Drugs like sumatriptan, which
are commonly known as triptans are believed to act
mainly at 5-HT1B and 5-HT1D subtype receptors and are
therefore sometimes referred to as 5HT1B/1D-receptor antagonists. Sumatriptan is used for the acute treatment of migraine
attacks and of cluster headache. It should not be used for prophylaxis.(7)
Zolmitriptan
is a selective serotonin (5-HT1) agonist with actions and uses
similar to those of sumatriptan. It is used for the
acute treatment of migraine attacks. Zolmitriptan
should not be used for prophylaxis.(7)
Various methods were used in determination of sumatriptan in its
different forms, such as spectrophotometry(8),HPLC(9)
and electrocatalytic determination(10) ,
for zolmitriptan the spectrophotometric method(11),
HPLC(12) and elecrochemical assay(13).
The present research aims chiefly to study the reaction of
DDQ , TCNQ and TCNE reagents (electron acceptors) as first time with sum. and zol. (electron donors) and use these reagents in
spectrophotometric determination of the given drugs in pure form and in some of
their dosage forms.
Zolmitriptan
Sumatriptan
Fig.
(1) Chemical structures of zolmitriptan and sumatriptan
MATERIAL AND METHODS:
Instrument:
He ƛios α UV-visible double beam
spectrophotometer with a 1.0 cm quartz cell was used.
Reagents and Chemicals:
All chemicals and solvents were used of analytical or
pharmaceutical grade. Sum. was supplied by SMS Pharmaceuticals Ltd, India and Zol. was supplied by Western Pharmaceutical Industries,
China. DDQ, TCNQ and TCNE were supplied by Aldrich company, U.S.A. Dosage forms
containing Sum. and Zol. were from local market
companies. GlaxoSmithKline for sum. (Imigran®)
and AstraZeneca for Zol. (Zomig®).
Fresh solutions of
DDQ and TCNE (2 mg/ml) in acetonitrile, TCNQ
(1mg/ml) in acetonitrile and zol.,
sum. (1mg/ml) in acetonitrile were prepared.
General analytical procedure:
Bulk sample:
Into 10 ml volumetric flasks 0.1-1.5 ml of 1mg/ml of sum.
stock solution or 0.1-1 ml of 1mg/ml of zol.
stock solution were added to 1 ml of DDQ, or TCNQ, or TCNE.The
mixture was mixed well and allowed to stand for 20 min. at 25±1°C.The volumes
were completed to the mark with acetonitrile. The
absorbance was measured at λmax= 459,
843 and 415 nm for DDQ, TCNQ and TCNE
respectively for the two drugs against a blank solution prepared in the
same manner without drugs. The drug concentrations were calculated from the
standard calibration curve prepared under the same identical conditions.
Procedure for assay of pharmaceutical dosage forms:
Weigh twenty tablets and thoroughly grind to fine powder.
Extract an accurate weighed portions of the obtained powder equivalent to 100
mg of sum. or zol. in 50 ml acetonitrile.
Shake for about 15 min, filter the solution in a 100 ml measuring flask, wash
the residues several times and dilute to the mark with acetonitrile.
The analysis was continued as described above and the nominal content was
calculated from the corresponding calibration curve or regression equation of
each drug.
Stoichiometric
relationship:
Job's method of continuous variation(14) was
employed to establish the stoichiometry of the coloured products. In this method a series of solutions was
prepared by mixing equimolar solutions (5 x10-3 M) of drug sum. or zol.
and DDQ, TCNQ and TCNE in varying proportions. Then the general analytical
procedures were followed.
Molar ratio method:
In this method the concentration of reagents DDQ, TCNQ or
TCNE were kept constant at 1 ml of 5x10-3
M. Mix well with a series of drug solutions varying from 0.1 to 2 ml of 5 x10-3
M then complete the volume of the reaction mixture to the mark with acetonitrile in 10 ml measuring flasks. Measure the
absorbance at the specific wavelength of each reagent.
RESULTS AND DISCUSSION:
The studied drugs have high electron density sites, so
they may act as powerful electron
donors. The structures of sum. and zol. are shown
in fig (1). They act as n-electron
donors to form charge transfer CT with an acceptor. Spectrophotometric
properties of the coloured CT complexes as well as
the different parameters affecting the colour
development between the different acceptors and drugs were extensively studied
to dominate the optimal conditions for the assay procedure. The reaction was
studied as a factor of volume of the reagent, nature of the solvent, time and stoichiometry.
Selection of the suitable wavelength:
Recently, the reactions of DDQ, TCNE and TCNQ with some
pharmaceutical compounds have been reported (15-20). In acetonitrile the reaction of DDQ, TCNE and TCNQ with sum.
and zol. results in the formation of intense coloured products which exhibit maximum absorptions at 459,
415 and 843 nm respectively for the two drugs indicating the formation of
electron donor-acceptor complexes fig (2,3,4). The interaction of sum. and zol. with DDQ, TCNE and TCNQ in non polar solvents such as dioxane and halogenated solvents was found to produce coloured charge-transfer CT complexes with low molar absorbitivity values. In polar solvents such as acetonitrile and alcohols, complete electron transfer from
donor to acceptor moiety takes place with the formation of intensely colored
radical ion with high molar absorbitivity values,
according to the following scheme:
The dissociation of the DA complex is promoted by the high
ionizing power of acetonitrile. Acetonitrile
was considered an ideal solvent as it afforded maximum sensitivity due to its
high dielectric constant 37.5(21) that promotes maximum yield of
radical anions in addition to the high solvating power of the reagents and
drugs.
Effect of time and temperature:
The optimum reaction time was determined by following up
the colour development at ambient temperature (25±1˚C).
Complete colour development was attained after 10
min, 25 min and 30 min in case of the reaction between zol.
and DDQ, TCNE and TCNQ respectively and after 30 min, 25 min and 75 min in case
of reaction between sum. and DDQ, TCNE and TCNQ respectively and was stable for
more than 1 hour, thus permitting quantitative analysis to be carried out with
good reproducibility. The CT complexes were gradually decreased with increasing
temperature, hence ambient temperature (25±1˚C) was found to be suitable
to carry out the study.
Fig(2)shows
absorption spectrum of CT complex with DDQ
Fig(3)shows
absorption spectrum of CT complex with TCNQ
Fig(4)shows
absorption spectrum of CT complex with TCNE
Effect of reagent volume:
Various volumes of DDQ, TCNE and TCNQ were added to fixed
volume of sum. and zol. (1 ml of 1mg/ml ) in a total
volume of 10 ml. 1ml of 2 mg/ml DDQ, 1 ml of 2 mg/ml TCNE and 1.5 ml of 1 mg/ml
of TCNQ were sufficient for the production of maximum reproducible colour intensity with the two drugs.
Stoichiometry
of the reaction:
The molar ratio of the studied drugs with DDQ, TCNE and
TCNQ, using Job’s method of continuous variation(14), it was found
to be drug donors (D) to the reagent acceptors (A) of the ratio 1:1 (D:A) in
case of sum. drug and 1:2 (D:A) in case of zol. drug
as shown in fig (5,6,7).
Fig (5)
shows continuous variation plots for DDQ associates with zol.
and sum.
Fig (6)
shows continuous variation plots for TCNE associates with zol.
and sum.
Fig (7)
shows continuous variation plot for TCNQ associates with zol.
and sum.
Validation
of the proposed methods:
Analytical
data:
The linear calibration graphs were obtained under the
optimum experimental conditions. The analytical results obtained from this
investigation are summarized in table (1). The calibration data obtained for
sum. and zol. drugs from linear regression analysis
of absorbance readings versus concentration of drug (µg/ml) were made. The
slope, intercept, Sandell’s sensitivity, molar absorbitivities and correlation coefficients were listed in
table (1). Beer's law limits 10-100,
10-100 and 10-70 µg/ml for DDQ, TCNQ and TCNE with sum. drug and 10-80, 10-50
and 10-40 µg/ml for DDQ, TCNQ and TCNE with zol. drug
respectively. The Sandell's sensitivities of the
complex formed with sum. was 0.0684 , 0.0532 and 0.0267 µg cm-2 and
for zol. 0.123, 0.227 and 0.039 µg cm-2 with DDQ, TCNQ and
TCNE respectively. The high molar absorbitivity and
lower Sandell’s sensitivity values reflect the good
and high sensitivity of the method. According to the International Conference
on Harmonization (ICH) Recommendation(22), the approached based on the standard deviation (SD) of the
response and the slope (b) of the calibration curve, was used for determination
the limits of detection and quantification of drug, the results are included in
table (1).
Precision and accuracy:
In order to study the accuracy and precision of the
proposed methods, three concentration levels of sum. and zol.
within the linearity range were selected. The within day precision (intraday
precision) was performed by taking three independent analyses at each
concentration level within one day during the stability time period. The daily
precision (interday precision) was measured by
assaying a single sample of each concentration on five consecutive days within
the stability time period. The mean recovery and RSD values are included in
table (2). The results obtained show that no significant difference for the
assay which is tested within day (repeatability) and between days (reproducibilty).
Application to pharmaceutical dosage form:
The proposed methods were applied to the determination of
sum. and zol. in the pharmaceutical dosage forms (details
are given in the experimental section). The results of the assay of sum. and zol. in the tablets with DDQ, TCNE and TCNQ were compared
with reported methods. Statistical comparison of the results were performed
with regard to accuracy and precision using the student’s t-test and F-test at
95% confidence level. From the results in table (4,5) it is clear that there is
no significant difference between the proposed method and the reported methods(23,24)
with regard to accuracy and precision.
The results of analysis of the commercial tablets and the
recovery study of the drugs suggested that there is no interference from any excepients which are present in the tablets, also the
extraction with acetonitrile from drug tablets could
eliminate any interference caused by common excepients.
CONCLUSION:
The suggested methods have the advantage of being simple,
accurate and sensitive and carried out in less equipped quality control
laboratories with good precision and accuracy. These methods utilize a single
step reaction and do not need any extraction process at the colour
development. The methods can be used successfully as alternative method to
chromatographic methods for routine determination of the drug in bulk powder
and in dosage forms.
