The H 501 pill is a prescription medication containing Hydroxyzine Hydrochloride 25 mg. Manufactured by Avet Pharmaceuticals (formerly Heritage Pharmaceuticals), it belongs to the class of first-generation receptor antihistamines.
Unlike over the counter antihistamines primarily used for seasonal allergies, hydroxyzine possesses significant central nervous system (CNS) effects and is frequently prescribed for anxiety, generalized itching (pruritus), hives (urticaria), and pre-operative sedation.
Pill Identification
Attribute Details
- Active Ingredient – Hydroxyzine Hydrochloride (25 mg)
- Imprint Code – H 501
- Color – White
- Shape – Round
- Form – Film-coated Oral Tablet
- Manufacturer – Avet Pharmaceuticals / Heritage Pharmaceuticals
- Brand Equivalence – Generic equivalent to Atarax (discontinued brand name)
- Drug Class – First-Generation Antihistamine / Anxiolytic / Sedative |
Mechanism of Action
Hydroxyzine functions through multiple central and peripheral neurochemical pathways:
- Peripheral & Central Receptor Antagonism: Hydroxyzine competes with free histamine for receptor sites on effector cells. By blocking histamine in the skin and respiratory tract, it eliminates itching, flare reactions, and hives.
- Serotonergic Receptor Antagonism: Unlike non-sedating antihistamines, hydroxyzine rapidly crosses the blood-brain barrier. It acts as an antagonist at serotonin receptors in the brain, contributing to its distinct anxiolytic (anti-anxiety) action. This reduces nervous tension without causing chemical dependence or addiction risk associated with benzodiazepines or opioids.
- Subcortical CNS Suppression: Hydroxyzine suppresses activity in key regions of the subcortical central nervous system, including the limbic system and reticular formation. This results in calming, sedating, and antiemetic (anti-nausea) effects.
Indications & Standard Dosage
Hydroxyzine hydrochloride is FDA-approved for short-term clinical management:
Adult Dosage Guidelines
- Generalized Anxiety & Tension:
- Typical Dose: 50 mg to 100 mg taken orally 4 times daily (or as needed).
- Maximum Daily Dose: Up to 400 mg/day. (Intended for short-term use, typically up to 4 months).
- Pruritus (Itching) & Chronic Hives:
- Typical Dose: 25 mg taken orally 3 to 4 times daily.
- Sedation (Pre- and Post-Operative):
- Typical Dose: 50 mg to 100 mg taken orally as a single dose prior to or following surgery.
Pediatric Dosage Guidelines
- Children 6 Years and Older: 50 mg to 100 mg per day divided into 3 to 4 doses.
- Children Under 6 Years: 50 mg per day divided into 2 to 4 smaller doses.
Side Effects
Because hydroxyzine affects central histamine, serotonin, and cholinergic receptors, adverse reactions can occur:
Most Common Side Effects
- Drowsiness and Somnolence: Significant daytime sedation or tiredness (often diminishes after a few days of consistent therapy).
- Dry Mouth (Xerostomia): Caused by mild anticholinergic effects.
- Dizziness & Headaches: Lightheadedness or mild mental grogginess.
Less Common / Rare Side Effects
- Motor Control Issues: Involuntary motor activity, including mild tremors or shakiness at higher doses.
- Gastrointestinal Distress: Nausea or constipation.
- Rare Allergic Skin Reactions: Acute Generalized Exanthematous Pustulosis (AGEP) – a rare skin condition marked by sudden fever and small non-follicular pustules. Discontinue immediately if a new skin rash appears.
Major Warnings & Precautions
Cardiac Risk: QT Prolongation & Torsade de Pointes
Hydroxyzine carries an explicit warning regarding the potential to prolong the cardiac QT interval on an electrocardiogram (ECG), which can lead to life-threatening ventricular arrhythmias such as Torsade de Pointes.
- Contraindication: Do not use if you have a history of congenital long QT syndrome, severe electrolyte imbalances (e.g., hypokalemia), uncompensated heart failure, or are taking other QT-prolonging drugs (such as amiodarone, macrolide antibiotics, or certain antipsychotics).
CNS Depression & Substance Interactions
- Potentiation: Hydroxyzine significantly enhances the sedating effects of alcohol, opioids, barbiturates, benzodiazepines, and sleeping medications. Concomitant use can cause severe respiratory depression, profound sedation, or coma.
- Machinery & Driving: Patients must refrain from driving, operating heavy machinery, or engaging in hazardous tasks until they are certain the medication does not impair their motor skills or alertness.
Geriatric Use Caution (Beers Criteria)
- Elderly individuals are substantially more sensitive to anticholinergic side effects (confusion, urinary retention, severe dry mouth, constipation) and cardiac risks.
- If hydroxyzine is deemed unavoidable in older adults, the recommended maximum daily dose should generally not exceed 50 mg/day.
Pregnancy & Lactation
- Pregnancy: Hydroxyzine is contraindicated during early pregnancy due to fetal risk demonstrated in animal studies.
- Breastfeeding: It is unknown whether hydroxyzine is excreted in human breast milk in significant amounts; its use is generally not recommended in nursing mothers to prevent infant sedation.