Pigmentation

Pigmentation is particularly seen with minocycline and is enhanced if the patient is on amitriptyline. The pigmentation presents in three ways: firstly, in and around the acne scars as localized blue-black marks in areas of previous activity, and especially in scars; secondly, as diffuse pigmentation distant from the face and often on the lower legs; thirdly, as the 'muddy skin syndrome', which presents as a diffuse, dark-grey discolouration, suggesting an off-colour suntan over much of the body with less darkening of nonexposed areas..

The pigmentation is due to the interaction of the minocycline with iron in the dermal macrophage. These phenomena are also seen in the normal skin but in smaller numbers.26 There is also hyperpigmentation of the basal layer of the epidermis; electronmicroscopy shows an increase in melanosomes within the basal keratinocyte.

A third reason for the pigmentation is a quinone-like derivative formed by oxidation of minocycline..

The pigmentation is self-limiting and slowly improves within several months of discontinuing the treatment. Usually this pigmentation is not an indication to stop the minocycline therapy.