lOMoAR cPSD| 66549320
H1 Antagonists (Antihistamines)
Adverse Effects of H1 Antagonists
H1 antagonists, commonly known as antihistamines, can have a range of side effects based on
their generation.
• First-Generation Antihistamines: Examples include diphenhydramine and
chlorpheniramine. They often cause sedation, dry mouth, blurred vision, constipation,
and urinary retention due to their anticholinergic properties.
• Second-Generation Antihistamines: Examples include loratadine and cetirizine. They
typically have fewer sedative effects as they are less likely to cross the blood-brain
barrier, but can still cause headaches and fatigue in some individuals.
Indications and Drug Selection
H1 antagonists are primarily used for treating allergic conditions.
• Common Indications: Allergic rhinitis, urticaria (hives), and allergic conjunctivitis.
• Drug Selection Considerations: Factors include patient age, severity of symptoms, and
sedation concerns. First-generation antihistamines are effective for immediate relief but
are better suited for nighttime use due to sedation. Second-generation antihistamines are
preferred for daytime use.
Sleep Aids and Long-term Use
Some first-generation H1 antagonists are used as over-the-counter sleep aids.
• Common Choices: Diphenhydramine and doxylamine are frequently used for their
sedative effects.
• Long-term Use Concerns: Not recommended due to potential tolerance, dependence,
and disturbances in sleep architecture. Alternative non-habit-forming sleep aids like
melatonin may be more appropriate for chronic insomnia.
Lifespan Considerations
Caution is advised when using antihistamines in different age groups.
Pediatrics: First-generation antihistamines may cause paradoxical reactions such as
agitation and hyperactivity.
, lOMoAR cPSD| 66549320
Older Adults: Increased sensitivity to anticholinergic effects can lead to confusion,
memory problems, and a higher risk of falls. Second-generation antihistamines are
generally safer for both children and the elderly.
Comparison of 1st Generation vs. 2nd Generation
Understanding the differences between the two generations of antihistamines is crucial for
effective treatment.
• First-Generation: Includes diphenhydramine and chlorpheniramine, known for their
sedative properties and anticholinergic effects.
• Second-Generation: Includes loratadine and cetirizine, considered non-sedating and
preferred for long-term allergy treatment. Differences include sedative effects, duration of
action, and incidence of adverse side effects.
Fexofenadine: Food-Drug Interactions
Impact of Grapefruit Juice
Grapefruit juice can significantly affect the pharmacokinetics of fexofenadine.
Study Reference: L. K. Zhang et al. (2010) found that grapefruit juice decreases plasma
concentration of fexofenadine due to inhibition of the OATP1A2 transporter, which is
crucial for its absorption.
Effect of Antacids
Certain antacids can reduce the absorption of fexofenadine.
Research Reference: R. J. McKinnon et al. (2003) indicated that antacids containing
aluminum and magnesium decrease peak plasma concentration and overall
bioavailability of fexofenadine, leading to reduced efficacy.
Timing of Food Intake
The timing of food intake can influence the effectiveness of fexofenadine.
Study Reference: A randomized controlled trial (G. Cheng et al., 2015) showed that
taking fexofenadine on an empty stomach results in higher plasma levels compared to
administration with a high-fat meal, which delays absorption.
https://www.stuvia.com/user/performance
, lOMoAR cPSD| 66549320
Recommendations for Patients
Patients should be advised on the timing and conditions for taking fexofenadine.
General Advice: Take fexofenadine with water and avoid grapefruit juice or certain
antacids within a specific time frame relative to taking the medication to ensure optimal
therapeutic outcomes.
Glucocorticoids
Mechanism of Action (MOA)
Glucocorticoids exert their effects primarily through the glucocorticoid receptor (GR).
• Gene Regulation: The glucocorticoid-receptor complex translocates to the nucleus,
binding to specific DNA sequences and regulating transcription of target genes, affecting
inflammation and immune responses.
• Cytokine Production Inhibition: They inhibit pro-inflammatory cytokines (IL-1, IL-6,
TNF-α), decreasing inflammation.
• Immune Cell Function Suppression: Glucocorticoids reduce the proliferation and
activity of immune cells, contributing to their immunosuppressive effects.
Pharmacologic Effects
Glucocorticoids have multiple pharmacologic effects.
• Anti-inflammatory: Used in conditions like asthma and rheumatoid arthritis.
• Immunosuppressive: Commonly used in organ transplant patients and autoimmune
disorders.
• Metabolic Effects: Can induce insulin resistance and raise blood sugar levels.
• Mineralocorticoid Activity: Some glucocorticoids affect electrolyte balance, influencing
blood pressure.
• CNS Effects: Can affect mood and behavior, leading to euphoria or depression.
Adverse Effects
Long-term use or high doses of glucocorticoids can lead to various side effects.
messages.downloaded_by https://www.stuvia.com/user/performance
H1 Antagonists (Antihistamines)
Adverse Effects of H1 Antagonists
H1 antagonists, commonly known as antihistamines, can have a range of side effects based on
their generation.
• First-Generation Antihistamines: Examples include diphenhydramine and
chlorpheniramine. They often cause sedation, dry mouth, blurred vision, constipation,
and urinary retention due to their anticholinergic properties.
• Second-Generation Antihistamines: Examples include loratadine and cetirizine. They
typically have fewer sedative effects as they are less likely to cross the blood-brain
barrier, but can still cause headaches and fatigue in some individuals.
Indications and Drug Selection
H1 antagonists are primarily used for treating allergic conditions.
• Common Indications: Allergic rhinitis, urticaria (hives), and allergic conjunctivitis.
• Drug Selection Considerations: Factors include patient age, severity of symptoms, and
sedation concerns. First-generation antihistamines are effective for immediate relief but
are better suited for nighttime use due to sedation. Second-generation antihistamines are
preferred for daytime use.
Sleep Aids and Long-term Use
Some first-generation H1 antagonists are used as over-the-counter sleep aids.
• Common Choices: Diphenhydramine and doxylamine are frequently used for their
sedative effects.
• Long-term Use Concerns: Not recommended due to potential tolerance, dependence,
and disturbances in sleep architecture. Alternative non-habit-forming sleep aids like
melatonin may be more appropriate for chronic insomnia.
Lifespan Considerations
Caution is advised when using antihistamines in different age groups.
Pediatrics: First-generation antihistamines may cause paradoxical reactions such as
agitation and hyperactivity.
, lOMoAR cPSD| 66549320
Older Adults: Increased sensitivity to anticholinergic effects can lead to confusion,
memory problems, and a higher risk of falls. Second-generation antihistamines are
generally safer for both children and the elderly.
Comparison of 1st Generation vs. 2nd Generation
Understanding the differences between the two generations of antihistamines is crucial for
effective treatment.
• First-Generation: Includes diphenhydramine and chlorpheniramine, known for their
sedative properties and anticholinergic effects.
• Second-Generation: Includes loratadine and cetirizine, considered non-sedating and
preferred for long-term allergy treatment. Differences include sedative effects, duration of
action, and incidence of adverse side effects.
Fexofenadine: Food-Drug Interactions
Impact of Grapefruit Juice
Grapefruit juice can significantly affect the pharmacokinetics of fexofenadine.
Study Reference: L. K. Zhang et al. (2010) found that grapefruit juice decreases plasma
concentration of fexofenadine due to inhibition of the OATP1A2 transporter, which is
crucial for its absorption.
Effect of Antacids
Certain antacids can reduce the absorption of fexofenadine.
Research Reference: R. J. McKinnon et al. (2003) indicated that antacids containing
aluminum and magnesium decrease peak plasma concentration and overall
bioavailability of fexofenadine, leading to reduced efficacy.
Timing of Food Intake
The timing of food intake can influence the effectiveness of fexofenadine.
Study Reference: A randomized controlled trial (G. Cheng et al., 2015) showed that
taking fexofenadine on an empty stomach results in higher plasma levels compared to
administration with a high-fat meal, which delays absorption.
https://www.stuvia.com/user/performance
, lOMoAR cPSD| 66549320
Recommendations for Patients
Patients should be advised on the timing and conditions for taking fexofenadine.
General Advice: Take fexofenadine with water and avoid grapefruit juice or certain
antacids within a specific time frame relative to taking the medication to ensure optimal
therapeutic outcomes.
Glucocorticoids
Mechanism of Action (MOA)
Glucocorticoids exert their effects primarily through the glucocorticoid receptor (GR).
• Gene Regulation: The glucocorticoid-receptor complex translocates to the nucleus,
binding to specific DNA sequences and regulating transcription of target genes, affecting
inflammation and immune responses.
• Cytokine Production Inhibition: They inhibit pro-inflammatory cytokines (IL-1, IL-6,
TNF-α), decreasing inflammation.
• Immune Cell Function Suppression: Glucocorticoids reduce the proliferation and
activity of immune cells, contributing to their immunosuppressive effects.
Pharmacologic Effects
Glucocorticoids have multiple pharmacologic effects.
• Anti-inflammatory: Used in conditions like asthma and rheumatoid arthritis.
• Immunosuppressive: Commonly used in organ transplant patients and autoimmune
disorders.
• Metabolic Effects: Can induce insulin resistance and raise blood sugar levels.
• Mineralocorticoid Activity: Some glucocorticoids affect electrolyte balance, influencing
blood pressure.
• CNS Effects: Can affect mood and behavior, leading to euphoria or depression.
Adverse Effects
Long-term use or high doses of glucocorticoids can lead to various side effects.
messages.downloaded_by https://www.stuvia.com/user/performance
