Unravelling the effect of non-drug spacers on a true drug-polymer and a comparative study of their antimicrobial activity

Several studies have been conducted on polymerisation of drug units using spacers or other polymeric units. In order to study the importance of spacers in drug polymers, we designed polymers with and without spacers. As a proof of concept, herein, we present a comparative study on the efficacy of antibacterial activity using a polymeric biocide (PB) C0P1 having no spacer (0%) and two other PBs with varied spacer content (C2P2:29%, C10P3:53%). We considered C0P1 as a potential new type of PB generated from a widely used fluoroquinolone antibiotic, ciprofloxacin 1, by a simple self-condensation activation with thionyl chloride. Monomer 2 (formylated methyl ester of 1) was polymerised with ethylenediamine (C2) and 1,10-diaminodecane (C10) to provide C2P2 and C10P3, respectively. The trend for minimum inhibitory concentration study against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was observed as 1>C0P1>C2P2=C10P3>>2. Further, after coating on nylon threads, the non-spacer polymer C0P1 showed enhanced zone of inhibition (ZOI) than monomer 1 as well as the spacer polymers owing to its superior coating ability and sustained drug release capabilities. Thus, this study clearly states that the bio-efficacy of a drug-polymer could be retained and enhanced in the absence of non-bioactive spacer units.