Drug Release Studies

Drug release data have been analyzed according to different kinetic models Higuchi, Korsmeyer and Peppas Sahlin [6,113,114]. Table 4.3 shows the results obtained for these models. 

As Table 4.3 shows, the obtained time exponents are close to 0.5 for the Korsmeyer equation, indicating that the drug release predominantly follows the mechanism of diffusion, with a low contribution of the erosion mechanism [113]. 

The results corresponding to the Peppas Sahlin equation (Table 4.3) are also in agreement with the previous conclusion, being that the values of the diffusion constant kj are more than 100 times higher than relaxation constant kj 114]. 

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Interaction with such properties does, however, not allow the investigator to answer the question of where the drug is localized in the particles (on the surface or in the crystal lattice). Thermal interactions were also observed when an incorporated drug or a second type of triglyceride formed a separate phase within the nanoparticles [3,37,64,68]. Drug release studies can provide supportive information on the accessibility of the drug to the aqueous phase [72,108], but separation of the effects from the nanoparticles from those of additional colloidal structures — if present — may be difficult. 

Volodkin D, Mohwald H, Voegel J-C et al (2007) Stabilization of negatively charged liposomes by polylysine surface coating. Drug release study. J Control Release 117 111-120... 

Chlorhexidini acetas and cimetidine were used as model drugs for drug release studies. Faster swelling of the gels resulting in more drug release at pH<6 in comparison to the pH >6 was observed [126,127]. 

The drug release studies were performed in HCl (pH 1.0) and phosphate buffer (pH 7.8) at an ionic strength 0.1 m/1. A pH dependent pulsed-release be-... 

The physical state of the drug incorporated in a powder drug delivery system (e.g., degree of crystallinity and possible interactions with the polymer) is assessed by differential scanning calorimetry (DSC) or Fourier transform infrared (FTIR) spectroscopy. These observations can clarify the results of other parameter investigations, especially the results of in vitro drug release studies. 

Hirasawa, N. Danjo, K. Haruna, M. Otsuka, A. Physio-chemical characterization and drug release studies of naproxen solid dispersions using lactose as a carrier. Chem. Pharm. Bull. 1998, 46 (6), 1027-1030. 

Esposito, E. et al., Biodegradable microparticles for sustained delivery of tetracycline to the periodontal pocket formulatory and drug release studies, J. Microencapsul., 14, 175, 1997. 

Kanke, M. Katayama, H. Nakamura, M. Application of curdlan to controlled drug delivery. II. In vitro and in vivo drug release studies of theophylline-containing curdlan tablets. Biol.Pharm.BulL, 1995, 18, 1104-1108... 

Leaving the well known toxicity of chromium aside, the drug release study of MIL-101 and MIL-100 shows the potential of MOFs for not only the loading but also the controlled release of an imbedded compound [49]. MIL-101 is able to take up four times as much Ibuprofen as MCM-41, which has comparable cage sizes. It also shows a slower delivery rate, which presents advantages for larger... 

In vitro drug release studies have been employed as a quality control procedure in pharmaceutical production, in product development, etc. Sensitive and reproducible release data derived from physicochemically and hydrodynamically defined conditions are necessary however, no standard in vitro method has yet been developed. Different workers have used apparatus of varying designs and under varying conditions, depending on the shape and application of the dosage form developed. 

Figure 19 Drug release studies from various Rifampicin formulations W/O/W multiple emulsions uneoated (X), coated ( ), uncoated formulation with serum (V), coated formulation with serum (+), plain drug (O). drug with albumin (A) (125).

Drug release studies of dry adsorbed emulsion particles were carried out us described below (Appendix I). 

To study the stability of dry adsorbed emulsions vs. time, two samples of form I were put in closed flasks and stored ut nmiii temperature in a dark closet. After a year, the product aspect looked unchanged, and the drug release study gave results comparable to those obtained with a freshly prepared form. At pH 1.2 and for the 1-year-old form, the drug release was 11% and 6% faster for the medium (800-1250 pm) and large (1250-2000 pm) particle size forms, respectively. The half-release times, /so, were 52 and 102 min for medium and large panicle size, respectively, as compared with the values 59 and 108 min shown in Table 3 for freshly prepared forms. 

Different properties of the prepared dry adsorbed emulsions were examined (yield value, deteiminadon of dry content, measurement of angle of repose, deter-iiiinatlou of flow rate, density, bulk density, percentage of porosity, particle size analysis. Karl Fisher titrimetry. drug release study, stability study) and the most appropriate selected for in vivo investigation. 

I ] 5. KPR Chowdaiy, CG Sankar. Eudragit microcapsules and its dispersions in HPMC-MCC. Physicochemical characteristics and drug release studies. Drug Dev. Ind. Pharm. 23 325-330. 1997. 

Nyqvist-Mayer, A. A., Brodin, A. F. and Frank, S. G., Drug release studies on an oil-water emulsion based on a eutectic mixture of lidocaine and prilocaine as the dispensed phase, J. Pharm. Sci, 75, 365-373 (1986). 

Soppimath, K. S. and Aminabhavi, T M.. Water transport and drug release study from cross-hnked polyacrylamide grafted guar gum hydrogel microspheres for the controlled release apphcation. Eur. J. Pharm. Biopharm., 53,87-98 (2002). 

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