Design of pH-sensitive microspheres for the colonic delivery of the immunosuppressive drug tacrolimus

Encapsulation of lipophilic drugs within enteric microparticles by a novel coacervation method

Enteric microparticles were prepared by a novel microencapsulation method in order to improve the oral bioavailability of lipophilic drugs. This method involved the addition of an aqueous polymer solution to an organic enteric polymer solution containing lipophilic drugs. In contrast to classical coacervation microencapsulation methods, the drugs were initially also dissolved and not dispersed in the organic polymer solution. The hydrophilic polymer (hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC) and Poloxamer 407) was dissolved in the aqueous phase and acted as a stabilizer for the coacervate droplets, preventing their coalescence and leading to the formation of enteric microparticles. The size of the enteric microparticles decreased with higher concentrations of the hydrophilic polymers, a higher pH of the aqueous polymer solution, a higher content of carboxyl groups of the enteric polymer and with better polymer solvents. Amide-containing lipophilic drugs, such as carbamazepine, lidocaine and cyclosporine A, were successfully encapsulated in the enteric microparticles in a non-crystalline state and were physically stable for 5 months. The high solubility of carbamazepine in the enteric polymer (>30%, w/w), a high partition coefficient between polymer-rich/-poor regions and strong drug/polymer interactions contributed to the high drug encapsulation efficiency (90%, w/w). In contrast, carboxyl-containing drugs (indomethacin, ibuprofen) and hydroxyl-containing drug (17beta-estradiol hemihydrate) crystallized inside or outside the polymeric matrix due to their low solubility in the enteric polymer.

Design and evaluation of colon specific drug delivery system containing flurbiprofen microsponges

The purpose of this study was to design novel colon specific drug delivery system containing flurbiprofen (FLB) microsponges. Microsponges containing FLB and Eudragit RS 100 were prepared by quasi-emulsion solvent diffusion method. Additionally, FLB was entrapped into a commercial Microsponge 5640 system using entrapment method. Afterwards, the effects of drug:polymer ratio, inner phase solvent amount, stirring time and speed and stirrer type on the physical characteristics of microsponges were investigated. The thermal behaviour, surface morphology, particle size and pore structure of microsponges were examined. The colon specific formulations were prepared by compression coating and also pore plugging of microsponges with pectin:hydroxypropylmethyl cellulose (HPMC) mixture followed by tabletting. In vitro dissolution studies were done on all formulations and the results were kinetically and statistically evaluated. The microsponges were spherical in shape, between 30.7 and 94.5microm in diameter and showed high porosity values (61-72%). The pore shapes of microsponges prepared by quasi-emulsion solvent diffusion method and entrapment method were found as spherical and cylindrical holes, respectively. Mechanically strong tablets prepared for colon specific drug delivery were obtained owing to the plastic deformation of sponge-like structure of microsponges. In vitro studies exhibited that compression coated colon specific tablet formulations started to release the drug at the 8th hour corresponding to the proximal colon arrival time due to the addition of enzyme, following a modified release pattern while the drug release from the colon specific formulations prepared by pore plugging the microsponges showed an increase at the 8th hour which was the time point that the enzyme addition made. This study presents a new approach based on microsponges for colon specific drug delivery.

Nanoparticles in inflammatory bowel disease: Particle targeting versus pH-sensitive delivery

Tacrolimus proved its distinct mitigating potential in the treatment of inflammatory bowel disease (IBD). Due to the risk for severe adverse effects and to achieve increased efficiency and tolerability, a selective delivery to the site of inflammation is of interest. Tacrolimus nanoparticles (NP) were tested for their efficiency in local treatment of inflamed bowel tissue in IBD. Drug loaded NP were prepared from either biodegradable poly(lactide-co-glycolide) (PLGA) or pH-sensitive Eudragit P-4135F by using a simple oil/water emulsification method. Tests on the therapeutic effect were conducted using dextran sulfate model colitis in mice receiving tacrolimus formulations daily for 12 days. Clinical activity score and myeloperoxidase activity decreased while colon length increased significantly after administration of all tacrolimus containing formulations. Oral NP formulations were less efficient in mitigating the experimental colitis compared to subcutaneous drug solution (PLGA: 7.88 +/- 0.83; P-4135F: 7.48 +/- 0.42; subcutaneous: 5.27 +/- 0.68 U/mg) but superior to drug solution given by oral route (oral: 8.75 +/- 1.34; untreated colitis control: 9.95 +/- 0.92, all U/mg tissue). Tacrolimus solution groups (oral/subcutaneous) exhibited increased levels of adverse effects, whereas both NP groups demonstrated their potential to reduce nephrotoxicity. Both strategies showed similar mitigating effects while nephrotoxic adverse effects were slightly less expressed with pH-sensitive NP.

Novel drug delivery strategies for the treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) encompasses two idiopathic inflammatory diseases of the intestinal tract: Crohn's disease and ulcerative colitis. Existing therapy for IBD consists mainly of orally or rectally administered small drug molecules, such as 5-aminosalicylates and corticosteroids, or potent systemic immune suppressants. IBD presents a challenging target for drug delivery, particularly by the oral route, as, contrary to most therapeutic regimens, minimal systemic absorption and maximal intestinal wall drug levels are desired. Several delivery strategies are employed to achieve this goal, including the chemical modification of the drug molecules, the use of controlled- and delayed-release formulations and the use of bioadhesive particles. The goal of this review is to summarise existing IBD therapy and examine novel approaches in intestinal drug delivery.

A pH-sensitive microsphere system for the colon delivery of tacrolimus containing nanoparticles

Nanoparticles (NP) are known to accumulate at the site of inflammation in inflammatory bowel disease. In order to avoid premature uptake or degradation of NP during their passage through the small intestine, it appeared necessary to devise a form of local delivery system for NP. Tacrolimus (FK506) loaded poly(lactic-co-glycolic acid) NP entrapped into pH-sensitive microspheres (NPMS) were designed to achieve greater selectivity to their site of action when administered orally. The therapeutic efficacy of this drug delivery system was tested in an experimental colitis in rats. The in vitro characterization showed a successful incorporation of FK506-NP and strongly pH-sensitive release kinetics of both NP and drug. During the in vivo studies, clinical activity, colon/body weight index, and myeloperoxidase activity were determined to assess the severity of inflammation. Systemic availability of a fluorescent dye entrapped in the microspheres was measured in order to determine possible adverse effects. The NPMS as well as the controls of NP and MS formulations exhibited significant mitigating effects in the clinical activity index after 3 days of treatment with similar levels for the various therapies. When observing colon/body weight index and myeloperoxidase activity, only the NPMS group reached statistically significant differences (P<0.05) compared to the colitis control group while other groups did not (colitis control: 21.94+/-4.97; FK506 solution: 15.81+/-3.42; FK506-NP: 17.03+/-5.52; FK506-MS: 15.17+/-7.81; and FK-NPMS: 10.26+/-7.76 U/mg tissue). Moreover, the NPMS system reduced the systemic absorption of the entrapped dye compared to the dye solution or simple NP formulation (relative biovailability-solution: 100+/-14.9%; NP: 46.8+/-8.6%; and NPMS: 29.4+/-3.3%). The results suggest that the NPMS system can provide selective delivery of NP in the colon and develop a significant mitigating effect, while the control group treatments appeared to be insufficient.

FK506 Microparticles Mitigate Experimental Colitis with Minor Renal Calcineurin Suppression

PURPOSE

FK506 microparticles providing selective colonic drug delivery were tested for their efficiency in a local treatment to the inflamed gut tissue in inflammatory bowel disease (IBD). Because FK506 proved its distinct mitigating potential in the treatment of IBD, risking, however, severe adverse effects, a more selective delivery to the site of inflammation may further improve efficiency and tolerability.

METHODS

A model colitis was induced to male Wistar rats by trinitrobenzenesulfonic acid. FK506 was entrapped into microspheres (MS) prepared with the pH-sensitive polymer Eudragit P-4135F in order to allow drug delivery to the colon. Clinical activity score, colon/body weight index, and myeloperoxidase activity were determined to assess the inflammation, and adverse effects of FK506 resulting from its systemic absorption were quantified as well.

RESULTS

The clinical activity score and myeloperoxidase activity decreased after the administration of all FK506-containing formulations. The MS formulations proved to be as efficient in mitigating the experimental colitis as the subcutaneous drug solution (myeloperoxidase activity, MS: 9.64+/-6.6 U/mg tissue; subcutaneous: 7.48+/-6.96 U/mg) and to be superior to drug solution given by oral route (oral: 12.66+/-5.46 U/mg; untreated colitis control: 21.88+/-4.12 U/mg). The FK506 subcutaneous group exhibited increased levels of adverse effects, whereas the FK506-MS group proved its potential to retain the drug from systemic absorption as evidenced by reduced nephrotoxicity.

CONCLUSIONS

The development of this selective delivery system for FK506 should be given particular consideration in the treatment of IBD, as it allows therapy that profits from FK506's high immune suppressive effect with a simultaneously reduced nephrotoxicity.