Aphakic Pupillary Block Medication
- Author: Mitchell V Gossman, MD; Chief Editor: Hampton Roy, Sr, MD more...
The goals of pharmacotherapy are to reduce morbidity and to prevent complications.
Carbonic anhydrase inhibitors (CAIs)
By slowing the formation of bicarbonate ions with subsequent reduction in sodium and fluid transport, they may inhibit CA in the ciliary processes of the eye. This effect decreases aqueous humor secretion, reducing IOP.
Reduces the formation of aqueous humor by direct inhibition of CA on secretory ciliary epithelium. More than 90% of CA must be inhibited before IOP reduction can occur. May reduce IOP by 40-60%. Effects are seen in about an hour, they peak in 4 h, and trough in about 12 h. Inhibits enzyme CA, reducing rate of aqueous humor formation, which in turn reduces IOP. Derived chemically from sulfa drugs. If one form is not well tolerated, another form may be better or lower dose of the drug may better tolerated.
Used concomitantly with other topical ophthalmic drug products to lower IOP. If more than one ophthalmic drug is being used, administer the drugs at least 10 min apart. Reversibly inhibits CA, reducing hydrogen ion secretion at renal tubule and increases renal excretion of sodium, potassium bicarbonate, and water to decrease production of aqueous humor.
The exact mechanism of ocular antihypertensive action is not established, but it appears to be a reduction of aqueous production.
Competes with catecholamines for beta2-adrenergic receptor sites, which results in a reduction of aqueous production. Maximal effect achieved in 1-2 h and lasts up to 24 h. Available in 0.25 and 0.5% concentrations.
Oral hyperosmotic agents
Oral hyperosmotic agents reduce the IOP by drawing water out of the eye. Intravenous hyperosmotic agents cause marked diuresis and thereby reduce the IOP. The maximal effect is seen within 30 min and lasts for up to 4-6 h.
Oral osmotic agent for reducing IOP. Able to increase tonicity of blood until finally metabolized and eliminated by the kidneys. Maximum reduction of IOP usually occurs 1 h after glycerin administration. Effect usually lasts approximately 5 h. Given as a solution in water or lemon juice. Strong diuretic. May cause nausea and vomiting. Not preferred in diabetics because it is metabolized to glucose. Maximum effect is seen in 1 h and lasts for 3 h.
May be used to abort an acute attack of glaucoma. In the eyes, it may create an osmotic gradient between the plasma and ocular fluids and induce diuresis by elevating the osmolarity of the glomerular filtrate. These effects may in turn inhibit the tubular reabsorption of water. This treatment is preferred when less risk of nausea and vomiting than that posed by other oral hyperosmotic agents is desired.
Reduces elevated IOP when the pressure cannot be lowered by other means. Initially, assess for adequate renal function in adults by administering a test dose of 200 mg/kg, given IV over 3-5 min. Should produce a urine flow of at least 30-50 mL/h of urine over 2-3 h. In children, assess for adequate renal function by administering a test dose of 200 mg/kg, given IV over 3-5 min. Should produce a urine flow of at least 1 mL/h over 1-3 h.
Has a lower molecular weight than mannitol. Diuretic effect is less than that of mannitol.
Both direct and indirect-acting agents contract the longitudinal fibers of the ciliary muscle, which pulls scleral spur to open the trabecular meshwork with a resultant increase of the aqueous humor outflow.
Direct acting parasympathomimetic, only on muscarinic sites. Low concentration leads to miosis. High concentration leads to pupillary block. Increases facility of outflow through the trabecular meshwork. Decreases uveoscleral outflow. Induces myopia. Not effective with very high IOP (eg, 40 mm Hg) due to ischemia. The pressure-lowering effect begins within 20 min, peaks in 1.5 h, and lasts up to 4 h. Continued therapy with this agent is only indicated in older patients who cannot tolerate a peripheral iridectomy or where iridotomy is not possible (eg, argon laser is not available).
The available concentrations are 1-4%. Once an initial reduction of IOP has been achieved with acetazolamide or timolol, a single drop of pilocarpine, preferably a 2% concentration, will break the angle closure associated with pupillary block.
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