General Medical Information

First-line Pharmacotherapy

Richard L. Mabry

Total avoidance of inciting allergens is not practical; therefore medications to relieve symptoms also must be offered to allergy patients. Several agents for this purpose are available over the counter—first-generation antihistamines, decongestants, and cromolyn. These drugs offer a first line of treatment of patients without the need for a prescription. Antihistamines compete with histamine for H1 receptor sites on the target organs during the allergic response and are most effective when taken before allergen exposure. They relieve the “wet” symptoms of allergy (itching, sneezing, and rhinorrhea) but have very little decongestant effect. The primary side effects of conventional antihistamines are sedation, excessive drying, and possibly aggravation of prostatism or narrow-angle glaucoma. Although some researchers argue the existence of antihistamine tolerance (tachyphylaxis), clinical observation shows that first-generation antihistamines can become less effective with prolonged use, necessitating a change to another class of antihistamine.

Antihistamines often are combined with decongestants to manage allergic rhinitis. Numerous combinations are available, and the physician is well advised to become familiar with a manageable number that represent each major antihistamine group and change preferences as pharmaceutical developments warrant. Decongestants reduce nasal mucosal edema. The chronic nature of nasal allergy readily leads to nose-drop habituation and rebound rhinitis. Therefore systemic administration of decongestants is recommended. Pseudoephedrine, a stereoisomer of ephedrine, usually is administered at dosages up to a total of 240 mg/d to adults and in proportionally smaller doses for children. Phenylpropanolamine has pharmacologic properties analogous to those of ephedrine but with less central nervous system stimulation. Because of a possible causal relationship to strokes in younger women, phenylpropanolamine has been withdrawn from common usage. Widely prescribed as a topical nasal decongestant, phenylephrine is much less effective in oral form and often is combined with another decongestant, the adult dosage averaging 40 mg/d.

All systemic decongestants exert an a-adrenergic effect, which can cause central nervous system stimulation, hypertension, and similar undesirable effects. Tricyclic antidepressants and monoamine oxidase (MAO) inhibitors potentiate these effects, which can persist as long as 14 days after the MAO inhibitor is discontinued. Therefore these combinations must be administered cautiously. Phenylpropanolamine may be more likely than the other compounds to elevate blood pressure among patients with labile hypertension, although all are probably safe for patients with normal blood pressure. Anorexia is a side effect of phenylpropanolamine, which is the major ingredient in many over-the-counter diet pills. Therefore patients must be asked about their use of such preparations before phenylpropanolamine is prescribed, because overdosage has been associated with convulsions.

Besides antihistamines and decongestants, nonprescription first-line pharmacotherapy of nasal allergy includes cromolyn nasal spray, which both prevents the allergic event and modifies the severity of an existing allergic reaction. Cromolyn stabilizes and protects mast cells from allergen-induced degranulation and prevents both the immediate and late allergic reaction. This action of preventing an allergic reaction rather than ameliorating its effects makes cromolyn unique among pharmacotherapeutic agents.

Cromolyn nasal spray prevents or lessens symptoms when applied before an anticipated allergen exposure. Used on a regular basis during the patient’s allergic season, cromolyn decreases sneezing, rhinorrhea, and nasal pruritus. Nasal cromolyn is delivered with a pump spray. Treatment begins with one spray in each nostril every 4 hours when the patient is awake until relief is evident (normally 4 to 7 days but possibly as long as 2 weeks in cases of severe or perennial allergic rhinitis) and is continued at the maintenance dose that is effective for the expected season or period of exposure. Additional treatments should precede anticipated allergen exposure.

Because a patent nasal airway is a prerequisite for treatment with cromolyn or any other topical nasal medication, a decongestant also is often prescribed. The presence of obstructing polyps calls for the use of measures other than cromolyn. Cromolyn is most effective in the care of patients with mild to moderate symptoms and may not be effective for those whose allergic symptoms are severe or perennial.