INFECTION: TETRACYCLINES

Question 1

TETRACYCLINES: INDICATIONS

Answer 1

• Acne vulgaris, particularly where there are inflamed papules, pustules and/or cysts (Proprionibacterium acnes)
• Lower respiratory tract infections including infective exacerbations of COPD (e.g. Haemophilus influenzae), pneumonia and atypical pneumonia (mycoplasma, Chlamydia psittaci, Coxiella burnetii [Q fever])
• Chlamydial infection including pelvic inflammatory disease
• Other infections such as typhoid, anthrax, malaria and Lyme disease (Borrelia burgdorferi).

Question 2

TETRACYCLINES: MOA

Answer 2

• Tetracyclines inhibit bacterial protein synthesis
• They bind to the ribosomal 30S subunit found specifically in bacteria
• This prevents binding of transfer RNA to messenger RNA, which prevents addition of new amino acids to growing polypeptide chains
• Inhibition of protein synthesis is ‘bacteriostatic’ (stops bacterial growth), which assists the immune system in killing and removing bacteria from the body

Question 3

TETRACYCLINES: ADVERSE EFFECTS

Answer 3

• Like most antibiotics, tetracyclines commonly cause nausea, vomiting and diarrhoea
• lowest risk antibiotics for Clostridium difficile infection
• Hypersensitivity reactions occur in ~1% people who take tetracyclines, including immediate and delayed
• As antibiotic structures are different, there is no cross-reactivity with penicillins or other β-lactam antibiotics.
• Tetracycline-specific side effects include: oesophageal irritation, ulceration and dysphagia; photosensitivity (an exaggerated sunburn reaction when skin is exposed to light); and discolouration and/or hypoplasia of tooth enamel if prescribed for children.
• Intracranial hypertension is a rare adverse effect causing headache and visual disturbance.

Question 4

TETRACYCLINES: WARNINGS

Answer 4

• Tetracyclines bind to teeth and bones during fetal development, infancy and early childhood and so should not be prescribed during pregnancy, breastfeeding or for children ≤12 years of age
• They should be avoided in people with renal impairment as their anti-anabolic effects can raise plasma urea and reduced excretion can increase the risk of adverse effects.

Question 5

TETRACYCLINES: INTERACTIONS

Answer 5

• Bind to divalent cations
• Should therefore not be given within 2 hours of calcium, antacids, iron which will prevent antibiotic absorption
• Enhance the anticoagulant effect of warfarin by killing normal gut flora that synthesis Vitamin K

Question 6

TETRACYCLINES: EXAMPLES

Answer 6

• doxycycline

- lymecycline