Affinity profiles of BTM-1086 and BTM-1041 at muscarinic receptor subtypes and at H1- and alpha 1-receptors

The affinities of the (+) and (-) enantiomers of the antimuscarinic benzothiazepinone derivative, cis-2,3-dihydro-3-(4-methyl-1-piperazinylmethyl)-2-phenyl-1,5-benzoth iazepin-4 (5H)-one (BTM-1041 and BTM-1086), for muscarinic receptor subtypes, histamine H1-receptors and alpha 1-adrenoceptors were determined in vitro using isolated organs: field-stimulated rabbit vas deferens (M1-receptors), guinea-pig left atrium (M2-receptors), guinea-pig ileum (M3- and histamine H1-receptors) and rat vas deferens (alpha 1-adrenoceptors). We also assessed the binding profile of BTM-1041 and BTM-1086 at muscarinic receptor subtypes in guinea-pig cortex (M1), heart (M2) and salivary glands (M3) as well as at alpha 1-adrenoceptors in rat cerebral cortex. Functional and binding experiments showed that the (-) enantiomer (BTM-1086) had a high affinity (pA2 = 7.98-8.81; pKi = 8.31-9.15) for the three muscarinic receptor subtypes, whereas the (+) enantiomer (BTM-1041) showed a low antimuscarinic potency (pA2 = 4.87-5.31; pKi = 4.85-5.55). This results in an extremely high stereoselectivity for these optical isomers [-)/(+) ratios = 1023 to 6918). The affinity of the (-) enantiomer BTM-1086 was lower for both histamine H1- and alpha 1-receptors than for muscarinic receptors, whereas the reverse was true for the (+) enantiomer, BTM-1041. Thus, the stereochemical demands for the two optical isomers were most stringent at muscarinic receptors but were inverse and less pronounced at histamine H1- and alpha 1-receptors (stereoselectivity ratios = 0.16-0.22).     

Bilastine for the relief of allergy symptoms

Bilastine is a potent inhibitor of the histamine H1 receptor. It was recently approved in 28 countries of the European Union for the symptomatic treatment of allergic rhinoconjunctivitis and urticaria in adults and children older than 12 years. Data from preclinical studies confirmed its selectivity for the histamine H1 receptor over other receptors, and demonstrated antihistaminic and antiallergic properties in vivo. Studies in healthy volunteers and patients have shown that bilastine does not affect driving ability, cardiac conduction or alertness. Bilastine has demonstrated a good safety profile, without serious adverse effects or antimuscarinic effects in clinical trials. There were no significant changes in laboratory tests, electrocardiograms or vital signs. In clinical studies, oral treatment with bilastine 20 mg once daily improved allergic rhinitis with greater efficacy than placebo and comparable to cetirizine and desloratadine. Bilastine 20 mg was more effective than placebo and equivalent to levocetirizine in chronic urticaria, relieving symptoms, improving quality of life and controlling sleep disorders.     

In vitro characterisation of the duration of action of the histamine-1 receptor antagonist azelastine

Azelastine is a selective antagonist at the human histamine-1 receptor and is used clinically in the treatment of allergic rhinitis. In this study we have investigated its duration of action in vitro in an effort to characterise the receptor and tissue components involved. Chinese hamster ovary cell membrane fragments were used to determine the kinetics of azelastine at the H? receptor in a radioligand binding assay. Further duration of action studies were completed in tissue preparations using guinea-pig trachea and human bronchus. In radioligand binding studies, azelastine reached steady state at the H? receptor after approximately 41 min and exhibited a significantly slower dissociation rate constant from the receptor than the first generation antihistamine, diphenhydramine. In washout studies completed in guinea-pig and human airway in vitro tissue preparations, azelastine continued to antagonise the effects of histamine at the H? receptor for at least 18 h post-washout of the antagonist. This outcome was reversed following removal of the epithelium from guinea-pig isolated tracheal strips. These studies indicate there is a tissue component contributing to azelastine's duration of action, in addition to its direct H? receptor binding, with evidence suggesting a role for the epithelial layer.     

Preclinical efficacy and safety pharmacology of SUN-1334H, a potent orally active antihistamine agent

OBJECTIVE: These studies aimed to outline the in vitro and in vivo histamine H(1) receptor antagonistic activity and safety pharmacology of SUN-1334H, a new potent antihistamine agent under clinical development. METHODS: In vitro antihistamine activity and selectivity of SUN-1334H was evaluated in a panel of receptor and enzyme assays and functional assays using isolated tissues. In vivo antihistamine and antiallergy efficacy were assessed following oral administration of SUN-1334H in histamine-induced bronchoconstriction in guinea pigs, skin wheal in beagle dogs and ovalbumin-induced rhinitis (sneezing, vascular permeability and intranasal pressure) in guinea pigs. Cardiovascular safety was assessed by CHO-K1/human ether-à-go-go related gene (hERG) K(+) current assay, dog telemetry and guinea-pig ECG. CNS safety was assessed by functional observational battery in rats and pentobarbital-induced sedation and pentylenetetrazol-induced convulsions in mice. The effect on intestinal motility was assessed in rats. RESULTS: In vitro receptor binding assays showed that SUN-1334H had high histamine H(1) receptor binding affinity with an inhibition constant value of 9.7 nmol/L and either no or insignificant affinity with a panel of receptors and enzymes. In functional assays, SUN-1334H caused potent inhibition of histamine-induced contractions of isolated guinea-pig ileum with an IC(50) (half the maximal inhibitory concentration) of 0.198 micromol/L. In contrast, SUN-1334H had no significant effect on isolated tissue contractions induced by cholinergic, H(2)-histaminergic, serotonergic, adrenergic receptor agonists or BaCl(2). In studies of animal models of histamine-mediated disorders, SUN-1334H potently inhibited histamine-induced bronchospasm over 24 hours following oral administration and completely suppressed histamine-induced skin wheal in beagle dogs and ovalbumin-induced rhinitis in guinea pigs. In CHO-K1/hERG cells, SUN-1334H did not modulate hERG K(+)-currents at concentrations as high as 100 micromol/L. Cardiovascular and CNS function and intestinal motility were not altered at doses several-fold greater than those required for efficacy, indicating a good safety profile of the drug. CONCLUSIONS: SUN-1334H is a potent, orally active, highly selective H(1) receptor antagonist with a long duration of action in its preclinical profile. It has potential for the treatment of disorders involving histamine as a mediator.     

Blockade of muscarinic, histamine H1 and histamine H2 receptors by antidepressants

The antagonistic effect of various antidepressants and of alprazolam on muscarinic and histamine H1 receptors has been studied in the guinea-pig ileum, and those on histamine H2 receptors on rat uterus. All antidepressants act like competitive antagonists on muscarinic and histamine H1 and H2 receptors. Alprazolam has shown competitive antagonism on muscarinic and histamine H1 receptors, and noncompetitive antagonism on histamine H2 receptors. Large differences in anticholinergic activity appear between the drugs studied, whereas all of them showed a higher histamine H1 receptor antagonistic activity. Most of the drugs studied showed a histamine H2 receptor antagonistic activity similar to that of cimetidine.     

In vivo pharmacological characterisation of bilastine, a potent and selective histamine H1 receptor antagonist

OBJECTIVE: We set out to establish the in vivo histamine H(1) receptor antagonistic (antihistaminic) and antiallergic properties of bilastine. METHODS: In vivo antihistaminic activity experiments consisted of measurement of: inhibition of increase in capillary permeability and reduction in microvascular extravasation and bronchospasm in rats and guinea pigs induced by histamine and other inflammatory mediators; and protection against lethality induced by histamine and other inflammatory mediators in rats. In vivo antiallergic activity experiments consisted of measurement of passive and active cutaneous anaphylactic reactions as well as type III and type IV allergic reactions in sensitised rodents. RESULTS: In the in vivo antihistaminic activity experiments, bilastine was shown to have a positive effect, similar to that of cetirizine and more potent than that of fexofenadine. The results of the in vivo antiallergic activity experiments showed that the properties of bilastine in this setting are similar to those observed for cetirizine and superior to fexofenadine in the model of passive cutaneous anaphylactic reaction. When active cutaneous anaphylactic reaction experiments were conducted, bilastine showed significant activity, less potent than that observed with cetirizine but superior to that of fexofenadine. Evaluation of the type III allergic reaction showed that of the antihistamines only bilastine was able to inhibit oedema in sensitised mice, although its effect in this respect was much less potent than that observed with dexamethasone. In terms of the type IV allergic reaction, neither bilastine, cetirizine nor fexofenadine significantly modified the effect caused by oxazolone. CONCLUSIONS: The results of our in vivo preclinical studies corroborate those obtained from previously conducted in vitro experiments of bilastine, and provide evidence that bilastine possesses antihistaminic as well as antiallergic properties, with similar potency to cetirizine and superior potency to fexofenadine.     

Structure-activity relationships of clonidine- and tolazoline-like compounds at histamine and alpha-adrenoceptor sites.

1 Thirty clonidine- and tolazoline-like compounds with differing phenyl ring substituents were tested for agonistic actions at histamine H1-receptors (guinea-pig ileum), histamine H2-receptors (guinea-pig driven right ventricular strips), post-junctional alpha-adrenoceptors (rat desheathed was deferens) and pre-junctional alpha-adrenoceptors (inhibition of sympathetic stimulation in guinea-pig driven left atria). 2 All compounds were inactive at histamine H1-receptors, while 21 of the 30 compounds displayed varying stimulant activity at H2-receptors. 3 At post-junctional alpha-receptors all 30 compounds produced stimulant actions, whereas at prejunctional alpha-receptors the compounds displayed either agonistic or antagonistic actions. 4 Thus structure-activity-relationships (SAR) could only be validated for histamine H2- and post-junctional alpha-receptor effects. These studies show that the most potent compounds are those with 2,6-phenyl substituents in which rotation is restricted so that the two rings are aplanar. Electronic effects of the substituents have a greater influence on activity at H2- than at alpha-receptors. 5 The major difference in SAR involves the influence of substituents in the 3, 4 or 5 positions on the phenyl ring. The presence of these substituents abolish significant activity at H2-receptors, while alpha-receptor stimulant activity is retained.     

Phosphoinositide hydrolysis mediated by histamine H1-receptors in rat brain cortex

Histamine stimulated the accumulation of [3H]inositol 1-phosphate in the presence of lithium in [3H]inositol-prelabelled slices from rat brain cortex in a concentration-dependent manner, with an EC50 value of 94.7 microM. High concentrations of antagonists of histamine H2 receptors, muscarinic receptors, alpha 1-adrenoceptors and serotonin receptors did not inhibit the effect. The histamine H1-receptor antagonists mepyramine, triprolidine, promethazine, d-chlorpheniramine and the tricyclic antidepressant doxepin inhibited the response with Ki values corresponding to an interaction with histamine H1-receptors. The EC50 for the response was about three times lower than the Ki value (approximately 300 microM) for the inhibition by histamine of [3H]mepyramine binding to membranes from rat brain cortex. Partial inactivation of H1-receptors with the alkylating antagonist phenoxybenzamine resulted in similar reductions in [3H]mepyramine binding sites and in the maximal histamine-induced [3H]inositol 1-phosphate accumulation, without affecting the KD for the radioligand or the EC50 for the response. The apparent dissociation constant for histamine calculated from these experiments (KA = 92.2 microM) was not different from the EC50 value. The present results indicate that histamine-stimulated phosphoinositide hydrolysis in rat brain cortex is mediated by H1-receptors and that no receptor reserve is present.     

In vitro isolated tissue studies with atiprosin (AY-28,228): a new antihypertensive compound

Using in vitro isolated tissue and binding studies we have defined a receptor activity profile for atiprosin. The most prominent action of the compound was significant alpha-adrenoceptor antagonist activity (pA2 = 8.11) that was less potent than prazosin (pA2 = 8.78) but more potent than either ketanserin (pA2 = 7.34) or indoramin (pA2 = 7.85). In addition, atiprosin was selective for alpha 1-adrenoceptors, since the compound was over 100-fold less potent as an antagonist at alpha 2-adrenoceptors (pA2 = 6.04). Atiprosin also displayed selective serotonin 5-HT2-receptor antagonist activity similar to that seen with ketanserin, but with a lesser potency (pA2 atiprosin, 6.87; ketanserin, 8.61). Although atiprosin also displayed significant histamine H1-antagonist activity (pA2 = 7.32), it was less potent as an H1-antagonist than as an alpha 1-adrenoceptor antagonist. In contrast, both indoramin and ketanserin displayed H1-antagonist activity (pA2 8.77 and 8.83, respectively) greater than their respective alpha 1-adrenoceptor antagonist activities. Atiprosin had little or no activity at either beta 1- or beta 2-adrenoceptors, muscarinic or histamine H2-receptors, nor any marked ability to produce smooth muscle relaxation either by a direct effect or via calcium entry blockade.     

The cardiovascular effects of thyrotropin-releasing hormone (TRH) are attenuated by cimetidine in rats.

The modulation of cardioventilator effects of thyrotropin-releasing hormone (TRH) by histaminergic mechanisms was studied in anaesthetized rats pretreated with histamine receptor antagonists. TRH (1-100 nmol/kg) into the lateral cerebral ventricle dose-dependently elevated mean arterial pressure, heart rate and stimulated respiration. The respiratory stimulating effect of TRH remained unchanged after pretreatments with histamine H1-receptor antagonist diphenhydramine or H2-receptor antagonists cimetidine and ranitidine, while the TRH-induced hypertension and tachycardia were attenuated by cimetidine. This antagonism was not due to an interaction between TRH and cimetidine at their central binding sites, since there was no displacement of [3H]MeTRH binding in the presence of cimetidine nor did TRH displace [3H]cimetidine in rat brain homogenates. Inability of diphenhydramine to modify the cardiovascular effects of TRH indicates that these effects are not due to histamine liberation, as cardiovascular stimulation after central administration of histamine is mainly mediated via H1-receptors. The antagonism of the cardiovascular responses to TRH by cimetidine was not due to blockade of H2-receptors, since another potent H2-receptor antagonist ranitidine was unable to affect the cardiovascular effects of TRH. Therefore, we suggest that cimetidine exerted antagonism of TRH by some non-specific action.     

Anaphylaxis in the guinea-pig isolated heart: Selective inhibition by burimamide of the positive inotropic and chronotropic effects of released histamine

1. Anaphylaxis was induced in the isolated heart of the guinea-pig in the presence of burimamide at concentrations of 4 x 10(-5)M and 2.7 x 10(-4)M.2. Burimamide did not affect the immunological release of histamine; however, it selectively antagonized the positive inotropic and chronotropic effects of released histamine. The antagonism of the positive chronotropic effect was concentration-dependent.3. Neither the negative dromotropic effect nor the decrease in coronary flow rate occurring during anaphylaxis were inhibited by burimamide.4. The results are in agreement with the double histamine receptor theory and suggest that, in the heart of the guinea-pig, H(2)-receptors are involved in the positive inotropic and chronotropic effects of released histamine, and H(1)-receptors in the negative dromotropic effect.     

The binding of doxepin to histamine H1-receptors in guinea-pig and rat brain

The affinity constant for doxepin obtained from inhibition of histamine-induced contraction of guinea-pig intestinal smooth muscle at 30 degrees C was 2.6 +/- 0.18 X 10(10)M-1. The slope of a Schild plot was not significantly different from unity. The affinity constant of doxepin did not vary markedly with temperature. At 37 degrees C it was 3.75 +/- 0.02 X 10(10)M-1 and at 25 degrees C 2.1 X 10(10)M-1. Doxepin was a competitive inhibitor of [3H]-mepyramine binding to guinea-pig cerebellar homogenates. The affinity constant derived for doxepin at 30 degrees C was 1.12 +/- 0.45 X 10(10)M-1. Hill coefficients for curves of doxepin or mepyramine inhibition of [3H]-mepyramine binding in guinea-pig cerebellum, cerebral cortex and hippocampus did not differ significantly from unity. The mean affinity of mepyramine for histamine H1-receptors in rat brain homogenates at 30 degrees C was 3.5 X 10(8)M-1. Hill coefficients for curves of doxepin or mepyramine inhibition of [3H]-mepyramine binding to homogenates of rat cerebral cortex or rat whole brain were near unity. These studies provide no evidence that doxepin binds preferentially to a sub-class of histamine H1-receptors in rat brain.     

A species comparison of the histamine H2-receptor on mast cells and basophils

The histamine H2-agonist dimaprit was employed in experiments to investigate the role of H2-receptors in mediator release systems from the rat, guinea-pig and man. Whereas inhibition of histamine release by dimaprit was observed in all 3 species, this effect appeared not always to be related to H2-receptor occupancy. Although the data in general support previous evidence for the presence of H2-receptors on human basophils and guinea-pig mast cells, the use of dimaprit as a pure H2-agonist in these studies is questioned. No evidence for H2-receptors on rat mast cells was obtained.     

Interactions of bilastine, a new oral H₁ antihistamine, with human transporter systems

Membrane transporters play a significant role in facilitating transmembrane drug movement. For new pharmacological agents, it is important to evaluate potential interactions (e.g., substrate specificity and/or inhibition) with human transporters that may affect their pharmacokinetics, efficacy, or toxicity. Bilastine is a new nonsedating H? antihistamine indicated for the treatment of allergic rhinoconjunctivitis and urticaria. The in vitro inhibitory effects of bilastine were assessed on 12 human transporters: four efflux [multidrug resistance protein 1 (MDR1) or P-glycoprotein, breast cancer resistance protein (BCRP), multidrug resistance associated protein 2 (MRP2), and bile salt export pump) and eight uptake transporters (sodium taurocholate cotransporting polypeptide, organic cation transporter (OCT)1, organic anion transporter (OAT)1, OAT3, OCT2, OATP2B1, OATP1B1, and OATP1B3). Only mild inhibition was found for MDR1-, OCT1-, and OATP2B1-mediated transport of probe substrates at the highest bilastine concentration assayed (300 μM; half-maximal inhibitory concentration: ≥300 μM). Bilastine transport by MDR1, BCRP, OAT1, OAT3, and OCT2 was also investigated in vitro. Only MDR1 active transport of bilastine was relevant, whereas it did not appear to be a substrate of OCT2, OAT1, or OAT3, nor was it transported substantially by BCRP. Drug-drug interactions resulting from bilastine inhibition of drug transporters that would be generally regarded as clinically relevant are unlikely. Additionally, bilastine did not appear to be a substrate of human BCRP, OAT1, OAT3, or OCT2 and thus is not a potential victim of inhibitors of these transporters. On the other hand, based on in vitro evaluation, clinically relevant interactions with MDR1 inhibitors are anticipated.     

Interactions of drugs active at opiate receptors and drugs active at alpha 2-receptors on various test systems.

1 The actions of the opiate receptor drugs, morphine, methionine-enkephalin (Met-enkephalin) and naloxone were compared with the actions of the alpha 2-receptor drugs, clonidine, xylazine and yohimbine on analgesic tests, in vitro bioassay (guinea-pig ileum and mouse vas deferens), and radioligand displacement studies on rat brain membrane preparations. 2. Both opiate and alpha 2-agonist drugs showed analgesic activity but whilst the alpha 2-agonist analgesic activity was antagonized by only alpha 2-antagonists, the analgesic activity of morphine was antagonized by both naloxone and yohimbine. In the in vitro tests, both groups of agonists inhibited electrically evoked activity; however in these experiments only antagonism of opiates by naloxone and alpha 2-agonists by yohimbine could be shown and it is concluded that in these systems the activity of the alpha 2-agonists is mediated via the presynaptic alpha 2-receptors only. 3 In the radioligand studies the drugs acting at alpha 2-receptors were active in the micromolar range at displacing labelled opioid ligands but opiates did not displace labelled alpha 2-ligands. 4 It is concluded that drugs which act on alpha 2-receptors interfere with the in vivo analgesic effects of opiates and weakly displace opioid radioligand binding, but opioids do not affect alpha 2 agonist analgesia and do not appear to displace alpha 2-agonist radioligand binding.     

Some Anti-allergic and Anti-inflammatory Actions of 2-N -Carboxamidinonormianserin (FCC5)

The aims of these studies were to examine the effects of FCC5 (2-carboxamidino-1,2,3,4,10,14b-hexahydrodibenzo (c,f) pyrazino (1,2,-a) azepine HCI), an analogue of mianserin, on immediate type hypersensitivity reactions in-vitro. The actions of FCC5 were examined on the Schultz-Dale reaction of guinea-pig ileum and on histamine and leukotriene release from human- and guinea-pig-sensitized lung fragments. FCC5 (applied topically) was assessed for anti-inflammatory activity in-vivo against phorbol-12-myristate-13-acetate (PMA)-induced oedema in the mouse ear. FCC5 (IC50 = 017 μM) was a potent inhibitor of the Schultz-Dale reaction in-vitro, as assessed by a concentration-dependent attenuation of egg albumin-induced contractions of sensitized guinea-pig isolated ileum. Using human and guinea-pig isolated sensitized lung fragments, FCC5 (1–100 μM) attenuated antigen-induced release of sulphidopeptidoleukotrienes and histamine. FCC5 (50 μg topically) resembled mianserin and indomethacin in attenuating PMA-induced mouse ear inflammation. These properties together with previously published evidence of long lasting antihistamine properties in-vivo, suggest that FCC5 has therapeutic potential as an anti-allergic agent, especially in pathological conditions where an inflammatory component is present.     

Rilmenidine differs from clonidine in that it lacks histamine-like activity

Studies were carried out to determine whether rilmenidine, a recently introduced antihypertensive agent with a similar mechanism of action of clonidine, possesses histamine-like activity on tissues responding to histamine H2-receptor agonists. In guinea-pig isolated atria, both histamine and clonidine caused concentration-dependent positive chronotropic effects which were blocked by the histamine H2-receptor antagonist cimetidine (5 microM); in contrast, rilmenidine produced a concentration-dependent negative chronotropic effect which was not altered by cimetidine. In stilboestrol-treated rat isolated uterus contracted by KCl, histamine and clonidine produces concentration-dependent relaxations which were blocked by cimetidine (5 microM); rilmenidine also produced relaxation, but this was not affected by cimetidine (5 microM). These findings suggest that rilmenidine, unlike clonidine, does not activate histamine H2-receptors in either guinea-pig atria or rat uterus.     

Histamine H1-receptor in endothelial and smooth muscle cells of guinea-pig aorta

The location of histamine H1-receptors in the thoracic aorta of guinea-pigs was studied with a [3H]mepyramine binding assay. [3H]Mepyramine binding studies of whole and rubbed aortas, and of cultured endothelial and smooth muscle cells showed that the Kd values were all in the range 0.53-0.76 nM, but that the Bmax values were 19.1, 10.1, 63.3 and 11.6 fmol/mg protein, respectively. Thus, the whole aorta contained more H1-receptors than the rubbed one (free of endothelium), and cultured endothelial cells contained more H1-receptors than smooth muscle cells. These results indicate that more histamine H1-receptors were concentrated in the endothelial cells than in the smooth muscle cells in guinea-pig aorta.     

Histamine H1 receptor occupancy in human brains after single oral doses of histamine H1 antagonists measured by positron emission tomography.

1. Histamine H1 receptor occupancy in the human brain was measured in 20 healthy young men by positron emission tomography (PET) using [11C]-doxepin. 2. (+)-Chlorpheniramine, a selective and classical antihistamine, occupied 76.8 +/- 4.2% of the averaged values of available histamine H1 receptors in the frontal cortex after its administration in a single oral dose of 2 mg. Intravenous administration of 5 mg (+)-chlorpheniramine almost completely abolished the binding of [11C]-doxepin to H1 receptors (H1 receptor occupancy: 98.2 +/- 1.2%). 3. Terfenadine, a nonsedative antihistamine, occupied 17.2 +/- 14.2% of the available H1 receptors in the human frontal cortex after its administration in a single oral dose of 60 mg. 4. There was no correlation between H1 receptor occupancy by terfenadine and the plasma concentration of the active acid metabolite of terfenadine in each subject. 5. PET data on human brain were essentially compatible with those on H1 receptor occupancy in guinea-pig brain determined by in vivo binding techniques, although for the same H1 receptor occupancy the dose was less in human subjects than in guinea-pigs. 6. The PET studies demonstrated the usefulness of measuring H1 receptor occupancy with classical and second-generation antihistamines in human brain to estimate their unwanted side effects such as sedation and drowsiness quantitatively.     

Bilastine: an environmental risk assessment

Context: Bilastine is a new oral selective, non-sedating histamine H₁ antagonist for the symptomatic treatment of allergic rhinoconjunctivitis and urticaria. The European Medicines Agency requires an Environmental Risk Assessment (ERA) for all novel medicines for human use. Objective: To calculate the bilastine predicted environmental concentration in surface water (PEC_sw; phase I ERA), and to determine the effects of bilastine on aquatic systems (phase II [tier A]). Materials and methods: Bilastine PEC_sw was calculated using the maximum daily dosage (20?mg), assuming that all administered bilastine was released into the aquatic environment. A persistence, bioaccumulation and toxicity assessment was conducted using the log K_ow from the molecular structure. In phase II (tier A), a ready biodegradability test was performed, and bilastine’s potential toxicity to various aquatic and sediment-dwelling micro-organisms was evaluated. Results: Bilastine PEC_SW was calculated as 0.1?μg?L^?1, and the compound was not readily biodegradable. Bilastine had no significant effects on Chironomus riparius midges, or on the respiration rate of activated sludge. For green algae, the bilastine no observed effect concentration (NOEC) was 22?mg?L^?1; bilastine had no effect on zebra fish development, or on the reproduction rate of daphnids. Discussion: Bilastine NOEC values against zebra fish, algae, daphnids, and aerobic organisms in activated sludge were at least 130?000-fold greater than the calculated PEC_SW value. Conclusion: No environmental concerns exist from bilastine use in patients with allergic rhinoconjunctivitis or urticaria.