Spectrofluorimetric determination of certain antidepressant drugs in human plasma
© Omar et al.; licensee Springer. 2013
Received: 13 March 2013
Accepted: 14 March 2013
Published: 18 April 2013
Certain antidepressant drugs namely Sertraline hydrochloride, Fluoxetine hydrochloride, Paroxetine hydrochloride, Thioridazine hydrochloride and Amineptine hydrochloride were studied throughout this work using spectrofluorimetric method.
The spectrofluorimetric method is based on the charge-transfer reaction of these drugs as n-electron donors with 7,7,8,8-tetracyanoquinodimethane (TCNQ) as π-electron acceptor. The drug-TCNQ complexes showed excitation maxima ranged from 290-301 nm and emission maxima ranged from 443-460 nm.
Results and discussion
The different experimental parameters affecting the formation and stability of the complexes were carefully studied and optimized. The calibration plots were constructed over the range of 50-450 ng mL-1 for Fluoxetine and Sertraline, 50-550 ng mL-1 for Paroxetine, 50-650 ng mL-1 for Thioridazine and 50-750 ng mL-1 for Amineptine. The proposed method was validated according to ICH and USP guidelines with respect to specificity, linearity, accuracy, precision and robustness.
A simple, reliable, sensitive and selective spectrofluorimetric method has been developed for determination of certain antidepressant. The proposed method was successfully applied to the analysis of the cited drugs in dosage forms. The high sensitivity of the proposed method allows determination of investigated drugs in spiked and real human plasma.
Structural formula of the studied drugs
(1S,4S)-4 [3,4-dichlorophenyl]- 1,2,3,4 tetrahydro-N-methyl-1-naphthylamine
(3S, 4R)-3-[(1,3-Benzodioxol-5-yloxy)methyl]-4-(4-fluorophenyl) piperidine hydrochloride
(3RS)-N-methyl-3-phenyl-3-[4-(trifluoromethyl) phenoxy] propane-1-amine hydrochloride
10-[2-(1-methylpiperidin-2-yl) ethyl] -2-methylsulfanyl-phenothiazine hydrochloride.
dihydro-IO,1 I-dibenzo[a,&ycloheptenyl-5-amino-7-heptanoic acid
The wide use of these drugs necessitates the development of simple, accurate, sensitive, applicable and cheaper method for their determination in pure forms, pharmaceutical formulations, spiked and real human plasma. So this study describes a simple and very sensitive spectrofluorimetric method for determination of these drugs depending on the formation of charge-transfer complexes.
Experimental and Methods
A perkin Elmer LS 45 Luminescence spectrometer (United Kingdom) connected to an IBM PC computer loaded with FL WINLABTM software.
SpectronicTM GenesysTM 2PC. Ultraviolet/Visible spectrophotometer (Milton Roy Co, USA) with matched 1 cm quartz cell connected to IBM computer loaded with winspecTM application software.
Milwakee SM 101 pH meter (Portugal).
Digital analytical balance (AG 29, Meltter Toledo, Glattbrugg, Switzerland).
Laboratory centrifuge 4000 rpm (Bremsen ECCO, Germany).
Materials and reagents
All materials were of analytical reagent grades and the solutions were prepared with double distilled water. Samples of investigated drugs were generously supplied by their respective manufacturers and were used without further purification; Sertraline hydrochloride was kindly provided by Pfizer Egypt, S.A.E., Cairo, Egypt. Fluoxetine hydrochloride was kindly provided by EIPICO, El Asher Ramadan City, Cairo, Egypt. Paroxetine hydrochloride was kindly provided by Pharaonia Pharmaceuticals Pharo Pharma, Alexandria, Egypt. Amineptine hydrochloride was kindly provided by Servier Egypt Industries Limited, 6th October City, Giza, Egypt and thioridazine hydrochloride was supplied by Delta Pharm, S.A.E, El Asher Ramadan City, Cairo, Egypt.
7,7,8,8-tetracyanoquinodimethane (TCNQ) (Sigma Che-mical Co., USA) was prepared as 1 × 10-3 M in acetonitrile. Solution was found to be stable for at least one week at 4°C. Acetonitrile, diethyl ether and methanol (Riendel-De-Haen AG, Germany). Chloroform, 1, 2 Dichloromethane, Ethanol and 33% W/V ammonia solution (El Nasr chemical Co., Abu Zabbal, Egypt).
Plasma was kindly provided by EL-Minia Hospital of Psychiatric medicine and kept frozen until assay.
The following available commercial preparations were analyzed; Lustral® tablets (Pfizer Egypt, S.A.E., Cairo, Egypt) labeled to contain 50 mg sertraline per tablet. Flutin® capsules (EIPICO, El Asher Ramadan City, Cairo, Egypt) labeled to contain 20 mg Fluoxetine per capsule. Paxetin® tablets (Pharaonia Pharmaceuticals Pharo Pharma, Alexandria, Egypt) labeled to contain 20.0 mg of paroxetine per tablet. Survector® tablets (Servier Egypt Industrial Limited, 6th October City, Giza, Egypt) labeled to contain 100.0 mg of Amineptine hydrochloride per tablet. Thiozine® tablets (Delta Pharm, S.A.E, El Asher Ramadan City, Cairo, Egypt) labeled to contain 100 mg of Thioridazine hydrochloride per tablet.
Preparation of standard solutions
An accurately weighed 20.0 mg salt of each investigated drugs, was transferred into 125-mL separating funnel containing about 20 mL of distilled water. The resultant solution was rendered distinctly alkaline with dropwise addition of 33% w/v aqueous ammonia solution. The librated free base was extracted with three potions of 5 mL chloroform. The combined chloroformic extracts were filtered through anhydrous sodium sulfate supported on Whitman filter paper. The filter paper was washed thoroughly with two portions of 5 mL chloroform. The combined extracts and washings were diluted to volume with chloroform to provide a stock standard solution containing 200.0 μg mL-1. This solution was further diluted with the same solvent to prepare working standard solutions containing 0.50 - 4.50 μg mL-1 of fluoxetine and sertraline, 0.50- 5.5 μg mL-1 of paroxetine, 1.0-6.5 μg mL-1 of thioridazine and 1.0-7.5 μg mL-1 of amineptine. The standard solutions were stable for seven days when kept in the refrigerator.
General analytical procedure
Into a series of 10 mL volumetric flasks, 1.0 mL of working standard solution of each drug was transferred over the cited concentration. One mL of 1 × 10-3 M TCNQ solution was added and mixed well. The reaction mixture was allowed to stand at room temperature (25.0 ± 5°C) for 40 min for fluoxetine, sertraline and paroxetine; 35 min for thioridazine and 45 min for amineptine then completed to the mark with chloroform. The fluorescence intensity of the complexes was measured at 443, 447, 447, 450 and 458 nm after excitation at 290, 291, 291, 295 and 301 nm for fluoxetine, sertraline, paroxetine, amineptine and thioridazine respectively. Blank experiment was carried out simultaneously. The relative fluorescence intensity of each sample solution for each investigated drugs was accurately measured and plotted against the final drug concentration (ng mL-1) to get the calibration graphs.
Procedure for pharmaceutical formulations (tablets and capsules)
A quantity of finely powdered twenty tablets or mixed capsules contents equivalent to 100.0 mg of active component was transferred to 50-mL volumetric flask, sonicated for about 10 minute with about 30 mL double distilled water. The volume was made up with distilled water, mixed well and filtered. The first portion of the filtrate was discarded; twenty mL of the clear solution was transferred quantitatively to a 125 mL separating funnel. The contents of the funnel were rendered alkaline with dropwise addition 33% w/v aqueous ammonia solution, and the procedure was completed as described under preparation of the standard solutions.
Procedure for spiked human plasma
5.0 mL of drug free human blood sample was taken from three healthy volunteers into a heparinized tubes, centrifuged at 3000 rpm for 30 minutes then 1.0 mL of the drug free plasma (supernatant) was spiked with 1.0 mL of investigated drugs containing 5.0-45.0 μg mL-1 of fluoxetine and sertraline, 5.0- 55.0 μg mL-1 of paroxeine, 10.0- 65.0 μg mL-1 of thioridazine and 10.0- 75.0 μg mL-1 of amineptine. 2.0 mL of acetonitrile was added as precipitating agent for protein then centrifuged at 4000 rpm for about 20 min. The supernatant was rendered alkaline by adding 1.0 mL of 33% w/v aqueous ammonia and then extract the librated free base three times with 3 × 3 mL of chloroform. The combined chloroformic extracts were filtered through anhydrous sodium sulfate supported on Whitman filter paper. The filter paper was washed thoroughly with two portions of 5 mL chloroform. The combined extracts and washings were diluted to volume with chloroform. Aliquotes covering the working concentration range was transferred into 10-mL volumetric flasks; then the general procedure was followed. A blank value was determined by treating the drug free blood sample in the same manner.
Procedure for real human plasma
For fluoxetine, 20.0 mg was taken orally once daily by three healthy human volanteers for 4 weeks. 5.0 mL of human blood sample was taken by using heperanized tube after an average of 6 hrs following the last oral administration and centrifuged at 3000 rpm for 30 minute. 3.0 mL of plasma obtained was treated with 2.0 mL of acetonitrile as precipitating agent for protein then centrifuged at 4500 rpm for about 20 minute. The supernatant was rendered alkaline by adding 1.0 mL of 33% w/v aqueous ammonia followed by extraction with 3 × 3 mL of chloroform. The combined extracts were diluted to volume with chloroform; then the general procedure was followed.
For paroxetine, 40.0 mg was taken orally once daily by three healthy human volanteers for 14 days. 10.0 mL of human blood sample was taken by using heperanized tube after an average of 12 hrs following the last oral administration and centrifuged at 3000 rpm for 30 minute. 6.0 mL of plasma obtained was treated with 4.0 mL of acetonitrile as precipitating agent for protein then centrifuged at 4500 rpm for about 20 minute; then the procedure was followed as described for fluoxetine starting from “The supernatant was rendered alkaline by…”.
For bupropion, 150.0 mg was taken orally every 12 hrs by three healthy human volanteers for 14 days. 5.0 mL of human blood sample was taken by using heperanized tube after an average of 6 hrs following the last oral administration; then the procedure was followed as described for fluoxetine.
For sertraline, 50.0 mg was taken orally once daily by three healthy human volanteers for 14 days. 5.0 mL of human blood sample was taken by using heperanized tube after an average of 12 hrs following the last oral administration; then the procedure was followed as described for fluoxetine.
For thioridazine, 100.0 mg was taken orally four times daily by three healthy human volunteers for 7 days. 5.0 mL of human blood sample was taken by using heperanized tube at 8 th day, 3 hrs after the last morning oral administration; then the procedure was followed as described for fluoxetine.
Results and discussion
The aim of this work is to establish a simple, sensitive, reliable, selective and cheap spectrofluorimetric method for the analysis of investigated drugs in pure forms, pharmaceutical formulations, spiked and real human plasma. The developed method was based on reaction of investigated drugs with 7,7,8,8-tetracyanoquinodimethane (TCNQ) to form highly fluorescent product, measured fluorometrically.
Optimization of variables
The spectrofluorimetric properties of the fluorescent product as well as the different experimental parameters affecting the development and stability of the CT-complex were carefully studied and optimized. Each factor was changed individually while the others were kept constant. The studied factors include diluting solvent, reaction time, temperature and concentration of the reagent.
In order to select the suitable solvent for CT-complex formation, the reaction of TCNQ with studied drugs was carried out in different solvents. The studied solvents are chloroform, acetonitrile, ethanol, methanol and 1,2-dichloroethane. It was found that chloroform was considered to be the best solvent for the fluorescence development proved by the highest RFI observed relative to other solvents.
Stoichiometry and Mechanism of the reaction
Validation of the proposed method
Concentration range (Topic Q2A 1994) was established by confirming that the analytical procedure provided a suitable degree of precision, accuracy and linearity when applied to the sample containing amount of analyte within or at the extreme of the specified range of the analytical procedure (Topic Q2B 1996; The United States Pharmacopoeia XXV and NF XX 2002). In this work, concentration ranging from 50 to 450 ng mL-1 (for fluoxetine and sertraline), 50 to 550 ng mL-1 (for paroxetine), 100 to 650 ng mL-1 (for thioridazine) and 100 to 750 ng mL-1 (for amineptine) were studied. The whole set of experiments were carried out within this range to ensure the validation of the proposed procedure. Linear calibration graphs were obtained for all the studied drugs by plotting the RFI of the studied drugs versus the drug concentration (ng mL-1) within the specified range.
Analytical parameters of spectrofluorimetric determination of investigated drugs with TCNQ
Linear range ng mL -1
Standard deviation of intercept (Sa)
Correlation coefficient (r)
LOD ng mL -1
LOQ ng mL -1
Evaluation of accuracy of the investigated analytical procedure at three concentration levels within the specified range
50.0 ng mL-1
Recovery %a 250.0 ng mL-1
450.0 ng mL-1
100.94 ± 1.29
99.80 ± 0.51
100.41 ± 0.28
99.84 ± 1.69
98.91 ± 0.55
100.14 ± 0.30
50.0 ng mL -1
Recovery % a 250.0 ngmL -1
550.0 ngmL -1
100.92 ± 1.28
100.09 ± 0.67
100.06 ± 0.31
100.0 ngmL -1
Recovery % a 350.0 ngmL -1
650.0 ngmL -1
100.44 ± 1.57
101.31 ± 0.95
100.48 ± 0.41
100.0 ngmL -1
Recovery % a 450.0 ngmL -1
750.0 ngmL -1
100.14 ± 1.87
98.81 ± 0.72
100.47 ± 0.44
Statistical analysis of the results obtained using the proposed procedures and reference method for spectrofluorimetric analysis of authentic samples using TCNQ
% Recovery ± SD
Reported method #
100.34 ± 0.89
99.95 ± 1.08
99.61 ± 1.57
99.67 ± 1.61
99.29 ± 1.02
99.38 ± 1.20
100.32 ± 1.24
100.39 ± 1.30
100.37 ± 1.04
100.57 ± 1.69
Evaluation of precision of the proposed spectrofluorimetric method for the determination of the investigated drugs
Where σ is the standard deviation of intercept. S is the slope of calibration curve.
The results are summarized in Table 2. The calculated detection limits for all the studied drugs were less than 12.48 ng mL-1 indicating good sensitivity of the proposed method.
The calculated quantitation limits for all the studied drugs were all less than 41.61 ngmL-1, as shown in Table 2, indicating good sensitivity of the proposed method. So it can be applied for analysis of drug in biological fluids.
Specificity and interference
Analysis of the investigated drugs (100.0 ng mL -1 ) in presence of some common excipients using the proposed spectrofluorimetric method
Amount Added μgmL -1
% Recovery d ± SD
100.07 ± 0.61
99.19 ± 0.72
99.85 ± 0.87
100.80 ± 0.78
101.29 ± 0.79
98.21 ± 0.91
99.83 ± 0.63
98.78 ± 0.61
100.73 ± 0.71
98.12 ± 0.45
101.25 ± 0.54
98.24 ± 1.25
101.58 ± 1.61
99.86 ± 0.33
101.62 ± 1.07
99.25 ± 0.59
98.82 ± 0.86
100.28 ± 0.89
101.98 ± 0.49
100.38 ± 1.58
98.21 ± 0.67
99.70 ± 0.51
99.81 ± 0.34
Application to pharmaceutical dosage forms
Statistical analysis of the results obtained using the proposed spectrofluorimetric and reported methods for analysis of the investigated drugs in pharmaceutical dosage forms
Pharmaceutical dosage forms
Proposed method ± SD (n = 5)
Reported methods 8-10 ± SD (n = 5)
100.94 ± 1.390
100.53 ± 1.46
t = 0.45 e F = 1.09 e
100.18 ± 1.15
100.13 ± 1.68
t = 0.06 F = 2.13
100.01 ± 1.196
99.98 ± 0.95
t = 0.04 F = 1.59
100.62 ± 0.663
100.22 ± 1.07
t = 0.71 F = 2.59
100.14 ± 1.26
99.88 ± 1.59
t = 0.29 F = 1.59
Application to spiked human plasma
Application of the proposed method to the determination of studied drugs in spiked human plasma
Concentration (ngmL -1)
% Recovery f
Mean ± SD
99.68 ± 1.99
100.03 ± 1.92
99.73 ± 1.73
99.76 ± 1.565
100.39 ± 1.33
Analysis of cited drugs in real human plasma
Fluoxetine is metabolized into its active metabolite norfluoxetine (Lemberger et al. 1985). Norfluoxetine concentrations are approximately equal to those of the parent drug during chronic therapy (Brunswick et al. 2002a). After a fixed daily dose of fluoxetine (20.0 mg day-1), the concentration of the drug and its active metabolite in the blood continued to grow through the first few weeks of treatment, and their steady concentration in the blood is achieved only after four weeks (Pérez et al. 2001; Brunswick et al. 2002b). Paroxetine is completely absorbed after oral administration and metabolized in the liver forming three main metabolites: the two isomers (3S,4R)-4-(4-fluorophenyl)- 3-[(4-hydroxy-3-methoxyphenoxy)methyl]-piperidine (M1), (3S,4R)-4-(4-fluorophenyl)-3-[(3-hydroxy-4-methoxyphenoxy)methyl]-piperidine(M2) and (3S,4R)-3-hydroxymethyl- 4-(4-fluorophenyl) piperidine (M3) (Hiemke & Hartter 2000). Steady-state plasma paroxetine concentrations were achieved after approximately 10 days following 40-mg once daily dose (Mandrioli et al. 2007). Thioridazine is mainly metabolized into mesoridazine and sulphoridazine. Steady-state plasma thioridazine concentrations were achieved after approximately 7 days following four 100-mg doses per day (Vanderheeren & Muusze 1977). Sertraline is mainly metabolized into N-desmethylsertraline. Steady state plasma concentration level for sertraline and its metabolite were achieved after approximately one week of a 50-mg once- daily dosing (Package Insert, Zolofi@, Pfizer Inc 1992; Mandrioli et al. 2006). Amineptine is mainly metabolized by beta-oxidation of the side chain, its principle metabolites has the same structure as the parent compound except that its side chain is reduced to five carbon atom (Lachatre et al. 1989). Steady state plasma level is achieved at 8 th day following two 100.0 mg doses per day (Rop Pok et al. 1990).
According to the reported metabolic pathway of all the cited drugs; the proposed method can be used specifically for determination of fluoxetine and sertraline only in presence of their metabolites in plasma because the metabolic products are considered as compounds containing primary amino group (as norfluoxetine and norsertraline); which should not interfere upon application of the suggested procedure, while for thioridazine, paroxetine and amineptine, their metabolites can interfere with the determination of the parent drugs because they contain the same function group (secondary or tertiary amine moiety) as well.
% Recovery in vivo is % recovery for drug in real human sample.
Concentration found is concentration of the drug founded in real human sample.
Concentration taken is concentration of the drug reported in real human sample.
While % recovery of thioridazine, paroxetine and amineptine and their metabolites in plasma were calculated by using the same equation
% Recovery in vivo is % recovery for drug and their metabolites in real human sample.
Concentration found is concentration of the drug and their metabolites founded in real human sample.
Concentration taken is reported concentration of the drug and their metabolites in real human sample.
% Recoveries after application of the proposed method for determination of investigated CNS drugs in real human plasma sample
% Recovery invivo
% Recovery invivo
Mean ± SD
91.53 ± 5.11
86.28 ± 5.27
Mean ± SD
88.83 ± 5.38
85.50 ± 5.947
Mean ± SD
76.76 ± 4.82
75.28 ± 7.94
Mean ± SD
91.53 ± 5.11
92.26 ± 2.73
Mean ± SD
86.29 ± 6.44
87.41 ± 3.87
The proposed spectrofluorimetric method has the advantage of being simple, highly sensitive and low cost method for determination of the investigated antidepressant drugs in pure forms, pharmaceutical formulations, without any interference from common excipients present and with minimum detection limits. Furthermore the proposed method was successfully applied for analysis of the cited drugs in spiked and real human plasma. Therefore, the developed method can be considered as suitable for routine analysis of investigated antidepressant drugs in quality control and clinical laboratories. Also it is suitable for selective determination of fluoxetine and sertraline only without their metabolites in human plasma.
The authors express their gratitude to Egyptian government for providing financial support to achieve this paper. Also, the authors express their gratitude to Dr. Monsef Mahfuz a consultant psychiatrist and manager of Minia hospital for psychiatric medicine (Minia, Egypt) for providing the plasma samples.
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