“the ointment will prevent them becoming infected; besides I put this on all cuts and scrapes!”
My heart sinks at the memory…
This practice is often followed in primary care settings as topical treatments are easily administered by the patient or carer. For example, topical Fusidic Acid is used for skin infections and topical Gentamicin for ear infections. However, as a general rule topical applications are not good treatments for established infections.
Because it is impossible to know how much antibiotic is being used and for how long it has been in contact with the bacteria. This can result in low level antibiotic exposure for sub-therapeutic periods of time; both of these factors are excellent ways of producing resistant bacteria. In fact, in the past, the use of low dose antibiotics to select out bacterial mutants resistant to antibiotics has been used to study how antibiotic resistance occurs. In the case of topical Fusidic Acid used to treat skin infections the speed by which these resistant bacteria is created is very quick, often within a day or two. Pseudomonas ssp. in ears takes a little longer; resistance starts to appear within a few weeks. It would therefore seem a little crazy to use a method to treat patients which is known to develop resistance; 9 times out of 10 the outcome will be a patient with altered normal flora including antibiotic resistant bacteria. The antibiotic kills off the normal sensitive flora leaving behind an ecological niche for resistance bacteria to exploit. The British National Formulary (BNF) recognises the risk of the use of topical antibiotics leading to antibiotic resistance and therefore suggests limitations to their use.
For the treatment of skin the BNF states that “acute impetigo on small areas of skin may be treated by short term topical application of Fusidic Acid. If the impetigo is extensive or longstanding an oral antibacterial such as Flucloxacillin should be used”. The BNF goes on to say “cellulitis requires systemic antibacterial treatment… lower leg infections or infections spreading around wounds are almost always cellulitis”, this would include the treatment of ulcers.
Another drawback to the use of topical antibiotics is the potential to cause side-effects. The BNF specifically says not to put topical Gentamicin or Polymyxin on large broken areas of skin, or into the ear if the tympanic membrane is not intact, as ototoxicity can occur in either case due to absorption of the antibiotics. Yes, ototoxicity (deafness and loss of balance) can even occur when these antibiotics are put on broken skin!
But it works, I hear you cry!
I know there will be those out there who say “...but these topical preparations work” and “...but my patients get better”, I would argue that there were other reasons why your patients improved:
- These ointments act as emollients and so they deal very nicely with conditions like eczema for which they are often prescribed, it is the moisturiser not the antibiotic which produces the effect (see NICE guidelines)
- These ointments are often combined with steroids which damp down any inflammatory component. It is therefore usually the steroid in the ointment that gets the patient better, despite the presence of an antibiotic. In fact 5 out of 7 topical antibiotics for the ear in the BNF are combined with a steroid. NICE does not specify what topical preparation to use for otitis externa and warns that the evidence is too low quality to make a definite recommendation. In their evidence, antibiotic + steroid is the same as steroid on its own and the type of antibiotic makes no difference. My conclusion from reading the NICE evidence is that the ear gets better with steroids not antibiotics
So what are the exceptions to my general rule?
Patients who are known to be colonised with certain bacteria may benefit from the use of topical antibiotics. In particular, the use of nasal mupirocin (Bactroban) as part of the suppression regimen of Meticillin Resistant Staphylococcus aureus, reduces the amount of MRSA in a colonised patient’s nose and therefore reduces the risk of infection at a time when a patient undergoes a procedure. However, this suppression therapy rarely eliminates the MRSA and eventually resistance occurs making the Mupirocin obsolete. These patients eventually get break-through infections with Mupirocin resistant MRSA. Suppression therapy therefore only delays the inevitable infections in the long run.
Another exception is the use of topical antibiotics to treat bacterial eye infections. In this situation topical antibiotics are the only real option as most systemic antibiotics do not give adequate concentrations in the eye. Ophthalmologists use many different topical antibiotics in their specialist care, but the rest of us are much more familiar with the common use of Chloramphenicol to treat bacterial conjunctivitis which is normally due to Streptococcus pneumoniae, Haemophilus influenzae or Staphylococcus aureus.
The final area where topical antibiotics have a value is in the treatment of acne vulgaris but only when the patient is unable to tolerate oral antibiotics.
So how should skin infections be treated?
- Well firstly, most apparent skin infections are not infections at all but inflammatory conditions and so antimicrobials are not indicated
- Where there is a definite infection e.g. cellulitis then the correct length and full dose of oral or IV antibiotic should be used, these treatment methods are more effective and less likely to lead to resistant bacteria evolving
As for topical Fusidic Acid for the treatment of blisters...I took a deep breath, smiled, and went to the bar to order another drink…after all I was on holiday!