Systemic medications for intraocular pressure (IOP) control are typically reserved for cases in which a significant temporary drop in IOP is required that cannot be achieved by any other means.
Oral preparations are most commonly used in cases of acute angle-closure glaucoma or surrounding intraocular surgery, in which substantial pressure spikes may arise.
Because these medications are not as often prescribed as our work-horse topical medications, we’ve put together a quick review of everything you need to know about oral glaucoma drugs in case you are in a situation where these are needed.
Systemic Carbonic Anhydrase Inhibitors (CAIs)
- Acetazolamide (Diamox®)
- Dosage for IOP control is typically 250mg every 6 hours
- Most commonly administered oral CAI
- It is often reserved for short-term IOP reduction only in patients with acute angle-closure or those with significant risk of vascular occlusion due to elevated IOP, but it can also be used in cases of macular edema
- Mechanism of Action:
- CAIs decrease active aqueous humor secretion by blocking carbonic anhydrase in the non-pigmented ciliary epithelial cells present in the ciliary processes
- During the process of aqueous production, carbonic anhydrase catalyzes the cellular production of bicarbonate. It is the bicarbonate anion that plays a key role in the formation of aqueous humor; therefore, if this reaction cannot take place, aqueous humor production will be inhibited
- Systemic administration of CAIs has been shown to produce approximately a 45-55% inhibition of aqueous formation
- Side Effects:
- Paresthesia (tingling and numbness) of the fingers, toes, hands, feet, and mucocutaneous junctions is the most common side effect and is essentially a universal feature
- Other side effects include: malaise, fatigue, depression, weight loss, decreased libido, gastric irritation, abdominal cramping, diarrhea, nausea, metallic taste, metabolic acidosis, hypokalemia, Stevens-Johnson syndrome
- Most serious side effects are blood dyscrasias; however, these are very rare
- Contraindications/Precautions:
- Patients with known sulfa hypersensitivity, impaired renal function, clinically significant liver disease, severe COPD, pregnancy, or those taking potassium-depleting diuretics or digitalis
Systemic Osmotic Agents
- Glycerol & Isosorbide
- Dosage is 1g/kg or body weight
- Peak action is within 1 hour and duration of action is up to 3 hours
- Glycerol is metabolized to glucose, so it should not be used in diabetics (Isosorbide is metabolically inert and may be given to diabetics)
- Mechanism of Action:
- These medications lower IOP by creating an osmotic gradient between the blood and the vitreous, which subsequently causes water to be drawn out from the vitreous (the greater the osmotic gradient created, the larger the reduction in IOP)
- Side Effects:
- Headache, nausea, backache, and mental confusion
- Most serious side effects include cardiovascular overload due to increased extracellular volume; therefore, these agents should be used with caution in patients with renal or cardiac disease
Although the likelihood of you needing to prescribe one of these medications is pretty slim, it’s always good to have a general understanding of treatment options in the back of your mind just in case you have a patient who walks in with super high pressures!
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Clinical Guide to Ophthalmic Glaucoma Medications book cover_Clinical Guide to Glaucoma Meds-06 Topical intraocular pressure (IOP) lowering medications are typically the first-line treatment for patients with elevated intraocular pressure. The drugs used to treat glaucoma are classified based on their active ingredient. Over the years, glaucoma medications have come and gone from the market, so we’ve put together a quick reference chart of all the currently utilized topical drugs, their formulations, dosage schedule, and mechanisms of action. Just click the download button!
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