Carbinoxamine (Carbinoxamine Maleate) - Description and Clinical Pharmacology

DESCRIPTION

Carbinoxamine maleate is a histamine-H₁ receptor blocking agent.

Each tablet contains 4 mg carbinoxamine maleate and the following inactive ingredients: anhydrous lactose, magnesium stearate, microcrystalline cellulose, and sodium starch glycolate.

Each 5 mL (teaspoonful) of oral solution contains 4 mg carbinoxamine maleate and the following inactive ingredients: artificial bubble gum flavor, citric acid (anhydrous), glycerin, methylparaben, propylene glycol, propylparaben, purified water, sodium citrate (hydrous) and sorbitol solution.

Carbinoxamine maleate is freely soluble in water. Its structure is:

2-[(4-chlorophenyl)-2-pyridinylmethoxy]-N, N-dimethyl-ethanamine (Z)-2-butenedioate (1:1)

C₁₆H₁₉CIN₂O•C₄H₄O₄

MW = 406.86

CLINICAL PHARMACOLOGY

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

Pediatric Patients

Carbinoxamine should not be used in newborn or premature infants. Neonates have an increased susceptibility to anticholinergic side effects, such as CNS excitation, which may lead to convulsions.

Pregnancy and Lactation

Safe use of carbinoxamine during pregnancy has not been established. Therefore, carbinoxamine should not be used in women who are, or may become pregnant. Carbinoxamine is in the FDA pregnancy Category C.

Women who are breast-feeding should avoid use of carbinoxamine, since small amounts appear to be distributed into breast milk.

Geriatric Patients

Carbinoxamine is more likely to cause dizziness, sedation, and hypotension in elderly patients. The incidence of adverse reactions is higher in the elderly; therefore, a dosing adjustment may be necessary in this sub-population.