Adrenergic Drugs and the Autonomic Nervous System

• The autonomic nervous system (ANS) consists of the sympathetic (SNS) which work together to maintain the homeostasis of bodily functions.

Adrenergic Drugs

• Adrenergic drugs, also known as adrenergic agonists or sympathomimetics, stimulate the SNS, and mimic SNS neurotransmitters.
• Catecholamines like norepinephrine, epinephrine, and dopamine, as well as synthetic drugs like dobutamine and phenylephrine hydrochloride, are key examples.
• Direct-acting sympathomimetics bind directly to receptors, causing a physiological response.
• Indirect-acting sympathomimetics release catecholamines from storage sites, which then bind to receptors.
• Mixed-acting sympathomimetics stimulate receptors directly and cause the release of stored neurotransmitters.

Therapeutic Effects of Adrenergic Drugs

• Stimulation of α1-adrenergic receptors leads to vasoconstriction, relaxation of GI smooth muscles, constriction of the bladder sphincter, contraction of the uterus, male ejaculation, and contraction of pupillary muscles.
• Stimulation of β1-adrenergic receptors increases heart contraction force, heart rate, and AV node conduction.
• Stimulation of β2-adrenergic receptors causes bronchodilation.

Indications for Adrenergic Drugs

• Asthma and bronchitis treatment: bronchodilators stimulate β2-adrenergic receptors of bronchial smooth muscles. Examples include formoterol, salbutamol, salmeterol, and terbutaline.
• Nasal congestion treatment: Intranasal application causes constriction of dilated arterioles, reducing nasal blood flow. Examples include oxymetazoline and phenylephrine.
• Relief of conjunctival congestion: Examples include epinephrine, naphazoline, phenylephrine, and tetrahydrozoline.
• Reduction of intraocular pressure and pupil dilation: Example: dipivefrin.
• Cardiovascular support during cardiac failure or shock: Vasoactive sympathomimetics affect α- and β-receptors. Examples include dobutamine, dopamine, midodrine, epinephrine, phenylephrine, and norepinephrine.

Adverse Effects of Adrenergic Drugs

• α-Adrenergic effects: Headache, restlessness, excitement, insomnia, euphoria, palpitations, tachycardia, vasoconstriction, hypertension, appetite loss, dry mouth, nausea, vomiting, and taste changes.
• β-Adrenergic effects: Mild tremors, headache, nervousness, dizziness, insomnia, euphoria, chest pain, increased heart rate, palpitations, hypertension, vasoconstriction, sweating, nausea, vomiting, and muscle cramps.

Cautions, Contraindications, and Interactions of Adrenergic Drugs

• Obtain a comprehensive health history, including allergies and asthma, and assess for hypertension, cardiac dysrhythmias, and other cardiovascular diseases.
• Assess renal, hepatic, and cardiac function before treatment.
• Interact with anesthetic drugs, digoxin, tricyclic antidepressants, MAOIs, antihistamines, and thyroid preparations.
• Combining two adrenergic drugs may cause severe cardiovascular effects like tachycardia or hypertension.
• Avoid over-the-counter medications due to potential interactions.

Nursing Implications for Adrenergic Drugs

• Check IV sites often for infiltration when administering intravenously.
• Use clear IV solutions and an infusion pump.
• Infuse drugs slowly to avoid dangerous cardiovascular effects, and monitor cardiac rhythm.

Adrenergic Antagonists

• Adrenergic blockers (sympatholytics) bind to adrenergic receptors, inhibiting or blocking SNS stimulation.
• Classified by blocked receptor type, like α1-, α2-, β1-, and β2-receptors.

Alpha-Blockers

• Alpha-blockers cause arterial and venous dilation, reducing peripheral vascular resistance and BP.
• They treat hypertension, reduce urinary obstruction, and relieve BPH effects. Examples include alfuzosin, phentolamine, prazosin, terazosin, tamsulosin, and doxazosin.
• Adverse effects include headache, abnormal ejaculation, and rhinitis.
• Contraindications include known drug allergy and concurrent use of erectile dysfunction drugs like sildenafil.

Beta-Blockers

• Beta-blockers block β-receptor stimulation in the SNS and compete with norepinephrine and epinephrine.
• Cardioselective β-blockers (β1) reduce heart stimulation, decrease heart rate, prolong sinoatrial node recovery, slow AV node conduction, and decrease myocardial contractility, reducing oxygen demand.
• Nonselective β-blockers (β1 and β2) have the same heart effects as cardioselective blockers, constrict bronchioles (narrowing airways and causing shortness of breath), and cause blood vessel vasoconstriction.
• Angina, MI, hypertension, cardioprotection, dysrhythmias, glaucoma, and migraine headaches. The adverse effects include bradycardia, hypotension, heart block, heart failure, and bronchoconstriction.

Specific Beta-Blockers

• Atenolol: Cardioselective β-blocker used to prevent future heart attacks, treat hypertension and angina, and manage thyrotoxicosis.
• Carteolol: Nonselective β-blocker and a selective ISA beta-blocker used for hypertension and glaucoma.
• Carvedilol: Nonselective β-blocker and α1-blocker used for heart failure, hypertension, and angina.
• Nonselective β-Blockers: Carvedilol, nadolol, labetalol, pindolol, propranolol, sotalol, timolol.
• Cardioselective β-Blockers: Acebutolol, atenolol, bisoprolol fumerate, esmolol, nebivolol, metoprolol.

Nursing Implications for Adrenergic-Blocking Drugs

• Assess for allergies and perform a thorough cardiac assessment.
• Avoid over-the-counter medications due to possible interactions.
• Take medications as prescribed and never stop abruptly.
• Change positions slowly to prevent postural hypotension.
• Avoid caffeine and alcohol.
• Notify physicians if palpitations, dyspnea, nausea, or vomiting occurs.
• Report weight gain of more than 1 kg in 24 hours or 2.3 kg in 1 week, edema, shortness of breath, excessive fatigue, weakness, syncope, or dizziness to the physician.