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Correspondence to Dr David Croitoru; [email protected]
Background
Cetirizine is a second-generation H1-inverse agonist selective for peripheral H1 receptors, primarily used in the treatment of allergic rhinitis and chronic idiopathic urticaria.1 2 Off-label, it is commonly used for a number of pruritic dermatological conditions as part of treatment and symptom management. Unlike first-generation antihistamines, second-generations have minimal anticholinergic activity; however, psychomotor impairment and central nervous system (CNS) effects have been described, including somnolence and paradoxical excitability.1–3 There have been multiple cases of first-generation antihistamine-induced psychosis with promethazine and other first-generation antihistamines in young and healthy populations.4–6
Case presentation
A man in his late 20s with no psychiatric history was brought by his mother to the emergency department in September 2020 due to two discrete episodes of unusual aggressive behaviour, agitation, paranoia, short-term memory loss and auditory and visual hallucinations, which began in the context of new cetirizine use for a pruritic cutaneous eruption. He presented to his family physician 2 weeks after onset of rash and was prescribed 20 mg cetirizine one time per day. He took cetirizine for 2 days before the onset of visual and auditory hallucinations of family members and paranoid delusions about an unidentified ‘family’ in his backyard targeting him. No other routine medications were taken. These symptoms resolved with cetirizine cessation; however, given the persistence of his rash and pruritus, he took a third dose on day 5, resulting in acute recurrence of his psychotic symptoms and aggressive behaviour. He was admitted to psychiatry for diagnostic clarification and stabilisation. He had a past medical history of treated primary syphilis and recurrent herpes simplex labialis. On review of systems by collateral and retrospectively since discharge, he had suffered from self-limited coryza, pharyngitis and subjective fever (chills, rigours), as well as a herpetic lesion in the week prior to the onset of rash, but no other systemic symptoms. He also retrospectively reported involvment in a motor vehicle collison (MVC) 4 months prior that led to physical injuries (brachial plexopathy) and has been experiencing depressive symptoms ever since.
On mental status examination, the patient appeared disorganised in thought process, responding non-linearly to questions and endorsing paranoia and persecutory delusions about his family members. He reported visual hallucinations of an unidentified ‘family’...