Acrivastine, a structural analog of triprolidine hydrochloride, exhibits H₁- antihistaminic activity in isolated tissues, animals, and humans, and has sedative effects in humans (see PRECAUTIONS). The propionic acid derivative of acrivastine is a metabolite in several animal species (as well as in man) and also exhibits H₁- antihistaminic activity.

Pseudoephedrine hydrochloride is an indirect sympathomimetic agent; that is, it releases norepinephrine from adrenergic nerves. In vitro tests and in vivo studies in animals of acrivastine and pseudoephedrine in combination failed to demonstrate evidence of any beneficial or deleterious pharmacologic interaction between the two agents.

Pharmacokinetics and Metabolism

Acrivastine was absorbed rapidly from the combination capsule following oral administration and was as bioavailable as a solution of acrivastine. After administration of SEMPREX-D Capsules, maximum plasma acrivastine concentrations were achieved at 1.14 ± 0.23 hours. A mass balance study in seven healthy volunteers showed that acrivastine is primarily eliminated by the kidneys. Over a 72-hour collection period, about 84% of the administered total radioactivity was recovered in urine and about 13% in feces, for a combined recovery of about 97%. Further, 67% of the administered radioactive dose was recovered in urine as the unchanged drug, 11% as the propionic acid metabolite, and 6% as other unknown metabolites.

Acrivastine exhibits linear kinetics over dosages ranging from 2 to 32 mg t. i. d. The mean ±SD terminal half-life for acrivastine was 1.9 ± 0.3 hours following single oral doses and increased to 3.5 ± 1.9 hours at steady state. The terminal half-life for the propionic acid metabolite was 3.8 ± 1.4 hours. Because of the short half-lives of both acrivastine and its metabolites, accumulation in the plasma following multiple dosing is not expected.

The steady- state maximum acrivastine plasma concentration was 227 ± 47 ng/mL. The oral clearance and apparent volume of distribution were 2.9 ± 0.7 mL/min/kg and 0.46 ± 0.05 L/kg, respectively, following a single oral dose; oral clearance did not change at steady state (2.86 ± 0.75 mL/min/kg). The apparent volume of distribution increased to 0.82 ± 0.6 L/kg to parallel the increase in the elimination half- life of the drug.

Acrivastine binding to human plasma proteins was 50 ± 2.0% and was concentration- independent over the range of 5 to 1000 ng/mL. The main binding protein was serum albumin although the drug was slightly bound to al-acid glycoprotein. No displacement interaction was observed between acrivastine and either phenytoin or theophylline. The binding of acrivastine was not affected by the presence of pseudoephedrine.

Pseudoephedrine hydrochloride was also rapidly absorbed from the combination capsule, and the capsule was as bioavailable as a solution of pseudoephedrine. Steady state maximum plasma concentration for pseudoephedrine was 498 ± 129 ng/mL. The terminal half-life, oral clearance and apparent volume of distribution were 6.2 ± 1.8 hours, 5.9 ± 1.7 mL/min/kg, and 3.0 ± 0.4 L/kg, respectively. Elimination of pseudoephedrine is primarily through the renal route as 55% to 75% of an administered dose appears unchanged in the urine. Pseudoephedrine elimination, however, is highly dependent upon urine pH; the plasma half-life decreased to about 4 hours at pH 5 and increased to 13 hours at pH 8. Pseudoephedrine did not bind to human plasma proteins over the concentration range of 50 to 2000 ng/mL.

Acrivastine and pseudoephedrine do not influence the pharmacokinetics of the other drug when administered concomitantly.

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