Antithrombin III (Human)
Antithrombin III (Human) (Thrombate III)
Antithrombin III
(an-tee- THROM-bin)
Pregnancy Category: B Thrombate III (Rx)

Classification: Antithrombin

Action/Kinetics: Antithrombin III (AT-III) is the major plasma inhibitor of thrombin. For therapeutic use it is obtained from plasma of human volunteers. Inactivation of thrombin by AT-III results from formation of a covalent bond causing an inactive 1:1 stoichiometric complex between thrombin and AT-III. AT-III also inactivates other components of the coagulation cascade including factors IXa, Xa, XIa, and XIIa, and plasmin. t 1/2: 2.5 days (based on immunologic assays).

Uses: Hereditary AT-III deficiency in pregnant clients, in clients requiring surgery, and in individuals with thromboembolism.

Special Concerns: Safety and effectiveness have not been determined in children. Even though special precautions are taken to screen plasma donors, clients may develop S&S; of viral infections, especially hepatitis C.

Side Effects: GI: Nausea, foul taste in mouth, bowel fullness. CNS: Dizzness, lightheadedness. Respiratory: Chest tightness, shortness of breath, chest pain. Miscellaneous: Chills, cramps, film over eye, hives, fever, oozing, hematoma.

Drug Interactions: The anticoagulant effect of heparin is increased when used concomitantly with AT-III; decrease the dose of heparin during AT-III therapy.

How Supplied: Powder for injection, lyophilized: 500 IU, 1000 IU

Dosage
?IV only
Individualize dose depending on the pretherapy plasma AT-III level. The dosage can be calculated from the following formula:  units required (IU) = [desired AT-III level (%) - baseline AT-III level (%)]/1.4 x body weight (kg).  The formula is based on an expected incremental recovery above baseline levels for AT-III of 1.4%/IU/kg given. Each bottle of AT-III has the functional activity, in international units (IU) stated on the label.

The following regimen may be used as a starting point for treatment; modification is based on actual plasma AT-III levels reached.

1. Calculate the initial loading dose to elevate plasma AT-III levels to 120%, assuming a rise over baseline plasma AT-III of 1.4% (functional activity)/IU/kg given.

2. Measure plasma AT-III levels preinfusion, 20 minutes postinfusion (peak), after 12 hr, and preceding the next infusion (trough level). Subsequently, measure AT-III levels preceding and 20 min after each infusion until predictable peak and trough levels have been reached (usually between 80% and 120%). Plasma levels between 80% and 120% may be maintained by giving maintenance doses of 60% of the initial loading dose q 24 hr. Adjust the maintenance dose or interval between doses based on actual plasma AT-III levels reached.