Urinary excretion of melanocyte metabolites during treatment with chloroquine phosphate

The antimalarial drug chloroquine is also used in the prevention of photodermatoses and in patients with inflammatory connective diseases. The drug binds strongly to melanin. Melanocytic activity can be studied by analysis of the urinary markers of eumelanin (6-hydroxy-5-methoxyindole-2-carboxylic acid, 6H5MI-2-C) and phaeomelanin (5-S-cysteinyl-dopa, 5-S-CD). To determine whether chloroquine interacts with this activity, we measured the urinary excretion of the two metabolites in 16 patients with either systemic or discoid lupus erythematosus, polymorphic light eruption or rheumatoid arthritis, during a period with and without treatment with chloroquine phosphate. Two control groups consisting of 7 untreated patients and 10 healthy subjects were also included in the study. During medication, there was a significant increase in 5-S-CD excretion, while the excretion of 6H5MI-2-C was not significantly affected. No significant changes in the excretion of any of the two urinary markers were found in the untreated patients, while a non-significant increase in 5-S-CD excretion was seen in the healthy controls at the follow-up.