b. Norepinephrine, Levarterenol (Levophed). This adrenergic drug acts
almost exclusively on alpha-receptors.
(a) Peripheral vasoconstriction. Norephinephrine causes marked
(b) Constriction of blood vessels in skeletal muscles. Unlike
epinephrine, norepinephrine produces constriction of blood vessels in skeletal muscles.
Increase in blood pressure. Norepinephrine causes a net increase
in blood pressure.
(2) Indication for the use of norepinephrine. Norepinephrine is used to
restore blood pressure in selected hypotensive states (that is, when hypotension occurs
during spinal anesthesia).
Cautions and warnings associated with the use of norepinephrine.
(a) Norepinephrine can cause local necrosis due to vasoconstriction
when it is injected intravenously. Therefore, it should be infused slowly into a rapidly
flowing vein, and the site into which the drug solution is being administered should be
changed every 12 hours.
The drug can produce anxiety and transient headaches.
(c) Norepinephrine should be used cautiously with patients who have
heart disease (that is, angina), hypertension, and hyperthyroidism.
c. Isoproterenol (Isuprel). Isoproterenol produces a powerful action on both
beta1 and beta2 receptors. It has no alpha activity. Injection or aerosol readily absorbs
Isoproterenol; however, oral absorption of the drug is unreliable.
(a) Cardiovascular effects. Isoproterenol produces increased cardiac
output and decreased blood pressure. Beta2 stimulation is responsible for the increase
in heart rate and the increase in the force of contraction. Isoproterenol causes a
reduction in blood pressure because of a decrease in peripheral resistance. Beta2
receptors cause vasodilatation in skeletal muscle.
(b) Smooth muscle. Smooth muscle is relaxed by isoproterenol. This
relaxation is most pronounced in the bronchi and gastrointestinal (G.I.) tract.