools, and
hematemesis which all could be indicative of occult (hidden) bleeding. The anti-
dote for the oral anticoagulants is Vitamin K (phytonadione) (AquaMEPHYTON).
Low Molecular Weight Heparins (LMWHs) are derivatives of standard heparin
and include enoxaparin sodium (Lovenox) and dalteparin sodium (Fragmin).
They are used for prevention of deep venous thrombosis (DVT).
Low Molecular Weight Heparins can be administered at home because PTT
monitoring is not necessary. They are given subcutaneously in the abdomen
twice a day. The average treatment is for 7 to 14 days. The half life of LMWH
is two to four times longer than that of heparin. Patients should not take
antiplatelet drugs such as aspirin while taking LMWHs. Bleeding is less likely
to occur and overdose is rare. However, protamine sulfate is the antidote if nec-
essary and the dose is 1 mg of protamine for every 1 mg of LMWH given.
A list of anticoagulant low molecular weight drugs is provided in the Appendix.
Detailed tables show doses, recommendations, expectations, side effects, con-
traindications, and more; available on the book’s Web site (see URL in Appendix).
CHAPTER 19 Cardiac Circulatory Medications^365