The characteristics of erythema induced by topical 5-aminolaevulinic acid

photodynamic therapy

Colin Clark, Robert S Dawe, Harry Moseley, James Ferguson, Sally H. Ibbotson

Photobiology Unit, Department of Dermatology, Ninewells Hospital and Medical School, Dundee DD1 9SY, Scotland

Background: Topical photodynamic therapy (PDT) is

increasingly used to treat superficial non-melanoma

skin cancers. Knowledge of the characteristics of

5-aminolaevulinic acid (ALA)-induced phototoxicity

will increase our understanding of PDT and may

facilitate optimisation of treatment regimes.

Methods: We examined the characteristics of ALA-

induced erythema in 10 healthy subjects and investi-

gated the effect of light source and body site.

Results and Conclusion: Maximal erythema occurred

within 1–2 h of PDT and inter-individual variation in

ALA-induced phototoxicity was seen. No detectable

differences were seen in the phototoxicity on back or

leg sites or between coherent and non-coherent light

sources. These data provide further information to

allow us to optimise topical PDT regimes.

Key words: 5-aminolaevulinic acid; erythema; fluore-

scence; minimal phototoxic dose; photodynamic therapy.

Topical 5-aminolaevulinic acid (ALA) photody-

namic therapy (PDT) is increasingly used to

treat superficial basal cell carcinoma, Bowen’s disease,

actinic keratosis and a range of other skin diseases (1).

No detailed study of the time course of topical ALA

PDT-induced erythema, beyond 24h, has been reported

previously, although it has been noted to persist for a

few days (2). The phototoxicity of PDT is clinically

manifest as erythema and it is this phototoxicity that

is essential for the therapeutic effects of PDT.

Increased knowledge of the erythemal response to

ALA PDT may be important in optimising therapeu-

tic regimens, for example, in selection of the light

sources used or targeting disease at different body

sites, or in explaining treatment failures, for example,

on the low leg. This information has certainly proved

to be essential in the refinement of delivery of

psoralen-ultraviolet A photochemotherapy (3).

In addition, we believe that when giving a treatment

such as PDT, which is known to induce erythema, we

should be able to advise patients on the severity and time-

course of erythema that they are likely to experience.

Materials and methodsTen healthy volunteers (skin phototypes II [n5 3], III

[6] and IV [1]) participated in this study, which was

approved by the Tayside Medical Research Ethics

Committee. Test areas on symmetrical sites on the

upper back, and an area on the lower leg, were

delineated in each volunteer. A subirritant concentra-

tion of ALA (10% in unguentum Ms, Crawford

Pharmaceuticals, Milton Keynes, UK) was applied

under occlusion to 1 cm diameter test sites on Finn

chamberss (Epitest Ltd, Tuusula, Finland) for 6 h

and then removed. The following day (24 h after

initial ALA application) fluorescence under Wood’s

lamp illumination was recorded according to a visual

grading score (grade 0: nil; grade 1: minimal; grade 2:

moderate; grade 3: marked). Preliminary investiga-

tions showed that strong fluorescence persisted at 24 h

and therefore irradiations were performed at this time

to facilitate practical timing of follow-up assessments.

Test sites were irradiated with a geometric series of

light doses (eight doses between 150 and 14000mJ/cm2).

A 630 nm continuous wave diode laser (Diomeds,

Diomed Limited, Cambridge, UK) was used for the

low leg site and one of the back sites, and a high-

pressure non-coherent 900W xenon arc discharge

lamp, filtered to produce a spectral output of

650 � 35 nm and delivered with a liquid-filled light

guide (H. Moseley, Dundee, Scotland), for the other

back site in each volunteer. The irradiance of both

Photodermatol Photoimmunol Photomed 2004; 20: 105–107Blackwell Munksgaard

CopyrightrBlackwellMunksgaard 2004

105

sources was 60mW/cm2. After irradiation, test areas

were protected from ambient light for 48 h. Assess-

ments were made at 1, 2 and 4 h after irradiation and,

subsequently, at 24 h intervals up to 7 days or until

resolution of erythema became apparent. The irradia-

tion dose required to cause just perceptible erythema

(minimal phototoxic dose, MPD) was recorded at

each assessment time. Measurements were also made

in triplicate using a reflectance device (4), and back-

ground values were measured and subtracted from

test site readings. Dose response curves were construc-

ted using these data and the D0.025, the dose response

curve equivalent of the visual MPD, was determined (5).

Analysis was performed by examination of raw and

summary data, and graphs of MPD and D0.025 plotted

against time for each site in each volunteer. When

appropriate, summary data are presented as median

(range), and non-parametric statistical methods (the

Kruskal–Wallis equality of populations test, the

Wilcoxon signed-rank test for paired data) were used.

Linear regression slopes were calculated for logMPD

plotted against assessment time for each site/source

(leg/laser, back/laser, back/non-coherent) in each

volunteer, and slopes were then compared to deter-

mine whether site or source affected MPD responses

over all assessment times. Spearman’s correlation

coefficient (rs) was used to assess the relationship

between fluorescence and lowest logMPD (peak

phototoxicity). For this small exploratory study

Po0.1 was taken as significant.

ResultsPeak erythema (lowest MPD) had occurred by the

first assessment, 1 h after irradiation, at all but one

(laser irradiation to back in one patient) test site (Fig. 1).

MPD had increased above the 1 h value by 1 day in

almost all patients, regardless of site and irradiation

source. Median D0.025 values were also lowest between 1

and 2h after irradiation (xenon at back site 350mJ/cm2;

laser at back site 883mJ/cm2; laser at leg site 1626mJ/

cm2). Erythema at all sites gradually resolved over 2–6

days. There was no significant difference between the

slopes of logMPD plotted against assessment time

according to source (laser vs. non-coherent) on back,

or between back vs. lower leg sites using the laser

source. There was no detectable difference between

median 1 h MPD following laser irradiation of back

compared with laser irradiation of leg sites (95%

confidence interval for difference in medians �1800 to

450mJ/cm2), or between laser and non-coherent

irradiation of back sites (95% confidence interval

for difference �225 to 1050mJ/cm2). Of interest,

pigmentation occurred at test sites in the majority of

subjects and requires further study.

30

06

00

12

00

48

00

96

00

24

00

min

ima

l p

ho

toto

xic

do

se

(m

J/c

m2)

1h 2h 4h D1 D2 D3 D4

assessment time

non-coherent, back laser, back

laser, lower leg

Fig. 1. The median minimal phototoxic dose (MPD) at each assessment time is shown for the non-coherent source(back), laser (back) and laser (lower leg). Note that the y-axis is on a log scale. Assessment time is given as hours(h) or days (D).

106

Clark et al.

Moderate (grade 2) to marked (grade 3) fluore-

scence was evident in 28 of 30 test sites 24 h after

commencement of the 6 h ALA application. The 2 of

30 test sites at which minimal (grade 1) fluorescence

developed were both on lower legs. There was no

detectable difference in fluorescence intensity according

to body site. There was a suggestion that as fluorescence

increased, 1 h MPD decreased on the leg (rs5�0.62,

P5 0.054), but this was not found with either

irradiation source on the back.

DiscussionWe showed that the peak erythemal response of

normal human skin to topical ALA PDT occurred

within 1–2 h after irradiation, and that erythema

subsequently gradually resolved. Responses varied

both within and between subjects. If we assume that

the peri-lesional skin of diseased tissue may behave in

a similar fashion, patients should be advised that

erythema is likely to be maximal within the first 2 h of

treatment, reducing thereafter, although usually

persists for up to 6 days. We did not detect any

differences between the body sites or light sources

studied, in erythemal responses over time after

irradiation, although this was a small study, and

moderately large differences may have been missed.

On leg skin (using the laser irradiation source) our

findings supported the earlier observation that MPD

is inversely correlated with fluorescence intensity prior

to irradiation (2). To summarise, ALA PDT erythema

in normal human skin is maximal within 1–2 h after

treatment, and appears similar for coherent (laser) and

non-coherent light sources, and does not appear to be

affected greatly by body site. Further studies are

required to assess larger numbers of subjects, and the

characteristics of ALA PDT erythema in diseased skin.

Acknowledgement

We would like to thank Lynn Fullerton and the

photobiology technicians for their help with the study

and the Tayside University Hospitals Grant Scheme

for funding the study.

References1. Morton CA, Brown SB, Collins S, et al. Guidelines for

topical photodynamic therapy: report of a workshop of the

British Photodermatology Group. Br J Dermatol 2002; 146:

552–567.

2. Rhodes LE, Tsoukas MM, Anderson RR, Kollias N.Iontophoretic delivery of ALA provides a quantitative model

for ALA pharmacokinetics and PpIX phototoxicity in human

skin. J Invest Dermatol 1997; 108: 87–91.

3. Man I, Kwok YK, Dawe RS, Ferguson J, Ibbotson SH. Thetime course of topical PUVA erythema following 15- and 5-

minute methoxsalen immersion. Arch Dermatol 2003; 139:

331–334.

4. Diffey BL, Oliver RJ, Farr PM. A portable instrument forquantifying erythema induced by ultraviolet radiation. Br J

Dermatol 1984; 111: 663–672.

5. Farr PM, Diffey BL. Quantitative studies on cutaneouserythema induced by ultraviolet radiation. Br J Dermatol

1984; 111: 673–682.

Accepted for publication 2 January 2004

Corresponding author:

Sally Ibbotson

Photobiology Unit

Department of Dermatology

Ninewells Hospital and Medical School

Dundee DD1 9SY, UK

Tel: 144 1382 425717

Fax: 144 1382 633925

e-mail: s.h.Ibbotson@dundee.ac.uk

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Characteristics of ALA PDT erythema