Med estimation for narrow band UV-B on type IV and type V skin in India

Introduction

311 nm narrow band UV-B is being effectively used in the treatment of various skin disorders. Determining MED helps in administering appropriate initial irradiation dose there by enhancing therapeutic efficacy. Based on clinical trials comparing PUVA and narrow band UV-B utilizing TL-01 lamps, TL-01 should be considered the first line treatment for psoriasis. TL-01 lamps have a relatively monochromatic spectrum of emission at 311+2 nm and has a reduced incidence of burning episodes, increased efficacy and longer remission which are distinct advantages over conventional broad band UVB sources. General advantages include safe use in children and pregnant women, no need for post treatment eye photoprotection, no drug induced nausea and absent drug costs. 311-nm narrow band UV-B is also widely used as an effective modality of therapy for atopic dermatitis, vitiligo, and photodermatoses.

As MED reaction becomes the primary basis for comparing therapeutic efficacy, other outcome comparisons eg: relative safety or toxic effects must be considered as a function of MED. In the absence of established data in literature regarding irradiation regimens, determining MED for different skin types helps in administering appropriate initial doses.

Materials and Methods

Spectra 311 narrow band UVB phototherapy cabinet by Daavlin containing 16 TL-01 lamps with a built in 2001 dose control system was used to determine MED. Of the 30 subjects in the study, 20 subjects [11 males and 9 females] had type IV skin and 10 subjects [3 males and 7 females] had type V skin.

Those with history of photosensitivity, any intake of systemic antibiotic or antiinflammatory drugs during the study and any inflammatory skin disorders like psoriasis,atopic dermatitis were excluded from the study. The preferred MED test site was the upper back where the template containing 8 windows [1.5x1.5] was put. The rest of the body was covered and photoprotective glasses were used. All of them were subjected to a test dose ladder of 300, 360,430.515,620,745,895,1075,1290,1550mj/cm of 311-nmUV-B radiation.

Results

Barely perceptible erythema 24 hrs after exposure was taken as MED. Of the 20 subjects with type IV skin 10[33.3%] developed erythema at 745mj,8[26.6%] at 620mj, 2[3.3%] of them developed erythema at 360mj and 515mj respectively. Of the 10 subjects with type V skin, 7 [23.3%] developed erythema at 1075mj and 3[10%] at 1290mj.

The average MED for narrow band UVB exposures for type IV skin was 600mj[range 515-755] and for type V skin 1100mj[range 895-1290mj]

Discussion

In our study, we noticed erythema as early as 3-4 hrs in 66.6% of the subjects, associated with mild tenderness in individuals with type IV skin. Average MED has been mentioned as 1000mj [range 400-1200mj/cm]. Though the average MED for type IV and type V skin falls within this range there can be individual variation as seen in one individual who developed erythema at 360mj. It has been noted that individuals with fair skin had MED that was higher or equal to those with more darkly pigmented skin. On the contrary in our study we found that subjects with fair skin developed erythema much earliar and at a lower dose than needed by individuals with type V skin. Therapy protocols should now be tailored to start the initial doses at 360-450mj for type IV skin 600-825mj for type V skin and gradually stepped up by 20% depending on the patients erythema response.