The four frequently used classes of adrenergic drugs are bronchodilators (see Chapter 37), ophthalmic drugs (see Chapter 57), nasal decongestants (see Chapter 36), and vasoactive drugs, which are emphasized in this chapter (see Drug Profiles) and in Chapter 24. The receptor selectivity for the alpha1, beta1 , and beta2
receptor subtypes is relative (as opposed to absolute ). Thus, there may be some overlap of drug effects between the different adrenergic classes of drugs, especially at higher dosages. In contrast, dopamine receptors are more specific for dopamine itself and/or specific dopaminergic drugs.
Adrenergics that have primarily cardioselective effects are referred to as vasoactive adrenergics. They are used to support a failing heart or to treat shock. They may also be used to treat orthostatic hypotension. These drugs have a wide range of effects on alpha- and beta-adrenergic receptors, depending on the dosage. The vasoactive adrenergics are very potent, quickacting, injectable drugs. Although dosage recommendations are given in the table on p. 304, all of these drugs are titrated to the desired physiologic response. All of the vasoactive adrenergics (with the exception of midodrine) are rapid in onset, and their effects very quickly cease when administration is stopped. Therefore, careful titration and monitoring of vital signs and electrocardiogram (ECG) are required.
Dobutamine (Dobutrex) is a beta1 -selective vasoactive adrenergic drug that is structurally similar to the naturally occurring catecholamine dopamine. Through stimulation of the beta1 receptors on heart muscle (myocardium), it increases cardiac output by increasing contractility ( positive inotropy), which increases the stroke volume, especially in patients with heart failure. Dobutamine is available only as an intravenous drug and is given by continuous infusion. (See Dosages table on p. 304.)
Pharmacokinetics: Dobutamine (Dobutrex)
Route Onset of Action Peak Plasma Elimination Duration of Action Concentration Half-life IV <2 minutes <10 minutes 2-5 minutes <10 minutes
Dopamine (Intropin) is a naturally occurring catecholamine neurotransmitter. It has potent dopaminergic as well as
beta1 - and alpha1 -adrenergic receptor activity, depending on the dosage. Dopamine, when used at low dosages, can dilate blood vessels in the brain, heart, kidneys, and mesentery, which increases blood flow to these areas (dopaminergic receptor activity). At higher infusion rates, dopamine can improve cardiac contractility and output (beta1- adrenergic receptor activity). At highest doses, dopamine causes vasoconstriction (alpha1 -adrenergic receptor activity). Use of dopamine is contraindicated in patients who have a catecholamine- secreting tumor of the adrenal gland known as a pheochromocytoma. The drug is available only as an intravenous injectable drug and is given by continuous infusion.
- Winter '16