The mechanism of action of Tofranil (imipramine) is not definitely known. However, it does not act primarily by stimulation of the central nervous system. The clinical effect is hypothesized as being due to potentiation of adrenergic synapses by blocking uptake of norepinephrine at nerve endings. The mode of action of the drug in controlling childhood enuresis is thought to be apart from its antidepressant effect.

Animal Pharmacology & Toxicology

A. Acute: Oral LD₅₀ ranges are as follows:

Rat 355 to 682 mg/kg

Dog 100 to 215 mg/kg

Depending on the dosage in both species, toxic signs proceeded progressively from depression, irregular respiration and ataxia to convulsions and death.

B. Reproduction/Teratogenic: The overall evaluation may be summed up in the following manner:

Oral: Independent studies in three species (rat, mouse, and rabbit) revealed that when Tofranil (imipramine) is administered orally in doses up to approximately 2-1/2 times the maximum human dose in the first 2 species and up to 25 times the maximum human dose in the third species, the drug is essentially free from teratogenic potential. In the three species studied, only one instance of fetal abnormality occurred (in the rabbit) and in that study there was likewise an abnormality in the control group. However, evidence does exist from the rat studies that some systemic and embryotoxic potential is demonstrable. This is manifested by reduced litter size, a slight increase in the stillborn rate, and a reduction in the mean birth weight.

Last reviewed on RxList: 12/27/2007
This monograph has been modified to include the generic and brand name in many instances.