Pharmacology for Dentistry

160 Section 3/ Drugs Acting on ANS

produces miosis, spasm of accommodation
and reduction in intraocular tension.

Neostigmine does not cross blood-brain
barrier, hence has no significant central action.

Neostigmine is a drug of choice in the
treatment of myasthenia gravis, a chronic
disease characterized by muscular weakness
and rapid fatiguability of the skeletal muscles
due to impaired neuromuscular transmission.
The defect may be presynaptic or postsynaptic.

Apart from neostigmine, pyridostigmine
and ambenonium are the other standard drugs
used in the treatment of myasthenia gravis.

Neostigmine preceded by atropine to
block muscarinic effects rapidly reverses
muscle paralysis induced by competitive
neuromuscular blockers (decurarization).

Neostigmine is also useful in
postoperative paralytic ileus/urinary
retention.

PYRIDOSTIGMINE

It structurally and pharmacologically
resembles neostigmine but has longer
duration of action and less potent than
neostigmine and better tolerated by
myasthenia gravis patients.

EDROPHONIUM

It is a quarternary ammonium anticho-
linesterase and structurally related to neostig-
mine but has got weak anticholinesterase

activity as compared to neostigmine. It is

mainly useful as diagnostic agent for myas-

thenia gravis and for postoperative

decurarization.

DISTIGMINE

It is a longer acting neostigmine

analogue and is used to treat atony of the

bladder and intestine and its action lasts for

24 hours. It is given daily before breakfast.

IRREVERSIBLE ANTICHOLINESTERASES

The organophosphorus cholinesterase

inhibitors like diisopropyl fluorophosphate,

phospholine, parathion, malathion etc. are

highly toxic compound and cause

irreversible inhibition of both true and

pseudocholinesterases. They are highly lipid

soluble compound and can easily cross the

blood-brain barrier.

DIISOPROPYL FLUOROPHOSPHATE

(DFP)

The pharmacological effects are those of

acetylcholine. It produces prolonged

inhibition of true and pseudocholinesterases.

They are inactivated in the body completely

by oxidation and hydrolysis and excreted in

urine.

The are mainly used for the treatment

of glaucoma, especially when other miotic

agents fail.