Pharmacokinetics of timolol in aqueous humor sampled by microdialysis after topical administration of thermosetting gels.

In order to develop a thermosetting gel-based formulation, the ocular pharmacokinetics of timolol was studied utilizing microdialysis sampling technique after topical administration. A linear microdialysis probe was characterized and implanted in the anterior chamber of a rabbit. Dialysate samples collected from the aqueous humor (AH) were directly injected into the HPLC system without any pre-treatment and no interference was observed in the blank sample. The measured in vitro recovery of the probe was 57.67%; however, the in vivo recovery significantly decreased to 16.78% when assessed by the retrodialysis method, which was used to calculate the timolol concentration in AH. Although in the initial 15 min the drug concentrations in AH were comparable to that of the timolol solution, increased Cmax and significantly improved ocular bioavailability were obtained for the gel. When sodium deoxycholate (DC) was incorporated in the gel as a penetration enhancer, a 2-fold increment in the ocular bioavailability was achieved with an increased Cmax and significantly suspended Tmax. The results demonstrated that microdialysis coupled to HPLC is a powerful tool to investigate the ocular pharmacokinetic, and hence facilitates the design of ophthalmic formulations.

Effect of iontophoresis on skin permeation of defibrase.

AIM: To investigate the effect of iontophoresis on skin permeation of defibrase. METHODS: Iontophoresis was carried out in side-by-side chambers, excised rat skin membrane (RSM) or human epidermis membrane (HEM). The effects of electrode polarity, permeation medium pH and ionic strength were evaluated. RESULTS: Permeation of defibrase caused by anodal iontophoresis was more effective [the apparent permeability coefficient was (1.2 +/- 0.4) x 10(-4) cm x h(-1)] than that of cathodal iontophoresis [(4.3 +/- 1.4) x 10(-5) cm x h(-1)]. The amount of permeated defibrase caused by anodal iontophoresis in pH 7.4 medium was (25 +/- 5) x 10(-14) mol x cm(-2), which was higher than that of in pH 6. 4 permeation medium [(15 +/- 4) x 10(-14) mol x cm(-2)]. CONCLUSION: Iontophoresis could enhance skin permeation of defibrase. Electroosmotic flow effect played an important role.

[Diffusion behaviors of drugs in thermosensitive in situ gels].

AIM: To study the diffusion behaviors of drugs in thermosensitive in situ gels, and provide valuable information for designing such delivery systems. METHODS: A free diffusion model was used to evaluate the effects of concentration, the property of drugs, as well as the gel compositions on the diffusivity of drugs. RESULTS: Drug transport through the aqueous channels of the gel followed Fickian mechanism, and no significant influence on the diffusivity was observed when the drug concentration was lowered from 5% to 0.25%. The diffusion coefficients of propranolol, timolol maleate, and salbutamol sulfate were 0.91, 1.32, and 3.30 x 10(-6) cm2 x s(-1), respectively. The flux of hydrophilic drug was 3.6 fold faster than that of the lipophilic one implied the latter partitioned into the hydrophobic micellar core, and consequently the diffusion was retarded. The diffusivity was decreased with increased poloxamer and sodium hyaluronate concentration, due to the distorted aqueous channels and higher microviscosity. CONCLUSION: The result suggested that sustained release could be achieved for the thermosensitive in situ gel by incorporating lipophilic drug or increasing polymer concentration.

[Cutaneous permeation kinetics and pharmacodynamics of topical lidocaine gel in rat].

AIM: To study the cutaneous permeation kinetics and pharmacodynamics of lidocaine gel. METHODS: The concentration of lidocaine in dermis following topical application in rats was determined by the cutaneous microdialysis technique and related parameters were calculated; the pharmacodynamics of the gel was evaluated by electric stimulation method with EMLA (eutectic mixture of local anesthetics) cream as a control. RESULTS: The peak of percutaneous absorption kinetic profile of lidocaine gel across rat skin occurred at 1.25 h; the onset time of local anesthetic action of lidociane gel was similar to that of EMLA, but both the duration and depth of anesthetic effect were superior to EMLA cream. CONCLUSION: Lidocaine gel showed good anesthetic effect. The minimum effective concentration of lidocaine in dermis is 12 mg.L-1.

[Enhancement of gastrointestinal absorption of chitosan-coated insulin-loaded poly (lactic-co-glycolic acid) nanoparticles].

AIM: To study chitosan-coated poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) on enhancing gastrointestinal absorption of insulin. METHODS: Insulin-loaded PLGA multiple emulsions were prepared by a double-emulsion method. Using chitosan as a stabilizer, chitosan-coated PLGA-NPs was prepared. The changes of the morphology, size distribution and Zeta potential of the NPs were examined. The encapsulation efficiency was determined by HPLC. The release behaviors in vitro were assessed, and the hypoglycemic effects were evaluated by monitoring the glucose levels in diabetic rats. RESULTS: Chitosan-coated PLGA-NPs showed a narrow size of distribution and regular surface with layer structure and their Zeta potential can be changed by chitosan. Chitosan-coating increased the encapsulation efficiency of insulin, reduced the initial burst and improved the release behavior of the NPs. About 14-16 h after intragastric administration of chitosan-coated INS-PLGA-NPs, the plasma glucose level decreased significantly compared with intragastric administration of same dose of non-coated NPs (P < or = 0.05), and the relative pharmacological availability was increased up to (15.4 +/- 1.2)%. CONCLUSION: Chitosan-coated PLGA-NPs could enhance gastrointestinal absorption of insulin.

Relationship between drug effects and particle size of insulin-loaded bioadhesive microspheres.

AIM: To formulate and characterize insulin-loaded adhesive microspheres (MP) and evaluate drug effects of MP with various sizes, 120, 350, and 1000 nm in diameter, in the alloxan-induced diabetic rats. METHODS: Insulin-loaded MP were formulated by an ionotropic gelation procedure. Particle size distributions were determined by photon correlation spectroscopy and optical microscopy. The factors that influenced the particle sizes and loading capacity were investigated, and the release properties were assessed in vitro. The hypoglycemic effect was investigated by monitoring the plasma glucose level of the alloxan-induced diabetic rats after oral administration. RESULTS: All the MPs with three sizes formulated were in the desired size range, and the loading capacity was 15.3 %+/-1.7 % (120 nm), 32.4 %+/-2.4 % (350 nm), and 53.3 %+/-2.7 % (1000 nm) respectively. The particle size also had an influence on the release property of the MPs. Half an hour later, 25 %+/-4 % (120 nm), 18.3 %+/-2.4 % (350 nm), and 8.6 %+/-1.3 % (1000 nm) of insulin were released. MP with different sizes had various degree of hypoglycemic effects after 10 h (P<0.05 vs control insulin solution). The plasma glucose level of 350 nm size particles remarkably decreased 15 h later (P<0.05 vs 120 nm) or 35 h later (P<0.01 vs others). The relative pharmacological availability was 10.2 %+/-0.5 % (120 nm), 14.9 %+/-1.3 % (350 nm), and 7.3 %+/-0.8 % (1000 nm) respectively. Particles of 350 nm showed a comparatively higher availability (P<0.05). CONCLUSION: Adhesive CS-MP were helpful in increasing the relative pharmacological bioavailability of insulin, and a distinct advantage of proper particle size helped to increase the drug effects.

Bioadhesive polysaccharide in protein delivery system: chitosan nanoparticles improve the intestinal absorption of insulin in vivo.

There are many ongoing investigations to improve the oral bioavailability of peptide and protein formulations. Bioadhesive polysaccharide chitosan nanoparticles (CS-NPs) would seem to further enhance intestinal absorption of them. In this study, Insulin-loaded CS-NPs were prepared by ionotropic gelation of CS with tripolyphosphate anions. Its particle size distribution and zeta potential were determined by photon correction spectroscopy and laser Dopper anemometry. The ability of CS-NPs to enhance intestinal absorption of insulin and increase the relative pharmacological bioavailability of insulin was investigated by monitoring the plasma glucose level of alloxan-induced diabetic rats after oral administration of various doses of insulin-loaded CS-NPs. CS-NPs had a particle size in the range of 250-400 nm and its polydispersity index was smaller than 0.1, positively charged, stable. Insulin association was found up to 80% and its in vitro release showed a great initial burst with a pH-sensitivity property. CS-NPs enhanced the intestinal absorption of insulin to a greater extent than the aqueous solution of CS in vivo. Above all, after administration of 21 I.U./kg insulin in the CS-NPs, the hypoglycemia was prolonged over 15 h and the average pharmacological bioavailability relative to SC injection of insulin solution was up to 14.9%.

Thermosetting gels with modulated gelation temperature for ophthalmic use: the rheological and gamma scintigraphic studies.

For ophthalmic drug delivery, Pluronic F127 solutions have a phase transition temperature too low for them to be instilled into the eye at room temperature. Refrigerator storage is usually required to make administration easier, whereas the potential irritation of cold to the sensitive ocular tissues may result in poor topical bioavailability. The purpose of this study is to develop a thermosetting gel with a suitable phase transition temperature by combining Pluronic analogs and to examine the influence of incorporating mucoadhesive polysaccharide, sodium hyaluronate (HA-Na), on the ocular retention of the gel. Dynamic rheological method and single photon emission computing tomography (SPECT) technique were used to ex/in vivo evaluate the thermosetting gels, respectively. An optimized formulation containing 21% F127 and 10% F68 increased the phase transition temperature by 9 degrees C as evaluated by elasticity modulus compared to that of individual 21% F127 solution. Rheological behaviors of the Pluronic solutions showed that the combined Pluronic formulation was free flowing liquid below 25 degrees C and converted to a firm gel under the physiological condition. Furthermore, this formulation possessed the highest viscosity both before and after tear dilution at 35 degrees C. Gamma scintigraphic data demonstrated that the clearance of the thermosetting gel labeled with 99mTc-DTPA was significantly delayed with respect to the phosphate buffered solution, and at least a threefold increase of the corneal residence time was achieved. However, no further improvement in the ocular retention was observed when adding HA-Na into the thermosetting gel due to the substantially decreased gel strength.

[Effect of solution viscosity on polymer precorneal residence time evaluated by in vitro method].

AIM: To evaluate how solution viscosity affects the precorneal residence of five water-soluble polymers with different properties. METHODS: Captive bubble technique was used, with the consecutive change of contact angle interpreted as an indication of desorption process, to study the residence of those polymers in vitro on freshly enucleated rabbit eyes under physiological conditions. RESULTS: Carbopol and sodium hyaluronate (HA), which adsorbed to isolated ocular surface more than 15 min, showed the optimum precorneal retentive capabilities. When the solution viscosity increased from 12 mPa.s to 50 mPa.s, the residence time of carbopol and HA were prolonged 10 min and 7 min, respectively, but that of sodium carboxymethylcellulose was not affected. CONCLUSION: The result suggested that higher viscosity is beneficial to improve the ocular residence time of bio-adhesive polymers.

[Study on preparation and oral efficacy of insulin-loaded poly(lactic-co-glycolic acid) nanoparticles].

AIM: To investigate the possibility of poly(lactic-co-glycolic acid) as a carrier for the delivery of macromolecular. METHODS: Insulin-loaded poly (lactic-co-glycolic acid) nanoparticles (INS-PLGA-NPs) was prepared by a double-emulsion solvent evaporation method. The size distribution was examined by photo-correlation spectrometry. The entrapment efficiency was determined by HPLC and important factors that affected the entrapment efficiency were investigated. The loading mechanism of different size nanoparticles was assayed by radioimmunoassay (RIA). INS-PLGA-NPs release behavior in vitro was carried out under sink condition. After oral administration of the nanoparticles to alloxan-induced diabetic rats, its glucose level was determined by glucose oxidize method and the oral pharmacological bioavailability in contrast to s.c. of insulin solution was calculated according to the area over the curve. RESULTS: The INS-PLGA-NPs was prepared with poloxamer 188 as a emulsifier, the mean diameter was 149.6 nm and the polydispersity index was decreased to 0.09. While the entrapment efficiency was increased to 42.8%. Most of the insulin loaded was adsorbed on the surface of the nanoparticles. The release behavior in vitro showed an initial burst effect followed by a slower rate stage. After oral administration of 10 u.kg-1 INS-PLGA-NPs, the plasma glucose level decreased significantly after 4 h (P < 0.05), 10 h later the glucose level decreased to the lowest (52.4% +/- 10.2%, P < 0.01) and the relative pharmacological bioavailability is (10.3 +/- 0.8)%. CONCLUSION: PLGA-NPs might be used as a new oral carrier for protein drug delivery systems in the future.

[The enhancing effect of electroporation and iontophoresis on the permeation of insulin through human skin].

AIM: To study the enhancing effect of electroporation and iontophoresis on the permeation of insulin through human cadaver skin in vitro. METHODS: Using side by side two-chamber diffusion cells, the flux of insulin achieved with iontophoresis and electrophoration were compared. RESULTS: The application of high-voltage pulse combined with iontophoresis resulted in higher flux transdermal permeation of insulin than either one technique alone (P < 0.05). Pulsing at a higher voltage increased the flux of insulin more dramatically than pulsing at a lower voltage (P < 0.01). The transdermal transport of insulin by 90 pulse of 500 V (exponential pulse generater, pulse time: 20-24 ms, pulse frequency: 3 pulse.min-1) followed by iontophoresis led to a quick input and a high steady flux. CONCLUSION: Electroporation combined with iontophoresis can enhance the permeation of insulin significantly.