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Pharmacodynamics

Fexofenadine (a pharmacologically active metabolite of terfenadine) is an antihistamine with selective antagonistic activity to H1 receptors without anticholinergic and blocking α1-adrenergic receptors. In addition, fexofenadine does not have a sedative effect or other CNS effects. In studies in humans on the assessment of histamine-induced blisters and hyperemia, the antihistamine action of fexofenadine, taken orally 1 or 2 times a day, manifests itself after 1 hour, reaches a maximum after 6 hours and continues for 24 hours after its administration. Even after 28 days of taking fexofenadine, there was no development of tolerance to the drug.With a single oral administration of fexofenadine, a dose-dependent increase in the antihistamine effect is observed with an increase in dose from 10 to 130 mg. Using the same model of antihistamine action, it was found that a dose of at least 130 mg was necessary for continuous action within 24 hours. The maximum suppression of the formation of blisters and hyperemia of the skin is more than 80%. In patients with seasonal allergic rhinitis who received up to 240 mg of fexofenadine 2 times a day for 2 weeks, the value of the corrected QTc interval (QT corrected) did not differ from that when taking a placebo. There were also no changes in the QTc interval when taking fexofenadine by healthy volunteers 60 mg 2 times a day for 6 months, 400 mg 2 times a day for 6.5 days and 240 mg per day for 1 year compared to the size of the interval QTc when taking a placebo. Even with a plasma concentration 32 times the therapeutic concentration in humans, fexofenadine did not affect the potassium channels of delayed rectification in the human heart.

Pharmacokinetics

Fexofenadine is rapidly absorbed after oral administration, Tmax is approximately 1-3 hours. The average Cmax value when taken 120 mg per day is approximately 289 ng / ml, and when taken 180 mg per day, approximately 494 ng / ml. Fexofenadine is 60–70% bound to plasma proteins. Fexofenadine is slightly metabolized in and out of the liver, which is confirmed by the fact that it is the only substance detected in significant quantities in the urine and feces of humans and animals. During the course of taking the drug, the curve of excretion of fexofenadine from plasma decreases biexponentially, and the final T1 / 2 is 11-15 hours. The pharmacokinetics with a single and course administration of fexofenadine (up to 120 mg twice daily orally) is linear. A dose of 240 mg 2 times a day gives a slightly larger than proportional (by 8.8%) increase in AUC, which indicates that the pharmacokinetics of fexofenadine is almost linear in the dose range from 40 to 240 mg per day. According to currently available data, most of the dose taken is unchanged excreted in the bile, and up to 10% of the drug in the urine.

Contraindications

  • hypersensitivity to any of the components of the drug;
  • pregnancy;
  • lactation period;
  • children under 12 years old.
  • With caution: in patients with chronic renal and hepatic insufficiency, as well as in elderly patients (lack of clinical experience with this category of patients); in patients with cardiovascular diseases, including and a history (antihistamines can cause palpitations and tachycardia, see “Side effects”).

    Pregnancy and lactation

    Pregnancy. There is not enough data on the use of fexofenadine in pregnant women. Limited animal studies have shown no signs of adverse effects on pregnancy, prenatal development, childbirth, and postnatal development. Fexofenadine should not be used during pregnancy.

    Lactation. There are no data on the content of fexofenadine in breast milk when taken by breast-feeding women. However, when taking terfenadine, its penetration into the breast milk of lactating women was observed. Therefore, the use of fexofenadine during the lactation period is not recommended.

    Side effects

    In placebo-controlled clinical trials, the most frequently observed (≥1 - ≤10%) adverse effects observed were headache (7.3%), drowsiness (2.3%), dizziness (1.5%), and nausea (1.5 %). When taking fexofenadine, the frequency of the above adverse effects was similar to that when taking placebo.In placebo-controlled studies with a frequency of less than 1% (the same when taking fexofenadine and placebo) and with post-marketing use of the drug, weakness, insomnia, and nervousness were noted; sleep disturbances or unusual dreams (paroniria), such as nightmares; tachycardia, palpitations; diarrhea.In rare cases (≥0.01 - ≤0.1%), exanthema, urticaria, pruritus, and other hypersensitivity reactions were observed, such as Quincke's edema, shortness of breath, shortness of breath, hyperemia of the skin, systemic anaphylactic reactions.

    Interaction

    With the combined use of fexofenadine with erythromycin or ketoconazole, the concentration of fexofenadine in the plasma increases by 2–3 times, but this is not associated with a significant lengthening of the QTc interval. There were no significant differences in the incidence of adverse effects when using these drugs in monotherapy and in combination. Animal studies have shown that the aforementioned increase in plasma concentrations of fexofenadine is likely to be associated with improved absorption of fexofenadine and a decrease in its biliary excretion or secretion into the lumen of the gastrointestinal tract.The interaction between fexofenadine and omeprazole is not observed.

    Does not interact with drugs metabolized in the liver.

    The intake of antacids containing aluminum or magnesium 15 minutes before taking fexofenadine leads to a decrease in the bioavailability of the latter as a result of, apparently, binding in the digestive tract.

    Dosage and administration

    Inside, before eating. Seasonal allergic rhinitis: the recommended dose for adults and children 12 years of age and older is 120 mg once a day. Chronic idiopathic urticaria: the recommended dose for adults and children 12 years of age and older is 180 mg once a day. Patients at risk. Studies in special risk groups (elderly patients with renal and hepatic insufficiency) showed that for patients of these categories no dosage regimen correction is required.

    Overdose

    Symptoms: dizziness, drowsiness, dry mouth. Healthy volunteers took single doses up to 800 mg and course doses up to 690 mg 2 times a day for 1 month or 240 mg 2 times a day for 1 year without any significant undesirable effects compared with placebo. The maximum tolerated dose for fexofenadine has not been established.

    Treatment: gastric lavage, the appointment of activated charcoal, if necessary - symptomatic and supportive therapy. Hemodialysis is ineffective.

    Special instructions

    It is recommended that the time interval between taking fexofenadine and antacids containing aluminum or magnesium hydroxide be at least 2 hours. For use in children from 6 to 11 years, 30 mg tablets are available. Influence on the ability to drive a car and perform work requiring concentration. When taking the drug, it is possible to carry out work requiring a high concentration of attention and speed of psychomotor reactions (with the exception of patients with a non-standard reaction). Therefore, it is recommended to check the individual response to taking fexofenadine before engaging in such activities.

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