Injectable Anticoagulants or Blood thinners
The most commonly used injectable anticoagulants are heparin and low molecular weight heparins.
Some anticoagulants are administered via injection. These include heparin, low molecular weight heparin, fondaparinux, lepirudin, bivalirudin, argatroban, danaparoid and drotrecogin alfa.
Heparin inhibits two clotting factors – Xa and IIa (Normally there are XIII factors in blood clotting mechanism), thus preventing clot formation. It is administered either into a vein or under the skin by a deep subcutaneous injection. It can be safely used during pregnancy. Its effect is monitored using a blood test called activated partial thromboplastin time (aPTT). Normally the aPTT is between 26 to 32 seconds in a normal individual. A patient on heparin is maintained on an aPTT of 1.5 to 2.5 times the normal or pretreatment value.
Side effects of Heparin - The main side effect of heparin is bleeding. It may also cause other side effects like decrease in the number of platelets, liver enzyme abnormalities, hair loss and allergic reactions. Osteoporosis or thinning of bone may result from high dose prolonged treatment.
Where should Heaprin be not used - It should not be used in any condition where there could be a risk of serious bleeding. Such conditions include bleeding disorders, severe hypertension, stomach ulcers, piles, large cancers, tuberculosis, and eye and brain surgery. It should also not be used in patients with subacute bacterial endocarditis (infection of heart valves), liver or kidney disease, or those who developed low platelet level with heparin treatment in the past. It should be used cautiously with other drugs that cause bleeding such as aspirin.
Low Molecular Weight Heparins (LMWH)
These include drugs such as enoxaparin (Brand name Lovenox), reviparin (Brand name Clivarine), nadroparin (Brand name Fraxiparine), dalteparin (Brand name Fragmin), pamparin (Brand name Fluxum), tinzaparin (Brand name Innohep) and ardeparin (Brand name Indeparin). These drugs are derived from heparin and have some benefits over the standard heparin.
- They inhibit only clotting factor Xa and reduce platelet levels less frequently. Thus they could cause less bleeding.
- They are better absorbed from a subcutaneous injection.
- Their effect lasts for a longer time, hence they may be administered once or twice a day. Their effect is more predictable, hence repeated monitoring of aPTT is not required.
- KD Tripathi. Essentials of Medical Pharmacology 6th Edition
- Goodman and Gilman. The Pharmacological Basis of Therapeutics 11th Edition