McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

Therapeutic actions and indications The antihaemophilic drugs replace clotting factors that are either genetically missing or low in a particu­ lar type of haemophilia. The drug of choice depends on the particular haemophilia that is being treated. Anti­ haemophilic factor is factor VIII, the clotting factor that is missing in classic haemophilia (haemophilia A). This agent and antihaemophilic factor recombinant (a genetically engineered product that does not use human blood) are used to correct or prevent bleeding episodes or to allow necessary surgery. Coagulation factor VIIa ( NovoSeven [NZ]) and factor IX complex are used for people with haemo­ philia A or B (see Table 48.4 for usual indications for each of these agents). Coagulation factor VIIa is a prepa­ ration made from mouse, hamster and bovine proteins that contains variable amounts of preformed clotting factors (see Contraindications and cautions). Factor IX complex contains plasma fractions of many of the clotting factors and increases blood levels of factors II, VII, IX and X. The drug of choice for any given person is determined by his or her particular coagulation abnormalities. Pharmacokinetics These agents replace normal clotting factors and are processed as such by the body. They must be given intra­ venously and are processed by the body in the same way that naturally occurring clotting factors are processed in the plasma, usually with a half-life of 24 to 36 hours. Contraindications and cautions Antihaemophilic factor is contraindicated in the presence of known allergy to mouse proteins to prevent hyper- sensitivity reactions . Factor IX is contraindicated in the presence of liver disease with signs of intravascular coag­ ulation or fibrinolysis to prevent serious aggravation of these disorders . Coagulation factor VIIa is contraindi­ cated with known allergies to mouse, hamster or bovine products to prevent hypersensitivity reactions . These drugs are not recommended for use during breast­ feeding, and caution should be used during pregnancy because of the potential for adverse effects on the baby or fetus. They should be used during pregnancy only if the benefit to the mother clearly outweighs the potential risk to the fetus. It is recommended that another method of feeding the baby be used if these drugs are needed during breastfeeding. Because these drugs are used to prevent serious bleeding problems or to treat bleeding episodes, there are few contraindications to their use. Adverse effects The most common adverse effects associated with anti­ haemophilic agents involve risks associated with the

use of blood products (e.g. hepatitis, AIDS). Headache, flushing, chills, fever and lethargy may occur as a reaction to the injection of a foreign protein. Nausea and vomiting may also occur, as may stinging, itching and burning at the site of the injection. Prototype summary: Antihaemophilic factor Indications: Treatment of classic haemophilia to provide temporary replacement of clotting factors to correct or prevent bleeding episodes or to allow necessary surgery. Actions: Normal plasma protein that is needed for the transformation of prothrombin to thrombin, the final step in the clotting pathway. Pharmacokinetics: Route Onset Peak Duration IV Immediate Unknown Unknown T 1/2 : 12 hours; cleared from the body by normal protein metabolism. Adverse effects: Allergic reaction, stinging at injection site, headache, rash, chills, nausea, hepatitis, AIDS (risks associated with the use of blood products). ■ ■ Assess for the following conditions, which could be cautions or contraindications to use of the drug : any known allergies to these drugs or to mouse proteins with antihaemophilic factor; liver disease. ■ ■ Assess for baseline status before beginning therapy to determine any potential adverse effects. ■ ■ Assess the following: body temperature; skin colour, lesions and temperature; affect, orientation and reflexes; pulse, blood pressure and perfusion; respirations and adventitious sounds; clotting studies; and hepatic function tests. Implementation with rationale ■ ■ Monitor clinical response and clotting factor levels regularly to arrange to adjust dose as needed. ■ ■ Monitor the person for any sign of thrombosis to arrange to use comfort and support measures as needed (e.g. support hose, positioning, ambulation, exercise). ■ ■ Administer by the IV route only to ensure therapeutic effectiveness. Care considerations for people receiving antihaemophilic agents Assessment: History and examination