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Dorzolamide, on the basis of its pharmacological profile and lack of undesirable side effects in safety assessment studies together with the fact that it could be formulated in solution at 2%, underwent extensive clinical studies. Early clinical studies in the development of dorzolamide have been described elsewhere (Maren, 1995; Serle and Podos, 1995). In a 1-year study in which a comparison was undertaken in patients for intraocular pressure lowering effects between 2% dorzolamide administered three times daily, 0.5% betaxolol twice daily, and 0.5% timolol twice daily, the peak reductions in intraocular pressure were 23, 21, and 25%, respectively. Tachyphylaxis did not develop to dorzolamide nor were electrolyte and/or systemic side effects encountered (Strahlman et al., 1995). The latter is consistent with results of a pharmacokinetic study in humans in which plasma levels of dorzolamide were lower than the limit of detection (5 ng/ml) at a time when the red blood cell content of dorzolamide had reached steady state which was appreciably less than the red blood cell content of the enzyme (Biollaz et al., 1995). Patients taking 0.5% timolol twice daily received either 2% dorzolamide twice daily or 2% pilocarpine four times daily for 6 months and the additional reductions in intraocular pressure elicited by dorzolamide and pilocarpine were very similar. However, pilocarpine usage resulted in a higher discontinuation rate (Strahlman et al., 1996). In a separate study in which dorzolamide and pilocarpine were compared at these dosage schedules, patients preferred dorzolamide to pilocarpine by a ratio of over 7 to 1 in terms of quality of life (Laibovitz et al., 1995). In summary, the quest for a topical, ocular hypotensive, CA inhibitor, though time-consuming, was a successful one with the introduction of dorzolamide into general clinical practice.

MK-927 (dl-5,6-dihydro-4-(2-methylpropylamino)-4H-thieno(2,3b)thiopyra n-2-sulfonamide-7,7-dioxide hydrochloride) is a water soluble, carbonic anhydrase inhibitor (CAI) possessing a Ki of 12.0 nM against purified human carbonic anhydrase II in vitro. The acute instillation of one drop (50 microliters) of 0.5%, 1% and 2% solutions of MK-927 maximally decreased the intraocular pressure (IOP) of ocular hypertensive, cynomolgus monkeys by 4.7, 5.9 and 9.6 mm Hg, respectively. The decline of 9.6 mm Hg represented a reduction of 27% from the corresponding vehicle-treated value of 35.3 mm Hg. Peak reductions in IOP were present at 2 to 4 hr after the instillation of the three doses and the ocular hypotensive effect was waning at 6 hr. The IOP of normotensive, monkey eyes was significantly lowered by 1% and 2% solutions of MK-927 with the effect being more transient in these eyes than in hypertensive eyes. The elevated IOP of alpha-chymotrypsinized rabbits was dose-dependently decreased by 0.01%, 0.1% and 0.5% solutions of MK-927. MK-927 modestly bound to rabbit ocular pigment in vitro and the concentrations of MK-927 in the iris + ciliary body of pigmented rabbits were higher than those in the same tissue of albino rabbits after dosing with 0.5% MK-927. The ocular hypotensive effect of 2% MK-927 was greater in magnitude and longer in duration in normal pigmented than in albino rabbits. The IOP lowering action of MK-927 was local as evidenced by results of ocular distribution studies and the observation that the unilateral instillation of 0.5% MK-927 into the contralateral eye was devoid of effect on the untreated, hypertensive eye of alpha-chymotrypsinized rabbits. MK-927 has been selected for topical evaluation in glaucoma patients.

Modification of the pharmacological profile of the vasodilating/beta-adrenergic blocking agent 2-[4-[3-(tert-butylamino)-2-hydroxypropoxy]phenyl]-4-(trifluoromethyl)imidazole (1) has been investigated. Introduction of selected substitutents onto the imidazole ring, in place of the trifluoromethyl group, has yielded highly cardioselective beta-adrenergic blocking agents such as 7, 17, and 18. The placement of alkyl or chloro groups onto the aryl ring of 1, as illustrated by 33, has produced a class of compounds characterized as antihypertensive beta-adrenergic blocking agents. In these examples, the acute antihypertensive activity does not appear to be due to either vasodilating or beta 2-agonist properties.

The synthesis of a series of isoelectronic analogues of (S)-2-[3-(tert-butylamino)-2-hydroxypropoxy]-3-cyanopyridine (1) are described; included in this group are examples of thiazole, isothiazole, thiadiazole, pyrazine, and the structurally related naphthyridines. All of the compounds are similar to 1 in that they contain a cyano group ortho to the aminohydroxypropoxy side chain and meta to the nitrogen heteroatom. In addition, several related examples, having additional nuclear substituents and/or groups other than CN in the position adjacent to the aminohydroxypropoxy group, were prepared, and beta-adrenoceptor antagonist activity and vasodilating potency were determined. Three compounds, thiazole 2 and isothiazoles 3 and 27, effectively lowered mean arterial pressure in the SH rat at 5 mg/kg. Compounds 2, 3, and 27 increased iliac blood flow and exhibited beta-adrenergic blocking properties in the dog.