HYPEROSMOTIC AGENTS

HYPEROSMOTIC AGENTS ORAL:

1.ORALGLYCEROL

2. ISOSORBIDE

INTRAVENOUS:

1.MANNITOL

2.UREA

INTRODUCTION:

• Hyperosmotic agents are being used since 25 years

• They are of great value in reducing the intraocular pressure preoperatively

• And in transient glaucomas like glaucoma in traumatic hyphemas

MECHANISM OF ACTION:

• Increase the osmolity of plasma leading to absorption of water from ocular tissues,this process is transient till the osmotic equilibrium is reestablished

• It may also decrease the aqueous humour production through central nervous system pathway

• Ideal hyperosmotic agents should have low molecular weight and should remain in the extra cellular fluid space

• The drug should not enter into the eye

ORAL AGENTS(INTRO):

• They are administered easily

• They are safe in patients with borderline cardiac status

• But they are slow in their action

• Drug absorption is also variable

• And so it is less predictable

1. ORAL GLYCEROL:

• Most widely used drug

• Usually administered as 50% solution in a dose of 1.5 to 3ml/kg

• Glycerol has an intense sweet taste

• It remains in the extracellular space and poorly penetrate the eye

• Repeated doses can be given but some patients develop vomiting

• Diabetic patients may have problem due to caloric value ,osmotic diuresis and dehydration

• Glycerol is metabolized in liver and produces 4.32 Kcal/g

2. ISOSORBIDE:

• It is an effective oral hyperosmotic agent administered as 45% solution

• It is different from isosorbide dinitrate which is a drug used in angina

• isosorbide is a dihydric alcohol derived from sorbitol

• It is less likely to produce nausea and vomiting but it produces diarrhea

• It doesn’t provide calories

• Therefore it is quite safe in diabetic patients

• Dose- 1.5 to 4ml/kg

3. ETHYL ALCOHOL:

• Because of unwanted central nervous system effect this agent is not used clinically

• Ethylalcohol produces hypotonic diuresis by inhibiting production of antidiuretic hormone

• Dose of absolute alcohol is 1.0 to 1.8 ml/kg body weight

• And it is diluted with appropriate mixtures

INTRAVENOUS AGENTS:

• They are rapid in action and more effective

• They are usually administered over 45 to 60 minutes

1. MANNITOL:

• 20% concentration of mannitol is less irritating to the blood vessels

• And it is the agent of choice for intravenous theraphy

• It is not metabolized and is excreted unchanged in urine

DOSE

• 2.5 to 7ml/kg of 20% solution is given intravenously

• It is not necessary to administer the full dose of the drug

• When the IOP falls to the desired level the infusion can be terminated

• Onset of action is in 30 minutes

• Duration of action is 6 hours

ADVANTAGES:

• It penetrate the eye poorly and mannitol is quite useful in inflammed eyes

• Extravasation of the drug from intravenous line will not cause necrosis

• More effective and it has rapid action

• Can be used in diabetic patients

• It is not contraindicated in renal failure patients

DISADVANTAGES:

• There is greater likelihood of cellular dehydration because of its confinement to the extracellular space

• Cardiovascular overload and pulmonary oedema are more common

2. UREA:

• It is less effective than mannitol

• It penetrates the eye readily

• It is administered as 30% solution

• Dose of 2 to 7ml/kg

DISADVANTAGES:

• When the drug is cleared from circulation rebound increase intraocular pressure is possible

• Old solutions decompose to ammonia.urea is contraindicated in renal failure

• Only the fresh solutions are used and it should be warmed to compensate for the endothermic reaction of dissolving drug

• If the drug extravasates it can cause thrombophlebitis and skin necrosis

Because of the side effects it is used less frequently than mannitol

USES

1. ANGLE CLOSURE GLAUCOMA:

• In addition to miotic,beta-blocker and oralglycerol,IV mannitol can terminate the acute attack in most of te cases

2. SECONDARY GLAUCOMA:

• In this glaucoma hyperosmotic patients are used to prepare the patient for surgery and to prevent optic nerve damage

• In many instances the glaucoma is transient as in trauma,laser iridectomy,laser trabeculoplasty etc

• In these transient conditions hyperosmotic agents can be given two to four times per day

3. CILIARY GLAUCOMA(MALIGNANT):

• In malignant glaucoma hyperosmotic agents are very useful

• They are administered in conjunction with phenylephrine,atropine,beta-blockr and acetazolamide

• Hyperosmotic agents absorb water from vitreous and vitreous face is moved backward

• Normal aqueous from posterior to anterior chamber is regained

PRECAUTIONS:

• Hyperosmotic patients should administer with caution in patients with cardiac,renal and hepatic disease

• Cellular hydration in cerebral tissue can cause disorientation

• Suddural haematoma is due to shrinkage of cerebral cortex and stretching of vessels resulting in rupture and hematoma formation

• Many of the side effects are dose related and minimum needed dose is used to avoid them

THANK YOU