McKenna's Pharmacology for Nursing, 2e

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P A R T 8  Drugs acting on the cardiovascular system

TABLE 44.1

DRUGS IN FOCUS Cardiotonic agents

Drug name

Dosage/route

Usual indications

Cardiac glycosides digoxin (Lanoxin, Sigmaxin)

Adult: loading dose 0.75–1.25 mg PO or 0.125–0.25 mg IV, then maintenance dose of 0.125–0.25 mg/day PO; decrease dose with renal impairment Paediatric (dose based on age): 10–60 mcg/kg PO or 8–50 mcg/kg IV loading dose, maintenance is 25%–30% of loading dose

Treatment of acute heart failure, atrial arrhythmias

Phosphodiesterase inhibitor milrinone (Primacor)

50 mcg/kg IV bolus over 10 minutes; then 0.375–0.75 mcg/kg/min IV infusion; do not exceed 1.13 mg/kg per day; reduce dose in renal impairment

Short-term management of HF in adults receiving digoxin and diuretics

Drug therapy across the lifespan

BOX 44.1

Cardiotonic agents CHILDREN

Digoxin is contraindicated in the following conditions: ventricular tachycardia or fibrillation, which are poten- tially fatal arrhythmias and should be treated with other drugs ; heart block or sick sinus syndrome, which could be made worse by slowing of conduction through the atrioventricular node ; idiopathic hypertrophic subaortic stenosis (IHSS) because the increase in force of contrac- tion could obstruct the outflow tract to the aorta and cause severe problems ; acute MI because the increase in force of contraction could cause more muscle damage and infarct ; renal insufficiency because the drug is PREGNANCY AND BREASTFEEDING The safety for the use of these drugs during pregnancy has not been established.They should not be used in pregnancy unless the benefit to the mother clearly outweighs the potential risk to the fetus.The drugs do enter breast milk, but they have not been associated with any adverse effects in the neonate. Caution should be used, however, if one of these drugs is needed during breastfeeding. OLDER ADULTS Older adults frequently are prescribed one of these drugs. They, like children at the other end of the life spectrum, are more susceptible to the toxic effects of the drugs and are more likely to have underlying conditions that could interfere with their metabolism and excretion. Renal impairment can lead to accumulation of digoxin in the body. If renal dysfunction is present, the dosage needs to be reduced and the person monitored very closely for signs of digoxin toxicity. The total drug regimen of the older person should be coordinated, with careful attention to interacting drugs or alternative therapies. For backup in situations of stress or illness, a significant other should be instructed in how to take the person’s pulse and the adverse effects to watch for while the person is taking this drug.

30 minutes when given intravenously). It is widely distributed throughout the body. Digoxin is primar­ ily excreted unchanged in the urine. Because of this, caution should be used in the presence of renal impair­ ment because the drug may not be excreted and could accumulate, causing toxicity. Contraindications and cautions Cardiac glycosides are contraindicated in the presence of allergy to any component of the digitalis preparation. Digoxin is used widely in children with heart defects and related cardiac problems.The margin of safety for the dosage of this drug is very small with children.The dosage needs to be very carefully calculated and should be double-checked by another healthcare provider before administration. Children should be monitored closely for any sign of impending digitalis toxicity and should have serum digoxin levels monitored. The phosphodiesterase inhibitors are not recommended for use in children. ADULTS Adults receiving any of these drugs need to be instructed as to what adverse reactions to report immediately. They should learn to take their own pulse and should be encouraged to keep track of rate and regularity on a calendar.They may be asked to weigh themselves in the same clothing and at the same time of the day to monitor for fluid retention. Any changes in diet, gastrointestinal activity, or medications should be reported to the healthcare provider because of the potential for altering serum levels and causing toxic reactions or ineffective dosing.