Question

TM, a 57-year-old man, has thrombophlebitis in the right lower leg. IV heparin, 5000 units by bolus, was given. Following the IV bolus, heparin 5000 units given subQ q6h was prescribed. Other therapeutic means to decrease pain and alleviate swelling and redness were also prescribed. An aPTT test was ordered.

            1. Was TM's heparin order within the safe daily dosage range?

            2. What are the various methods for administering heparin?

Answer 1

1). The loading dose of heparin in adults is generally 5000 Units by IV bolus and is followed by maintenance dose for every 6 hours. The maintenance dose is based on the plasma levels of the drug. As TM is being administered with the NSAIDS (non-steroidal anti-inflammatory drugs used to treat pain, redness and swelling), the dose of heparin need to be reduced in the follow-up dose, This is because the NSAIDS act as antiplatelet drugs also, so, the dose of heparin needs to be reduced, otherwise, it increases the risk of bleeding.

2).

Heparin is not absorbed from the gut because of its charge and large size and is therefore, given intravenously or subcutaneously (intramuscular injections would cause hematomas). After intravenous injections of a bolus dose, there is a phase of rapid elimination followed by a more gradual disappearance owing both to saturable processes (involving binding sites on endothelial cells and macrophages) and slower first –order kinetic processes including renal excretion. As a result, once the dose exceeds the saturating concentration, a greater proportion is dealt with by these slower processes and the apparent half-life increases with increasing dose. Through the blood circulation, heparin also binds to plasma proteins and reduces its anticoagulant activity.

Heparin acts immediately following intravenous administration but the onset is delayed by up to 60 minutes when it is given subcutaneously. The elimination half-life is approximately 40-90 minutes. In urgent situations, it is, therefore, usual to start treatment with a bolus intravenous dose, followed by a constant-rate infusion.