Pharmacokinetics of3H-phenylephrine in man

Abstract

7-3H-phenylephrine was given to 15 volunteers by a short-infusion n = 4) or p.o. (10 volunteers, 1 patient with porto-caval anastomosis). Analysis of serum for free 3H-phenylephrine and fractionation of urinary radioactivity was performed by ion-exchange and thin-layer chromatography. As almost the same 3H-activity was excreted in urine after i.v. and p.o. administration, 86% and 80% of the dose respectively, complete enteral absorption can be assumed. A considerable difference was seen in the fraction of free phenylephrine, i.v. 16% of the dose versus p.o. 2.6%, which suggested reduced bioavailability. This was confirmed by comparison of the areas under the serum curve, which showed a bioavailability factor of 0.38. The result for the patient with porto-caval anastomosis was comparable to that in the normal volunteers. The biological half-life of 2 to 3h was comparable to that of structurally related amines, as were the total clearance of 2 l/h, and the volume of distribution of 340 l. Metabolism to phenolic conjugates mainly after oral ingestion, and to m-hydroxymandelic acid after i.v. injection, again demonstrated that m-hydroxylated amines are predominantly conjugated during the "first-pass" metabolism.

Bioavailability of paracetamol, phenylephrine hydrochloride and guaifenesin in a fixed-combination syrup versus an oral reference product

“…10,11 Both phenylephrine hydrochloride and its metabolites are eliminated in urine. 10 Elimination t ½ between 2 and 3 h have been reported.…”

An Electrochemical Sensor for Phenylephrine Based on Molecular Imprinting

“…7 It can be used to increase alertness, and to reduce fatigue. Also, it is a decongestant, working by constricting blood vessels in the body.…”

Substitution of phenylephrine for pseudoephedrine as a nasal decongeststant. An illogical way to control methamphetamine abuse

“…The main difference between the decongestants is that after oral administration PE is subject to extensive presystemic metabolism by monoamine oxidase in the gut wall [10,13]. As a consequence of metabolism, systemic bioavailability of PE is only around 40% [13]. Only about 3% of an oral dose of PE is excreted unchanged in the urine [10].…”

“…It is difficult to be confident about the true Table 1 Comparison of pharmacology and metabolism of phenylephrine and pseudoephedrine [10,11,13,15,16] Phenylephrine Pseudoephedrine 4 incidence of side effects and adverse events associated with PE and PDE, as they are usually formulated as combination medicines with analgesics and antihistamines. However, despite the great exposure of the general public to PE and PDE there is no consistent history of adverse events in the medical literature, and this indicates that PE and PDE in various OTC combination medicines are safe if taken as indicated.…”