Iranian Journal of Pharmaceutical Research (2003) 111-115 Received: January 2002 Accepted: May 2003
Photostability Determination of Commercially Available Nifedipine Oral Dosage Forms in Iran
Katayoun Javidnia *a,b, Ramin Miria,b, Ladan Movahedb, Shohreh GolrangibaMedicinal & Natural Products Chemistry Research Centre, Shiraz University of The Medical Sciences, Shiraz, Iran. bDepartment of Medicinal Chemistry, Faculty of Pharmacy, Shiraz University of Medical Sciences, Shiraz, Iran. Abstract
Nifedipine (NIF) a 1, 4-dihydropyridine calcium channel antagonist, undergoes
photodegradation to nitroso analogues of dehydronifedipine (NDNIF) when exposed to sunlight. Photodegradation products of NIF have no clinical activity, so different formulations of NIF must remain unchanged. If NIF preparations become unstable in exposure to light, they could cause therapeutic failure. The present study was carried out in order to investigate the photostability of commercially available NIF products, in Iran. Three oral NIF formulations available in Iran were studied using indirect sunlight (daylight) and continuous artificial light exposure extending over a period of 12 weeks. The extent of photodecomposition of NIF was determined using a specific reversed phase high performance liquid chromatography (HPLC) method. NIF photodegradation was measured using both pure NIF powder as well as a methanolic NIF solution to determine differences in the effectiveness of artificial light and natural indirect sunlight sources used in this study. All the tested NIF formulations were likely to be photostable up to at least 12 weeks of continuous artificial and natural day light exposure, compared with pure NIF powder and methanolic solution. Photodegradation of NIF powder and methanolic solution exposed to indirect sunlight was faster than the artificial light.
Keywords: Nifedipine; Photostability; HPLC; Daylight; Artificial light. Introduction
important chemical changes, accompained by
alternation in their activities and in some cases
Nifedipine (NIF), 1,4-dihydro-2,6-dimethyl-
total loss of their therapeutic activity (5). NIF is
4-(2-nitrophenyl)-3,5-pyridine dicarboxylic very highly sensitive to photooxidation. NIF acid dimethyl ester (Figure 1), is the prototype
exposure to ultraviolet-visible irradiation
compound of the dihydropyridine class of produces both aromatization in the calcium channel antagonists. Calcium dihydropyridine moiety (turning it into a antagonists inhibit the influx of calcium ion
pyridine ring) and a reduction of nitro group in
through plasma membrane channels and thus
to nitroso groups (NDNIF). In addition, its
dilate vascular smooth muscle contraction. NIF
is a selective arterial dilator, and is used for the
dehydronifedipine (DNIF) (6-9) (Figure 1).
treatment of hypertension, angina pectoris, and
other cardiovascular disorders (1-4). The
pharmacological activity. Several studies
exposure of some drugs to light leads to related to its photodecomposition have been photodecomposition. These drugs undergo reported (10-13) but to our knowledge this
* Corresponding author: E-mail: firstname.lastname@example.org
K Javidnia , R Miri , L Movahed , Sh Golrangi / IJPR 2003, 2: 111-115
solution was mixed with 1 ml of the tested
concentrations of NIF (12.5–150 µg/ml) and 20
µl of the mixed solution was injected to HPLC.
Melting point was determined on a kofler
hot stage apparatus. 1H-NMR spectra was run
on a Varian Unity Plus 400 MHz spectrometer.
TMS was used as the internal standard. Mass
spectra was measured with a Finnigan TSQ-70
Synthesis of Isopropyl-3-amido-2, 6- dimethyl-4-(1-methyl 5-nitro 2-imidazolyl)- 1,4-dihydropyrinine-5-carboxylate(Internal
standard) Figure 1. Structures of A: Nifedipine(NIF), B: Dehydronifedipine(DNIF), C: Nitroso-analogue of
A solution of acetoacetamide (0.5g, 5mmol)
dehydronifedipine (NDNIF), D: Internal standard
in MeOH (3 ml) was added to a solution of
photostability of oral dosage forms used in our
1-methyl-5-nitro-imidazole-2-carboxaldehyde (0.77 g, 5 mmol) and isopropyl 3-amino
crotonate (0.72 g , 5 mmol) in EtOH (4 ml) and
stirred constantly for a period of 5 min. The
resistant coating and/or packing to minimize
reaction was heated at reflux temperature for 14
their photodegradation. Long term exposure to
h, cooled to 25°C. The resulting precipitate was
sunlight or artificial light may also occur if NIF
filtered and purified by recrystalization from
formulations are improperly stored by patients.
MeOH (yield= 48%; mp = 217-219°C) (15).
decrease clinical efficacy of NIF products (14).
Differences in the degree of light protection
7.94 (s, 1H, imidazole H-4), 5.14(s, 1H, C4-H),
may exist between different formulation types.
4.21(s, 3H, N-CH3), 4.12(m, 3H, CO2CH &
In this paper, we report the photostability of
NH2), 2.25(s, 6H, C2-CH3 & C6-CH3), 1.28
commercially available NIF products, in Iran.
&1.18 (twod, J=7.2 Hz, 3H each, CH (CH3)2).
photodegradation of authentic NIF powder and
methanolic NIF solution obtained from three
Irradiation test Experimental
For artificial light irradiation, a 40 W
tungsten lamp was used. NIF samples were
Sigma-Aldrich placed 50 cm from the lamp in a cabinet
Chemie GmbH (Deisenhofen, Germany). (1 m × 1 m × 0.75 m). Protected samples from Methanol and chloroform were obtained from
extraneous light were placed in aluminum foils.
Merck (Darmstadt, Germany). All reagents Exposure to indirect sunlight was also used were analytical or HPLC grade.
during the spring months in Shiraz to compare
Ten mg liquid filled immediate release the efficacy of artificial light and natural room
capsules of NIF were obtained from Zahravi
Co. (Tabriz, Iran) and Apotex Inc. (Toronto,
Samples were irradiated from 0-12 weeks in
Canada); and 10 mg tablets were obtained from
artificial light and indirect sunlight. Samples
Toliddarou Co. (Tehran, Iran). These three were collected at 0, 1, 2, 4, 6, 8, 10 and 12 formulations are the commercially available
weeks intervals (n=3). NIF powder samples (10
NIF products in Iran. The NIF stock solution
mg) were placed in 10 ml clean glass vials,
irradiated from 0-12 days and samples were
standard solutions were obtained by serial collected at 0, 1, 2, 3, 7, 10 and 12 days. Also a dilution. The Internal standard solution (IS) was
total of 11 × 1 ml methanolic NIF solution
prepared (40 µg/ml) in methanol. 1 ml of IS
samples (10 µg/ml) were placed in 5 ml clear glass vials and irradiated for a period of 0-360
Photostability Determination of Commercially Available…
min. Samples were taken at 0, 5, 10, 15, 20, 30,
45, 60, 120, 240, 360 mins. The experiments
were conducted at ambient temperature (14).
Sample preparation Nifedipine tablets: Three NIF tablets were
Identification of the NDNIF
crushed into fine particles and a quantity
0.2 mg/ml of NIF methanolic solution was
equivalent to 10 mg of NIF was placed in a
exposed to indirect sunlight. At 5 min intervals
centrifuge tube and 2 ml of chloroform was
10 µl of the solution were injected to HPLC
30 s and centrifuged for 5 min. Twenty µl of
chromatogram (15 min). The solution was then
supernatant was drawn by Hamiltonian syringe
evaporated over nitrogen stream. The mass
and added to a tube containing 100 µl of IS
spectrum of the residue was obtained on a
solution (40 µg/ml). This solution was Finnigan Mat at 70 eV ionization potential.
evaporated to a dry residue under Nitrogen
stream. Two hundred µl of mobile phase was
Results and Discussion
added to the residue and vortexed for 10 s.
Aliquots of 10 µl were injected to HPLC (14).
In the present study photostability of NIF
Nifedipine softgel capsules: a 20 µl volume
formulations available in Iran was determined
solution from each NIF capsule was withdrawn
after exposure to indirect natural light and
using a 25 µl Hamiltonian syringe and was
continuous artificial light. NDNIF, NIF and IS
diluted with 0.5 ml of chloroform. One hundred
were eluted at approximately 5.5, 7.0 and 11.5
µl of IS solution (40 µg/ml) was added and
min respectively. Resolution between NIF and
mixed on a vortex for 30 s. Further sample
NDNIF was adequate (R>1.5) and no buffer
preparation and evaporation was as described
and pH adjustment was required with this
Nifedipine powder samples: each of the photodecomposition product produced major
irradiated NIF powder samples were diluted
fragments at 328 (M+, 28%), 298 (15%), 269
with 2 ml of chloroform and vortexed for 20 s.
(100%) and 253 (50%), that confirmed the
Twenty µl of this solution was mixed with 100
structure of NDNIF. Figure 2 shows a typical
µl of IS solution (40 µg/ml), and dried over
nitrogen stream, then 1 ml of mobile phase was
methanolic solution irradiated with artificial
added and vortexed for 10 s, Finally, 10 µl of
methanolic solution irradiated with indirect
Nifedipine methanolic solution: One natural sunlight for 1 min and c) a commercial
hundred µl of IS was added to the vials 10 mg NIF tablet irradiated for 12 weeks with containing 1 ml of NIF (100 µg/ml) and indirect natural sunlight. vortexed, and then 10 µl of the solution was injected to HPLC.
Chromatography and instrumentation Analytical separation was accomplished
using a Bondapack C18 (250×4.6 mm) column.
Mobile phase flow rate was 1.5 ml/min and consisted of methanol/water (60/40). It was continuously degassed with Helium (60 ml/min). The HPLC system employed consisted of a model 604 solvent delivery system and a
486 tunable uv/vis absorbance detector set at
Figure 2. Chromatograms of: (a) methanolic NIF solution
350 nm (Waters). Sample preparation and irradiated by artificial light for 120 min, and (b) methanolic NIF
solution irradiated by natural sunlight for 1 min, and (c) a
analysis were conducted under sodium lamp
commercial 10 mg NIF tablet irradiated by natural sunlight for 12
weeks. Peak identification: (1) NDNIF; (2) NIF; (3) I.S.
K Javidnia , R Miri , L Movahed , Sh Golrangi / IJPR 2003, 2: 111-115
Table 1. Risults obtained from the photodegradation of Table 2. Results obtained from the photodegradation of
various nifedipine formulations by exposure to artificial
Various nifedipine formulations by exposure to natural
whether manufacturers in Iran can produce NIF
formulations in a photoprotective condition. For
tungsten artificial light have similar effects in
this reason three formulations, two produced in
the photodecomposition of NIF. But in our
Iran, and another a commercially available form
study NIF methanolic solution exposed to of NIF used in Iran (Apotex Inc.), as a control
natural indirect sunlight was completely sample, were chosen. The percentage of NIF
photodecomposed in 10 min. On the other hand
content (w/w initial NIF content) was measured
photodecomposition of NIF methanolic solution
in all three tested formulations irradiated for up
exposed to artificial light exceeded 7.3 % in
to 12 weeks by artificial and natural light. Table
approximately 10 min. This result shows that
the efficacy of natural indirect sunlight in formulation after 0, 2 and 12 week exposure to
photodecomposition of NIF is more than artificial light and Table 2 shows this
artificial light in Iran and it can be due to the
photodegradation data for each formulation
fact that the intensity of natural light in Iran is
after 0, 2 and 12 week exposure to natural
more than Canada. Therefore, these results are
indirect sunlight. Results obtained in this study
evidence for that artificial light can not be used
showed that differences between data obtained
alone in photodecomposition studies. were not significant and none of the tested NIF
Photodegradaition plots of NIF methanolic formulations underwent any appreciable
solution (A) and NIF powder (B) after artificial
decomposition (> 10%), even after 12 weeks
light irradiation are shown in Figure 3. irradiation.
Photodegradation of NIF powder measured as
In conclusion, based on our results it is
the loss percentage of NIF, exceeded 5.6 % and
unlikely that a photostability degradation
16.8%, in approximately 24 h after artificial and
would be the primary contributing factor,
natural indirect light irradiation respectively.
should therapeutic failure of the tested NIF
Our major goal in this study was to find that
Council of Medical Sciences, University of
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