Background: Aqueous solutions for patch testing may dry out without ensuring sufficient penetration of tested haptens into the skin. Evaporation may also affect the final amount and concentration of hapten. Petrolatum seems a better vehicle for haptens, however, polar molecules are hardly dispersible in it. This can be solved by the use of emulsifiers.
Objectives: To compare patch tests results to methylisothiazolinone/methylchloroisothiazolinone 1:3 (MI/MCI) and formaldehyde carried out with commercial aqueous solutions and novel formulations in petrolatum/emulsifier vehicle.
Methods: One thousand and twenty-six patients with chronic/recurrent eczema were patch tested to formaldehyde 1% aq. (F-002A) and MI/MCI 0.01% aq. (C-009A), as well as two novel petrolatum/emulsifier-based formulations of formaldehyde 1% pet. (Dor-695) and MI/MCI 0.01% pet. (Dor-696). On day 1, the test substances were applied for 2 days in IQ Ultra chambers on the patient's back, with subsequent readings on days 3, 5 and 8. COI: Materials used for this study were supplied free of charge by Chemotechnique Diagnostics.
Results: Positive reactions to at least one of the compared formaldehyde formulations were recorded in 68 patients (6.6%), including 2 who reacted to both, 11 to F-002 only, and 55 to Dor-695 only (chi2: p=0.16). The positivity rate was 1.3% for F-002 (13 positive reactions, including 2 rated as clinically relevant), and 5.6% for Dor-695 (57 positive, 24 relevant). Positive reactions to at least one of the compared MI/MCI formulations were recorded in 69 (6.7%) patients, including 17 who reacted to both formulations, 9 to C-009A only, and 43 to Dor-696 only (chi2: p<0.001). The positivity rate for C-009A was 2.5% (26 positive, 19 relevant), while for Dor-695 it was 5.8% (60 positive, 39 relevant). No irritant reactions to the new petrolatum/emulsifier preparations were observed.
Conclusion: Petrolatum/emulsifier preparations of water-soluble haptens formaldehyde and methylisothiazolinone/methylchloroisothiazolinone yield more positive reactions on patch testing, and detect more clinically relevant sensitizations, as compared to aqueous solutions.
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Document created: 29 May 2017, last updated: 30 May 2017.