- Dose and Dosage: The typical adult dosage of diphenhydramine for allergies or insomnia is 25 to 50 mg every 4 to 6 hours as needed, up to 300 mg per day. For motion sickness, the dose is usually 25 to 50 mg taken 30 minutes before travel and repeated every 4 to 6 hours as needed.
- Frequency: Diphenhydramine is usually taken every 4 to 6 hours as needed, with a maximum of 300 mg per day for adults.
- Route of Administration (ROA): Diphenhydramine is available in various formulations, including tablets, capsules, oral liquids, and topical creams. It can be taken orally or applied topically.
- Mechanism of Action (MOA): Diphenhydramine is a first-generation antihistamine that works by blocking the effects of histamine, thereby reducing symptoms such as sneezing, itching, watery eyes, and runny nose.
- Pharmacokinetics (PK): Diphenhydramine is well-absorbed after oral administration, with peak plasma concentrations reached within 2 to 3 hours. It undergoes hepatic metabolism and has a half-life of 2 to 9 hours.
- Pharmacodynamics (PD): Diphenhydramine exerts its effects by competitively inhibiting histamine binding at H1-receptor sites, thereby preventing histamine-mediated allergic reactions.
- Pathophysiology: Diphenhydramine alleviates symptoms associated with allergies, insomnia, motion sickness, and certain other conditions by blocking the effects of histamine in the body.
- Indications: Diphenhydramine is indicated for the relief of symptoms associated with allergic reactions, insomnia, motion sickness, and mild cases of Parkinsonism.
- Contraindications: Contraindications include hypersensitivity to diphenhydramine, acute asthma attacks, newborn or premature infants, and individuals taking monoamine oxidase inhibitors (MAOIs).
- Drug Interactions: Diphenhydramine may interact with other central nervous system depressants, anticholinergic drugs, and medications that increase the risk of QT prolongation.
- Precautions: Use caution when driving or operating machinery, as diphenhydramine can cause drowsiness and impair cognitive function. Avoid alcohol consumption while taking diphenhydramine.
- Monitoring and Laboratory Tests: There are no specific monitoring parameters or laboratory tests routinely recommended for patients taking diphenhydramine. However, healthcare providers may monitor for signs of adverse effects or drug interactions in certain cases.
Medication Information and Guidelines
- Purpose: Diphenhydramine is primarily used to relieve symptoms associated with allergies, such as sneezing, itching, watery eyes, and runny nose. It’s also used to treat insomnia by promoting sleepiness and aiding in the initiation of sleep.
- Usage Instructions: Diphenhydramine is usually taken orally as directed by your healthcare provider. It can be taken with or without food. Follow the dosage instructions provided on the label or by your doctor. Do not exceed the recommended dose or frequency of use unless instructed to do so by your healthcare provider.
- Other Uses: Besides allergies and insomnia, diphenhydramine may be used to alleviate symptoms of motion sickness, such as nausea and vomiting, and to manage mild cases of Parkinsonism.
- Precautions: While taking diphenhydramine, be cautious about activities requiring mental alertness, such as driving or operating machinery, as it can cause drowsiness and impair cognitive function. Avoid alcohol consumption, as it may enhance the sedative effects of diphenhydramine.
- Dietary Considerations: There are no specific dietary restrictions associated with diphenhydramine use. However, it’s essential to maintain a balanced diet and stay hydrated while taking this medication.
- Missed Dose: If you forget to take a dose of diphenhydramine, take it as soon as you remember. However, if it’s almost time for your next dose, skip the missed dose and resume your regular dosing schedule. Do not double the dose to catch up.
- Side Effects: Common side effects of diphenhydramine may include drowsiness, dizziness, dry mouth, constipation, and blurred vision. Serious side effects are rare but may include allergic reactions, difficulty urinating, and irregular heartbeat. Seek medical attention if you experience severe or persistent side effects.
- Storage and Disposal: Store diphenhydramine at room temperature away from moisture and heat. Keep it out of reach of children and pets. Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard expired or unused medication following local regulations.
- Overdose or Emergency: In case of an overdose or emergency situation, such as severe drowsiness, difficulty breathing, or loss of consciousness, seek immediate medical attention or contact your local poison control center. Be prepared to provide information about the medication you’ve taken.