Alpha-specific adrenergic agonists, or alpha-agonists, are drugs that bind primarily to alpha-receptors rather than to beta-receptors. Three drugs belong to this class: Clonidine (Catapres), midodrine (generic), and phenylephrine (Neo-Synephrine, and others).
Therapeutic effects of the alpha-specific adrenergic agonists result from the stimulation of alpha-receptors within the SNS. The uses are varied, depending on the specific drug and the route of administration.
α特异性肾上腺素能激动剂的疗效源于SNS内α受体刺激。途径多样，取决于具体的药物及给药途径
Phenylephrine, a potent vasoconstrictor and alpha1-agonist with little or no effect on the heart or bronchi, is used in many combination cold and allergy products. Parenterally, it is used to treat shock or shock-like states, to overcome paroxysmal supraventricular tachycardia, to prolong local anesthesia, and to maintain blood pressure during spinal anesthesia. Topically, it is used to treat allergic rhinitis and to relieve the symptoms of otitis media. Ophthalmically, it is used to dilate the pupils for eye examination, before surgery, or to relieve elevated eye pressure associated with glaucoma. Phenylephrine is found in many cold and allergy products because it is so effective in constricting topical vessels and decreasing the swelling, signs, and symptoms of rhinitis.
Midodrine is an oral drug that is used to treat orthostatic hypotension in patients who do not respond to traditional therapy. It activates alpha1-adrenergic receptors, leading to peripheral vasoconstriction and an increase in vascular tone and blood pressure. This effect can cause a serious supine hypertension. Patients need to be monitored in the standing, sitting, and supine positions to determine whether this will be a problem.
Midodrine is a grandfathered drug that had never gone through rigorous testing. In 2010, when the drug was tested, its effectiveness was not clear and the manufacturer was required to put the drug through testing to establish effectiveness. So far, that testing has not been done and it is not clear how long the drug will be available.
Clonidine specifically stimulates CNS alpha2-receptors. This leads to decreased sympathetic outflow from the CNS because the alpha2-receptors moderate the release of norepinephrine from the nerve axon. Clonidine is available in oral and transdermal forms for use to control hypertension and as an injection for epidural infusion to control pain in cancer patients. Because of its centrally acting effects, clonidine is associated with many more CNS effects (bad dreams, sedation, drowsiness, fatigue, headache) than other sympathomimetics. It can also cause extreme hypotension, heart failure, and bradycardia due to its decreased effects of the sympathetic outflow from the CNS.
alpha-specific -- α特异性
alpha-agonist – n. α激动剂
alpha-receptor – n. α受体
beta-receptor – n. β受体
clonidine – n. 可乐定 Catapres – n. 可乐宁
midodrine – n. 米多君
phenylephrine – n. 苯福林 Neo-Synephrine – n. 新昔奈福林
vasoconstrictor – n. 血管收缩剂
alpha1-agonist – n. α1激动剂
paroxysmal – a. 阵发的，发作性的
supraventricular – a. 室上的
paroxysmal supraventricular tachycardia – 阵发性室上性心动过速
prolong – v. 延长
spinal anesthesia -- 脊椎麻醉
rhinitis – n. 鼻炎
otitis media – n. 中耳炎
vascular tone – 血管张力
supine hypertension – 仰卧位高血压
grandfathered drug – 祖父药
sympathetic outflow – 交感神经传出
Alpha Adrenergic Receptor Types Location and Function
★Test ★
1. The nurse is preparing to administer medication to the following clients. Which medication should the nurse question administering?
A. Metformin to a client with type 1 diabetes who is receiving insulin.
B. Bumetanide to a client diagnosed with essential HTN.
C. Erythropoietin to a client diagnosed with end-stage renal failure.
D. Clonidine to a client diagnosed with heart failure.
2. The nurse on the substance abuse unit is administering medications. Which medication should the nurse question administering?
A. Chlordiazepoxide to a client admitted for alcohol detoxification.
B. Haloperidol to a client diagnosed with phencyclidine (PCP) psychosis.
C. Clonidine to client with a blood pressure of 88/60.
D. Thiamine intravenously to a client diagnosed with Wernicke-Korsakoff syndrome.
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答案 Answers 1. D. Clonidine to a client diagnosed with heart failure Rationale: Clonidine (Catapres) is an alpha agonist. The nurse would question administering Catapres to a client with decreased cardiac output (heart failure), because this medication acts within the brain stem to suppress sympathetic outfl ow to the heart and blood vessels. The result is vasodilation and reduced cardiac output, both of which lower blood pressure. 2. C. Clonidine to client with a blood pressure of 88/60. Rationale: Clonidine (Catapres), an alpha-adrenergic agonist, is administered primarily to treat hypertension, but it is also used to reduce the symptoms of withdrawal from opioids, nicotine, and alcohol. The nurse would question administering this medication because of the client’s low blood pressure no matter why it is being prescribed.
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