CLINICAL PHARMACOLOGY
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 test 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 7 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
α-1-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.
Special Populations
A single dose pharmacokinetic study showed that the
elimination half-lives of acrivastine, the propionic acid metabolite of
acrivastine, and pseudoephedrine were prolonged in patients with chronic renal
insufficiency. Compared to normal volunteers, the elimination half-life of
acrivastine was about 50% increased in patients with mild renal insufficiency
(creatinine clearance = 26 to 48 mL/min) and was increased by about 130% in
patients with moderate (creatinine clearance = 12 to 17 mL/min) or severe (creatinine
clearance 6 to 10 mL/min) renal insufficiency. Oral clearance of acrivastine
was diminished by the same magnitude as the half-life was prolonged in each of
the three renally impaired groups. The elimination half-life of the propionic
acid metabolite of acrivastine was about 140% increased in patients with mild
renal insufficiency and about 5 times increased in patients with moderate or
severe renal insufficiency.
Compared to normal volunteers, the elimination half-life
of pseudoephedrine was about 3 times increased in patients with mild renal
insufficiency, about 7 times increased in patients with moderate renal
insufficiency, and about 10 times increased in patients with severe renal
insufficiency. Oral clearance of pseudoephedrine was diminished by about the
same magnitude as the half-life was prolonged in each of the three renally
impaired groups (see PRECAUTIONS, Use in Patients with Diminished
Renal Function).
The total body load removed by dialysis is approximately
20%, 27% and 38% for acrivastine, the propionic acid metabolite of acrivastine,
and pseudoephedrine, respectively, and therefore, a supplemental dose after a
dialysis session is not required.
Based on a multiple dose cross study comparison, the
apparent volume of distribution for acrivastine was 44% lower in elderly (n=36,
65-75 yr) than in young volunteers (n=16, 19-33 yr). This difference could be
attributed to the decrease in total body water that occurs with aging. Despite
this difference, no appreciable differences in plasma acrivastine
concentrations were seen in the elderly compared to the young, and no
appreciable accumulation of acrivastine occurred in plasma at steady-state. The
elimination half-life for pseudoephedrine was 18% longer in elderly (7.9 hours)
than in younger subjects (6.7 hours), presumably due to the decline in average
renal function that occurs with aging. Despite this difference, clearance of
pseudoephedrine was not appreciably different in elderly and younger subjects.
Elderly patients can therefore be given the same dosage as younger patients.
SEMPREX-D Capsules are not recommended, however, in patients with renal
impairment (see PRECAUTIONS, Use in Patients with Diminished Renal
Function and Geriatric Use).
The effect of age and sex on the pharmacokinetic parameters
of acrivastine and pseudoephedrine was determined in 93 healthy volunteers who
participated in various studies. All of the 93 volunteers were Caucasian (81
males and 12 females); 57 were between the ages of 18 and 38 years and 36 were
between the ages of 65 and 75 years. There were no age-or sex-related
differences in the pharmacokinetic parameters of either acrivastine or
pseudoephedrine.
The effect of race on acrivastine and pseudoephedrine
pharmacokinetics was examined by screening data obtained from 1035 patients,
age 12 to 71 years, who participated in the eight safety and efficacy studies.
No race-related differences were observed in the pharmacokinetics of either
acrivastine or pseudoephedrine.
Clinical Studies
In healthy volunteers, histamine-induced wheal and flare
areas were significantly reduced relative to placebo at 30 minutes after
administration of a single dose of acrivastine 8 mg. Maximum reductions of
wheal and flare occurred by 1 to 2 hours and significant reductions relative to
placebo persisted for up to 6 hours after a single oral dose of acrivastine 8
mg. No additional reductions of wheal and flare were observed following single
doses of acrivastine up to 24 mg. The exact correlation between responses on
skin testing and clinical efficacy is not established.
Five randomized, placebo-and/or active-controlled trials
compared SEMPREX-D with its acrivastine and pseudoephedrine components for the
symptomatic relief of seasonal allergic rhinitis. In these studies, 696
patients received four daily doses of acrivastine 8 mg plus pseudoephedrine
hydrochloride 60 mg (i.e., SEMPREX-D Capsules or bioequivalent formulations
administered concurrently) or the same doses of the components for 14 days. The
combination reduced the intensity of sneezing, rhinorrhea, pruritus, and
lacrimation more than pseudoephedrine and reduced the intensity of nasal
congestion more than acrivastine, demonstrating a contribution of each of the
components. The onset of antihistaminic and nasal decongestant actions occurred
within one or two hours after the first dose of SEMPREX-D Capsules. Somnolence
occurred in about 12% of patients given SEMPREX-D compared with about 6% on
placebo.