A-adrenergic agonists

Preventive measures for patients who may be prone to hypotension include accurate determination of the dry weight and maintaining a constant ultrafiltration rate. Midodrine is an a-adrenergic agonist that is effective in reducing hypotension in patients with autonomic dysfunction that is taken with each dialysis session or as chronic therapy. Midodrine can be administered at doses of 2.5 to 10 mg prior to HD or 5 mg twice daily for chronic hypotension. Side effects of midodrine include pruritus and paresthesias. 

In contrast to this, there are no such structural constraints on a-adrenergic agonists or antagonists. Some of the most active a-sympathomimetic agents in fact contain an imidazoline moiety as part of the pharmacophore. The appropriate ring system can be... 

The direct-acting adrenomimetics described next are a-adrenergic agonists that are structurally very different from the drugs described above. 

Tolazoline Tolazoline, 2-benzyl-2-imidazoline (12.2.7), is synthesized by the heterocy-clation of the ethyl ester of iminophenzylacetic acid with ethylendiamine (12.2.6), which forms the desired product (12.2.7) [32-35]. The structure of tolazoline is strikingly similar to a-adrenergic agonists, which are antiedema sympathomimetics. 

Glucagon Vasopressin a-Adrenergic agonists /1-Adrenergic antagonists ... 

Clonidine. As with the rationale for P-blockers in the treatment of social phobia, clonidine hydrochloride, an a-adrenergic agonist, has been used in an attempt to target the physiological symptoms of the disorder. In a case report by Goldstein [1987], one subject with social phobia who experienced a primary symptom of blushing was treated with clonidine 0.1 mg twice a day after trials with alprazolam, phenelzine, and propranolol failed to provide symptom relief. The patient reported a dramatic decrease in the frequency and intensity of blushing episodes after 1 week of treatment. At 4-month follow-up, his symptoms remained well controlled and he denied any side effects. 

A rather simpler compound includes both a benzodioxan nucleus and the imidazoline function associated with a-adrenergic agonists such as clonidine. As in the standard approach for preparing imidazolines, the treatment of nitrile (60-1) with alcoholic hydrogen chloride leads to the iminoether (60-2). Reaction of that intermediate with ethylenediamine then affords idazoxin (60-3) [70], a compound that interacts with a-adrenergic receptors. 

Phenylephrine, Nasal (Neo-Synephrine Nasal) (OTC) [Vasopressor/Decongestant] Uses Can be used prior to nasal intubation and NG tube insertion to reduce bleeding Action a-Adrenergic agonist Dose Adults Peds. 1-2 sprays/nostril q4h (usual 0.25%).Caution [C, +/-] HTN, acute pancreatitis, Hep, coronary Dz, NAG, hyperthyroidism Contra Bradycardia, arrhythmias Disp Nasal soln (0.125-0.25%) SE Arrhythmias, HTN, nasal irritation, dryness, sneezing, HA Interactions May effects OF nitrates EMS Ocular instillation may dilate pupil... 

Uses Mydriasis, ocular redness [OTC], periop mydriasis, posterior synechiae, uveitis w/ posterior synechiae Action a-Adrenergic agonist Dose Adults. Redness 1 gtt 0.12% q3-4h PRN Exam mydriasis 1 gtt 2.5% (15 min-1 h for effect) Preop 1 gtt 2.5—10% 30-60 min preop Ocular disorders 1 gtt 2.5-10% daily-tid Peds. As adult, only use 2.5% for exam, preop, and ocular conditions Caution [C (may cause late-term fetal anoxia/bradycardia), +/-] HTN, w/ elderly w/ CAD Contra NAG Disp Ophth soln SE Tearing, HA, irritation, eye pain, photophobia, arrhythmia, tremor EMS None OD Unlikely but may cause exaggeration of nl SEs symptomatic and supportive... 

---