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Reservoir systems corneal barrier. In Fig. 9.38, results of application of 0.5% epinephrine (adrenaline) (VI) and 0.16% of the dipivoyl derivative of epinephrine (dipivefrine) (VII) are shown. The more hydrophobic derivative is absorbed to a greater extent and is then hydrolysed to the active parent molecule in the aqueous humour.

Derivatives of pilocarpine such as the hexa-decanoyloxymethylene chloride (VIII) similarly show the advantages of the epinephrine prodrug.

Reservoir systems

Since the advent of soft contact lenses, attempts have been made to use these as drug reservoirs;19 a drug such as pilocarpine is imbibed from solutions into the polymer matrix and when this is placed in the eye the drug leaches out, generally over a period of up to 24 hours. Levels of prednisolone applied in a copolymer of 2-hydroxyethyl methacrylate and N-vinyl-2-pyrrolidone were compared with levels in aqueous humour, cornea and

Figure 9.37 Influence of drug lipophilicity (log P) on the permeability coefficients (Papp) of beta-blockers across (a) the conjunctiva and (b) the cornea of the pigmented rabbit. Plot (c) shows the influence of log P on the ratio of the corneal (C) and conjunctival (J) permeability coefficients.

Reproduced from W. Wong et al., Curr. Eye Res., 6, 571 (1991).

Figure 9.37 Influence of drug lipophilicity (log P) on the permeability coefficients (Papp) of beta-blockers across (a) the conjunctiva and (b) the cornea of the pigmented rabbit. Plot (c) shows the influence of log P on the ratio of the corneal (C) and conjunctival (J) permeability coefficients.

Reproduced from W. Wong et al., Curr. Eye Res., 6, 571 (1991).

Figure 9.38 The action of 0.5% epinephrine (VI) and 0.16% dipivoyl epinephrine (VII) on intraocular pressure.

Reproduced from D. A. McClure, in Prodrugs as Novel Drug Delivery Systems (ed. T. Higuchi and V. Stella), American Chemical Society, Washington DC, 1975.

Figure 9.38 The action of 0.5% epinephrine (VI) and 0.16% dipivoyl epinephrine (VII) on intraocular pressure.

Reproduced from D. A. McClure, in Prodrugs as Novel Drug Delivery Systems (ed. T. Higuchi and V. Stella), American Chemical Society, Washington DC, 1975.

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