Minocycline (MCN) is a second-generation semisynthetic tetracycline derivative first introduced in 1967. It inhibits protein synthesis by binding to the 30s ribosomal subunit in bacteria. MCN is highly lipid soluble and turns black upon oxidation. Pigmentation is asymptomatic and is the most commonly observed cutaneous side effect of MCN therapy (2.4-14% incidence). Other reported sites of pigment deposition include thyroid gland, oral mucosa, nails, teeth, bone, conjunctiva, gingiva, substantia nigra, heart valves, atherosclerotic plaques, lymph nodes, and breast milk. MCN-induced hyperpigmentation is generally observed after prolonged therapy (after cumulative dose of 50-100 grams) but can occur regardless of dosage or treatment duration. It has been reported to occur as soon as 3 weeks after initiation of MCN therapy.
