Anti-histamines_PHARM

Question 1

Physiological function of histamine

Answer 1

1. vasodilation
2. vascular permeability
3. bronchoconstriction
4. mucous secretion
5. CNS neurotransmitter - cognition, memory, anti-seizure
6. Itching
7. pain
8. Hives

Question 2

Physiological release of histamine in tissue and blood

Answer 2

1. Mast cells
   - store histamine in tissues
2. Basophils
   - store histamine in blood
3. Allergic release
   - IgE binds antigen
   - release of histamine from mast cell or basophil
4. non allergic release
   - Complement cascade activated
   - C3a and C5a
   - release of histamine
   - inflammatory response

Question 3

Two receptors for histamine

Answer 3

H1 receptors
- throughout body
- Function: vasodilation, vascular permeability, bronchoconstriction, mucous secretion, itching, pain, hives

H2 receptors
- gastric parietal cells
- Function: gastric acid secretion

Question 4

Caution when prescribing anti-histamines to …

Answer 4

• old people - confusion, sedation, delirium
• young people - respiratory depression, paradoxical reaction, seizures
• epilepsy patients
• anti-cholinergic medications , CNS depressants
• urinary retention (BPH), hypertension (BP), glaucoma, asthma
• pregnancy and breastfeeding

Question 5

Anti-histamine
Patient education

Answer 5

take at night time
sips of water
avoid CNS depressants, operating machines
paradoxical reactions
respiratory depression
delirium onset
*do not take if pregnant or breastfeeding

Question 6

First generation H1 inhibitors

Answer 6

diphenhydramine (Benadryl) PO, IM, IV
Promethazine (Phenergan), PO , IM , IV
- CNS depression most prominent

Pheneramine, PO

Clemastine

Question 7

First generation anti-histamines
SE/Contraindications

Answer 7

Cross the BBB
cause sedation, CNS depression, respiratory depression
Do not take pregnancy breast feeding

Question 8

Second generation anti-histamine benefits

Answer 8

Do not cross BBB
no CNS depression

*still have
paradoxical reaction children
older people delirium
safer in pregnancy

Question 9

anti-histamines and pregnancy

Answer 9

teratogenic
avoid in third trimester
first generation > second generation crossing BBB and placenta

Question 10

List of second generation anti-histamines

Answer 10

• cetirizine (reactine)
• fexofenadine (allegra) *best efficacy and safety
• loratadine (claritin)
• desloratadine (aerius)

Question 11

Juice and second generation anti-histamines

Answer 11

decreases absorption
don’t drink juice 4 hours before 1-2 hours after
decreases absorption

Question 12

Indication anti-histamines

Answer 12

1. mild allergic reactions
   - pruritis, urticaria, bronchoconstriction, pain
2. motion sickness (h1 receptors in vesticular center brain)
   - need to have first generation anti-histamine to cross BBB
3. seasonal allergies
   - second generation non-sedating antihistmaine
4. chronic idiopathic urticaria

Question 13

Age limit for anti-histamines

Answer 13

Children > 6 years of age
Promethazine > 2 years of age