Abstract
Aim: We aimed to develop methods to determine gabapentin (GAB) in biological samples using high-performance liquid chromatography (HPLC) with application in pharmacokinetics and therapeutic drug monitoring. Methods: Simple, rapid and efficient HPLC-UV methods to quantify GAB in human plasma and urine were developed and validated for clinical analysis of GAB. The 1-fluoro-2,4-dinitrobenzene (FDNB) was used as derivatization agent. For plasma samples, protein precipitation using acetonitrile was performed, before the derivatization reaction. Urine samples were cleaned-up by liquid-liquid extraction with dichloromethane:n-butanol (1:1, v/v) after derivatized. Amlodipine besilate was used as internal standard (IS). Results: Gabapentin and IS were resolved on LiChrospher® C18 RP column and a mixture of 50 mM sodium phosphate buffer (pH 3.9):methanol (27:73, v/v) as mobile phase, at 1.2 mL/min. The methods used small sample volumes, 100 and 50 μL of plasma and urine, respectively. Linearity was obtained in the interval of 0.2-14 μg/mL in plasma and 2-120 μg/mL in urine. Both methods showed to be selective, without carry-over effect, precise, accurate and stable in different conditions. GAB plasma concentration in patients receiving 600 to 3600 mg/day of GAB ranged between 0.40 to 11.94 μg/mL at steady-state. Conclusions: The methods described in this study were simple, rapid and fulfill all validation requirements. They were easily and successfully applied for population pharmacokinetics and therapeutic drug monitoring of GAB in patients with chronic pain.
Highlights
Pain is considered a public health problem[1]
This study aimed to develop and validate simple, rapid and efficient bioanalytical methods using small sample volume to quantify GAB in human plasma and urine by high-performance liquid chromatography (HPLC)-UV with appropriate concentrations range to use in clinical analysis of GAB in patients with chronic pain
Linearity was obtained between 0.2-14 μg/mL plasma (y=0.07957x-0.00605, r2=0.99257) and 2-120 μg/mL urine (y=0.01088x-0.00415, r2=0.99741) concentrations using the weighting 1/x2
Summary
In 2019, around 20% of adults reported chronic pain in the past 3 months in the U.S, according to the National Health Interview Survey[2]. In the Brazilian population the prevalence of chronic pain varied between 29.3 to 73.3%3. The number of people affected by neuropathic pain should increase even more due to the increase of elderly population, diabetes incidence and higher survival from cancer[4]. In the context of drugs to treat neuropathic pain, TDM can be a tool to monitor patient adherence, to help physicians decide the best treatment for the patient and to avoid unnecessary opioid prescription. Opioids are the third-line treatment for neuropathic pain, but show high risk of addiction[5,10]
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