Unit Code 80826:
Gabapentin, Plasma or Serum
Useful For
Monitoring serum concentration of gabapentin
Assessing compliance
Assessing signs of toxicity
Clinical Information
Gabapentin is an antiepileptic drug recently approved by the Food
and Drug Administration which is effective as add-on therapy in
treating complex partial seizures and partial seizures with secondary
generalization. Although designed as a gamma amino butyric acid
(GABA) analogue, gabapentin does not bind to GABA receptors, nor
does it affect the neuronal uptake or content of GABA; its precise
mechanism of action is not known.
Gabapentin circulates essentially unbound to serum proteins.
Unlike most antiepileptic drugs, gabapentin does not undergo
hepatic metabolism; it is eliminated almost entirely by renal excretion
with a clearance that approximates the glomerular filtration rate.
The elimination half-life is 5-7 hours in patients with normal renal
function. Because gabapentin does not bind to serum proteins and is not
metabolized by the liver, it does not exhibit pharmacokinetic inter-
actions with other antiepileptic drugs; its serum concentration is
not changed following the addition or discontinuation of other
common anticonvulsants (e.g., phenobarbital, phenytoin, carbama-
zepine, valproic acid) nor is their serum concentration altered
upon adding or discontinuing gabapentin.
Adverse effects are infrequent and usually resolve with continued
treatment. The most common side effects include somnolence,
dizziness, ataxia, and fatigue. Experience to date indicates that gabapentin
is safe and relatively nontoxic.
Reference Values
2.0-12.0 ug/mL
Diminished therapeutic efficacy may occur at
serum concentrations <2.0 ug/mL.
Interpretation
A therapeutic range and toxic level have not been established for
gabapentin.
Serum concentrations <2.0 ug/mL are associated with a significant
decrease in therapeutic efficacy.
Patients with normal renal function receiving doses within the
recommended range will usually attain steady-state gabapentin
concentrations between 2.0-12.0 ug/mL.
Some patients require high doses to achieve response, resulting in
concentrations as high as 80 ug/mL. Dosage reduction should be
based on signs of toxicity, not the serum concentration.
Cautions
No significant cautionary statements.
Clinical Reference
Goa KL, Sorkin EM: Gabapentin: A review of its pharmacological
properties and clinical potential in epilepsy. Drugs 46:409-427,
1993
Hengy H, Ernst-Ulrich K: Determination of gabapentin in plasma
and urine by high performance liquid chromatography and pre-column
labeling for ultraviolet detection. J Chromatog 341:473-478, 1985
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