Tetracyclines : doxycycline

Question 1

What are tetracyclines used for?

Answer 1

1) Acne Vulgaris (inflamed papules, pustules and/or cysts)
2) Lower Respiratory tract infections (exacerb of COPD, pneumonia and atypical pneumonia)
3) Chlamydial infection including pelvic inflammatory disease.
4) typhoid, anthrax, malaria, lyme disease

Question 2

What pathogen could cause an exacerbation of COPD?

Answer 2

haemophilus influenzae

Question 3

What are some causes of atypical pneumonia treated by doxycycline?

Answer 3

• mycoplasma
• chlamydia psittaci
• coxiella burnetii (Q fever)

Question 4

How do tetracyclines (doxycycline) work?

Answer 4

Tetracyclines inhibit protein synthesis.
- they bind to 30s subunit
This stops bacterial growth (bacteriostatic)

Question 5

What are the side effects of tetracyclines?

Answer 5

• GI upset (nausea, vomiting, diarrhoea)
• Hypersensitivity reactions occur in 1% of people who take tetracyclines.
• oesophageal irritation (ulceration and dysphagia)
• Photosensitivity (sunburn)
• discolouration of tooth enamel
• Intracranial hypertension

Question 6

what are the contraindications of tetracyclines?

Answer 6

• pregnancy
• breastfeeding
• children under 12
• renal impairment

Question 7

What are the drug reactions of tetracyclines (doxycycline)?

Answer 7

• do not give within 2 hours of calcium, antacids, or iron.

- tetracyclines enhance the anticoagulant effect of warfarin by killing the normal gut flora that synthesise vitamin K.

Question 8

What is the prescription of doxycycline/

Answer 8

100 - 200 mg orally daily
for 5 to 7 days for infective exacerbations of COPD or 8 weeks for acne.

(can only be given PO not IV)