P.J. Dykes

Determination of terbinafine in nail samples during systemic treatment for onychomycoses

A combination of alkali treatment and proteinase K digestion was used to solubilize nail samples from patients with onychomycosis treated orally with terbinafine. The samples were extracted and the levels of terbinafine and its metabolite measured by high‐pressure liquid chromatography. The results showed a relatively rapid penetration of terbinafine into normal nail plate, suggesting that diffusion via the nail plate is the primary route of entry into this tissue. The levels of terbinafine achieved in nail samples exceeded the range of MICs for dermatophytes at the earliest time point (4 weeks) tested in 50% of patients and remained stable, without accumulation, during periods of treatment of up to 3 months.

How orally administered terbinafine reaches the stratum corneum

The route of terbinafine (Lamisil) penetration into the stratum corneum after oral administration was studied in five patients. Serial skin surface biopsy samples of stratum corneum were taken after 1, 3, 7 and 14 days of treatment and terbinafine levels measured by high-performance liquid chromatography. Terbinafine was detected in the stratum corneum as early as 24 hours after the start of treatment in three of five patients. In all cases terbinafine was first detected in the deeper levels of stratum corneum, indicating that the route of delivery to stratum corneum after oral administration is initially by epidermal diffusion.

Nail matrix kinetics of oral terbinafine in onychomycosis and normal nails

Nail matrix kinetics were studied in 12 patients with onychomycosis taking terbinafine (Lamisil) 250 mg daily for up to 48 weeks. Terbinafine was first detected in distal nail clippings from affected nails 3–18 weeks after starting therapy. During the study the mean terbinafine nail levels ranged from 0.25 to 0.55 ng/mg, rapidly reaching a stable level within this range. The kinetics profile of terbinafine in unaffected fingernails was not significantly different from that of affected nails. The kinetics of demethyl terbinafine in nail plate closely paralleled that of terbinafine.

Phenytoin has little effect on in-vitro models of wound healing

Summary It has been reported that phenytoin induces gingival and connective tissue hyperplasia and may be of use in wound healing. In this study the effect of phenytoin on human epidermal keratinocytes and skin fibroblasts has been investigated in vitro. Cell cultures were exposed to increasing concentrations of phenytoin from 10−9 to 10−4 M in the presence of 1 and 10% serum supplemented medium. In addition the effect of phenytoin on epidermal cell migration (epiboly) has been investigated using organ culture of human skin. No stimulation of cell growth was observed, and only a mild toxicity affecting keratinocytes was seen at the highest concentrations. Similarly, no effect on epidermal cell migration in vitro was observed. The lack of a direct effect in vitro suggests that any in‐vivo effect was not the result of interaction between phenytoin and keratinocytes or fibroblasts but possibly due to indirect modulation via other cell types, such as inflammatory or lymphoreticular cells.

The effect of cyclosporin on human epidermal keratinocytes in vitro

Cyclosporin A has been shown to be effective in the treatment of severe, recalcitrant psoriasis, but it is uncertain whether the mode of action is primarily by immune suppression or by other mechanisms. Cyclosporin‐dependent growth‐inhibition has recently been demonstrated in vitro using several non‐human and transformed epithelial cell lines. In this study the effect of cyclosporin on human epidermal keratinocytes and skin fibroblasts was investigated. Secondary cultures of human epidermal keratinocytes were grown on collagen‐coated dishes in the presence of increasing concentrations of cyclosporin. Inhibition of growth was observed at 6–8 μM. An almost identical dose‐response curve was obtained for the cytotoxic drug, cis‐platin. Short‐term exposure (i h) to cyclosporin did not have any effect on epidermal cell growth, suggesting that direct membrane‐related effects were not involved. Analysis of cellular proteins by SDS‐PAGE indicated no effect of continuous cyclosporin exposure on in vitro differentiation. The observation that human epidermal keratinocyte growth is inhibited by cyclosporin suggests that a topical form of therapy for psoriasis may be an effective alternative to oral treatment.

The effect of area of application on the intensity of response to a cutaneous irritant

Summary The intensity of the cutaneous response was assessed after application of a standard irritant to increasing areas of normal forearn skin. Twenty subjects were tested to determine the minimal irritant does (MID) to dilutions of aqueous sodium dodecyl sulphate. Each subject was then treated under occlusion for a period of 24 hours with different areas of filter paper (9.25,100, 225 and 400 mm2) soaked with the concentration required to give the individuals MID. At 25 and 48 hours the degree of erythema was assessed using a 0–4 arbitrary scale, a 10‐cm visual analogue scale (VAS) and an erythema meter. Cutaneous blood flow was measured with a laser‐Doppler device and cutaneous oedema measured by pulsed A‐scan ultrasound. The results at 25and 48hours were almost identical. Both forms of visual assessment (arbitrary scale and VAS) showed an increase in perceived erythema with increasing area and this was confirmed by the erythema meter. Further area‐related changes were noted with both cutaneous blood flow and ultrasound measurements.

Pharmacokinetics of topically applied terbinafine: results from studies in healthy volunteer subjects and patients with pityriasis versicolor

The percutaneous penetration of the antimycotic terbinafine (Lamisil, SF86–327) has been assessed after topical application in patients with pityriasis versicolor and normal volunteer subjects. Plasma samples were analysed by high-pressure liquid chromatography (HPLC). In 10 patients with pityriasis versicolor plasma levels over a 28–day period did not exceed 24.8 ng/ml. There was no evidence of long-term accumulation in these patients. Similar results were obtained with a group of 8 normal volunteer subjects where the maximum plasma level recorded after application of 1% terbinafine cream over 8 days was 11.4 ng/ml. Significantly higher values were not recorded in normal subjects with reduced barrier function. The two main metabolites of terbinafine, carboxybutyl and demethyl carboxybutyl terbinafine, were also measured by HPLC in the urine of the normal volunteer subjects. There was no evidence of long-term accumulation of the terbinafine or its metabolites in these subjects.

Descriptive correlations between various doses of oral terbinafine and concentrations in nail

In order to plan optimum drug regimens for the treatment of onychomycosis with terbinafine, it is necessary to have information concerning the pharmacokinetics of terbinafine in the nail plate. A group of 24 patients with mycology culture-positive onychomycosis took 125, 250 or 500 mg terbinafine once daily for 16 weeks in a double-blind parallel-group study. Distal nail clippings, proximal nail samples and blood samples were taken at frequent intervals during therapy and during a follow-up of up to 36 weeks. Of the 24 patients, 17 completed the study. There was an apparent dose response with regard to concentration of terbinafine and its main metabolite demethylterbinafine in the distal and proximal part of affected nails as well as in plasma. The length of time during which terbinafine could be detected after stopping treatment increased with increasing dosage. The results suggest that short-term therapy with the higher dosage regimens is likely to have a higher efficacy rate.

Efficacy of topical dimetindene in experimentally induced pruritus and weal and flare reactions

Double-blind, placebo-controlled studies were performed to assess the effect of 0.1% dimetindene gel on the itch threshold to intracutaneous histamine and on the weal and flare reaction after intracutaneous injection of histamine in normal volunteer subjects. Treatment of the forearm skin in 20 volunteers resulted in an increase in itch threshold with dimetindene gel compared to placebo. Treatment of the forearm skin with dimetindene gel in 32 volunteers had no significant effect on weal thickness in subjects treated for 10, 30 or 60 min, but there was a significant reduction in weal thickness in those subjects treated for 120 min. Topical dimetindene may be of value in treating conditions mediated through histamine release.

In vivo stratum corneum pharmacokinetics of econazole following once daily and twice daily application to human skin

The stratum corneum pharmacokinetics and microbiological activity of 1% 3H-econazole nitrate cream following non-occlusive once-daily or twice-daily applications to the forearm for 14 days were compared in 16 healthy male volunteers. The distribution of econazole within the stratum corneum, as measured by levels of 3H-econazole in serial forearm skin surface biopsies at various intervals post-therapy, was similar after either once-daily or twice-daily applications. Frequency of application also had no effect on the elimination of econazole from the stratum corneum or on its antifungal activity as measured by zones of inhibition of Candida albicans by stratum corneum specimens. Stratum corneum econazole levels far exceeded previously reported minimum inhibitory concentrations for dermatophytes and yeasts for up to 7 days following once- or twice-daily applications. Similarly, C. albicans growth was inhibited for up to 5 days after either treatment regimen. These data provide evidence of a long-lasting stra...