To

Figure 9.36 Aqueous humour levels after dosing with pilocarpine and fluorometholone in ointment and aqueous solution. •, 10~2 mol dm03 pilocarpine solution; O, 10~2 mol dm03 pilocarpine ointment; saturated fluorometholone solution; A, 0.1% fluorometholone ointment.

Reproduced from reference 16.

Polymeric vehicles

Hydrophilic polymeric vehicles, such as poly (vinyl alcohol) (PVA) and hydroxypropyl-methylcellulose (HPMC), are used in ophthalmic formulations.18 PVA increases the effectiveness of the drug substance. HPMC has likewise been found to reduce the effective dose of neomycin sulfate required to prevent infection of corneas of experimental animals (Table 9.11).

Eye drops are often formulated to be isotonic with tear fluid but deviations from tonicity do not cause problems, although hypertonicity may cause stinging of the eye and hypotonicity may increase the permeability of the cornea.

Table 9.11

Calculated effective dose (ED50) of neomycin sulfate required to prevent infection in 50% of rabbit corneas when incorporated into various vehiclesa

Vehicle

Derived values (mg base per cm3)

0 0

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