Interacting drugs- summary
 

+ Anticholinesterase

Aminoglycoside antibiotics/ Neomycin,streptomycin / Kanamycin 
a mild but definite nondeploarizing blocking action which may  accentuate neuromuscular block

Atropine/   Belladona derivatives
 routine admin. of atropine or belladonna  derivatives  with  these agents suppress the parasympathomimetic   ( muscarinic ) symptoms of excessive GI  stimulation, leaving
  only the more serious symptoms of paralysis of voluntary  muscles as sign of leakage 

Corticosteroids
 anticholinesterase effect  antagonised in myasthenia gravis

Depolarizing muscle relaxants /succinyl choline / decamethonium
 neostigmine prolong the phase I block of these agents.Use these  drugs in myasthenic patients only when definitely indicated. Make careful adjustment of cholinesterase dosage

Local and some  anesthetics , / antiarrhythmics
 interfere with neuromuscular transmission. Use cautiously  if at all ,   in myastenis patients

Magnesium
 has a direct depressant effect on skeletal muscle, and antagonise  the beneficial effect of anticholinesterase therapy

Mecamylamine 
 do not administer to patients receiving ganglionic blocking effect

Methocarbamol
 a single report indicates this drug has impaired the effect of  pyridostigmine in  patient with myasthenia gravis

Succinylcholine
neuromuscular blocking agents effects may be increased. Prolonged  respiratory depression with extended periods of apnea occur

Myasthenia gravis

The side effects of pyridostigmine are of two types- muscarinic and nicotinic.

The muscarinic side effects are-Nausea, diarrhea, abdominal cramps, increased bronchial secretions, miosis and diaphoresis.

Nictotinic side effects- muscle cramps, fasciculation and weakness.

Other side effects include- skin rash, which usually subside after discontinuation of the therapy.

Hypersensitivity.

Contraindicated in mechanical intestinal or urinary obstruction and particular caution should be used in admininistration in bronchial asthma.

Care should be taken in the use of of atropine for counteracting side effects.

Special Precaution:

Pyridostigmine is excreted mainly through urine.

Care should be taken in patients with renal impairment.

Indication-

Myasthenia gravis

Dosage-

Usual dosage- 0.3 to 1.g given by mouth, in divided doses.

Pharmacology:

Pyridostigmine is a potent reversible inhibitor of acetycholinesterase, the enzyme responsible for destroying acetylcholine.. By inhibiting the enzyme, it permits free transmission of nerve impulses across the neuromuscular junction. Pyridostigmine has a carbonyl ester linkage that is hydrolysed by acetylcholinesterase but much more slowly than acetycholine itself.

Pharmacokinetics.

Pyridostigmine is poorly and variably absorbed from the gastrointestinal tract. The plasma half life range from 0.38 to 1.9 hrs. It is extensively metabolised and excreted mainly in the urine as unchanged drug and metabolites.