In vitro and in vivo characteristics of celecoxib in situ formed suspensions for intra-articular administration.

The research article describes how an in situ suspension-forming system of the drug celecoxib might be used to ensure the drug is released at a sustained rate into the targeted area—specifically, the joint cavity—after intra-articular administration. The study details the formulation process, the performance in vitro and in vivo, including the release profiles and the variation in suspension formation in synovial fluid. In an animal study, the celecoxib suspension was effective in providing ongoing drug exposure in the joint.

Formulation of Celecoxib Suspension

• The study focused on using an in situ suspension forming system for celecoxib, a drug used for pain and inflammation, aiming to provide sustained drug exposure in the joint cavity after intra-articular (within a joint) administration.
• In vitro (in a lab, outside of a living organism), precipitates of celecoxib were formed by adding a solution of celecoxib in polyethylene glycol 400 (PEG 400) to a phosphate buffer (pH 7.4), or to synovial fluid (the lubricating fluid found in joints).

Release Profiles

• The in vitro release profiles of the celecoxib in situ suspensions demonstrated an initial fast release of the drug, followed by a period of slower, constant release (flux).
• Interestingly, the release rate in the buffer solutions was found to be comparable to a pre-made suspension of celecoxib in its most stable crystal form, even though the in situ formed precipitates contained a mixture of two crystal forms of celecoxib.

Variation in Synovial Fluid

• In contrast, the in situ suspension formation of the celecoxib in synovial fluid showed a much higher degree of variability. The reason for this variation was not specified and may warrant future research.

In Vivo Findings

• In an in vivo experiment, a relatively high dose of celecoxib in the form of a PEG 400 solution was injected into the joint of four horses. Over a period of 10 days, celecoxib was still detectable in the blood samples taken from the horses, and upon autopsy, it was also found in the joint tissue.
• The presence of celecoxib in the joint tissue post mortem strongly indicates that a sustained drug exposure in joints can be achieved using the in situ suspension formation method, implying potential efficacy for pain and inflammation relief in relevant clinical conditions.