May 24, 2017
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(timolol maleate) Ophthalmic Solution


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-morpholino1,2,5-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.

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

ISTALOL® (timolol maleate ophthalmic solution) Structural Formula Illustration

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® is stable at room temperature. Istalol® 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 the active ingredient 5 mg of timolol (6.8 mg of timolol maleate) with the inactive ingredients benzalkonium chloride (0.05 mg/mL), monobasic sodium phosphate monohydrate, potassium sorbate 0.47%, sodium chloride, sodium hydroxide, and purified water.

What are the possible side effects of timolol ophthalmic?

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using this medication and call your doctor at once if you have any of these serious side effects:

  • swelling or redness of your eyelids;
  • eye redness, discomfort, or sensitivity to light;
  • drainage, crusting, or oozing of your eyes or eyelids;
  • depressed mood, confusion, hallucinations, unusual thoughts or behavior;
  • wheezing, gasping, or other breathing problems;
  • swelling,...

Read All Potential Side Effects and See Pictures of Istalol »

Last reviewed on RxList: 3/20/2017
This monograph has been modified to include the generic and brand name in many instances.

Report Problems to the Food and Drug Administration


You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.

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