Introduction to Cyclizine
Cyclizine is an antihistamine and anti-sickness (antiemetic) medication used to prevent and treat nausea, vomiting, and dizziness. Discovered in 1947, it has a long history of use and is included on the World Health Organization's List of Essential Medicines. It is available by prescription and over-the-counter in many countries, sold under brand names like Marezine, Valoid, and Cyclivert. The medication is available as oral tablets, as a solution for injection, and can also be administered rectally. Its effectiveness in combating motion sickness was recognized by NASA, which chose it as a space antiemetic for the first crewed moon flight.
How Does Cyclizine Work?
Cyclizine's primary mechanism of action involves blocking histamine H1-receptors in the brain. The body's vomiting response is controlled by the 'vomiting center' in the medulla, which contains an area called the chemoreceptor trigger zone (CTZ). This center is rich in histamine and muscarinic cholinergic receptors. By acting as a histamine H1-receptor antagonist, cyclizine blocks signals from being sent to the vomiting center, thereby reducing the sensation of nausea.
Furthermore, cyclizine has anticholinergic (antimuscarinic) properties, meaning it also blocks muscarinic receptors. This dual action is particularly effective for motion sickness, where overstimulation of the vestibular system (the part of the inner ear responsible for balance) sends conflicting signals to the brain. By depressing labyrinth excitability and conduction in vestibular-cerebellar pathways, cyclizine helps the body maintain its sense of balance.
Primary Uses of Cyclizine
Cyclizine is a versatile medication used to manage nausea and vomiting from various causes.
Motion Sickness
One of the most common uses for cyclizine is the prevention and treatment of motion sickness. For this purpose, it is recommended to take the medication before traveling as directed by a healthcare professional or the product packaging. It works by counteracting the confusing signals between the inner ear and the brain that occur during travel.
Post-Operative Nausea and Vomiting (PONV)
Nausea and vomiting are common after surgery, often due to general anesthetics and opioid painkillers. Cyclizine can be administered, often by injection, before the end of surgery to prevent PONV. It is also effective in treating nausea that develops from opioid use.
Vertigo and Inner Ear Problems
Conditions that affect the inner ear, such as Ménière's disease or other vestibular disturbances, can cause severe dizziness, or vertigo, accompanied by nausea. Cyclizine helps alleviate these symptoms by acting on the vestibular system.
Other Causes
Cyclizine is also used to treat nausea and vomiting associated with:
- Morning sickness: While the manufacturer advises caution, it is commonly used to treat nausea and vomiting in pregnancy (hyperemesis gravidarum).
- Cancer treatment: It can relieve nausea caused by some cancer therapies like radiotherapy.
Dosage and Administration
Cyclizine comes in multiple forms, including tablets and a solution for injection. The appropriate dosage and frequency depend on the individual's age, weight, and the specific condition being treated, and should always be determined by a healthcare professional or by following the instructions on the product packaging.
- Administration: For motion sickness, administration typically occurs before travel. Oral tablets can be taken with or without food. The effects of an oral dose begin within a certain timeframe and last for several hours.
Potential Side Effects and Precautions
Like all medications, cyclizine can cause side effects. It is important to avoid alcohol while taking cyclizine, as it can significantly increase drowsiness and other side effects.
Common Side Effects:
- Drowsiness or sleepiness
- Dry mouth
- Blurred vision
- Constipation
Serious Side Effects:
While rare, some side effects require immediate medical attention:
- Allergic reactions (hives, swelling of the face, difficulty breathing)
- Fast or irregular heartbeat (tachycardia)
- Difficulty urinating or urinary retention
- Sudden eye pain or vision changes, which could indicate glaucoma
Who Should Be Cautious?
Individuals with certain medical conditions should consult a doctor before using cyclizine. These include glaucoma, liver disease, epilepsy, an enlarged prostate, or severe heart failure.
Cyclizine vs. Other Antiemetics: A Comparison
Cyclizine is one of several available antiemetic drugs. Its profile differs from others in its class and mechanism.
| Feature | Cyclizine | Promethazine | Ondansetron (Zofran) | Metoclopramide |
|---|---|---|---|---|
| Drug Class | Antihistamine, Anticholinergic | Antihistamine, Anticholinergic | 5-HT3 antagonist | Dopamine antagonist |
| Primary Use | Motion sickness, vertigo, PONV | Nausea, allergies, sedation | Chemotherapy-induced and post-operative nausea | Gastroparesis, GERD, PONV |
| Sedation Level | Moderate, less sedating than some other antihistamines | High | Low / None | Low, but can cause restlessness |
| Effect on Motion Sickness | Highly effective | Effective | Not effective | Limited effectiveness |
Conclusion
Cyclizine is a well-established and effective medication for managing nausea and vomiting stemming from a variety of causes, most notably motion sickness, post-operative recovery, and inner ear issues. Its mechanism of action targets key receptors in the brain's vomiting center and vestibular system. While generally safe and available over-the-counter in some regions, it causes drowsiness and has important interactions and contraindications to consider. Patients should always adhere to guidelines for use and consult a healthcare provider to ensure it is the right choice for their specific condition.
For more information from an authoritative source, you can visit the NHS page on Cyclizine.
