Hydroxyzine: Uses, Dosage, Side Effects, Contraindications & Safety

Medicine Name

Hydroxyzine

Drug Class

First-generation antihistamine
(Central & Peripheral H1 receptor blocker)

H1 receptors are present in:

• Brain → Sedation, anxiety modulation
• Skin → Itching, urticaria
• Lungs → Allergic responses
• Nose → Sneezing, rhinorrhea
• Blood vessels → Vasodilation, edema

Peripheral H1 receptors are present in

• Lungs→ Allergy symptoms
• Skin
• Nose
• Blood vessels

Central H1 receptors are present in

• Brain

Brand Names

India:

Atarax, Hyzine, Hynid, Vistaril (less common)

USA

Vistaril, Atarax

UK / Europe:

Atarax

Approved By

• FDA (United States)
• CDSCO (India)

Available Strengths & Dosage Forms

• Tablet: 10 mg, 25 mg, 50 mg
• Syrup / Suspension: 10 mg / 5 ml (paediatric use)
• Injection: 25 mg / ml (IM use, hospital setting)

Purpose / Indications

Hydroxyzine is used to treat allergic conditions, anxiety, pruritus, and insomnia due to its antihistaminic, sedative, and anxiolytic properties.

Symptoms Hydroxyzine May Cure

• Itching (pruritus)
• Urticaria (hives)
• Allergic skin rashes
• Anxiety & tension
• Insomnia (short-term)
• Motion sickness
• Pre-operative sedation
• Nausea & vomiting (adjunct use)

Dosage

Adults

• Allergy / Pruritus: 25 mg 1–3 times daily
• Anxiety: 50–100 mg/day in divided doses
• Insomnia: 25–50 mg at bedtime

Children

• ≤6 years: up to 50 mg/day (divided doses)
• >6 years: up to 100 mg/day (divided doses)

⚠️ Dose should be individualized and prescribed by a physicia.

Mechanism of Action of hydroxyzine

Hydroxyzine competitively blocks H1 histamine receptors in both the central nervous system and peripheral tissues.

It also:

• Suppresses activity in subcortical regions of the brain
• Produces sedation and anxiolysis
• Has mild anticholinergic and antiemetic effects

Detailed Explanation

Hydroxyzine is a first-generation antihistamine that easily crosses the blood–brain barrier.

Step-by-step explanation:

1. During allergic reactions, histamine is released from mast cells.
2. Histamine binds to H1 receptors, causing:
   • Vasodilation
   • Increased capillary permeability
   • Itching, redness, swelling
3. Hydroxyzine blocks H1 receptors → prevents histamine action
4. Because it enters the brain:
   • Causes sedation
   • Reduces anxiety
   • Induces sleep

Results:

• Itching & rashes are reduced
• Anxiety is relieved
• Sleep is promoted

Additional pharmacological points:

• Crosses the blood–brain barrier
• Causes sedation
• Has anticholinergic activity
• Hydroxyzine is metabolized in the liver to cetirizine, which is its major active metabolite.
  [yes you read it right!]

What is histamine & anti histamine, receptors invloved, anti histamine generations?

Summary statement:

Hydroxyzine blocks central and peripheral H1 receptors, effectively treating allergic symptoms while also providing sedative and anxiolytic effects, making it useful in pruritus, anxiety, and insomnia.

Side Effects

Common Side Effects

• Drowsiness
• Dry mouth
• Sedation
• Dizziness

Less Common / Rare

• Blurred vision
• Constipation
• Urinary retention
• Confusion (elderly)

Contraindications

• Known hypersensitivity to hydroxyzine
• Early pregnancy
• Severe CNS depression
• Patients with prolonged QT interval (caution)

Dosage Frequency

• Usually 2–3 times daily
• Often prescribed at night due to sedative effect

In patients where pain or inflammation is a dominant symptom, antihistamines like cetirizine may be used along with other drug classes such as analgesics or NSAIDs, depending on the clinical condition.

Use in Special Populations

Hydroxyzine in Pregnancy

• Contraindicated (Category C / avoid)
  Especially first trimester
  Use only if benefits outweigh risks

A drug is placed in Category B when animal reproductive studies have not shown a risk to the fetus, but there are no adequate and well-controlled studies in pregnant women. That means:

• Animal studies: Did not show evidence that the medicine causes fetal harm.
• Human data: Not enough good studies yet to confirm whether it’s absolutely safe or risky.

So Category B suggests the medicine may be safer than other categories, but this is not a guarantee—doctors still use it only if benefits outweigh potential risks.

Lactation

• Not recommended
• May cause sedation in infant

Elderly

• Increased risk of confusion & sedation
• Start with lowest possible dose

Drug Interactions

• Alcohol (↑ sedation)
• Benzodiazepines
• Opioids
• Other CNS depressants
• Anticholinergic drugs

Storage Instructions

• Store at room temperature
• Protect from moisture & heat
• Keep out of reach of children

Disclaimer

This information is for educational purposes only and should not be used as a substitute for professional medical advice. Always consult a doctor or pharmacist before using any medication.

Extras

• Hydroxyzine is NOT suitable for daytime allergy relief
• Cetirizine is its active metabolite
• Preferred when itching + anxiety / sleep disturbance coexist

Key points / Revision

Point	Details
Drug Name	Hydroxyzine
Drug Class	First-generation antihistamine
Receptor Blocked	H1 (Central + Peripheral)
Blood–Brain Barrier	Crosses BBB
Sedation	High (sedating)
Generation	First generation
Main Uses	Allergy, pruritus, urticaria, anxiety, insomnia
Special Uses	Pre-operative sedation, motion sickness
Mechanism of Action	Blocks H1 receptors → reduces histamine effects + CNS sedation
Metabolism	Metabolized in liver
Active Metabolite	Cetirizine
Anticholinergic Effect	Mild
Daytime Use	Not preferred
Night Use	Preferred
Dosage (Adult)	25–50 mg (1–3 times daily)
Dosage (Children)	Up to 50–100 mg/day (age dependent)
Common Side Effects	Drowsiness, dry mouth, dizziness
Serious Side Effects	Confusion (elderly), QT prolongation (rare)
Pregnancy	Avoid (especially 1st trimester)
Lactation	Not recommended
Elderly	Use low dose
Drug Interactions	Alcohol, benzodiazepines, opioids
Best For	Allergy + itching + anxiety/sleep issues
Not Ideal For	Daytime allergy relief