Final - 29. Systemic Antihistamines

Question 1

Histamine

Answer 1

• chemical messenger found in high conc. in MAST CELLS, BASOPHILS, and CNS neurons
• occurs in most tissues – high amounts found in lung, skin and GI tract
• Allergic & Inflammatory reactions
  (H1: skin- dilation, nerve endings - itching, lungs - bronchoconstricition)
• Gastric acid secretion (H2: gastrointestinal tract)

Question 2

H1RAs - H1 Receptor Antagonists

Answer 2

• Antiemetic action seems to be due to blockade of central H1 and M1 muscarinic receptors

Therapeutic use:
- Motion Sickness and Nausea
- ex: dimenhydrinate (Dramamine), meclizine (bonine), diphenhydramin (Bendaryl)

Question 3

Somnifacients (sleep aid for insomnia)
- H1 Receptor Antagonist

Answer 3

• First Gen Antihistamines, strong sedative properties
• diphenhydramine (Benadryl)

Question 4

Scopolamine
(Transdermal: motion sickness)

Answer 4

• anticholinergic agent
• prevent nausea/vomiting associated with motion sickness and recovery

Question 5

Antihistamines: 1st Generation (H1 Receptors antagonists

Answer 5

• mainly causes sedation (penetrates CNS)
• can produce adverse effects

Ex:
– Diphenhydramine (Benadryl) - allergies, insomnia, motion sickness
- Dimenhydrinate (Dramamine) - motion sickness
- Chlorpheniramine (Chlor-Trimeton) - allergies
- Meclizine (Bonine) - motion sickness

Question 6

Antihistamines: 2nd Generation (H1 receptor anatogonist)

Answer 6

• less sedation: more polar and does not penetrate CNS
• specific for peripheral H1 receptors
• have no value as somnifacients

Non-Sedating Antihistamines Examples:
- Loratadine (Claritin, Alavert) - allergies
- Desloratadine (Clarinex) - allergies
- Fexofenadine (Allegra) - allergies

Less-Sedating Antihistamines Examples:
- Cetirizine (Zyrtec) - allergies
- Levocetirizine (Xyzal) - allergies

Question 7

Pseudoephedrine (Sudafed)

Answer 7

By itself
- Nasal decongestant

• alpha & beta agonist* -
• mechanism of action:
  stimulates alpha-adrenergic receptors of respiratory mucosa causing vasoconstriction and beta-adrenergic receptors causing bronchial relaxation, **increased heart rate and contractility

**not good for any patients with high blood pressure, heart dysrhythmia, or ischemic heart disease
*caution in patients with prostatic hyperplasia (BPH)

Question 8

Antihistamines: Adverse Effects ANTICHOLINERGIC side effects

Answer 8

• First generation
• ABCD’S- Anorexia, Blurry Vision, Constipation/Confusion, Dry Mouth, Sedation/Stasis of Urine
• potentiation of effects other CNS depressants

Question 9

Antihistamines: Adverse Effects
CNS Effects

Answer 9

• sedation - 1st generation antihistamines (diphenhydramine)

less common in 2nd generation

Question 10

Antihistamines: Disease Related Concerns

Answer 10

• caution in patients with increase IOP or angle-closure glaucoma
• caution in patients with prostatic hyperplasia, bladder neck obstruction

Question 11

Antihistamines - Ophthalmic adverse effects

Answer 11

• blurred vision
• diplopia

contraindicated in
- narrow angle glaucoma
- benign prostatic hypertrophy (BPH)
- patients with peptic ulcer disease
- patients with bladder obstruction (urinary obstruction)