Timolol is a propanolamine derivative and a non-selective beta-adrenergic antagonist with antihypertensive property. Timolol competitively binds to beta-1-adrenergic receptors in the heart and vascular smooth muscle and beta-2-receptors in the bronchial and vascular smooth muscle, resulting in a decrease in beta-adrenergic stimulation. Beta-1-receptor blockade results in a decrease in resting and exercise heart rate and cardiac output, a decrease in both systolic and diastolic blood pressure, and, possibly, a reduction in reflex orthostatic hypotension. Beta-2-blockade results in an increase in peripheral vascular resistance. The ultimate results include vasodilation and negative chronotropic and inotropic cardiac effects. In addition, timolol reduces intra-ocular pressure possibly by decreasing aqueous humor production by reduction of blood flow to the ciliary processes and cAMP synthesis.
As eye drops it is used to treat increased pressure inside the eye such as in ocular hypertension and glaucoma. By mouth it is used for high blood pressure, chest pain due to insufficient blood flow to the heart, to prevent further complications after a heart attack, and to prevent migraines.
Mechanism of Action of Timolol
Like propranolol and nadolol, timolol competes with adrenergic neurotransmitters such as catecholamines for binding at beta(1)-adrenergic receptors in the heart and vascular smooth muscle and beta(2)-receptors in the bronchial and vascular smooth muscle. Beta(1)-receptor blockade results in a decrease in resting and exercise heart rate and cardiac output, a decrease in both systolic and diastolic blood pressure, and, possibly, a reduction in reflex orthostatic hypotension. Beta(2)-blockade results in an increase in peripheral vascular resistance. The exact mechanism whereby timolol reduces ocular pressure is still not known. The most likely action is by decreasing the secretion of aqueous humor.
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Following topical application to the eye, timolol maleate reduces both elevated and normal intraocular pressure in patients with or without open angle (chronic simple, noncongestive) glaucoma or ocular hypertension. Timololreduces intraocular pressure with little or no effect on accommodation or pupillary size. In patients with elevated intraocular pressure, timolol reduces mean intraocular pressure by about 25-33%. The drug appears to be equally effective in light and dark colored eyes. … The exact mechanism by which beta-blockers, including timolol, reduce intraocular pressure has not been clearly defined. Fluorophotometric studies suggest that reduced aqueous humor formation is the predominant effect. beta-Adrenergic blocking agents may block endogenous catecholamine stimulated increases in cyclic adenosine monophosphate concentrations within the ciliary processes and subsequent formation of aqueous humor. Timolol appears to cause little or no change in aqueous humor outflow facility. In some studies, timolol maleate applied topically to one eye reduced intraocular pressure in both eyes; the mechanism of this effect has not been elucidated. A slight decrease in the intraocular hypotensive effect may occur during the first 3 wk of timolol therapy, and tolerance may develop with prolonged use; however, the intraocular pressure lowering effect has been maintained for at least 3 yr with continuous use of the drug in some patients.
Indications of Timolol
- Anginal Pain
- Cardiovascular Events
- Elevated Intraocular Pressure
- A migrainous Headache
- Ocular Hypertension
- Glaucoma, Open Angle
- Intraocular Hypertension
- In its oral form it is used to treat high blood pressure and prevent heart attacks, and occasionally to prevent migraine headaches. In its ophthalmic form, it is used to treat open-angle and occasionally secondary glaucoma.
Contra-Indications of Timolol
- Overactive thyroid gland
- Diabetes
- Low blood sugar
- Myasthenia Gravis
- Complete heart block
- Partial heart block
- Sinus bradycardia
- Suddenly serious symptoms of heart failure
- Emphysema
- Severe Chronic Obstructed Lung Disease
- Bronchospasm
- General Anesthesia
- Blood Circulation Failure due to Serious Heart Condition
- Brain Blood Flow Problem
- Anaphylactic Shock due to Allergy Shots
- Allergies to beta-Blockers (Beta-Adrenergic Blocking Agents)
Side Effects of Timolol
The most common
Common
- depression,
- memory loss,
- fever,
- lightheadedness,
- low blood pressure,
- the blueness of the hands or feet,
- a sore throat,
- shortness of breath, or
- wheezing.
- muscle aching or cramping
- chest pressure or squeezing pain inthe chest
- discomfort in arms, shoulders, neck or upper back
- sudden drowsiness or need to sleep sharp pain when taking a deep breath
- coughing up blood decreased amount of urine
Rare
- Anxiety
- change in vision
- chest pain or tightness
- confusion
- a cough
- Agitation
- arm, back, or jaw pain
- blurred vision
- chest pain or discomfort
- convulsions
- extra heartbeats
- fainting
- hallucinations
- a headache
- irritability
- lightheadedness
- mood or mental changes
Drug Interactions
Timolol may interact with the following drug, supplements, & may change the efficacy of the drug
- antiarrhythmics (e.g., amiodarone, disopyramide, propafenone)
- beta-2 agonists (e.g., salbutamol, formoterol, terbutaline)
- medications that lower blood pressure
- other beta-adrenergic blockers (e.g., atenolol, propranolol, sotalol)
- other eye drops
Pregnancy Catagory
FDA Pregnancy Category C
Pregnancy
Timolol has not been studied for use by pregnant women. This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.
Lactation
This medication passes into breast milk. If you are a breastfeeding mother and are using timolol eye drops, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding. Timolol eye drops are not currently recommended for use by children.
References
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https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=TIMOLOL+MALEATE
https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=COMBIGAN
https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=COSOPT
https://dailymed.nlm.nih.gov/dailymed/search.cfm?labeltype=all&query=TIMOLOL
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