Sir,

Low-dose oral tetracycline is often used in the management of chronic blepharitis.1 Tetracyclines are broad-spectrum antibiotics and one of their side effects is discolouration of teeth that occurs inevitably in children.2 We report an adult patient who developed reversible brown discolouration on her normal dentition after taking oral tetracycline for blepharitis.

Case report

A 54-year-old lady suffered from blepharitis. Because of local allergic reactions, fusidic acid was withdrawn from treatment. She remained symptomatic despite lid scrubs. A course of oral tetracycline 250 mg four times/day was prescribed. After 4 weeks of treatment, she noticed brown discolouration of her incisor teeth (Figure 1, top). The staining was completely removed by abrasive cleansing by dental surgeon (Figure 1, bottom). Prior to this incidence, this patient had not had any regular check-up or cleansing by dentist for over a year.

Figure 1
figure 1

Top: Brown discolouration of teeth after 1 month's oral tetracycline; bottom: brown staining completely removed after cleansing by dental surgeon.

Full size image

Comment

Chronic blepharitis is frequently associated with sebaceous gland dysfunction, plugging and inflammation of the meibomian glands.3 Tetracyclines inhibit matrix metalloproteinase expression and bacterial lipase production, with a resultant change in the concentration of inflammatory free fatty acids in the tear film.1, 4 Tetracycline is known to cause permanent discolouration during odontogenesis in children by the formation of insoluble tetracycline–calcium orthophosphate complexes in the dentine and enamel which darken upon exposure to light.2, 5 The relative lack of free calcium protects the erupted permanent adult dentition against tetracycline-induced tooth discolouration. However, minocycline, a tetracycline derivative, has been reported to stain adult dentition in 3–6% of patients taking a daily dose >100 mg for longer than 1 month.6 Owing to the full reversibility of discolouration in our patient, an ‘extrinsic theory’ could be one of the plausible mechanisms of staining. The theory states that minocycline is excreted in high concentration in saliva. The drug or its breakdown product forms insoluble salts by chelating with divalent metal ions in saliva and gingival fluid.7 An alternative mechanism is explained by the attachment of minocycline to the acquired pellicle's glycoproteins. This etches the enamel, and demineralization/remineralization cycles occur. It oxidizes to an insoluble black quinone on exposure to air or from bacterial degradation of the aromatic ring.8 Since these mechanisms of tooth staining involve excretion of concentrated minocycline in saliva and formation of insoluble black quinone from bacterial degradation of miniocycline, dehydration, poor oral and dental hygiene may be risk factors for the staining. UV radiation is also a possible aetiological factor as the upper incisors were most affected in our patient.5 When prescribing oral tetracycline for the treatment of blepharitis in adult patients, it is important to advise on oral hygiene measures and on avoidance of sunlight to minimize staining of teeth. Patients should also be reassured that the stain may be removed with abrasive cleansing by dental surgeon.