It is not too surprising that there is a difference in the results of the studies we reported1 and the study reported above by Norris et al and the study reported by Bijlmer-Lest et al,2 as there were differences in study design and there are differences in the mechanism of action of the two compounds investigated.
As to study design, we administered cysteine for 12 weeks, Norris et al administered N-acetylcysteine for 4 weeks, and Bijlmer-Lest administered N-acetylcysteine for 3 weeks, although the dosage used by both groups was higher than ours. The fact that the Dutch group found no significant alteration between groups in red blood cell— reduced glutathione and glutathione reductase would also suggest too short a period of medication. Additionally, the parameters measured differed somewhat. The Dutch group recorded the time it took to develop delayed erythema on phototest; they stated that immediate erythema on
Mathews-Roth MM, Roberts JE. Treatment of Erythropoietic Protoporphyria With N-Acetylcysteine-Reply. Arch Dermatol. 1995;131(3):355. doi:10.1001/archderm.1995.01690150120027