PharmacokineticsThe pharmacokinetics of fexofenadine hydrochloride in subjects
with seasonal allergic rhinitis were similar to those in healthy volunteers.
Absorption
Fexofenadine hydrochloride and pseudoephedrine hydrochloride
administered as ALLEGRA-D 24 HOUR tablets are absorbed at a similar rate and are
equally available under single-dose and steady-state conditions as the separate
administration of the components. Coadministration of fexofenadine and
pseudoephedrine does not significantly affect the bioavailability of either
component. The administration of ALLEGRA-D 24 HOUR tablets 30 minutes or 1.5
hour after a high-fat meal decreased the bioavailability of fexofenadine by
approximately 50% (AUC 42% and Cmax 54%). Pseudoephedrine
pharmacokinetics were unaffected when coadministered with a high-fat meal.
Therefore, ALLEGRA-D 24 HOUR should be taken on an empty stomach with water (see
DOSAGE AND ADMINISTRATION).
A pharmacokinetic study following single and multiple oral doses over 7 days
of ALLEGRA-D 24 HOUR in 66 healthy volunteers showed that fexofenadine, the
immediate release component of ALLEGRA-D 24 HOUR, was rapidly absorbed with mean
maximum plasma concentrations of 634 ng/mL and 674 ng/mL after single and
multiple doses, respectively. The median time to maximum concentration of
fexofenadine was 1.8–2.0 hours post-dose. In the same study, the mean maximum
plasma concentrations of pseudoephedrine, the extended-release component of
ALLEGRA-D 24 HOUR, were 394 ng/mL and 495 ng/mL after single and multiple doses,
respectively, with median time to maximum concentration of 12 hours post-dose.
Pseudoephedrine concentrations at the end of the dosing interval (mean: 172
ng/mL) at steady state were equivalent to those observed from a comparator
pseudoephedrine hydrochloride 240 mg tablet.
Distribution
Fexofenadine hydrochloride is 60% to 70% bound to plasma
proteins, primarily albumin and α1-acid glycoprotein. The
protein binding of pseudoephedrine in humans is not known. Pseudoephedrine
hydrochloride is extensively distributed into extravascular sites (apparent
volume of distribution between 2.6 and 3.5 L/kg).
Metabolism
Approximately 5% of the total dose of fexofenadine hydrochloride
and less than 1% of the total oral dose of pseudoephedrine hydrochloride were
eliminated by hepatic metabolism.
Elimination
The mean terminal elimination half-life of fexofenadine was 14.6
hours following administration of ALLEGRA-D 24 HOUR tablets in healthy
volunteers, which is consistent with observations from separate administration.
Human mass balance studies documented a recovery of approximately 80% and 11% of
the [14C]-fexofenadine hydrochloride dose in the feces
and urine, respectively. Because the absolute bioavailability of fexofenadine
hydrochloride has not been established, it is unknown if the fecal component is
primarily unabsorbed drug or the result of biliary excretion. The mean terminal
half-life of pseudoephedrine was 7 hours following single-dose administration of
ALLEGRA-D 24 HOUR tablets.
Pseudoephedrine has been shown to have a mean elimination half-life of 4–6
hours which is dependent on urine pH. The elimination half-life is decreased at
urine pH lower than 6 and may be increased at urine pH higher than 8.
Special Populations
Pharmacokinetics in special populations (for renal, hepatic
impairment, and age), obtained after a single dose of 80 mg fexofenadine
hydrochloride, were compared to those from healthy volunteers in a separate
study of similar design.
Effect of Age
In older subjects (≥65 years old), peak plasma levels of
fexofenadine were 99% greater than those observed in younger subjects (less than 65
years old). Mean fexofenadine elimination half-lives were similar to those
observed in younger subjects.
Renally Impaired
In subjects with mild (creatinine clearance 41–80 mL/min) to
severe (creatinine clearance 11–40 mL/min) renal impairment, peak plasma levels
of fexofenadine were 87% and 111% greater, respectively, and mean elimination
half-lives were 59% and 72% longer, respectively, than observed in healthy
volunteers. Peak plasma levels in subjects on dialysis (creatinine clearance ≤10
mL/min) were 82% greater and half-life was 31% longer than observed in healthy
volunteers. No data are available on the pharmacokinetics of pseudoephedrine in
renally impaired subjects. However, most of the oral dose of pseudoephedrine
hydrochloride (43–96%) is excreted unchanged in the urine. A decrease in renal
function is, therefore, likely to decrease the clearance of pseudoephedrine
significantly, thus prolonging the half-life and resulting in accumulation. (See
PRECAUTIONS and DOSAGE AND ADMINISTRATION.)
Hepatically Impaired
The pharmacokinetics of fexofenadine hydrochloride in subjects
with hepatic disease did not differ substantially from that observed in healthy
volunteers. The effect on pseudoephedrine pharmacokinetics is unknown.
Effect of Gender
Across several trials, no clinically significant gender-related
differences were observed in the pharmacokinetics of fexofenadine hydrochloride.