Topical antibiotics
Absorption, distribution, metabolism, excretion in otology
-
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
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.
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.

℞