Decongestants may be classified as systemic or topical, depending on how they’re administered.
As sympathomimetic drugs, systemic decongestants stimulate the sympathetic nervous system to reduce swelling of the respiratory tract’s vascular network. Systemic decongestants include:
Topical decongestants are also powerful vasoconstrictors. When applied directly to swollen mucous membranes of the nose, they provide immediate relief from nasal congestion. These drugs include:
• ephedrine, epinephrine, and phenylephrine (sympathomimeticamines)
• naphazoline and tetrahydrozoline (imidazoline derivatives of sympathomimetic amines).
The pharmacokinetic properties of decongestants vary.
When taken orally, the systemic decongestants are absorbed read-ily from the GI tract and widely distributed throughout the body into various tissues and fluids, including cerebrospinal fluid, the placenta, and breast milk.
Systemic decongestants are slowly and incompletely metabolized by the liver and excreted largely unchanged in urine within 24 hours of oral administration.
Topical decongestants act locally on the alpha receptors of the vascular smooth muscle in the nose, causing the arterioles to con-strict. As a result of this local action, absorption of the drug is neg-ligible
The properties of systemic and topical decongestants vary slightly.
Systemic decongestants cause vasoconstriction by stimulating alpha-adrenergic receptors in the blood vessels of the body. This reduces the blood supply to the nose, which decreases swelling of the nasal mucosa. They also cause contraction of urinary and GI sphincters, dilated pupils, and decreased insulin secretion.
These drugs may also act indirectly, causing the release of norepi-nephrine from storage sites in the body, which results in peripher-al vasoconstriction.
Like systemic decongestants, topical decongestants stimulate alpha-adrenergic receptors in the smooth muscle of nasal blood vessels, resulting in vasoconstriction. The combination of reduced blood flow to the nasal mucous membranes and decreased capil-lary permeability reduces swelling. This action improves respira-tion by helping to drain sinuses, clear nasal passages, and open eustachian tubes.
Systemic and topical decongestants are used to relieve the symp-toms of swollen nasal membranes resulting from:
§ acute coryza (profuse discharge from the nose)
§ allergic rhinitis (hay fever)
§ the common cold
§ vasomotor rhinitis.
Systemic decongestants are commonly given with other drugs, such as antihistamines, antimuscarinics, antipyretic analgesics, and antitussives.
Topical decongestants provide two major advantages over sys-temics: minimal adverse reactions and rapid symptom relief.
Because they produce vasoconstriction, which reduces drug ab-sorption, topical decongestants seldom produce drug interactions.Systemic decongestants, however, may interact with other drugs.
(See Adverse reactions to decongestants.)
Increased CNS stimulation may occur when systemic deconges-tants are taken with other sympathomimetic drugs, including epi-nephrine, norepinephrine, dopamine, dobutamine, isoproterenol, metaproterenol, terbutaline, and phenylephrine, and tyramine-containing foods.
Use of systemic decongestants with MAOIs may cause
severe hypertension or a hypertensive crisis, which can be life-threatening. These drugs shouldn’t be used together.
Alkalinizing drugs may increase the effects of pseudoephedrine by reducing its urinary excretion.