Chapter 24

This chapter discusses the actions, indications, pharmacokinetics, dosing, and adverse effect profiles of vasopressor drugs that are pertinent to emergency medicine practice. Specific medications also are discussed. Please also see Chapter 25, Approach to the Patient in Shock.

### Dobutamine

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Dobutamine (Dobutrex) is a synthetic sympathomimetic drug that exerts potent inotropic and mild chronotropic activities. Dobutamine is formulated as a racemic mixture with β1- and β2-adrenergic and α-adrenergic agonist activities that are offset by α-adrenergic antagonist activity (Table 24-1). The net result is an increase in myocardial contractility and systemic vasodilation, with minimal changes in heart rate. Doses of up to 20 micrograms/kg/min will increase cardiac output, decrease peripheral vascular resistance, and decrease pulmonary occlusive pressures. Conversely, doses >20 micrograms/kg/min will increase the heart rate and induce arrhythmias.

Table 24-1 Ability of Commonly Used Sympathomimetic Agents to Stimulate Adrenergic Receptors

#### Pharmacokinetics

The onset of action of dobutamine is 1 to 2 minutes, and the peak response occurs within 10 minutes after IV administration. The apparent volume of distribution (Vd) is 0.2 L/kg, and the drug is metabolized primarily in tissue and the liver to inactive metabolites. The elimination half-life is 1 to 2 minutes, with the majority of the drug being eliminated within 48 hours in the urine as inactive metabolites.

#### Indications

Dobutamine is indicated for short-term positive inotropic support for the treatment of cardiovascular decompensation secondary to ventricular dysfunction or low-output heart failure. It is the preferred agent in septic shock with depressed cardiac output despite adequate left ventricular filling pressures. Dobutamine is also usually the preferred agent in the management of cardiogenic shock. It increases cardiac output and renal and mesenteric blood flow without direct stimulation of the heart rate and decreases systemic vascular resistance.

Dobutamine is administered only as a continuous IV infusion. The dosage range is 2 to 20 micrograms/kg/min; however, most patients can be maintained on 10 micrograms/kg/min. Doses larger than 20 micrograms/kg/min increase the risk of tachyarrhythmia. To assess effectiveness of the dose administered, patients should be monitored with a central venous pressure or pulmonary artery catheter. Unlike many pressor agents, dobutamine may safely be given peripherally.

The primary adverse effects of dobutamine are modest increases in heart rate (increases >5 to 15 beats/min are uncommon), blood pressure ...

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