Design of supersaturable formulation of telmisartan with pH modifier: in vitro study on dissolution and precipitation

Effect of pH Modifiers on the Solubility, Dissolution Rate, and Stability of Telmisartan Solid Dispersions Produced by Hot-melt Extrusion Technology

The aim of the current study was to investigate the dual effect of an amorphous solid dispersion generated by hot melt extrusion and the addition of pH modifiers on the solubility and stability of telmisartan. Hydroxypropyl methylcellulose acetate succinate L grade was used as a polymeric carrier and recrystallization inhibitor, and meglumine, sodium carbonate, or Neusilin S2 were incorporated as pH modifiers to generate a desirable microenvironmental pH in the solid dispersions. Differential scanning calorimetry, powder X-ray diffraction, and Fourier transform infrared spectroscopy were incorporated to obtain the solid-state characterizations of telmisartan, and the results confirm a partial transformation of telmisartan to an amorphous state. An in vitro release study revealed that the transformation of telmisartan to an amorphous material improved its dissolution rate by 2-fold compared to pure drug and by up to 5-fold with the incorporation of pH modifiers. Results of the stability studies demonstrated that the samples have no significant degradation under accelerated stability conditions at 40 °C/75% RH.

Supersaturable self-microemulsifying drug delivery system enhances dissolution and bioavailability of telmisartan

To enhance the dissolution and oral bioavailability of telmisartan (TMS), a poorly water-soluble anti-hypertensive drug, a supersaturable self-microemulsifying drug delivery system (SuSMEDDS) was developed. Amorphous alkalinized TMS (AAT) was formulated into a SMEDDS, composed of Capmul® MCM (oil), Cremophor^® RH40 (surfactant), and tetraglycol (co-surfactant). Although the SMEDDS was rapidly dissolved (>80% within 5 min) in a limited condition (500 mL, pH 6.8), drug precipitation was observed over time, resulting in a decrease in dissolution levels. The precipitation was due to drug recrystallization, as determined by differential scanning calorimetry and powder X-ray diffraction analyses. Several polymers, including Soluplus^® (SOL), were screened as precipitation inhibitors; ultimately, SuSMEDDS-SOL was prepared by admixing SOL and the SMEDDS at a 5:100 (w/w) ratio. SuSMEDDS-SOL was superior in terms of dissolution efficiency (>90% over 2 h) and dissolution-retaining time (no precipitation over 2 h). An in vivo pharmacokinetic study in rats revealed that the oral bioavailability of SuSMEDDS-SOL was 4.8-, 1.3-, and 1.2-fold greater than those of the TMS suspension, AAT solution, and SMEDDS, respectively. Therefore, SuSMEDDS-SOL is a promising candidate to enhance the dissolution and oral bioavailability of TMS.

Improved In vivo Effect of Chrysin as an Absorption Enhancer Via the Preparation of Ternary Solid Dispersion with Brij®L4 and Aminoclay

Background

Chrysin is a strong inhibitor of breast cancer resistance protein (BCRP) but it is practically insoluble in water. Effective solubilization of chrysin is critical for its pharmaceutical application as an absorption enhancer via inhibition of BCRP-mediated drug efflux.

Objective

This study aimed to develop an effective oral formulation of chrysin to improve its in vivo effect as an absorption enhancer.

Method

Solid dispersions (SDs) of chrysin were prepared with hydrophilic carriers having surface acting properties and a pH modulator. In vitro and in vivo characterizations were performed to select the optimal SDs of chrysin.

Results

SDs with Brij®L4 and aminoclay was most effective in increasing the solubility of chrysin by 13-53 fold at varying drug-carrier ratios. Furthermore, SDs significantly improved the dissolution rate and extent of drug release. SDs (chrysin: Brij®L4: aminoclay=1:3:5) achieved approximately 60% and 83% drug release within 1 h and 8 h, respectively, in aqueous medium, while the dissolution of the untreated chrysin was less than 13%. XRD patterns indicated the amorphous state of chrysin in SDs. The SD formulation was effective in improving the bioavailability of topotecan, a BCRP substrate in rats. Following oral administration of topotecan with the SDs of chrysin, the Cmax and AUC of topotecan was enhanced by approximately 2.6- and 2-fold, respectively, while the untreated chrysin had no effect.

Conclusion

The SD formulation of chrysin with Brij®L4 and aminoclay appeared to be promising in improving the dissolution of chrysin and enhancing its in vivo effect as an absorption enhancer.

Analysis of the Complicated Nonlinear Pharmacokinetics of Orally Administered Telmisartan in Rats Using a Stable Isotope-IV Method

This study aimed to kinetically analyze the nonlinear absorption and systemic exposure of telmisartan (TEL) after oral administration to rats by using a stable isotope-IV method. Rats were orally administered different dose of TEL, followed by the intravenous injection of 0.005 mg/kg of deuterium-labeled TEL (TEL-d3). Assuming that TEL-d3 shows same pharmacokinetic properties with TEL, systemic clearance (CL_tot), oral bioavailability (F_oral), and intestinal and hepatic availability (F_a*F_g, F_h) of TEL were calculated in each individual rat. AUC_po of TEL increased disproportionately with dose and showed a sigmoid-type relation, indicating the involvement of multi-nonlinear processes in oral absorption of TEL. F_a*F_g of TEL increased with dose at the low-dose range while decreased at the high-dose range. In contrast, F_h increased and CL_tot decreased significantly in the middle range (2 to 6 mg/kg). As main factors of nonlinearity, saturations of solubility, efflux transport in the intestine, and the hepatic uptake of TEL were indicated. In conclusion, this study demonstrated a high possibility of a stable isotope-IV method to characterize complicated pharmacokinetic properties of oral drugs in animals, which can help to consider the future risks in their clinical use.

Optimization of self-microemulsifying drug delivery system for phospholipid complex of telmisartan using D-optimal mixture design

To improve the dissolution behavior of telmisartan (TMS), a poorly water-soluble angiotensin II receptor blocker, TMS-phospholipid complex (TPC) was prepared by solvent evaporation method and characterized by differential scanning calorimetry and powder X-ray diffractometry. The crystalline structure of TMS was transited into an amorphous state by TPC formation. The equilibrium solubility of TPC (1.3-6.1 mg/mL) in various vehicles was about 100 times higher than that of TMS (0.009-0.058 mg/mL). TPC-loaded self-microemulsifying drug delivery system (SMEDDS) formulation was optimized using the D-optimal mixture design with the composition of 14% Capryol 90 (oil; X1), 59.9% tween 80 (surfactant; X2), and 26.1% tetraglycol (cosurfactant; X3) as independent variables, which resulted in a droplet size of 22.17 nm (Y1), TMS solubilization of 4.06 mg/mL (Y2), and 99.4% drug release in 15 min (Y3) as response factors. The desirability function value was 0.854, indicating the reliability and accuracy of optimization; in addition, good agreement was found between the model prediction and experimental values of Y1, Y2, and Y3. Dissolution of raw TMS was poor and pH-dependent, where it had extremely low dissolution (< 1% for 2 h) in water, pH 4, and pH 6.8 media; however, it showed fast and high dissolution (> 90% in 5 min) in pH 1.2 medium. In contrast, the dissolution of the optimized TPC-loaded SMEDDS was pH-independent and reached over 90% within 5 min in all the media tested. Thus, we suggested that phospholipid complex formation and SMEDDS formulation using the experimental design method might be a promising approach to enhance the dissolution of poorly soluble drugs.

Tablet Formulation of a Polymeric Solid Dispersion Containing Amorphous Alkalinized Telmisartan

To overcome the poor dissolution of telmisartan (TMS) at weak acidic pH, amorphous alkalinized TMS (AAT) was prepared by introducing sodium hydroxide as a selective alkalizer. AAT-containing polymeric solid dispersions were prepared by a solvent evaporation method; these solid dispersions were AAT-PEG, AAT-PVP, AAT-POL, and AAT-SOL for the polymers of PEG 6000, PVP K30, Poloxamer 407, and Soluplus, respectively. The characteristics of the different formulations were observed by differential scanning calorimetry, powder X-ray diffraction, Fourier transform infrared spectroscopy, and scanning electron microscopy. To compare the supersaturation behavior, a dissolution test was performed at 37 ± 0.5 °C either in 900 ml (plain condition) or 500 ml (limited condition) of pH 6.8-simulated intestinal fluid used as a medium. AAT-SOL exhibited enhanced dissolution, indicating the probability of extended supersaturation in the limited condition. AAT-SOL was further formulated into a tablet by introducing other excipients, Vivapur 105 and Croscarmellose, as a binder and superdisintegrant, respectively, using a direct compression method. The selected AAT-SOL tablet was superior to Micardis (the reference product) in the aspect of supersaturation maintenance during dissolution in the limited condition, suggesting that it is a promising candidate for practical development that can replace the commercial product in the future.

Sustained-release solid dispersion of pelubiprofen using the blended mixture of aminoclay and pH independent polymers: preparation and in vitro/in vivo characterization

The present study aimed to develop the sustained-release oral dosage form of pelubiprofen (PEL) by using the blended mixture of 3-aminopropyl functionalized-magnesium phyllosilicate (aminoclay) and pH-independent polymers. The sustained-release solid dispersion (SRSD) was prepared by the solvent evaporation method and the optimal composition of SRSD was determined as the weight ratio of drug: Eudragit® RL PO: Eudragit® RS PO of 1:1:2 in the presence of 1% of aminoclay (SRSD(F6)). The dissolution profiles of SRSD(F6) were examined at different pHs and in the simulated intestinal fluids. The drug release from SRSD(F6) was limited at pH 1.2 and gradually increased at pH 6.8, resulting in the best fit to Higuchi equation. The sustained drug release from SRSD(F6) was also maintained in simulated intestinal fluid at fasted-state (FaSSIF) and fed-state (FeSSIF). The structural characteristics of SRSD(F6) were examined by using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR), indicating the change of drug crystallinity to an amorphous form. After oral administration in rats, SRSD(F6) exhibited the prolonged drug exposure in plasma. For both PEL and PEL-transOH (active metabolite), once a day dosing of SRSD(F6) achieved oral exposure (AUC) comparable to those from the multiple dosing (3 times a day) of untreated drug. In addition, the in vivo absorption of SRSD(F6) was well-correlated with the in vitro dissolution data, establishing a good level A in vitro/in vivo correlation. These results suggest that SRSD(F6) should be promising for the sustained-release of PEL, thereby reducing the dosing frequency.