Mechanism of Action
Fexofenadine hydrochloride, the major active metabolite of
terfenadine, is an antihistamine with selective peripheral H1-receptor antagonist activity. Fexofenadine hydrochloride
inhibited antigen-induced bronchospasm in sensitized guinea pigs and histamine
release from peritoneal mast cells in rats. In laboratory animals, no
anticholinergic or alpha1-adrenergic-receptor blocking
effects were observed. Moreover, no sedative or other central nervous system
effects were observed. Radiolabeled tissue distribution studies in rats
indicated that fexofenadine does not cross the blood-brain barrier.
Pseudoephedrine hydrochloride is an orally active sympathomimetic amine and
exerts a decongestant action on the nasal mucosa. Pseudoephedrine hydrochloride
is recognized as an effective agent for the relief of nasal congestion due to
allergic rhinitis. Pseudoephedrine produces peripheral effects similar to those
of ephedrine and central effects similar to, but less intense than,
amphetamines. It has the potential for excitatory side effects. At the
recommended oral dose, it has little or no pressor effect in normotensive
adults.
Pharmacokinetics
The pharmacokinetics of fexofenadine hydrochloride in subjects
with seasonal allergic rhinitis were similar to those in healthy
volunteers.
Absorption
The pharmacokinetics of fexofenadine hydrochloride and
pseudoephedrine hydrochloride when administered separately have been well
characterized. Fexofenadine pharmacokinetics were linear for oral doses of
fexofenadine hydrochloride up to a total daily dose of 240 mg (120 mg twice
daily). Peak fexofenadine plasma concentrations were similar between adolescent
(12–16 years of age) and adult subjects.
The bioavailability of fexofenadine hydrochloride and pseudoephedrine
hydrochloride from the extended-release tablets is similar to that achieved with
separate administration of the components. Coadministration of fexofenadine and
pseudoephedrine does not significantly affect the bioavailability of either
component.
Fexofenadine hydrochloride was rapidly absorbed following single-dose
administration of the 60 mg fexofenadine hydrochloride/120 mg pseudoephedrine
hydrochloride tablet with median time to mean maximum fexofenadine plasma
concentration of 191 ng/mL occurring 2 hours post-dose. Pseudoephedrine
hydrochloride produced a mean single-dose pseudoephedrine peak plasma
concentration of 206 ng/mL which occurred 6 hours post-dose. Following multiple
dosing to steady-state, a fexofenadine peak concentration of 255 ng/mL was
observed 2 hours post-dose. Following multiple dosing to steady-state, a
pseudoephedrine peak concentration of 411 ng/mL was observed 5 hours post-dose.
The administration of Fexofenadine Hydrochloride and Pseudoephedrine
Hydrochloride Extended-Release Tablets with a high fat meal decreased the
bioavailability of fexofenadine by approximately 50% (AUC 42% and Cmax 46%).
Time to maximum concentration (Tmax) was delayed by 50%.
The rate or extent of pseudoephedrine absorption was not affected by food.
Therefore, Fexofenadine Hydrochloride and Pseudoephedrine Hydrochloride
Extended-Release Tablets should be taken on an empty stomach with water (see DOSAGE AND ADMINISTRATION).
Distribution
Fexofenadine 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 elimination half-life of fexofenadine was 14.4 hours
following administration of 60 mg fexofenadine hydrochloride, twice daily, to
steady-state in healthy volunteers. 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.
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 subjects in a separate study
of similar design.
Effect of Age
In older subjects (greater than or equal to 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 less than or equal to 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.
Based on increases in bioavailability and half-life of fexofenadine
hydrochloride and pseudoephedrine hydrochloride, a dose of one tablet once daily
is recommended as the starting dose in patients with decreased renal function
(see 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.
PharmacodynamicsWheal and Flare
Human histamine skin wheal and flare studies following single and
twice daily doses of 20 mg and 40 mg fexofenadine hydrochloride demonstrated
that the drug exhibits an antihistamine effect by 1 hour, achieves maximum
effect at 2–3 hours, and an effect is still seen at 12 hours. There was no
evidence of tolerance to these effects after 28 days of dosing. The clinical
significance of these observations is unknown.
Effects on QT
cIn dogs (30 mg/kg orally twice daily for 5 days) and rabbits (10
mg/kg intravenously over 1 hour), fexofenadine hydrochloride did not prolong
QTc at plasma concentrations that were at least 17 and 38
times, respectively, the therapeutic plasma concentrations in man (based on a 60
mg twice daily fexofenadine hydrochloride dose). No effect was observed on
calcium channel current, delayed K+ channel current, or
action potential duration in guinea pig myocytes, Na+
current in rat neonatal myocytes, or on the delayed rectifier K+ channel cloned from human heart at concentrations up to 1 ×
10-5 M of fexofenadine. This concentration was at least
21 times the therapeutic plasma concentration in man (based on a 60 mg twice
daily fexofenadine hydrochloride dose).
No statistically significant increase in mean QTc
interval compared to placebo was observed in 714 subjects with seasonal allergic
rhinitis given fexofenadine hydrochloride capsules in doses of 60 mg to 240 mg
twice daily for 2 weeks or in 40 healthy volunteers given fexofenadine
hydrochloride as an oral solution at doses up to 400 mg twice daily for 6
days.
A 1-year study designed to evaluate safety and tolerability of 240 mg of
fexofenadine hydrochloride (n=240) compared to placebo (n=237) in healthy
volunteers, did not reveal a statistically significant increase in the mean
QTc interval for the fexofenadine hydrochloride treated
group when evaluated pretreatment and after 1, 2, 3, 6, 9, and 12 months of
treatment.
Administration of the 60 mg fexofenadine hydrochloride/120 mg pseudoephedrine
hydrochloride combination tablet for approximately 2 weeks to 213 subjects with
seasonal allergic rhinitis demonstrated no statistically significant increase in
the mean QTc interval compared to fexofenadine
hydrochloride administered alone (60 mg twice daily, n=215), or compared to
pseudoephedrine hydrochloride (120 mg twice daily, n=215) administered
alone.
Clinical Studies
In a 2-week, multicenter, randomized, double-blind,
active-controlled trial in subjects 12–65 years of age with seasonal allergic
rhinitis due to ragweed allergy (n=651), the 60 mg fexofenadine
hydrochloride/120 mg pseudoephedrine hydrochloride combination tablet
administered twice daily significantly reduced the intensity of sneezing,
rhinorrhea, itchy nose/palate/throat, itchy/watery/red eyes, and nasal
congestion.
In three, 2-week, multicenter, randomized, double-blind, placebo-controlled
trials in subjects 12–68 years of age with seasonal allergic rhinitis (n=1634),
fexofenadine hydrochloride 60 mg twice daily significantly reduced total symptom
scores (the sum of the individual scores for sneezing, rhinorrhea, itchy
nose/palate/throat, itchy/watery/red eyes) compared to placebo. Statistically
significant reductions in symptom scores were observed following the first 60 mg
dose, with the effect maintained throughout the 12-hour interval. In general,
there was no additional reduction in total symptom scores with higher doses of
fexofenadine hydrochloride up to 240 mg twice daily. Although the number of
subjects in some of the subgroups was small, there were no significant
differences in the effect of fexofenadine hydrochloride across subgroups of
subjects defined by gender, age, and race. Onset of action for reduction in
total symptom scores, excluding nasal congestion, was observed at 60 minutes
compared to placebo following a single 60 mg fexofenadine hydrochloride dose
administered to subjects with seasonal allergic rhinitis who were exposed to
ragweed pollen in an environmental exposure unit.