Pharmacokinetics, pharmacodynamics, and tolerance of single- and multiple-dose fexofenadine hydrochloride in healthy male volunteers

Biowaiver Monograph for Immediate-Release Solid Oral Dosage Forms: Fexofenadine

In this monograph, the potential use of methods based on the Biopharmaceutics Classification System (BCS) framework to evaluate the bioequivalence of solid immediate-release (IR) oral dosage forms containing fexofenadine hydrochloride as a substitute for a pharmacokinetic study in human volunteers is investigated. We assessed the solubility, permeability, dissolution, pharmacokinetics, pharmacodynamics, therapeutic index, bioavailability, drug-excipient interaction, and other properties using BCS recommendations from the ICH, FDA and EMA. The findings unequivocally support fexofenadine's classification to BCS Class IV as it is neither highly soluble nor highly permeable. Further impeding the approval of generic equivalents through the BCS-biowaiver pathway is the reference product's inability to release ≥ 85 % of the drug substance within 30 min in pH 1.2 and pH 4.5 media. According to ICH rules, BCS class IV drugs do not qualify for waiving clinical bioequivalence studies based on the BCS, even though fexofenadine has behaved more like a BCS class I/III than a class IV molecule in pharmacokinetic studies to date and has a wide therapeutic index.

Twenty-five years: The fexofenadine clinical experience

Allergic rhinitis (AR) and urticaria affect a sizable portion of the population worldwide, resulting in reduced quality-of-life and productivity and increased healthcare costs. Fexofenadine (FEX) is a non-sedating second-generation H1 antihistamine with pronounced efficacy and a very good safety profile, used for the treatment of allergic diseases. In addition to its antihistaminic properties, FEX also has anti-inflammatory effects. FEX has a wide therapeutic window and is not associated with any sedative effects, even at higher than recommended doses. There is a need for an integrated management system for AR and urticaria which includes safe and effective treatment options. An ideal anti-allergic formulation should provide fast relief of symptoms and long-lasting effect without drowsiness. Data from randomized clinical trials show that FEX meets these criteria and is an effective treatment option with a favourable safety profile, improving the quality of life of patients suffering from AR and urticaria.

Bioequivalence of 2 Pediatric Formulations of Fexofenadine Hydrochloride Oral Suspension

Fexofenadine hydrochloride (HCl) is a second-generation, nonsedating, histamine H1-receptor antagonist used to manage seasonal allergic rhinitis and chronic idiopathic urticaria. A new oral pediatric suspension of fexofenadine HCl has been developed, with the preservative potassium sorbate replacing parabens. The objective of this phase 1 single-center, open-label, randomized, 2-treatment, full-replicated, 4-period, 2-sequence crossover study in healthy adult volunteers was to assess the bioequivalence of 30 mg of the new oral suspension of fexofenadine HCl (test) versus 30 mg of the marketed pediatric oral suspension of fexofenadine HCl (reference). The replicate design was based on the high intra-individual variability of fexofenadine (>30% on Cmax ). The study comprised 68 randomized and treated volunteers. Plasma concentrations of fexofenadine were similar following the administration of a single dose of each formulation. Cmax , AUClast , AUC, median tmax , and mean t1/2z were similar between administrations of the same fexofenadine formulation and between formulations. A high intra-individual variability was confirmed with both formulations. Bioequivalence of the test and reference fexofenadine HCl formulations was demonstrated as the 90% confidence intervals of the geometric least squares mean ratio for Cmax , AUClast , and AUC of fexofenadine were all within the bioequivalence range of 0.80-1.25. There were no serious adverse events (AEs) or study discontinuations due to treatment-emergent AEs with either fexofenadine HCl formulation. The new paraben-free fexofenadine HCl 30-mg oral suspension and marketed fexofenadine HCl 30-mg pediatric oral suspension are bioequivalent under fasting conditions, with no safety concerns and a safety profile consistent with the known profile of fexofenadine.

Exposure of fexofenadine, but not pseudoephedrine, is markedly decreased by green tea extract in healthy volunteers

Green tea (GT) alters the disposition of a number of drugs such as nadolol and lisinopril. However, it is unknown whether GT affects disposition of hydrophilic anti-allergic drugs. The purpose of this study was to investigate whether pharmacokinetics of fexofenadine and pseudoephedrine are affected by catechins, major GT components. A randomized, open, 2-phase crossover study was conducted in 10 healthy Japanese volunteers. After overnight fasting, subjects were simultaneously administered fexofenadine (60 mg) and pseudoephedrine (120 mg) with an aqueous solution of green tea extract (GTE) containing (-)-epigallocatechin gallate (EGCG) of approximately 300 mg or water (control). In vitro transport assays were performed using human embryonic kidney (HEK) 293 cells stably expressing organic anion transporting polypeptide (OATP)1A2 to evaluate the inhibitory effect of EGCG on OATP1A2-mediated fexofenadine transport. In the GTE phase, the area under the plasma concentration-time curve and the amount excreted unchanged into urine for 24h of fexofenadine were significantly decreased by 70% (P < 0.001) and 67% (P < 0.001), respectively, compared with control. There were no differences in T_max and the elimination half-life of fexofenadine between phases. Fexofenadine was confirmed to be a substrate of OATP1A2, and EGCG (100 and 1000 μM) and GTE (0.1 and 1 mg/mL) inhibited OATP1A2-mediated uptake of fexofenadine. On the contrary, the concomitant administration of GTE did not influence the pharmacokinetics of pseudoephedrine. These results suggest that intake of GT may result in a markedly reduced exposure of fexofenadine, but not of pseudoephedrine, putatively by inhibiting OATP1A2-mediated intestinal absorption.

Fexofenadine: review of safety, efficacy and unmet needs in children with allergic rhinitis

Allergic rhinitis (AR) is the most common undiagnosed chronic condition in children. Moderate/severe AR symptoms significantly impair quality of life, and cause sleep disruption, absenteeism and decreased productivity. Additionally, untreated AR predisposes children to asthma and other chronic conditions. Although intranasal corticosteroids are the most effective pharmacologic treatment for AR, oral antihistamines are often preferred. First-generation antihistamines may be chosen to relieve AR symptoms as they are inexpensive and widely available; however, they cause sedative and cardiovascular negative effects due to poor receptor selectivity. Therefore, second-generation antihistamines were developed to reduce adverse effects while retaining efficacy. There are fewer clinical trials in children than adults, therefore, efficacy and safety data is limited, particularly in children under 6 years, highlighting the need to generate these data in young children with AR. Fexofenadine, a highly selective second-generation antihistamine, effectively alleviates symptoms of AR, is non-sedating due to decreased blood-brain barrier permeability, and is devoid of cardiovascular side effects. Importantly, fexofenadine relieves the ocular symptoms of allergic conjunctivitis, which occur concomitantly with AR, improving quality of life. Overall, fexofenadine displays a favorable safety profile and results in greater treatment satisfaction in children compared with other second-generation antihistamines. This review aimed to evaluate and compare the safety and efficacy of fexofenadine with other available first- and second-generation antihistamines in children with AR.

Efficacy and Safety of Non-brain Penetrating H1-Antihistamines for the Treatment of Allergic Diseases

H₁ receptor antagonists, known as H₁-antihistamines (AHs), inactivate the histamine H₁-receptor thereby preventing histamine causing the primary symptoms of allergic diseases, such as atopic dermatitis, pollinosis, food allergies, and urticaria. AHs, which are classified into first-generation (fgAHs) and second-generation (sgAHs) antihistamines, are the first line of treatment for allergic diseases. Although fgAHs are effective, they cause adverse reactions such as potent sedating effects, including drowsiness, lassitude, and cognitive impairment; anticholinergic effects, including thirst and tachycardia. Consequently, the use of fgAHs is not recommended for allergic diseases. Today, sgAHs, which are minimally sedating and, therefore, may be used at more effective doses, are the first-line treatment for alleviating the symptoms of allergic diseases. Pharmacologically, the use of sedating fgAHs is limited to antiemetics, anti-motion sickness drugs, and antivertigo drugs. The use of histamine H₁-receptor occupancy (H₁RO) based on positron emission tomography (PET) has been developed for the evaluation of brain penetrability. Based on the results of the H₁RO-PET studies, non-brain-penetrating AHs (nbpAHs) have recently been reclassified among sgAHs. The nbpAHs are rapidly acting and exhibit minimal adverse reactions and, thus, are considered first-line drugs for allergic diseases. In this review, we will introduce recent topics on the pharmacodynamics and pharmacokinetics of AHs and make recommendations for the use of nbpAHs as first-line treatment options for allergic diseases.

Histamine H1 and H2 receptors are essential transducers of the integrative exercise training response in humans

Exercise training is a powerful strategy to prevent and combat cardiovascular and metabolic diseases, although the integrative nature of the training-induced adaptations is not completely understood. We show that chronic blockade of histamine H₁/H₂ receptors led to marked impairments of microvascular and mitochondrial adaptations to interval training in humans. Consequently, functional adaptations in exercise capacity, whole-body glycemic control, and vascular function were blunted. Furthermore, the sustained elevation of muscle perfusion after acute interval exercise was severely reduced when H₁/H₂ receptors were pharmaceutically blocked. Our work suggests that histamine H₁/H₂ receptors are important transducers of the integrative exercise training response in humans, potentially related to regulation of optimal post-exercise muscle perfusion. These findings add to our understanding of how skeletal muscle and the cardiovascular system adapt to exercise training, knowledge that will help us further unravel and develop the exercise-is-medicine concept.

Effect of histamine-receptor antagonism on leg blood flow during exercise

Histamine mediates vasodilation during inflammatory and immune responses, as well as following endurance exercise. During exercise, intramuscular histamine concentration increases, and its production, appears related to exercise intensity and duration. However, whether histamine contributes to exercise hyperemia and promotes exercise blood flow in an intensity- or duration-dependent pattern is unknown. The purpose of this study was to compare leg blood flow across a range of exercise intensities, before and after prolonged exercise, with and without histamine-receptor antagonism. It was hypothesized that combined oral histamine H₁/H₂-receptor antagonism would decrease leg blood flow, and the effect would be greater at higher intensities and following prolonged exercise. Sixteen (7F, 9M) volunteers performed single-leg knee-extension exercise after consuming either placebo or combined histamine H₁/H₂-receptor antagonists (Blockade). Exercise consisted of two graded protocols at 20, 40, 60, and 80% of peak power, separated by 60 min of knee-extension exercise at 60% of peak power. Femoral artery blood flow was measured by ultrasonography. Femoral artery blood flow increased with exercise intensity up to 2,660 ± 97 mL/min at 80% of peak power during Placebo (P < 0.05). Blood flow was further elevated with Blockade to 2,836 ± 124 mL/min (P < 0.05) at 80% peak power (9.1 ± 4.8% higher than placebo). These patterns were not affected by prolonged exercise (P = 0.13). On average, femoral blood flow during prolonged exercise was 12.7 ± 2.8% higher with Blockade vs. Placebo (P < 0.05). Contrary to the hypothesis, these results suggest that histamine receptor antagonism during exercise, regardless of intensity or duration, increases leg blood flow measured by ultrasonography.NEW & NOTEWORTHY Leg blood flow during exercise was increased by taking antihistamines, which block the receptors for histamine, a molecule often associated with inflammatory and immune responses. The elevated blood flow occurred over exercise intensities ranging from 20 to 80% of peak capacity and during exercise of 60 min duration. These results suggest that exercise-induced elevations in histamine concentrations are involved in novel, poorly understood, and perhaps complex ways in the exercise response.

Structural and clinical impact of anti-allergy agents: An overview

Allergic disorders are markedly rising in industrialized countries. The identification of compounds that trigger the immunoglobulin E (IgE)-dependent allergic reaction remain the means to improve the quality of life by limiting patient's exposure to critical allergens. Information concerning the treatment and onset of allergic disorders including atopic dermatitis, allergic rhinitis, and bronchial asthma has been provided by the research over the past decade. Recent studies also indicated that allergic inflammation is associated closely with their exacerbation and progression and indeed is the basic pathophysiology of allergic diseases. As a result of immunological and molecular biological studies our understanding of the mechanism of allergic inflammation with regard to therapeutic agents has improved. While much effort has been paid to developing a new anti-allergic agent, the allergic disease has yet to be completely conquered. The more extensive research will allow the development of new therapeutics to combat allergic diseases. Currently, with respect to mechanism of action anti-allergy drugs are classified into five types including histamine H₁ antagonists, leukotriene antagonists, Th₂ cytokine inhibitors, thromboxane A₂ inhibitors and mediator-release inhibitors. The use of two or more anti-allergy agents together is not acknowledged at present, but this will be the subject of research in the future because with different mechanisms of action anti-allergy agents used at the same time will theoretically increase their effects. This review article focuses on anti-allergy agents highlighting their applications, clinical trials and recent advancement on drugs.

Second-Generation Histamine H1 Receptor Antagonists Suppress Delayed Rectifier K+-Channel Currents in Murine Thymocytes

BACKGROUND/AIMS

Voltage-dependent potassium channels (Kv1.3) are predominantly expressed in lymphocyte plasma membranes. These channels are critical for the activation and proliferation of lymphocytes. Since second-generation antihistamines are lipophilic and exert immunomodulatory effects, they are thought to affect the lymphocyte Kv1.3-channel currents.

METHODS

Using the patch-clamp whole-cell recording technique in murine thymocytes, we tested the effects of second-generation antihistamines, such as cetirizine, fexofenadine, azelastine, and terfenadine, on the channel currents and the membrane capacitance.

RESULTS

These drugs suppressed the peak and the pulse-end currents of the channels, although the effects of azelastine and terfenadine on the peak currents were more marked than those of cetirizine and fexofenadine. Both azelastine and terfenadine significantly lowered the membrane capacitance. Since these drugs did not affect the process of endocytosis in lymphocytes, they were thought to have interacted directly with the plasma membranes.

CONCLUSIONS

Our study revealed for the first time that second-generation antihistamines, including cetirizine, fexofenadine, azelastine, and terfenadine, exert suppressive effects on lymphocyte Kv1.3-channels. The efficacy of these drugs may be related to their immunomodulatory mechanisms that reduce the synthesis of inflammatory cytokine.

Histamine-Receptor Antagonists Slow 10-km Cycling Performance in Competitive Cyclists

Histamine is released within skeletal muscle during exercise. In humans, antihistamines have no effect on speed, power output, or time-to-completion of short-duration high-intensity exercise. In mice, blocking histamine's actions decreases speed and duration of endurance tasks. It is unknown if these opposing outcomes are the result of differences in histamine's actions between species or are related to duration and/or intensity of exercise, as blocking histamine during endurance exercise has not been examined in humans.

PURPOSE

Determine the effects of histamine-receptor antagonism on cycling time trial performance in humans, with and without a preceding bout of sustained steady-state exercise.

METHODS

Eleven (3F) competitive cyclists performed six 10-km time trials on separate days. The first two time trials served as familiarization. The next four time trials were performed in randomized-block order, where two were preceded by 120 min of seated rest (rest) and two by 120 min of cycling exercise (Exercise) at 50% V˙O2peak. Within each block, subjects consumed either combined histamine H1 and H2 receptor antagonists (Blockade) or Placebo, before the start of the 120-min Rest/Exercise.

RESULTS

Blockade had no discernible effects on hemodynamic or metabolic variables during Rest or Exercise. However, Blockade increased time-to-completion of the 10-km time trial compared with Placebo (+10.5 ± 3.7 s, P < 0.05). Slowing from placebo to blockade was not different between rest (+8.7 ± 5.2 s) and Exercise (+12.3 ± 5.8 s, P = 0.716).

CONCLUSIONS

Exercise-related histaminergic signaling appears inherent to endurance exercise and may play a role in facilitating optimal function during high-intensity endurance exercise.

Utilization of data below the analytical limit of quantitation in pharmacokinetic analysis and modeling: promoting interdisciplinary debate

Traditionally, bioanalytical laboratories do not report actual concentrations for samples with results below the LOQ (BLQ) in pharmacokinetic studies. BLQ values are outside the method calibration range established during validation and no data are available to support the reliability of these values. However, ignoring BLQ data can contribute to bias and imprecision in model-based pharmacokinetic analyses. From this perspective, routine use of BLQ data would be advantageous. We would like to initiate an interdisciplinary debate on this important topic by summarizing the current concepts and use of BLQ data by regulators, pharmacometricians and bioanalysts. Through introducing the limit of detection and evaluating its variability, BLQ data could be released and utilized appropriately for pharmacokinetic research.

Effects of antihistamines on the H295R steroidogenesis - Autocrine up-regulation following 3β-HSD inhibition

Millions of people of all ages suffer from allergies worldwide and as a consequence antihistamines are among the most commonly prescribed pharmaceuticals in the world. We investigated the disruptive effects of three antihistamines, promethazine (PMZ), cetirizine (CET) and fexofenadine (FEX) on the H295R steroidogenesis. A multi-steroid LC-MS/MS method was used to quantify 13 steroid hormones in the steroidogenesis. In addition, real-time RT-PCR was used to determine if exposure to antihistamines altered gene expression in the cell line. When exposing the H295R cells to PMZ and CET, significant increases in Δ⁵-steroids and significant decreases in Δ⁴-steroids were observed, indicating an inhibition of 3β-hydroxysteroid dehydrogenase (3β-HSD). A sequential decrease in corticosteroids, androgens and estrogens were also observed. Overall, FEX had no effect on the steroidogenesis even though minor effects were observed at the highest concentrations. Real-time RT-PCR showed that PMZ resulted in significant up-regulation of 3β-HSD and 17β-HSD, whereas CET only resulted in up-regulation of 3β-HSD. This indicated that the decrease in steroids downstream from 3β-HSD following PMZ and CT exposure induced a compensatory autocrine response in 3β-HSD gene expression. The effects on the steroidogenesis were observed at concentrations 30-50 times higher than the therapeutic plasma concentrations. However, antihistamines are lipophilic and may accumulate in adrenals and gonads. Thus, disruptive effects of PMZ and CET on human steroidogenesis cannot be excluded.

Effect of Garlic, Gingko, and St. John's Wort Extracts on the Pharmacokinetics of Fexofenadine: A Mechanistic Study

The aim of this study was to determine the effects of garlic and ginkgo herbal extracts on the pharmacokinetics of the P-glycoprotein (P-gp)/organic anion-transporting polypeptides (Oatps) substrate fexofenadine. Male rats were dosed orally with garlic (120 mg/kg), ginkgo (17 mg/kg), St. John's wort (SJW; 1000 mg/kg; positive control), or Milli-Q water for 14 days. On day 15, rats either were administered fexofenadine (orally or i.v.), had their livers isolated and perfused with fexofenadine, or had their small intestines divided into four segments (SI-SIV) and analyzed for P-gp and Oatp1a5. In vivo, SJW increased the clearance of i.v. administered fexofenadine by 28%. Garlic increased the area under the curve_0-∞ and maximum plasma concentration of orally administered fexofenadine by 47% and 85%, respectively. Ginkgo and SJW had no effect on the oral absorption of fexofenadine. In the perfused liver, garlic, ginkgo, and SJW increased the biliary clearance of fexofenadine with respect to perfusate by 71%, 121%, and 234%, respectively. SJW increased the biliary clearance relative to the liver concentration by 64%. The ratio of liver to perfusate concentrations significantly increased in all treated groups. The expression of Oatp1a5 in SI was increased by garlic (88%) and SJW (63%). There were no significant changes in the expression of P-gp. Induction of intestinal Oatp1a5 by garlic may explain the increased absorption of orally administered fexofenadine. Ginkgo had no effect on the expression of intestinal P-gp or Oatp1a5. A dual inductive effect by SJW on opposing intestinal epithelial transport by Oatp1a5 and P-gp remains a possibility.

Effect of acute aerobic exercise and histamine receptor blockade on arterial stiffness in African Americans and Caucasians

African Americans (AA) exhibit exaggerated central blood pressure (BP) and arterial stiffness measured by pulse wave velocity (PWV) in response to an acute bout of maximal exercise compared with Caucasians (CA). However, whether potential racial differences exist in central BP, elastic, or muscular arterial distensibility after submaximal aerobic exercise remains unknown. Histamine receptor activation mediates sustained postexercise hyperemia in CA but the effect on arterial stiffness is unknown. This study sought to determine the effects of an acute bout of aerobic exercise on central BP and arterial stiffness and the role of histamine receptors, in AA and CA. Forty-nine (22 AA, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either histamine receptor antagonist or control placebo. Central blood BP and arterial stiffness measurements were obtained at baseline, and at 30, 60, and 90 min after 45 min of moderate treadmill exercise. AA exhibited greater central diastolic BP, elevated brachial PWV, and local carotid arterial stiffness after an acute bout of submaximal exercise compared with CA, which may contribute to their higher risk of cardiovascular disease. Unexpectedly, histamine receptor blockade did not affect central BP or PWV in AA or CA after exercise, but it may play a role in mediating local carotid arterial stiffness. Furthermore, histamine may mediate postexercise carotid arterial dilation in CA but not in AA. These observations provide evidence that young and healthy AA exhibit an exaggerated hemodynamic response to exercise and attenuated vasodilator response compared with CA.NEW & NOTEWORTHY African Americans are at greater risk for developing cardiovascular disease than Caucasians. We are the first to show that young and healthy African Americans exhibit greater central blood pressure, elevated brachial stiffness, and local carotid arterial stiffness following an acute bout of submaximal exercise compared with Caucasians, which may contribute to their higher risk of cardiovascular disease. Furthermore, African Americans exhibit attenuated vasodilator response compared with Caucasians.

A single dose of histamine-receptor antagonists before downhill running alters markers of muscle damage and delayed-onset muscle soreness

Histamine contributes to elevations in skeletal muscle blood flow following exercise, which raises the possibility that histamine is an important mediator of the inflammatory response to exercise. We examined the influence of antihistamines on postexercise blood flow, inflammation, muscle damage, and delayed-onset muscle soreness (DOMS) in a model of moderate exercise-induced muscle damage. Subjects consumed either a combination of fexofenadine and ranitidine (blockade, n = 12) or nothing (control, n = 12) before 45 min of downhill running (-10% grade). Blood flow to the leg was measured before and throughout 120 min of exercise recovery. Markers of inflammation, muscle damage, and DOMS were obtained before and at 0, 6, 12, 24, 48, and 72 h postexercise. At 60 min postexercise, blood flow was reduced ~29% with blockade compared with control (P < 0.05). Markers of inflammation were elevated after exercise (TNF-ɑ, IL-6), but did not differ between control and blockade. Creatine kinase concentrations peaked 12 h after exercise, and the overall response was greater with blockade (18.3 ± 3.2 kU·l^-1·h^-1) compared with control (11.6 ± 2.0 kU·l^-1·h^-1; P < 0.05). Reductions in muscle strength in control (-19.3 ± 4.3% at 24 h) were greater than blockade (-7.8 ± 4.8%; P < 0.05) and corresponded with greater perceptions of pain/discomfort in control compared with blockade. In conclusion, histamine-receptor blockade reduced postexercise blood flow, had no effect on the pattern of inflammatory markers, increased serum creatine kinase concentrations, attenuated muscle strength loss, and reduced pain perception following muscle-damaging exercise.NEW & NOTEWORTHY Histamine appears to be intimately involved with skeletal muscle during and following exercise. Blocking histamine's actions during muscle-damaging exercise, via common over-the-counter antihistamines, resulted in increased serum creatine kinase, an indirect marker of muscle damage. Paradoxically, blocking histamine's actions attenuated muscle strength loss and reduced perceptions of muscle pain for 72 h following muscle-damaging exercise. These results indicate that exercise-induced histamine release may have a broad impact on protecting muscle from exercise-induced damage.

Antihistamine from Tragia involucrata L. leaves

BACKGROUND

Synthetic antihistamine drugs cause various adverse effects to overcome these problems with natural phytomedicine or phytoconstituents.

METHODS

Tragia involucrata leaves were extracted with soxhlet apparatus and fractionated with column chromatography the homogenized fractions were monitored with thin layer chromatography (TLC) and characterized by using UV-visible, FT-IR, 1H NMR, 13C NMR and MS spectral studies. Isolated compounds were screened their antihistamine activity on ileum preparation, bronchoconstriction and triple response on histamine-induced guinea pig.

RESULTS

Antihistamine 5-hydroxy-1-methylpiperidin-2-one has been isolated and characterized from the leaves of Tragia involucrata L. A promising muscle relaxant, bronchorelaxant and anti-allergic effect of 5-hydroxy-1-methylpiperidin-2-one was observed in histamine-induced guinea pig and found to be 55.54±2.78% protection at the dose level of 12.5 mg/kg in bronchoconstriction effect and 49.05±2.45% protection in triple response. These findings were confirmed by in silico molecular docking also against histamine H1 receptor compared with chlorpheniramine maleate and mepyramine. This shows that the 5-hydroxy-1-methylpiperidine-2-one possess good inhibitory effect on histamine-induced guinea pig. The muscle relaxant, bronchodilating and anti-allergic potency of 5-hydroxy-1-methylpiperidin-2-one has been discussed in context with its probable profile as an anti-asthmatic agent from T. involucrata L. leaves.

CONCLUSIONS

We can conclude that isolated 5-hydroxy-1-methylpiperidin-2-one from T. involucrata L. has potent antihistamine agent on histamine-induced guinea pig.

Evidence of a broad histamine footprint on the human exercise transcriptome

KEY POINTS

Histamine is a primordial signalling molecule, capable of activating cells in an autocrine or paracrine fashion via specific cell surface receptors, in a variety of pathways that probably predate its more recent role in innate and adaptive immunity. Although histamine is normally associated with pathological conditions or allergic and anaphylactic reactions, it may contribute beneficially to the normal changes that occur within skeletal muscle during the recovery from exercise. We show that the human response to exercise includes an altered expression of thousands of protein-coding genes, and much of this response appears to be driven by histamine. Histamine may be an important molecular transducer contributing to many of the adaptations that accompany chronic exercise training.

ABSTRACT

Histamine is a primordial signalling molecule, capable of activating cells in an autocrine or paracrine fashion via specific cell surface receptors. In humans, aerobic exercise is followed by a post-exercise activation of histamine H1 and H2 receptors localized to the previously exercised muscle. This could trigger a broad range of cellular adaptations in response to exercise. Thus, we exploited RNA sequencing to explore the effects of H1 and H2 receptor blockade on the exercise transcriptome in human skeletal muscle tissue harvested from the vastus lateralis. We found that exercise exerts a profound influence on the human transcriptome, causing the differential expression of more than 3000 protein-coding genes. The influence of histamine blockade post-exercise was notable for 795 genes that were differentially expressed between the control and blockade condition, which represents >25% of the number responding to exercise. The broad histamine footprint on the human exercise transcriptome crosses many cellular functions, including inflammation, vascular function, metabolism, and cellular maintenance.

Differential Post-Exercise Blood Pressure Responses between Blacks and Caucasians

Post-exercise hypotension (PEH) is widely observed in Caucasians (CA) and is associated with histamine receptors 1- and 2- (H1R and H2R) mediated post-exercise vasodilation. However, it appears that blacks (BL) may not exhibit PEH following aerobic exercise. Hence, this study sought to determine the extent to which BL develop PEH, and the contribution of histamine receptors to PEH (or lack thereof) in this population. Forty-nine (22 BL, 27 CA) young and healthy subjects completed the study. Subjects were randomly assigned to take either a combined H1R and H2R antagonist (fexofenadine and ranitidine) or a control placebo. Supine blood pressure (BP), cardiac output and peripheral vascular resistance measurements were obtained at baseline, as well as at 30 min, 60 min and 90 min after 45 min of treadmill exercise at 70% heart rate reserve. Exercise increased diastolic BP in young BL but not in CA. Post-exercise diastolic BP was also elevated in BL after exercise with histamine receptor blockade. Moreover, H1R and H2R blockade elicited differential responses in stroke volume between BL and CA at rest, and the difference remained following exercise. Our findings show differential BP responses following exercise in BL and CA, and a potential role of histamine receptors in mediating basal and post-exercise stroke volume in BL. The heightened BP and vascular responses to exercise stimulus is consistent with the greater CVD risk in BL.

No major effects of vitamin D3 (1,25 dihydroxyvitamin D3) on absorption and pharmacokinetics of folic acid and fexofenadine in healthy volunteers

PURPOSE

In Caco-2 cells, folate uptake via the proton-coupled folate transporter (PCFT) increases significantly by a 3-day treatment with 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). Additionally, mRNA content and protein expression of the transporter OATP1A2 were increased up to ninefold with 1,25(OH)2D3. We investigated whether these in vitro findings can be confirmed in humans in vivo.

METHODS

Ten healthy volunteers (six women) received 5 mg folic acid orally once before and once together with the last intake of a 10-day course of 0.5 μg 1,25(OH)2D3 orally. One hundred twenty milligrams fexofenadine, an OATP1A2 substrate, was taken in 1 day before the first folic acid intake, and again on the ninth day of 1,25(OH)2D3 intake. Duodenal biopsies were taken for transporter mRNA assessments once before and once on the ninth or tenth day of the vitamin D3 course. Serum folic acid and fexofenadine concentrations were quantified with a chemiluminescence immunoassay and LC-MS/MS, respectively. Pharmacokinetics were compared between periods with standard bioequivalence approaches.

RESULTS

While geometric mean folic acid AUC0-2h, which mainly reflects absorption, was 0.403 and 0.414 mg/L·h before and after the vitamin D3 course (geometric mean ratio (GMR), 1.027; 90 % confidence interval (90 % CI), 0.788-1.340), the geometric mean fexofenadine AUC0-2h was 1.932 and 2.761 mg/L·h, respectively (GMR, 1.429; 90 % CI, 0.890-2.294). PCFT- and OATP1A2-mRNA expressions in duodenal biopsies were essentially unchanged.

CONCLUSIONS

No significant changes in folic acid and fexofenadine absorption were observed after a 10-day course of 1,25(OH)2D3 in humans in vivo. This study underlines the importance of confirming in vitro findings in vivo in humans.

Effect of antioxidants on histamine receptor activation and sustained postexercise vasodilatation in humans

NEW FINDINGS

What is the central question of this study? Is exercise-induced oxidative stress the upstream exercise-related signalling mechanism that leads to sustained postexercise vasodilatation via activation of H1 and H2 histamine receptors? What is the main finding and its importance? Systemic administration of the antioxidant ascorbate inhibits sustained postexercise vasodilatation to the same extent as seen previously with H1 and H2 histamine receptor blockade following small muscle-mass exercise. However, ascorbate has a unique ability to catalyse the degradation of histamine. We also found that systemic infusion of the antioxidant N-acetylcysteine had no effect on sustained postexercise vasodilatation, suggesting that exercise-induced oxidative stress does not contribute to sustained postexercise vasodilatation. An acute bout of aerobic exercise elicits a sustained postexercise vasodilatation that is mediated by histamine H1 and H2 receptor activation. However, the upstream signalling pathway that leads to postexercise histamine receptor activation is unknown. We tested the hypothesis that the potent antioxidant ascorbate would inhibit this histaminergic vasodilatation following exercise. Subjects performed 1 h of unilateral dynamic knee extension at 60% of peak power in three conditions: (i) control; (ii) i.v. ascorbate infusion; and (iii) ascorbate infusion plus oral H1 /H2 histamine receptor blockade. Femoral artery blood flow was measured (using Doppler ultrasound) before exercise and for 2 h postexercise. Femoral vascular conductance was calculated as flow/pressure. Postexercise vascular conductance was greater for control conditions (3.4 ± 0.1 ml min(-1) mmHg(-1) ) compared with ascorbate (2.7 ± 0.1 ml min(-1) mmHg(-1) ; P < 0.05) and ascorbate plus H1 /H2 blockade (2.8 ± 0.1 ml min(-1) mmHg(-1) ; P < 0.05), which did not differ from one another (P = 0.9). Given that ascorbate may catalyse the degradation of histamine in vivo, we conducted a follow-up study, in which subjects performed exercise in two conditions: (i) control; and (ii) i.v. N-acetylcysteine infusion. Postexercise vascular conductance was similar for control (4.0 ± 0.1 ml min(-1) mmHg(-1) ) and N-acetylcysteine conditions (4.0 ± 0.1 ml min(-1) mmHg(-1) ; P = 0.8). Thus, the results in the initial study were due to the degradation of histamine in skeletal muscle by ascorbate, because the histaminergic vasodilatation was unaffected by N-acetylcysteine. Overall, exercise-induced oxidative stress does not appear to contribute to sustained postexercise vasodilatation.

Effect of H1- and H2-histamine receptor blockade on postexercise insulin sensitivity

Following a bout of dynamic exercise, humans experience sustained postexercise vasodilatation in the previously exercised skeletal muscle which is mediated by activation of histamine (H1 and H2) receptors. Skeletal muscle glucose uptake is also enhanced following dynamic exercise. Our aim was to determine if blunting the vasodilatation during recovery from exercise would have an adverse effect on blood glucose regulation. Thus, we tested the hypothesis that insulin sensitivity following exercise would be reduced with H1- and H2-receptor blockade versus control (no blockade). We studied 20 healthy young subjects (12 exercise; eight nonexercise sham) on randomized control and H1- and H2-receptor blockade (fexofenadine and ranitidine) days. Following 60 min of upright cycling at 60% VO2 peak or nonexercise sham, subjects consumed an oral glucose tolerance beverage (1.0 g/kg). Blood glucose was determined from "arterialized" blood samples (heated hand vein). Postexercise whole-body insulin sensitivity (Matsuda insulin sensitivity index) was reduced 25% with H1- and H2-receptor blockade (P < 0.05), whereas insulin sensitivity was not affected by histamine receptor blockade in the sham trials. These results indicate that insulin sensitivity following exercise is blunted by H1- and H2-receptor blockade and suggest that postexercise H1- and H2-receptor-mediated skeletal muscle vasodilatation benefits glucose regulation in healthy humans.

How First-Time-in-Human Studies Are Being Performed: A Survey of Phase I Dose-Escalation Trials in Healthy Volunteers Published Between 1995 and 2004

First-time-in-human studies are small, time-lagged dose-escalation studies including volunteer subjects evaluating safety and tolerability. There is little consensus in the design of a first-time-in-human study, and it is difficult to get an overview of studies performed. One hundred five studies comprising 3323 healthy volunteers published in the 5 major clinical pharmacology journals since 1995 were analyzed. The average trial was placebo controlled, double blind including 32 subjects at 5 dose levels but with great variation in cohort size and dose-escalation method. The parallel single-dose design was the most common design, with the crossover designs being more frequent in the early publications. Despite discussions on the optimization of phase I trials, little seems to be happening. The development of study designs and evaluation methods for cancer trials is extensive, but formal statistically based methods and more scientific study designs are unusual in phase I dose-escalation trials in healthy volunteers.

Pharmacology of antihistamines

This article reviews the molecular biology of the interaction of histamine with its H1-receptor and describes the concept that H1-antihistamines are not receptor antagonists but are inverse agonists i.e. they produce the opposite effect on the receptor to histamine. It then discourages the use of first-generation H1-antihistamines in clinical practice today for two main reasons. First, they are less effective than second generation H1-antihistamines. Second, they have unwanted side effects, particularly central nervous system and anti-cholinergic effects, and have the potential for causing severe toxic reactions which are not shared by second-generation H1-antihistamines. There are many efficacious and safe second-generation H1-antihistamines on the market for the treatment of allergic disease. Of the three drugs highlighted in this review, levocetirizine and fexofenadine are the most efficacious in humans in vivo. However, levocetirizine may cause somnolence in susceptible individuals while fexofenadine has a relatively short duration of action requiring twice daily administration for full all round daily protection. While desloratadine is less efficacious, it has the advantages of rarely causing somnolence and having a long duration of action. Lastly, all H1-antihistamines have anti-inflammatory effects but it requires regular daily dosing rather than dosing 'on-demand' for this effect to be clinically demonstrable.

Pharmacology of antihistamines

This article reviews the molecular biology of the interaction of histamine with its H₁-receptor and describes the concept that H₁-antihistamines are not receptor antagonists but are inverse agonists i.e. they produce the opposite effect on the receptor to histamine. It then discourages the use of first-generation H₁-antihistamines in clinical practice today for two main reasons. First, they are less effective than second generation H₁-antihistamines. Second, they have unwanted side effects, particularly central nervous system and anti-cholinergic effects, and have the potential for causing severe toxic reactions which are not shared by second-generation H₁-antihistamines. There are many efficacious and safe second-generation H₁-antihistamines on the market for the treatment of allergic disease. Of the three drugs highlighted in this review, levocetirizine and fexofenadine are the most efficacious in humans in vivo. However, levocetirizine may cause somnolence in susceptible individuals while fexofenadine has a relatively short duration of action requiring twice daily administration for full all round daily protection. While desloratadine is less efficacious, it has the advantages of rarely causing somnolence and having a long duration of action. Lastly, all H₁-antihistamines have anti-inflammatory effects but it requires regular daily dosing rather than dosing 'on-demand' for this effect to be clinically demonstrable.

Sustained postexercise vasodilatation and histamine receptor activation following small muscle-mass exercise in humans

A sustained postexercise vasodilatation, which is histamine receptor mediated, has been observed following single bouts of whole-body exercise, but the mechanisms that regulate activation of histamine receptors following exercise are undefined. Exploration of vasodilatation after small muscle-mass dynamic or resistance exercise could provide novel insight into the pathways responsible for histamine receptor activation. We hypothesized that there would be a vasodilatation of the previously exercised limb following small muscle-mass dynamic and resistance exercise, which would be mediated by histamine receptors. We studied men and women before and after single-leg dynamic (n = 9) or resistance knee-extension exercise (n = 12) on control and blockade days (combined oral H(1) and H(2) receptor antagonism with fexofenadine and ranitidine). We measured arterial blood pressure (automated brachial oscillometry) and femoral artery blood flow (Doppler ultrasound). Dynamic exercise elevated leg vascular conductance in the active leg by 27.2 ± 8.4% at 60 min postexercise (P < 0.05 versus pre-exercise), but did not alter conductance in the rested leg (change, 4.6 ± 3.5%; P = 0.8 versus pre-exercise). The rise in conductance was abolished on the blockade day (change, 3.7 ± 5.1%; P = 0.8 versus pre-exercise, P = 0.2 versus control). Resistance exercise did not produce a sustained vasodilatation (change, -4.3 ± 4.7% at 60 min postexercise; P = 0.7 versus pre-exercise). These data indicate that histamine receptors are activated following dynamic, but not resistance, exercise. Furthermore, these data suggest that local factors associated with aerobic exercise, and not systemic factors or factors associated with high muscle force, are responsible for activation of histamine receptors in the previously exercised muscle.

A randomized control trail of stepwise treatment with fluticasone propionate nasal spray and fexofenadine hydrochloride tablet for seasonal allergic rhinitis

BACKGROUND

In Japan, oral antihistamines are frequently used as the initial treatment for seasonal allergic rhinitis (SAR), and intranasal steroids are added when nasal symptoms worsen. This study aimed to evaluate whether starting treatment with fluticasone propionate nasal spray (FP) from the beginning of pollinosis symptoms and adding fexofenadine hydrochloride tablet (FEX) when SAR is aggravated could achieve improved amelioration of nasal symptoms throughout the pollen season in comparison with a treatment that involves starting with FEX and later adding FP.

METHODS

In this pragmatic, randomized, open-label, parallel-group trial, 51 Japanese cedar pollinosis patients (age, 16-85 years) were randomly divided and administered FP 100 mcg twice daily as an initial drug with FEX 60 mg twice daily as an additional drug and the same treatment in the reverse order. Nasal symptoms were evaluated in a daily dairy using a 4-point scale. The primary outcome was area under curve of the line representing the daily total nasal symptom score in the pollen season on a graph.

RESULTS

Initial treatment with FP was significantly (P = 0.0015) more effective than initial treatment with FEX in improving the primary outcome. The average daily total nasal symptom score in the initial treatment with FP group was better than that in the initial treatment with FEX group throughout the pollen season.

CONCLUSIONS

Initiating treatment with FP and adding FEX might lead to improved outcomes for nasal symptoms in comparison with the same drugs administered in the reverse order.

Effects of bepotastine and fexofenadine on histamine-induced flare, wheal and itch

BACKGROUND

Urticaria is mainly caused by mast cell-derived histamine through the histamine H(1) receptor. Antihistamines are occasionally used on demand upon a recurrence of urticaria; therefore, rapidly acting agents should be explored. The onset of action is assumed to depend on time to maximum concentration (T(max)), but the speed of action needs to be evaluated not only through blood concentration analysis but also by measuring in vivo effectiveness.

METHODS

In this study, we chose two representative second-generation antihistamines (bepotastine and fexofenadine) with relatively short T(max) values and evaluated their effects on histamine-induced skin responses using both visual and laser Doppler imaging scales.

RESULTS

Suppression of histamine-induced flare and itch was observed 3 and 6 h after administration of both antihistamines. Attenuation of itch was seen 30 min after the administration of each drug and thereafter until 6 h. In addition, bepotastine suppressed flare formation after only 30 min following application.

CONCLUSION

These results suggest that antihistamines suppress histamine-induced itch and flare, followed by wheal formation, and that bepotastine suppresses skin symptoms sooner after administration than fexofenadine does, which is relatively consistent with the T(max) results.

The impact of P-glycoprotein mediated efflux on absorption of 11 sedating and less-sedating antihistamines using Caco-2 monolayers

Caco-2 cells were used to compare P-gp mediated efflux and passive permeability using bidirectional transport of 11 antihistamines. An efflux ratio >2 indicated active efflux, with PSC833 and GF120918 used as functional P-gp inhibitors. Antihistamines were measured directly by HPLC or LC/MS. Fexofenadine had an efflux ratio of 37, yet had negligible passive permeability, even in the presence of a pH gradient (0.1 × 10(-6) cm/sec). Its precursor, terfenadine, had an efflux ratio of 2.5, while cetirizine, desloratadine and hydroxyzine were 4, 7 and 14, respectively. After incubation with P-gp inhibitors, these ratios dropped significantly. Loratadine, by contrast, had equivalent transport in both directions and passive permeability was high (24 × 10(-6) cm/sec). Dimenhydrinate was the only other sedating antihistamine to exhibit efflux, with a ratio of 10. Gradient conditions of pH (6/7.4) increased efflux of terfenadine and desloratadine to over 31 and 38 fold respectively, yet this increased efflux was not associated with P-gp. Altering functional P-gp in the gut is likely to influence absorption of some sedating antihistamines such as dimenhydrinate and hydroxyzine and most less-sedating antihistamines except loratadine. In addition, desloratadine exhibits pH dependent efflux which could further induce variable absorption of this antihistamine.

QTc interval prolongation by fexofenadine in healthy human volunteers and its correlation with plasma levels of fexofenadine: A demonstration of anticlockwise hysteresis

Aim:

The study was designed to establish relationship between the plasma concentration and QTc interval prolonging effect of fexofenadine and demonstrate the phenomenon of anticlockwise hysteresis.

Materials and Methods:

Six subjects were given fexofenadine 60 mg tablet orally under stable conditions, and their drug concentrations were measured at regular intervals. At predetermined time, their ECGs were recorded. Data were analyzed and plotted graphically.

Design and Setting:

Randomized parallel design, single group study conducted at clinical research organization of Ahmadabad.

Results:

In all subjects time taken for maximum plasma concentration of fexofenadine (T_max) was around 3 h and the value of average maximum plasma concentration was 460.63 ng/mL, the effect of fexofenadine on the heart (measured as QTc interval prolongation) was maximum (E_max) after 6 h and average QTc interval was 469.75 ms. Thus, the time to maximum concentration of fexofenadine did not match with the maximum effect on the heart as measured by QTc interval.

Conclusion:

The relationship between the drug concentration and drug effect on the heart are at two different time scales. It can be understood by two-compartment model of pharmacokinetics, and this retardation or lagging of an effect behind the concentration is known as hysteresis. The increase of QTc was not beyond 500 ms and not sustained, demonstrating overall cardiac safety of fexofenadine.

Coexistence of passive and carrier-mediated processes in drug transport

The permeability of biological membranes is one of the most important determinants of the pharmacokinetic processes of a drug. Although it is often accepted that many drug substances are transported across biological membranes by passive transcellular diffusion, a recent hypothesis speculated that carrier-mediated mechanisms might account for the majority of membrane drug transport processes in biological systems. Based on evidence of the physicochemical characteristics and of in vitro and in vivo findings for marketed drugs, as well as results from real-life discovery and development projects, we present the view that both passive transcellular processes and carrier-mediated processes coexist and contribute to drug transport activities across biological membranes.

Fexofenadine: biochemical, pharmacokinetic and pharmacodynamic properties and its unique role in allergic disorders

BACKGROUND

Fexofenadine is one of several second-generation H(1)-antihistamines approved for the treatment of various allergic disorders; however, it shows numerous unique properties that make it an optimal choice for many patients.

OBJECTIVE

To review the pharmacology, efficacy and safety of fexofenadine and the attributes differentiating it from other H(1)-antihistamines.

METHODS

We performed a literature search in PubMed/MEDLINE (1966 - March 2009) using the keywords fexofenadine, antihistamine, allergic rhinitis and chronic urticaria. We also reviewed data provided by the manufacturer in addition to reports from various governmental agencies.

RESULTS/CONCLUSIONS

Fexofenadine is devoid of sedative and anticholinergic effects and may offer equivalent or greater efficacy in treating allergic disorders compared with other currently available second-generation H(1)-antihistamines. In addition, fexofenadine may offer cost savings over other selected H(1)-antihistamines owing to its recent availability in generic form in the US.

ESRD impairs nonrenal clearance of fexofenadine but not midazolam

ESRD can affect the pharmacokinetic disposition of drugs subject to nonrenal clearance. Cytochrome P450 (CYP) enzymes, including CYP3A, and multiple intestinal and hepatic drug transporters are thought to mediate this process, but the extent to which kidney disease alters the function of these proteins in humans is unknown. We used midazolam and fexofenadine to assess CYP3A (intestinal and hepatic) and drug transport, respectively, in patients with ESRD and healthy control subjects. We evaluated the effect of uremia on CYP3A and transporter expression in vitro by incubating normal rat hepatocytes and enterocytes with serum drawn from study participants. ESRD dramatically reduced nonrenal transporter function, evidenced by a 63% decrease in clearance (P < 0.001) and a 2.8-fold increase in area under the plasma concentration-time curve for fexofenadine (P = 0.002), compared with control subjects. We did not observe significant differences in midazolam or 1'-hydroxymidazolam clearance or area under the curve after oral administration, suggesting that CYP3A function is not changed by ESRD. Changes in hepatocyte and enterocyte protein expression in the presence of uremic serum were consistent with in vivo results. These findings demonstrate a mechanism for altered drug disposition in kidney disease, which may partially account for the high rates of drug toxicity in this population.

Toward an increased understanding of the barriers to colonic drug absorption in humans: implications for early controlled release candidate assessment

The purpose of this study was to increase the understanding of in vivo colonic drug absorption in humans by summarizing and evaluating all regional in vivo human absorption data with focus on the interpretation of the colonic absorption data in relation to intestinal permeability and solubility. In addition, the usefulness of the Biopharmaceutics Classification System (BCS) in early assessment of the in vivo colonic absorption potential of controlled release drug candidates was investigated. Clinical regional absorption data (Cmax, Tmax, and AUC) of 42 drugs were collected from journal articles, abstracts, and internal reports, and the relative bioavailability in the colon (Frel(colon)) was obtained directly or calculated. Bioavailability, fraction dose absorbed, and information if the compounds were substrates for P-glycoprotein (P-gp) or cytochrome P450 3A (CYP3A) were also obtained. The BCS I drugs were well absorbed in the colon (Frel(colon) > 70%), although some drugs had lower values due to bacterial degradation in the colon. The low permeability drugs (BCS III/IV) had a lower degree of absorption in the colon (Frel(colon) < 50%). There was a clear correlation between in vitro Caco-2 permeability and Frel(colon), and atenolol and metoprolol may function as permeability markers for low and high colonic absorption, respectively. No obvious effect of P-gp on the colonic absorption of the drugs in this study was detected. There was insufficient data available to fully assess the impact of low solubility and slow dissolution rate. The estimated in vivo fractions dissolved of the only two compounds administered to the colon as both a solution and as solid particles were 55% and 92%, respectively. In conclusion, permeability and solubility are important barriers to colonic absorption in humans, and in vitro testing of these properties is recommended in early assessment of colonic absorption potential.

New oral H1 antihistamines in children: facts and unmeet needs

BACKGROUND

Second-generation antihistamines differ from first-generation ones because of their elevated specificity and affinity for peripheral H1-receptors and because of their lower penetration to the central nervous system, having fewer sedative effects as a result. Over the last few years, new compounds with different pharmacokinetic properties have been synthesized. More recent improvements of the molecules, generally in the form of active metabolites, led to the synthesis of new-generation antihistamines.

METHODS

Recommendations on the minimum criteria that would have to be met for compounds to be classified as new-generation antihistamines have been recently established by a consensus statement. In the past, the pharmacokinetics and pharmacodynamics of H1 antihistamines have not been optimally investigated in the pediatric population, especially in infants and young children.

RESULTS

The pharmacology of second-generation H1 antihistamines has been investigated relatively deeper than old antihistamines in children. In the pediatric population, clinical studies with new-generation antihistamines are still limited in number and, with rare exceptions, of brief duration. Comparative trials on the efficacy and safety between different compounds are also lacking.

CONCLUSIONS

Properly designed, long-term trials with new-generation H1 antihistamines need to be performed in single age groups, in order to better define the effects of these drugs in all pediatric population.