Phenylephrine dosing

Phenylephrine. Phenylephrine hydrochloride is an a -adrenoceptor agonist. Phenylephrine produces powerful vasoconstrictor and hypertensive responses. This results in baroreceptor activation of a reflex bradycardia and thus is useful in the treatment of supraventricular tachyarrhythmias. Unlike epinephrine [51-43-4] the actions of which are relatively transient, phenylephrine responses are more sustained (20 min after iv dosing and 50 min after subcutaneous dosing) (86). 

Topical intranasal decongestants (e.g., oxymetolazine, xylome-tolazine, phenylephrine, and naphazoline) are OTC options that provide prompt relief of nasal congestion. Nasal decongestants are dosed multiple times daily.15 Tachyphylaxis, rebound congestion, and rhinitis medicamentosa may occur with chronic use therefore, use should be limited to 3 to 5 days.8,12 These may be used 5 to 10 minutes before administration of intranasal corticosteroids in patients with blocked nasal passages.15... 

Phenylephrine, Nasal (Neo-Synephrine Nasal) (OTC) [Vasopressor/Decongestant] Uses Can be used prior to nasal intubation and NG tube insCTtion to reduce bleeding Action a-Adren gic agonist Dose Adults Feds. 1—2 sprays/nostril q4h (usual 0.25%).Caution [C, +/—] HTN, acute pancreatitis, H, coronary Dz, NAG, h5 pCTth5Toidism Contra Bradycardia, arrhythmias Disp Nasal soln (0.125-0.25%) SE Arrh5rthmias, HTN, nasal irritation, dryness, sneezing, HA Interactions May -1- effects OF nitrates EMS Ocular instillation may dilate pupil... 

When phenylephrine is administered by slow infusion of the therapeutic dose, which is the most likely effect illustrated in the following table increase (t) decrease (i) no change (0)7... 

Spasmolytic activity. Ethanol (95%), ethanol/glycerin, and glycerin extracts of the leaf, administered to guinea pigs at a dose of 50 mg/kg, was active vs vasopressin-induced coronary spasms as determined from electrocardiogram ". Ethanol (30%) extract of the dried leaf, administered to rabbits at a concentration of 1 mg/mL, was active on aorta vs K -induced contractions ". Decoction of the dried leaf, administered to rats, was active on aorta, IC501.12 mg/mL. The effect of the lyophilized extract on phenylephrine-induced contraction and endothelium was present. Decoction of the dried leaf, administered to rats, was active on the aorta vs phenylephrine-induced contraction, IC501.16 mg/mL. Water extract of the dried leaf, administered to rats at a dose of 3 mg/mL, was active on trachea vs acetylcholine-induced contractions ". Superoxide production inhibition. Seed oil, administered to rats at a concentration... 

Drugs fhat may require an increase in dose wifh smoking cessafion isoprof erenol, phenylephrine... 

Mild to moderate hypotension SC,1M 2-5mg(range 1-10 mg), repeated no more than every 10-15 minutes. Maximum initial dose 5 mg. IV 0.2 mg (range 0.1 to 0.5 mg), given no more frequently than every 10-15 minutes. Maximum initial dose 0.5 mg. Severe hypotension, severe shoch IV Initially, 100-180 mcg/minlVinfusion,withdose titration to the desired MAP and SVR. A maintenance infusion rate of 40-60 mcg/min IV is usually adequate after blood pressure stabilizes. If necessary to produce the desired pressor response, additional phenylephrine in increments of 10 mg or more may be added to the infusion solution and the rate of flow adjusted according to the response of the patient. 

Alpha receptors are widely expressed in vascular beds, and their activation leads to arterial and venoconstriction. Their direct effect on cardiac function is of relatively less importance. A relatively pure agonist such as phenylephrine increases peripheral arterial resistance and decreases venous capacitance. The enhanced arterial resistance usually leads to a dose-dependent rise in blood pressure (Figure 9-... 

Effects of autonomic blockade on the response to phenylephrine (Phe) in a human subject. Left The cardiovascular effect of the selective K-agonist phenylephrine when given as an intravenous bolus to a subject with intact autonomic baroreflex function. Note that the increase in blood pressure (BP) is associated with a baroreflex-mediated compensatory decrease in heart rate (HR). Right The response in the same subject after autonomic reflexes were abolished by the ganglionic blocker trimethaphan. Note that resting blood pressure is decreased and heart rate is increased by trimethaphan because of sympathetic and parasympathetic withdrawal. In the absence of baroreflex buffering, approximately a tenfold lower dose of phenylephrine is required to produce a similar increase in blood pressure. Note also the lack of compensatory decrease in heart rate. 

Combining agonists with some local anesthetics greatly prolongs the duration of infiltration nerve block the total dose of local anesthetic (and the probability of toxicity) can therefore be reduced. Epinephrine, 1 200,000, is the favored agent for this application, but norepinephrine, phenylephrine, and other agonists have also been used. Systemic effects on the heart and peripheral vasculature may occur even with local drug administration but are usually minimal. 

The anesthetic effect of the agents with short and intermediate durations of action can be prolonged by increasing the dose or adding a vasoconstrictor agent (eg, epinephrine or phenylephrine). The vasoconstrictor slows the removal of the local anesthetic from the injection site. In addition, it decreases the blood level and the probability of cardiovascular and CNS toxicity. 

Recently, Tsubosaka et al. (2010a) reported that halichlorine was also revealed to inhibit L-type Ca2+ channels, which leads to inhibit smooth muscle contraction. In their report, the direct effect of halichlorine on vascular contractility was investigated. Then, halichlorine was found to inhibit both high concentration of K+- and phenylephrine-induced contractions in rat aorta dose dependently. The effect of halichlorine on high K+-induced contraction was shown to be stronger than that on phenylephrine-induced contraction. Because known L-type Ca2+ channel blockers, verapamil and nifedipine, were observed to show the similar effect by them, it was suggested that halichlorine selectively inhibits L-type Ca2+ channels. Then, the effect of halichlorine on intracellular Ca2+ concentration in vascular smooth muscle tissue was examined using a fluorescent Ca2+ indicator, Fura-2. 

Central nervous system toxicity is rarely observed with catecholamines or drugs such as phenylephrine. In moderate doses, amphetamines commonly cause restlessness, tremor, insomnia, and anxiety in high doses, a paranoid state may be induced. Cocaine may precipitate convulsions, cerebral hemorrhage, arrhythmias, or myocardial infarction. Therapy is discussed in Chapter 59 Management of the Poisoned Patient. 

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