Removal of residual colonic ciprofloxacin in the rat by activated charcoal entrapped within zinc-pectinate beads

Abstract

Residual antibiotics reaching the colon have many deleterious effects on the colonic microbiota including the selection of new antibiotic resistances. In order to avoid the selection of ciprofloxacin resistance, intestine or colon-targeted zinc-pectinate beads containing activated charcoal (AC) were designed for the inactivation of residual ciprofloxacin in the gastrointestinal tract of rats. Bead stability after oral administration was adjusted by tuning the concentration of zinc in the gelling bath and the number of washings. Intestine and colon-targeted beads were administered along with 50 mg/kg of ciprofloxacin and ciprofloxacin was dosed in the plasma and the feces using HPLC. Ciprofloxacin pharmacokinetics was not affected by the oral co-administration of beads. The co-administration of intestine-targeted beads led to a significant decrease of the residual fecal free ciprofloxacin with a pronounced dose effect. Our study suggests the rat model is not appropriate for the investigation of bacteria responsive colon-targeted beads probably due to the important anatomical and physiological differences between human and rat gastrointestinal tracts. The ability of AC loaded zinc-pectinate beads to selectively decrease the intestinal residual fraction of ciprofloxacin could provide a better protection of the intestinal microbiota and may prevent the emergence of ciprofloxacin resistance in the gastrointestinal tract.

Introduction

The introduction of antimicrobial drugs into clinical use had a striking impact on the treatment of infectious diseases and dramatically decreased mortality (Cohen, 2000). However, despite number of successes in therapeutics of infectious diseases, they remain an important global public health problem causing over 11 million deaths annually (Fauci, 2001, Nathan, 2004). Indeed, pathogenic bacteria have developed relentlessly a significant resistance to one class of antibiotic after another (Amyes, 2000). The widespread and inappropriate use of these drugs greatly accelerated the process. In roughly 50 years of the antibiotic era, an estimated one million tons of antibiotics have been produced and disseminated, including those for animal and agricultural uses (Walsh, 2003).

Emergence of resistance in bacteria can result from two different sequences of events, including either a direct one-step selection of resistant clones at the site of infection, or an indirect two-steps process in which commensal resistant bacteria are first selected in the natural ecosystems of humans. They can then transfer resistance mechanisms horizontally to pathogenic species (Andremont, 2004). It is now established that this second two-steps mechanism is the major route of evolution of bacterial resistance. Indeed, the diversity of bacterial species and their resistance genes present in the natural ecosystems become a quasi unlimited source of new or variant resistance mechanisms (Andremont, 2004, Salyers et al., 2004). The intestinal tract is the site where a lot of antibiotic resistances develop (Nikolich et al., 1994, O’Brien et al., 1980). Indeed, the incomplete absorption of orally administered antibiotics and the secretion of the antimicrobial agent by the salivary glands, in the bile and from the intestinal mucosa disturb the colonization resistance of the intestinal microbiota giving rise to the emergence of resistance to antibiotics by the indirect two-steps process described above (Khoder et al., 2009). In spite of the essential role of the intestinal microbiota in the selection of new antibiotic resistances, its protection has been scarcely considered among the numerous clinical strategies developed for reducing antibiotic resistance (Andremont, 2004, O’Brien et al., 1980). In this context, the inactivation of residual active antimicrobial agents inside the intestinal tract to avoid the direct contact with the intestinal microbiota may scientifically reduce the emergence of new resistances (van der Waaij and Nord, 2000). Antimicrobial agents are often naturally inactivated to variable extent in the intestine by bacterial enzymes or by binding to bacteria and other fecal components (Edlund et al., 1988). Nevertheless, the remaining activity in the gastrointestinal (GI) tract of many antimicrobial agents is sufficiently high to disturb the ecological balance. Several studies have shown the efficacy of the oral administration of β-lactamases enzymes to protect the intestinal microbiota against residual β-lactams (Bourgeois et al., 2005, Bourgeois et al., 2008, Harmoinen et al., 2004, Harmoinen et al., 2003, Hoffman et al., 2008, Stiefel et al., 2005, Stiefel et al., 2003, Tarkkanen et al., 2009).

Although the enzymatic inactivation has the advantage to be irreversible, it is restricted to only a few antibiotic classes. Furthermore, enzymes are difficult to formulate due to their poor stability. Hence, non-enzymatic inactivation is promising since it could be applied to all antibiotics classes including those for which no hydrolysing enzymes have been identified (van der Waaij and Nord, 2000). We have recently designed a formulation of activated charcoal (AC) encapsulated within zinc-pectinate beads coated with Eudragit^® RS. The adsorption studies in simulated intestinal and colonic media showed that the adsorption capacity of AC was not affected after its encapsulation within pectin beads making the elimination of antibiotic reaching the colon clinically feasible (Khoder et al., 2009). The goal of the present study was to design intestine and colon-targeted zinc-pectinate beads loaded with AC and to assess in vivo, in the experimental rat model, the potentiality of such systems to achieve a selective intra-intestinal inactivation of residual ciprofloxacin without modifying antibiotic pharmacokinetics.