Timolol

Use in ophthalmology

The primary indication for timolol is the treatment of glaucoma. As a non-selective $\beta$-blocker, it effectively lowers intraocular pressure.

Its mechanism of action is exclusively related to the reduction of aqueous humor production (secretion). An important clinical feature of the drug is that, unlike cholinergic agents, timolol has absolutely no effect on accommodation or pupil size. This makes its use more comfortable for patients, as visual quality is not impaired by accommodation spasm or miosis.

The pharmacokinetics of the eye drop formulation are quite predictable:

• Onset of action: develops rapidly, within 10–30 minutes after instillation into the conjunctival sac.
• Peak effect: maximum pressure reduction is observed after 1–2 hours.
• Duration of action: the effect persists for a long time, up to 24 hours, allowing the drug to be administered once or twice daily.

Side effects and resorptive action

Despite topical administration, timolol can cause both local and systemic adverse reactions.

Local side effects include:

• Reduced tear production (development of "dry eye" syndrome);
• Conjunctivitis;
• Local allergic reactions.

Systemic effects (resorptive action): Although the class of hydrophilic $\beta$-blockers generally penetrates barriers poorly, timolol specifically is a lipophilic substance. Due to its high lipophilicity, it is easily and rapidly absorbed through the vascular-rich mucosa of the nasolacrimal duct, entering the systemic circulation.

This can lead to systemic reactions typical of $\beta$-blockers: bradycardia, arterial hypotension, and general weakness. The danger is particularly high for patients with bronchial asthma, as systemic absorption of a non-selective $\beta$-blocker can trigger severe bronchospasm.

Systemic use

In addition to ophthalmology, timolol is also prescribed systemically (orally, per os). In cardiology, the drug is used to treat:

• Arterial hypertension;
• Angina pectoris.

Properties of hydrophilic $\beta$-blockers (reference)

To contrast with lipophilic timolol, it is important to understand the properties of truly hydrophilic $\beta$-blockers. They have low lipophilicity, which determines their pharmacokinetics:

1. Absorption: absorption from the gastrointestinal tract is incomplete, with bioavailability limited to 30–35%.
2. Distribution: drugs in this group penetrate the blood-brain barrier (BBB) poorly. The clinical consequence of this is the absence of depressive effects on the central nervous system, whereas lipophilic analogues may cause central effects.
3. Elimination: they undergo minimal metabolism and are excreted mainly by the kidneys unchanged.
4. Safety profile: general contraindications and side effects are similar to propranolol, but central side effects are significantly less pronounced in hydrophilic agents.

Class and exam questions

What else to study on this topic

• Characteristics of drug absorption through the nasolacrimal duct mucosa
• Comparison of the pharmacokinetics of lipophilic and hydrophilic beta-blockers
• Principles of glaucoma treatment and drug classes used
• Systemic effects of topical ophthalmic medications

Other topics in the section "Drugs Acting on Adrenergic Synapses"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.