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17 Cards in this Set
- Front
- Back
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H1 antihistamine - 1st generation |
Diphenhydramine (less specific) |
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H1 antihistamine- 2nd generation |
Loratadine (specific for H1) |
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How are H1 antihistamines differentiated? |
By their side effect profiles: 1st gen - sedating 2nd gen- non-sedating Most are metabolized by the liver |
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What confirmation at H1 first gen antihistamines at physiological pH? |
Neutral and can readily cross the BBB |
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Effects of 1st gen H1 antagonist |
Cause cholinergic (dry mouth), alpha adrenergic (hypotension) and serotonergic (increased appetite) antagonists effects too Direct H1 effect will decrease allergic inflammation and Symptoms |
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Are H1 receptor antagonists really antagonists? |
Inverse agonists - more towards the inactive state and stabilize the receptor |
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Examples of second gen H1 antagonists |
Fexofenadine and loratidine |
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How are the second gen H1 antagonists different? |
Decreased CNS penetration compared to 1st gen; they are ionized at physiological pH; have high binding affinity to albumin and are P-glycoproteins substrate- limits ability to cross membrane. |
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What are the main side effects of second gen H1 antagonists? |
• cardiotoxicity effects at high concentrations- terfenadine caused fatal ventricular arrhythmias and was withdrawn from the market - when taken with grapefruit juice or erythromycin as was metabolized by Cyp P450: caution with other drugs detoxified by P450 |
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When are 1st generation H1 antagonists favored? |
• acute use as are inexpensive and available without prescription •anticholinergic effects are beneficial to relieve symptoms of runny nose during allergic rhinitis |
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When are 2nd generation H1 antagonists favored? |
• for extended use because of reduced sedative effect • when patients need to be alert to carry out their work eg. Operate heavy machinery |
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How do H2 antagonists differ from H1? |
Contain an intact 5-members ring and uncharged side chain |
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What is the MoA of H2 antagonists? |
Competitively bind to H2 receptors on parietal cells to reduce gastric secretion (decrease cAMP) e.g. Cimetidine They are used in the treatment of heartburn and peptic ulcer disease They have low CNS penetration because they are ionized at physiological pH |
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What is a major side effect of the H2 antagonist Cimetidine? |
Inhibition of Cyp P450 mediated drug metabolism - it decreases the metabolites and increases drug levels; these drugs have a narrow therapeutic index so will become toxic if even slightly too high Drugs include: warfarin, diazepam, phenytoin, quinidine, carbamazepine, theophylline, imipramine |
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Why are enzyme inducers slower than enzyme inhibitors? |
Induction needs transcription and translation |
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Name a H3 receptor antagonist |
Pitolisant (inverse agonist) Used in narcolepsy treatment, brought to clinical use in 2017 |
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What is the MOA of Pitolisant? |
Inverse agonist of the presynaptic H3 receptor |
