Topical antibiotics

Absorption, distribution, metabolism, excretion in otology 

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• Only the external ear is easily accessible for direct drug administration. The main problem secondary to their application comes from skin irritation

• Tympanic membrane separates external ear from middle ear. The middle ear is only susceptible to drug effect if incision made in tympanic membrane i.e. injected drug.

• Inner ear not accessible for direct drug administration either. Drugs administered to the middle ear may be taken up by inner ear.

• No capacity for drug metabolism within inner ear.  

• Drugs administered systemically to act on inner and middle ear must be able to cross blood inner ear barrier 

• Earwax is slightly acidic to prevent growth of microbes. pH of drops is a consideration to reduce microbial growth (more acidic). 

Ear Drops: easy to administer but likely to run out of the ear. Increasing the viscosity of ear drops makes them more likely to stay in place. Can add cotton wool as a physical barrier to stop the drops running out 

Pregnancy & lactation

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No risk with topical ear drops – no systemic absorption (if no perforated ear drum). If using in perforation, theoretical risk of foetal ototoxicity and nephrotoxicity if systemic absorption.

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Lactation: minimal absorption into breast milk from topical administration. If it can be used in paediatrics, it would be generally safe in lactation. Avoid quinolones.