Tetracyclines

Question 1

What are generic and brand examples of tetracyclines?

Answer 1

• Doxycycline (Periostat)

* Lymecycline (Tetralysal)

Question 2

What is the method of action of tetracyclines?

Answer 2

• Inhibit bacterial protein synthesis
• Bind to ribosomal 30S subunit
• Prevents binding of transfer RNA to messenger RNA
• Prevents the additions of new amino acids to grow polypeptide chains

Question 3

What are the indications for tetracyclines?

Answer 3

• Acne vulgaris (Proprionibacterium acnes)
• LRTI – inc. infective exacerbations of COPD (Haemophilus influenza), pneumonia and atypical pneumonia
• Chlamydial infections – i.e PID
• Other infections: typhoid, anthrax, malaria and Lyme disease

Question 4

What are the contraindications for tetracyclines?

Answer 4

• Pregnancy – binds to teeth and bones during foetal development, infancy and early childhood
• Breastfeeding – binds to teeth and bones during foetal development, infancy and early childhood
• Children < 12 years old – binds to teeth and bones during foetal development, infancy and early childhood
• Renal impairment – anti-anabolic effects can ↑ plasma urea

Question 5

What are the side effects of tetracyclines?

Answer 5

• Nausea/vomiting
• Diarrhoea (lowest C.Diff risk)
• Hypersensitivity reaction
• Oesophageal irritation, ulceration and dysphagia
• Photosensitivity – worsened sun burn reaction when exposed to light
• Discolouration of tooth enamel – if prescribed in children
• Intercranial hypertension – rare but causes headaches and visual disturbances

Question 6

What are drug interactions with tetracyclines?

Answer 6

• Calcium – Tetracyclines bind to divalent cations so 2h should be left between doses
• Antacids – Tetracyclines bind to divalent cations so 2h should be left between doses
• Iron – Tetracyclines bind to divalent cations so 2h should be left between doses
• Warfarin - ↑ anticoagulant affect due to killing normal gut flora that synthesis Vit K

Question 7

By what routes are tetracyclines eliminated by?

Answer 7

• Urine and faeces

Question 8

What information should be given to a patient taking tetracyclines?

Answer 8

• Swallow with plenty of water whilst sitting/standing to stop capsules/tablets getting stuck
• Take on a full stomach (but avoid mixing with dairy)