Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

5.1     Pharmacodynamic properties

ATC code: C01CA06
Mechanism of action

Vasoconstriction caused by phenylephrine lasts 20 minutes after intravenous injection and up to 50 minutes after subcutaneous injection. Phenylephrine slows the heart rate and increases systolic volume without affecting the heart rate.
Phenylephrine is a postsynaptic alpha-adrenergic receptor agonist with limited effect on beta receptors in the heart. In therapeutic doses, it does not induce either stimulation of the spinal cord or brain, or a moderate stimulation. Repeated injections may enable comparable effects to be obtained.
Phenylephrine acts mainly on the cardiovascular system. Parenteral administration causes an increase in systolic and diastolic blood pressure in humans and in other species. The pressor response to phenylephrine is accompanied by marked reflex bradycardia which can be inhibited by atropine; after administration of atropine, high doses of the medicinal product increase the heart rate only to a limited extent. In humans, the minute volume of the heart is slightly reduced and the peripheral resistance is considerably increased. The circulation time is slightly prolonged and the venous pressure slightly increased; there is no marked venous constriction. Most of the vascular beds are narrowed; renal, splanchnic, cutaneous and limb blood supply is reduced; coronary circulation is increased. The pulmonary vessels are narrowed and the pulmonary arterial pressure increases.

Clinical efficacy

No data available.

Pharmacokinetic Properties

5.2    Pharmacokinetic properties

Absorption

In case of oral absorption, the bioavailability is 38%.
Distribution

The distribution half-life is 5 minutes and the distribution volume is greater than 40 liters. After IV administration, the volume of distribution of the central compartment is comparable to the extracellular volume (approx. 40 liters), while the volume of distribution at steady state is 340 liters.

Metabolism

Phenylephrine is metabolized to m-hydroxymandelic acid and phenolic conjugates. Degradation to phenolic conjugates is increased with oral administration and reduced with intravenous administration.
Metabolisation takes place in the liver and intestinal wall.

Elimination

In case of IV administration, the elimination half-life is 2-3 hours, renal excretion is 80-86%, and 16% of the active substance is excreted in the urine unchanged. The elimination half-life is 2-3 hours.

Kinetics of special patient groups

No data available.