Promethazine

Common Uses

Promethazine is primarily used to manage various conditions involving the histamine response, the central nervous system, and the digestive system. Its applications include:

• Allergic Reactions: It helps relieve symptoms such as sneezing, runny nose, itchy or watery eyes, and skin conditions like hives or rashes. It may also be used as an additional treatment for severe allergic reactions (anaphylaxis) alongside other emergency medications.
• Nausea and Vomiting: It is frequently used to prevent and control nausea and vomiting, particularly those occurring after surgery.
• Motion Sickness: It is effective in preventing and treating the symptoms of motion sickness.
• Sedation: Promethazine is used to help patients feel relaxed or sleepy before and after surgical procedures or during labor.
• Pain Relief: It may be used in combination with other pain medications to help manage pain after surgery.

Mechanism of Action

Promethazine belongs to a class of medications known as phenothiazines. It works in several different ways to address various medical conditions:

• Antihistamine effects: It works by competing with histamine for H1-receptor sites in the body. By blocking these receptors, it prevents histamine from causing common allergy symptoms such as itching, sneezing, and a runny nose. It does not stop the body from releasing histamine, but it changes how the body responds to it.
• Antiemetic effects: To treat nausea and vomiting, promethazine acts on the chemoreceptor trigger zone in the brain. This helps suppress the signals that lead to the feeling of being sick.
• Motion sickness prevention: It affects the parts of the brain and the inner ear that control balance and motion, which helps prevent the dizziness and nausea caused by travel.
• Sedative effects: Promethazine has significant sedative properties because it affects the central nervous system. This makes it useful for helping patients relax or sleep before and after surgery.

In addition to these actions, promethazine also has anticholinergic properties, which can contribute to its overall effects in the body.

Common Side Effects

Many people experience mild side effects when taking promethazine. These often include:

• Drowsiness or dizziness
• Dry mouth, nose, or throat
• Blurred vision
• Nausea or vomiting
• Constipation
• Ringing in the ears
• Loss of coordination

Serious Side Effects

Contact a healthcare provider immediately if you experience any of the following serious symptoms:

• Breathing problems: Slow, shallow, or labored breathing.
• Movement disorders: Uncontrollable movements of the face, tongue, or limbs, as well as tremors or muscle stiffness.
• Mental changes: Confusion, hallucinations, or extreme nervousness.
• Heart issues: Fast, slow, or irregular heartbeat.
• Jaundice: Yellowing of the skin or the whites of the eyes.
• Seizures
• Allergic reactions: Severe rash, hives, or swelling of the face, lips, or throat.
• Fainting

Boxed Warnings

Respiratory Depression in Children: Promethazine should not be used in pediatric patients younger than 2 years of age because of the risk of fatal respiratory depression (severely slowed breathing). Cases of respiratory depression and death have been reported in this age group even at therapeutic doses. Caution is required when administering this medication to children 2 years of age and older.

Severe Tissue Injury: When administered by injection, promethazine can cause severe chemical irritation and tissue damage. If the medication is accidentally injected into an artery or under the skin rather than into a muscle or vein, it can lead to gangrene, tissue death, and may require surgical intervention or amputation. Deep intramuscular injection is the preferred method of administration.

General Precautions

• Central Nervous System Effects: This medication may cause significant drowsiness and impair the mental or physical abilities required for tasks such as driving or operating machinery. These effects are increased when combined with alcohol, or other central nervous system depressants like opioids or sedatives.
• Neuroleptic Malignant Syndrome (NMS): A potentially fatal condition called NMS has been reported with promethazine use. Symptoms may include high fever, muscle rigidity, altered mental status, and irregular pulse or blood pressure.
• Seizure Risk: Promethazine may lower the seizure threshold. It should be used with caution in individuals with a history of seizures or those taking other medications that may also lower the seizure threshold.
• Involuntary Movements: Use may lead to extrapyramidal symptoms, such as involuntary muscle movements or restlessness. There is also a risk of tardive dyskinesia, a condition involving repetitive, involuntary movements, particularly with long-term use.
• Other Medical Conditions: Caution is advised for individuals with narrow-angle glaucoma, bone marrow depression, enlarged prostate, bladder neck obstruction, or severe liver or heart disease.

Contraindications

Promethazine is contraindicated in patients who are in a comatose state or who have a known hypersensitivity to promethazine or other phenothiazines. It should not be used in patients with lower respiratory tract symptoms, including asthma.

Pregnancy

The safety of promethazine during pregnancy has not been extensively studied in humans. It is generally recommended that this medication be used during pregnancy only if clearly needed and prescribed by a healthcare provider. Animal reproduction studies have not been conducted, and it is unknown if the drug can cause fetal harm or affect reproductive capacity.

When used during labor and delivery, either alone or with narcotic pain medications, limited data suggest that promethazine does not significantly affect the duration of labor or increase the risk that a newborn will require resuscitation. However, pregnant individuals should discuss the potential risks and benefits with their clinician.

Breastfeeding

It is not known whether promethazine passes into human breast milk. Because many drugs are excreted in milk and there is a potential for serious adverse reactions in nursing infants, a decision must be made whether to stop nursing or stop the medication. Healthcare providers will consider the importance of the drug to the mother when making this recommendation. Potential concerns for the nursing infant include excessive drowsiness or other side effects.

Oral Formulations

Promethazine is commonly administered by mouth. The available oral forms include:

• Tablets
• Syrup (also referred to as an oral solution)

Rectal Formulations

For patients who are unable to swallow medication or are experiencing severe nausea and vomiting, promethazine is available as:

• Suppositories

Injectable Formulations

In clinical settings, healthcare providers may administer promethazine through the following methods:

• Intramuscular injection
• Intravenous injection

FDA Approval and Indications

Promethazine is approved by the U.S. Food and Drug Administration (FDA) for several uses, including the treatment of allergic reactions, motion sickness, and nausea or vomiting. It is also used as a sedative before or after surgery and to help manage pain following medical procedures.

Boxed Warnings

The FDA has issued several boxed warnings for promethazine products:

• Pediatric Safety: Promethazine is contraindicated for use in children younger than 2 years of age because it can cause severe, potentially fatal respiratory depression (slowed breathing). Caution is advised when administering the drug to children 2 years of age and older.
• Injection Risks: For injectable forms of the drug, there is a boxed warning regarding the risk of severe tissue injury. If the medication is accidentally injected into an artery or under the skin (subcutaneously) rather than into a muscle or vein, it can cause gangrene, tissue death, and may require surgical intervention or amputation.

Regulatory Safety Communications

The FDA has required updates to the labeling of promethazine hydrochloride injection products to emphasize the risks of severe tissue injury. Healthcare providers are instructed to follow specific administration guidelines, such as preferring deep intramuscular injection and limiting the concentration and rate of intravenous administration to reduce these risks.

How Promethazine Treats Cough

Promethazine is used to provide temporary relief from coughs and upper respiratory symptoms associated with the common cold or allergies. While it is an antihistamine, it is frequently combined with other active ingredients, such as dextromethorphan or codeine, to more effectively suppress coughing.

Important Safety Information

There are significant safety considerations when using promethazine for cough:

• Age Restrictions: Promethazine must not be used in children under the age of 2 due to the risk of severe, potentially fatal respiratory depression (slowed breathing).
• Pediatric Caution: For children aged 2 and older, the lowest effective dose should be used, and it should be administered with extreme caution.
• Drowsiness: This medication often causes significant drowsiness. Patients should avoid driving or operating heavy machinery until they know how the drug affects them.

Common Side Effects

When used for cough and cold symptoms, promethazine may cause:

• Dizziness or lightheadedness
• Dry mouth, nose, or throat
• Blurred vision
• Confusion or disorientation