Buccal absorption through golden hamster cheek pouch in vitro and in vivo of 17β-estradiol from hydrogels containing three types of absorption enhancers

In vivo, ex vivo and in vitro assessment of buccal permeation of drugs from delivery systems

Introduction: Buccal mucosa has been described as an attractive site for local and systemic drug delivery, owing its accessibility, safety, and excellent blood supply. The absorption of drugs through buccal mucosa has been assessed by in vivo, ex vivo and in vitro permeability studies, using animal and cell-based models with close resemblance to the human buccal mucosa.Areas covered: This paper focuses on the current in vivo, ex vivo and in vitro permeability studies to analyze the absorption of compounds of interest through buccal mucosa, as well as their advantages and limitations in the preclinical studies of the drugs absorption profiles. The techniques for preparation and preservation of the animal buccal tissue are also discussed to evaluate their interference in the integrity and permeability of the tissues.Expert opinion: Overall, the permeability studies have been useful to evaluate the drugs absorption and to clarify the mechanism of transport of drugs across human buccal mucosa, as well as to explain the enhancement of permeability provided by certain dosage forms. Currently, several researchers have demonstrated particular interest in ex vivo permeability studies, due to their effectiveness in the evaluation of drug absorption and low costs in the acquisition of buccal mucosa samples.

An overview of polymeric dosage forms in buccal drug delivery: State of art, design of formulations and their in vivo performance evaluation

Owing to the ease of the administration, the oral cavity is an attractive site for the delivery of drugs. The main difficulty for administration via the buccal route is an effective physiological removal mechanism of the oral cavity that takes way the formulation from the buccal site and decreases the bioavailability of drugs. The use of mucoadhesive polymers in buccal drug delivery shows assessing buccal drug permeation and absorption, however some studies bring an in vivo performance. This review points to the use of polymers in the manufacture of drug delivery systems (hydrogels, films and tablets) and shows the results of their in vivo performance tests.

Development of topical ophthalmic In Situ gel-forming estradiol delivery system intended for the prevention of age-related cataracts

The goal of this study was to develop and characterize an ion-activated in situ gel-forming estradiol (E2) solution eye drops intended for the prevention of age-related cataracts. Accordingly, in situ gelling eye drops were made using gellan gum as an ion-activated gel-forming polymer, polysorbate-80 as drug solubilizing agent, mannitol as tonicity agent, and combination of potassium sorbate and edetate disodium dihydrate (EDTA) as preservatives. The formulations were tested for the following characteristics: pH, clarity, osmolality, antimicrobial efficacy, rheological behavior, and in vitro drug release. Stability of the formulation was also monitored for 6 months at multiple storage conditions per ICH Q1A (R2) guidelines. The solution eye drops resulted in an in-situ phase change to gel-state when mixed with simulated tear fluid (STF). The gel structure formation was confirmed by viscoelastic measurements. Drug release from the gel followed non-fickian mechanism with 80% of drug released in 8 hr. The formulations were found to be clear, isotonic with suitable pH and viscoelastic behavior and stable at accelerated and long-term storage conditions for 6 months. In vitro results suggest that the developed formulation is suitable for further investigation in animal models to elucidate the ability of estrogen to prevent and delay cataracts.

Comparative pharmacokinetics and bioavailability of intranasal and rectal midazolam formulations relative to buccal administration in rabbits

The rectal and intranasal formulations under current development demonstrated comparative potential for administering midazolam in treating seizures in a medical emergency service.

Strategic approaches for enhancement of in vivo transbuccal peptide drug delivery in rabbits using iontophoresis and chemical enhancers

PURPOSE

To evaluate the feasibility of iontophoresis and the combination effects with chemical enhancers on in vivo hypocalcemic effect of transbuccally delivered salmon calcitonin (sCT).

METHODS

N-acetyl-L-cysteine (NAC), sodium deoxyglycocholate (SDGC), and ethanol were used as chemical enhancers; and 0.5 mA/cm(2) fixed electric current was employed as a physical enhancer. sCT hydrogel was applied to rabbit buccal mucosa, and blood samples were obtained via the central auricular artery. Blood calcium level was measured by calcium kit and the conformational changes of buccal mucosa were investigated with FT-IR spectroscopy. Hematoxylin/eosin staining was used for the histological evaluation of buccal mucosa.

RESULTS

Iontophoresis groups except iontophoresis-NAC group showed significant hypocalcemic effect compared to negative control, in particular iontophoresis-SDGC combination group showed fast onset of action as well as sustained hypocalcemic effect (p < 0.05). FT-IR result demonstrated the reduction of buccal barrier function, and the histological study showed a decrease in buccal thickness as well as minor damage to the dermal-epidermal junctions in the enhancing method groups; however, the damaged tissues virtually recovered within 24 h after the removal of electrodes.

CONCLUSIONS

Iontophoresis and combination with SDGC were found to be safe and potential strategies for transbuccal peptide delivery in vivo.

Effect of experimental temperature on the permeation of model diffusants across porcine buccal mucosa

The influence of experimental temperature on the permeability of model diffusants across porcine buccal mucosa was investigated in vitro. The permeability increased significantly as the experimental temperature was increased in increments of approximately 7°C. It was observed that the apparent permeability and temperature were related by an exponential relationship that conformed to the Arrhenius equation. Diffusants with higher lipophilicities--buspirone and bupivacaine--had lower activation energies for diffusion when compared to hydrophilic diffusants--antipyrine and caffeine. The activation energy for diffusion of the model diffusants decreased linearly with increasing distribution coefficients across porcine buccal mucosa. The results suggested that the buccal mucosa acts as a stronger barrier to the diffusion of hydrophilic diffusants than the lipophilic ones. The log-linear relationship between permeability and temperature indicates that temperature should be carefully controlled in diffusion experiments. These results also point to the possibility of developing heat-generating buccal delivery devices, especially for hydrophobic diffusants.

Biodegradable thermogelling hydrogel of P(CL-GL)-PEG-P(CL-GL) triblock copolymer: degradation and drug release behavior

Degradation and drug release behavior of thermogelling hydrogel of poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide) [P(CL-GL)-PEG-P(CL-GL) (1880-1540-1880)] triblock copolymer were investigated. The copolymer aqueous solution (25 wt%) underwent sol-gel transition at 35 degrees C as the temperature increased and formed a stable gel at body temperature. After incubation in PBS buffer solution (0.1 M) at 37 degrees C, the gel degraded completely into a viscous liquid at 14th week. Chemical microstructural analysis of the degraded samples by (1)H-NMR revealed the degradation occurring mainly on the glycolyl sequences of the copolymer. The pH value of the gel buffer solution maintained neutral during the initial 8 weeks, which may be beneficial for the preservation of activity of pH-sensitive drugs. Incorporation of drugs into the gel was formulated at room temperature without the use of any organic solvent. The gel formed a controlled release depot with delivery times of 12, 32, and 25 days for isoniazid, rifampicin and bovine serum albumin, respectively. Controlled release of hydrophobic rifampicin was achieved with insignificant burst effect due to the distribution of the drug mainly in the hydrophobic polyester regions of the gel.

Chronobiology, drug delivery, and chronotherapeutics

Biological processes and functions are organized in space, as a physical anatomy, and time, as a biological time structure. The latter is expressed by short-, intermediate-, and long-period oscillations, i.e., biological rhythms. The circadian (24-h) time structure has been most studied and shows great importance to the practice of medicine and pharmacotherapy of patients. The phase and amplitude of key physiological and biochemical circadian rhythms contribute to the known predictable-in-time patterns in the occurrence of serious and life-threatening medical events, like myocardial infraction and stroke, and the manifestation and severity of symptoms of chronic diseases, like allergic rhinitis, asthma, and arthritis. Moreover, body rhythms can significantly affect responses of patients to diagnostic tests and, most important to the theme of this special issue, medications. Rhythmicity in the pathophysiology of disease is one basis for chronotherapeutics--purposeful variation in time of the concentration of medicines in synchrony with biological rhythm determinants of disease activity--to optimize treatment outcomes. A second basis is the control of undesired effects of medications, especially when the therapeutic range is narrow and the potential for adverse effects high, which is the case for cancer drugs. A third basis is to meet the biological requirements for frequency-modulated drug delivery, which is the case for certain neuroendocrine peptide analogues. Great progress has been realized with hydrogels, and they offer many advantages and opportunities in the design of chronotherapeutic systems for drug delivery via the oral, buccal, nasal, subcutaneous, transdermal, rectal, and vaginal routes. Nonetheless, innovative delivery systems will be necessary to ensure optimal application of chronotherapeutic interventions. Next generation drug-delivery systems must be configurable so they (i) require minimal volitional adherence, (ii) respond to sensitive biomarkers of disease activity that often vary in time as periodic (circadian rhythmic) and non-periodic (random) patterns to release medication to targeted tissue(s) on a real time as needed basis, and (iii) are cost-effective.

Precipitation Complexation Method Produces Cannabidiol/β-Cyclodextrin Inclusion Complex Suitable for Sublingual Administration of Cannabidiol

In the present study, the precipitation complexation method was used to prepare a complex of cannabidiol (CBD) with beta-CD. The effect of beta-CD-complexation on the sublingual absorption of CBD was studied in rabbits. A solid CBD/beta-CD inclusion complex was prepared by precipitation and the effect of complex formation on the dissolution rate of CBD was studied. The absorption of CBD (a 250 microg/kg dose of CBD in all formulations) after sublingual administration of solid CBD/beta-CD complex and ethanolic CBD solution, and after oral administration of ethanolic CBD solution, was studied in vivo in rabbits. The dissolution rate of solid CBD/beta-CD complex in vitro was significantly (p<0.05) higher than that of plain CBD. The absorption of CBD (AUC0-300 min) decreased in the following order: sublingual ethanolic CBD solution (420+/-120 ngxmin/mL; mean+/-SD; n=4)>sublingual solid CBD/beta-CD complex (270+/-120 ngxmin/mL)>oral ethanolic CBD solution (concentrations in plasma below the quantitation limit). The results demonstrate that sublingual administration of a solid CBD/beta-CD complex enhances the absorption of CBD in rabbits when compared to oral administration of ethanolic CBD. Furthermore, the solid CBD/beta-CD complex may provide an alternative formulation for sublingual administration of CBD.

Transbuccal permeation, anti-inflammatory activity and clinical efficacy of piroxicam formulated in different gels

In attempts to avoid the systemic side effects of piroxicam (PC) (e.g. gastrotoxicity), several buccal gel formulations containing PC were prepared and their effects on the characteristics of the drug permeation through rabbit buccal mucosa in-vitro were evaluated using a Franz-type diffusion cell. The general rank order of the total flux of 0.5% PC from gels was found to be: hydroxypropylmethylcellulose (HPMC, 2.5%) > hydroxypropylcellulose (HPC, 2.5%) >or= sodium alginate (Na alg., 7%) > methylcellulose (MC, 3%) > hydroxyethylcellulose (HEC, 1.5%) > carbopol 934 (Carb. 934, 1%) >or= sodium carboxymethylcellulose (NaCMC, 2%) > pluronic F-127 (PF-127, 20%) > polyvinyl alcohol (PVA, 10%). The effect of various penetration enhancers 1% sodium lauryl sulphate (NaLS), 3% sodium deoxycholate (NaDC), 3% sodium tauroglycocholate (NaTGC) on the rate of permeation across the excised buccal mucosa (of 0.5% PC in gels prepared using 3% MC, 2.5% HPMC or 7% Na alg. base) and histology of the buccal epithelium was also investigated. Pharmacodynamic evaluation of the anti-inflammatory activity of PC in these gel formulations (containing 3% NaDC as an enhancer) was carried out using the kaolin-induced rat paw oedema method. The results obtained indicated that PC administered in 7% Na alg. or 2.5% HPMC gel bases was significantly more effective than the 3% MC gel and oral drug solution in suppressing oedema formation in rats. Comparative clinical studies were conducted in patients with post-operative dental pain and oedema following maxillofacial operations. The results revealed that 7% Na alg. and 2.5% HPMC gel formulations applied to the buccal mucosa were slightly better than or equally effective to the orally administered commercial product (Feldene Flash) tablet) in reducing pain level, swelling and tenderness within a period of 4 days. These findings suggest that PC (0.5%) administered in the buccal gel may present a potential therapeutical use as a strong anti-inflammatory and analgesic agent.

Design of a novel hydrogel-based intelligent system for controlled drug release

The present work focused on the design of an assembled drug delivery system (DDS) to provide multifunctions, such as drug protection, self-regulated oscillatory release, and targeted uni-directional delivery by a bilayered self-folding gate and simple surface mucoadhesion. In this device, a pH-sensitive hydrogel together with a poly(hydroxyethyl methacrylate) (HEMA) barrier was used as a gate to control drug release. In addition, poly(HEMA) coated with poly(ethylene oxide)/poly(propylene oxide)/poly(ethylene oxide) (PEO-PPO-PEO) surfactant was utilized to enhance mucoadhesion on the device surface. The release profiles of two model drugs, acid orange 8 (AO8) and bovine serum albumin (BSA) were studied in this assembled system, which compared with the conventional drug-entrapped carriers and enteric-coating systems. Furthermore, targeted uni-directional release was demonstrated in a side-by-side diffusion cell. In conclusion, for such an assembled device, the poly(HEMA) layer not only affects the folding direction but also serves as a barrier to protect the model drugs. The release time can be controlled by the thickness of the bilayered gate and the drug reservoir. Due to the reversible swelling behavior of poly(methyacrylic acid-g-ethylene glycol) (p(MAA-g-EG)) gels, the bilayered gate can sense the environmental pH change and achieve an oscillatory release pattern. Moreover, the local targeting and uni-directional release have been successfully demonstrated in vitro.