STUDIES ON THE TOXICITY AND PHARMACOLOGICAL ACTIONS OF SYMMETRICAL AND UNSYMMETRICAL DIETHYL BIS (DIMETHYLAMIDO) PYROPHOSPHATE

¹ Department of Pharmacology, University of Chicago, Chicago 37, Illinois

1. Measurements of the acute toxicity of the symmetrical (6499) and unsymmetrical (6515) analogs of diethyl bis (dimethylamido) pyrophosphate were conducted using several species of animals. The following approximate LD₅₀ values in mgm./kgm. were obtained for 6499: male rats 11.5, female rats 10, male mice 16.4, female mice 17, and guinea pigs between 13 and 16. The corresponding values for 6515 in mgm./kgm. were as follows: male rats 2.7, female rats 2.4, male mice 4.9, female mice 4.7, and guinea pigs between 5 and 7. When given intravenously to dogs the LD₅₀ of 6499 was between 25 and 30 mgm./kgm. while the value for 6515 was between 5 and 10 mgm./kgm. After oral administration to rats the approximate LD₅₀ of 6499 was 12.4 mgm./kgm. and the value for 6515 was 3.8 mgm./kgm. indicating that the compounds are well-absorbed from the gastrointestinal tract.

2. Toxicity studies on rats which received 6515 and 6499 dermally indicated that these agents are well-absorbed through the skin. The prior application of a polyoxy ethylene alkylaryl phenol (Thiosolve 8139) increased the dermal lethal dose of both compounds about six times.

3. The symptoms produced in all of the species employed were similar and typical of those produced by cholinergic drugs except that symptoms referable to stimulation of the central nervous system were insignificant.

4. The predominant cardiovascular effect of moderate intravenous doses in dogs is a pressor action and a moderate slowing of the heart. After lethal doses a marked bradycardia develops, accompanied by a lowered blood pressure and a depression of respiration. Respiratory paralysis occurs several minutes before complete cessation of the heart beat.

5. Measurements of the anticholinesterase action of 6515 in vitro demonstrated that 50 per cent inhibition of the cholinesterase activity of rat brain homogenates occurs with a final concentration of 2.8 x 10^-7 M whereas 4.7 x 10^-7 M 6499 produced 50 per cent inhibition of cholinesterase activity.

6. After intraperitoneal administration of of the LD₅₀ doses of 6515 and 6499 to rats marked inhibition of the cholinesterase activity of serum, submaxillary gland, skeletal muscle and ileum was noted while the cholinesterase activity of brain was only slightly inhibited. Maximal inhibition occurred within 15 minutes after administration of the compounds.

7. The inhibitory action of 6515 and 6499 on the cholinesterase activity of submaxillary gland and skeletal muscle persisted for several days after sublethal doses of the compounds while the enzyme activity of serum and ileum returned to nearly normal values within four days.

8. Premedication with atropine protected mice against two times the LD₅₀ of 6515 and 6499. Premedication with atropine and eserine increased the LD₅₀ values of each compound 10 to 12-fold in rats and mice.

9. Possible advantages of 6515 and 6499 in the treatment of myasthenia gravis are enumerated.