Not All Antihistamines Are Created Equal: Alimemazine As A Cause Of Drug Induced Parkinsonism

Abstract

Abstract Background A 67year old female presented to a Movement Disorder Service for assessment of tremor. She had a history of presbycusis, dermatitis herpetiformis, bronchiectasis, osteoporosis and stage A chronic lymphocytic leukaemia. History elucidated hypophonia, somniloquy, REM-sleep behaviour disorder, bruxism, presence hallucinosis, insidious bradykinesia and of titubation of increasing prevalence and amplitude over 20years. Examination demonstrated cognitive impairment (Montreal Cognitive Assessment 12+1/30) in the domains of visuospatial function, executive thinking, naming, attention, language, abstraction and anterograde recall. Luria test was 0/6. Also found was: micrographia, left exotropia, reduced left arm and leg swing, kinetic tremor asymmetry, decrement of amplitude and frequency of rapid repetitive movements asymmetrically, mandibular and lingual tremor, positive Kinnier-Wilson test and orthostatic deterioration in yes-yes titubation. Drg history identified use of Alimemazine 10mg for insomnia for approximately 20years. Methods Modified Simpson Angus Scale score was 6 indicating a clinically significant degree of extrapyramidal side effects. Unified Parkinson’s Disease Rating Scale part III was 17. Results Functional dopamine uptake imaging did not indicate a parkinsonian syndrome. Drg induced parkinsonism was diagnosed. 0.0097% of the Northern Ireland population were prescribed Alimemazine in 2022 for non-dermatological reasons, representing 73.49% of all dispensed preparations. In the first financial quarter of 2024 in Northern Ireland, all dispensed prescriptions cost £218,395. Conclusion Not all antihistamines are created equal. Alimemazine is an older phenothiazine derivative antihistamine with central sedative effects equivalent to Chlorpromazine but without anti-adrenaline action. It is rarely prescribed and easily overlooked as “just another antihistamine”. It is commonly prescribed by dermatologists for urticaria. It has substantial pharmacoeconomic implications given its cost disparity with other antihistamines. Extrapyramidal features of tremor, akinesia and hypertonicity are more common in older people; usually developing within weeks or months of commencement. Stopping the drug is the first-line intervention. Resolution of symptoms is not guaranteed.