Novel Thioester Prodrug of N-acetylcysteine for Odor Masking and Bioavailability Enhancement

The mucolytic N-acetylcysteine (NAC) is used to control the excessive mucus secretion if mucus is the underlying cause of broncho-constriction. Its major drawbacks are poor bioavailability due to extensive first pass effect, poor lipophilicity, high protein binding and offensive odor.

For minimizing above shortcomings of NAC, in present study thioester (A1) prodrug of NAC was synthesized by conventional as well as microwave-assisted methods. Release studies of A-1 were carried out using HPLC and pharmacological evaluation was performed in ovalbumin-induced model of pulmonary inflammation in Sprague dawley rats.

A-1 was found to be stable in HCl buffer, phosphate buffer, stomach homogenates but furnished 30% NAC in 6h and 1.7% of NAC in 4h when incubated with small intestinal and liver homogenates respectively. Upon oral administration of A-1 to rats, 4.85% NAC was detected in blood at 8h. Urine samples pooled over a period of 24h exhibited 0.75% NAC while negligible concentration was found in 24 h pooled samples of feces.

The findings of this preliminary investigation demonstrated significant effects of thioester prodrug A-1 as compared to NAC through reduction of lung inflammation, airway eosinophilia and reversal of lung function parameters in ovalbumin- challenged rats at half the equimolar dose of NAC. Interestingly masking thiol group through thioester formation resulted in odorless prodrug. We propose that thioester prodrug using palmitic acid as a carrier is a promising strategy to enhance bioavailability of NAC by increasing its lipophilicity/ absorption and minimizing its first pass metabolism.