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  • Medical Science


Cyclines are also called tetracyclines and are a family of antibiotics used in many situations such as sexually transmissible infections (STI) like Chlamydia or Gonococcus infections. Some respiratory tract infections such as pneumonia are also treated with cyclines. On the other hand, for reasons of resistance they are not indicated for use in Streptococcal sore throat. Doxycycline, minocycline, and tetracycline belong to this category of antibiotics.

How do cyclines work?

Cyclines enter inside cells. They inhibit the synthesis of bacterial proteins. They are bacteriostatic medicines which block the multiplication of bacteriabut do not kill them whereas bactericides do.

Do they have any contraindications or precautions?

Cyclines can cause gastro-intestinal problems. In addition, these antibiotics can also cause irreversible yellow discolouration of the teeth if they are prescribed to children under 8 years of age. Patients are also advised to avoid exposure to sunlight during treatment as they carry a risk of skin photosensitisation. They must be administered with meals to reduce the risk of oesophageal injury or even vestibular syndrome. Cyclines are also contraindicated in pregnant women as they cross the placenta and can therefore affect the unborn child. Lastly, some cyclines such as the tetracyclines can reduce the effectiveness of the oral contraceptive pill.


  • Merck Manual – 4th Edition ;
  • Transparency sheets, anti-infectious medicines in community-acquired diseases, Afssaps, 2004

The cyclines can cause yellow spots to appear on teeth.  ©Phovoir The cyclines can cause yellow spots to appear on teeth. ©Phovoir

Cycline - 1 Photo


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