Orally administered astemizole is well absorbed but undergoes an extensive first-pass metabolism to O-desmethylastemizole. Desmethylastemizole is formed in the human microsomal systems of the small intestine as well as the liver, which suggests the role of cytochromes P450 (P450s) in the first-pass metabolism of astemizole. Human P450s involved in the O-demethylation of astemizole have, however, not been identified, and the involvement of twelve known drug-metabolizing P450s were denied. During the course of the P450 identification study, higher activities of the astemizole O-demethylation in the rabbit small intestine than in the liver (about 3-fold) were found. These data suggest the possible involvement of CYP2J, since P450 included in this subfamily is dominantly expressed in the small intestine of rabbits. ...
... Three metabolites of astemizole were detected in a /human/ liver microsomal system, i.e. desmethylastemizole (DES-AST), 6-hydroxyastemizole (6OH-AST) and norastemizole (NOR-AST) at the ratio of 7.4:2.8:1. Experiments with recombinant P450s and antibodies indicate a negligible role for CYP3A4 on the main metabolic route of astemizole, i.e. formation of DES-AST, although CYP3A4 may mediate the relatively minor metabolic routes to 6OH-AST and NOR-AST. Recombinant CYP2D6 catalyzed the formation of 6OH-AST and DES-AST. Studies with human liver microsomes, however, suggest a major role for a mono P450 in DES-AST formation. ...
Second-generation, relatively nonsedating histamine H1-receptor antagonists (H1-RA) are extensively used worldwide for the symptomatic treatment of allergic rhinoconjunctivitis and chronic urticaria. Information about the pharmacokinetics and pharmacodynamics of these medications, while still incomplete, is now sufficient to permit optimisation of therapy. Published pharmacokinetic and pharmacodynamic information on these H1-RA is summarised here, and areas where more data are required are delineated. Serum concentrations of most second-generation H1-RA are relatively low, and are usually measured by radioimmunoassay. After oral administration, peak concentrations are observed within 2 or 3 h. Bioavailability has not been well studied, due to the lack of intravenous formulations. Most H1-RA are metabolised in the hepatic cytochrome P450 system: terfenadine, astemizole, loratadine, azelastine, and ebastine have 1 or more active metabolites which are present in serum in higher concentrations than the respective parent compound, and therefore can be measured by high performance liquid chromatography. Cetirizine, an active metabolite of the first generation H1-receptor antagonist hydroxyzine, is not further metabolised to any great extent in vivo, and is eliminated via renal excretion. Levocabastine is also eliminated primarily by excretion. Serum elimination half-life values differ greatly from 1 H1-RA to another, and are 24 h or less for terfenadine, astemizole, loratadine, cetirizine, azelastine and ebastine, and the active metabolites of terfenadine, loratadine and ebastine. The active metabolite of azelastine (demethylazelastine) has a serum elimination half-life value of about 2 days, while that of astemizole (demethyl-astemizole) has a value of 9.5 days. From the few published studies in which the apparent volumes of distribution of the second-generation H1-RA have been calculated, it appears that tissue distribution is extensive. In children, the half-lives of H1-RA are generally shorter than are found in adults; there is no published information on the pharmacokinetics of astemizole, loratadine, azelastine, or ebastine in children. In some elderly adults, terfenadine, loratadine and cetirizine may have longer half-lives than in young healthy adults. There is little published data on the pharmacokinetics of the second-generation H1-RA in patients with impaired hepatic function. The half-life of cetirizine is prolonged in those with impaired renal function. There is a paucity of information on the pharmacokinetics of H1-RA in neonates, in pregnancy or during lactation.
The antiallergic effects of astemizole and its metabolites were studied in rats and guinea pigs. All of the metabolites of astemizole tested were more active than the parent compound in inhibiting contraction of the ileum and bronchoconstriction induced by histamine in guinea pigs. Desmethylastemizole was about the same as astemizole in inhibiting mepyramine binding in guinea pig cerebellum. In heterologous passive cutaneous anaphylaxis (PCA) and homologous PCA, the metabolites caused almost equipotent inhibition to that seen with astemizole. No H2-antagonistic activity was seen with astemizole or desmethylastemizole.
Astemizole competes with histamine for binding at H<sub>1</sub>-receptor sites in the GI tract, uterus, large blood vessels, and bronchial muscle. This reversible binding of astemizole to H<sub>1</sub>-receptors suppresses the formation of edema, flare, and pruritus resulting from histaminic activity. As the drug does not readily cross the blood-brain barrier and preferentially binds at H1 receptors in the peripehery rather than within the brain, CNS depression is minimal. Astemizole may also act on H<sub>3</sub>-receptors, producing adverse effects.
来源:Toxin and Toxin Target Database (T3DB)
毒理性
致癌物分类
对人类不具有致癌性（未被国际癌症研究机构IARC列名）。
No indication of carcinogenicity to humans (not listed by IARC).
Cardiovascular adverse events. In some cases, recognition of severe arrhythmias has been preceded by episodes of syncope. Similarly, rare cases of hypotension, palpitations, and dizziness have also been reported with Astemizole use, which may reflect undetected ventricular arrhythmia. (L1864)
来源:Toxin and Toxin Target Database (T3DB)
毒理性
暴露途径
口腔。从胃肠道快速吸收。
Oral. Rapidly absorbed from the gastrointestinal tract.
Section 1. IDENTIFICATION OF THE SUBSTANCE/MIXTURE Product identifiers Product name : Astemizole CAS-No. : 68844-77-9 Relevant identified uses of the substance or mixture and uses advised against Identified uses : Laboratory chemicals, Manufacture of substances Section 2. HAZARDS IDENTIFICATION Classification of the substance or mixture Classification according to Regulation (EC) No 1272/2008 [EU-GHS/CLP] Skin irritation (Category 2) Eye irritation (Category 2) Specific target organ toxicity - single exposure (Category 3) Classification according to EU Directives 67/548/EEC or 1999/45/EC Harmful if swallowed. Irritating to eyes, respiratory system and skin. Label elements Labelling according Regulation (EC) No 1272/2008 [CLP] Pictogram Signal word Warning Hazard statement(s) H315 Causes skin irritation. H319 Causes serious eye irritation. H335 May cause respiratory irritation. Precautionary statement(s) P261 Avoid breathing dust/ fume/ gas/ mist/ vapours/ spray. P305 + P351 + P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing. Supplemental Hazard none Statements According to European Directive 67/548/EEC as amended. Hazard symbol(s) R-phrase(s) R22 Harmful if swallowed. R36/37/38 Irritating to eyes, respiratory system and skin. S-phrase(s) S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice. S36 Wear suitable protective clothing. Other hazards - none Section 3. COMPOSITION/INFORMATION ON INGREDIENTS Substances Formula : C28H31FN4O Molecular Weight : 458,57 g/mol Component Concentration Astemizole CAS-No. 68844-77-9 - EC-No. 272-441-9 Section 4. FIRST AID MEASURES Description of first aid measures General advice Consult a physician. Show this safety data sheet to the doctor in attendance. If inhaled If breathed in, move person into fresh air. If not breathing, give artificial respiration. Consult a physician. In case of skin contact Wash off with soap and plenty of water. Consult a physician. In case of eye contact Rinse thoroughly with plenty of water for at least 15 minutes and consult a physician. If swallowed Never give anything by mouth to an unconscious person. Rinse mouth with water. Consult a physician. Most important symptoms and effects, both acute and delayed Indication of any immediate medical attention and special treatment needed no data available Section 5. FIREFIGHTING MEASURES Extinguishing media Suitable extinguishing media Use water spray, alcohol-resistant foam, dry chemical or carbon dioxide. Special hazards arising from the substance or mixture Carbon oxides, nitrogen oxides (NOx), Hydrogen fluoride Advice for firefighters Wear self contained breathing apparatus for fire fighting if necessary. Further information no data available Section 6. ACCIDENTAL RELEASE MEASURES Personal precautions, protective equipment and emergency procedures Use personal protective equipment. Avoid dust formation. Avoid breathing vapors, mist or gas. Ensure adequate ventilation. Evacuate personnel to safe areas. Avoid breathing dust. Environmental precautions Do not let product enter drains. Methods and materials for containment and cleaning up Pick up and arrange disposal without creating dust. Sweep up and shovel. Keep in suitable, closed containers for disposal. Reference to other sections For disposal see section 13. Section 7. HANDLING AND STORAGE Precautions for safe handling Avoid contact with skin and eyes. Avoid formation of dust and aerosols. Provide appropriate exhaust ventilation at places where dust is formed. Conditions for safe storage, including any incompatibilities Store in cool place. Keep container tightly closed in a dry and well-ventilated place. Recommended storage temperature: 2 - 8 °C Store with desiccant. Light sensitive. Specific end uses no data available Section 8. EXPOSURE CONTROLS/PERSONAL PROTECTION Control parameters Components with workplace control parameters Exposure controls Appropriate engineering controls Handle in accordance with good industrial hygiene and safety practice. Wash hands before breaks and at the end of workday. Personal protective equipment Eye/face protection Safety glasses with side-shields conforming to EN166 Use equipment for eye protection tested and approved under appropriate government standards such as NIOSH (US) or EN 166(EU). Skin protection Handle with gloves. Gloves must be inspected prior to use. Use proper glove removal technique (without touching glove's outer surface) to avoid skin contact with this product. Dispose of contaminated gloves after use in accordance with applicable laws and good laboratory practices. Wash and dry hands. The selected protective gloves have to satisfy the specifications of EU Directive 89/686/EEC and the standard EN 374 derived from it. Body Protection impervious clothing, The type of protective equipment must be selected according to the concentration and amount of the dangerous substance at the specific workplace. Respiratory protection For nuisance exposures use type P95 (US) or type P1 (EU EN 143) particle respirator.For higher level protection use type OV/AG/P99 (US) or type ABEK-P2 (EU EN 143) respirator cartridges. Use respirators and components tested and approved under appropriate government standards such as NIOSH (US) or CEN (EU). Section 9. PHYSICAL AND CHEMICAL PROPERTIES Information on basic physical and chemical properties a) Appearance Form: solid b) Odour no data available c) Odour Threshold no data available d) pH no data available e) Melting point/freezing no data available point f) Initial boiling point and no data available boiling range g) Flash point no data available h) Evaporation rate no data available i) Flammability (solid, gas) no data available j) Upper/lower no data available flammability or explosive limits k) Vapour pressure no data available l) Vapour density no data available m) Relative density no data available n) Water solubility no data available o) Partition coefficient: n- no data available octanol/water p) Autoignition no data available temperat
