antithrombin III, human

antithrombin III, human (AT-III, heparin cofactor 1)

Thrombate III

Pharmacologic class: Blood derivative, coagulation inhibitor

Therapeutic class: Antithrombin

Pregnancy risk category B

Action

Inactivates thrombin and activated forms of factors IXa, Xa, XIa, and XIIa, thereby inhibiting coagulation and thromboembolism formation

Availability

Injection: 500 international units, 1,000 international units

Indications and dosages

Thromboembolism related to AT-III deficiency

Adults: Initial dosage is individualized to amount required to increase AT-III activity to 120% of normal (determined 20 minutes after administration). Usual infusion rate is 50 to a maximum of 100 international units/minute I.V. Dosage calculation is based on anticipated 1.4% increase in plasma AT-III activity produced by 1 international unit/kg of body weight.

Use this formula to calculate dosage: Required dosage (international units) equals desired activity (%) minus baseline AT-III activity (%) multiplied by weight (kg) divided by 1.4 (international units/kg).

Maintenance dosage is individualized to amount required to maintain AT-III activity at 80% of normal.

Contraindications

None

Precautions

Use cautiously in:

• pregnant or breastfeeding patients

• children (safety and efficacy not established).

Administration

• Reconstitute drug concentrate with 10 ml of sterile water, normal saline solution, or dextrose 5% in water.

• Use filter needle provided by manufacturer to draw up solution.

• Don't shake vial.

• Know that drug may be diluted further in same solution if desired.

• Don't mix with other solutions.

• Infuse over 10 to 20 minutes.

• Administer within 3 hours of reconstitution.

If adverse reactions occur, decrease infusion rate or, if indicated, stop infusion until symptoms disappear.

Adverse reactions

CNS: dizziness, light-headedness, headache

CV: vasodilation, reduced blood pressure, chest pain

EENT: perception of "film" over eyes

GI: nausea, sensation of intestinal fullness

GU: diuresis

Musculoskeletal: muscle cramps

Respiratory: dyspnea, shortness of breath

Skin: urticaria, oozing lesions, hives, hematoma

Other: foul taste, chills, fever

Interactions

Drug-drug. Heparin: increased anticoagulant effect

Patient monitoring

• Monitor AT-III activity levels regularly.

Watch for signs and symptoms of too-rapid infusion, such as dyspnea and hypertension.

• Monitor vital signs and temperature.

• Assess fluid intake and output to detect dehydration.

Patient teaching

Instruct patient to immediately report chest tightness, dizziness, and fever.

• Caution patient to avoid driving and other hazardous activities until he knows how drug affects concentration and alertness.

• Advise patient to minimize GI upset and unpleasant taste by eating small, frequent servings of healthy food and drinking plenty of fluids.

• Tell patient that he'll undergo regular blood testing during therapy.

• As appropriate, review all other significant adverse reactions and interactions, especially those related to the drugs mentioned above.