Mechanical characterization and drug permeation properties of tetracaine-loaded bioadhesive films for percutaneous local anesthesia.

In the development of bioadhesive patch devices for percutaneous local anesthesia, the tensile properties of the films produced after the casting of the gel intermediates is of key importance to the clinical compliance of the product, and its effective delivery of the local anesthetic agent. A range of bioadhesive patches were formulated and their mechanical and in vitro permeation properties determined. Altering formulation significantly altered the mechanical properties of films. The tensile properties of the films could be modified to allow concomitant benefits in the mechanical and drug permeation properties of the films, ensuring that patches not only exerted clinically beneficial effects, but are also mechanically robust. Tetracaine was found to plasticize films and while this effect was weak, it was significant both statistically and potentially also in the effect it has on the clinical use of these devices. Drug release from tetracaine patches demonstrate the same trends as found previously across polydimethylsiloxane films. By altering the formulation of the patch device, the drug release from the device to the skin is readily and accurately controlled, and was not solely a function of the stratum corneum barrier properties but additionally of the formulation.

Randomized trial of novel tetracaine patch to provide local anaesthesia in neonates undergoing venepuncture.

BACKGROUND: Procedures such as venepuncture or heel prick are painful and may cause considerable stress to newborn infants. Topical local anaesthetics are effective for venepuncture but need to be applied for at least 60 min and the delivered dose will vary. We assessed a novel tetracaine-based self-adhesive patch in providing controlled local anaesthesia before venepuncture. METHODS: A placebo-controlled, double-blind trial was conducted using a tetracaine patch formulated from hydroxypropylcellulose discs (0.283 cm(2)) containing tetracaine (1 mg x cm(-2)) surrounded by a low tack pressure-sensitive adhesive backing layer. Thirty-two newborn infants of gestation 32-42 weeks (median 36 weeks), aged 3-18 days (median 6 days) were randomized to receive a tetracaine-containing patch or a placebo device applied to the dorsum of the hand 30 min before venepuncture to obtain blood samples. Pain was assessed in response to needle insertion using a validated adaptation of the neonatal facial coding score (NFCS) and the presence of crying. RESULTS: Of 15 tetracaine-treated neonates, 14 (93%) presented little or no pain in response to the procedure compared with six of 17 (35%) who had the placebo patch applied (P=0.01). CONCLUSIONS: The tetracaine patch produced effective pain relief during the venepuncture procedure in both term and pre-term infants. There were no adverse effects, either local or systemic.

Synthesis, hydrolysis kinetics and anti-platelet effects of isosorbide mononitrate derivatives of aspirin.

Two isomeric aspirin derivatives of isosorbide-5-mononitrate (ISMN) were prepared and evaluated as potential mutual prodrugs of aspirin and nitric oxide. The hydrolysis of both compounds was studied in pH 7.4 phosphate buffer solution, buffered alpha-chymotrypsin solution and 10% buffered rabbit plasma. The benzodioxin-4-one derivative was hydrolysed to salicylic acid and ISMN acetate in buffer solution (t(1/2) 32.1 h), 10% buffered rabbit plasma (t(1/2) 25.7 min) and alpha-chymotrypsin (t(1/2) 86.6 min). The carboxylic acid ester derivative ISMNA was hydrolysed via the salicylate ester in buffer solution (t(1/2) 48.5 h) but was rapidly and almost exclusively hydrolysed to aspirin and ISMN in plasma solution (t(1/2) 2.8 min). The hydrolysis appeared to be enzyme mediated as it was suppressed by co-incubation with eserine. ISMNA was evaluated for its ability to inhibit platelet aggregation in rabbit PRP in response to the following agonists: arachidonic acid (AA) (100 microM), ADP (1.2 microM), phorbol ester (0.5 microM), platelet activating factor (PAF) (5 nM) and the thromboxane mimic U46619 (1.5 microM). ISMNA suppressed platelet response to AA at 1 microM whereas 10 microM aspirin showed no inhibitory effects.

Novel bioadhesive delivery system for percutaneous local anaesthesia.

We have assessed the efficacy of a novel bioadhesive amethocaine patch device, compared to Ametop gel, in a randomized, double-blinded trial. Patch and gel formulations, including placebos, were applied to the forearms of volunteers (n = 30) for 40 min. Once the formulations were removed from the skin, anaesthesia was assessed by volunteers using a conventional pinprick test. Pain scores were recorded for 4 h after removal of gels and patches. Statistical analysis of the results indicated that both amethocaine gel and patch preparations were superior to placebo (P < 0.05). No significant difference was observed between amethocaine gel and patch formulations (P > 0.05) in either onset time or duration of action for percutaneous local anaesthesia. The results of this study indicate therefore that the novel bioadhesive patch provides clinically comparable anaesthesia to the established gel formulation in a more defined dosage form.

Effect of percutaneous local anaesthetics on pain reduction during pulse dye laser treatment of portwine stains.

We have used EMLA, 4% amethocaine gel and placebo for facial portwine stains, for a period of 1 h, in a double-blind study. After removal of the preparations from the skin surface, each area was treated with six pulses of the laser, each 5 mm in diameter. Any pain noted immediately after treatment was recorded using both visual analogue (VAS) and verbal rating (VRS) scores. Twenty nine patients completed the study and statistical analysis of the results indicated that both EMLA and 4% amethocaine gel were superior to placebo (P < 0.001). However, when EMLA and 4% amethocaine gel were compared, the amethocaine preparation was significantly better (P < 0.05, VAS; P < 0.005 VRS) than EMLA in reducing pain caused by the laser treatment.

A randomised controlled trial evaluating a novel cytotoxic drug delivery system for the treatment of cervical intraepithelial neoplasia.

OBJECTIVE: To investigate the efficacy of a novel method for the treatment of cervical intraepithelial neoplasia. A cytotoxic drug delivery system using a bilaminar bioadhesive polymeric film was applied directly to the cervix. This cytotoxic drug delivery system allowed the dose, the site and the duration of application of the cytotoxic drug (5-fluorouracil) to be controlled. DESIGN: A prospective, double-blind randomised controlled trial. SETTING: The Departments of Obstetrics and Gynaecology and Pathology of Belfast City Hospital and The Queen's University of Belfast, and the Department of Pharmacy of The Queen's University of Belfast. PARTICIPANTS: One hundred and four patients who had been referred to the colposcopy outpatient clinic because of abnormal cervical cytology were recruited into the trial. They were assessed colposcopically and biopsies for histopathology were obtained. Only patients with cervical intraepithelial neoplasia lesions Grades 1 and 2 were recruited. INTERVENTIONS: All patients were re-assessed one, three, and six months after application of the cytotoxic drug delivery system by colposcopy. Clinical endpoints were noted. MAIN OUTCOME MEASURES: Pre-treatment histopathological biopsy results were compared with those obtained after treatment. RESULTS: The cytotoxic drug delivery system fulfilled the requirements for treatment of cervical intraepithelial neoplasia without causing any architechtural damage, but the chemotherapeutic agent, 5-fluorouracil, did not provide effective treatment of disease. CONCLUSIONS: This study showed that the delivery system was effective, and further studies using this mechanism are now possible.

Autoradiographic imaging of the distribution of 5-fluorouracil through cervical tissue following in vitro surface application of a bioadhesive cervical patch.

The distribution of 5-fluorouracil through cervical tissue has been assessed following the in vitro application of a bioadhesive patch to excised human cervix. The bioadhesive matrix contained a total of 20 mg of 5-fluorouracil spiked with 5-fluorouracil-6-3H and was applied for fixed periods of either 4 or 24 hours. Tissue slices were sectioned perpendicular to the plane of the applied patch and the autoradiographic image developed by placing a frozen tissue slice on Hyperfilm with subsequent instant thawing and refreezing, the resulting bilayer being maintained at -18 degrees C for 24 hours. The developed image was analysed by scanning densitometry and raster scans were visualised with three-dimensional contouring software. The autoradiograms showed darker areas surrounding tissue ducts, suggesting that 5-FU was spilling from the lumen into the surrounding stroma. Transport of 5FU via aqueous channels may thus make an important contribution to the rapid penetration of the drug through the cervical stroma. Three-dimensional autoradiographic images showed that, for a 4-hour patch application, there were areas of relatively low drug concentration within the upper 5 mm of tissue, where CIN lesions can exist in the glandular tissue or cervical crypts. However, extending the application time to 24 hours produced areas of high drug concentration extending throughout this region.

Liquid scintillation spectrometry of 5-fluorouracil in cervical tissue following in vitro surface application of a bioadhesive cervical patch.

The potential use of bioadhesive technology for the treatment of cervical intraepithelial neoplasia was investigated. A cervical patch was designed containing 5-fluorouracil in a bioadhesive matrix and polyvinyl chloride as the backing layer. The concentration of 5-fluorouracil at specified tissue depths from the cervical surface was determined in vitro in relation to the ability of the drug to reach precancerous foci in cervical crypts up to 4 mm below the tissue surface. Thus, tissue was exposed to drug-loaded patches spiked with 5-fluorouracil-6-3H and subsequently sectioned to obtain tissue slices at different depths. The concentration of 5-fluorouracil was determined by liquid scintillation spectrometry. Drug penetration into cervical tissue exceeded a depth of 5.5 mm. Furthermore, the concentration in the tissue depended on the drug loading in the patch. Patches containing 10 and 20 mg of 5-fluorouracil produced a linear drug gradient that was established after a 4 hour application of the patch and persisted over 24 hours. However, patches containing 3.5 mg of 5-fluorouracil displayed signs of drug exhaustion after 24 hours. The penetration characteristics of 5-fluorouracil through cervical tissue using the cervical patch delivery system were sufficiently favourable to warrant further clinical investigations.

New patch delivery system for percutaneous local anaesthesia.

We have assessed the release of amethocaine from a new patch delivery system and subsequent drug diffusion through human stratum corneum and whole skin. We found that the patch system was more efficient than an amethocaine gel preparation. It was also observed, both in vitro and in vivo, that the stratum corneum acted as a reservoir for amethocaine. A double-blinded clinical trial, using 30- and 60-min application times, indicated that there was no statistical difference between patch and gel formulations in onset of percutaneous local anaesthesia. Furthermore, a 30-min application of the patch was sufficient to provide profound and prolonged topical anaesthesia in all volunteers. In contrast, although a 60-min application of EMLA was necessary to ensure satisfactory onset of percutaneous anaesthesia, the duration of action was much shorter than that of the amethocaine patch.

The effects of three non-antibiotic, antimicrobial agents on the surface hydrophobicity of certain micro-organisms evaluated by different methods.

The effects of three non-antibiotic, antimicrobial agents (taurolidine, chlorhexidine acetate and providone-iodine) on the surface hydrophobicity of the clinical strains Escherichia coli, Staphylococcus saprophyticus, Staphylococcus epidermidis and Candida albicans were examined. Three recognized techniques for hydrophobicity measurements, Bacterial Adherence to Hydrocarbons (BATH), the Salt Aggregation Test (SAT) and Hydrophobic Interaction Chromatography (HIC) were compared. At concentrations reported to interfere with microbial-epithelial cell adherence, all three agents altered the cell surface hydrophobicity. However, these effects failed to exhibit a uniform relationship. Generally, taurolidine and povidone-iodine treatments decreased the hydrophobicity of the strains examined whereas chlorhexidine acetate effects depended upon the micro-organism treated. Subsequently, the exact contribution of altered cell surface hydrophobicity to the reported microbial anti-adherence effects is unclear. Comparison of the three techniques revealed a better correlation between the results obtained with the BATH test and HIC than the results obtained with the BATH and SAT or SAT and HIC. However, these differences may be due to the inaccuracy associated with the visual assessment of results employed by the SAT.

Clinical experiences with a novel percutaneous amethocaine preparation: prevention of pain due to venepuncture in children.

1. The efficacy and safety of a novel percutaneous anaesthetic preparation based on amethocaine has been investigated in the paediatric clinical environment. 2. There were 1241 recorded applications on a named patient basis made to patients from infant to age 16 years. Of these, 88.7% had satisfactory anaesthesia to venepuncture challenge, rising to approximately 90% when the infant group was excluded. 3. A 30 min application time was found to be adequate for reliable topical anaesthesia. 4. There were no serious adverse reactions to the preparation. Of the total 6.9% recorded reactions, 6.3% were of a mild, transient erythema later identified as due to the vasodilator action of the drug. 5. A total of 123 patients received more than one application of the preparation. There was no evidence of sensitisation on subsequent exposure to the preparation. 6. The short application time required was found to be advantageous to ward and clinic routines.

Local anaesthesia of the skin.

Local anaesthesia of intact skin is of growing importance given the increased use of minor surgical procedures on an out-patient basis. Specific pain receptors (nociceptors) are responsible for sensing cutaneous pain. Mechanisms of pain perception and the role of local anaesthetics in reversibly blocking nociception are considered. Effective routes of administration are dermal infiltration or, more recently, anaesthesia by topical application of specifically formulated preparations which promote percutaneous absorption of the drug (percutaneous local anaesthesia). Although many other topical anaesthetic products are also available these do not permit the anaesthetic to reach the nociceptors underlying the stratum corneum and are therefore only suitable for mucosal anaesthesia or for application to damaged skin. The chemical characteristics of local anaesthesia drugs are identified. Those agents suitable for cutaneous anaesthesia are reviewed with respect to potency, onset and duration of anaesthesia and possible systemic or local adverse reactions.

In vivo assessment of percutaneous local anaesthetic preparations.

This study has demonstrated greater efficacy of a new percutaneous amethocaine preparation relative to Eutectic Mixture of Local Anaesthetics (EMLA). Initially, a double-blinded trial was undertaken on each preparation individually against placebo, as the recommended method of application was different for EMLA (2.5 g applied for 60 min under an occlusive dressing) and the amethocaine formulation (0.5 g applied for 30 min). Thereafter, the two preparations were compared directly, in a double-blinded study using a standardized application for both formulations. The results indicated that both preparations provided significant (chi-square; P less than 0.001) percutaneous local anaesthesia when compared with placebo. The amethocaine preparation produced significant anaesthesia (chi-square, P less than 0.001) after 30 min application. Furthermore, the amethocaine formulation demonstrated both increased rapidity of action and increased duration of effect, as determined by a two-tailed unpaired t test, in comparison with EMLA when application times of both 30 and 60 min were used for each preparation. The results of this study indicate that the amethocaine preparation provided more rapid and prolonged anaesthesia than EMLA.

Concentration-response analysis of percutaneous local anaesthetic formulations.

The percutaneous absorption of amethocaine has been measured for different concentrations of the drug in three different formulations, A, B and C. Statistical analysis indicated that a concentration of 4% produced effective percutaneous local anaesthesia to pin-prick, together with an acceptable onset time of approximately 40 min. Increasing the concentration did not reduce the onset time further, although there was some increase in the duration of anaesthesia. Formulations A and B were hydrophilic, whereas C was an oil-in-water cream. Effective anaesthesia with formulation C required a higher drug concentration (12%), perhaps because of partitioning of the lipophilic anaesthetic into the lipid phase of the vehicle. The rate-limiting step was considered to be diffusion by the lipophilic anaesthetic through the stratum corneum, shown by onset of anaesthesia after removal of the formulation from the test site.

Pain-free cutting of split skin grafts by application of a percutaneous local anaesthetic cream.

The use of a novel percutaneous anaesthetic preparation for the pain-free cutting of split skin grafts has been assessed in a series of 80 patients, age range 12 to 96 years. The technique was completely successful in 80% of these cases, with complete analgesia established within one hour of initial application. Duration of anaesthesia was such that pain-free cutting of the skin was possible up to 5 hours after initial application of the preparation. Failures of the technique were largely attributed to a loss of anaesthetic potency in the preparation, application of an inadequate amount to the site or patient anxiety. The use of the percutaneous anaesthetic preparation was found to offer considerable advantages over conventional infiltration anaesthesia for this type of surgery. Several additional surgical applications of percutaneous anaesthesia are also considered.

Comparative in vivo and in vitro assessment of the percutaneous absorption of local anaesthetics.

The percutaneous absorption of local anaesthetics in a standard formulation has been compared in vitro and in vivo. In vitro data were obtained with a modified Sartorius absorption system and silastic as a lipophilic barrier membrane. With this system the greatest steady-state flux values and permeability coefficients were obtained with amethocaine and lignocaine. These drugs also performed best in an in vivo volunteer trial. However, statistical analysis revealed that amethocaine was significantly better at producing full-depth anaesthesia to the challenge of insertion of a sterile needle. An optimized amethocaine formulation may therefore be expected to meet most closely the ideal profile for a percutaneous local anaesthetic preparation.

A comparative study of the microbial antiadherence capacities of three antimicrobial agents.

The antimicrobioal agents, taurolidine, chlorhexidine and povidone-iodine were examined for microbial anti-adherence activity. Two adherence systems were investigated using light microscopic and radio-isotopic assay methods: that of an oral isolate of Candida albicans to human buccal epithelial cells and of a urine isolate of Escherichia coli to human uroepithelial cells. Each of the three agents exhibited significant anti-adherence activity which was concentration dependent. The activity was expressed at subminimum inhibitory concentrations of the agents. Treatment of either the microbial or epithelial cells resulted in significant reductions in adhering micro-organisms. Consideration of the data in respect of the skewness coefficient and percentage clear epithelial cells indicated that the agents exhibited a broadly based anti-adherence capacity.

On the statistical evaluation of adherence assays.

Parametric (unpaired t-test) and non-parametric (Mann-Whitney U-test) methods have been used in the evaluation of adherence assays on the non-antibiotic antimicrobial agent, Taurolin. In all but one case, where the anti-adherence effect was known to be marginal, both statistical methods gave similar results although there were some minor differences in the levels of significance achieved. The effect of the agent on the deviation of adherence data from normality was quantified by calculation of the skewness coefficient for each data set. A significant anti-adherence effect appears to result in a decrease in the skewness of the adherence assay data. It was concluded that either parametric or non-parametric statistical evaluation of adherence assay data is valid for large numbers of observations. In future studies of this type it is suggested that attention should also be given to the effect of the anti-adherence agent on the deviation of adherence data from normality as denoted by the skewness coefficient.

Reduced adherence of micro-organisms to human mucosal epithelial cells following treatment with Taurolin, a novel antimicrobial agent.

Taurolin, a non-antibiotic antimicrobial agent, significantly reduced the adherence of buccal and vaginal strains of Candida albicans blastospores and urine isolates of Escherichia coli and Staphylococcus saprophyticus to epithelial cells. Light microscopy and radio-isotopic counting methods were used to quantify the adherence of the micro-organisms to either uroepithelial or buccal epithelial cells. A maximum reduction in adherence of approximately 65% was obtained. The anti-adherence capacity was time-dependent, requiring a contact time of 30 min to achieve maximum effect. Taurolin at sub-minimum inhibitory concentrations (MIC) significantly reduced the adherence of Candida and E. coli. A concentration slightly higher than the MIC was required for Staph. saprophyticus. Treatment of either epithelial cells or micro-organisms with Taurolin resulted in reduced adherence of microorganisms.