Duogab™

[Gabapentin]

Duogab

Active Ingredients

  • DUOGABTM 100: Each capsule contains Gabapentin 100mg
  • DUOGABTM 300: Each capsule contains Gabapentin 300mg
  • DUOGABTM 400: Each capsule contains Gabapentin 400mg

    Description / Properties

    Pharmacological Action

    Mechanism of Action: Gabapentin is related to the neurotransmitter GABA (gamma-aminobutyricacid). Gabapentin has proven affinity for special site in brain tissues such as neocortex and hippocampus. Though exact mechanism of its CNS depressant and anticonvulsant activity is not fully understood, it is thought to be active through peptide-binding sites (receptors).

    Pharmacokinetics and Metabolism

    Absorption: Gabapentin achieves peak plasma concentration within 2 – 3 hours absolute bioavailability of 300 and 400mg Gabapentin approximately 55%. Pharmacokinetics of Gabapentin is not affected by food. With increased dose of Gabapentin, excess drug is excreted and absorption decrease. Absolute bioavailability following doses of 300 and 600mg DUOGAB is 57% and 42%, respectively. Elimination half-life is 5- 7 hours in normal subjects.

    Distribution

    Gabapentin is not bound to plasma proteins and has an apparent volume distribution of 57.7 litres. In patients with epilepsy, its concentrations in CSF ranged from 8-34% of corresponding steady-state trough plasma concentrations.

    Excretion

    Gabapentin elimination rate, plasma clearance and half-life are dependent on creatinine clearance as it is exclusively removed by renal excretion. Its metabolism is not affected by liver enzyme system.

    Elderly

    Due to age related deterioration in renal functions in elderly patients (>60), there will be decrease in Gabapentin plasma clearance and increase in elimination half-life. Its excretion will be directly proportional to creatinine clearance. Gabapentin can be removed from plasma by haemodialysis.

    Indications

    There are many evolving indications of Gabapentin under trial. Its main indications are for the treatment of neuropathic pain and epilepsy. 1) Neuropathic Pain: Neuropathic pain is pain due to diseases involving the nervous system. Variety of different diseases such as diabetes, shingles, nerve injury and other diseases affecting nervous system cause it. DUOGAB is effective in various types of neuropathic pain.

    DUOGAB is recommended in neuropathic pain of: a) Peripheral Diabetic Neuropathies, b) Trigeminal Neuralgia, c) Post herpetic neuralgia (Shingles)

    2) Epilepsy: DUOGAB is used to treat various forms of epilepsy. It is effective as adjunctive therapy with other anti-epileptic drugs in patients who have shown no or poor response in achieving seizure control DUOGAB is effective in controlling both simple and complex partial seizures with or without secondarily generalized tonic clonic seizures. DUOGAB (Gabapentin) studies are in progress to establish its efficacy in the treatment of restless leg syndrome, depression, maniac disorders, unspecified headache and migraine.

    Contraindication

    DUOGAB is contra-indicated in patients who are hypersensitive to Gabapentin. Enough data is not available for its safety in children, during pregnancy and lactation. Caution should be exercised in renal compromised patients

    Drug Interactions

    There are no interactions with other anti-epileptics such as phenobarbitone, phenytoin & valproic acid. DUOGAB steady-state pharmacokinetics are similar for healthy subjects and patients with epilepsy receiving anti-epileptic agents. Concurrent administration of Gabapentin with oral contraceptives containing norethindron and/or ethinyl estradiol, does not influence the overall pharmacokinetics of either component. Antacid containing magnesium and aluminium reduces Gabapentin’s bioavailability almost by 24%. It is recommended that Gabapentin be taken about two hours following antacid administration. Renal excretion of Gabapentin is unaltered by probenecid. A slight decrease in renal excretion of Gabapentin observed when it is co-administered with cimetidine is not expected to be of clinical importance.

    Side Effects

    In addition to the commonly occurring events (somnolence, dizziness, ataxia, headache, nystagmus, tremor, fatigue, diplopia, nausea and/or vomiting and rhinitis), following table depicts the events that occurred in descending order of frequency against different body systems.

    There are reports of 8 sudden and unexplained deaths in a cohort of 2203 patients treated with Gabapentin. However the incidence of 0.0038 deaths per patient year with Gabapentin is not much different from 0.0005 to 0.003 in a similar population of patients with epilepsy. Additional post-marketing adverse events reported include pancreatitis, erythema multiforme, Stevens-Johnson syndrome and elevated liver enzymes.

    Warning and Precautions

    Usage in Pregnancy As the animal studies does not establishes clear cut guideline for its safe use in pregnancy, this drug should be used in pregnancy only if the potential benefits to the patient justifies the potential risk to the fetus.

    Usage in Nursing Mothers

    In nursing mother, decision of continuing Gabapentin Should be made taking into account the importance of the drug to the mother.

    General

    Sudden and abrupt withdrawal of Gabapentin in epileptic patients should be avoided as it may precipitate status epilepticus. This should be done gradually over a period of one week. Patients driving, operating machinery or performing any hazardous tasks should take special care.

    Known Symptoms of Overdosage and Particulars of its Treatment

    No specific information is available on the treatment of overdose with Gabapentin, although haemodialysis has been shown to be effective in eliminating Gabapentin. Treatment is symptomatic and supportive, consistent with established medical care. Overdoses of Gabapentin up to 49 g ingested at one time have been reported in four people, all of whom recovered fully. Symptoms of overdose included dizziness, double vision, slurred speech, drowsiness, lethargy and mild diarrhoea. In patients with renal impairment haemodialysis may be indicated. Reduced absorption of Gabapentin at higher doses may limit drug absorption and hence minimize toxicity at the time of overdosing.

    Dosage

    1. Adult & children over 12 years: Usual effective dose: 900-1800mg/day in 2-3 divided doses. Care should be taken to avoid a period of more than 12 hour between two doses. In certain patients, such as elderly patients, it may be preferable to up titrate the dose up to an effective level. A suggested schedule is to start with 100 mg at night and increase with 100 mg per day up to 600 mg in 2 -3 divided doses. Further increase can be made depending on patients' response. 2. Pediatric use: Safety and effectiveness of Gabapentin in children under 12 years have not been established. However, physicians can decide to prescribe taking into account the necessity and safety issues. 3. Elderly: When prescribing Gabapentin to elderly patients (> 65 years), careful monitoring should be carried out for adverse events. Older patient may require dosage adjustment depending on their baseline renal functions (creatinine clearance). 4. Compromised renal function: Patients with impaired renal function should be prescribed with caution depending upon the state of their creatinine clearance as elimination of DUOGAB is decreased in patients with impaired renal function.

    Renal Function

    In patients with Haemodialysis, loading dose of 300-400 mg with maintenance dose of 200-300 mg after four hours of each dialysis session.

    • DUOGAB can be used as concomitant therapy with Phenobarbital, phenytoin, valproic acid and carbamazepine without concern for alteration of the plasma concentrations or serum concentrations of Gabapentin or the other anti-epileptic agents. • While discontinuing DUOGAB, a slow process should be adopted. Likewise, addition of an alternate medication should be incremental.

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