Dorzolamide/Timolol

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[edit] BRAND NAMES

[edit] STRUCTURE

[edit] MECHANISM OF ACTION

Dorzolamide and Timolol decrease elevated intraocular pressure (IOP) primarily by reducing aqueous humour secretion, but do so by different mechanisms of action.

  • Dorzolamide, is a carbonic-anhydrase inhibitor, an enzyme found in many tissues of the body, including the eye. Inhibition of carbonic anhydrase in the ciliary processes of the eye decreases aqueous humour secretion, presumably by slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport. The result is a reduction in intraocular pressure (IOP).
  • Timolol is a nonselective beta-blocker that works by lowering the intraocular pressure by reducing the production of aqueous humor in the ciliary epithelium. The precise mechanism of action is not clearly established, but inhibition of the increased cyclic AMP synthesis caused by endogenous beta-adrenergic stimulation is probable.

Raised pressure inside the eye causes damage to the retina and to the optic nerve. This can result in serious loss of vision and even blindness. By lowering the pressure inside the eye, the combination Dorzolamide/Timolol reduces the risk of damage to these structures.

[edit] INDICATIONS

Treatment of elevated intraocular pressure in patients with ocular hypertension or open-angle glaucoma, who are insufficiently responsive to beta-blockers (Timolol).

[edit] DOSAGE

One drop into the affected eye(s) 2 times daily. If more than one type of eye-drop medicine is being used, each one should be given at least 5-10 minutes apart.

When using nasolacrimal occlusion or closing the eyelids for 2 minutes, the systemic absorption is reduced. This may result in a decrease in systemic side effects and an increase in local activity.

[edit] DOSAGE FORMS AND STRENGTHS

Solution containing 20 mg/mL dorzolamide and 5 mg/mL timolol

[edit] CONTRAINDICATIONS

  • Hypersensitivity to any component of the product
  • Hypersensitivity to sulfonamides
  • Bronchial asthma or with a history of bronchial asthma, or severe chronic obstructive pulmonary disease
  • Sinus bradycardia; second and third degree atrioventricular block; overt cardiac failure; cardiogenic shock (Timolol may cause worsening of cardiac symptoms)

[edit] WARNINGS AND PRECAUTIONS

  • Dorzolamide is a sulfonamide and although administered topically is absorbed systemically. Therefore the same types of adverse reactions that are attributable to sulfonamides may occur with topical administration. Patients should be advised that if serious or unusual reactions including severe skin reactions or signs of hypersensitivity occur, they should discontinue the use of the product.
  • Timolol may cause severe worsening of asthma and COPD symptoms including death due to bronchospasm
  • Timolol may cause worsening of cardiac symptoms (See contraindications)

[edit] INTERACTIONS

  • Acetazolamide (Diamox): Acetazolamide is an oral carbonic anhydrase inhibitor. Therefore, there is potential for an additive effect when taken with Dorzolamide (topically applied Dorzolamide can be absorbed systemically).

[edit] PREGNANCY AND LACTATION

  • Pregnancy Category C (US). Dorzolamide/Timolol should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.
  • Nursing Mothers: A decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

[edit] SIDE EFFECTS

Most frequent adverse events (30% of patients) were ocular burning, stinging, or discomfort immediately following ocular administration, taste perversion (bitter, sour, or unusual taste).

Conjunctival hyperemia, blurred vision, superficial punctate keratitis or eye itching were reported between 5-15% of patients.

Rare side effects include : shortness of breath, visual changes, irregular heartbeat, slowing of your heart rate and severe skin reactions

[edit] RELATED LINKS

Understanding Glaucoma

[edit] BIBLIOGRAPHY

[edit] REFERENCES