P11: Clozapine-Induced Thrombocytopenia: Whether or Not to Continue Clozapine Treatment when Platelet Count Falls

Objectives: To determine if and when to continue clozapine in patients with clozapine-induced thrombocytopenia. Methods: A case report and literature review of a geriatric patient with Parkinson’s disease (PD) psychosis, on longstanding treatment with clozapine with recent development of thrombocytopenia, is presented. Results: 85-year-old male with a history of PD complicated with sialorrhea, constipation, levodopa-induced dyskinesia, rapid eye movement sleep behavior disorder, neurocognitive impairment, and PD psychosis who follows up with the Emory Brain Health Center. Medications include carbidopa-levodopa, clozapine, donepezil, and rasagiline. He reports distressing delusional jealousy and egodystonic visual hallucinations. He has tried multiple antipsychotics with insufficient response. He has been on clozapine for nearly 10 years with moderate efficacy. His current dose is 62.5mg daily. Absolute neutrophil counts have been normal, but he developed thrombocytopenia. Though he had normal platelets at baseline, his platelets fell to 134,000/μL and have gradually decreased within a year, most recently to 82,000/μL. He has been asymptomatic without easy bleeding or bruising. His clozapine dose has remained the same with ongoing laboratory monitoring. He follows with his primary care doctor and was referred to hematology. Conclusions: The literature on clozapine-induced thrombocytopenia is limited. Incidence is variable and ranges from 0.083%-8.2% in larger samples. Most cases occur within the first 18 weeks of clozapine initiation. It is generally transient and self-resolving, usually lasting under 13 weeks, though a case report noted it to last up to 40 months. It is imperative to have hematologic baselines. The manufacturer recommends discontinuing the drug when platelet counts fall below 100,000/μL, resuming therapy when they return to normal, and permanently discontinuing if this reoccurs. UK guidelines recommend that if platelet counts fall below 50,000/μL, clozapine should be discontinued, with monitoring frequency increased. Therapy can be resumed once platelet counts normalize and if asymptomatic. Special caution must be taken in geriatric patients who are prone to fall and balance-related injuries.