Diphenhydramine 50mg/ml Inj, 1ml
It is used to ease allergy signs.It is used to help motion sickness.It is used to treat signs like Parkinson's disease caused by other health problems.
Drug Class
Antihistamine
Pharmacologic Class
First-generation H1-receptor antagonist
Pregnancy Category
Category B
FDA Approved
Mar 1946
DEA Schedule
Not Controlled
Overview
What is this medicine?
Diphenhydramine is an antihistamine that helps relieve allergy symptoms like itching, sneezing, and runny nose. It can also help with motion sickness, certain movement disorders, and can cause drowsiness, which is why it's sometimes used for sleep.
How to Use This Medicine
Taking Your Medication Correctly
To use this medication safely and effectively, follow your doctor's instructions carefully. Read all the information provided to you and adhere to the guidelines.
This medication is administered via injection into a muscle or vein. It's essential to note that injecting this medication into the skin or subcutaneous tissue (the fatty layer under the skin) can cause tissue damage. If you have any concerns, discuss them with your doctor.
Storing and Disposing of Your Medication
If you need to store this medication at home, consult with your doctor, nurse, or pharmacist to determine the best storage method.
Missing a Dose
If you miss a dose, contact your doctor promptly to receive guidance on what to do next.
To use this medication safely and effectively, follow your doctor's instructions carefully. Read all the information provided to you and adhere to the guidelines.
This medication is administered via injection into a muscle or vein. It's essential to note that injecting this medication into the skin or subcutaneous tissue (the fatty layer under the skin) can cause tissue damage. If you have any concerns, discuss them with your doctor.
Storing and Disposing of Your Medication
If you need to store this medication at home, consult with your doctor, nurse, or pharmacist to determine the best storage method.
Missing a Dose
If you miss a dose, contact your doctor promptly to receive guidance on what to do next.
Lifestyle & Tips
- Avoid driving or operating heavy machinery until you know how this medication affects you, as it can cause significant drowsiness.
- Avoid alcohol and other CNS depressants while taking this medication, as they can increase drowsiness and other side effects.
- Inform your healthcare provider about all medications you are taking, including over-the-counter drugs and herbal supplements.
- Stay hydrated to help manage dry mouth.
Available Forms & Alternatives
Available Strengths:
- Diphenhydramine 50mg/ml Inj, 1ml
- Diphenhydramine Hcl 50mg Caps
- Diphenhydramine 50mg Capsules
- Diphenhydramine 12.5mg/5ml Elixir
- Diphenhydramine 25mg Tablets
- Diphenhydramine 25mg/10ml Liquid
- Diphenhydramine 12.5mg/5ml Liquid
- Diphenhydramine 12.5mg/5ml Liquid
- Diphenhydramine 25mg Caps
- Diphenhydramine 25mg Capsules
- Diphenhydramine 50mg/ml Inj, 1ml
- Diphenhydramine 25mg Tablets
- Diphenhydramine 25mg Capsules
Dosing & Administration
Adult Dosing
Standard Dose:
25 to 50 mg IM or IV, every 4 to 6 hours as needed
Dose Range:
25 - 100 mg
Condition-Specific Dosing:
allergic_reactions:
25 to 50 mg IM or IV, may repeat every 4 to 6 hours; max 400 mg/day
motion_sickness:
25 to 50 mg IM or IV, 30 minutes prior to exposure, then every 4 to 6 hours as needed
parkinsonism_drug_induced_extrapyramidal_symptoms:
10 to 50 mg IM or IV, 3 to 4 times daily; max 400 mg/day
Pediatric Dosing
Neonatal:
Not established (contraindicated in premature infants and neonates)
Infant:
Not established (contraindicated in premature infants and neonates)
Child:
5 mg/kg/day or 150 mg/m2/day, divided into 4 doses (IM or IV); max 300 mg/day. For allergic reactions/motion sickness: 1.25 mg/kg (or 37.5 mg/m2) IM or IV, 4 times daily, not to exceed 300 mg/day.
Adolescent:
25 to 50 mg IM or IV, every 4 to 6 hours as needed; max 400 mg/day
Dose Adjustments
Renal Impairment:
Mild:
No specific adjustment recommended, use with caution.
Moderate:
No specific adjustment recommended, use with caution.
Severe:
Consider dose reduction or extended dosing interval (e.g., every 6-8 hours) due to prolonged half-life of metabolites. Use with caution.
Dialysis:
Not significantly dialyzable. Administer after dialysis if needed. Use with caution.
Hepatic Impairment:
Mild:
No specific adjustment recommended, use with caution.
Moderate:
Consider dose reduction or extended dosing interval due to impaired metabolism. Use with caution.
Severe:
Consider significant dose reduction or extended dosing interval. Use with extreme caution or avoid.
Confidence:
Medium
Pharmacology
Mechanism of Action
Diphenhydramine is a first-generation antihistamine that competitively antagonizes H1-receptors, thereby blocking the effects of histamine. It also possesses significant anticholinergic (muscarinic), antiemetic, and sedative properties due to its ability to cross the blood-brain barrier and act on central H1 and muscarinic receptors.
Pharmacokinetics
Absorption:
Bioavailability:
Not available (IV/IM administration bypasses absorption phase)
Tmax:
IV: immediate; IM: 20-30 minutes
FoodEffect:
Not applicable for injection
Distribution:
Vd:
170-330 L (adults)
ProteinBinding:
78-99%
CnssPenetration:
Yes
Elimination:
HalfLife:
2.4 to 9.3 hours (average 4.3 hours in healthy adults); prolonged in elderly and those with hepatic/renal impairment.
Clearance:
Not available
ExcretionRoute:
Urine (primarily as metabolites)
Unchanged:
1% (urine)
Pharmacodynamics
OnsetOfAction:
IV: immediate; IM: 15-30 minutes
PeakEffect:
IV: 15-30 minutes; IM: 1-3 hours
DurationOfAction:
4-8 hours
Confidence:
Medium
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Changes in balance
Feeling less alert than usual
Other Possible Side Effects
Like all medications, this drug can cause side effects. Although many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms that bother you or persist, contact your doctor for advice:
Dizziness or drowsiness
Thickening of mucus in the nose or throat
Feeling nervous or excitable
Upset stomach or vomiting
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
While rare, some people may experience severe and potentially life-threatening side effects when taking this medication. If you notice any of the following symptoms, contact your doctor or seek immediate medical attention:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Severe dizziness or fainting
Changes in balance
Feeling less alert than usual
Other Possible Side Effects
Like all medications, this drug can cause side effects. Although many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms that bother you or persist, contact your doctor for advice:
Dizziness or drowsiness
Thickening of mucus in the nose or throat
Feeling nervous or excitable
Upset stomach or vomiting
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects. If you have questions or concerns about side effects, consult your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Severe drowsiness or dizziness
- Difficulty breathing
- Fast or irregular heartbeat
- Severe dry mouth or difficulty swallowing
- Difficulty urinating
- Blurred vision or eye pain
- Confusion or hallucinations
- Seizures
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction and its symptoms.
If you are breastfeeding or plan to breastfeed, as you may need to avoid breastfeeding while taking this medication.
If the patient is a premature baby or newborn, as this form of the medication should not be given to them.
This medication may interact with other medications or health conditions. Therefore, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
Your health problems, including any medical conditions or diseases
Before starting, stopping, or changing the dose of any medication, including this one, you must consult with your doctor to ensure your safety. It is your responsibility to verify that it is safe to take this medication with all your other medications and health conditions.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the allergic reaction and its symptoms.
If you are breastfeeding or plan to breastfeed, as you may need to avoid breastfeeding while taking this medication.
If the patient is a premature baby or newborn, as this form of the medication should not be given to them.
This medication may interact with other medications or health conditions. Therefore, it is crucial to provide your doctor and pharmacist with a comprehensive list of:
All prescription and over-the-counter (OTC) medications you are taking
Any natural products or vitamins you are using
Your health problems, including any medical conditions or diseases
Before starting, stopping, or changing the dose of any medication, including this one, you must consult with your doctor to ensure your safety. It is your responsibility to verify that it is safe to take this medication with all your other medications and health conditions.
Precautions & Cautions
It is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are taking this medication.
To minimize the risk of severe side effects, do not exceed the dosage prescribed by your doctor. Taking more than the recommended amount can increase your chances of experiencing adverse effects. Additionally, do not use this medication for a longer duration than specified by your doctor.
Until you understand how this medication affects you, avoid operating a vehicle or engaging in activities that require alertness.
Do not combine this medication with other products containing diphenhydramine. It is also recommended to avoid consuming alcohol while taking this drug.
Before using marijuana, cannabis, or any prescription or over-the-counter medications that may cause drowsiness, consult with your doctor.
Note that different brands of this medication may be suitable for children of various ages. Therefore, it is crucial to consult with your doctor before administering this medication to a child. Furthermore, do not use this medication as a sleep aid for children; instead, discuss alternative solutions with your doctor.
If you are 60 years or older, exercise caution when using this medication, as you may be more susceptible to side effects. Similarly, when administering this medication to children, use it with caution, as they may have a higher risk of experiencing excitability.
If you are pregnant or planning to become pregnant, inform your doctor, as it is necessary to discuss the potential benefits and risks associated with using this medication during pregnancy.
To minimize the risk of severe side effects, do not exceed the dosage prescribed by your doctor. Taking more than the recommended amount can increase your chances of experiencing adverse effects. Additionally, do not use this medication for a longer duration than specified by your doctor.
Until you understand how this medication affects you, avoid operating a vehicle or engaging in activities that require alertness.
Do not combine this medication with other products containing diphenhydramine. It is also recommended to avoid consuming alcohol while taking this drug.
Before using marijuana, cannabis, or any prescription or over-the-counter medications that may cause drowsiness, consult with your doctor.
Note that different brands of this medication may be suitable for children of various ages. Therefore, it is crucial to consult with your doctor before administering this medication to a child. Furthermore, do not use this medication as a sleep aid for children; instead, discuss alternative solutions with your doctor.
If you are 60 years or older, exercise caution when using this medication, as you may be more susceptible to side effects. Similarly, when administering this medication to children, use it with caution, as they may have a higher risk of experiencing excitability.
If you are pregnant or planning to become pregnant, inform your doctor, as it is necessary to discuss the potential benefits and risks associated with using this medication during pregnancy.
Overdose Information
Overdose Symptoms:
- Severe drowsiness or deep sleep
- Dilated pupils
- Flushed skin
- Dry mouth and eyes
- Fever
- Agitation, hallucinations, delirium
- Ataxia (loss of coordination)
- Tremors
- Seizures
- Tachycardia (fast heart rate)
- Arrhythmias (irregular heartbeats)
- Urinary retention
- Coma
- Respiratory depression
What to Do:
Seek immediate medical attention. Call 911 or your local emergency number. For poison control, call 1-800-222-1222. Treatment is supportive and symptomatic, including activated charcoal (if oral ingestion), IV fluids, and benzodiazepines for seizures or agitation. Physostigmine may be considered for severe anticholinergic toxicity but carries risks.
Drug Interactions
Contraindicated Interactions
- Monoamine Oxidase Inhibitors (MAOIs) - concurrent use or within 14 days of MAOI discontinuation (may intensify and prolong anticholinergic and CNS depressant effects)
Major Interactions
- CNS depressants (e.g., alcohol, opioids, benzodiazepines, barbiturates, tricyclic antidepressants, other antihistamines, sedatives, hypnotics) - increased sedation and respiratory depression
- Anticholinergic drugs (e.g., atropine, scopolamine, tricyclic antidepressants, phenothiazines, quinidine) - increased anticholinergic effects (dry mouth, blurred vision, urinary retention, constipation)
- Potassium chloride (oral) - increased risk of GI lesions due to decreased GI motility
Moderate Interactions
- Beta-2 agonists (e.g., albuterol) - potential for additive anticholinergic effects (e.g., tachycardia)
- Cholinesterase inhibitors (e.g., donepezil) - antagonism of therapeutic effect of cholinesterase inhibitors
- Metoclopramide - antagonism of prokinetic effect
Minor Interactions
- Not available
Monitoring
Baseline Monitoring
Patient history (allergies, pre-existing conditions like glaucoma, prostatic hypertrophy, asthma, cardiovascular disease)
Rationale: To identify contraindications or conditions requiring caution
Timing: Prior to administration
Medication reconciliation
Rationale: To identify potential drug-drug interactions, especially with CNS depressants or anticholinergics
Timing: Prior to administration
Routine Monitoring
Level of consciousness/Sedation
Frequency: During and after administration, as clinically indicated
Target: Appropriate for clinical situation
Action Threshold: Excessive sedation, somnolence, or respiratory depression
Vital signs (heart rate, blood pressure, respiratory rate)
Frequency: During and after administration, as clinically indicated
Target: Within normal limits for patient
Action Threshold: Significant changes (e.g., tachycardia, hypotension, respiratory depression)
Anticholinergic side effects (dry mouth, blurred vision, urinary retention, constipation)
Frequency: Regularly assess patient symptoms
Target: Absence or mild
Action Threshold: Severe or bothersome symptoms
Symptom Monitoring
- Drowsiness
- Dizziness
- Blurred vision
- Dry mouth
- Urinary retention
- Constipation
- Nausea
- Vomiting
- Nervousness
- Restlessness
- Tremor
- Palpitations
Special Patient Groups
Pregnancy
Generally considered Category B (oral) or C (injection, older classification). Studies in animals have not shown harm, but human data is limited. Use only if clearly needed and potential benefits outweigh risks.
Trimester-Specific Risks:
First Trimester:
Limited data, but generally not associated with major birth defects. Avoid if possible, especially during organogenesis.
Second Trimester:
Generally considered safer than first trimester, but still use with caution.
Third Trimester:
Use with caution, especially near term, as it may cause irritability or tremors in the neonate due to anticholinergic effects.
Lactation
L3 (Moderate Risk). Diphenhydramine is excreted into breast milk and can cause drowsiness, irritability, or anticholinergic effects (e.g., dry mouth, decreased feeding) in the infant. It may also decrease milk supply. Use with caution, observe infant for side effects, and consider alternatives, especially in newborns or premature infants.
Infant Risk:
Moderate risk of sedation, irritability, or anticholinergic effects. Potential for decreased milk supply.
Pediatric Use
Contraindicated in premature infants and neonates due to increased susceptibility to anticholinergic side effects and paradoxical excitation. Use with caution in older children; dosage must be carefully calculated based on weight or body surface area. Children may experience paradoxical excitation (restlessness, nervousness) rather than sedation.
Geriatric Use
Elderly patients are more susceptible to the sedative and anticholinergic side effects (e.g., confusion, dizziness, urinary retention, constipation, dry mouth, falls). Use lower doses and titrate carefully. Avoid in elderly patients with dementia due to increased risk of cognitive impairment.
Clinical Information
Clinical Pearls
- Diphenhydramine injection is a common first-line agent for acute allergic reactions (adjunct to epinephrine) and drug-induced extrapyramidal symptoms.
- Due to its significant sedative effects, it is often used as a sedative or for insomnia, but tolerance to this effect can develop.
- Be aware of its strong anticholinergic properties, which can exacerbate conditions like glaucoma, prostatic hypertrophy, and urinary retention.
- Paradoxical excitation (restlessness, nervousness) can occur, especially in children and sometimes in the elderly.
- Administer IV slowly to minimize the risk of hypotension and CNS stimulation.
- Avoid subcutaneous administration due to tissue irritation.
Alternative Therapies
- For allergic reactions: Epinephrine (for anaphylaxis), corticosteroids (e.g., methylprednisolone, dexamethasone), other antihistamines (e.g., hydroxyzine, cetirizine, fexofenadine, loratadine)
- For motion sickness: Scopolamine (transdermal), meclizine, promethazine
- For drug-induced extrapyramidal symptoms: Benztropine, trihexyphenidyl
- For insomnia: Zolpidem, eszopiclone, ramelteon, melatonin, other sedatives
Cost & Coverage
Average Cost:
Varies widely, typically low cost per 1ml vial
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic)
General Drug Facts
If your symptoms or health problems persist or worsen, it is essential to contact your doctor for further guidance. To ensure safe use, never share your medication with others, and do not take medication prescribed for someone else. Store all medications in a secure location, out of reach of children and pets, to prevent accidental ingestion. Dispose of unused or expired medications properly; do not flush them down the toilet or pour them down the drain unless instructed to do so by a healthcare professional. If you are unsure about the correct disposal method, consult your pharmacist, who can also inform you about potential drug take-back programs in your area. Some medications may come with an additional patient information leaflet, which your pharmacist can provide. If you have any questions or concerns about your medication, discuss them with your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately contact your local poison control center or seek medical attention. Be prepared to provide information about the medication taken, the amount, and the time it was taken to ensure prompt and effective treatment.