Latanoprost is the most widely prescribed topical antihypertensive in the United Kingdom. In 2011, over 3.5 million bottles were dispensed in England alone (ePACT data). At that time Xalatan, at £12.48, was the most costly multidose product in its class;1 hence, the introduction of generic forms of this preparation in January 2012 was a milestone in glaucoma treatment as far as the cost was concerned.

The frequently quoted ‘80–125% bioavailability’ rule applied to generic versions of systemic drugs does not apply to eye drops. Topically applied medication is subject to different guidelines. Bioavailability and efficacy studies are required only if there is a change in the following:

  • active ingredient(s) \with regard to specification of the physical properties;

  • inactive ingredient(s); and

  • application with regard to application device (eg, inhalation chamber).2

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