CYCLIZINE

Day 1: #cyclizine is an antihistamine with its clinical niche as an antiemetic. It bears chemical similarity to the ‘piperine’ structure found in the black pepper plant. Developed in 1947, its popularity increased after NASA selected it to treat space sickness for the Apollo missions

Day 2: UK indications for #cyclizine include nausea, vomiting, vertigo, motion sickness, labyrinthine disorders and nausea and vomiting in palliative care. Oral, i.v., i.m, s.c (palliative); Adults 50–150 mg/day, children > 1month (dose variable, injection unlicensed + tablets < 6yr). Unlicensed use for morning sickness (if persistent symptoms)

Day 3: Mode of action; emetic stimuli, such as labyrinthine disturbance and triggers to vomiting centre/chemoreceptor trigger zone, evokes histamine 1(H1) + muscarinic M1 receptors. #cyclizine is an antagonist at both H1 and muscarinic receptors. Also CNS depressant but precise antiemetic mechanism unknown

Day 4: Kinetics #cyclizine; good oral absorption, effects within 30 mins lasting 4–6 hrs. Oral t½ 20 hours, i.v 13 hours. Elimination poorly understood; clearance believed to be extra-renal. Absence of detail in drug literature possibly because of age and/or quality of supporting data