Caffeine: A potential complexing agent for solubility and dissolution enhancement of celecoxib

Abstract

Complexation of caffeine with the drug celecoxib was used to enhance its solubility as well as in vitro dissolution in the present investigation. Caffeine was extracted from tea leaves using the sublimation method. A molecular complex (1:1) of caffeine–celecoxib was prepared using the solubility method. The solubility of celecoxib in distilled water and the caffeine complex was determined using a HPLC method at a wavelength of 250 nm. Dissolution studies of pure celecoxib, a marketed capsule (Celebrex^®), and the complex were performed using USP dissolution apparatus I for pure celecoxib and the complex and apparatus II for the capsule in distilled water. The highest solubility (48.32 mg/mL) as well as percent dissolution (90.54%) of celecoxib was obtained with the caffeine–celecoxib complex. The results for solubility and dissolution were highly significant as compared to pure celecoxib and the marketed capsule (p < 0.01). These results suggest that caffeine is a promising complexing agent for solubility as well as dissolution enhancement of the poorly soluble drug celecoxib.

Keywords::

• Caffeine
• celecoxib
• complexation
• dissolution
• solubility

Introduction

Celecoxib (CXB) is a selective cyclo-oxygenase-2 (COX-2) inhibitor, used in the treatment of various types of pain, arthritis, and osteoarthritis (Baboota et al., 2007a; Shakeel et al., 2008a, 2008b). It is also used in the treatment of various types of cancers such as colon cancer (Kawamori et al., 1998), ultraviolet (UV) light-induced skin cancer (Fisher et al., 1999), and breast cancer (Harris et al., 2000).

Caffeine is a naturally occurring pseudo-alkaloid found in tea leaves, coffee, cocoa, guarana, and kola nuts (Murray & Hansen, 1995; Hampp, 1996). It also has stimulant, vasodilating, and diuretic activities (increases urination). Caffeine has been proved to be a good complexing agent to improve the therapeutic efficacy of many drugs (Leiberman et al. 1987; Ammar et al., 1997; Evstigneew et al., 2006a, 2006b). Recently, some reports have indicated potential anticancer activities of caffeine (Sarkaria et al., 1999; Michal & Andrzej, 2008; Tomita & Tsuchiya, 2008). Therefore, caffeine could produce synergistic anticancer activities by molecular complexation with CXB. The solubility, permeability, and dissolution are very important parameters for in vivo performance of solid dosage forms. The in vitro dissolution of the drug from the dosage form determines the in vivo bioavailability (Ahmed et al., 1993). In the case of a poorly soluble drug (CXB), dissolution is the rate-limiting step in the process of drug absorption, and hence causes a potential bioavailability problem (Popli et al., 1994). Complexation with caffeine has been used successfully to improve the solubility, dissolution rate, and in vivo efficacy of many drugs (Leiberman et al. 1987; Ammar et al., 1997; Evstigneew et al., 2006a, 2006b). Because the poor aqueous solubility of CXB (5 μg/mL) poses a dissolution-related absorption problem, an attempt was made to improve the solubility as well as dissolution of CXB using complexation with caffeine (Baboota et al., 2007a).

Improved solubility and dissolution of CXB could further enhance the therapeutic effects such as anticancer activities and anti-inflammatory effects, as well as in vivo bioavailability.

Materials and methods

Materials

CXB was a kind gift sample from Ranbaxy Research Laboratory (Haryana, Laboratory is in Benghazi, Libya, India). Caffeine was extracted from tea leaves in the phytochemistry laboratory. Dried tea leaves were purchased from a local market, Benghazi (Libya), and were identified by Dr Rajinder Singh a taxonomist of the Al-Arab Medical University, Benghazi, Libya. All other chemicals used in the study were of AR grade.

Extraction of caffeine from tea leaves

The dried tea leaves (30 g) were taken in a beaker and mixed with 250 mL of distilled water and 5 g of sodium carbonate with the help of a glass rod. The contents of the beaker were boiled on a water bath for 15 min, cooled at room temperature, and then filtered using a muslin cloth. The filtrate was transferred to a separating funnel and extracted four times with a sufficient quantity of dichloromethane. After each extraction, the organic layer was removed. Anhydrous sodium sulfate was added to the extracts to remove any water and water-soluble salts. Then the contents were filtered again to remove the solid sodium sulfate, and the “ nonaqueous” solution was transferred to a previously weighed beaker and evaporated to dryness by boiling on a water bath. The residue obtained was crude caffeine (Hampp, 1996). It was purified by sublimation at 170°C. The melting point of the obtained crystals was determined using a capillary method.

Preparation of caffeine–CXB molecular complex

A 1:1 molecular complex of caffeine and CXB was prepared using the solubility method. Caffeine and CXB were dissolved in distilled water and methanol, respectively. These two solutions were mixed properly with the help of a glass rod. The solvents were evaporated to dryness at 50°C using a water bath. The resulting residue was used as the molecular complex of caffeine and CXB.

Solubility determination

The solubility of CXB in distilled water as well as in the complex was determined by a high performance liquid chromatography (HPLC) method at a wavelength of 250 nm (Baboota et al., 2007b). Excess amounts of pure CXB or its complex were added in distilled water in conical flasks in triplicate. These conical flasks were kept in a water bath with mechanical shaker (Mammert, Germany) at a temperature of 25 ± 1°C for 72 h to achieve equilibrium. After reaching equilibrium, the flasks were removed from the shaker bath, and the contents filtered, diluted suitably with distilled water, and subjected to analysis of drug content by HPLC at a wavelength of 250 nm (Baboota et al., 2007b).

Dissolution studies

Dissolution studies of pure CXB, complex, and a marketed capsule were performed using USP dissolution apparatus I (for pure CXB and complex) and apparatus II (for the capsule) in distilled water. These studies were performed at 37 ± 1°C and 50 rpm. Samples were withdrawn at regular time intervals (0, 15, 30, 45, 60, 90, and 120 min) and replaced every time with freshly prepared distilled water. The content of CXB release (% dissolution) was determined by HPLC at a wavelength of 250 nm (Baboota et al., 2007b).

Statistical analysis

The results for solubility and dissolution were compared by applying one-way analysis of variance (ANOVA) followed by the Tukey–Kramer multiple comparisons test using GraphPad Instat software (GraphPad Software Inc., CA, USA).

Results

Caffeine was successfully extracted from tea leaves. Smooth crystals were obtained. The melting point of caffeine was found to be 238.5°C by the capillary method, which is similar to the reported melting point of caffeine (238.5°C). This indicated the purity of the caffeine. The solubility of CXB in the complex was determined and compared with its aqueous solubility. The solubility of CXB in distilled water and in the complex is shown in Table 1. The solubility of CXB in distilled water at 25°C was found to be 0.006 ± 0.0001 mg/mL. The solubility of CXB in the complex was 48.32 ± 2.32 mg/mL (Table 1). The solubility of CXB in the complex was highly significant as compared to its aqueous solubility (p < 0.01). The enhancement in solubility was 8053.33-fold in the complex as compared to its aqueous solubility. Dissolution studies of CXB from pure drug, the complex, and a marketed capsule were performed in distilled water. The percent dissolution of CXB after 120 min was lowest in pure CXB (35%) and highest in the complex (90.54%), as shown in Figure 1. The percent dissolution of CXB in the complex was extremely significant as compared to pure CXB and the marketed capsule (p < 0.001). This indicates that the presence of caffeine as a complexing agent can significantly enhance the dissolution of a poorly soluble drug. These results indicate that complexation of caffeine with CXB can be successfully used to enhance solubility, as well as dissolution. The enhancement of solubility and dissolution will further result in an improvement of therapeutic efficacy as well as bioavailability of CXB.

Figure 1.  Comparative dissolution (mean ± SD, n = 3) profile of CXB from pure drug (pure CXB), complex, and marketed capsule.

Table 1.  Solubility of CXB in distilled water and its complex at 25°C.

Sample matrix	Solubility (mg/mL)^a	Enhancement in solubility
Distilled water^b	0.006 ± 0.0001	—
Caffeine–CXB complex	48.32 ± 2.32	8053.33-fold

^aMean ± SD, n = 3.

^bDistilled water was used as control.

Conclusion

The results of these studies indicate that caffeine is a promising complexing agent for solubility and dissolution enhancement of a poorly soluble drug such as CXB. However, more in vivo investigations are required to prove the therapeutic efficacy of this complex.

Acknowledgement

The authors are thankful to Ranbaxy Research Laboratory (Haryana, India) for providing the gift sample of celecoxib.

Declaration of interest: The authors report no conflicts of interest.