Abstract
The objective of the study was to establish bioequivalence between a local generic against the innovator product of gabapentin 300 mg. The study design was a standard two-way crossover, open-label, randomised and single dose study in 24 healthy male volunteers under fasting condition. The washout period was 7 days between both periods to allow adequate drug elimination. Liquid chromatography tandem mass spectrometry was utilised to determine gabapentin concentration in plasma. Non-compartmental model was used to analyse Tmax, Cmax, AUC0-t, AUC0-∞, t1/2 and ke. Potential adverse events were closely monitored and recorded throughout the study. The study found all pharmacokinetic parameters were within the bioequivalence limit of 80.00%-125.00%, with minimum side effects. In conclusion, the generic product was bioequivalent to the innovator product.
Highlights
Gabapentin (1-(aminomethyl)cyclohexaneacetic acid) is licensed for use in Malaysia as adjunct therapy to intractable partial epilepsy and treatment for neuropathic pain [1]
Gabapentin is a chemical analogue to gamma-aminobutyric acid (GABA) but it does not interact with GABA receptors nor does it interfere with GABA metabolism [2]
Instead it is found that gabapentin is a ligand to the α2δ subunit of the voltage-gated calcium channel, where it acts by disrupting calcium channel trafficking thereby blocking new synapse formation [3]
Summary
Gabapentin (1-(aminomethyl)cyclohexaneacetic acid) is licensed for use in Malaysia as adjunct therapy to intractable partial epilepsy and treatment for neuropathic pain [1]. Plasma concentration of gabapentin does not show proportionality with the dose ingested [4]. This is mainly due to the saturable absorption pathway of gabapentin, namely a zero-order pharmacokinetic process [5,6]. Gabapentin does not bind to plasma protein [7] and it is not metabolized in humans [8]. Gabapentin exhibit zero-order absorption pharmacokinetic, and poor oral bioavailability (absolute bioavailability varies from 60% to 33% with increasing dose from 900 to 3600 mg daily) [7]. The peak plasma concentration of gabapentin is reached within 2 to 3 hours after ingestion of an immediate-release formulation [9] whereby administration with food does not appreciably affect the absorption. Gabapentin has an elimination half-life of 5 to 7 hours [9]
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