Minocycline
(Minocin, Dynacin, Solodyn) is a derivative of tetracycline. Minocycline
has the same basic ring structure as tetracycline, but lacks a functional group
at C6 and has a substitution of a dimethylamino group at C7.1 These small
modifications increase both the lipophilicity (increased lipid solubility) and
the half-life of minocycline. Unfortunately, like tetracycline,
minocycline can stain the teeth; however, it is through a process that is
different from that of tetracycline. Because of the differences in
mechanism of this effect, minocycline has the potential to cause this adverse
effect in all patients exposed to the drug, not just those 8 years old or
younger.1,2 This is important given the likelihood of longer courses of
therapy with minocycline (in particular Solodyn) for the treatment of
acne. Staining of the teeth in this population may compound the negative
psychological impact of their condition.1,3
How does
minocycline cause teeth discoloration and how is it different from tetracycline?
Minocycline's
contact with the teeth occurs through a few different processes, all of which
are likely to contribute to the staining of the teeth. The first
influence has been called the "intrinsic theory", which occurs upon
absorption. Minocycline is highly protein bound in the blood and appears
to bind to higher collagen containing tissue (e.g., bone and teeth) as well,
which results in discoloration.1,2 The second proposed influence has been
called the "extrinsic theory", which occurs when the surface of the
teeth come in contact with minocycline. There is substantial
contact of minocycline with the teeth as concentrations of the drug in the
saliva are about 30-60% of the concentrations seen in serum.4 In
addition, minocycline can attain gingival crevicular fluid concentrations 5
times greater than concentrations attained in the serum.4 The gingival
crevicular fluid is found in the groove on the external surface of the tooth
where the gingiva (gums) meets the enamel of the teeth (gum line). This
high concentration is thought to etch into the enamel where the minocycline
gets oxidized (turn black in color) upon exposure to oxygen or bacterial
activity.5-8 The other contributor to teeth discoloration is chelation of
haemosiderin (a breakdown product of minocycline) with iron to form an
insoluble complex within the teeth.2,9
Since the cause for
teeth staining or discoloration is different than tetracycline, are there any
other differences that are important to know?
Yes.
One characteristic that is different from tetracycline is that minocycline
induced staining does not fluoresce under UV light. In addition, the
discoloration is a distinct blue-gray band, possibly found more in the incisal
and middle third of the crown as compared to tetracycline, where the brownish
discoloration primarily occurs in the gingival third of the crown.1,10
Similar
to tetracycline, minocycline induced staining of the teeth is more likely to
occur during longer durations of therapy and when used at higher doses
(especially over 100 mg per day possibly). The overall prevalence of
teeth staining has been reported to be 3-4% with tetracycline and 3-6% with
minocycline.1,7 Given the growing number of indications for the long-term
use of minocycline (MRSA infections, acne, etc.), this adverse drug event would
be important to consider when no alternative therapy exists.
References:
- Sanchez AR, Rogers RS 3rd, Sheridan PJ. Tetracycline and
other tetracycline-derivative staining of the teeth and oral cavity.
Int J Dermatol 2004;43:709-15.
- Good ML, Hussey DL. Minocycline: stain devil? Br J Dermatol 2003;149:237-9.
- Scopp IW, Kazandjian G. Tetracycline-induced staining of teeth. Postgrad Med 1986;79:202-3.
- Ciancio
SG, Mather ML, McMullen JA. An evaluation of minocycline in patients
with periodontal disease. J Periodontol 1980;51:530-4.
- Fendrich P, Brooke RI. An unusual case of oral pigmentation. Oral Surg Oral Med Oral Pathol 1984;58:288-9.
- Salman RA, Salman DG, Glickman RS et al. Minocycline induced pigmentation of the oral cavity. J Oral Med 1985;40:154-7.
- Berger RS, Mandel EB, Hayes TJ et al. Minocycline staining of the oral cavity. J Am Acad Dermatol 1989;21:1300-1.
- Bowles
WH, Bokmeyer TJ. Staining of adult teeth by minocycline: binding of
minocycline by specific proteins. J Esthet Dent 1997;9:30-4.
- Rosen T, Hoffman TJ. Minocycline-induced discoloration of the permanent teeth. J Am Acad Dermatol 1989;21:569.
- Poliak SC, DiGiovanna JJ, Gross EG et al. Minocycline-associated tooth discoloration in young adults. JAMA 1985;254:2930-2.
