Flunarizine, sold under the brand name Sibelium among others, is a drug classified as a calcium antagonist which is used for various indications.
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
Heart 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
sedative 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 D
2 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
. 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 hydroxyl derivatives and . 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 from cell death and muscle atrophy and extended survival by 40% in an animal model of spinal muscular atrophy.
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Therapeutic Choices, sixth edition, Canadian Pharmacists Association, 2011.
