Podcast
Questions and Answers
Diphenhydramine's mechanism of action primarily involves:
Diphenhydramine's mechanism of action primarily involves:
- Enhancing the degradation of histamine
- Inhibiting the release of histamine from mast cells
- Stimulating histamine H2 receptors
- Blocking histamine H1 receptors (correct)
Which of the following is a common adverse effect associated with first-generation antihistamines like diphenhydramine, but less so with second-generation antihistamines like cetirizine?
Which of the following is a common adverse effect associated with first-generation antihistamines like diphenhydramine, but less so with second-generation antihistamines like cetirizine?
- Excessive urination
- Drowsiness and sedation (correct)
- Increased appetite
- Nasal congestion
Which drug interaction is most likely to occur with diphenhydramine, potentially leading to increased central nervous system depression?
Which drug interaction is most likely to occur with diphenhydramine, potentially leading to increased central nervous system depression?
- Concurrent use of alcohol or benzodiazepines (correct)
- Concurrent use of a statin like atorvastatin
- Concurrent use of an NSAID like ibuprofen
- Concurrent use of a proton pump inhibitor like omeprazole
Antihistamines are frequently combined with nasal decongestants in cold and allergy medications because:
Antihistamines are frequently combined with nasal decongestants in cold and allergy medications because:
A patient taking cetirizine reports experiencing dry mouth and slight drowsiness. What advice is most appropriate?
A patient taking cetirizine reports experiencing dry mouth and slight drowsiness. What advice is most appropriate?
Compared to cetirizine, diphenhydramine is more likely to:
Compared to cetirizine, diphenhydramine is more likely to:
Which of the following medications would be LEAST likely to cause a significant drug interaction with cetirizine?
Which of the following medications would be LEAST likely to cause a significant drug interaction with cetirizine?
A patient with allergic rhinitis also has benign prostatic hyperplasia (BPH). Which antihistamine would be the LEAST appropriate choice?
A patient with allergic rhinitis also has benign prostatic hyperplasia (BPH). Which antihistamine would be the LEAST appropriate choice?
Why might a healthcare provider recommend cetirizine over diphenhydramine for daytime allergy relief?
Why might a healthcare provider recommend cetirizine over diphenhydramine for daytime allergy relief?
Which of the following accurately describes a difference between first and second-generation antihistamines?
Which of the following accurately describes a difference between first and second-generation antihistamines?
A patient taking diphenhydramine complains of blurred vision. This adverse effect is most likely due to diphenhydramine's activity on which receptor?
A patient taking diphenhydramine complains of blurred vision. This adverse effect is most likely due to diphenhydramine's activity on which receptor?
A pharmacist is reviewing a patient's medication list and notices they are taking both diphenhydramine and a medication for motion sickness. What is the primary concern regarding this combination?
A pharmacist is reviewing a patient's medication list and notices they are taking both diphenhydramine and a medication for motion sickness. What is the primary concern regarding this combination?
A patient with seasonal allergies is looking for an over-the-counter antihistamine. They need to drive a car for several hours. Which antihistamine would be the MOST appropriate recommendation?
A patient with seasonal allergies is looking for an over-the-counter antihistamine. They need to drive a car for several hours. Which antihistamine would be the MOST appropriate recommendation?
A patient is prescribed both cetirizine and pseudoephedrine for allergies and nasal congestion. What is the MOST likely reason for combining these medications?
A patient is prescribed both cetirizine and pseudoephedrine for allergies and nasal congestion. What is the MOST likely reason for combining these medications?
A patient taking diphenhydramine regularly reports experiencing constipation. What is the MOST likely pharmacological reason for this side effect?
A patient taking diphenhydramine regularly reports experiencing constipation. What is the MOST likely pharmacological reason for this side effect?
Which of the following best describes the mechanism by which cetirizine reduces allergy symptoms?
Which of the following best describes the mechanism by which cetirizine reduces allergy symptoms?
A patient is concerned about potential drug interactions with their new cetirizine prescription. Which of the following medications, if taken concurrently, would warrant the LEAST concern for a clinically significant interaction?
A patient is concerned about potential drug interactions with their new cetirizine prescription. Which of the following medications, if taken concurrently, would warrant the LEAST concern for a clinically significant interaction?
A patient with a history of angle-closure glaucoma is seeking an antihistamine for allergy relief. Which antihistamine would be the LEAST appropriate for this patient?
A patient with a history of angle-closure glaucoma is seeking an antihistamine for allergy relief. Which antihistamine would be the LEAST appropriate for this patient?
Why is cetirizine often preferred over diphenhydramine for treating allergic rhinitis in elderly patients?
Why is cetirizine often preferred over diphenhydramine for treating allergic rhinitis in elderly patients?
Which characteristic differentiates first-generation antihistamines, such as diphenhydramine, from second-generation antihistamines, such as cetirizine?
Which characteristic differentiates first-generation antihistamines, such as diphenhydramine, from second-generation antihistamines, such as cetirizine?
Flashcards
Antihistamine MOA
Antihistamine MOA
Block histamine receptors, reducing allergy symptoms.
Antihistamine Adverse Effects
Antihistamine Adverse Effects
Drowsiness, dry mouth, blurred vision, urinary retention.
Antihistamine Drug Interactions
Antihistamine Drug Interactions
Increased sedation with alcohol and other CNS depressants.
Antihistamine/Decongestant Combination
Antihistamine/Decongestant Combination
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Antihistamine Examples
Antihistamine Examples
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Study Notes
- Antihistamines are a class of medications that reduce or block histamines in the body
- Diphenhydramine and cetirizine are examples of antihistamines
Diphenhydramine
- Diphenhydramine is a first-generation antihistamine
- It is commonly used to relieve symptoms of allergies, such as runny nose, sneezing, itchy eyes/nose/throat, skin rash, and hives
- It is also used to prevent and treat motion sickness, and as a sleep aid
Mechanism of Action
- Diphenhydramine works by blocking the H1 histamine receptor
- Histamine is a naturally occurring chemical in the body that can cause allergy symptoms
- By blocking histamine, diphenhydramine helps to relieve these symptoms
- It is an inverse agonist of the H1 receptor
- It binds to the H1 receptor and shifts the equilibrium toward the inactive state
Adverse Effects
- Common side effects include drowsiness, dizziness, dry mouth, blurred vision, and urinary retention
- Due to its anticholinergic properties, it can cause constipation
- May cause cognitive impairment, especially in the elderly
- Can cause paradoxical excitation in some children
- Overdose can cause seizures, coma, and death
Drug Interactions
- Diphenhydramine can enhance the sedative effects of other central nervous system (CNS) depressants such as alcohol, benzodiazepines, and opioids
- It can also interact with monoamine oxidase inhibitors (MAOIs), potentially causing serious side effects
- Anticholinergic drugs can increase the anticholinergic effects
Cetirizine
- Cetirizine is a second-generation antihistamine
- It is used to relieve allergy symptoms such as sneezing, runny nose, itchy eyes/nose/throat, and skin rashes
- It is also used to treat hives and itching
Mechanism of Action
- Cetirizine selectively blocks peripheral H1 receptors
- This action prevents histamine from binding to these receptors and causing allergy symptoms
- Cetirizine is a more selective H1 receptor antagonist compared to first-generation antihistamines like diphenhydramine
- It has less penetration into the central nervous system
Adverse Effects
- Common side effects include drowsiness, dry mouth, and headache
- Cetirizine is generally less sedating than first-generation antihistamines
- Some people may still experience significant drowsiness
- Other less common side effects include dizziness, fatigue, and abdominal discomfort
Drug Interactions
- Cetirizine has fewer drug interactions compared to first-generation antihistamines
- It may enhance the sedative effects of other CNS depressants, but to a lesser extent than diphenhydramine
- It is recommended to avoid alcohol or other sedatives while taking cetirizine
- No significant interactions with MAOIs have been reported
Combination with Nasal Decongestants
- Antihistamines are often combined with nasal decongestants like pseudoephedrine or phenylephrine to provide more complete relief of allergy and cold symptoms
- Antihistamines reduce the effects of histamine, while decongestants help to clear stuffy noses and sinuses
Rationale
- Antihistamines primarily target symptoms like sneezing, itching, and runny nose
- Nasal decongestants target nasal congestion and sinus pressure
- Combining these medications addresses a broader range of symptoms, providing enhanced relief
Mechanism of Action
- Nasal decongestants work by constricting blood vessels in the nasal passages
- This reduces swelling and congestion, making it easier to breathe through the nose
- When combined with an antihistamine, the decongestant helps to alleviate the stuffiness that the antihistamine alone may not fully address
Benefit
- The combination can be particularly useful for individuals experiencing both upper respiratory allergy symptoms and nasal congestion
- Some combination products are available over-the-counter, making them easily accessible
- It is important to use these medications as directed and to be aware of potential side effects, especially for individuals with certain medical conditions like high blood pressure or heart problems
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