The objective of the present investigation was to study the protection afforded by a single administration of
pralidoxime against the muscle
necrosis induced by the
organophosphate compound
metamidophos at different times after intoxication. The fiber
necrosis of the diaphragm muscle was quantified by a morphometric technique, comparing the area fraction occupied by necrotic muscle fibers in animals that received
pralidoxime at different times after intoxication, i.e., 0, 1, 3, 6, and 12 h.
Pralidoxime administration protected
metamidophos-induced muscle
necrosis in all groups studied except for the 12-h group. The earlier the administration of
pralidoxime the greater the protection against muscle
necrosis. This protection was not accompanied by complete reactivation of plasma
cholinesterase activity. Results support the current opinion that
pralidoxime should be administered as soon as possible after
organophosphate intoxication, because in addition to reversing the
muscarinic effects, early administration of
pralidoxime also prevents muscle
necrosis--which could impair muscular function and respiratory condition. The time difference between recovery of plasma
cholinesterase activity and muscle
necrosis protection indicates that this method is not completely trustworthy for patient follow-up, since some improvement may occur in spite of the low plasma
cholinesterase activity.