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May 1980

Phthalazinol, Thrombocytopenia, and Amyotrophic Lateral Sclerosis

Author Affiliations

From the Neuromuscular Diseases Section, National Institute of Neurological and Communicative Disorders and Stroke, Bethesda, Md.

Arch Neurol. 1980;37(5):320. doi:10.1001/archneur.1980.00500540098023

Side effects of a drug sometimes lead to new uses. Phthalazinol is an inhibitor of cyclic adenosine monophosphate (cAMP) phosphodiesterase (and cyclic guanine monophosphate (cGMP) phosphodiesterase to a much lesser extent), with no serious side effects.1-3 We have used phthalazinol, 30 to 75 mg/kg/day, in patients during a period of four years, for as long as 33/4 years in one patient, attempting to treat amyotrophic lateral sclerosis.1 Phthalazinol raised to normal the low CSF levels of cAMP, but did not raise the low levels of cGMP.3.4 Phthalazinol did not benefit the disease in 20 patients.3 One 69-year-old man with only bulbar involvement, which had progressed for 30 months before treatment, has had no further progression during 47 months of phthalazinol therapy, 35 mg/kg/day. Whether arrest was related to the phthalazinol or a spontaneous plateauing of his disease is not yet known.3 Transient side effects in a

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