A1,
A2,
B,
C1,
C2,
D,
E,
F,
G-H,
I-K,
L,
M,
N,
O,
P1,
P2,
Q-R,
S,
T,
U-V,
W-Z
Neo-Synephrine Pharmacology, Pharmacokinetics, Studies, Metabolism - Phenylephrine (Injection)
Neo-Synephrine Pharmacology, Pharmacokinetics, Studies, Metabolism - Phenylephrine (Injection)
CLINICAL PHARMACOLOGY
Phenylephrine hydrochloride produces vasoconstriction that lasts longer
than that of epinephrine and ephedrine. Responses are more sustained than
those of epinephrine, lasting 20 minutes after intravenous and as long
as 50 minutes after subcutaneous injection. Its action on the heart contrasts
sharply with that of epinephrine and ephedrine, in that it slows the heart
rate and increases the stroke output, producing no disturbance in the
rhythm of the pulse.
Phenylephrine is a powerful postsynaptic alpha-receptor stimulant with
little effect on the beta receptors of the heart. In therapeutic doses,
it produces little if any stimulation of either the spinal cord or cerebrum.
A singular advantage of this drug is the fact that repeated injections
produce comparable effects.
The predominant actions of phenylephrine are on the cardiovascular system.
Parenteral administration causes a rise in systolic and diastolic pressures
in man and other species. Accompanying the pressor response to phenylephrine
is a marked reflex bradycardia that can be blocked by atropine; after
atropine, large doses of the drug increase the heart rate only slightly.
In man, cardiac output is slightly decreased and peripheral resistance
is considerably increased. Circulation time is slightly prolonged, and
venous pressure is slightly increased; venous constriction is not marked.
Most vascular beds are constricted; renal, splanchnic, cutaneous, and
limb blood flows are reduced but coronary blood flow is increased. Pulmonary
vessels are constricted, and pulmonary arterial pressure is raised.
The drug is a powerful vasoconstrictor, with properties very similar
to those of norepinephrine but almost completely lacking the chronotropic
and inotropic actions on the heart. Cardiac irregularities are seen only
very rarely even with large doses.
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