CLINICAL PHARMACOLOGY
Neostigmine inhibits the hydrolysis of acetylcholine by competing with acetylcholine for attachment to
acetylcholinesterase at sites of cholinergic transmission.
It enhances cholinergic action by facilitating the
transmission of impulses across neuromuscular junctions. It also has a direct cholinomimetic effect on
skeletal muscle and possibly on autonomic ganglion cells and neurons of the central nervous system.
Neostigmine undergoes hydrolysis by cholinesterase and is also metabolized by microsomal enzymes in
the liver. Protein binding to human serum albumin ranges from 15 to 25 percent.
Following intramuscular administration, Neostigmine is rapidly absorbed and eliminated. In a study of five
patients with myasthenia gravis, peak plasma levels were observed at 30 minutes, and the half-life ranged
from 51 to 90 minutes. Approximately 80 percent of the drug was eliminated in urine within 24 hours;
approximately 50% as the unchanged drug and 30 percent as metabolites. Following intravenous
administration, plasma half-life ranges from 47 to 60 minutes have been reported with a mean half-life of
53 minutes.
The clinical effects of Neostigmine usually begin within 20 to 30 minutes after intramuscular injection and
last from 2.5 to 4 hours.
INDICATIONS AND USAGE
Neostigmine Methylsulfate Injection, USP is indicated for:
- the symptomatic control of myasthenia gravis when oral therapy is impractical.
- the prevention and treatment of postoperative distention and urinary retention after mechanical
obstruction has been excluded.
- reversal of effects of non-depolarizing neuromuscular blocking agents (e.g., tubocurarine,
metocurine, gallamine or pancuronium) after surgery.
CONTRAINDICATIONS
Neostigmine Methylsulfate Injection, USP is contraindicated in patients with known hypersensitivity to the
drug. It is also contraindicated in patients with peritonitis or mechanical obstruction of the intestinal or
urinary tract.
WARNINGS
Neostigmine Methylsulfate Injection, USP should be used with caution in patients with epilepsy, bronchial
asthma, bradycardia, recent coronary occlusion, vagotonia, hyperthyroidism, cardiac arrhythmias or peptic
ulcer. When large doses of Neostigmine are administered, the prior or simultaneous injection of Atropine
Sulfate may be advisable. Separate syringes should be used for the Neostigmine and Atropine. Because
of the possibility of hypersensitivity in an occasional patient, Atropine and anti-shock medication should
always be readily available. Pregnancy: Teratogenic Effects. Pregnancy Category C. There are no adequate or well-controlled studies
of Neostigmine Methylsulfate in either laboratory animals or in pregnant women. It is not known whether
Neostigmine can cause fetal harm when administered to a pregnant woman or can affect reproductive
capacity. Neostigmine Methylsulfate Injection, USP should be given to a pregnant woman only if clearly
needed.
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