Gabapentin is an oral anti-epileptic agent, it is an antiepileptic drug indicated as add-on therapy for partial seizures with or without secondary generalisation in patients who have not achieved satisfactory control with, or who are intolerant to, standard anticonvulsants. Gabapentin affects chemicals and nerves in the body that are involved in the cause of seizures and some types of pain. Although its structure resembles gaba aminobutyric acid, a pain inhibitor in the central nervous system, it does not appear to have its effect through this pathway. Its actual mode of action is unknown, although it appears to bind to specific sites unevenly distributed through the brain. These sites appear to be localized to neuronal cell bodies in regions of the brain associated with excitatory amino acid input. Pain physicians began using gabapentin soon after its release as an alternative to carbamazepine, phenytoin and valproic acid, all of which are more toxic. News of its efficacy in certain neuropathic pain disorders spread rapidly.
Gabapentin is not metabolized in the liver and is thought not to interfere with most drugs. This is especially relevant with drugs such as coumadin. Gabapentin has a much lower incidence of side effects than other anti-convulsants. Its main side effect is somnolence, to which, if continued over a period of two weeks, the patient becomes tolerant. The usual dosage regimen used at our Pain Center is 100 mg to 300 mg (depending on frailty of the individual) qhs for two nights. If the patient is tolerating the medication, the dosage is increased to one tablet tid. If there is no pain relief at this dosage, the medication is increased to 600 mg tid. If no relief is experienced at this dosage, gabapentin should be discontinued. If somnolence occurs, the patient is asked to decrease the dose by 1 to 2 capsules and remain at that level for a period of up to two weeks for tolerance to occur. After this time, the dose can usually be increased without further problems. Anecdotally, we have found that if patients are going to respond they have a response usually at 300 mg bid to tid.
Gabapentin is a useful addition to our adjuvant therapy for neuropathic pain. It is used to help control some types of seizures, and must be taken continuously. This drug prevents erratic electrical discharges from traveling through the brain. Blood levels are monitored regularly to measure the amounts of Gabapentin in the body to prevent under- or over-dosing. It is used with other drugs in the treatment of some types of seizures and for the management of postherpetic neuralgia (nerve pain caused by the herpes virus or shingles). Gabapentin may also be used for purposes other than those listed in this medication guide.