McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

TABLE 48.1

DRUGS IN FOCUS Drugs affecting clot formation and resolution (continued)

Drug name

Dosage/route

Usual indications

Anticoagulant adjunctive therapy (continued) vitamin K (Konakion Adult, Konakion MM)

Konakion Adult: Adult: 2.5–10 mg PO or IV Konakion MM: Neonatal prophylaxis: 2 mg PO at birth, repeated at 3–5 days and 4 weeks, or 1 mg IM at birth

Treatment of anticoagulant-induced prothrombin deficiency

Haemorheologic agent oxypentifylline (Trental)

400 mg PO t.d.s. with meals

Treatment of intermittent claudication to improve function and reduce symptoms; improve blood flow in vascular diseases

Pharmacokinetics Abciximab, eptifibatide and tirofiban are adminis­ tered intravenously (IV). Antiplatelet agents that are administered orally include anagrelide, aspirin, cilosta­ zol, clopidogrel, prasugrel, ticagrelor and ticlopidine. Dipyridamole is used orally or as an IV agent. These drugs are generally well absorbed and highly bound to plasma proteins. They are metabolised in the liver and excreted in urine, and they tend to enter breast milk (see Contraindications and cautions). Contraindications and cautions Antiplatelet agents are contraindicated in the presence of allergy to the specific drug to avoid hypersensitivity reactions . Caution should be used in the following con­ ditions: the presence of any known bleeding disorder because of the risk of excessive blood loss ; recent surgery because of the risk of increased bleeding in unhealed vessels ; and closed head injuries because of the risk of bleeding from the injured vessels in the brain. Although there are no adequate studies of these drugs in pregnancy, they are contraindicated because of the potential for increased bleeding (see Adverse effects); they should be used during pregnancy only if the benefits to the mother clearly outweigh the potential risks to the fetus. These drugs are also contraindicated during breastfeed­ ing because of the potential adverse effects on the fetus or neonate ; if they are needed by a breastfeeding woman, she should find another method of feeding the baby. Anagrelide should be used with caution with any history of thrombocytopenia because it decreases the production of platelets in the bone marrow . Platelet levels should be checked regularly to monitor for throm­ bocytopenia if a person is on this drug. Adverse effects The most common adverse effect seen with these drugs is bleeding, which often occurs as increased bruising and bleeding while brushing the teeth. Other common problems include headache, dizziness and weakness; the cause of these reactions is not understood. Nausea

A ntiplatelet agents Antiplatelet agents decrease the formation of the platelet plug by decreasing the responsiveness of the platelets to stimuli that would cause them to stick and aggregate on a vessel wall. Antiplatelet agents avail­ able for use include abciximab ( ReoPro ), anagrelide ( Agrylin ), aspirin, cilostazol ( Pletal [not available in New Zealand]), clopidogrel ( Plavix ), dipyridamole ( Persantin ), eptifibatide ( Integrilin ), prasugrel ( Effient ), ticagrelor ( Brilinta ), ticlopidine ( Tilodene ), and tirofiban ( Aggrastat ). Therapeutic actions and indications The antiplatelet agents inhibit platelet adhesion and aggregation by blocking receptor sites on the platelet membrane, preventing platelet–platelet interaction or the interaction of platelets with other clotting chemicals. One drug, anagrelide, blocks the production of platelets in the bone marrow. These agents are used effectively to treat cardiovascular diseases that are prone to produce occluded vessels; for the maintenance of venous and arterial grafts; to prevent cerebrovascular occlusion; and as adjuncts to thrombolytic therapy in the treat­ ment of myocardial infarction (MI) and the prevention of reinfarction after MI. The prescriber’s choice of drug depends on the intended use and the person’s tolerance of the associated adverse effects. See Table 48.1 for usual indications for each of these agents. Many herbal therapies can cause problems when used with drugs that affect blood coagulation. People taking these drugs should be cautioned to avoid angelica, cat’s claw, chamomile, chondroitin, feverfew, garlic, ginkgo, goldenseal, grape seed extract, green leaf tea, horse chestnut seed, psyllium and turmeric. If a person who is taking an anticoagulant presents with increased bleeding and no other interaction or cause is found, question the person about the possibility of use of herbal therapies. Herbal and alternative therapies BOX 48.2