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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Brand Name
Promethazine Hydrochloride
Generic Name
Promethazine Hydrochloride
Active Ingredient
PromethazineCategory
Other
Salt Form
Hydrochloride
Variants
114
References used for this content
This page is for informational purposes only and does not replace medical advice. Before using any prescription or over-the-counter medication for Promethazine Hydrochloride, you must consult a qualified healthcare professional.
| 25 mg/mL | INJECTION | INTRAMUSCULAR, INTRAVENOUS | 0641-6208 |
| 50 mg/1 | TABLET | ORAL | 85766-110 |
| 6.25 mg/5mL | SYRUP | ORAL | 27808-051 |
| 6.25 mg/5mL | SOLUTION | ORAL | 29033-500 |
| 50 mg/1 | TABLET | ORAL | 43063-876 |
| 25 mg/1 | TABLET | ORAL | 50090-4750 |
| 12.5 mg/1 | TABLET | ORAL | 50090-6216 |
| 25 mg/1 | TABLET | ORAL | 51655-085 |
| 12.5 mg/1 | TABLET | ORAL | 53746-745 |
+ 38 more variants
Detailed information about Promethazine Hydrochloride
Promethazine is a versatile phenothiazine derivative used primarily as an antihistamine, antiemetic, and sedative. It works by blocking H1 receptors and providing significant anticholinergic effects for various clinical conditions.
The dosage of promethazine is highly individualized based on the condition being treated and the patient's response to the medication. Healthcare providers typically follow these general guidelines:
CRITICAL WARNING: Promethazine must NEVER be used in children under the age of 2 years due to the risk of fatal respiratory depression (slowed breathing).
For children 2 years of age and older, the dose is usually calculated based on body weight. Healthcare providers typically use the following ranges:
While specific dosage adjustment guidelines for renal (kidney) impairment are not strictly defined in the manufacturer's labeling, promethazine should be used with caution. Since metabolites are excreted renally, patients with severe kidney disease may require lower doses or longer intervals between doses to prevent accumulation.
Because promethazine is extensively metabolized by the liver, patients with hepatic (liver) impairment are at a higher risk of toxicity. Healthcare providers may recommend a lower starting dose and frequent monitoring of liver function tests.
Geriatric patients are often more sensitive to the sedative and anticholinergic effects of promethazine (e.g., confusion, dizziness, dry mouth, urinary retention). The 'Beers Criteria' for potentially inappropriate medication use in older adults suggests avoiding promethazine if possible. If used, healthcare providers typically start at the lowest possible dose.
If you miss a dose, take it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and return to your regular dosing schedule. Do not 'double up' or take extra medicine to make up for a missed dose, as this increases the risk of severe sedation and respiratory depression.
Signs of a promethazine overdose can be life-threatening and include severe drowsiness, loss of consciousness, dilated pupils, flushing, rapid heart rate (tachycardia), muscle tremors, or seizures. In children, an overdose may paradoxically cause excitation or hallucinations before progressing to CNS depression. If an overdose is suspected, contact emergency services (911) or a poison control center immediately.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.
The most frequently reported side effect of promethazine is significant somnolence (drowsiness). This effect is often dose-dependent and can interfere with the ability to perform tasks requiring mental alertness. Other common effects include:
Promethazine is a potent medication that requires careful clinical oversight. Patients must be aware that this drug can significantly impair mental and physical abilities. It is vital to avoid activities requiring high levels of alertness until you know how the medication affects you. Furthermore, promethazine can mask the symptoms of other conditions; for example, its antiemetic effect may hide the signs of an intestinal obstruction or a brain tumor.
1. Pediatric Warning: Promethazine Hydrochloride is contraindicated for use in pediatric patients less than two years of age. There is a high risk of fatal respiratory depression in this population. In children 2 years and older, the lowest effective dose should be used, and concurrent use of other drugs with respiratory depressant effects should be avoided.
2. Severe Tissue Injury: When administered by injection, promethazine can cause severe damage to the skin and underlying tissues. If you feel any burning or pain at the injection site, notify medical staff immediately. Healthcare providers are advised that deep intramuscular injection is the safest route.
Certain medications must never be used in conjunction with promethazine due to the risk of fatal complications:
There are several scenarios where promethazine must NEVER be used because the risks far outweigh any potential benefits:
Promethazine is classified under FDA Pregnancy Category C. This means that animal reproduction studies have shown an adverse effect on the fetus, and there are no adequate and well-controlled studies in humans. However, the potential benefits may warrant use of the drug in pregnant women despite potential risks.
It is not known whether promethazine is excreted in human milk. However, because many drugs are excreted in human milk and because of the potential for serious adverse reactions in nursing infants (especially the risk of respiratory depression and sedation), a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. Nursing infants may also be more sensitive to the antihistaminic effects, potentially leading to irritability or sleepiness.
Promethazine is a phenothiazine derivative that acts as a potent H1-receptor antagonist. It competes with free histamine for binding at H1-receptor sites in the GI tract, uterus, large blood vessels, and bronchial muscle. By occupying these receptors, it prevents the physiological effects of histamine release.
Its antiemetic effect is thought to result from its action on the chemoreceptor trigger zone (CTZ) in the medulla, where it likely blocks dopaminergic and muscarinic signaling. Its sedative properties are a result of its high affinity for H1 receptors in the brain and its interference with the ascending reticular activating system.
Common questions about Promethazine Hydrochloride
Promethazine is primarily used to treat symptoms of allergies, such as itching, runny nose, and hives, by blocking histamine in the body. It is also a very effective medication for preventing and treating nausea and vomiting, especially after surgery or due to motion sickness. Additionally, healthcare providers use it as a sedative to help patients relax before medical procedures or to manage pain after surgery. Because it causes significant drowsiness, it is sometimes used as a sleep aid, though this is usually for short-term situations. It is also used to treat the symptoms of the common cold, though it does not cure the virus itself.
The most common side effect of promethazine is profound drowsiness, which affects a large majority of patients. Many people also experience dry mouth, blurred vision, and a feeling of dizziness or lightheadedness when they stand up too quickly. Some patients may feel confused or 'foggy,' particularly older adults who are more sensitive to the drug's effects. Constipation and a dry nose or throat are also frequently reported due to the medication's anticholinergic properties. While these effects are usually manageable, they can impair your ability to drive or perform complex tasks safely.
No, you should strictly avoid drinking alcohol while taking promethazine. Alcohol is a central nervous system depressant, and when combined with promethazine, it can dangerously increase sedation and respiratory depression. This combination can lead to extreme dizziness, loss of consciousness, and a life-threatening slowing of your breathing. Even small amounts of alcohol can significantly impair your judgment and motor skills when this medication is in your system. It is best to wait until the drug is completely out of your body—usually at least 24 to 48 hours after your last dose—before consuming alcohol.
Promethazine is classified as FDA Pregnancy Category C, which means its safety has not been fully established in pregnant women. While it is sometimes used for severe nausea (morning sickness) when other treatments fail, it should only be used if the potential benefits outweigh the risks to the fetus. Using it near the time of delivery can cause issues for the newborn, such as breathing problems or impaired blood clotting. If you are pregnant or planning to become pregnant, you must discuss the risks and benefits with your healthcare provider. They may suggest safer alternatives depending on your specific needs and trimester.
The onset of promethazine depends on how it is administered. When taken by mouth (tablets or syrup) or rectally, it typically begins to work within 20 minutes, with the full effect occurring about 2 to 3 hours later. If given by intramuscular injection, the onset is also around 20 minutes. Intravenous (IV) administration works almost immediately, which is why it is often used in hospital settings for acute nausea. The effects of a single dose generally last between 4 and 6 hours, although some people may feel sleepy for up to 12 hours after taking it.
If you have only been taking promethazine occasionally for motion sickness or a mild allergic reaction, you can usually stop taking it without any issues. However, if you have been taking it daily for a long period, stopping suddenly might cause 'rebound' symptoms like nausea, dizziness, or a return of your original symptoms. It is not considered an addictive drug in the same way as opioids, but your body can become accustomed to its effects. Always consult your healthcare provider before stopping a long-term prescription. They may recommend gradually reducing your dose over a few days to ensure your body adjusts comfortably.
If you miss a dose of promethazine, take it as soon as you remember, unless it is almost time for your next scheduled dose. In that case, skip the missed dose and continue with your regular schedule. Never take two doses at once to make up for a missed one, as this significantly increases the risk of severe side effects like extreme drowsiness or slowed breathing. If you are taking it 'as needed' for nausea or allergies, simply take the next dose when you feel you need it, ensuring you don't exceed the maximum daily limit. If you are unsure about what to do, contact your pharmacist for guidance.
Weight gain is not a commonly reported side effect of short-term promethazine use. However, because it is a phenothiazine derivative, long-term use could theoretically lead to metabolic changes or increased appetite in some individuals, similar to other drugs in its class. Additionally, the significant sedation it causes might lead to decreased physical activity, which could contribute to weight gain over time. If you notice an unusual increase in weight while taking this medication, discuss it with your doctor. They can help determine if the medication is the cause or if other factors are involved.
Promethazine has many potential drug interactions, some of which are very serious. It should not be taken with other medications that cause sleepiness, such as opioid pain relievers, anxiety medications (benzodiazepines), or other antihistamines, without strict medical supervision. It can also interact with certain antidepressants, blood pressure medications, and medications for Parkinson's disease. Even over-the-counter herbal supplements like St. John's Wort or Valerian can increase its sedative effects. Always provide your healthcare provider with a complete list of all medications and supplements you are taking to avoid dangerous interactions.
Yes, promethazine hydrochloride is widely available as a generic medication in many forms, including tablets, oral solutions, and injectable forms. The generic version is typically much more affordable than brand-name versions like Phenergan (which is no longer widely marketed under that brand name in the U.S.). Generic promethazine is required by the FDA to have the same active ingredient, strength, and effectiveness as the original brand-name drug. You can find generic promethazine at most retail pharmacies with a valid prescription from your healthcare provider.
Other drugs with the same active ingredient (Promethazine)
> Warning: Stop taking Promethazine and call your doctor immediately if you experience any of these.
With prolonged use, patients may develop a tolerance to the sedative effects, requiring higher doses for the same result. Chronic use is also associated with a higher risk of dental issues due to persistent dry mouth and potential cognitive decline in geriatric populations. There is also a risk of developing 'tardive dyskinesia,' a movement disorder that can become irreversible if the medication is not discontinued promptly upon the first signs of rhythmic involuntary movements.
Promethazine carries two significant FDA Black Box Warnings:
Report any unusual symptoms to your healthcare provider.
For patients on long-term promethazine therapy, healthcare providers may require regular monitoring, including:
Because of the high incidence of profound drowsiness and dizziness, patients are strictly advised against driving, operating heavy machinery, or engaging in dangerous activities for at least 24 hours after taking promethazine, or until they are certain the medication does not impair their coordination and judgment.
Alcohol consumption is strictly contraindicated while taking promethazine. Alcohol significantly enhances the sedative effects of the drug and increases the risk of life-threatening respiratory depression and profound CNS impairment.
While promethazine is not typically associated with a physical withdrawal syndrome like opioids, abrupt discontinuation after long-term high-dose use may cause 'rebound' symptoms such as nausea, vomiting, and dizziness. Healthcare providers generally recommend a gradual tapering of the dose if the patient has been taking the medication daily for an extended period.
> Important: Discuss all your medical conditions with your healthcare provider before starting Promethazine.
Promethazine can interfere with several diagnostic tests:
For each major interaction, the mechanism usually involves either pharmacodynamic synergy (both drugs doing the same thing to the body, like depressing the CNS) or pharmacokinetic interference (one drug changing how the liver processes the other). Management usually involves dose reduction or choosing an alternative medication.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.
Healthcare providers must perform a careful risk-benefit analysis in the following conditions:
Patients who have had a severe reaction to other phenothiazine antipsychotics (e.g., Compazine, Thorazine) are at a high risk of having a similar reaction to promethazine. This is because these drugs share a similar chemical backbone. Symptoms of cross-sensitivity can range from a mild rash to severe movement disorders or anaphylaxis.
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Promethazine.
As established, the most critical pediatric consideration is the contraindication for those under 2 years of age. For children 2 and older, healthcare providers must use the lowest effective dose. There is a higher incidence of 'paradoxical excitation' in children, where the drug causes them to become hyperactive or agitated rather than sleepy. It should be used with caution in children with a family history of Sudden Infant Death Syndrome (SIDS) or sleep apnea.
Clinical studies of promethazine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. However, in practice, elderly patients are known to have a higher risk of:
In patients with significant kidney disease, the clearance of promethazine metabolites may be reduced. While not explicitly dialyzable, the drug's high protein binding suggests that standard hemodialysis is unlikely to remove significant amounts of the drug in the event of an overdose.
Since the liver is the primary site of metabolism, patients with cirrhosis or hepatitis are at a significant risk for 'drug-induced coma' or severe toxicity. Dose reductions of 50% or more are often necessary, and use in severe (Child-Pugh Class C) hepatic impairment is generally discouraged.
> Important: Special populations require individualized medical assessment.
| Parameter | Value |
|---|---|
| Bioavailability | ~25% (Extensive first-pass metabolism) |
| Protein Binding | 76% - 93% |
| Half-life | 10 - 19 hours |
| Tmax | 2 - 3 hours (Oral) |
| Metabolism | Hepatic (CYP2D6, CYP2B6) |
| Excretion | Renal (~70%), Fecal (~10%) |
Promethazine is a first-generation antihistamine and a phenothiazine derivative. It is therapeutically categorized as an antiemetic, sedative, and antivertigo agent. It is chemically related to antipsychotics like chlorpromazine but has much weaker dopamine-blocking activity at standard doses.