flunarizine flunarizine flunarizine, sold under the brand name sibelium among others, is a drug classified as a calcium antagonist which is used for various indications. it is not available by prescription in the united states or japan. the drug was discovered at janssen pharmaceutica (r14950) in 1968. flunarizineclinical datatrade namessibelium, othersother names1--4-cinnamyl-piperazineahfs/drugs.commicromedex detailed consumer informationpregnancycategory c routes ofadministrationby mouthatc coden07ca03 (who) legal statuslegal status in general: ℞ (prescription only) pharmacokinetic dataprotein binding>99%metabolismmainly cyp2d6metabolites≥15elimination half-life5–15 hrs (single dose)18–19 days (multiple doses)excretionfeces, <1% urineidentifiers iupac name 1--4-piperazine cas number52468-60-7 ypubchem cid941361drugbankdb04841 ychemspider819216 yuniir7pla2dm0jkeggd07971 ychemblchembl30008 ycomptox dashboard (epa)dtxsid6045616 echa infocard100.052.652 chemical and physical dataformulac26h26f2n2molar mass404.505 g·mol−13d model (jsmol)interactive imagemelting point251.5 °c (484.7 °f) (dihydrochloride) smiles fc1ccc(cc1)c(c2ccc(f)cc2)n3ccn(cc3)c\c=c\c4ccccc4 inchi inchi=1s/c26h26f2n2/c27-24-12-8-22(9-13-24)26(23-10-14-25(28)15-11-23)30-19-17-29(18-20-30)16-4-7-21-5-2-1-3-6-21/h1-15,26h,16-20h2/b7-4+ ykey:smanxxcatutddt-qpjjxvbhsa-n y (verify) medical uses flunarizine is effective in the prophylaxis of migraine, occlusive peripheral vascular disease, vertigo of central and peripheral origin, and as an add-on in the treatment of epilepsy where its effect is weak and not recommended. it has been shown to significantly reduce headache frequency and severity in both adults and children. contraindications flunarizine is contraindicated in patients with depression, in the acute phase of a stroke, and in patients with extrapyramidal symptoms or parkinson's disease. it is also contraindicated in hypotension, heart failure and arrhythmia. side effects common side effects include drowsiness (20% of patients), weight gain (10%), as well as extrapyramidal effects and depression in elderly patients. interactions the effects of other sedating drugs and alcohol, as well as antihypertensives, can be increased. no relevant pharmacokinetic interactions have been described. pharmacology mechanism of action flunarizine is a selective calcium antagonist with moderate other actions including antihistamine, serotonin receptor blocking and dopamine d2 blocking activity. compared to other calcium channel blockers such as dihydropyridine derivatives, verapamil and diltiazem, flunarizine has low affinity to voltage-dependent calcium channels. it has been theorised that it may act not by inhibiting calcium entry into cells, but rather by an intracellular mechanism such as antagonising calmodulin, a calcium binding protein. pharmacokinetics flunarizine is well absorbed (>80%) from the gut and reaches maximal blood plasma concentrations after two to four hours, with more than 99% of the substance bound to plasma proteins. it readily passes the blood–brain barrier. when given daily, a steady state is reached after five to eight weeks. concentrations in the brain are about ten times higher than in the plasma. it is metabolised in the liver, mainly by the enzyme cyp2d6. at least 15 different metabolites are described, including (in animals) n-desalkyl and hydroxy derivatives and glucuronides. less than 1% is excreted in unchanged form, and the main excretion path is via bile and faeces. elimination half life varies widely between individuals and is about 5 to 15 hours after a single dose, and 18 to 19 days on average when given daily. chemistry flunarizine is a diphenylmethylpiperazine derivative related to the antihistamines hydroxyzine and cinnarizine (an older molecule also discovered by janssen). research flunarizine may help to reduce the severity and duration of attacks of paralysis associated with the more serious form of alternating hemiplegia, as well as being effective in rapid onset dystonia-parkinsonism (rdp). both these conditions arise from specific mutations in the atp1a3 gene. flunarizine extended motor neuron survival in spinal cord, protected skeletal muscles from cell death and atrophy and extended survival by 40% in an animal model of spinal muscular atrophy. flunarizine has also shown promise as an anti-prion medication. synthesis flunarazine has been compared with lomerizine. orig patent: synthesis: prec: the 4,4'-difluorobenzophenone (1) is reduced with sodium borohydride giving bis(4-fluorophenyl)methanol (4,4'-difluorobenzhydrol) (2). this is halogenated in concentrated muriatic acid giving 4,4'-difluorobenzhydryl chloride (3). the alkylation of this with piperazine would give 1-(4,4'-difluorobenzhydryl)piperazine (4). alkylation of the remaining secondary nitrogen by cinnamyl chloride (5) completed the synthesis of flunarizine (6). alternatively, 3 can be alkylated by cinnamylpiperazine in a convergent method.