Gabapentin
Gabapentin
is an amino acid structurally related to gamma-aminobutyric acid (GABA), the
major endogenous inhibitory neurotransmiter in the brain, and is used in the
treatment of partial seizures by combining with other anticonvulsants. It acts
by enhancing the promoted release of GABA, though the exact mechanism is
unclear. It does not interact with GABA recep-tors and it is not an inhibitor
of GABA uptake or degradation.
Gabapentin
is used as an add-on anticonvulsant agent in the treatment of refractory
partial seizures. It also appears effective in generalised seizures.
Gabapentin
is well-absorbed after oral administration and is not metabolised at all. It is
excreted unchanged in the urine.
Common
adverse effects include drowsiness, vertigo, ataxia, nystagmus, hypertension,
and fatigue. Hypertension has been reported following therapeutic doses, as
also alopecia. Serious leukopenia has been reported rarely. Impotence has
occurred following therapeutic doses. Weight gain and painful gynaecomastia
have also been reported. Abrupt cessation of gabapentin after prolonged use can
cause withdrawal (seizures or catatonia).
Therapeutic
serum levels have not been established. Some investigators report a reference
range for therapeutic gabapentin serum level of 2 to 15 mcg/ml.
Overdose
results in slurred speech, diplopia, ataxia,dizziness, somnolence, and sedation. Other effects have
included gastrointestinal effects, especially diarrhoea. Symptoms usually
resolve in 18 to 24 hours without specific therapy. Overdoses as high as 108
grams have been reported with full recovery following symptomatic therapy.
Gastric
lavage may be done if the patient is seen within 3 hours. Monitor vital signs
regularly. For mild/moderate asymp-tomatic hypertension, pharmacologic
intervention is generally not necessary. Sedative agents such as
benzodiazepines may be helpful in treating hypertension and tachycardia in
agitated patients, especially if a sympathomimetic agent is involved in the
poisoning. For hypertensive emergencies (severe hyperten-sion with evidence of
end organ injury (CNS, cardiac, renal), or emergent need to lower mean arterial
pressure within one hour, nitroprusside is preferred.
Gabapentin
can be removed by haemodialysis; however, since toxicity after acute overdose
is generally mild it is unlikely to be necessary. Haemodialysis may be
indicated by the patient’s clinical status or in patients with significant
renal impairment.
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