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Alpha blockers, Prostaglandin analogues:, For closed angle glaucoma, Non…
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Prostaglandin analogues:
PGF 2alpha increases uveoscleral outflow. Latanoprost, bimatoprost and unoprostone are PGF 2alpha derivatives useful in glaucoma.
These are now the drug of choice for POAG.
Bimatoprost causes growth of eyelashes as an adverse effect which can be utilized for the treatment of hypotrichosis.
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Other important points:
Prazosin and other alpha1 blockers are useful for the treatment of scorpion sting.
Major adverse effect of these drugs is postural hypotension.
It is seen with first few doses or on dose escalation(first dose effect). If used continuously tolerance develops to this adverse effect.
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Tamsulosin and sildosin
Tamsulosin and sildosin selectively inhibits subtype of alpha1 receptors present in the prostate alpha1A
without affecting those present in blood vessels.
These are therefore preferred for the treatment of BHP because of their reduced propensity to cause postural hypotension.
These has been found to cause intra-operative floppy iris syndrome during cataract surgery.
Indoramin and urapidil are occasionally used for hypertensive emergencies.
glaucoma
Characterized by progressive damage to optic nerve associated with raised intraocular pressure > 21mm Hg.
Rise in intraocular tension is either due to excessive production or due to less drainage of aqueous humor.
So the drugs used for glaucoma act by either decreasing the secretion( B blockers, alpha 2 agonists and carbonic anhydrase inhibitors)
or by increasing the outflow( miotics, dipivefrine and prostaglandins) of aqueous humor.
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Phenoxybenzamine
Phenoxybenzamine is used to prevent hypertensive episodes during operative manipulation of tumor in pheochromocytoma.
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B blockers:
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Non selective: timolol, levobunolol and carteolol.
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B blockers
Timolol, betaxolol, levobetaxolol, levobunolol, carteolol and metipranolol have been approved for use in glaucoma.
Levobunolol is the longest acting whereas betaxolol is cardioselective therefore less efficacious but safe in asthmatics B blocker.
Alpha agonists:
dipivefrine(prodrug of adrenaline) and adrenaline act by increasing trabecular outflow(main action), reducing aqueous secretion and increasing uveoscleral outflow.
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Miotics:
pilocarpine(directly acting cholinomimetic) and physostigmine(indirectly acting cholinomimetic) increase aqueous outflow by causing miosis.
Pilocarpine is short acting, therefore requires frequent daily dosing.
Demacarium and ecothiophate(both are long acting cholinomimetics) are rarely used because they accelerate the cataract development.