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Biomedical subjects

P M Farr

Publications and source records attributed to P M Farr.

At least 73 records · Page 4Linked to original sources
PubMed1991

Sunscreen protection against UVB, UVA and blue light: an in vivo and in vitro comparison.

The photoprotection against UVB, UVA and blue light provided by a widely prescribed sunscreen (RoC 15+ A+B) was compared with two new products containing microfine titanium dioxide (Sun E45 lotion SPF 15 and Sun E45 cream SPF 25) [corrected]. Comparisons were made in vivo using photosensitive patients with either chronic actinic dermatitis or erythropoietic protoporphyria, and in vitro using a newly developed spectrophotometric assay. Good agreement was obtained between the in-vivo and in-vitro methods at each waveband. All products showed high protection against UVB radiation, but the products containing microfine titanium dioxide showed significantly higher protection against both UVA and blue light than RoC 15+ A+B. Products containing microfine titanium dioxide are likely to offer superior photoprotection in those patients who are abnormally sensitive to long wavelength ultraviolet radiation than products which are currently available on prescription.

Adult↗
PubMed1991

PUVA treatment of psoriasis in the United Kingdom.

Information concerning the operation of 134 PUVA units in 96 dermatology centres in the U.K. was collected by a postal questionnaire. The most common protocol was to give PUVA three times weekly in the treatment of psoriasis, and to choose the initial dose of UVA according to skin type. However, the initial UVA dose encompassed a range of five or more within each skin type.

Clinical Protocols↗
PubMed1991

The action spectrum between 320 and 400 nm for clearance of psoriasis by psoralen photochemotherapy.

We have compared the effectiveness of oral 8-methoxypsoralen photochemotherapy (PUVA) using ultraviolet fluorescent lamps with peak emission at either 325, 352 or 370 nm in the treatment of 24 patients with psoriasis. The forearms of each patient were treated three times weekly with two of the three lamps. The erythemal sensitivity of each patient was tested before the first treatment to ensure that equally erythemal doses of radiation were given from each of the lamps. A side-to-side comparison was used to assess response to treatment at weekly intervals for the 6 weeks of the trial. The lamp with peak emission at 325 nm was shown to be significantly superior to either of the other lamps in terms of response assessed at weekly intervals, and time to clearance of psoriasis. An action spectrum, constructed from the median doses required for clearance of psoriasis using each of the lamps, showed that the effectiveness of the radiation decreased exponentially with increasing wavelength throughout the UVA waveband, such that radiation at 320 nm was an order of magnitude more effective than at 360 nm. This suggests that lamps with peak emission around 325 nm will be more effective than those conventionally used in PUVA units with a peak emission at 352 nm. Lamps with peak emission around 325 nm are also highly effective in the treatment of psoriasis with phototherapy alone. Thus a single treatment unit containing these lamps could be used either for PUVA or ultraviolet phototherapy of psoriasis, avoiding duplication or irradiation equipment.

Adolescent↗
PubMed1991

The relationship between plasma psoralen concentration and psoralen-UVA erythema.

The plasma 8-methoxypsoralen (8-MOP) concentration was measured in 60 patients commencing psoralen photochemotherapy (PUVA). At the time of blood sampling each patient was phototested using a series of 10 exposures to UVA. The resulting erythema was measured objectively 72 h after irradiation and dose-response curves for psoralen-UVA erythema were constructed. Although the dose of 8-MOP was calculated according to body weight, patients receiving 30 mg of 8-MOP had a significantly lower mean plasma concentration than those receiving higher doses. There was no significant correlation between plasma 8-MOP concentration and minimal phototoxic dose, either estimated visually or calculated from the dose-response curves. However the slope of the dose-response curve showed significant correlation with plasma 8-MOP concentration. The variation between patients in the rate of increase of the erythemal response, but not the variation in threshold sensitivity, can be explained by difference in plasma psoralen concentration.

Adolescent↗
PubMed1991

Measurement of cutaneous inflammatory reactions using a scanning laser-Doppler velocimeter.

The performance of a new scanning laser-Doppler velocimeter (LDV), which can rapidly measure blood flux over a large area of skin without contact with the skin surface, was compared with that of a conventional laser-Doppler instrument. The vascular response was measured to a range of doses of UVB, and dilutions of contact allergens and sodium lauryl sulphate. The detection threshold of the scanning LDV was equal to, or lower than, that of the conventional instrument. For allergic contact hypersensitivity reactions (ACH), the coefficient of variation was significantly less using the scanning LDV. The scanning LDV allowed accurate measurement of the change in area that occurs with increasing intensity of inflammatory reaction. For ACH reactions the area of inflammation continued to increase at dilutions where blood flux had reached a plateau. The flare area was found to increase linearly with log dose of histamine with no change in blood flux.

Dermatitis↗
PubMed1990

Inhibition of photosensitivity in erythropoietic protoporphyria with terfenadine.

The effect of terfenadine on the response to irradiation with blue light was measured in seven patients with erythropoietic protoporphyria. Terfenadine caused significant inhibition of the immediate flare reaction, but did not alter the erythemal response localized to the irradiation sites. Treatment with beta-carotene had no effect on the flare and erythemal responses. However, the flare reaction was still inhibited by terfenadine during treatment with beta-carotene. These results show that histamine release is involved in the mechanism of porphyrin photosensitivity. H1 receptor antagonists may be of use in the treatment of patients with erythropoietic protoporphyria.

Adolescent↗
PubMed1990

The permissive effect of sebum in seborrhoeic dermatitis: an explanation of the rash in neurological disorders.

The hypothesis that sebum permits the growth of Pityrosporum ovale, and hence the development of seborrhoeic dermatitis, was tested by observing whether a reduction of sebum production by isotretinoin would improve the disorder. In 10 male patients with seborrhoeic dermatitis, treatment with isotretinoin for 6 weeks reduced the mean sebum excretion rate by 70% and improved the severity of the rash, but with a site difference in magnitude of response. It is concluded that the residual pool of sebum is important for the growth of P. ovale and that, within the physiological range, sebum has a permissive effect on the growth of this yeast. Variation in the pools of residual sebum explains a number of features of the disease such as site of involvement and greater prevalence in males than females. The pathological increase in the residual pool of sebum due to immobility explains the frequent occurrence of seborrhoeic dermatitis in patients with a variety of neurological disorders.

Adult↗
PubMed1989

Adverse effects of sunscreens in photosensitive patients.

Experimental and epidemiological evidence shows that the common photosensitive disorder of polymorphic light eruption is caused by the ultraviolet A component of sunlight. Sunscreens protect mainly against ultraviolet B; consequently they reduce sunburn and allow longer periods of exposure to the sun and to greater doses of ultraviolet A than would otherwise be possible. Patients with polymorphic light eruption who intend to obtain a tan by sunbathing should not, therefore, be treated with sunscreens which may worsen their rash, but should be advised to sunbathe without sunscreens for a shorter time.

Disease Susceptibility↗
PubMed1989

Effect of indomethacin on UVB- and UVA-induced erythema in polymorphic light eruption.

The effect of topical indomethacin on the intensity of UVB- and UVA-induced erythema was measured by reflectance spectrophotometry in 23 patients with polymorphic light eruption. Thirteen patients showed a response to indomethacin that was identical to that seen in normal subjects (i.e., inhibition of UVB-induced erythema; no effect on the intensity of UVA-induced erythema). In the remaining 10 patients indomethacin caused abnormal augmentation of UVB- and UVA-induced erythema. These results show for the first time that the term polymorphic light eruption embraces at least two disease states that have different mechanisms of photosensitivity and that can be distinguished on the basis of clinical features and results of photobiologic investigation.

Administration, Topical↗
PubMed1989

The normal range in diagnostic phototesting.

The minimal erythema doses (MED) to UVB and UVA radiation were measured in 254 normal subjects. Bivariate correlation analysis applied to the data showed a strong positive correlation between the UVB and UVA MEDs. By calculating the probability that a given combination of UVB and UVA MEDs is likely to occur in normal subjects, it was shown that, in some instances, both the UVB MED and UVA MED observed in a given subject may be within their respective normal ranges, but that the particular combination is more in keeping with abnormal photosensitivity.

Erythema↗
PubMed1989

Treatment of actinic prurigo with PUVA: mechanism of action.

Five patients with actinic prurigo were treated twice weekly with PUVA. One area on the back was shielded from UVA throughout the 15-week treatment period. Before PUVA, all patients had increased erythemal sensitivity to UVA and showed abnormal augmentation of UVB erythema by topical indomethacin. After PUVA, all patients were free of photosensitive symptoms and skin that had been exposed to UVA showed normal erythemal responses. By contrast, the areas of skin that had been protected from UVA showed erythemal responses that were unchanged from pre-PUVA values. Augmentation of UVB erythema by topical indomethacin persisted, both on UVA exposed and UVA protected skin. These results show that, although PUVA is an effective treatment in actinic prurigo, it does not alter the underlying mechanism of photosensitivity. The protective effect is local and is due presumably to an increase in melanin pigmentation and epidermal thickness.

Adult↗
PubMed1989

A comparison of the dose-response relationship for psoralen-UVA erythema and UVB erythema.

Twenty patients with psoriasis were phototested to determine their erythemal responses to UVB and psoralen-UVA (PUVA) (oral 8-methoxypsoralen). The smallest ultraviolet radiation doses to produce erythema (minimal erythema dose and minimal phototoxic dose, respectively) were recorded and dose-response curves were constructed for UVB (24 hours after irradiation) and PUVA (48 hours) using objective measurement. The choice of a 48-hour measurement was validated by phototesting an additional 11 subjects to determine the time course of PUVA erythema. No correlation was demonstrated between minimal erythema dose for UVB, minimal phototoxic dose for PUVA, and sun-reactive skin type. The mean slope of the dose-response curve for UVB erythema was four times steeper than that for PUVA. Psoralen-UVA erythema reached a broad maximum between 48 and 96 hours after irradiation. Using objective methods we have demonstrated that the commonly accepted view of a steep dose-response relationship for PUVA erythema is not valid.

Adult↗