Mucoadhesive In Situ Rectal Gel Loaded with Rifampicin: Strategy to Improve Bioavailability and Alleviate Liver Toxicity

Abstract

Although it is a front-line in tuberculosis treatment, rifampicin (RF) exhibits poor oral bioavailability and hepatotoxicity. Rectal mucoadhesive and in situ rectal gels were developed to overcome drug drawbacks. A RF/polyethylene glycol 6000 co-precipitate was first prepared in different ratios. Based on the drug solubility, the selected ratio was investigated for drug/polymer interaction and then incorporated into in situ rectal gels using Pluronic F127 (15%) and Pluronic F68 (10%) as a gel base and mucoadhesive polymers (HPMC, sodium alginate and chitosan). The formulations were assessed for gelation temperature and gel strength. The selected formulation was investigated for in vivo assessments. The results showed that a 1:1 drug/polymer ratio exhibited satisfying solubility with the recorded drug/polymer interaction. Depending on their concentrations, adding mucoadhesive polymers shifted the gelation temperature to lower temperatures and improved the gel strength. The selected formulation (F4) did not exhibit any anal leakage or marked rectal irritation. Using a validated chromatographic analytical method, F4 exhibited higher drug absorption with a 3.38-fold and 1.74-fold higher bioavailability when compared to oral drug suspension and solid suppositories, respectively. Toxicity studies showed unnoticeable hepatic injury in terms of biochemical, histopathological and immunohistochemical examinations. Together, F4 showed a potential of enhanced performance and also offered lower hepatic toxicity, thus offering an encouraging therapeutic alternative.

Keywords: hepatotoxicity; mucoadhesive; rectal in situ gelling; rifampicin.

Figure 1

Solubility of rifampicin RF after co-precipitation with different polyethylene glycol (PEG) 6000 ratios. The values are expressed in mean values ± SD, n = 3.

Figure 2

Differential scanning calorimetry (DSC) thermograms of (A) PEG 6000, (B) RF, (C) RF/PEG 6000 co-precipitate and (D) RF/PEG 6000 physical mixture.

Figure 3

Fourier transform infrared spectroscopy (FTIR) spectra of RF, PEG 6000, the RF/PEG 6000 physical mixture and the RF/PEG 6000 co-precipitate.

Figure 4

Histological alterations in rectum sections stained by hematoxylin/eosin of; (A) normal control rabbits and (B) rabbits after the rectal administration of F4 (magnification 100×, bar 100 µm).

Figure 5

The plasma level-time curve after a single-dose administration of the RF oral suspension, RF rectal conventional suppository and F4. The values are expressed in mean values ± SD, n = 6.

Figure 6

Histopathological alterations in hepatic sections stained by hematoxylin/eosin of; (A,B) normal control rabbits presenting normal hepatic cells and (C,D) rabbits that received the RF suspension, showing hydropic degeneration, blood vessel congestion and infiltration by mononuclear inflammatory cells. Magnification for; (A) ×100 and bar 100 µm, (B–D) ×400 and bar 50 µm.

Figure 7

Histological changes in liver sections stained by hematoxylin/eosin of; (A,B) rabbits that received solid suppositories, showing moderate improvement of hepatic histology and moderate hydropic degeneration and (C,D) rabbits that received F4, showing mild hepatocytes swelling in centrilobular zone with narrowing of hepatic sinusoids. Magnification for; (A,B,D) ×400 and bar 50 µm, (C), ×100 and bar 100 µm.

Figure 8

Immunostained liver sections for tumor necrosis factor α (TNF-α) of (A) rabbits that received saline presenting an unnoticeable expression of TNF-α, (B) rabbits that received the RF oral suspension showing a positive reaction, (C) rabbits that received solid suppositories presenting some sporadic cells and (D) rabbits administered F4 presenting a minimal positive reaction. Magnification ×400 and bar 50.

Figure 9

Morphometric analysis of immunohistochemical (IHC) positive staining score of TNF-α reaction in different groups. The values are expressed in mean values ± SD, n = 6.