Lecture 38: Compounding Otic Preparations

Where is the local delivery of Otic solution to?

Ear canal

What are the 3 layers of the tympanic membrane (eardrum)- which is an ear barrier?

• Outer epidermal layer

• Middle fibrous layer w/ collagen

• Inner mucosal layer

What does the tympanic membrane (eardrum) act as a barrier for?

Drug delivery to the middle & inner ear

• Artificially breached by transtympanic injection

What is the blood-perilymph barrier (BPLB) of the ear?

• Formed by continuous capillary endothelium lining blood vessels in the cochlea

• Endothelial cells are connected w/ tight junctions & no fenestrations

• Physical barrier

• Also biochemical barrier w/ efflux pump systems

• Only permeable to small liposoluble molecules, whereas high molecular weight, water-soluble, & charged molecules are unlikely to diffuse passively

What does the round window have & do as an ear barrier?

• Composed of 3 layers:

  • Outer epithelium

  • Inner epithelium

  • Separated by core of connective tissue

• Able to transport drugs into cochlea

• Main passage for drug delivery to the inner ear from middle ear

• Low-molecular-weight & large molecules can diffuse through

What are the advantages of intratympanic administration?

• Treatment of middle ear & inner ear diseases

• Minimized systemic exposure

• Short & middle term local drug delivery (several days to weeks)

• Minimally invasive

• Usually outpatient procedure

What are the disadvantages of intratympanic administration?

• Require diffusion through the round window for access to cochlea

• Not adapted for liquid formulations

What are the advantages of intracochlear administration?

• Treatment of inner ear diseases

• Minimized systemic exposure

• Long term local drug delivery (several months to years)

• Adapted for liquid formulations

What are the disadvantages of intracochlear administration?

• Invasive

• Requires hospitalization

What are the properties of Otic preparations?

• Sterility: preferred, not required unless perforated eardrum

• Tonicity- isotonic preferred, not required

• pH- 3.5-7.5

• Viscosity- increasing can retain product longer

• Solvents & vehicles- glycerin, propyleneglycol, low weight PEG

  • Alcohol only for topical use/irrigation (can use at full strength)