Vigabatrin

drugbox
IUPAC_name = 4-aminohex-5-enoic acid


width = 138
CAS_number = 60643-86-9
ATC_prefix = N03
ATC_suffix = AG04
ATC_supplemental =
PubChem = 5665
DrugBank = APRD00282
C = 6 | H = 11 | N = 1 | O = 2
molecular_weight = 129.157 g/mol
bioavailability = 80-90%
protein_bound = 0
metabolism = Almost no metabolic transformation occurs
elimination_half-life = 5-8 hours in young adults, 12-13 hours in the elderly.
pregnancy_category =
legal_status = Not a controlled substance
routes_of_administration = Oral
excretion = Renal

Vigabatrin is an anticonvulsant that inhibits the catabolism of GABA. It is an analog of GABA, but it is not a receptor agonist.Long, Phillip W. [http://www.mentalhealth.com/drug/p30-s07.html "Vigabatrin."] Internet Mental Health. 1995–2003.]

Indications

Epilepsy

In Canada, vigabatrin is approved for use as an adjunctive treatment (with other drugs) in treatment resistant epilepsy, complex partial seizures, secondary generalized seizures, and for monotherapy use in infantile spasms in West syndrome.

As of 2003, vigabatrin is approved in Mexico for the treatment of epilepsy that is not satisfactorily controlled by conventional therapy (adjunctive or monotherapy) or in recently diagnosed patients who have not tried other agents (monotherapy). [http://www.facmed.unam.mx/bmnd/plm/mex/productos/10130.htm DEF MEXICO: SABRIL] "Diccionario de Especialdades Farmaceuticas." Edicion 49, 2003.]

Vigabatrin is also indicated for monotherapy use in secondarily generalized tonic-clonic seizures, partial seizures, and in infantile spasms due to West syndrome.

ubstance dependence

Fechtner et al found in an eight week study that vigabatrin was effective in the treatment of cocaine and/or methamphetamine dependence. Twenty-eight subjects were enrolled; only twenty stayed after the escalation phase and out of those, only eighteen completed the study and follow-up. Out of those, sixteen subjects tested negative for cocaine and methamphetamine during the last six weeks. No ocular adverse effects were noted.cite journal | first = Robert D. | last = Fechtner | coauthors = Albert S. Khouri, Emilia Figueroa, Marina Ramirez, MD; Martha Federico, Stephen L. Dewey, Jonathan D. Brodie | month = September | year = 2006 | title = Short-term Treatment of Cocaine and/or Methamphetamine Abuse With Vigabatrin: Ocular Safety Pilot Results | journal = Archives of Ophthalmology | volume = 124 | issue = 9 | pages = 1257–62 | pmid = 16966620 | url = http://archopht.ama-assn.org/cgi/content/full/124/9/1257 | accessdate = 2007-10-20 | doi = 10.1001/archopht.124.9.1257]

Other

In November 2001, a team of scientists lead by Peter Zwanzger of the University of Munich reported that vigabatrin reduced cholecystokinin tetrapeptide-induced symptoms of panic disorder, in addition to elevated cortisol and ACTH levels, in healthy volunteers.cite journal | author=Zwanzger P, Baghai TC, Schuele C, Strohle A, Padberg F, Kathmann N, Schwarz M, Moller HJ, Rupprecht R | title=Vigabatrin decreases cholecystokinin-tetrapeptide (CCK-4) induced panic in healthy volunteers | journal=Neuropsychopharmacology | volume=25 | issue=5 | year=2001 | pages=699–703 | pmid=11682253 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=11682253&dopt=ExternalLink | doi=10.1016/S0893-133X(01)00266-4]

In 1994, Feucht and Brantner-Inthaler reported that vigabatrin reduced seizures by 50-100% in 85% of children with Lennox-Gastaut syndrome who had poor results with a valproate.cite journal | author=Feucht M, Brantner-Inthaler S | title=Gamma-vinyl-GABA (vigabatrin) in the therapy of Lennox-Gastaut syndrome: an open study | journal=Epilepsia | volume=35 | issue=5 | year=1994 | pages=993–8 | pmid=7925171 | url=http://www.blackwell-synergy.com/doi/pdf/10.1111/j.1528-1157.1994.tb02544.x| format=PDF| accessdate=2006-05-25 | doi=10.1111/j.1528-1157.1994.tb02544.x]

In 1984, a double-blind crossover-study of six Huntington's disease patients—five of them on antipsychotics—reported that vigabatrin did little, if anything, to improve hyperkinetic movements, the ability to carry out daily activities, or normalize motor function.cite journal | author=Scigliano G, Giovannini P, Girotti F, Grassi MP, Caraceni T, Schechter PJ | title=Gamma-vinyl GABA treatment of Huntington's disease | journal=Neurology | volume=34 | issue=1 | year=1984 | pages=94–6 | pmid=6228746 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=6228746&dopt=ExternalLink]

Mechanism of action

Vigabatrin is an irreversible 'suicide' inhibitor (see Suicide inhibition) of gamma-aminobutyric acid transaminase (GABA-T), the enzyme responsible for the catabolism of GABA, which increases the level of GABA in the synapses.

Vigabatrin is a racemic compound, and its [S] -enantiomer is pharmacologically active.cite journal | first = G. | last = Sheean | coauthors = Schramm T, Anderson DS, Eadie MJ. | year = 1992 | title = Vigabatrin--plasma enantiomer concentrations and clinical effects | journal = Clinical and Experimental Neurology | volume = 29 | pages = 107–16 | pmid = 1343855] ^,cite journal | author=Gram L, Larsson OM, Johnsen A, Schousboe A | title=Experimental studies of the influence of vigabatrin on the GABA system | journal=British Journal of Clinical Pharmacology | volume=27 | issue=Suppl 1 | year=1989 | pages=13S–17S | pmid=2757904]

Adverse effects

Central nervous system

Out of 2,081 subjects, somnolence (12.5%), headache (3.8%), dizziness (3.8%), nervousness (2.7%), depression (2.5%), memory disturbances (2.3%), diplopia (2.2%), aggression (2.0%), ataxia (1.9%), vertigo (1.9%), hyperactivity (1.8%), vision abnormalities (1.6%), confusion (1.4%), insomnia (1.3%), impaired concentration (1.2%), personality disorder (1.1%). Out of 299 children, 33 (11%) became hyperactive.

Some patients develop psychosis during the course of vigabatrin therapy,cite journal | author=Sander JW, Hart YM | title=Vigabatrin and behaviour disturbance | journal=Lancet | volume=335 | issue=8680 | year=1990 | pages=57 | pmid=1967367 | doi=10.1016/0140-6736(90)90190-G] which is more common in adults than in children.cite journal | author=Chiaretti A, Castorina M, Tortorolo L, Piastra M, Polidori G | title= [Acute psychosis and vigabatrin in childhood] | journal= La Pediatria Medica e Chirurgica : Medical and surgical pediatrics | volume=16 | issue=5 | year=1994 | pages=489–90 [Article in Italian] PMID 7885961] This can happen even in patients with no prior history of psychosis.cite journal | author=Sander JW, Hart YM, Trimble MR, Shorvon SD | title=Vigabatrin and psychosis | journal=Journal of Neurology, Neurosurgery, and Psychiatry | volume=54 | issue=5 | year=1991 | pages=435–9 | pmid=1865207] Other rare CNS side effects include anxiety, emotional lability, irritability, tremor, abnormal gait, and speech disorder.

Gastrointestinal

Abdominal pain (1.6%), constipation (1.4%), vomiting (1.4%), and nausea (1.4%). Dyspepsia and increased appetite occurred in less than 1% of subjects in clinical trials.

Body as a Whole

Fatigue (9.2%), weight gain (5.0%), asthenia (1.1%).

Teratogenicity

A teratology study conducted in rabbits found that a dose of 150mg/kg/day caused cleft palate in 2% of pups and a dose of 200 mg/kg/day caused it in 9%. This may be due to a decrease in methionine levels, according to a study published in March 2001.cite journal | author=Abdulrazzaq YM, Padmanabhan R, Bastaki SM, Ibrahim A, Bener A | title=Placental transfer of vigabatrin (gamma-vinyl GABA) and its effect on concentration of amino acids in the embryo of TO mice | journal=Teratology | volume=63 | issue=3 | year=2001 | pages=127–33 | pmid=11283969 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=11283969&dopt=ExternalLink | doi=10.1002/tera.1023] In 2005, a study conducted at the University of Catania was published stating that rats whose mothers had consumed 250-1000 mg/kg/day had poorer performance in the water maze and open-field tasks, rats in the 750-mg group were underweight at birth and did not catch up to the control group, and rats in the 1000 mg group did not survive pregnancy.cite journal | author=Lombardo SA, Leanza G, Meli C, Lombardo ME, Mazzone L, Vincenti I, Cioni M | title=Maternal exposure to the antiepileptic drug vigabatrin affects postnatal development in the rat | journal=Neurological Sciences | volume=26 | issue=2 | year=2005 | pages=89–94 | pmid=15995825 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=15995825&dopt=ExternalLink | doi=10.1007/s10072-005-0441-6]

There is no controlled teratology data in humans to date.

ensory

In 2003, vigabatrin was shown by Frisén and Malmgren to cause irreversible diffuse atrophy of the retinal nerve fiber layer in a retrospective study of 25 patients.cite journal | author=Frisén L, Malmgren K | title=Characterization of vigabatrin-associated optic atrophy | journal=Acta Ophthalmologica Scandinavica | volume=81 | issue=5 | year=2003 | pages=466–73 | pmid=14510793 |url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=14510793&dopt=ExternalLink | doi=10.1034/j.1600-0420.2003.00125.x] This has the most effect on the outer area (as opposed to the macular, or central area) of the retina.cite journal | author=Buncic JR, Westall CA, Panton CM, Munn JR, MacKeen LD, Logan WJ | title=Characteristic retinal atrophy with secondary "inverse" optic atrophy identifies vigabatrin toxicity in children | journal=Ophthalmology | volume=111 | issue=10 | year=2004 | pages=1935–42 | pmid=15465561 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=15465561&dopt=ExternalLink | doi=10.1016/j.ophtha.2004.03.036] Visual field defects had been reported as early as 1997 by Tom Eke and others, in the UK. Some authors, including Comaish et al believe that visual field loss and electrophysiological changes may be demonstrable in up to 50% of Vigabatrin users.

Drug interactions

A study published in 2002 found that vigabatrin causes a statistically significant increase in plasma clearance of carbamazepine.cite journal | first=Agustín | last=Sanchez-Alcaraz | coauthors = Quintana MB, Lopez E, Rodriguez I, Llopis P | title=Effect of vigabatrin on the pharmacokinetics of carbamazepine | journal=Journal of Clinical Pharmacology and Therapeutics | volume=27 | issue=6 | year=2002 | pages=427–30 | pmid=12472982 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=12472982&dopt=ExternalLink | doi=10.1046/j.1365-2710.2002.00441.x]

In 1984, Drs Rimmer and Richens at the University of Wales reported that administering vigabatrin with phenytoin lowered the serum phenytoin concentration in patients with treatment-resistant epilepsy.cite journal | author=Rimmer EM, Richens A | title=Double-blind study of gamma-vinyl GABA in patients with refractory epilepsy | journal=Lancet | volume=1 | issue=8370 | year=1984 | pages=189–90 | pmid=6141335 | doi=10.1016/S0140-6736(84)92112-3] The concentration of phenytoin falls to 23% within five weeks, according to an experiment published in 1989 by the same two scientists that tried and failed to elucidate the mechanism behind this interaction.cite journal | author=Rimmer EM, Richens A | title=Interaction between vigabatrin and phenytoin | journal=British Journal of Clinical Pharmacology | volume=27 | issue=Suppl 1 | year=1989 | pages=27S–33S | pmid=2757906]

Pharmacokinetics

With most drugs, elimination half-life is a useful predictor of dosing schedules and the time needed to reach steady state concentrations. In the case of vigabatrin, however, it has been found that the half-life of biologic activity is far longer than the elimination half-life.cite journal | author=Browne TR | title=Pharmacokinetics of antiepileptic drugs | journal=Neurology | volume=51 | issue=5 suppl 4 | year=1998 | pages=S2–7 | pmid=9818917 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=9818917&dopt=ExternalLink]

For vigabatrin, there is no range of target concentrations because researchers found no difference between the serum concentration levels of responders and those of non-responders.cite journal | author=Lindberger M, Luhr O, Johannessen SI, Larsson S, Tomson T | title=Serum concentrations and effects of gabapentin and vigabatrin: observations from a dose titration study | journal=Therapeutic Drug Monitoring | volume=25 | issue=4 | year=2003 | pages=457–62 | pmid=12883229 | url=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&list_uids=12883229&dopt=ExternalLink | doi=10.1097/00007691-200308000-00007] Instead, the duration of action is believed to be more a function of the GABA-T resynthesis rate; levels of GABA-T do not usually return to their normal state until six days after stopping the medication.

Brand names

Vigabatrin is sold as Sabril in Canada, [http://www.drugs.com/cons/Vigabatrin.html drugs.com Vigabatrin Drug Information] ] Mexico,and the United Kingdom. [http://www.nmhct.nhs.uk/pharmacy/epi5.htm Treatments for Epilepsy - Vigabatrin] Norfolk and Waveney Mental Health Partnership NHS Trust] The brand name in Denmark is Sabrilex.

References and end notes