What intraocular pressure (IOP) can be expected after adding Combigan (brimonidine/timolol) to a patient's current therapy of Lumigan (bimatoprost) with an IOP of 20 mmHg?

From the Guidelines

Adding Combigan to a patient's current therapy of Lumigan can be expected to reduce the intraocular pressure (IOP) by approximately 20% based on the Ocular Hypertension Treatment Study (OHTS) 1, which would result in an IOP of around 16 mmHg. When considering the addition of Combigan (brimonidine/timolol) to Lumigan (bimatoprost), it's essential to understand the mechanisms of action and potential additive effects. Combigan works by reducing aqueous humor production and increasing uveoscleral outflow through its alpha-2 adrenergic agonist (brimonidine) and beta-blocker (timolol) components. Lumigan, as a prostaglandin analog, primarily increases uveoscleral outflow. The combination of these medications can provide a synergistic effect in reducing IOP.

Key points to consider when adding Combigan to Lumigan include:

• The expected reduction in IOP is based on the principle of achieving a 20% reduction from the baseline IOP, as suggested by the OHTS 1.
• Potential side effects such as ocular hyperemia, allergic conjunctivitis, and systemic effects like bradycardia or hypotension should be monitored, especially in patients with pre-existing cardiovascular conditions.
• Patients should be instructed on the proper use of eye drops, including waiting at least 5 minutes between different eye drops to prevent washout effects.
• Regular follow-up is crucial to assess the efficacy of the treatment and to monitor for any adverse effects.

Given the information and the context of the question, the most likely expected IOP after adding Combigan to Lumigan would be approximately 16 mmHg, considering the baseline IOP of 20 mmHg and the expected 20% reduction based on the OHTS findings 1.

From the FDA Drug Label

Brimonidine tartrate and timolol maleate ophthalmic solution, 0.2%/0.5% BID provided an additional 1 to 3 mmHg decrease in IOP over brimonidine treatment TID and an additional 1 to 2 mmHg decrease over timolol treatment BID during the first 7 hours post dosing.

The expected IOP measurement after adding Combigan to the patient's current therapy of Lumigan can be estimated by considering the additional decrease in IOP provided by Combigan.

• The patient's current IOP on Lumigan is 20 mmHg.
• Combigan is expected to provide an additional 1 to 3 mmHg decrease in IOP.
• Therefore, the expected IOP measurement after starting Combigan would be approximately 17 to 19 mmHg. Given the options, the closest answer would be D 19 mmHg or possibly C 16 mmHg if taking the higher end of the decrease, but since the question asks for an "approximately" value and considering the range provided, D 19 mmHg seems a reasonable expectation, keeping in mind the actual decrease could vary within the 1 to 3 mmHg range 2.

From the Research

Expected IOP Measurement

• The patient is currently on Lumigan (bimatoprost) with an IOP of 20 mmHg.
• Combigan (brimonidine/timolol) is added to the current therapy.
• According to the studies, the expected IOP reduction with Combigan can be estimated.

IOP Reduction with Combigan

• A study published in 2021 3 found that the mean IOP change from baseline to month 12 was -4.1 mmHg with FCBT (fixed-combination brimonidine tartrate/timolol maleate).
• Another study published in 2012 4 found that the relative reduction for mean diurnal IOP was 28.1% for brimonidine/timolol.
• Assuming a similar IOP reduction, the expected IOP measurement after adding Combigan can be estimated.

Estimated IOP Measurement

• Based on the study published in 2021 3, the expected IOP reduction is approximately 4.1 mmHg.
• With an initial IOP of 20 mmHg, the estimated IOP measurement after adding Combigan would be around 15.9 mmHg.
• However, considering the options provided, the closest estimate would be around 16 mmHg.

Comparison with Options

• Option A: 10 mmHg seems too low considering the expected IOP reduction.
• Option B: 13 mmHg is possible but slightly lower than the estimated IOP measurement.
• Option C: 16 mmHg is the closest estimate based on the expected IOP reduction.
• Option D: 19 mmHg seems too high considering the expected IOP reduction.