Narrow-band ultraviolet B (NB-UVB) phototherapy is a mainstay in the treatment of psoriasis, with dosage related to the minimal erythema dose (MED), with initial dose at 50-70%, followed by dose increments.

To determine the MED of Filipino adult patients with psoriasis using NB-UVB phototherapy at a tertiary government hospital.

This is an analytical, observational, cross-sectional study with prospective data collection among Filipino adults with psoriasis, at Dr. Jose N. Rodriguez Memorial Hospital and Sanitarium, from March 2023 to June 2024. Participants underwent MED determination using NB-UVB phototherapy cabinet. MED was defined as the square with definite redness, very light pink, or faintly detectable erythema over the entire exposed site after 24 hours. Clinicodemographic information were gathered and analyzed for possible associations with obtained MED.

Forty-eight participants were enrolled with MED as follows: 600 mJ/cm² (47.92%), 800 mJ/cm² (25%), 1000 mJ/cm² (12.50%), 1200 mJ/cm² (10.42%), and 400 mJ/cm² (4.17%). Age appeared to be directly proportional to MED dose (p-value =0.047). A statistically significant association of having lower MED values (p=0.017) were observed in patients with concomitant diabetes mellitus. Sex, Fitzpatrick skin type, psoriasis severity, and the body site used for testing, had no association with obtained MED values.

The median MED was 600 mJ/cm². Based on this, the suggested initial dosage of NB-UVB at 50-70% is 300-420 mJ/cm². These findings demonstrate that the current starting dose being used at DJNRMHS can either be maintained at 300 mJ/cm² or can be safely increased up to 420 mJ/cm².