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Tiagabine Hcl (Monohydrate or Ahydrous)

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(Antiepilepsy Drug)

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CAS No: 115103-54-3

GABITRIL (tiagabine HCl) is an antiepilepsy drug available as 2 mg, 4 mg, 12 mg, and 16 mg tablets for oral administration. Its chemical name is (-)-(R)-1-[4,4-Bis(3-methyl-2-thienyl)-3-butenyl]nipecotic acid hydrochloride, its molecular formula is C 20 H 25 NO 2 S 2 HCl, and its molecular weight is 412.0. Tiagabine HCl is a white to off-white, odorless, crystalline powder. It is insoluble in heptane, sparingly soluble in water, and soluble in aqueous base.

The structural formula is:

Formula: C20H25NO2S2.HCL

GABITRIL tablets contain the following inactive ingredients: Ascorbic acid , colloidal silicon dioxide, crospovidone, hydrogenated vegetable oil wax, hydroxypropyl cellulose, hypromellose, lactose, magnesium stearate, microcrystalline cellulose, pregelatinized starch, stearic acid, and titanium dioxide.

Technology discussion:

How to Separate the S(+) and R(-)-enantiomers of tiagabine.HCl and its two chiral precursors by chiral chromatography: application to chiral inversion studies. Following is the detail.

Chiral HPLC methods were developed and validated for tiagabine.HCl and its two chiral precursors to determine the chiral purity of the three compounds to ensure the quality of the final product which is used as a new antiepileptic drug. Tiagabine.HCl was derivatized with 1-napthalenemethylamine and was chromatographed on a Pirkle type phenyl glycine column with a mobile phase of 69:31, 0.1 M ammonium acetateacetonitrile (v/v). The two chiral precursors were chromatographed on a Chiralcel-OG column with a mobile phase of hexane, isopropanol etc. Each of the three HPLC methods have a selectivity factor (@a) of 1-2 or higher. The validation of the methods was done by conducting standard addition and recovery studies of the S(+)-enantiomers in the samples. The %RSD of all three methods were <5 with a limit of quantification of 0.05% (peak area) or lower. By using these methods, a study was conducted to investigate the effect of pH, temperature, and trace levels of transition metals such as Fe^3^+, Co^2^+, and Ni^2^+ on the conversion of R(-)-enantiomer to the S(+)-enantiomer of tiagabine.HCl and its two chiral precursors. The results of this study demonstrated that the two chiral precursors of tiagabine.HCl under reflux conditions are more sensitive to chiral inversion than tiagabine.HCl. Under reflux conditions, in the presence of trace metal ions and different pH, approximately 10, 11, and 1% of the R(-)-enantiomer was converted to the S(+)-enantiomer for ethyl nipecotate, ethylester of tiagabine, and tiagabine.HCl, respectively. However, at room temperature, tiagabine.HCl appears to be less chirally stable than its two chiral precursors. Approximately 0.4% R(-)-enantiomer of tiagabine.HCl was converted to the S(+)-enantiomer at room temperature and acidic conditions. Under similar conditions, the S(+)-enantiomer of ethyl nipecotate and ethylester of tiagabine.HCl was <0.05%. The initial S(+)-enantiomer content for all three compounds was <0.1%.

About Tiagabine Hcl

What is tiagabine?

The exact way that tiagabine works is unknown. However, it is believed that it alters chemical impulses in the brain that cause seizures.
Tiagabine is used to control seizures.
Tiagabine may also be used for purposes other than those listed in this medication guide.

DRUG ABUSE AND DEPENDENCE

The abuse and dependence potential of GABITRIL have not been evaluated in human studies.

OVERDOSAGE

Human Overdose Experience: Human experience of acute overdose with GABITRIL is limited. Eleven patients in clinical trials took single doses of GABITRIL up to 800 mg. All patients fully recovered, usually within one day. The most common symptoms reported after overdose included somnolence, impaired consciousness, agitation, confusion, speech difficulty, hostility, depression, weakness, and myoclonus. One patient who ingested a single dose of 400 mg experienced generalized tonic-clonic status epilepticus, which responded to intravenous phenobarbital.

From post-marketing experience, there have been no reports of fatal overdoses involving GABITRIL alone (doses up to 720 mg), although a number of patients required intubation and ventilatory support as part of the management of their status epilepticus. Overdoses involving multiple drugs, including GABITRIL, have resulted in fatal outcomes. Symptoms most often accompanying GABITRIL overdose, alone or in combination with other drugs, have included: seizures including status epilepticus in patients with and without underlying seizure disorders, nonconvulsive status epilepticus, coma, ataxia, confusion, somnolence, drowsiness, impaired speech, agitation, lethargy, myoclonus, spike wave stupor, tremors, disorientation, vomiting, hostility, and temporary paralysis. Respiratory depression was seen in a number of patients, including children, in the context of seizures.

Management of Overdose: There is no specific antidote for overdose with GABITRIL. If indicated, elimination of unabsorbed drug should be achieved by emesis or gastric lavage; usual precautions should be observed to maintain the airway. General supportive care of the patient is indicated including monitoring of vital signs and observation of clinical status of the patient. Since tiagabine is mostly metabolized by the liver and is highly protein bound, dialysis is unlikely to be beneficial. A Certified Poison Control Center should be consulted for up to date information on the management of overdose with GABITRIL.

What should I avoid while taking tiagabine?

Tiagabine may cause drowsiness, dizziness, decreased concentration, vision problems, or poor coordination. Do not drive, operate dangerous machinery, or perform other hazardous activities until you know how tiagabine affects you. If you experience drowsiness, dizziness, decreased concentration, vision problems, or poor coordination, avoid these activities.
Do not drink alcohol while taking tiagabine. Alcohol may increase drowsiness or dizziness caused by tiagabine. Alcohol may also increase the risk of seizures.

DOSAGE AND ADMINISTRATION

General:

The blood level of tiagabine obtained after a given dose depends on whether the patient also is receiving a drug that induces the metabolism of tiagabine. The presence of an inducer means that the attained blood level will be substantially reduced. Dosing should take the presence of concomitant medications into account.

GABITRIL (tiagabine HCl) is recommended as adjunctive therapy for the treatment of partial seizures in patients 12 years and older.

The following dosing recommendations apply to all patients taking GABITRIL:

Induced Adults and Adolescents 12 Years or Older: The dosing recommendations apply to patients who are already taking enzyme-inducing antiepilepsy drugs (AEDs) (e.g., carbamazepine, phenytoin, primidone, and phenobarbital). Such patients are considered induced patients when administering GABITRIL.

In adolescents 12 to 18 years old, GABITRIL should be initiated at 4 mg once daily. Modification of concomitant antiepilepsy drugs is not necessary, unless clinically indicated. The total daily dose of GABITRIL may be increased by 4 mg at the beginning of Week 2. Thereafter, the total daily dose may be increased by 4 to 8 mg at weekly intervals until clinical response is achieved or up to 32 mg/day. The total daily dose should be given in divided doses two to four times daily. Doses above 32 mg/day have been tolerated in a small number of adolescent patients for a relatively short duration.

In adults, GABITRIL should be initiated at 4 mg once daily. Modification of concomitant antiepilepsy drugs is not necessary, unless clinically indicated. The total daily dose of GABITRIL may be increased by 4 to 8 mg at weekly intervals until clinical response is achieved or, up to 56 mg/day. The total daily dose should be given in divided doses two to four times daily. Doses above 56 mg/day have not been systematically evaluated in adequate and well-controlled clinical trials.

What are the possible side effects of tiagabine?

If you experience any of the following serious side effects, stop taking tiagabine and seek emergency medical attention or contact your doctor immediately:
, an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);
, increasing frequency or worsening of seizures;
, irregular back-and-forth movements of the eyes (nystagmus);
, weakness; or
, rash.
Other, less serious side effects may be more likely to occur. Continue to take tiagabine and talk to your doctor if you experience
, dizziness, poor coordination, or drowsiness;
, nausea and vomiting;
, agitation or nervousness; or
, tremor.
Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.


What other drugs will affect tiagabine?

Tiagabine interacts with many of the other drugs used to treat seizures. Before taking tiagabine, tell your doctor about all other medications you are taking. You may require a dosage adjustment or special monitoring during treatment if you are taking a combination of medications to treat seizures. Continue to take all medications prescribed to treat seizures exactly as directed.
Tiagabine may increase the effects of other drugs that cause drowsiness, including antidepressants, alcohol, antihistamines, sedatives (used to treat insomnia), pain relievers, anxiety medicines, and muscle relaxants. Do not take other medications that may increase drowsiness without first talking to your doctor.
Drugs other than those listed here may also interact with tiagabine or affect your condition. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including herbal products.