Hyperosmotic agents

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1. HYPEROSMOTIC AGENTS

2. HYPEROSMOTIC AGENTS ORAL: 1.ORALGLYCEROL 2. ISOSORBIDE INTRAVENOUS: 1.MANNITOL 2.UREA

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. INTRAVENOUS AGENTS: They are rapid in action and more effective They are usually administered over 45 to 60 minutes

10. 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

11. 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

12. DISADVANTAGES: There is greater likelihood of cellular dehydration because of its confinement to the extracellular space Cardiovascular overload and pulmonary oedema are more common

13. 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

14. 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

15. USES 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

16. 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

17. 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

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