Antihistamines Flashcards
Cimetidine (Tagamet)
Type: Antiulcer, H2 blocker
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MOA:
Blocks the effects of histamine at H2 receptors of gastric parietal cells, leading to a reduction of gastric acid volumn and gastric aciditiy
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Indications: Gastric or duodenal ulcers | GERD | Adjunct in treating hives and/or itching in pts w/ an allergic reaction that’s NOT responding to H1 blockers alone (ex: diphenhydrAMINE)
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Contraindications: Known hypersensitivity to cimetidine or other H2 blockers
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Adverse Reactions: Headache | Dizziness | Diarrhea | Muscle aches | Skin rashes | Fatigue
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Drug Interactions: Inhibition of specific liver enzymes may result in increased plasma levels of certain drugs, including: warfarin-type anticoagulants, TCAs, Class I antidysrhythmics, calcium channel blockers, diazepam, phenytoin, theophylline, propranolol, and metoprolol
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Dosages:
Adult.
400 mg orally four times daily; Maximum is 1,200 mg/day
Paediatric.
Use is NOT recommended; 20 to 40 mg/kg per day in divided doses; maximum is 40mg/kg perday for most indications
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Duration: Onset: 60 minutes | Peak effect: 45 to 90 minutes | Duration: 4 to 5 hours
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Special Conditions: Pregnancy safety: Category B | Can be given orally or IV in conjunction with diphenhydrAMINE for urticaria
DiphenhydrAMINE HCl (Benadryl)
Type: Antihistamine (H1 blocker)
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MOA:
Blocks H1 receptors in the respiratory tract, blood vessels, and GI smooth muscle | Reverses extrapyramidal reactions
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Indications: Symptomatic allergic reactions | Symptomatic dystonia | Extrapyramidal signs or symptoms caused by phenothiazines | Antiemetic | Chemical restraint
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Contraindications: Known hypersensitivity, newborns and premature infants, breastfeeding | Use with caution in patients with severe vomiting, asthma, narrow-angle glaucoma, benign prostatic hypertrophy, or alcohol intoxication | Use is controversial in patients with lower respiratory tract disease (including acute asthma)
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Adverse Reactions: Drowsiness | Sedation | Seizures | Dizziness | Headache | Blurred vision | Wheezing | Thickening of bronchial secretions | Palpitations | Hypotension | Dysrhythmias | Dry mouth | Diarrhea | N/V | Hallucinations, confusion, and paradoxical CNS excitation can occur in children
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Drug Interactions: Potentiates the effects of alcohol and other CNS depressants | MAOIs prolong and intensify anticholinergic (drying) effects
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Dosages:
Adult.
Urticaria or pruritus, anaphylaxis, or allergic reaction: 1 mg/kg up to maximum 50-mg dose IM, IV, or orally - IV prefered for shock
Antiemetic: 12.5 to 25 mg IV/IM or orally
Dystonic/extrapyramidal symptoms: 25 to 50 mg IV/IM
Paediatric.
Urticaria or pruritus, anaphylaxis, or allergic reaction: 1 mg/kg up to maximum 50-mg dose IM, IV, or orally
Antiemetic w/ Older than age 2 and weight greater than 12 kg: 0.1 mg/kg IV (maximum: 25 mg)
Dystonic/extrapyramidal symptoms: Give 1 to 1.25 mg/kg IV/IO or IM (25 mg maximum single dose)
Chemical restraint: Give 1 mg/kg IM/IV or orally (25 mg maximum dose)
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Duration: Onset: 10 to 15 minutes | Peak effect: 1 hour | Duration: 6 to 8 hours
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Special Conditions: Pregnancy safety: Category B | Increases the effectiveness of epinephrine | Can be given in conjunction with any H2-blocking antihistamine
Famotidine (Pepcid)
Type: Antiulcer, H2 blocker
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MOA:
Inhibits the volume and concentration of gastric secretions
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Indications: GI ulcer | Suspected upper GI bleeding | GERD | As an adjunct in the treatment of urticaria and/or pruritus in pts experiencing an allergic reaction that does not respond to an H1 blocker alone (ex: diphenhydraAMINE)
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Contraindications: Known hypersensitivity to famotidine or other H2 blockers
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Adverse Reactions: Constipation | Diarrhea | Rhabdomyolysis | Seizures | Pneumonia | Agitation | Vomiting | Headache | Dizziness | Vitamin B12 deficiency | Prolonged QT interval | Confusion, hallucinations, disorientation, agitation, and seizures in older adults
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Drug Interactions: Decreased absorption of iron | Decreased effects of ketoconazole, naproxen, pseudoephedrine | Increased action of metformin
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Dosages:
Adult.
20 mg IV, 20 mg orally twice daily
Paediatric.
0.25 mg/kg/dose every 12 hours IV (20 mg/dose maximum) ; 0.5 mg/kg orally (40 mg/dose maximum)
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Duration: Onset: 60 minutes | Peak effect: 1 to 3 hours | Duration: 10 to 12 hours
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Special Conditions: Pregnancy safety: Category B | More potent H2 blocker w/ fewer adverse effects and drug interactions and a longer duration of action than cimetidine | Can be given orally or IV in conjunction w/ diphenhydrAMINE for urticaria
Promethazine Hydrochloride (Phenergan)
Type: Phenothiazine, Antiemetic, Antihistamine
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MOA:
H1 receptor antagonist; Blocks the action (but not the release) of histamine; Possesses sedative, antimotion, antiemetic, and anticholinergic activity; Potentiates the effects of opioids to induce analgesia
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Indications: Nausea and vomiting
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Contraindications: Known hypersensitivity to any phenothiazines | Concurrent use of large amounts of CNS depressants | Reye syndrome | Lower respiratory symptoms | Children younger than 2 years | Use with caution, if at all, in patients with a history of sleep apnea, acute or chronic respiratory impairment, or seizure disorders
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Adverse Reactions: Headache | Dizziness | Drowsiness | Confusion | Restlessness | Wheezing | Chest tightness | Thickening of bronchial secretions | Palpitations |Bradycardia | Reflex tachycardia | QT prolongation | Postural hypotension | Diarrhea, nausea, vomiting
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Drug Interactions: Additive with other CNS depressants | Increased extrapyramidal effects with MAOIs
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Dosages:
Adult.
12.5 to 25 mg deep IM
Paediatric.
Older than age 2 years: 0.25 to 0.5 mg/kg deep IM
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Duration: Onset: 20 minutes | Peak effect: 30 to 60 minutes | Duration: 4 to 6 hours
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Special Conditions: Pregnancy safety: Category C ; use caution w/ pregnant women ; contraindicated for breastfeeding women | Convulsions and sudden death have been reported when used with children | Do NOT administer if haloperidol or droperidol with be or has been given | Monitor the QT interval with a 12-lead ECG if feasible | Document the QT interval and relay the findings to the receiving facility staff | Deep IM injection is the recommended route of administration
