Diphenhydramine

Diphenhydramine

Diphenhydramine, a common medicine found in many households, influences various aspects of our health. From helping with allergies to aiding sleep, this versatile drug has become a go-to solution for many. But what exactly is diphenhydramine, and how does it work its magic?

In this comprehensive blog, we'll explore diphenhydramine's many uses and discuss its effects on the body. 

What is Diphenhydramine?

Diphenhydramine is a medication that belongs to the class of antihistamines. It is a versatile drug widely used to treat various conditions and alleviate symptoms. Its sedative properties make it a common ingredient in over-the-counter sleep aids. Diphenhydramine is available in both prescription and over-the-counter forms.

Common Diphenhydramine Uses

Diphenhydramine is a versatile medication with several common uses, including:

• Allergy Relief: One of the most well-known uses of diphenhydramine is to provide relief from the common cold and hay fever. It can alleviate discomfort caused by allergic reactions, such as rash, itching, watery eyes, itchy nose and throat, cough, runny nose, and sneezing.
• Motion Sickness Treatment: Diphenhydramine effectively prevents and treats nausea, vomiting & dizziness associated with motion sickness. 
• Sleep Aid: Diphenhydramine's sedative characteristics make it a popular management choice for promoting relaxation and inducing sleep. 
• Parkinson's Disease Management: In early-stage Parkinson's disease or movement disorders caused by certain medications, diphenhydramine can help control abnormal movements and improve muscle control and balance.
• Cough Suppression: Diphenhydramine relieves cough caused by minor throat or airway irritation, temporarily relieving persistent coughing.

How to Use Diphenhydramine

Diphenhydramine is available in various forms, such as tablets, capsules, solutions, injections, and topical applications. The method of administration and dosage depends on the specific ailment and the severity of the symptoms.

Oral Administration

• Tablets and Capsules: Diphenhydramine tablets and capsules can be taken orally with or without food. Chewable tablets should be first chewed completely before swallowing, while capsules or tablets should be swallowed whole without attempting to break them.
• Oral Solutions: If taking the liquid form, use the measuring device provided (e.g., a measuring cup or spoon) to ensure accurate dosing. 
• Rapidly Disintegrating Tablets: Place the rapidly dissolving tablet on your tongue, then allow it to dissolve completely before swallowing, with or without water.
• Oral Powder: Oral powder formulations can be taken with or without water. Avoid dividing the packet into halves.

Side Effects of Diphenhydramine Tablet

While diphenhydramine is generally well-tolerated, it can cause a range of side effects. Some of the most common diphenhydramine side effects include:

Common Side Effects:

• Drowsiness or dizziness
• Constipation
• Stomach upset
• Blurred vision
• Dry mouth, nose, or throat
• Serious Side Effects:

In some cases, diphenhydramine can cause more severe side effects, including:

• Mental or mood changes (e.g., restlessness, confusion)
• Difficulty urinating
• Fast or irregular heartbeat

Potentially Life-threatening Side Effects: In rare cases, diphenhydramine can cause potentially life-threatening side effects, such as:

• Seizures
• Allergic Reaction: Although rare, a severe allergic reaction to diphenhydramine is possible. Seek immediate medical guidance if you notice any symptoms of a serious allergic reaction, including:
  • Rash
  • Trouble breathing
  • Itching or swelling on the tongue, throat or facial region
  • Severe dizziness

Precautions

Diphenhydramine should not be taken in the following cases:

• Hypersensitivity or allergic reaction to diphenhydramine
• Premature infants and neonates, as it can cause life-threatening reactions
• Breastfeeding mothers, as diphenhydramine can pass into breast milk and potentially harm the nursing infant
• Additionally, diphenhydramine should be used with caution during pregnancy (Category B) and only if needed, as it may pose risks to the developing foetus.

How Diphenhydramine Works

Diphenhydramine belongs to a class of medicines called antihistamines.

Diphenhydramine predominantly works by antagonising H1 (Histamine 1) receptors. These H1 receptors are located in various tissues, including respiratory smooth muscles, vascular endothelial cells, the gastrointestinal tract (GIT), cardiac tissue, immune cells, the uterus, and central nervous system (CNS) neurons.

When the H1 receptor gets stimulated in these tissues, it produces a variety of actions, such as:

• Increased vascular permeability
• Promotion of vasodilation, causing flushing
• Decreased atrioventricular (AV) node conduction time
• Stimulation of sensory nerves in airways, producing coughing
• Smooth muscle contraction of bronchi and the GIT
• Eosinophilic chemotaxis, which promotes the allergic immune response

By antagonising histamine receptors, diphenhydramine effectively relieves these symptoms.

Can I Take Diphenhydramine with Other Medicines?

Diphenhydramine can interact with various medications, potentially leading to adverse effects or altering the effectiveness of the drugs involved. Here are some notable interactions to be aware of:

• Sedatives and Sleep Medications: Diphenhydramine can cause drowsiness; combining it with other sleep medications or sedatives can worsen this effect. 
• Opioids: Diphenhydramine can interact with opioids and can result in increased sedation and potential breathing problems. When taken with benzodiazepines, diphenhydramine can intensify many side effects with benzodiazepines, such as drowsiness, confusion, and dizziness.
• Anticholinergics: If taken with another anticholinergic medication, diphenhydramine's complications, such as dry mouth, constipation, blurred vision, and confusion, could worsen. 
• Tricyclic Antidepressants (TCAs): Similar to diphenhydramine, TCAs cause sedation by blocking histamine. Combining these two drugs can cause excessive sedation, dizziness, blurred vision, and dry mouth.
• Muscle Relaxants: Taking a muscle relaxant together with diphenhydramine can lead to severe sedation, potentially impairing coordination and increasing the risk of falls or accidents. 
• Alcohol: Diphenhydramine can amplify the sedative effects of alcohol, leading to dizziness, confusion, and impaired alertness. 

Dosing Information

The typical diphenhydramine dosage for adults is 25-50 milligrams every 4 to 6 hours. However, the maximum daily dose limit is 300 mg when taken orally or 400 mg when administered intramuscularly (IM) or intravenously (IV).

Conclusion

Diphenhydramine is a versatile medication with many uses, from allergy relief to sleep aid. Its effectiveness in managing various symptoms has made it a go-to solution for many. However, it's crucial to understand how to use it properly and be aware of potential complications and interactions with other medications.

While diphenhydramine can be incredibly helpful, it's not without risks. Always follow the dosage instructions, and if you have any concerns or questions, don't hesitate to talk to your doctor. They can accurately advise you to use diphenhydramine safely and effectively for your needs.

FAQs

1. Is diphenhydramine an anticholinergic?

Yes, diphenhydramine is an anticholinergic drug that blocks the action of acetylcholine, a neurotransmitter involved in various bodily functions. This anticholinergic property contributes to some of diphenhydramine's effects, such as drying up bodily fluids (e.g., reducing watery eyes and runny nose) and causing drowsiness.

2. Who should avoid using diphenhydramine?

Diphenhydramine should be avoided or used with caution in the following cases:

• Premature infants and neonates, as it can cause life-threatening reactions
• Breastfeeding mothers, as diphenhydramine can pass into breast milk and potentially harm the nursing infant
• Individuals with a documented hypersensitivity or allergic reaction to diphenhydramine
• Patients with certain medical conditions, such as asthma, emphysema, chronic bronchitis, glaucoma, ulcers, difficulty urinating (e.g., due to an enlarged prostate), heart disease, high blood pressure, history of seizures, or overactive thyroid gland (hyperthyroidism)
• Older adults (65 years and above). As they may be more susceptible to side effects like drowsiness, dizziness, confusion, constipation, and urinary retention, which can increase the risk of falls

3. Can diphenhydramine be used daily?

Diphenhydramine is generally not recommended for daily or long-term use due to the potential for adverse effects and the risk of developing tolerance or dependence.

4. When is the best time to take diphenhydramine?

The best time to take diphenhydramine depends on the purpose for which it is being used:

• For allergies or cold symptoms, take diphenhydramine every 4 to 6 hours 
• For motion sickness prevention, take diphenhydramine 30 minutes before the event or activity that may cause motion sickness.
• As a sleep aid, take diphenhydramine 30 minutes before bedtime. 

5. Does diphenhydramine raise blood pressure?

When taken alone, diphenhydramine is generally not known to raise blood pressure.