01synthesis caracterization and evaluation

Pharmaceutical Chemistry Journal

Vol. 35, No. 7, 2001

SYNTHESIS, CHARACTERIZATION, AND EVALUATION OF THE LOCAL IRRITANT ACTION OF AN IBUPROFEN – b-CYCLODEXTRIN INCLUSION COMPLEX M. V. Gavrilin1 and A. V. Pogrebnyak1 Translated from Khimiko-Farmatsevticheskii Zhurnal, Vol. 35, No. 7, pp. 48 – 49, July, 2001. Original article submitted October 19, 2000.

tical density of a working standard sample (SS) of ibuprofen with a concentration of 0.02% was measured under the same conditions. Based on these data, the content of the parent compound (X, %) in the complex preparation was calculated by the formula

Ibuprofen is a widely used nonsteroidal antiinflammatory drug (NSAID). Despite a somewhat lower specific activity in comparison to that of indomethacin and diclofenac sodium, ibuprofen exhibits lower toxicity, which allows this drug to be used without prescription. At the same time, ibuprofen is capable of producing a local irritation effect – a disadvantage inherent in all NSAID preparations. Some researchers [1, 2] recommended using ibuprofen in combination with cyclodextrins in order to eliminate the negative effect of the drug on the mucous membrane of the stomach. The purpose of our study was to obtain an inclusion complex of ibuprofen with b-cyclodextrin (b-CD), to confirm the complex formation, and to evaluate the local irritation effect of the new preparation. The experiments were performed with ibuprofen from Agio Pharma (India) and b-CD from Sigma (USA).

X (%) =

D x × C SS × 50 , D SS × a

where Dx is the optical density of the sample solution, DSS is the optical density of the working standard sample solution, CSS is the known concentration of the standard solution (%), and a is the weight of the sample measured (g). It was found that the weight fraction of ibuprofen in the inclusion complex was about 14%, which corresponds to about 95% of the theoretical value and corresponds to an ibuprofen/b-CD molar ratio of 1 : 1.

EXPERIMENTAL CHEMICAL PART Ibuprofen – b-CD inclusion complex. To a solution of 11.5 g (0.01 mole) b-CD in 200 ml of hot water was added a solution of 2.06 g (0.01 mole) ibuprofen in 20 ml of a 95% ethyl alcohol. The mixture was thoroughly stirred for 1 h and allowed to stand for one day at 4°C. The white precipitated product was separated by filtration and dried at 60°C for 10 h. The product yield was 67 – 70%. For the quantitative determination of the content of ibuprofen in the complex preparation, an exactly weighed amount of the product (about 0.05 g) was placed in a 50-ml measuring flask and dissolved with shaking in 20 – 30 ml of an 0.1 M aqueous sodium hydroxide solution, after which the flask was filled with the same solution to the mark. The optical density of the sample solution was measured on an SF-56 spectrophotometer (LOMO, Russia) at 264 nm in a 1-cm-thick optical cell. In a parallel experiment, the op1

TABLE 1. Frequencies (cm – 1) of The Main Absorption Bands in the IR Spectra of Ibuprofen, b-Cyclodextrin, and Their Inclusion Complex Ibuprofen

3692 3624 1708 1608 1512 1068 1044 1020 928 848 624 – –

Pyatigorsk State Pharmaceutical Academy, Pyatigorsk, Russia.

395

Inclusion complex

b-Cyclodextrin

3176 1708 1658 1640 1204 1156 1020 936 848 572 524 428 412

3342 1640 1300 1248 1150 1028 940 848 576 532 436 – –

0091-150X/01/3507-0395$25.00 © 2001 Plenum Publishing Corporation

396

M. V. Gavrilin and A. V. Pogrebnyak

TABLE 2. Proton Chemical Shifts in the 1H NMR Spectra of b-CD and Ibuprofen – b-CD Inclusion Complex b-CD protons:

b-CD Inclusion complex

H3

H2

H4

H5

H6

1

2

3

4

5

1

2

3

1

2

1

1

2

3.608

3.596

3.575

3.563

3.552

3.935

3.904

3.872

3.522

3.491

3.786

3.817

3.798

3.588

3.576

–

–

–

3.842

3.811

3.782

3.521

–

3.545

3.809

3.809

The IR absorption spectra of the ibuprofen – b-CD inclusion complex preparation and both initial compounds were measured on an IKS-40 spectrophotometer (Russia) using samples in the form of 25% suspensions in the Vaseline oil with a thickness of 0.011 mm. The main absorption bands observed in the spectra are listed in Table 1. As can be seen from these data, the IR spectrum of ibuprofen contains a strong absorption band at 1708 cm – 1 due to carboxy group and the bands corresponding to vibrations of the aromatic ring and the isobutyl fragment (1608, 1512, 1044, and 1020 cm – 1). On passing to the inclusion complex, the bands at 1708 and 1020 cm – 1 retain their positions. At the same time, the main bands attributed to the aromatic ring and isobutyl residue (a hydrophobic part of the drug molecule) exhibit significant changes. These results indicate that this very part of the ibuprofen molecule enters a cavity in the b-CD structure. In order to confirm these conclusions, we have studied the inclusion complex and the initial b-CD by 1H NMR spectroscopy. The measurements were performed on a Bruker Model 300 spectrometer (Germany) operating at a working frequency of 300 MHz. The samples were dissolved in a deuterated water. The chemical shifts of protons in the initial b-CD and the same matrix with encapsulated ibuprofen (expressed in ppm relative to the chemical shift of water, the latter shift being 4.75 ppm with resect to TMS) are listed in Table 2. As can be seen from the 1H NMR data, the b-CD proton signals change their positions as a result of the interaction with ibuprofen; this change involves the protons (at C3 and C5 carbons) occurring inside the cavity of b-CD, which is evidence that ibuprofen enters the b-CD cavity. However, the signals from protons (at C2 and C4) occurring on the outer surface of the b-CD molecule are also considerably changed, Thus, we may suggest that the ibuprofen molecule enters the b-CD cavity from the wide edge. The b-CD cavity accommodates the isobutyl radical and, probably, a part of the aromatic ring (the p electron system of which interacts with the b-CD protons). Some fragments of the ibuprofen molecule remain outside the cavity and interact with the outer protons.

EXPERIMENTAL BIOLOGICAL PART In order to compare the local irritant action of ibuprofen and its inclusion complex with b-CD, we used the HET-CAM test based on determining the chorioallantoic shell damage of the chicken embryo (Leupka, 1985) [3]. In view of the fact that the solubilities of both ibuprofen and the inclusion complex are below 100 g/liter, the tests were performed with supernatant liquids obtained from 100 g/liter suspensions of the tested substances upon a one-day infusion at 37°C. The tests were performed on 10-day chicken embryos. Prior to testing, the egg were mounted with the dull end upward, the air cavity was cleaned from the eggshell, and the undershell membrane was wetted with an isotonic sodium chloride solution and removed. Then a 300 ml sample of the tested liquid was applied onto the chorioallantoic shell (water served as the control). Each test was performed with three embryos. The results were evaluated after a 100-sec exposure and expressed in terms of a 5-step scale depending on the pattern of chicken embryo shell damage. It was established that pure ibuprofen can be rated 5 with respect to to the irritant action. Almost immediately after application of the ibuprofen solution, a thrombosis was observed in both small and large vessels, followed by the blocking of blood flow and bleeding over the entire surface treated with the drug solution, and by cardiac arrest 50 – 60 sec after application of the drug. According to the comparative experimental data, the ibuprofen – b-CD inclusion complex was rated 3 with respect to to the irritant action. By the end of the observation time (100 sec), the membrane became reddish, the blood flow rate dropped, and thrombosis developed in some capillaries; the embryos survived for at least 30 min. The results of our investigation showed that b-CD and ibuprofen interacting in aqueous solutions under the conditions studied form a true inclusion complex. This form allows the local irritant action of the nonsteroidal antiinflammatory drug to be significantly reduced. REFERENCES 1. H. Veda, T. Nagai, N. Nambu, et al., Chem. Pharm. Bull., 26(12), 3609 – 3612 (1978). 2. M. Halsas, R. Simelius, and A. Kivinieni, S. t. p. Pharma. Sci, 8(3), 155 – 161 (1998). 3. Vedom. Farmakol. Kom., No. 3, 25 – 27 (1998).