Acne Flashcards
What drugs would you use for acne?
Tetracyclines
What are the common indications for tetracyclines?
- Acne vulgaris, particularly where there are inflamed papules, pustules and/or cysts (Propionibacterium 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).
What is the spectrum of activity for tetracyclines?
Tetracyclines have a relatively broad spectrum of activity against many Gram-positive and Gram-negative organisms, including chlamydia, mycoplasma and spirochaetes. However, their utility may be limited by increasing bacterial resistance.
Mechanisms of action
What is the mechanism of action for tetracyclines?
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. Tetracyclines were discovered in 1945 and have been widely used. Consequently, bacteria are increasingly resistant. A common mechanism is an efflux pump, which allows bacteria to pump out tetracyclines, preventing cytoplasmic accumulation.
What are the important adverse affects of tetracyclines?
Like most antibiotics, tetracyclines commonly cause nausea, vomiting and diarrhoea, although with a lower risk of Clostridium difficile infection than other broad-spectrum antibiotics (see Penicillins, broad-spectrum). Hypersensitivity reactions occur in about 1%, including immediate and delayed reactions (see Penicillins). 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 in children. Rare, but potentially serious, adverse effects include hepatotoxicity and intracranial hypertension, the latter causing headache and visual disturbance.
What are the warnings associated with tetracyclines?
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 used with caution in ▴renal impairment as their antianabolic effects can raise serum urea and reduced excretion can increase the risk of adverse effects.
What are the important interactions for tetracyclines?
Tetracyclines bind to divalent cations. They should therefore not be given within 2 hours of calcium, antacids or iron, which will prevent antibiotic absorption. Tetracyclines can enhance the anticoagulant effect of warfarin by killing normal gut bacteria that synthesise vitamin K.
Give examples of tetracyclines?
doxycycline, lymecycline
How should tetracyclines be prescribed?
Tetracyclines are primarily available for oral administration. The dose and frequency of administration vary between individual drugs, e.g. doxycycline 200 mg on day 1, then 100–200 mg orally daily, lymecycline 408–816 mg orally 12-hrly. As with other antibiotics, higher doses are prescribed for more severe or difficult-to-treat infections. The duration of treatment depends on the indication: for example, 5–7 days in infective exacerbations of COPD, 8 weeks in acne.
How are tetracyclines administered?
Tetracyclines are usually formulated as capsules or tablets. These should be swallowed whole with plenty of water while sitting or standing to stop them getting stuck in the oesophagus where they may cause ulceration
What important things should be communicated about tetracyclines?
Explain to patients that the aim of treatment is to get rid of infection and improve symptoms. Before prescribing, always check with patients personally or get a collateral history to ensure they have no allergy to tetracyclines. Warn them to seek medical advice if a rash or other unexpected symptoms develop. If an allergy develops during treatment, give the patient written and verbal advice not to take this antibiotic in the future and make sure that the allergy is clearly documented in the patient’s medical records. Advise patients to take the treatment during a meal with a full glass of water when sitting or standing. They should avoid indigestion remedies and medicines containing iron or zinc 2 hours before and after taking the antibiotic. During treatment they should protect their skin from sunlight, even on cloudy days.
What monitoring should be carried out for tetracyclines?
Check that infection resolves by resolution of symptoms, signs (e.g. reduction in inflamed papules, pustules and cysts in acne) and blood markers (e.g. resolution of inflammatory markers in respiratory infection) as appropriate.
What is the cost of tetracyclines?
Tetracyclines are inexpensive. For example, a 1-week course of doxycycline 100 mg for respiratory infection costs around £1
Shay is the clinical top for tetracyclines?
Clinical tip—Demeclocycline is a tetracycline notable for its ability to increase serum sodium concentrations in patients with syndrome of inappropriate antidiuretic hormone (SIADH). It appears to do this by blocking the binding of antidiuretic hormone (ADH) to its receptor, although the mechanism is poorly understood. Other non-antibiotic properties of tetracyclines, including antiinflammatory, immune-modulating and neuroprotective effects, are being tested in clinical trials and may lead to new therapeutic applications in the future.
