Pharmacology and Ophthalmology

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. 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

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. 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

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
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

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