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