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Biomedical subjects

A C Watkinson

Publications and source records attributed to A C Watkinson.

At least 19 recordsLinked to original sources
PubMed1998

Comparison of the transdermal delivery of estradiol from two gel formulations.

OBJECTIVE: Conventional oral oestrogen replacement therapy can relieve postmenopausal symptoms but is associated with undesirable side-effects which can be minimised by avoiding the fluctuating hormonal blood levels resulting from oral therapy and eliminating hepatic first-pass metabolism by the use of the transdermal route. The two commercially available transdermal gel formulations differ in composition and application recommendations. Sandrena Gel contains 0.1% (w/w) and Oestrogel 0.06% (w/w) estradiol and recommended dosages are 0.5-1.5 g over 200-400 cm2 (Sandrena Gel) and 2.5 g gel over 720 cm2 (Oestrogel). In transdermal therapy the formulation composition may have a significant effect on drug delivery and we have therefore compared the permeation of estradiol from these formulations across human skin in vitro. METHODS: The in vitro percutaneous penetration of estradiol from the formulations through epidermal membranes prepared from excised female human thing skin was assessed over a 24 h period using static type Franz diffusion cells. RESULTS: Permeation of the active was similar from each formulation representing (at 24 h) 18.2 +/- 3.5% of the applied dose from Sandrena Gel and 17.4 +/- 4.8% of the applied dose from Oestrogel. These percentages equate to cumulative skin permeations of 0.65 +/- 0.15 microgram/cm2 and 0.45 +/- 0.15 microgram/cm2 respectively. CONCLUSION: The results suggest that the two formulations are bioequivalent at the recommended dose levels.

Administration, Cutaneous↗
PubMed1997

Percutaneous penetration of N-nitroso-N-methyldodecylamine through human skin in vitro: application from cosmetic vehicles.

The human skin penetration of N-nitroso-N-methyldodecylamine (NDOMA) from isopropyl myristate (IPM) and two vehicles representative of cosmetic/personal care formulations was determined in vitro. When applied as an infinite dose in IPM (1 microgram/microliter) the average total absorption over 48 hr was 0.10 +/- 0.01% of the applied dose (all data are expressed as means +/- SE). When applied as a finite dose in a representative oil-in-water emulsion formulation the average total absorption over 48 hr was 4.66 +/- 0.76% of the applied dose. When applied as a finite dose in a representative shampoo formulation for 10 min, followed by rinsing (to represent in-use exposure conditions), the average total absorption over 48 hr was 0.75 +/- 0.17% of the applied dose. Approximately 72% of the NDOMA in the applied shampoo formulation was removed by rinsing. The overall data indicated that NDOMA could penetrate the skin but that penetration was low. The rate and extent of absorption, however, could be affected by differences in the vehicle of application, time of exposure and whether the formulation is (and the conditions are designed to mimic) a rinse-off or leave-on product.

Carcinogens↗
PubMed1997

Percutaneous penetration of octyl salicylate from representative sunscreen formulations through human skin in vitro.

The human skin penetration of [14C]octyl salicylate from two representative sunscreen vehicles was determined in vitro. 3H-sucrose was incorporated into all formulations and provided a marker for membrane integrity. When applied as a finite dose in an oil-in-water emulsion vehicle containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.65+/-0.16% of the applied dose (representing a total amount permeated of 1.58+/-0.36 microg/cm2). When applied as an infinite dose in the oil-in-water emulsion vehicle the average total absorption of 14C over 48 hr was 0.47+/-0.22% of the applied dose (representing a total amount permeated of 27.54+/-13.91 microg/cm2). When applied as a finite dose in a representative hydroalcoholic formulation containing 5% (w/w) octyl salicylate, the average total absorption of 14C over 48 hr was 0.59+/-0.09% of the applied dose (representing a total amount permeated of 1.58+/-0.25 microg/cm2). When applied as an infinite dose in the hydroalcoholic formulation the average total absorption of 14C over 48 hr was 0.23+/-0.05% of the applied dose (representing a total amount permeated of 11.28+/-2.55 microg/cm2). The penetration of [14C]salicylic acid [applied at a concentration of 2.7% (w/w), in the oil-in-water emulsion] was also determined. When applied as a finite dose the average total absorption of 14C over 48 hr was 1.14+/-0.23% of the applied dose (representing a total amount permeated of 1.65+/-0.39 microg/cm2). These results suggest that the in vitro human skin permeation of octyl salicylate is relatively low. The amounts of octyl salicylate and salicylic acid permeated when applied in similar vehicles were remarkably similar over 48 hr (1.58 microg/cm2 and 1.65 microg/cm2, respectively). This suggests the possibility that the 14C label appearing in the receptor fluid may, in both cases, represent salicylic acid. If this is the case, then it is possible that the amount of octyl salicylate permeating through the skin is much less than that suggested by the data obtained here. This supposition is, however, entirely speculative and has yet to be confirmed experimentally.

Administration, Cutaneous↗
PubMed1996

The relative effect of Azone and Transcutol on permeant diffusivity and solubility in human stratum corneum.

PURPOSE: The purpose of this work was to analyse the mechanism of the enhancement of percutaneous penetration demonstrated by the known enhancers Azone and Transcutol. METHODS: Enhancer induced changes in the diffusivity and solubility of a model permeant (4-cyanophenol) in human stratum corneum were monitored (in-vitro) using Attenuated total reflectance Fourier transform infra-red (ATR-FTIR) spectroscopy and compared to the gross effects of the enhancers on flux as measured using simple Franz-type diffusion cells. RESULTS: It has been shown by both the well-established Franz diffusion cell technique and the use of ATR-FTIR spectroscopy that the enhancers studied both increase the flux of cyanophenol across human skin in-vitro by a factor of approximately two. Furthermore, it has been demonstrated by ATR-FTIR that these enhancers are likely to exert their effects by different mechanisms. It is probable that Azone reduces the diffusional resistance of the stratum corneum and that Transcutol increases the solubility of the penetrant in this barrier. CONCLUSIONS: There is increasing interest in the apparently synergistic nature in which certain enhancers appear to work. The exact nature of these multiplicative and/or additive effects is not known although there are numerous suggestions in the current literature. The application of ATR-FTIR spectroscopy to such enhancing systems will allow the mechanisms of the observed enhancements to be probed in greater depth.

Analysis of Variance↗
PubMed1995

Use of ATR-FTIR spectroscopy to study the diffusion of ethanol through glycerogelatin films.

The use of ATR-FTIR spectroscopy to study the permeability of a glycerogelatin film is described. Measurement of the diffusion coefficient of ethyl alcohol-d in the film showed excellent reproducibility. Comparison of results from this technique with those previously obtained using an air-flow receptor phase diffusion cell show good agreement in terms of lag time assessed diffusion coefficients. ATR-FTIR spectroscopy revealed time-dependent changes in the composition of the glycerogelatin film during the diffusional process. It was also demonstrated that the concurrent assessment of both diffusant penetration and film composition is feasible.

Diffusion↗
PubMed1992

The effect of disinfection procedures on flexural properties of denture base acrylic resins.

This study evaluates the effects of long-term disinfection immersion on the flexural properties of denture base resins; it was conducted against a background of increasing awareness of the importance of cross-infection control in dental clinics and laboratories. The transverse bend testing procedure used followed that specified in the International Standard for denture base polymers. The results demonstrate that alcohol-based disinfectants are not suitable for use with denture base materials of non-cross-linked acrylic resin.

Acrylic Resins↗
PubMed1992

Experience with ITI osseointegrated implants at five centres in the UK.

Experience with the two-part ITI titanium implant system at five centres in the UK is reported. A total of 461 implants were inserted in 176 patients, who received 189 prostheses. Criteria for the assessment of success following implantation are listed. Results over a 3-year period showed a success rate of 94% when implants were used for mandibular overdentures and crown and bridge prosthetics. A lower success rate in the edentulous maxilla was recorded.

Adolescent↗
PubMed1988

Electromyographic biofeedback and sustained masseter muscle contraction in man.

Twenty-two human subjects performed sustained voluntary contractions of the mandibular elevator muscles firstly without and secondly with visual biofeedback. The level of electromyographic activity of the masseter muscle during the second clench exceeded that during the first clench by a mean of 36%. This differential indicates the ability of the subjects to override the central factors which normally limit muscle activity during a fatiguing contraction.

Adult↗
PubMed1987

The mandibular rest position and electromyography--a review.

The objective of clinical methods for the establishment of the rest position of the mandible is to establish a position at which masticatory muscle activity is minimal. Several methods are in clinical use but these methods may not elicit a position which is coincident with the lowest level of muscle activity as determined electromyographically.

Electromyography↗
PubMed1984

Prevalence of different strains of Candida albicans in patients with denture-induced stomatitis.

Eighteen resistogram strains of Candida albicans were found among isolates obtained from 10 oral sites sampled prior to treatment in 22 patients with denture stomatitis. Eight strains were isolated from single patients, but two were found in four patients and one was found in five patients. Fifteen of the 18 strains were isolated from sites including the fitting surface of the denture or the denture-bearing mucosa. Twelve patients, sampled on a second occasion after treatment, harboured at least one strain on both occasions.

Candida albicans↗