International Journal of Pharmaceutics (v.193, #2)

Physicochemical properties and bioavailability of carbamazepine polymorphs and dihydrate by Yumiko Kobayashi; Shusei Ito; Shigeru Itai; Keiji Yamamoto (137-146).
The dissolution behaviors of carbamazepine (CZP) polymorphs and pseudopolymorphs (form I, form III and dihydrate) and the bioavailabilities (BA) of each form in dogs after oral administration were investigated. Bioavailability tests were carried out at a dose of either 40 mg/body or 200 mg/body. The results of dissolution tests in JP13 first fluid (pH 1.2) at 37°C indicated that the initial dissolution rate was in the order of form III>form I>dihydrate, while form III was transformed to dihydrate more rapidly than form I, resulting in decrease of the dissolution rate. The solubilities of both anhydrates (form I and form III), calculated from the initial dissolution rate of each anhydrate, were 1.5–1.6 times that of the dihydrate. At the dose of 40 mg/body, there were no significant differences in the area under the curve (AUC) between forms; their AUCs were nearly equal to that of CZP solution using polyethyleneglycol 400. These findings suggested that most crystalline powder of each form administered at the low dose was rapidly dissolved in gastrointestinal (GI) fluid. On the other hand, for the dose of 200 mg/body, significant differences in plasma concentration–time curves of CZP among polymorphic forms and dihydrate were observed. The order of AUC values was form I>form III>dihydrate. The inconsistency between the order of initial dissolution rates and that of AUC values at the high dose may have been due to rapid transformation from form III to dihydrate in GI fluids.
Keywords: Carbamazepine; Polymorph; Dihydrate; Dissolution rate; Transformation; Bioavailability;

Maintenance of constant drug levels in the body for those drugs that are used in management of hypertension is extremely beneficial. This can be successfully achieved by delivering the antihypertensives as osmotically-controlled drug-delivery system that essentially eliminates the influence of pH on the drug release. The main objective of this study was to evaluate the main effects of the formulation variables on the release of captopril from osmotically-controlled drug-delivery system coated with a custom-made cellulose acetate (CA) pseudolatex reported earlier. A secondary objective was to identify a suitable antioxidant for incorporating in the formulation as the drug undergoes metal-catalyzed oxidative degradation. The drug showed good stability (≥90% intact captopril) in solution in the presence of ascorbic acid for a period of 48 h. A seven-factor, 12-run Plackett–Burman screening design was employed to study the main effects of amounts of Polyox® N10 and N80, Carbopol® 934P and 974P, sodium chloride, orifice size, and % coating weight gain. The response variable was cumulative percent of drug released in 12 h, Y 3, with constraints on lag time Y 1 and time for 50% drug released Y 2. Quantitative evaluation of the screening design variables revealed that Polyox® N10, Carbopol® 974P, and % coating weight gain had a greater influence on the drug release than the rest of the factors. The main effects decreased in the order: Polyox® N10 (−8.07)=% Coating weight gain (−8.07)>Carbopol® 974P (6.83)>Carbopol® 934P (−5.3)>Polyox® N80 (5)>orifice size (2.6)>amount of sodium chloride (1.97).
Keywords: Captopril; Experimental design; Formulation variables; Gastrointestinal therapeutic system; Pseudolatex;

In this study, serum stability and target-sensitivity of phosphatidylethanolamine (PE) immunoliposomes prepared with dioleoylphosphatidylethanolamine (DOPE), HYB-241 monoclonal antibody that targets p-glycoproteins, and various levels of polyethyleneglycol 2000 dioleoylphosphatidylethanolamine (PEG2000–DOPE) were determined. Incubation of calcein-laden pegylated immunoliposomes prepared with different levels of PEG2000–DOPE (0.3, 0.5 and 1.0 mol%) with p-glycoprotein rich bovine brain microvessel endothelial cells in 10% serum cell culture medium, all resulted in time-dependent release of calcein from the liposomes. The release of calcein was greatest for immunoliposomes prepared with 0.3 mol% PEG2000–DOPE (66% in 1 h). Contrarily, the release of calcein from the other two immunoliposomes reached only ∼10–3% after same period of incubation. When serum-induced leakage of calcein was investigated for the above liposome preparations, liposomes prepared with 0.3 and 0.5 mol% PEG2000–DOPE had the highest leakage level (10% in 1 h). Contrarily, the release of calcein from liposomes prepared with 1.0 mol% PEG2000–DOPE reached only 3% after same period of incubation. Together, it would appear that release of calcein from the immunoliposomes prepared with 0.3 mol% PEG2000–DOPE is a result of both serum-induced and target-induced destabilization of liposomes. The net release of calcein due to target-induced destabilization of liposomes is calculated to be at ∼56%. In contrast, there is no target-induced leakage of calcein from immunoliposomes prepared with either 0.5 or 1.0 mol% PEG2000–DOPE.
Keywords: Immunoliposome; Blood–brain barrier; p-Glycoprotein; Target-sensitive; Liposome; Sterically stabilized;

Substituted amylose (SA) matrix drug tablets prepared by direct compression show sustained drug-release properties. The influence of compression force (CF) and tablet weight (TW) on release properties was studied. CF ranging from 0.5 to 5.0 tons/cm2 has no significant effect on the release properties of SA,G (glycidol) polymers, with a degree of substitution (DS) greater than 1.5. For a low DS, an augmentation of CF increases the release time of acetaminophen, used as a model drug, until a certain limit is reached. On the other hand, TW has a major effect on the release time of acetaminophen. Release time is directly proportional to TW. The effect of the nature of the active material, its solubility and its concentration in the formulation on the release properties of SA,G polymers was also evaluated, demonstrating the versatility of the system.
Keywords: Substituted amylose; Direct compression; Tablet weight; Drug solubility; Drug loading;

Fluid bed agglomeration with a narrow droplet size distribution by S.H Schaafsma; P Vonk; N.W.F Kossen (175-187).
In the fluid bed agglomeration processes liquid distribution influences the agglomerate growth. We developed a new nozzle that produces uniform droplets, which allows droplets to be easily controlled in size independently of liquid- and airflow of the nozzle. It was found that the spray rate and the mixing in the spray zone determine the average granule size and that there is linear relation between the number of droplets of which a granule consists and its volume, at the early stage of the process. The nucleation ratio factor introduced in this paper depends on the material properties of binder liquid and powder particles and is a useful parameter to describe the binder liquid efficiency. The decline of the growth rate of granules during the agglomeration process was due to the less sufficient rewetting of granules resulting in less growth. A linear relation was found between tracer mass added to the binder liquid and the granule mass in an early stage of the process. Solubility of the tracer was found not to influence its distribution. The new nozzle proves to be a good tool to study the effect of wetting and growth of granules.
Keywords: Fluid bed; Agglomeration; Nozzle;

All trans-retinoic acid (RA) was dispersed by sonication with soybean phosphatidylcholine (PC). The particle size in the dispersion was increased to 240 nm up to the RA mol fraction range (X RA) of 0.4. At X RA=0.5, the RA/PC mixture was difficult to disperse and the macroscopic oil/water phase separation was observed. On the other hand, by the addition of sesame oil (SO) to RA (molar ratio of RA:SO=1:1), stable aqueous dispersions (diameter: 40–80 nm) were obtained in the mol fraction range RA and SO mixture (X M) of 0.1–0.8. In order to clarify these dispersal mechanism, the dispersed particles were characterized and the interaction among RA, SO and PC was investigated using several physicochemical techniques. The trapped aqueous volume inside the RA/PC particles was determined using the aqueous space marker, calcein and it was increased with the addition of RA into small unilamellar vesicles of PC. On the other hand, that of RA/SO/PC particles was decreased remarkably with increase in X M and the decline in the fraction of vesicular particles was also confirmed by fluorescence quenching of N-dansylhexadecylamine in the PC membrane by the addition of the quencher CuSO4. These results indicate that the interaction of RA with PC bilayers and the structure of RA/PC mixture will be changed by the addition of SO.
Keywords: Retinoic acid; Soybean phosphatidylcholine; Sesame oil; Membrane; Structure;

Chitosan films and hydrogels of chlorhexidine gluconate for oral mucosal delivery by S Şenel; G İkinci; S Kaş; A Yousefi-Rad; M.F Sargon; A.A Hıncal (197-203).
Topical delivery of antimicrobial agents is the most widely accepted approach aimed at prolonging active drug concentrations in the oral cavity. As most antifungals do not posses inherent ability to bind to the oral mucosa, this is best achieved through improved formulations. Chitosan, a partially deacetylated chitin, which is a biologically safe biopolymer, prolongs the adhesion time of oral gels and drug release from them. Chitosan also inhibits the adhesion of Candida albicans to human buccal cells and has antifungal activity. The antifungal agent, chlorhexidine gluconate (Chx), also reduces C. albicans adhesion to oral mucosal cells. The aim of this study was to design a formulation containing chitosan for local delivery of Chx to the oral cavity. Gels (at 1 or 2% concentration) or film forms of chitosan were prepared containing 0.1 or 0.2% Chx and their in vitro release properties were studied. The antifungal activity of chitosan itself as well as the various formulations containing Chx was also examined. Release of Chx from gels was maintained for 3 h. A prolonged release was observed with film formulations. No lag-time was observed in release of Chx from either gels or films. The highest antifungal activity was obtained with 2% chitosan gel containing 0.1% Chx.
Keywords: Chitosan; Chlorhexidine gluconate; Oral mucosal delivery; Antifungal;

Mucoadhesive suppositories of ramosetron hydrochloride utilizing Carbopol® by R Yahagi; Y Machida; H Onishi; Y Machida (205-212).
Suppositories are the preferable dosage form for patients at home or experiencing nausea. Serotonin (5-HT3)-receptor antagonists are used to treat vomiting in intravenous or oral administration but not suppository form. Ramosetron hydrochloride (RAM) is a new 5-HT3 antagonist which effectively inhibits vomiting, and we prepared RAM suppositories using Witepsol® H-15 (H-15) containing Carbopol® 934P (CP). The viscosity of suppository base and RAM release properties from suppositories were examined. Plasma RAM concentrations after administration of suppositories to rabbits were estimated and irritation of rectal tissues were observed. Antiemetic effects of suppositories were studied using ferrets. The base viscosity increased with addition of CP. Suppositories containing CP exhibited better absorption in rabbits compared to H-15 suppositories, correlated with release behavior. Suppositories containing 2% CP had 2.5 times larger AUC0–24 h than H-15 suppositories, and the MRT was prolonged by 5.8 h compared with i.v. administration. 10% CP suppositories administered to rabbits for 5 days did not irritate the tissues. Antiemetic studies indicated that 2% CP suppository of RAM might have the same effect as i.v. administration. These results suggest that RAM suppositories containing CP are safe and useful in once-a-day dosage form for treatment of chemotherapy-induced nausea.
Keywords: Mucoadhesive suppository; Carbopol®; Serotonin receptor antagonist; Antiemetic; Ramosetron;

Enhanced efficacy by percutaneous absorption of piroxicam from the poloxamer gel in rats by Sang-Chul Shin; Cheong-Weon Cho; In-Joon Oh (213-218).
The pharmacokinetics and anti-inflammatory activity of piroxicam from the poloxamer 407 gel were determined to investigate percutaneous absorption of piroxicam from poloxamer gels in rats. The poloxamer 407 gel containing 1% piroxicam showed significant inhibition of carragenin-induced rat foot swelling when compared to the control group. The extent of inhibition of swelling (%) showed a linear relationship with the logarithm of piroxicam dose within ∼0.4–3.2 mg/kg. The enhancing effect of polyoxyethylene-2-oleyl ether, non-ionic surfactant on the percutaneous absorption of piroxicam from poloxamer 407 gel was evaluated in rats. The piroxicam gel containing polyoxyethylene-2-oleyl ether increaesd the relative bioavailability ∼1.8-fold compared with the gel without enhancer. Percutaneous administration of piroxicam gel containing polyoxyethylene-2-oleyl ether to rats showed a relatively constant, sustained blood concentration with minimal fluctuation.
Keywords: Piroxicam; Poloxamer 407 gel; Percutaneous absorption;

Safety assessment of selected cyclodextrins — effect on ciliary activity using a human cell suspension culture model exhibiting in vitro ciliogenesis by Remigius Uchenna Agu; Mark Jorissen; Tom Willems; Guy Van den Mooter; Renaat Kinget; Norbert Verbeke; Patrick Augustijns (219-226).
The objective of this study was to assess the cilio-inhibitory effect of a series of cyclodextrins using a human cell suspension culture system exhibiting in vitro ciliogenesis. Enzymatically released human nasal epithelial cells were cultured as sequential monolayer-suspension culture showing in vitro ciliogenesis. Ciliary beat frequency (CBF) was determined by computerized microscope photometry. Among the cyclodextrins investigated (γ-cyclodextrin, hydroxypropyl-β-cyclodextrin, anionic-β-cyclodextrin polymer, dimethyl-β-cyclodextrin and α-cyclodextrin), it was shown that after 30 min of exposure, γ-cyclodextrin (10% w/v), hydroxypropyl-β-cyclodextrin (10.0% w/v) and anionic-β-CD polymer (8.0% w/v) were not significantly cilio-inhibitory (P>0.05). Similarly, CBF remained stable upon cell exposure to α-cyclodextrin (2.0% w/v) and dimethyl-β-cyclodextrin (1.0% w/v). However, higher concentrations of α-cyclodextrin and dimethyl-β-cyclodextrin resulted in mild to severe cilio-inhibition after 45 min of exposure. The effect of α-cyclodextrin (5.0% w/v; 54±4% cilio-inhibition) was partially reversible while dimethyl-β-cyclodextrin (10% w/v; 36±4% cilio-inhibition) was irreversible. The cilio-inhibition observed in this model was lower than reported for chicken trachea model. Given the fact that (1) irreversible cilio-inhibition observed in this study occurred only at concentrations exceeding those used in pharmaceutical formulations and/or at an unusual exposure time (45 min) and that (2) in an in vivo situation, dilution and mucociliary clearance contribute to further decrease in local concentrations of the applied compound, the results of this study confirm the safety of the cyclodextrins investigated as nasal absorption enhancers.
Keywords: Ciliary beat frequency; Cilio-toxicity; Cell culture; Absorption enhancers; Cyclodextrins;

In vitro analysis of inhaled formulations measures, among other parameters, the variability in delivered dose, while a corresponding in vivo analysis also includes the variability caused by patient performance and distribution of drug between the oropharynx and the lungs. In vitro, the dose variability is higher for Turbuhaler® than for the corresponding pMDI, whereas in vivo, the converse is true: the variability in lung deposition is significantly higher, both between and within subjects, for pMDI than for Turbuhaler. The observation can be due to several factors such as the non-continuous working principle of inhalation via pMDI as opposed to the continuous working principle of inhalation via Turbuhaler.
Keywords: Inhalers; Variability; Lung deposition; Patients;

A systematic investigation on the influence of two cellulose polymers, methyl cellulose (MC) and hydroxypropyl cellulose (HPMC) on supersaturation and permeation of hydrocortisone acetate (HA) is reported. Diffusion of HA from a 0.5% Carbopol gel across a model silicone membrane was investigated using the Franz-cell technique. At constant polymer concentration, the flux increases proportionally with the degree of saturation up to 4.8× but decreases thereafter. For a particular degree of supersaturation (4.8×), the flux increases with the concentration of polymer up to 1% and decreases at higher concentrations. The behaviour is found to be consistent with crystallisation experiments. The results suggest that optimisation of supersaturation and polymer content is necessary to achieve both high permeation rates and inherent stability.
Keywords: Supersaturation; Cosolvents; In vitro diffusion; Hydrocortisone acetate; Hydroxypropyl methyl cellulose; Methyl cellulose;

The effect of liquid crystalline structure on chlorhexidine diacetate release by E Farkas; R Zelkó; Zs Németh; J Pálinkás; S Marton; I Rácz (239-245).
The aim of this study was to examine different liquid crystalline preparations containing chlorhexidine diacetate and to find connection between their structure and the kinetic of drug release. Nonionic surfactant, Synperonic A7 (PEG7–C13–15) was selected for the preparation of the examined liquid crystalline systems. Mixtures of different ratios of Synperonic A7 and water were produced. By increasing the water content of the systems, lamellar and hexagonal liquid crystal structures were observed. For the analysis of the prepared liquid crystalline systems polarising microscopy, rheology study, differential scanning calorimetry and dynamic swelling tests were carried out. The chlorhexidine diacetate release was examined by Franz-type vertical diffusion cell apparatus. The chlorhexidine diacetate release from hexagonal liquid crystalline preparations was characterised by zero-order release kinetics, while the drug release from lamellar liquid crystalline systems was described by anomalous (non-Fickian) transport. The results indicate that the drug release kinetic is strongly dependent on the liquid crystalline structure.
Keywords: Liquid crystals; Hexagonal and lamellar structure; Release kinetics;

Characterisation of the influence of micronisation on the crystallinity and physical stability of revatropate hydrobromide by Martyn D. Ticehurst; Patricia A. Basford; Christopher I. Dallman; Timothy M. Lukas; Peter V. Marshall; Gary Nichols; David Smith (247-259).
Micronised particles of revatropate hydrobromide were observed to agglomerate when stored in uncontrolled conditions. Dynamic vapour sorption (DVS), isothermal microcalorimetry, microscopy and particle size measurement by laser diffraction have been used to study micronised revatropate hydrobromide. The rate and extent of agglomeration were dependent on the energy of the micronisation process, the sampling point for bulk within the mill and the humidity during storage. The agglomeration was attributed to the recrystallisation of disordered regions on the particles of revatropate hydrobromide generated during micronisation. This recrystallisation was assessed qualitatively and quantitatively, compared against spray-dried amorphous material, using DVS and isothermal microcalorimetry, respectively. A correlation was established between the energy of micronisation and the level of disorder within the micronised powder. A comparison of the DVS profiles of freshly prepared and aged micronised revatropate hydrobromide suggests an increased physical stability for the aged material.
Keywords: Micronisation; Crystallinity; Particle size; Agglomeration; Dynamic vapour sorption; Microcalorimetry;

The influence of the physicochemical characteristics and pharmacokinetic properties of selected NSAID’s on their transdermal absorption by Estelle Beetge; Jeanetta du Plessis; Douw Gerbrandt Müller; Colleen Goosen; Francois Janse van Rensburg (261-264).
The purpose of this study was to determine the plasma concentrations of selected NSAIDs after topical gel administration and to determine the influence of the physicochemical characteristics of these drugs on transdermal absorption. Plasma concentrations of the drugs were determined using high performance liquid chromatography. The log  P values obtained from literature for piroxicam, ketoprofen, naproxen, ibuprofen and indomethacin, (1.8, 0.97, 3.22, 3.6 and 3.8, respectively) correlated with the area under the plasma–time curve (AUC) values. The AUC values determined were 527.00 (piroxicam) 269.45 (ketoprofen) 258.65 (naproxen) 243.22 (indomethacin) and 88.09 (ibuprofen) μg/ml per h. It was concluded that the most reliable parameter for transdermal absorption was the lipophilic character of a drug (log  P value). The molecular mass, solubility constraint and percentage unionized moiety can only be used in combination with other properties in the prediction of possible transdermal drug delivery.
Keywords: Transdermal; Indomethacin; Ketoprofen; Piroxicam; Naproxen; Ibuprofen; Physicochemical; Pharmacokinetic;

Index (267-268).