Term
| What are the four common antihistamines used in psychiatry? |
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Definition
Diphenhydramine (Benadryl)
Hydroxyzine (Atarax, Vistaril)
Proimethazine (Phenergan)
Cyproheptadine (Periactin) |
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Term
| How are antihistamines metabolized? |
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Definition
Diphenhydramine, hydroxyzine and promethazine - in the liver (caution in cirrhosis)
Cyproheptadine is excreted in urine |
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Term
| What is the mechanism of action for antihistamines? |
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Definition
H1 receptor antagonists
Also, some antimuscarinic cholinergic activity |
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Term
| How does cyproheptadine differ from other antihistamines in its mechanism of action? |
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Definition
| Cyproheptadine is unique among antihistamines because it is a potent 5-HT2 antagonist. |
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Term
| What are the 4 therapeutic indications for antihistamine therapy (in psychiatry)? |
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Definition
Neuroleptic-induced parkinsonism, neuroleptic-induced acute dystonia, and neuroleptic-induced akathisia - alternatives to anticholinergics and amantadine.
Hypnotics - not superior to BZDs. |
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Term
| What are the 4 unique indications for cyproheptadine therapy? |
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Definition
1. Delayed orgasm - esp. if SSRI-induced
2. Anorexia nervosa - becuase it promotes weight gain
3. Reduces recurrent nightmares in PTSD
4. Serotonin syndrome |
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Term
| What are the three common side effects of antihistamines? |
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Definition
Sedation
Dizziness
Hypotension
All are more severe in the elderly |
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Term
| What are the 5 GI side-effects of antihistamines? |
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Definition
Nausea
Epigastric distress
Vomiting
Diarrhea
Constipation |
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Term
| Can antihistamines sometimes cause a paradoxical effect? |
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Definition
| In a small percentage of patients - excitationg and agitation |
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Term
| What 4 conditions are relative CI to antihistamine therapy? |
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Definition
Narrow-angle glaucoma
obstructive GI, prostate or bladder conditions |
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Term
| Which 2 antihistamines can cause a central anticholinergic syndrome? |
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Definition
Cyproheptadine
Diphenhydramine |
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Term
| What warning should be given to all users of antihistamines? |
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Definition
| Avoid operating heavy machinery |
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Term
| What 3 major drug interactions are important in antihistamines? |
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Definition
1. Additive sedative effect
2. Additive anticholinergic effect
3. Cyproheptadine may counteract the benefits of SSRIs |
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Term
| What are the 4 lab interferences of antihistamines? |
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Definition
1. Render allergy tests useless
2. Promethazine - interfere with pregnancy tests, ↑glucose
3. Diphenhydramine - false (+)ive in urine test for PCP
4. Hydroxyzine - false ↑ of 17-hydroxycorticosteroids in urine tests |
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Term
| How are different age groups affected by antihistamines? |
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Definition
| Children and elderly patients are more sensitive to the effects of antihistamines. |
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