Characterisation of bioadhesives for periodontal and oral mucosal drug delivery

Whilst there is keen interest in developing improved drug delivery devices to the periodontal pocket and oral mucosa, there are few reports which have examined the physical properties of gels and semi-solid formulations which favour retention and bioadhesion in situ. Hydration and rheological properties appear to be of prime importance in this context and this study aimed to correlate the measurement of these properties with observed bioadhesion, both in vitro and in vivo. Three candidate bioadhesives were selected from previous experiments which had used in vitro organ culture models. These were chitosan, xanthan gum and poly (ethylene oxide) aqueous formulations. Hydration rates with various media were determined in specially constructed cells. Rheological properties were measured using a controlled stress rheometer under carefully regulated conditions. These findings were also correlated with in vivo assessments in the periodontal pocket and oral mucosa. The results demonstrated that three formulations with differing bioadhesive properties also possessed widely different physical characteristics. Hydration experiments indicated a direct relationship between the rate of hydration and bioadhesion or retention. Rheological studies suggested that possession of a gel structure could be an important determinant of retention where shear displacing forces are present in vivo, e.g. the oral mucosa. Furthermore, these studies indicated that formulations which could demonstrate resistance to changes in rheological properties on hydration would also favour retention in situ. Physical characterisation therefore appears to have an important place in screening polymeric formulations prior to clinical testing in the periodontal pocket and oral mucosa.

An investigation of bioadhesion for periodontal and oral mucosal drug delivery

Gel delivery vehicles have ideal placement characteristics for periodontal and oral mucosal drug delivery. However, the retention of the vehicle at the site may be of short duration thereby limiting its therapeutic effect. Bioadhesion has received little attention as a means of enhancing vehicle retention in the periodontal pocket and this study aimed to investigate the possible role of this phenomenon to aid oral drug delivery. Chitosan, xanthan gum and poly (ethylene oxide) were selected as potential vehicles from previous in vitro studies, since all 3 had shown good bioadhesive properties. Retention in the periodontal pocket was assessed by means of an insoluble fluorescein marker in 8 patients, and to the oral mucosa by the retention of a small plastic film in 12 subjects. The results showed that fluorescein release from the periodontal pocket was significantly longer for chitosan than for other gels or a water control. In contrast, xanthan gum gave the most prolonged adhesion time on the oral mucosa (153.5 min) followed by poly (ethylene oxide) (89.3 min) and chitosan (42.6 min), and these times were all significantly different from each other (p < 0.05). The results from this study would tend to suggest that the bioadhesive properties of an aqueous gel may be directly related to its retention both in the periodontal pocket and on the oral mucosa. However, other important factors for mucosal adhesion include the patient acceptability of the formulation and the choice of application site.

An in-vitro study of the effect of hydrocolloid patch occlusion on the penetration of triamcinolone acetonide through skin in man

The aim of this study was to evaluate the effect of occlusion using hydrocolloid-containing patches on in-vitro triamcinolone acetonide (TACA) penetration of the epidermis while monitoring the uptake of water by the patches as a result of transepidermal water loss. The hydrocolloid patches were a laminate of a pressure-sensitive hydrophobic adhesive (containing a dispersion of 39% of either pectin or carmellose sodium) and a polyethylene film. The diffusion of a representative corticosteroid (TACA) through isolated epidermal sheet was shown to depend on the site from which the skin was removed. The two patch-types exhibited markedly different hydration rates when applied to the membranes. For example, after 96 h the carmellose sodium patch showed ten times the weight increase of the pectin patch. Epidermal diffusion rates were, however, similar, both showing a 3-4-fold enhancement over unoccluded conditions. The increase in TACA diffusion with the patches can be explained by the increase in skin hydration that occurs during occlusion. Despite the large differences in transepidermal water transfer through the epidermal membranes with the two types of hydrocolloid patch, however, this level of stratum corneum hydration was apparently similar. As the rate of diffusion was also independent of hydrocolloid patch component, it seems possible that the hydrophobic component of the patch matrix may also influence the level of skin hydration and consequent drug diffusion.

Surface modification of albumin microspheres

Submicron sized hydrophobic and hydrophilic albumin microspheres (MS) were prepared using a chemical crosslinking technique. Spermine was linked to the surface of the hydrophilic MS. The degree of hydrophobicity for these three types of MS was investigated using a novel technique of sedimentation volume. The surface tension of the hydrophobic MS was 31 mN m-1. The ST of the hydrophilic MS was 68 mN m-1, whereas the surface tension of spermine-linked MS corresponded to 62, 65.5, 69 and 71 mN m-1 indicating heterogeneous hydrophilic characteristics. Ligands can be successfully linked to MS using a water-soluble carbodiimide.

The effects of transcervical monofilament insertion on the microbial status of the uterus in guinea-pigs

The monofilament marker tail attached to intra-uterine contraceptive devices (IUCDs) has been implicated in the development of pelvic infection because it acts as a substrate for bacterial adhesion, and facilitates the transmission of vaginal bacteria into the uterus. A guinea-pig model was used to investigate the role of transcervical monofilaments in the transmission of vaginal bacteria into the uterus. By 21 days the degree of uterine contamination was significantly lower than after 24 h (P < 0.05), but was still significantly greater than control values (P < 0.01). Coating the monofilaments with poly (2-hydroxyethyl-methacrylate) (polyHEMA) had no effect on uterine bacterial counts at 24 h. After 21 days, however, contamination within the uteri fitted with polyHEMA-coated monofilaments had significantly increased from levels observed at 24 h (P < 0.01). These counts were also significantly greater than those recorded for the uncoated and control groups at the same time interval. In animals fitted with monofilaments, in which chlorhexidine had been incorporated into the polyHEMA coating, the level of uterine contamination after 24 h was significantly lower than that observed with uncoated threads at the same time interval (P < 0.02). After 21 days there was no significant difference between uterine bacterial counts from the chlorhexidine group and control animals. It is concluded that the use of such drug-loaded monofilaments offers the potential to minimize infections associated with the transcervical insertion of IUCDs.

Potential use of microencapsulation for sustained drug delivery to the respiratory tract

Microencapsulation has long been regarded as a means of achieving sustained drug delivery. In these studies, a spray drying technique was used to produce salbutamol-loaded albumin microparticles with a view to formulating a controlled release system to be used in respiratory drug delivery. Encapsulation efficiencies (40-60 % w/w) obtained using this technique compared very favourably with those obtained using emulsification procedures (1-2 % w/w).

No added benefit from nebulized amiloride in patients with cystic fibrosis

In cystic fibrosis (CF) airway epithelial sodium absorption is increased 2-3 fold. Since sodium absorption is inhibited by the sodium channel blocker amiloride, our aim was to assess its therapeutic benefit in cystic fibrosis. A randomized, double-blind, placebo-controlled, cross-over trial of nebulized amiloride was performed in 23 patients with cystic fibrosis. Amiloride or placebo was administered four times daily for two six month periods. Existing treatment was continued, and any infective exacerbations treated in the usual way. Fourteen patients completed the study. No significant changes occurred in forced expiratory volume in one second, forced vital capacity, oxygen saturation, body weight, sputum volume, culture and rheology, serum urea, and electrolytes, white cell count and erythrocyte sedimentation rate during either treatment period. The frequency of infective exacerbations was also not different in either treatment period. We were thus unable to confirm the benefit shown in the only other clinical trial of nebulized amiloride in cystic fibrosis and conclude that, in the presence of established treatment for cystic fibrosis lung disease, nebulized amiloride offers no additional clinical benefit.

No added benefit from nebulized amiloride in patients with cystic fibrosis

In cystic fibrosis (CF) airway epithelial sodium absorption is increased 2-3 fold. Since sodium absorption is inhibited by the sodium channel blocker amiloride, our aim was to assess its therapeutic benefit in cystic fibrosis. A randomized, double-blind, placebo-controlled, cross-over trial of nebulized amiloride was performed in 23 patients with cystic fibrosis. Amiloride or placebo was administered four times daily for two six month periods. Existing treatment was continued, and any infective exacerbations treated in the usual way. Fourteen patients completed the study. No significant changes occurred in forced expiratory volume in one second, forced vital capacity, oxygen saturation, body weight, sputum volume, culture and rheology, serum urea, and electrolytes, white cell count and erythrocyte sedimentation rate during either treatment period. The frequency of infective exacerbations was also not different in either treatment period. We were thus unable to confirm the benefit shown in the only other clinical trial of nebulized amiloride in cystic fibrosis and conclude that, in the presence of established treatment for cystic fibrosis lung disease, nebulized amiloride offers no additional clinical benefit.

Bromhexine plus oxytetracycline: the effect of combined administration upon the rheological properties of mucus from the mini-pig

Three adult mini-pigs were employed to assess the effects of a twice daily dosage (40 mg kg-1) of oxytetracycline hydrochloride (OTC) and a combination of OTC with (0.5 mg kg-1) bromhexine hydrochloride (BHC) on the rheological properties and wet weight of secreted tracheal mucus. Mucus was collected daily from open-ended tracheal pouches established surgically in the mini-pigs. After a five day control period, either OTC or OTC plus BHC was administered twice daily with the normal diet. Each study period was followed by a five day washout period when mucus was collected but no drug given. The viscoelastic properties of each mucus sample were determined using creep compliance analysis. OTC was shown to increase the residual shear viscosity IP < 0.01) and increase the instantaneous compliance (P < 0.01). An increase in the wet weight of the collected mucus occurred in one pig only (P < 0.01). When BHC was co-administered with OTC, all of these changes were abolished. Evidence was obtained to suggest that BHC increased the concentration of OTC within the secreted mucus. BHC appeared to reverse the mucospissic activity of OTC in-vivo.

The mitigating effects of phosphatidylcholines on bile salt- and lysophosphatidylcholine-induced membrane damage

The effects, at pH 7.0, of a series of 0.2 mM phosphatidylcholines (PC), namely dicaproyl-PC (DCPC), didecanoyl-PC (DDPC), dilauroyl-PC (DLaPC), dimyristoyl-PC (DMPC), dipalmitoyl-PC (DPPC), dioleoyl-PC (DOPC) and dilinoleoyl-PC (DLPC) and a series of 0.2 mM fatty acid salts (namely sodium myristate, palmitate, stearate, oleate and linoleate) upon the erythrocyte haemolysis induced by 2 mM sodium taurodeoxycholate (STDC) were determined. The influence of egg PC and dihexadecyl phosphate (DHDP) concentration upon the haemolysis induced by 1.4 mM sodium deoxycholate (SDC), 2 mM STDC and 0.1 mM lysophosphatidylcholine (LPC) were also established. A bile salt:egg PC mole ratio of 0.5 virtually abolished the haemolysis induced by SDC and STDC, whereas the same ratio of LPC:egg PC only reduced haemolysis from 65 to 40% (maximum haemolysis). DHDP had no effect on the haemolytic action of SDC or STDC. The salts of the fatty acids were non-haemolytic, and when mixed with STDC did not affect the level of haemolysis induced by the bile salt. In contrast, DDPC and DLaPC enhanced the haemolysis of STDC and DCPC had no effect, whereas DMPC, DPPC, DSPC, DOPC, DLPC and egg PC all reduced haemolysis. Maximum reduction was determined for DMPC and egg PC. The mixed micelle preparation temperature (either room or 60 degrees C) and temperature of incubation (either 20 degrees C for 30 min or 37 degrees C for 5 min) had only minor effects on the net haemolysis induced by STDC. These findings may be of significance in understanding the aetiology of certain gastrointestinal diseases and in determining whether mixed bile salt micelles have a role as drug penetration enhancers.

The use of a radiolabelled saccharin solution to monitor the effect of the preservatives thiomersal, benzalkonium chloride and EDTA on human nasal clearance

The effect of thiomersal, benzalkonium chloride and ethylenediaminetetraacetic acid (EDTA) on the nasal mucociliary clearance of healthy volunteers has been investigated using a modified saccharin test and gamma scintigraphy concomitantly. A significant correlation was found between the two techniques. Using each subject as his/her own control, none of the preservatives significantly altered the rate of clearance or proportion cleared from the nasal cavity after the administration of a single dose. This result is at variance with some in-vitro findings.

The effect of bromhexine hydrochloride on the viscoelastic properties of mucus from the mini-pig

Mucus was collected daily from open-ended pouches established surgically in three mini-pigs. After a five day control period bromhexine hydrochloride (BHCl) was administered to each pig at dose levels of 0.5, 1.0 and 2.0 mg.kg-1 twice daily for five days. Each study period was followed by a five day washout period, when mucus was collected but no drug given. The viscoelastic properties of each mucus sample were determined using creep compliance analysis. BHCl was shown to reduce the residual shear viscosity (p less than 0.05) and increase the instantaneous shear compliance at all dose levels (p less than 0.005), despite the large inherent intra- and inter-animal variation in the rheological properties of the daily samples. No change was found in the wet weight of the mucus samples throughout any of the study periods. This experimental model would appear to provide a valuable in vivo method of assessing the mucoregulatory potential of administered compounds.

The effect of bromhexine hydrochloride on the viscoelastic properties of mucus from the mini-pig

Mucus was collected daily from open-ended pouches established surgically in three mini-pigs. After a five day control period bromhexine hydrochloride (BHCl) was administered to each pig at dose levels of 0.5, 1.0 and 2.0 mg.kg-1 twice daily for five days. Each study period was followed by a five day washout period, when mucus was collected but no drug given. The viscoelastic properties of each mucus sample were determined using creep compliance analysis. BHCl was shown to reduce the residual shear viscosity (p less than 0.05) and increase the instantaneous shear compliance at all dose levels (p less than 0.005), despite the large inherent intra- and inter-animal variation in the rheological properties of the daily samples. No change was found in the wet weight of the mucus samples throughout any of the study periods. This experimental model would appear to provide a valuable in vivo method of assessing the mucoregulatory potential of administered compounds.

The effect of some preservatives used in nasal preparations on the mucus and ciliary components of mucociliary clearance

Efficient mucociliary clearance is a function of the physical properties of the mucus coupled to appropriately functioning cilia and may be altered by substances affecting ciliary beat frequency (CBF). Therefore the effect of preservatives on CBF was investigated using a photoelectronic technique. Methyl-p-hydroxybenzoate, propyl-p-hydroxybenzoate, chlorbutol and chlorocresol inhibited beat frequency, an effect which was reversible upon rinsing out the first three compounds but not chlorocresol. The effect of chlorhexidine and phenylmercuric borate on CBF was complicated by an interaction with chloride ions in the media used. EDTA did not appear to be ciliotoxic, while the effect of benzalkonium chloride was variable. Thiomersal halted ciliary beating after 40-100 min. Mucociliary clearance may also be affected by an alteration of the physical properties of the mucus layer, therefore the effect of each compound on the rheological properties of purified pig gastric mucus glycoprotein was investigated. None of the preservatives significantly altered the viscoelastic properties of the gel, measured using dynamic techniques.

The effect of some preservatives used in nasal preparations on mucociliary clearance

The effect of methyl-p-hydroxybenzoate, propyl-p-hydroxybenzoate, chlorbutol, chlorocresol, EDTA, benzalkonium chloride, chlorhexidine, phenylmercuric nitrate and phenylmercuric borate on mucociliary transport rate of the frog palate has been examined. Following a variable number of applications all these preservatives halted transport, the first three reversibly. However, applications of thiomersal (0.01%) were well tolerated. The frog palate possesses a ciliated epithelium protected by mucus, since some of our findings are at variance with those previously reported results where the protective effect of mucus was negligible in the in-vitro model (usually trachea) employed, it would appear that the contribution of mucus to effective mucociliary clearance should not be underestimated.

The migration of bacteria through gels in the presence of IUCD monofilament tails

An in vitro model was developed to investigate the migration of a variety of bacteria of different characteristics through a gel system in the presence or absence of a wide range of polymer monofilament threads. The bacteria were unable to migrate through the gel from the point of inoculation in the absence of a solid substrate. Migration occurred along all thread types tested, including those used as IUCD marker tails and the extent of bacterial migration appeared to be determined primarily by the motility of the microorganisms. The implications of these findings in relation to the development of pelvic infections in IUCD wearers is discussed.

Effects of phosphatidylcholine on the topical bioavailability of corticosteroids assessed by the human skin blanching assay

A non-occluded multiple application skin blanching assay has been used to determine the effect of applied phosphatidylcholine (PC) on the bioavailability of corticosteroids. One forearm of each of ten volunteers was treated twice daily for one week with PC presented as a liposomal suspension in Sørensen's (pH 5.0) phosphate buffer (2.5 mg PC/0.5 mL) while the other arm was treated with 0.5 mL of phosphate buffer. For the following two weeks this treatment regimen was continued but in addition, each of four corticosteroid formulations (containing (i) hydrocortisone 0.1%, (ii) clobetasone butyrate 0.05%, (iii) betamethasone 0.1% and (iv) clobetasol propionate, 0.05%) was applied to sites on both arms. 5 +/- 1 mg of each cream was applied twice daily to the sites on day 1, then once daily for a further four days; after two days of no application, the protocol was repeated. Estimation of pallor was usually made four times daily. At the end of the second week of corticosteroid application the blanching response to all four formulations on the PC treated arms was significantly higher than on the buffer treated arm. Tachyphylaxis to the applied corticosteroids was markedly less apparent on the lipid-treated arms. It is proposed that the applied phospholipid either supplements the lipid content of the skin or provides a thin film in intimate epidermal contact. Such a film may promote hydration of the stratum corneum and also provide an environment into which corticosteroids initially partition before a subsequent, more controlled, release to the underlying tissue.

The influence of native porcine gastric mucus gel on hydrogen ion diffusion: the effect of potentially ulcerogenic agents

Experiments were carried out to investigate the ability of native gastric mucus gels to retard hydrogen ion diffusion. Mucus held between two polycarbonate membrane filters in a diffusion cell, separating equimolar solutions of NaCl and HCl, significantly reduced the rate of hydrogen ion diffusion and increased the time for the mean hydrogen ion front to traverse the mucus compartment (lag time) when compared to an unstirred layer of saline (P less than 0.01). N-acetylcysteine, sodium taurodeoxycholate and acetylsalicylic acid significantly increased the diffusion rate (P less than 0.025); the lag time was significantly reduced by N-acetylcysteine (P less than 0.001). In addition mucus gels were found to have buffering capacity at a pH greater than 2. These observations suggest that native gastric mucus gels can retard hydrogen ion diffusion and that this retardation of diffusion is reduced by agents which are potentially damaging to the gastric mucosa.

Membrane damage by bile salts: the protective function of phospholipids

The direct toxicity of sodium deoxycholate (SDC) and lysophosphatidylcholine (LPC) to biological membranes was assessed by measurement of goldfish overturn time. When phosphatidylcholine (PC) was incorporated into the aqueous media, the toxicity of both SDC and LPC was reduced, as indicated by increased overturn time. Fish were also pretreated for various times in media containing (a) 1 mM SDC and (b) 1 mM SDC with 1 mM PC. Subsequent transfer to solution, 100 mg litre-1 quinalbarbitone sodium showed that reciprocal overturn times for fish treated using method (a) increased linearly with duration of pretreatment up to a limiting value, obtained after 20 min exposure; 40 min exposure to 1 mM SDC was directly toxic. Fish pretreated using regimen (b) survived longer when challenged with barbiturate, and the reciprocal overturn times were a linear function of time of pretreatment up to at least 40 min. PC also provided protection against membrane damage caused by the synthetic surfactant sodium dodecyl sulphate. Mixed micelle formation between PC and surfactant is thought to account for the protective effects. The results are of significance in the consideration of reflux hypothesis for the aetiology of gastric ulceration and also the possible formulation of drug delivery systems intended to enhance absorption whilst minimizing gastrointestinal damage.

The efficacy of acupuncture as an aid to stopping smoking

The present study examines the usefulness of acupuncture as an aid to stopping smoking. Results from 405 subjects show acupuncture can help between 5 and 15 percent of the population to stop smoking for at least six months. Using chronically implanted press needles, previously reported 'effective' auricular acupuncture points for smoking cessation are shown to be no better than 'placebo' auricular points. Additional electroacupuncture on the hand neither increases the probability of stopping smoking nor enhances the reduction in smoking at three week, three month or six month follow-up periods. It is therefore likely that a large psychological component is attached to acupuncture to stop people smoking.

The solubilization of progesterone by mixed bile salt-phospholipid sols

The solubility of progesterone was determined in several different bile salt-phospholipid mixtures, and it is concluded that: (1) The solubility in unconjugated bile salts is greater than in the conjugated analogues, and the solubility in deoxycholate solutions is twice that in cholate solutions. (2) Substitution of hydroxyl groups in the 11 and 21 positions of progesterone increases solubility, whilst substitution in the 17-position decreases solubility in bile salt solutions. (3) Progesterone solubility in mixed bile salt solutions is proportional to the mole ratio of the surfactant mixture. (4) Sodium deoxycholate (SDC)-phospholipid sols show no such linear solubilizing properties; a minimum occurring at a mole ratio of SDC to phospholipid of 1 : 4. (5) There is a break in the solubility curve of progesterone in lysophosphatidycholine (LPC)/phosphatidylcholine (PC) mixtures at a mole ratio of 65 : 35 coincident with maximum viscosity. (6) Introduction of SDC into LPC/PC mixtures results in decreased progesterone solubility.

Direct effect of bile salts and phospholipids on the physical properties of mucus

Reflux of duodenal contents into the stomach has been implicated in the disruption of mucosal defence and the subsequent occurrence of gastric ulcer. The change produced in the rheological properties following the addition of bile salts and phospholipids to mucus samples was used to assess resultant structural changes. Sodium deoxycholate, sodium taurodeoxycholate, sodium glycocholate, and lysophosphatidylcholine decreased both viscosity and elasticity, indicating that structural breakdown had occurred, whereas phosphatidylcholine could not be shown to have any effect. It is therefore suggested that some of the ulcerogenic activity of naturally occurring surfactants may be associated with their ability directly to reduce mucus consistency.