ISTALOL (timolol maleate ophthalmic solution) 0.5% is a non-selective beta-adrenergic receptor blocking agent. Its chemical name is (-)-1-(tert-butylamino) –3- [(4-morpholino-1, 2, 5-thiadiazol-3-yl)oxy]-2-propanol maleate (1:1) (salt). Timolol maleate possesses an asymmetric carbon atom in its structure and is provided as the levo-isomer. The optical rotation of timolol maleate is:

25°[α] in 1.0N HCl (C = 5%) = -12.2°(-11.7°to -12.5°) 405 nm

Its molecular formula is C₁₃H₂₄N₄O₃S-C₄H₄O₄ and its structural formula is:

Timolol maleate has a molecular weight of 432.49. It is a white, odorless, crystalline powder which is soluble in water, methanol, and alcohol. ISTALOL (timolol maleate ophthalmic solution) is stable at room temperature. ISTALOL (timolol maleate ophthalmic solution) ophthalmic solution is supplied as a sterile, isotonic, buffered, aqueous solution of timolol maleate in a single strength. It has a pH of 6.5-7.5 and an osmolality of 275-330 mOsm/kg.

Each mL of ISTALOL contains 5 mg of timolol (6. 8 mg of timolol maleate). Inactive ingredients: monobasic sodium phosphate monohydrate, potassium sorbate 0.47%, sodium chloride, sodium hydroxide, and purified water. Benzalkonium chloride 0.005% is added as preservative.

Last reviewed on RxList: 3/27/2009
This monograph has been modified to include the generic and brand name in many instances.