Used as either monotherapy or adjunctive therapy in focal seizures. Not commonly used in primary generalised seizures.
Also widely used to treat peripheral neuropathic pain and Gabapentin is used occasionally as migraine prophylaxis.
Contraindications
There are no complete contraindications to Gabapentin, other than hypersensitivity to the drug.
Caution
Caution must be given to the elderly, diabetic patients, and those with a history of psychotic illnesses.
Cases of misuse, abuse and dependence have been reported. Caution should be exercised in patients with a history of substance abuse and the patient should be monitored for symptoms of gabapentin misuse, abuse or dependence (development of tolerance, dose escalation, drug-seeking behaviour have been reported).
The precise mechanism of Gabapentin is unknown. The drug has a very similar chemical structure to that of GABA - a neurotransmitter which has valuable inhibitory effects on neurones. The original thought was that Gabapentin acts as a GABA agonist, and therefore increases the amount of GABA in the CNS, preventing neurones from "firing" in seizures.
However the main mechanism of action seems to be by blocking T-type calcium channels and inhibiting other modulators and neurotransmitters.
Oral.
Gabapentin has a slightly better side-effect profile than other anti-epileptics such as carbamazepine and phenytoin. However there are a number of side-effects which patients may experience.
These can include:
- Nausea, vomiting & diarrhoea
- Abdominal pain & constipation
- Hypertension
- Headache
- Ataxia
Gabapentin has also been associated with mood changes and depression. There are a number of cases linking the use of Gabapentin to suicidal tendencies, and whilst these are probably very rare, this should always be considered when prescribing the drug. It is for this reason that Gabapentin should be given with caution to patients who have previous psychiatric illness.
Compared with other anti-epileptic drugs, Gabapentin has a very favourable profile when it comes to drug interactions. Whilst a small percentage is metabolised via the cytochrome P450 system, the majority of the drug is not metabolised, and it has been documented as having no serious interactions with other drugs.
See Anti-Epileptic Therapy.
A small fraction of Gabapentin is metabolised in the liver via the cytochrome P450 system, but the majority is not metabolised at all - the main reason for its low side-effect profile.
