April 1988
Volume 29, Issue 4
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Articles  |   April 1988
Low dose O-butyryl timolol improves the therapeutic index of timolol in the pigmented rabbit.
Author Affiliations
  • S C Chang
    University of Southern California, School of Pharmacy, Los Angeles 90033.
  • H Bundgaard
    University of Southern California, School of Pharmacy, Los Angeles 90033.
  • A Buur
    University of Southern California, School of Pharmacy, Los Angeles 90033.
  • V H Lee
    University of Southern California, School of Pharmacy, Los Angeles 90033.
Investigative Ophthalmology & Visual Science April 1988, Vol.29, 626-629. doi:
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    • Get Citation

      S C Chang, H Bundgaard, A Buur, V H Lee; Low dose O-butyryl timolol improves the therapeutic index of timolol in the pigmented rabbit.. Invest. Ophthalmol. Vis. Sci. 1988;29(4):626-629.

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Abstract

The degree of enhancement in the ocular absorption of timolol afforded by its O-butyryl prodrug and the possibility of reducing its systemic absorption through a proportional reduction in its instilled dose were investigated in the pigmented rabbit. A reversed phase HPLC procedure was used to assay for timolol and O-butyryl timolol in the aqueous humor and plasma over 120 min post-instillation of 25 microliter of drug solutions. We found that the ocular absorption of the O-butyryl prodrug of timolol from a 15 mM solution was 5.5 times greater than that of the parent drug while the systemic absorption was comparable. When a lower concentration of the prodrug (3.75 mM) was used the therapeutic index as assessed by the ratio of aqueous humor to plasma concentrations seemed to improve fifteenfold. Therefore, it is possible to significantly reduce the systemic absorption of timolol without reducing its ocular absorption by using a low dose of its O-butyryl prodrug.

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