Although conventional tablets are widely accepted oral solid-dosage forms, pediatric, geriatric, and bedridden patients experience difficulties in swallowing them. Moreover, for poorly soluble drugs, dissolution of the drug from the tablet is the rate-limiting step in the process of drug absorption (7). Because the rate and extent of drug absorption is determined by the rate and extent of drug dissolution from tablets, drugs with poor aqueous solubility as a result of erratic or incomplete absorption from the gastrointestinal tract are known to pose potential bioavailability problems (8).
Because nabumetone is practically insoluble in water, its absorption is expected to be dependent on dissolution rate (9). This study attempts to resolve this problem by formulating the drug previously complexed with β-cyclodextrin (β-CD) as a porous rapidly dispersing tablet. These tablets were intended to disintegrate quickly and dissolve completely to facilitate complete drug absorption following oral administration. Inclusion complexes have been used successfully to improve solubility, dissolution, and bioavailability of poorly soluble drugs (10–14).Materials and methods
Materials. Nabumetone was donated by Micro Labs (Bangalore, India). β-CD manufactured by Roquette Freres (Lestrem cedex, France) was donated by Signet Chemical Corp., (Mumbai, India). Crospovidone (polyplasdone XL) and mannitol (Paerlitol) were samples from Zydus Health Care Ltd., (Bangalore). The other samples of ammonium bicarbonate, saccharine sodium, and polyvinyl pyrollidone-K30 (PVP-K30) were of analytical grade and purchased from S.D. Fine Chemicals (Mumbai).
Phase solubility studies. Phase solubility studies were performed in triplicate at room temperature (25 °C) according to the method reported in the literature (10). Excess amounts of nabumetone were added to distilled water containing various concentrations of β-CD (0.3–1.5 mM) in a series of stoppered volumetric flasks and shaken for 72 h on a rotary shaker (Secor Laboratory Instruments, New Delhi, India). The resulting suspensions were filtered through 0.45-μm filter, diluted suitably, and assayed spectrophotometrically (model UV 1700 PC Shimadzu Corp., Kyoto, Japan) at 270 nm using reagent blanks prepared with the same concentrations of β-CD in distilled water. The apparent stability constant (Ks) of the complexes was calculated from the slope and the intercept of the phase solubility diagram using Equation 1:
Preparation of the complexes. The drug β-CD complexes were prepared using the kneading method (10). Nabumetone was mixed with equimolar quantities of β-CD in a mortar with a small amount of water and kneaded for 45 min to obtain a homogeneous paste. The resulting paste was dried in an oven at 45 °C for 48 h, and the solid obtained was ground and sieved through a 150-μm sieve. A physical mixture of the drug and β-CD at a 1:1 molar ratio prepared by simple mechanical admixing was used as a reference during characterization of the kneaded complex.
Fourier transform infrared (FTIR)spectrophotometry. The samples were powdered and mixed with dry powdered potassium bromide. The mixtures were taken in a diffuse reflectance sampler and infrared spectra of the drug, β-CD, and the inclusion complexes were recorded by scanning the 400–4000 cm–1 wavelength region in an FTIR spectrophotometer (model 460 Plus, Jasco, Japan).