Mechanism of Actions

Carbinoxamine maleate, an ethanolamine derivative, is an antihistamine with anticholinergic (drying) and sedative properties. Carbinoxamine appears to compete with histamine (type H1) for receptor sites on effector cells in the gastrointestinal tract, blood vessels and respiratory tract.

Pharmacokinetics and Metabolism

Carbinoxamine is well absorbed from the GI tract and appears to be extensively metabolized by the liver, and excreted in the urine as inactive metabolites within 24 hours. Virtually no intact drug is extended in the urine.

In a study comparing a controlled release suspension and a solution of carbinoxamine, healthy volunteers were administered a single dose of 8 mg carbinoxamine. A time to maximum concentration (Tmax) was between 1.5 hours to 5 hours, a peak plasma concentration (Cmax) of about 24 ng/mL was observed, and extent of exposure (AUC) was about 286 ng hr/mL. The serum half-life is reported to be 10 to 20 hours.

Drug/Food Interactions

Carbinoxamine should not be used in patients with hypersensitivity to carbinoxamine. Carbinoxamine may increase the effects of other drugs such as barbiturates, TCAs, MAO inhibitors such as Phenelzine (Nardil), Tranylcypromine (Parnate), or Selegiline (Eldepryl), alcohol, other antihistamines, and CNS depressants. Carbinoxamine can be taken with or without food.

Cardiovascular Effects

Cardiac effects, including prolongation of QT interval have not been adequately studied. Unlike other newer antihistamines, severe adverse cardiovascular effects are uncommon, and usually limited to over dosage situations.

Special Populations

General

As many other antihistamines, carbinoxamine maleate has an atropine-like action and, therefore, should be used with caution in patients with: increased intraocular pressure, hyperthyroidism, cardiovascular disease, hypertension.

Antihistamines such as carbinoxamine maleate should not be used to treat lower respiratory tract symptoms, including asthma.

Information for Patients

Carbinoxamine maleate may cause drowsiness; alcohol, sedatives, and tranquilizers may increase the drowsiness effect. Avoid alcoholic beverages while taking this product. Do not take this product if you are taking sedatives or tranquilizers, without first consulting your doctor. Use caution when driving a motor vehicle or operating machinery.

Drug Interactions

Monoamine oxidase inhibitors prolong and intensify the anticholinergic (drying) effects of antihistamines. Carbinoxamine maleate has additive effects with alcohol and other CNS depressants (hypnotics, sedatives, tranquilizers, etc.).

Carcinogenesis, Mutagenesis, Impairment of Fertility

No long-term studies in animals have been performed to determine the possible effects of carbinoxamine maleate on carcinogenesis, mutagenesis, and fertility.

Pregnancy

Nursing Mothers

Because of the higher risk of antihistamines for infants generally and for newborns and prematures in particular, use of carbinoxamine maleate is contraindicated in nursing mothers (see CONTRAINDICATIONS).

Pediatric Use

Carbinoxamine maleate is contraindicated in children younger than 2 years of age (see CONTRAINDICATIONS).

Neonates have an increased susceptibility to anticholinergic side effects, such as CNS excitation, which may lead to convulsions.

Carbinoxamine maleate may diminish mental alertness in children. In the young child, particularly, they may produce excitation.

Geriatric Use

Carbinoxamine maleate is more likely to cause dizziness, sedation, and hypotension in elderly patients (approximately 60 years or older). Sedating drugs may also cause confusion and over sedation in the elderly. Therefore, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Manifestations

Antihistamine overdosage reactions may vary from central nervous system depression to stimulation. Stimulation is particularly likely in children. Atropine-like signs and symptoms- dry mouth; fixed, dilated pupils; flushing; and gastrointestinal symptoms may also occur.

Especially in infants and children, antihistamine overdosage may cause hallucinations, convulsions, or death.

The oral LD 50 of carbinoxamine maleate in guinea pigs is 411 mg/kg.

Treatment

The treatment of overdosage with carbinoxamine maleate is essentially symptomatic and supportive. Vital signs (including respiration, pulse, blood pressure, and temperature) and EKG should be monitored. Induction of vomiting is not recommended. Activated charcoal should be given and gastric lavage should be considered after ingestion of a potentially life-threatening amount of drug. In the presence of severe anticholinergic effects, physostigmine may be useful. Vasopressors may be used to treat hypotension.