Antihistamines Flashcards
Histamine
- histamine is found throughout the body, including the vesicles of mast cells or basophils, and is abundant in the mast cells in areas particularly susceptible to tissue injury (e.g. nose, mouth, feet, internal body surface, and blood vessels)
Four Type of Histamine Receptors
H1
H2
H3
H4
** Currently available histamines affect H1 and/or H2
Antihistamines: Routes of Administration
- oral
- topical
- nasal preparation
- intramuscularly
- ocular administration
- intravenously
What are 1st Generation Antihistamines (H1 antagonists) used to treat?
- sleep aids
- prevent or reduce motion sickness
- suppress extrapyramidal symptoms caused by antipsychotics (diphenhydramine)
- manage non-allergic rhinorrhea
- allergic rhinitis
- allergic reactions
Side Effects of 1st Generation Antihistamines (H1 antagonists)
- xerostomia (dry mouth)
- sedation “hangover” (excitatory effects in pediatrics)
- dry eyes
- urinary retention
- constipation
- cognitive disturbances
1st Generation Antihistamine (H1 antagonists) Contraindications
- closed-angle glaucoma
- urinary retention
- peptic ulcer disease
- uncontrolled asthma
- history of taking monoamine oxidase inhibitors (MAOIs) within past 2 weeks
1st Generation Antihistamine (H1 antagonists) should be used with caution with…
- other anticholinergic meds such as tricyclic antidepressants (TCAs)
- Elderly (BEERS list)
1st Generation Antihistamine (H1 antagonists) Toxicity Symptoms
- convulsions
- hallucinations
- postural hypotension
- cardiac arrhythmias
- overdose with cytochrome P450 inhibiting medications
- CNS depression can be addictive when antihistamines are combined with other medication with sedative properties or alcohol
Examples of 1st Generation Antihistamines (H1 antagonists)
- Brompheniramine
- Carbinoxamine
- Chlorpheniramine
- Clemastine
- Cyproheptadine
- Diphenhydramine
- Doxylamine
- Promethazine
- Triprolidine
- Dimenhydrinate
- Hydroxyzine
- Meclizine
2nd Generation Antihistamines (H1 antagonists)
- 1st and 2nd generation antihistamines are equally efficacious
- however, 2nd generation do NOT cross the blood-brain barrier to the same extent
- therefore, they are less sedating and have fewer antimuscarinic and anticholinergic effects, and is the preferred class in treating pediatrics and elderly patients
Examples of 2nd Generation Antihistamines (H1 antagonists)
- Acrivastine
- Cetirizine
- Desloratadine
- Fexofenadine
- Levocetirizine
- Loratadine
- Azelastine
Antihistamines vs Decongestants
Antihistamines
- block histamine at H1/H2 receptor
- treats symptoms associatied with allergic rhinitis “hay fever” (sneezing, runny nose, and itching)
- sprays do not cure rebound swelling
Decongestants
- constricts blood vessels
- improves stuffiness
- use for more than a few days can cause rebound swelling of the nasal mucosa
Antihistamine Considerations
- new generation antihistamines are less sedating but still may cause sedation in patients
- most are available OTC
- 1st generations are more likely to cause serious side effects such as rapid HR and urinary retention
- both can cause coordination problems, fatigue, cognitive impairment, and long-term cognitive decline in elderly who take regularly
- 1st generation for motion sickness
- assess for risk factors
Risk Factors that should be considered before prescribing antihistamines
- narrow-angle glaucoma
- COPD
- renal disease
- prostate problems
- HTN
- DM
- heart disease
- thyroid problems
H2 Antagonists
- inhibit the secretion of gastric acid
- GERD
- Allergic reactions or
anaphylaxis
