Introduction

The IUPAC name of pregabalin is given as (S)-3-(aminomethyl)-5-methylhexanoic acid (Fig. 01). Pregabalin is a potent ligand for alpha- 2-delta subunit of voltage gated calcium channel in the central nervous system which shows analgesic, anticonvulsant & anxiolytic activity [1]. It is a structural analog of, but functionally dissimilar to naturally occurring transmitter GABA (Gamma aminobyuteric acid). It is generally used for the epilepsy, neuropathic pain and anxiety condition. It is soluble in aqueous solution and partially soluble in nonpolar solvent like DMSO, ethanol, DMF. It is acrystalline substance which is occur in single morphic form & it is nonhygroscopic It is thermally stable and not solvated.The molecular weight of pregabalin is 159.23g/mol and has the melting point at 186-188ºC. The compound has one stereogenic center [10].

Figure1: Structure of pregabalin

Mechanism of action

Pregabalin shows high affinity binding to the α2δ subunit of P/Q type of voltage gated channel. The voltage gated calcium channel are closed to resting membrane potential, the depolarization by action potential causes channel to open which leads the entry of Ca2+into the cell. Axonal membrane depolarizes when the action potential travels down to the neuron. When voltage gated calcium channel opens which cause intrinsic current, Neurotransmitters release from synaptic vesicle and multiplication of neurotransmission. In the presence of Ca2+exocytosis of neurotransmitter and membrane fusion occurs.`

Figure 2: Voltage-gated calcium channel

Pregabalin target the voltage-gated calcium channel which consists of four subunit. (Fig No.2)The α1 subunit is transmembrane array forms a pores through which Ca2+ enters into cell. The α2δ subunit contains δ protein linked by a disulphide bond to α2 protein. Which have high affinity to pregabalin binding site. The β subunit is intracellular & it modifies the functioning of α2δ subunit. While the γ subunit is a glycoprotein which inline in cell membrane. [4,5]

Figure 3: Mechanism of action of pregabalin.

Pragabalin pharmacokinetics

Pragabalin is quickly absorbs and shows linear pharmacokinetics after oral administration. Its oral bioavailability is ≥90% peak plasma concentration arises 1hr after oral administration& constant concentration achieve within 24-48 hrs. 20-25% peck plasma level decreases by the food intake & increase time to peak level by 3 hours. [6,8]. This studies includes the single dose and multi dose tolerance studies. [5] Pregabalin has comparatively short half-life which has volume of distribution 0.5L/kg which does not bind to plasma protein. Pharmacokinetic investigation of clinical studies shows that pharmacokinetics PGB were not significantly influence by sex or race.[6,8]

Adsorption

Pregabalin is fastly and widely absorbed after oral administration in the fasted state which shows maximum plasma concentration after 1hr in single or multiple doses and steady state being obtained within 24-48hr after repeated dosing [3]. These fast absorption properties reflect observed onset of efficacy as soon as weak one in clinical trialsperformed in patient with partial epilepsy.

Distribution, metabolism and elimination

Pregabalin is substrate of the system L carrier which is capable for the transport of large amino acid across the brain and gut. Coherent with this pregabalin can speedily cross the blood brain barrier conducted in mice during the preclinical studies which is obvious advantage for a drug that increases the CNS activity. Pregablin goes through negligible metabolism in the humans (<2%) and is excreted nearly unaffected by the kidney. Pregabalin could not bind to the plasma protein. [3]. It also not inflicts to hepatic metabolism and does not cross or restrict enzymes like cytochrome P450 system. That’s why pregabalin is improbable to cause or subject to pharmacokinetic drug-drug intraction and the anticipation that has been proved in clinical pharmacokinetic studies [9].

Analytical Accounts on Pregabalin

The widespread literature survey exposed multiple analytical techniques like UV spectrophotometry method, HPLC, HPTLC, LC-MS/MS, for the determination of pregabalin in bulk and pharmaceutical formulation. These reported method describe the evaluation of PGB in various dosage form in single constituent and in combination with gabapentin, MCA, paracetamol, methylcobalamine, mecobalamin, vigabatrin, sildenafil, amitriptyline spectracles different analytical method carry out for estimation of pregabalin.

Spectrophotometric method

Till the date numerous spectroscopic method have been accounted for the determination of pregabalin sole and in combination. This review complies the 10 papers describing spectrophotometric method for estimation of pregabalin and 2 papers for the same in combination. Table1 consist of spectrophotometric method for pregabalin and Table 2 consist of spectrophotometric method for pregabalin in combination.

Santosh G. S.et al.It can be used for the routine quality control analysis of pregabalin in bulk and pharmaceutical formulation which gives the accurate & precise method. The reportated method involves the calculation of absorbance at 210nm [11].

ARMAGAN, Onalconveyed a modest spectrophotometric scheme for estimation of pregabalin in pharmaceutical preparations. It will be determine by the three method among them first two methods were the PGB acts as n-electron donor with the DDQ and TCNQ as п acceptors which gives extremely colored compound. These compounds were determined at 494 & 841nm. The third process based on cooperation of ninhydrin with primary amine. From the three reagents TCNQ is more preferable then other two reagents based on higher molar absorptivity and lower detection limit [12].

Armagan onal, olcay sagirli The estimation of pregabalin in bulk and pharmaceutical preparation by the spectrophotometric and spectrofluorometric method pregabalin is primary amine compound which alloy which act with 7-chloro-4-nitrobenzofurazon which is extremely sensitive fluorogenic and chromogenic indicator used in many analysis. This method is relevant for routine quality control of bulk & pharmaceutical preparations without intrusion of excipients which predict to present in formulation. Spectrofluorometric method shows the higher sensitivity [13].

Rajinder Singh GujralSettled a spectrophotometric scheme for the analysis of pregablin in pure, marketed formulations and human urine sample. This process was based on reaction of drug with the blend of potassium iodate and potassium iodide. In addition this method has larger linear dynamic extent with excellent accuracy and precision. It may assist in determining influence of this drug on human being meanwhile the treatment [14]

Kaur NavneetFrom the research it is discover that the IUPAC name of pregabalin does not contain chromophoric group but it is necessary to have the chromophoric group in the structure to be UV sensitive that’s why the main objective of this research paper is to add the chromophoric group in the pregabalin structure. Which is accomplish by changing the primary amine group of pregabalin in UV sensitive product through reaction with benzyl chloride. It is concluded that throughbenzoylationmethod gives UV sensitive derivative of PGB [16]

436. D. PatelOutline a spectrophotometric scheme for simultaneous estimation of multicomponent dosage form which include PGB, Methylcobalmin& alpha lipoic acid by using water as solvent system. Analysis was performed at wavelength of 436.2, 307.3, 383nm. The co-efficient co- relation found to be 99.5% for PGB, 99.56% for MCA and 99.61% ALA [20]

 Table No1: spectrophotometric method for analysis of Pregabalin

Table No 2: Spectrophotometric for analysis of pregabalin in combination

Chromatographic overview

Apart from methods many HPLC method have been reported the determination of pregabalin in alone and in combination. In current review, a sum of 8 papers for estimation of pregabalin in sole are presented, while total sum of 7 are presented for estimation of PGB in combination are presented. The summary of reported HPLC method particularizing the mobile phase used for determination, sample matrix, λmax and linearity for PGB alone is shown in Table no. 3. While the summary of the reported HPLC method for PGB in combination is shown in table no.4.

Rajinder Singh Gujral prostrated an RP-HPLC method for the assessment of pregabalin (PGB) from bulk drug and pharmaceutical formulation. Author spent a hypersil C18 column (250mm × 4.6mm) by isocratic elusion. Mobile phase system is blend of methanol: acetonitrile: potassium hydrogen orthophosphate (3:1:16v/v/v). The main benefit of this method involve short retention time, without depletion with other reagent, stability of solvent, no requirement for the earlier separation and purification. The less chromatographic time create this method appropriate for the processing of numerous sample in definite period of time. This process can also be employ for determination of unabsorbed PGB in urine sample by very easy, cost efficient, quick and effective method. [22].

4. S. Nagaraju Outlines a reverse phase HPLC scheme for evaluation of pregabalinin tablet dosage form.The mobile phase contain methanol: ammonium acetate (50:50v/v). By using phenomenex C18 column (150 × 4.6mm).The affect of acid, alkaline, photolytic stress, oxidative stress condition on PGB analyse. [23].

Reza AhmadkhanihaIn this analysis stable HPLC scheme for estimation of pregabalin in human plasma is develop. From the analysis it is concluded that the method is based on the derivatization of PGB with FDED in alkaline solution. The colored product can be found by UV detector at less concentration. From the literature review, the estimation of PGB by plasma shows that the best limit of detection was found to be 0.13μg/ml. [26].

4. A. Mohansettled a RP-HPLC scheme for the concurrent estimation of pregabalin (PGB), mecobalamin, alpha lipoic acid (ALA) in capsule. Consuming an Enable make C18 column (250 × 4.6mm) as static phase and potassium dihydrogen orthophosphate buffer(balanced to pH 6 by utilizing NAOH solvent): acetonitrile: methanol (75:10:15v/v/v) as a mobile phase. The RSD value was found to be 0.84% for PGB, 1.07% for both mecobalamin and ALA.[32].

BostjanMartincsettled an analytical method for simultaneous estimation of four second generation antiepileptic drugs which include pregabalin (PGB), Gabapentin (GBP), Vigabatrin (VGB), Topiramate (TOP). Analytes were elicit from blood plasma by the help of extensive solid phase extraction derivatized with 4-chloro-7-nitrobenzofurazan and detection of HPLCwith florescence detection. The scheme is confirm acceptable for all four analytes and relevant for daily use [37].

Table No3: HPLC method for analysis of pregabalin

Table No 4: HPLC method for analysis of pregabalin in combination

Hptlc Method

1. B. PatilThe concurrent determination pf pregabalin and aceclofenac stability indicating method in pure and formulation. Chromatographic departure was carry out on aluminium plate smear with silica gel 60 F254 and the mobile phase was selected as toluene: methanol: formic acid (7:3:0.2v/v/v). This method all parameters were meets with the acceptable standards.[39]

Sunil More The discriminating, accurate high performance liquid chromatographic scheme for concurrent estimation of pregabalin and amitriptyline hydrochloride with densitometry in pharmaceutical preparations. The silica gel 60F254 is used as static phase and for the mobile phase toluene, methanol and formic acid (7:2.5:0.5v/v/v) is used. This scheme conclude that the establish method have many benefits like less cost consuming, relatively fast, stable, distinct, easily reproducible.[40]

Table 5: HPTLC methods for analysis of pregabalin in combination

LC-MS/MS

LC-MS is the adaptable analytical tool which blends liquid chromatography resolving strength with mass spectrometry detection specificity. Sample compounds are isolated by liquid chromatography and then added to mass spectrometer. The mass spectrometer generate the charge ions which then tracked. The estimation of pregablin in alone and in combination is shown in table no. 6 & 7which includes different parameters like stationary phase, mobile phase, detector, internal standard etc.

1. Kosticthis research paper includes determination of pregablin by novel LC-MS method in the dried matrix sport (DMS). The appealing method of sample accumulation in micro quantity was utilized in the form of dried blood sport (DBS) and dried plasma sport(DPS) followed by pre-column derivatization method. From the analysis it is concluded that the DPS is certainly can become appropriate component for all parameters using plasma matrix. Nevertheless the potential deracination of plasma by DBS depend on overcoming hematocrit issue. [43]

Pawel DzygielA simple, accurate, delicate method for simultaneous determination of pregabalin, sildenafil and active desmethyl metabolite of sildenafil. This method can be concurrently estimate by tree analyte within the in vivo concentration ranges in rat plasma. It utilizes solid-phase elicitation pursue by HPLC conjoin with mass spectrometry. It gives accuracy and precision over dyanamic ranges. [49]

Table 6: LC-MS/MS methods for analysis of pregabalinin combination

Conclusion

The present review elaborate various analytical approaches exercised for the appraisal of pregabalin. Numerous investigation has been performed including HPLC, HPTLC, UV-spectrometry, LC-MS/MS, GC-MS, UPLC-MS/MS etc. for the estimation of PGB in bulk drug, pharmaceutical preparations & in plasma. Further method were reported for its pharmacokinetic as well as bioequivalence studies. Few chromatography methodologies like HPLC, Stability indicating HPLC, HPTLC are also reported in literature.

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