MACROMOLECULAR PRODRUGS OF SOME ANTIBIOTICS ONTO POLYGLUCANS: FABRICATION, CHARACTERIZATION, APPLICATIONS AND STUDIES OF NANO-ASSEMBLIES IN SOLUTION

Abstract

Present study reports the synthesis and characterization of hydroxypropylcellulose (HPC) based macromolecular prodrugs (MPDs) of a broad spectrum class of antibacterial agents; fluoroquinolones. Prodrugs of some fluoroquinolones, i.e., moxifloxacin, ofloxacin, levofloxacin and ciprofloxacin were fabricated as ester conjugates of HPC in various mole ratios using p-toluenesulfonyl chloride as carboxylic acid activating agent. All prodrugs were found organo- as well as water-soluble. Structural characterization of HPC-fluoroquinolone conjugates 1-17 was carried out by FTIR, 1H, 13 C and 2D NMR spectroscopic techniques. Covalently loaded drug content (DC) of the conjugates was determined by UV/Vis spectrophotometry as well as by HPLC/UV method. Degree of substitution (DS) of the conjugates was derived from the respective DC of each conjugate. DS of all conjugates was also determined by acid-base titration after saponification and found to be 0.27-0.38, 0.53- 0.71, 0.57-0.64 and 0.87-1.15 per AGU for moxifloxacin, ofloxacin, levofloxacin and ciprofloxacin, respectively. Nano-assembly behavior of HPC-fluoroquinolone conjugates at solvent interface (DMSO/H2O) was assessed by transmission electron microscopy (TEM). TEM images showed that HPC-fluoroquinolone conjugates behaved differently; HPC- moxifloxacin conjugate 3 self-assembled into nanowires of 30 nm diameter, while HPC- ofloxacin conjugate 7, HPC-levofloxacin conjugate 11 and HPC-ciprofloxacin conjugate 15 self-assembled onto nanoparticles having diameter range of 200-270, 50-250 and 150-250 nm, respectively. In vitro drug release studies revealed higher release from prodrugs in simulated intestinal fluid (SIF) as compared to simulated gastric fluid (SGF). Conjugates 3, 7, 11 and 15 showed release of 49, 39, 44 and 43%, respectively, in SIF after first 6 h. While these conjugates showed only 12-15% release in SGF in the same time period. Higher release in SIF confirmed that the synthesized prodrugs could be used as devices for achieving colon targeted drug delivery. Pharmacokinetic studies of the conjugates in rabbit models indicated enhanced bioavailability of the respective drugs. Following single oral dose, conjugates 3, 7, 11 and 15 showed half-life of 25.20, 18.07, 18.08 and 10.87 h, respectively. These enhanced half-life values suggest the potential of the fabricated MPDs for once daily dosage formulation. Thermal analyses of the synthesized prodrugs were carried out to assess their pharmaceutical performance parameters. Thermal stability of HPC, drugs and prodrugs was compared in terms of thermal degradation temperatures (Tdi, Tdm,Tdf). Comparable Tdm values of drugs and conjugates suggested that no thermal stress was developed after the attachment of bulky drug molecules to polymer backbone. Thermal stability of conjugates was also evaluated in terms of integral procedure decomposition temperature (IPDT) and index of thermal stability (ITS). Conjugate 3, 7, 11 and 15 showed IPDT values of 450, 442, 464 and 486 °C, respectively. The ITS values were found to be 0.51, 0.52, 0.46 and 0.51, respectively, for these conjugates. Significantly higher IPDT and ITS values also confirmed the intrinsic thermal stability of these conjugates. Modulated differential scanning calorimetry was also performed to analyze glass-transition temperatures (Tg) imparted due to attachment with polymer. Tg values observed were 111.60, 84.16, 113.85 and 61.91 °C for conjugates 3, 7, 11 and 15, respectively. PXRD studies confirmed that some crystallinity was imparted to MPDs of fluoroquinolones. Powder X-ray analysis also confirmed the amorphous characteristics of the conjugates. Therefore, such MPDs can be used for colon targeted delivery of fluoroquinolones with enhanced bioavailability and reduced dosage frequency.