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Dental Therapeutics Final Exam > Antihistamines > Flashcards

Antihistamines Flashcards

1
Q

Histamine

A

1st Immediate Response
Transient Response
Stored in Mast cells and Basophils
Releasing Agent needed (Morphine can displace histamine from protein complex within cells)
Combines with 4 specific cell membrane receptors (H1-H4)

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2
Q

Histamine Receptor

A

H1 - GPCR; Vasodilation, Edema, Vascular Permeability;

Acts on sensory nerves and elicits itching and discomfort

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3
Q

H1 Receptor

A

Smooth m., Endothelial cells, Sensory n., CNS
Chlorpheniramine antagonist
Antagonist = Inverse Agonists
Stabilize inactive form of H1 receptor on effector cells (Block constitutive histamine action)

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4
Q

H2 Receptor

A

Gastric parietal cells, Cardiac and Smooth m., Mast cells, CNS
Ranitidine antagonist

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5
Q

H3 Receptor

A

CNS: presynaptic, myenteric plexus

Thioperamide antagonist

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6
Q

H4 Receptor

A

Cells of hematopoietic origin

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7
Q

Epinephrine

A

Physiologic Antagonist
Agonist at alpha and beta adrenergic receptors
Vasoconstriction
Airway smooth muscle relaxation

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8
Q

Antihistamine Actions

A

Vascular Smooth m. - Indirect by inhibit NO production by endothelium; Histamine to pre capillary dilation, post capillary constriction to edema and immediate vasodilation (H1)
Endothelial cells - Prevent increase permeability
Sensory nerve ending - Prevent itching
Mucus glands - Prevent increased secretion
Airway Smooth m. - Prevent histamine contraction (Not useful in asthma)
GI Smooth m. - Prevent histamine contraction
CNS receptors - Antagonize histamine waking

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9
Q

Histamine and Waking

A

Cells Located Tuberomammillary Nucleus (TMN) in Posterior Hypothalamus; Diffuse projections to cerebral cortex, striatum, hippocampus and LDT/PPT; Histaminergic TMN and GABAergic VLPO in Ant. hypothalamus are antagonistic, TMN inhibits VLPO and VLPO inhibits TMN; Sedating

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10
Q

Other H1 Property Drugs

A 
Antipsychotics
1st and 2nd gen Tricyclic Antidepressants (Not selectives)
Antiserotonergics - Cyproheptidine
Antidopaminergic - Prochorperazine
Antimuscarinic - Benzotropine
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11
Q

Antihistamine Cardiac

A

Bind to and inhibit hERG (KCNH2) Kv 11.1 potassium channels
hERG K - Primary repolarization ion channel in heart and block produces long QT interval and might cause cardiac arrhythmia
Torsades de pointes - Fatal
Antihistamines (Astemizole) - Cardiac toxicity and deaths
Antihistamines w/P450 inhibitors increase toxicity
2nd generation - Low drowsiness, Withdrawn (Older block hERG but drowsiness limit)

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12
Q

Antihistamine Other Effects

A

Atypical antipsychotic drugs with strong antihistaminergic properties - Weight gain and diabetes worsen (Recent studies - Antiserotonergic and Anticholinergic receptors; Drug induced insulin resistance; CNS action - less prominent in 2nd gen agents)

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13
Q

Ethanolamines

A

Diphenhydramine (Benedryl, generic)

Antihistamine, First gen

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14
Q

Alkylamines

A

Chlorpheniramine (ChlorTrimeton, generic)

Antihistamine, First gen

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15
Q

Piperazines

A

Hydroxyzine (Atarax)

Antihistamine, First gen

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16
Q

Phenothiazines

A

Promethazine (Phenergan, generic)

Antihistamine, First gen

17
Q

Antihistamine Pharmacokinetics and Side Effects (First Gen)

A

Pharmacokinetics: Good absorption from GI tract, Cross blood-brain barrier and placenta (hydroxyzine contraindicated), Onset at 1-2hrs, duration 3-6hrs of action w/in 30mins, Max effect, Metabolized in liver by CYP2D6 (some 2A6)
Side Effects: Intensity varies, CNS drugs with similar side effects; Sedation, Anti-cholinergic action, Little or no respiratory depression (OTC sleep aids), Hypersensitivity (Use with Epi to treat hypersensitivity rxn), Weight gain, Arrhythmias; Loss of effectiveness - Tolerance, Paradoxical CNS stimulation in children and overdose (No anesthesia may cause seizures)

18
Q

Second Gen Prototypes

A

Antihistamines - Low Drowsiness
Loratadine (Claritin)
Fexofenadine (Allegra)
Desloratadine (Clarinex)

19
Q

Antihistamine Pharmacokinetics and Side Effects (Second Gen)

A

Pharmacokinetics: Absorption altered if taken w/grapefruit juice (3A4), Little or no crossing blood brain barrier or placenta, Longer half life, Most metabolized in liver by CYP3A4, CYP2D6
Side effects: Cardiac arrhythmias - Astemizole, Terfenadine - High (2-10X) doses, Normal doses in patients w/ Ketoconazole, Troleandomycin, Erythromycin and other Macrolide antibiotics; Little or no sedation, Little or no anticholinergic action, Less diabetogenic action

20
Q

Antihistamine Therapeutic Use

A

Prophylactically to prevent symptoms of allergy and anaphylaxis, Part of treatment in common cold, Sedative 1st gen (OTC sleep aids), Prophylactically to prevent motion sickness, Treat early Parkinsons disease (Primary 1st gen)

21
Q

Antihistamine Use in Dentistry

A

Pre-procedural sedation (Promethazine, Hydroxyzine, Diphenhydramine) - Sedative and anxiolytic, Block actions of histamine being released by opiates, Decrease salivary secretions (anticholinergic effect), Act as antiemetic/anti gagging, Produce mild analgesia
Use of local anesthetic
Treat allergic lesions or oral mucosa

22
Q

H1 Antihistamine Drug Interactions (First Gen)

A

Potentiate actions of other sedatives (Potentiate sedative actions of opiates - Opiate and antihistamine dose cut in half when drugs in combo)
P450 blockers impact actions

23
Q

H2 Receptor Antagonists

A

Decreases actions of histamine by blocking H2 on effector cells
Effective in inhibiting Histamine action on gastric parietal cells (Vascular smooth m. - Direct - Delayed vasodilation; Cardiac m. - Direct - Histamine is ionotropic + chronotropic)

24
Q

H2 Receptor Antagonist Prototypes

A

Cimetidine (Tagamet)

Famotidine (Pepcid)

25
Q

H2 Receptor Antagonist Pharmacokinetics and Side-Effects

A

Pharmacokinetics: Rapid absorption from GI, Long duration of action - Administer hs or bid, Crosses placenta, Most excreted in urine
Side-effects: Dizziness, Mental confusion, Seizures
Cimetidine - High dose - Block androgen receptors to result in gynecomastia, impotence and galactorrhea

26
Q

H2 Receptor Antagonist Drug Interactions

A

Cimetidine inhibits cytochrome P450 (1A2, 2C9, 2C19, 2D6, 2E1, 3A4); Inhibit metabolism of drugs like warfarin, theophylline, phenytoin, lidocaine, beta blockers, opiates (two mechs, also decreases hepatic blood flow)

27
Q

H3 Receptor Antagonist

A

Auto receptors reduce release of histamine from histaminergic CNS nerves, Antagonists act as stimulants; Regional diff in basal ganglion, appear as postsynaptic receptors; H3 in 20 isoforms, Heteroreceptors regulate release of transmitter (Improve sleep, attention, learning, Treat narcolepsy, epilepsy, obesity, psychiatric disorders, Parkinsons, Alzheimers, neuropathic pain, Tourettes syndrome)

28
Q

H4 Receptor Antagonist

A

Treat inflammatory conditions - Asthma, pruritus, allergic reactions, pain, neuro-inflammation, neuro-protection

Dental Therapeutics Final Exam (7 decks)

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