Diphenhydramine Flashcards Preview

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Flashcards in Diphenhydramine Deck (31):
1

What is the trade name for diphenhydramine?

Benadryl

2

What drug class is diphenhydramine in?

First generation antihistamine/ H1-receptor antagonist

3

What are the clinical uses of diphenhydramine?

-Prevent or treat allergic/hypersensitivity reactions to other drugs, blood products, or common allergens; given along with epinephrine in anaphylaxis
-Treatment of motion sickness, parkinsonism, sedative/mild hypnotic, antiemetic
-antipruritic, antitussive, anticholinergic, antinausea and topical anesthetic properties
-treatment of antipsychotic induced extrapyramidal symptoms

4

What is diphenhydramine usually given in combination with for prophylaxis?

Cimetidine (H2-antagonist) and steroids for prophylaxis in patients with chronic atopy (hereditary predisposition to developing allergies), latex allergy, and before chemonucleolysis and dye studies which are known to be associated with allergic reactions

5

What is the MOA of diphenhydramine?

-Blocks Histamine-1 receptor by competing with histamine on the effector cell receptor sites, thus preventing the effects of histamine peripherally

6

Where are the effector cells (that have H1 receptors) for Diphenhydramine?

effector cells for this medication are in the GI tract, blood vessels, and respiratory tract

7

What is the onset and duration of action of diphenhydramine?

Onset: RAPID
DOA: 4-6hours

8

What is the half-life of diphenhydramine? what is different for the elderly?

-2-8hrs
-13.5 hours in the elderly

9

How is diphenhydramine metabolized?

Extensive hepatic metabolism with smaller degrees in the pulmonary and renal systems; SIGNIFICANT first-pass effect

10

What is the elimination route for Diphenhydramine?

A portion of the drug is excreted unchanged in the urine
(not much info on extensive pharmacokinetics)

11

What is the Volume of Distribution of diphenhydramine?

widely distributed in the body, and its distribution includes the CNS

12

Is diphenhydramine protein bound, if so how much?

78% protein bound

13

What is the Bioavailability of oral diphenhydramine?

40-60%

14

What are the side effects of diphenhydramine?

-moderate somnolence, drying of nasal mucosa, dry mouth
-Hypotension, dizziness, tachycardia, urinary retention, seizures, epigastric distress, thickening of bronchial secretions, irritability, constipation
-nervousness, fatigue, photosensitivity, N/V, wt gain, anorexia, hemolytic anemia, thrombocytopenia, agranulocytosis, tremor, palpitations, paresthesia, blurred vision, disturbed coordination, paradoxical excitement, insomnia, euphoria, confusion, rash, angioedema, diarrhea, urinary frequency
-seizures

15

What is different regarding adults and pediatric populations vs young pediatric populations as side effects of diphenhydramine? what about elderly patients?

-in adults and pediatric patients, this drug can cause decreased alertness, while in YOUNG pediatric patients it may produce excitation
-elderly patients more likely to cause dizziness, sedation, hypotension

16

What can diphenhydramine administration do with your anesthesia?

Due to sedative side effects, administration immediately before end of anesthesia may delay recovery

17

What are the contraindications to diphenhydramine?

-all first generation H1 receptor antagonists are contraindicated for use when DRIVING or operating heavy machinery
-This drug is contraindicated in premature infants, neonates, or nursing mothers
-dont use as local anesthetic
-dont give to ppl with known hypersensitivity reaction

18

Why should you NOT use diphenhydramine as a local anesthetic?

due to the risk of local necrosis!

19

When should you use CAUTION with diphenhydramine?

-use with caution in pts with lower respiratory disease, increased IOP, hyperthyroidism, CV disease, hypertension, narrow-angle glaucoma, stenosing peptic ulcer, pyloroduodenal obstruction, symptomatic prostatic hypertrophy, or bladder neck obstruction

20

What does diphenhydramine do to the hepatic enzymes? Which enzymes?

Moderately inhibits CYP2D6!!!!!

21

What drugs does diphenhydramine have additive effects with?

Alcohol and other CNS depressants

22

What drug can intensify and prolong the anticholinergic effects of diphenhydramine?

MAOIs

23

Co-administration with any of these drugs (3) can cause anticholinergic syndrome

Amantadine
Rimantadine
Anticholinergic drugs

24

What can diphenhydramine cause with beta blockers (such as atenolol)

increase the bioavailability of atenolol

25

What do cholinergic agents do to the effects of Diphenhydramine?

(includes donepezil, rivastigmine, and tacrine) cholinergic agents antagonize the therapeutic effects

26

What can diphenhydramine do to Digoxin and/or levodopa?

May decrease gastric degradation and increase the amount of digoxin and levodopa absorbed by delaying gastric emptying!

27

What does administration with diphenhydramine and neuroleptics do?

therapeutic effects may be antagonized

28

What herbs/nutraceuticals should you avoid with diphenhydramine? why?

Valerian, St Johns Wort, Kava Kava, Gotu Kola
-may increase CNS depression

29

What is the IV dosage of diphenhydramine?

10-50mg IV q6-8hrs

30

What is the oral dosage of diphenhydramine?

25-50mg oral q6-8hrs

31

What is the available IV concentration of diphenhydramine?

IV form is available in concentration of 50mg/mL with a pH adjusted to a range of 5-6