Timolol can significantly decrease the increase in myocardial lipid peroxidation levels in diabetic rats. Timolol can create a well-balanced ratio between oxidative stress and antioxidant defense systems in diabetic mice, and has an essential cardioprotective effect on diabetes-induced ERS and associated apoptosis [3].

Timolol inhibits the ERS response in diabetic rats, which has cardioprotective effects [3].

Animal/Disease Models: Experimental diabetes model: 3-month-old male Wistar rat [3].
Doses: 5 mg/kg
Route of Administration: Timolol (5 mg/kg daily for 12 weeks)
Experimental Results: demonstrated cardioprotective effects.

Absorption, Distribution and Excretion
The systemic bioavailability of the ophthalmic eyedrop in one study of healthy volunteers was 78.0 ± 24.5%, indicating that caution must be observed when this drug is administered, as it may be significantly absorbed and have various systemic effects. Another study measured the bioavailability of timolol eyedrops to be 60% in healthy volunteers. The peak concentration of ophthalmic timolol in plasma, Cmax was about 1.14 ng/ml in most subjects within 15 minutes following the administration of timolol by the ophthalmic route. The mean area under the curve (AUC) was about 6.46 ng/ml per hour after intravenous injection and about 4.78 ng/ml per hour following eyedrop administration.
Timolol and its metabolites are mainly found excreted in the urine.
1.3 - 1.7 L/kg Timolol is distributed to the following tissues: the conjunctiva, cornea, iris, sclera, aqueous humor, kidney, liver, and lung.
One pharmacokinetic study in healthy volunteers measured the total plasma clearance of timolol to be 557 ± 61 ml/min. Another study determined the total clearance 751.5 ± 90.6 ml/min and renal clearance to be 97.2 ± 10.1 ml/min in healthy volunteers.
The degree of systemic absorption of timolol after topical application to the eye has not been fully elucidated; however, some absorption can apparently occur, since adverse systemic effects have occurred following ophthalmic instillation of the drug. Following topical adminstration of timolol 0.5% solution twice daily to the eye in a limited number of individuals, mean peak plasma concentrations were 0.46 or 0.35 ng/ml following the morning or afternoon dose, respectively. In individuals receiving topical timolol 0.5% as the gel-forming ophthalmic solution once daily in the morning, mean peak plasma concentrations following the dose were 0.28 ng/ml. Following topical application to the eye of a 0.25 or 0.5% solution of the drug, reduction in IOP usually occurs within 15-30 minutes, reaches a maximum within 1-5 hours, and persists about 24 hours.
Approximately 90% of an oral dose of timolol maleate is rapidly absorbed from the GI tract. Absorption of the drug is not reduced by food. Only about 50% of an oral dose reaches systemic circulation as unchanged drug since timolol undergoes extensive metabolism on first pass through the liver. Peak plasma concentrations of the drug usually are reached within 1-2 hr after oral administration. Considerable interindividual variation in plasma concentrations attained have been reported with a specific oral dose of timolol.
Timolol is 10-60% bound to plasma proteins, depending on the assay method employed. The drug is distributed into milk.
Timolol has a plasma half-life of 3-4 hr; plasma half-life is essentially unchanged in patients with moderate renal insufficiency. Approximately 80% of timolol is metabolized in the liver to inactive metabolites. The unchanged drug and its metabolites are excreted in urine. Only small amounts of the drug are removed by hemodialysis.
Plasma kinetics and beta-receptor blocking and -binding activity of timolol was studied in six healthy volunteers following its intravenous 0.25 mg dose. Timolol concentrations were measured using radioreceptor assay (RRA), blocking activity by comparing the dose ratios (DRs) of the infusion rates of isoprenaline required to increase heart rate by 25 bpm (I25) and binding activity by determining the extent to which timolol occupied beta 1 -receptors of rabbit lung and beta 2-receptors of rat reticulocytes in undiluted plasma samples. Timolol was eliminated from plasma with a mean half-life for the elimination phase of 2.6 hours. The dose antagonized potently isoprenaline-induced tachycardia at least for four hours. The effect was excellently correlated with the estimated beta 2-receptor binding activity of timolol in the circulating plasma. In conclusion, the small intravenous timolol dose was eliminated from plasma by a fashion, which was very similar to its eighty-fold higher oral doses reported earlier in the literature. The 0.25 mg dose was of considerable systemic beta-receptor blocking and -binding activity, that may help to explain its reported side-effects following ocular drug administration. The extent to which beta-blocking agents occupy rabbit lung beta 1- and rat reticulocyte beta 2-receptors in the circulation appears to predict the intensity and selectivity of their beta-blocking effects in healthy volunteers.

---

Metabolism / Metabolites
Timolol is metabolized in the liver by the cytochrome P450 2D6 enzyme, with minor contributions from CYP2C19. 15-20% of a dose undergoes first-pass metabolism. Despite its relatively low first pass metabolism, timolol is 90% metabolized. Four metabolites of timolol have been identified, with a hydroxy metabolite being the most predominant.
It is metabolized extensively by the liver, and only a small amount of unchanged drug appears in the urine.
The metabolism of timolol maleate to its ring cleavage ethanolamine and glycine products was studied in 108 patients with essential hypertension who received 10 mg oftimolol maleate, administered as a single oral dose. The metabolism of timolol maleate was determined to be partly under monogenic control of the debrisoquine-type. The mean plasmatimolol maleate concentration in poor metabolizers of debrisoquine were double that of extensiv metabolizers. /Timolol maleate/
Timolol has known human metabolites that include 4-[4-[3-(tert-butylamino)-2-hydroxypropoxy]-1,2,5-thiadiazol-3-yl]morpholin-2-ol.

---

Biological Half-Life
Timolol half-life was measured at 2.9 ± 0.3 h hours in a clinical study of healthy volunteers.
Plasma half-life 3-5 hr

Toxicity Summary
IDENTIFICATION: Timolol is an adrenergic beta-receptor blocking agent and a Class II antiarrhythmic drug. The drug is a white, odorless powder. Soluble in water, alcohol, in chloroform; soluble in methanol; practically insoluble in ether. HUMAN EXPOSURE: Main risks and target organs: Beta-blocking agents exert their effects by competing with endogenous and/or exogenous beta-adrenergic agonists. Timolol is a non-cardioselective beta-blocker (it has similar affinity for beta1 and beta2 receptors) and it has no intrinsic sympathomimetic or membrane stabilizing effect. The main risks might be an impairment of atrioventricular conduction and a negative inotropic effect. Summary of clinical effects: Only one case of acute poisoning after ingestion in a 24 year old man has been reported. The patient showed moderate toxic symptoms: drowsiness, vertigo, headache, and first degree atrioventricular block which was treated with atropine and isoproterenol. The patient recovered without sequelae. Adverse systemic effects have been reported in patients treated with timolol eye drops. Indications: Oral administration: Timolol has been used in the treatment of hypertension, angina pectoris, cardiac arrhythmias, migraine and for the reduction of mortality following myocardial infarction. Ocular administration: Ophthalmic solutions of timolol are used in the treatment of glaucoma to reduce intraocular pressure. Contraindications: Timolol is contraindicated in patients with asthma, second and third degree AV block, and cardiogenic shock. Timolol should be used cautiously in patients with chronic obstructive pulmonary diseases, sinus bradycardia, cardiac failure, myasthenia gravis, Raynaud's syndrome. Timolol should not be administered with other beta-blockers. Routes of entry: Oral: Poisoning after ingestion of timolol tablets may occur but only one case has been actually reported. Eye: Systemic toxic symptoms may occur after treatment with timolol eye drops. Absorption by route of exposure: Oral: Timolol is almost completely (90%) absorbed from the gastrointestinal tract. The peak plasma concentration occurs 0.5-3 hours after ingestion. Timolol is subject to a moderate first pass effect. Ocular: The onset of the ocular hypotensive action occurs after 10-20 minutes and lasts for at least 24 hours. Timolol is absorbed systemically. Distribution by route of exposure: Oral: Bioavailability is about 60%. Apparent volume of distribution is 1.3 - 1.7 L/kg. Plasma protein binding is approximately 10%. Timolol crosses the placenta Ocular: Timolol is distributed in conjunctiva, cornea, sclera, iris, aqueous humor, liver, kidney and lung. Transdermal: After cutaneous application of timolol ointment, 50 to 60% is absorbed systemically. Biological half-life by route of exposure: Oral: After oral administration, the half-life is 2.5 - 5 hours. The half-life varies according to genetic differences in hepatic metabolism: half-lives of 3.7 and 7.5 hours were reported in extensive and poor metabolizers, respectively. Metabolism: Oral: Timolol is extensively metabolized in the liver by hydrolytic cleavage of the morpholino ring with subsequent oxidation. Following an oral dose, 80% is metabolized and 20% is eliminated unchanged in urine. Metabolism is dependent on genetic polymorphism. Elimination by route of exposure: Oral: Kidney: About 20% of the dose is eliminated unchanged in the urine and 40 to 60% as metabolites. Breast milk: Timolol is present in breast milk. Following a maternal oral dose, the milk/plasma ratio is 0.80. Ocular: Breast milk: Following ocular instilation, the concentration in breast milk was approximately 6 times higher than in serum. Pharmacology and toxicology: Mode of action: Toxicodynamics: At toxic doses, timolol may exert a pronounced negative chronotropic and negative inotropic cardiac effect. Pharmacodynamics: The exact mechanism whereby timolol reduces ocular pressure is still not known. The most likely action is by decreasing the secretion of aqueous humor. At therapeutic doses, timolol slightly decreases heart rate, supraventricular conduction and cardiac output. Adults: Only one case of acute poisoning with timolol has been reported; this patient showed moderately severe symptoms. Children: An 18 month old girl developed bradycardia, respiratory depression and cyanosis 30 minutes after the administration of timolol eye drops. Teratogenicity: No epidemiological studies of congenital abnormalities among infants born to women treated with timolol during pregnancy have been reported. Interactions: Sinus bradycardia has been reported after concomitant treatment with timolol eye drops and quinidine. Clinical effects: Acute poisoning: Eye contact: Adverse systemic effects have been reported after treatment with ophthalmic solutions of timolol. Chronic poisoning: Eye contact: Dryness of the eye has been reported in a man treated with timolol 75 mg daily. Corneal anesthesia was observed in a patient treated with timolol eye drops. Systematic description of clinical effects: Cardiovascular: Acute: First-degree atrioventricular block has been reported after ingestion of blood pressure was 120/80 mmHg and the heart rate was 58/min. Bradycardia, hypotension, atrioventricular block and congestive cardiac failure may occur after administration of timolol. Respiratory: Acute: Reversible respiratory arrest was observed in a 62-year-old woman after instillation of timolol eye drops and may occur after oral administration. Bronchospasm may occur in susceptible patients after administration of timolol. Neurological: CNS: Acute: Drowsiness, vertigo, headache have been reported in one case. Fatigue, confusion, depression, hallucinations have been reported after administration of timolol. Peripheral nervous system: Acute: Worsening of myasthenia gravis may occur after administration of timolol. Autonomic nervous system: Acute: Effects of beta-blockade. Gastrointestinal: Acute: abdominal pain, nausea, vomiting and diarrhea may occur after administration of timolol orally or as eye drops. Dermatological: Acute: Urticaria may be observed. Eye, ear, nose, throat: local effects: Acute: Eyelid erythema and edema has been reported following ocular administration. Metabolic: Acid-base disturbances. Fluid and electrolyte disturbances: Hyperkalemia has been reported. Other clinical effects: Sexual dysfunction following usual doses of topical ocular timolol has been reported and may also occur after oral administration. Special risks: Timolol is eliminated in breast milk. No epidemiological studies of congenital anomalies among infants born to women treated with timolol during pregnancy have been reported.

---

Hepatotoxicity
Mild-to-moderate elevations in serum aminotransferase levels occur in less than 2% of patients on timolol and are usually transient and asymptomatic, resolving even with continuation of therapy. Despite its wide spread use, timolol has not been convincingly linked to instances of clinically apparent liver injury. Other beta-blockers have been implicated in rare instances of acute liver injury with a latency to onset ranging from 2 to 24 weeks, a hepatocellular pattern of serum enzyme elevations and a mild, self-limiting course without evidence of hypersensitivity or autoimmune reactions.
Likelihood score: E (unlikely cause of clinically apparent acute liver injury).

---

Effects During Pregnancy and Lactation
◉ Summary of Use during Lactation
Because of the variability in excretion of timolol into breastmilk and minimal reported experience during breastfeeding, other agents may be preferred, especially while nursing a newborn or preterm infant.
Ophthalmic use of timolol by the mother should pose little risk to the breastfed infant, although some guidelines state that gel formulations are preferred over solutions. To substantially diminish the amount of drug that reaches the breastmilk after using eye drops, place pressure over the tear duct by the corner of the eye for 1 minute or more, then remove the excess solution with an absorbent tissue.
◉ Effects in Breastfed Infants
None reported, but beta-adrenergic blocking drugs with similar breastmilk excretion characteristics have caused adverse effects in breastfed newborns.
No side effects were reported in one case report of a 9-week-old breastfed infant whose mother was using 0.5% ophthalmic timolol drops twice daily in one eye.
A mother who was taking 2 drops of timolol 0.5% eye drops daily as well as using pilocarpine eye drops twice daily and acetazolamide 250 mg orally twice daily and delivered a preterm infant at 36 weeks of gestation. The infant began 5 months of exclusive breastfeeding at 6 hours after birth. On day 2, the infant developed electrolyte abnormalities consisting of hypocalcemia, hypomagnesemia, and metabolic acidosis. The infant was treated with oral calcium gluconate and a single dose of intramuscular magnesium sulfate. Despite continued breastfeeding and maternal drug therapy, the infant's mild metabolic acidosis disappeared on day 4 of life and the infant was gaining weight normally at 1, 3 and 8 months, but had mild hypotonicity. The authors considered the metabolic effects to be caused by transplacental passage of acetazolamide that resolved despite the infant being breastfed. The infant gained weight adequately during breastfeeding, but had some mild, residual hypertonicity of the lower limbs requiring physical therapy.
A newborn infant was breastfed during maternal therapy with various combinations of ocular timolol, dipivifrin, dorzolamide, brimonidine and several doses of acetazolamide. Ultimately, the mother was treated with timolol gel-forming solution 0.5% and dorzolamide 2% drops. The drugs were given immediately following breastfeeding with punctal occlusion and no apnea or bradycardia was observed in the infant.
◉ Effects on Lactation and Breastmilk
Relevant published information on the effects of beta-blockade or timolol during normal lactation was not found as of the revision date. A study in 6 patients with hyperprolactinemia and galactorrhea found no changes in serum prolactin levels following beta-adrenergic blockade with propranolol.

---

Protein Binding
The plasma protein binding of timolol is not extensive and is estimated to be about 10%.

---

Interactions
When used in conjunction with topical miotics, topical dipivefrin, topical epinephrine, and/or systemically administered carbonic anhydrase inhibitors, the effect of timolol maleate in lowering intraocular pressure may be additive. This effect may be used to therapeutic advantage in the treatment of glaucoma. However, the long term efficacy of combined therapy with an adrenergic agonist (eg, dipivefrin, epinephrine) and a beta-adrenergic blocking agent remains to be clearly established. Although topical timolol used alone has little or no effect on pupil size, mydriasis resulting from concomitant therapy with topical timolol and epinephrine has been reported occasionally. /Timolol maleate/
The possibility of an additive effect on intraocular pressure and/or systemic beta-adrenergic blockade should be considered in patients who are receiving a systemic beta-adrenergic blocking agent and topical timolol concomitantly.
When topical timolol is administered concomitantly with a catecholamine depleting drug (eg, reserpine), the patient should be observed closely for possible additive effects and the production of hypotension and/or marked bradycardia, which may result in vertigo, syncope, and or postural hypotension.
Concomitant administration of timolol with reserpine may increase the incidence of hypotension and bradycardia as compared with timolol alone, because of reserpine's catecholamine depleting activity. Timolol also is additive with and may potentiate the hypotensive actions of other hypotensive agents (e.g., hydralazine, methyldopa). This effect usually is used to therapeutic advantage, but dosage should be adjusted carefully when these drugs are used concurrently.
For more Interactions (Complete) data for TIMOLOL (8 total), please visit the HSDB record page.

---

Non-Human Toxicity Values
LD50 Mouse female 1190 mg/kg /Timolol maleate/
LD50 Rat female 900 mg/kg /Timolol maleate/

[1]. James Barnes; Majid Moshirfar. Timolol.

[2]. Treatment of open-angle glaucoma and ocular hypertension with preservative-free tafuprost/timolol fxed-dose combination therapy: 6 case reports and clinical outcomes. BMC Ophthalmol. 2022 Apr 2;22(1):152.

[3]. Beta-blocker timolol alleviates hyperglycemia-induced cardiac damage via inhibition of endoplasmic reticulum stress. J Bioenerg Biomembr. 2014 Oct;46(5):377-87.

Therapeutic Uses
Adrenergic beta-Antagonists; Anti-Arrhythmia Agents; Antihypertensive Agents; Sympatholytics
Antihypertensive, antiarrhythmic, antianginal, antiglaucoma agent.
In ophthalmology, topical timolol maleate is used to reduce elevated intraocular pressure in various conditions, including open angle glaucoma, aphakic glaucoma, ocular hypertension, and some secondary glaucomas. Reduction in intraocular pressure may reduce or prevent glaucomatous visual field loss or optic nerve damage and obviate the need for surgery. /Timolol maleate/
Timolol is used in the management of hypertension. The drug has been used as monotherapy or in combination with other classes of antihypertensive agents. Timolol's efficacy in the management of hypertension is similar to that of the other beta-adrenergic blocking agents.
For more Therapeutic Uses (Complete) data for TIMOLOL (13 total), please visit the HSDB record page.

---

Drug Warnings
Patients receiving topical timolol and a systemic beta-adrenergic blocking agent concomitantly should be observed carefully for potential additive effects on intraocular pressure and/or systemic effects of beta-adrenergic blockade.
Patients who have a history of atopy or of a severe anaphylactic reaction to a variety of allergens reportedly may be more reactive to repeated accidental, diagnostic, or therapeutic challenges with such allergens while taking beta-adrenergic blocking agents and may be unresponsive to usual doses of epinephrine used to treat anaphylactic reactions.
Bacterial keratitis has been reported with the use of multidose containers of topical ophthalmic preparations. These containers had been contaminated inadvertently by patients who, in most cases, had a concurrent corneal disease or disruption of the ocular epithelial surface. Patients should be informed that improper handling of ocular solutions can result in contamination of the solution by common bacteria known to cause ocular infections and should be instructed to avoid allowing the tip of the dispensing container to contact the eye or surrounding structures. Serious damage to the eye and subsequent loss of vision may result from using contaminated ophthalmic solutions. Patients also should be advised to seek their physician's advice immediately regarding the continued use of the present multidose container if an intercurrent ocular condition (eg, trauma, ocular surgery or infection) occurs.
Because timolol has little or no effect on pupil size, the drug should not be used alone in patients with angle closure glaucoma, but only in combination with a miotic. Timolol ophthalmic solution should not be used concomitantly with another ophthalmic beta-adrenergic blocking agent; in patients being transferred from another beta-blocker to timolol, the other beta-blocker should be discontinued before initiating timolol.
For more Drug Warnings (Complete) data for TIMOLOL (26 total), please visit the HSDB record page.

---

Pharmacodynamics
Timolol, when administered by the ophthalmic route, rapidly reduces intraocular pressure. When administered in the tablet form, it reduces blood pressure, heart rate, and cardiac output, and decreases sympathetic activity.. This drug has a fast onset of action, usually occurring within 20 minutes of the administration of an ophthalmic dose. Timolol maleate can exert pharmacological actions for as long as 24 hours if given in the 0.5% or 0.25% doses.

C13H24N4O3S

316.41966

316.157

26839-75-8

(S)-Timolol Maleate;26921-17-5;(Rac)-Timolol-d5 maleate;1217260-21-3;Timolol hemihydrate;91524-16-2

33624

Typically exists as solid at room temperature

1.224 g/cm3

487.2ºC at 760 mmHg

71.5 - 72.5ºC

248.5ºC

2.62E-10mmHg at 25°C

1.548

0.958

2

8

7

21

310

1

CC(C)(C)NC[C@@H](COC1=NSN=C1N2CCOCC2)O

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

May dissolve in DMSO (in most cases), if not, try other solvents such as H2O, Ethanol, or DMF with a minute amount of products to avoid loss of samples

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

---

Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

View More

Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

---

Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

View More

Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

---

Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

---

 (Please use freshly prepared in vivo formulations for optimal results.)