Overdose
The most common symptoms of primidone overdose are coma with loss of deep tendon reflexes and, during the recovery period, if the patient survives, disorientation, dysarthria, nystagmus, and ataxia, lethargy, somnolence, vomiting, nausea, and occasionally, focal neurological deficits which lessen over time. Complete recovery comes within five to seven days of ingestion. The symptoms of primidone poisoning have generally been attributed to its biotransformation to phenobarbital; however, primidone has toxic effects independent of its metabolites in humans. The massive crystalluria that sometimes occurs sets its symptom profile apart from that of phenobarbital. The crystals are white, needle-like, shimmering, hexagonal plates consisting mainly of primidone.
In the Netherlands alone, there were thirty-four cases of suspected primidone poisoning between 1978 and 1982. Out of these, Primidone poisoning was much less common than phenobarbital poisoning. Twenty-seven of those adult cases were reported to the Dutch National Poison Control Centre. Out of these, one person taking it with phenytoin and phenobarbital died, twelve became drowsy and four were comatose.
Treatments for primidone overdose have included hemoperfusion with forced diuresis, a combination of bemegride and amiphenazole; and a combination of bemegride, spironolactone, caffeine, pentylenetetrazol, strophanthin, penicillin and streptomycin.
In the three adults who are reported to have succeeded, the doses were 20–30 g. However, two adult survivors ingested 30 g 25 g, and 22.5 g. One woman experienced symptoms of primidone intoxication after ingesting 750 mg of her roommate's primidone.
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