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.
The pharmacokinetics of fexofenadine hydrochloride in subjects with seasonal allergic rhinitis were similar to those in healthy volunteers.
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 ALLEGRA-D (fexofenadine hcl and pseudoephedrine hcl) 12 HOUR 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 ALLEGRA-D (fexofenadine hcl and pseudoephedrine hcl) 12 HOUR 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, ALLEGRA-D (fexofenadine hcl and pseudoephedrine hcl) 12 HOUR should be taken on an empty stomach with water
(see DOSAGE AND ADMINISTRATION).
Fexofenadine is 60% to 70% bound to plasma proteins, primarily albumin and a1-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).
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.
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.
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 ( ≥ 65 years old), peak plasma levels
of fexofenadine were 99% greater than those observed in younger subjects (<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.
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
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.
Wheal 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 QTc. In 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 x 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
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.
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.