Ocular cellular barriers

Aminoglycosides are not well absorbed from the gastrointestinal tract but are well absorbed after intramuscular or subcutaneous injection. Effective concentrations are achieved in synovial, pleural, peritoneal, and pericardial fluids. Intrauterine and intramammary administration is also effective, but significant tissue residues result. Aminoglycosides do not bind significantly to plasma proteins, and as they are large polar molecules, they are poorly lipid-soluble and do not readily enter cells or penetrate cellular barriers. This means that therapeutic concentrations are not easily achieved in cerebrospinal or ocular fluids. Tlieir volumes of distribution are small, and the half-lives in plasma are relatively short (1-2 h). Elimination is entirely via the kidney. 

Barriers to ocular drug delivery. The presence of epithelial tight junctions and rapid drainage of the instilled drug solution by tears from the precorneal area result in the permeation of less than 5 percent of the applied dose of a drug.66,67 The cellular calcium levels and actin filaments of the cytoskeleton play a major role in the integrity of tight... 

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