HEENT 12: External Ear and Otic Drug Delivery

Question 1

Describe the basic anatomy of the outer ear.

Answer 1

auricle (pinna) – ear lobe

• 3 tissue layers: cartilage, perichondrium, thin vascularized skin
• tragus

external auditory meatus/ear canal

• outer ⅓: mobile cartilage (hair, sebaceous and ceruminous glands)
• inner ⅔: rigid bone
• isthmus – narrowing of canal
• S-shaped – upward and backward (adults), or downward and backward (kids) to straighten

Question 2

What are the 5 drug families known to cause ototoxicity?

Answer 2

• aminoglycosides – gentamicin > tobramycin > amikacin > neomycin
• other antibiotics – erythromycin, tetracycline
• chemotherapeutic agents – cisplatin, 5-fluorouracil (reversible)
• salicylates – high dose ASA (reversible)
• antimalarials – quinine, chloroquine (reversible)

Question 3

What are the concerns regarding fluoroquinolone otic products?

Answer 3

• local irritation
• development of P. aeruginosa resistance with chronic use

Question 4

What are the concerns regarding aminoglycoside otic products?

Answer 4

• ototoxic

Question 5

What topical antibiotics should be avoided if tympanic membrane is not intact?

Answer 5

• acetic acid or acidifying agents
• polymyxin B

Question 6

External Otic Drug Delivery

Answer 6

• topical application effective

Question 7

Middle Otic Drug Delivery

Answer 7

• delivery blocked by tympanic membrane

Question 8

Inner Otic Drug Delivery

Answer 8

• delivery blocked by tympanic membrane
• systemic delivery limited (blood labyrinth barrier) – high systemic concentration required

Question 9

What contributes to sterility of otic drugs? (2)

Answer 9

• benzalkonium chloride
• ethylene-diamine-tetraacetic acid (EDTA)

Question 10

pH and Buffers

Answer 10

• some formulations formulated at low pH to kill bacteria
• sodium hydroxide, hydrochloric acid, or acetic acid
• buffered with phosphate buffers

Question 11

What contributes to tonicity of otic drugs?

Answer 11

• sodium chloride used for isotonicity

note: not necessary for otic preparations unlike ophthalmic formulations

Question 12

What contributes to viscosity of otic drugs?

Answer 12

methylcellulose, hydroxyethylcellulose, hydroxyethyl cellulose, polyvinyl alcohol

• increases contact time with ear canal