Nursing care
Promethazine: what to check before you give it
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated September 2026
Short answer
Promethazine is a phenothiazine antihistamine used for nausea, vomiting, allergic reactions, and sedation. The defining nursing consideration is IV extravasation risk: it can cause severe tissue necrosis if it leaks from the vein, so deep intramuscular injection is preferred, and it is contraindicated in children under two years of age due to respiratory depression risk.
What it does and why it is prescribed
Promethazine is a first-generation phenothiazine with strong antihistamine, antiemetic, and sedative properties. It blocks H1 histamine receptors and also has anticholinergic and antidopaminergic activity, which is why it works against nausea and vomiting through the chemoreceptor trigger zone as well as through histamine pathways.
You'll see it prescribed for allergic reactions, motion sickness, preoperative sedation, and postoperative or chemotherapy-related nausea. It's also used as an adjunct for pain control in some settings, where its sedative and antihistamine properties potentiate opioids, though this combination increases the risk of respiratory depression and needs closer monitoring.
Nursing considerations before giving it
The route matters more with promethazine than with most drugs on the ward. IV administration carries a serious risk of extravasation, and if the drug leaks into surrounding tissue it can cause severe damage, from blistering to full-thickness necrosis requiring surgical debridement or amputation in extreme cases. Deep intramuscular injection into a large muscle is the preferred route specifically to avoid this.
If IV administration is unavoidable, confirm the line is patent, use a large vein, dilute per protocol, and infuse slowly while watching the site continuously. Never give it subcutaneously. Confirm the patient's age before administering: promethazine is contraindicated in children under two years of age because of the risk of fatal respiratory depression, and the FDA carries a black box warning on this point.
What to monitor
Monitor respiratory rate and depth closely, especially in older adults, patients on other CNS depressants, and anyone with pre-existing respiratory compromise. Sedation level should be reassessed after each dose, since oversedation is the most common reason a dose gets held.
Watch the IV site throughout administration and for a period afterward, checking for pain, swelling, redness, or blanching, which can signal extravasation before it becomes severe. Blood pressure is worth checking too, since promethazine can cause hypotension, particularly in volume-depleted or older patients.
Side effects versus adverse effects
Common side effects include drowsiness, dry mouth, blurred vision, and mild dizziness, all consequences of its anticholinergic and antihistamine activity. These are expected and usually don't require the dose to be held unless they're significant enough to affect safety.
Adverse effects are a different tier: respiratory depression, extrapyramidal symptoms such as dystonia or akathisia, neuroleptic malignant syndrome in rare cases, and the tissue necrosis that follows extravasation. Any of these warrants stopping the drug and notifying the prescriber, rather than simply noting it and continuing.
What to hold for and when to call
Hold the dose and call the provider for respiratory rate below the threshold set by unit protocol, typically under 10 to 12 breaths per minute, for significant sedation that impairs the patient's ability to protect their airway, or for any sign of extravasation at an IV site. Hold for suspected extrapyramidal symptoms, including tremor, rigidity, or involuntary movements.
Call immediately if you suspect neuroleptic malignant syndrome, which presents with high fever, muscle rigidity, altered mental status, and autonomic instability, as this is a medical emergency. Also flag any child under two years for whom the drug has been ordered, since that order should not be administered.
Patient teaching
Tell the patient that drowsiness is expected and that they shouldn't drive or operate machinery until they know how the drug affects them. Warn against combining it with alcohol or other sedating medications, since the combined CNS depression can be dangerous.
If the drug was given IV, explain the importance of reporting any burning, pain, or swelling at the injection site immediately, since early reporting limits the extent of tissue damage if extravasation has occurred. Advise on sun sensitivity, since phenothiazines can cause photosensitivity, and recommend sunscreen and protective clothing during treatment.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our pharmacology practice questions are the closest set to what this page covers.
One question from the pharmacology set
A client with heart failure is started on furosemide 40 mg PO daily. Which findings should the nurse report to the provider before administering the next dose? Select all that apply.
Rationale
Furosemide is a loop diuretic, so the two things you are watching are potassium and kidney function. A potassium of 2.9 mEq/L is below the 3.5–5.0 reference range and puts the client at risk for dysrhythmia — hold and report. Muscle cramps with palpitations are the clinical face of that same hypokalemia, so they are reported together, not separately. A creatinine that doubles signals the diuresis has outrun renal perfusion. A blood pressure of 132/78 and a 1 kg loss are the expected response to the drug working, not reasons to hold it.
Answer: A, D, E
Common questions
Why is promethazine given IM instead of IV when possible?
IV administration carries a documented risk of severe tissue injury if the drug extravasates, ranging from blistering to necrosis requiring surgical intervention. Deep intramuscular injection avoids that risk, which is why many facilities restrict IV use or require it only through a running, well-secured line with close monitoring.
Why is promethazine contraindicated under age two?
It carries a black box warning for fatal respiratory depression in children under two years old. Even above that age, it's used cautiously and at the lowest effective dose in the paediatric population.
What should I do if I suspect promethazine has extravasated?
Stop the infusion immediately, leave the cannula in place initially to aspirate any residual drug, and notify the provider and follow facility protocol for extravasation management, which may include specific antidotes or measures depending on the extent. Document the site, the estimated volume, and the time of onset.
Can promethazine be given subcutaneously?
No. Subcutaneous injection is not recommended because it increases the risk of tissue damage similar to that seen with extravasation. Deep intramuscular injection into a large muscle is the correct alternative when the IV route isn't preferred.
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