#46: promethazine (Phenergan) | Motion Sickness, Allergic Conditions, and Sedation

Promethazine, also known as Phenergan and Promethegan, is a first generation H1 histamine antagonist. It comes as a solution, suppositories, syrup, and tablets. There are a wide variety of indications for adults and children 2 years of age and older such as for allergic conditions, motion sickness, and sedation. A typical dosing range is between 25-50 mg tid-qid if PO and 6.25-25 mg IM/IV tid-qid. The max dose is 100 mg/day. Promethazine works through strong alpha adrenergic inhibition from blockade of postsynaptic mesolimbic dopaminergic receptors in the brain. It is metabolized via the CYP2D6 and CYP2B6 pathways. The onset of action is around 20 minutes with the duration of action of around 4-6 hours with a max of 12 hours. Common side effects are drowsiness, dizziness, blurred vision, and confusion. Serious side effects are seizures and QT prolongation. There is a Black Box Warning for respiratory depression and gangrene/severe tissue injury. When taken orally, take with food, water, or milk to avoid GI distress.

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