Abstract
Minocycline is a semisynthetic second-generation tetracycline derivative that is widely used as a broad-spectrum antibiotic and anti-inflammatory agent1. Long-term treatment with tetracycline and its related derivatives causes discoloration and hyperpigmentation of the skin, bone, teeth, sclerae, thyroid, and oral mucosa2-11. Minocycline shares the same basic ringed structure found in other tetracyclines, with the exception of a dimethylamino group substitution at C7 and a functional group absence at C6. These differences in chemical structure result in more lipophilic properties than in other members of the tetracycline family12. Whereas tetracycline is known to cause discoloration in bone by oxidation-induced color change after binding irreversibly to hydroxyapatite, which is later deposited at the mineralization front on unmineralized mature osteoid, minocycline poorly chelates calcium and is thought to cause bone discoloration by a less well-understood mechanism13. Findings, including minocycline’s ability to discolor fully formed mature teeth as well as the presence of iron with trace amounts of calcium in minocycline-induced dark pigment, give credence to this idea14-16. Because of its lipophilic nature, minocycline is believed to achieve extensive tissue penetration, and in vitro protein-binding studies have also shown minocycline to bind collagen6,17. Once deposited, it is believed that minocycline is either degraded or lysosomally oxidized from its naturally yellow crystalline appearance to a black deposit3,18. Gross examination often reveals a bluish-gray or black discoloration of the bone and surrounding soft tissue, although these findings can be mutually exclusive1. The incidence of minocycline-induced discoloration of bone is unknown since it is more commonly found as an incidental finding during routine surgical procedures. However, staining of adult dentition has been reported to occur in 3% to 6% of patients on long-term minocycline …
Published Version
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