Rectal Administration of Celecoxib Liquid Suppositories with Enhanced Bioavailability and Safety in Rats

Celecoxib is generally used for the treatment of rheumatoid arthritis, however its poor bioavailability and cytotoxicity in pure form have reduced its therapeutic efficacy. This study aims to develop celecoxib liquid suppositories with improved bioavailability and reduced toxicity.

The celecoxib liquid suppositories were prepared by thoroughly mixing celecoxib, poloxamer 188 and poloxamer 407, and tween-20, respectively used as drug, polymers and surfactant, in triple distilled water using cold technique. The developed liquid suppositories were characterized in terms of their gelation temperature, gelation time, and gel strength. Moreover, the muco-adhesive force was determined for the suppositories. The release behavior of the liquid suppositories was investigated in distilled water and compared with drug suspension. Furthermore, pharmacokinetics and morphological studies were carried out in rats after rectal administration of the celecoxib liquid suppository compared with drug suspension.

Poloxamer 188 and Tween-20 concentrations have significantly reduced the gelation temperature and time; however, the gel strength and bio-adhesive force were significantly enhanced. The concentration of celecoxib has no significant effect on the properties of liquid suppositories. A significantly enhanced and potentially sustained drug release was observed from the celecoxib liquid suppositories as compared with the drug suspension. The optimized formulation was easy to administer rectally because it quickly forms gel upon insertion into the body due to a suitable gelation temperature of about 31.7 °C. After rectal administration in rats, the celecoxib liquid suppository gave a significantly increased pharmacokinetic profile including enhanced plasma concentration and 9.7 fold improved area under the curve (AUC) compared to the drug suspension. Additionally, the morphology study exhibited no toxicity to the rectal tissue, no signs of irritation, or injury after the application of suppository. However, severe rectal tissue toxicity and irritation was observed in the suspension treated rectum.

It can be concluded that the liquid suppository system may significantly enhance the solubilization and bio-availability of sparingly water-soluble drugs as evident in the case of celecoxib with no toxicity at the site of application.