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| What type of cells release histamines? |
mast cells and basophils |
| Histamine receptors are of which family? |
Serpentine -- G coupled second messengers |
| What happens with activation of H1 receptors? |
1. NO --> inc capillary dilation --> dec BP, 2. inc cap permeability --> inc edema, 3. IP3 and DAG release --> inc bronchiolar smooth muscle contraction, 4. inc activation of peripheral nociceptive receptors --> inc pain and pruritis, 5. dec AV nodal cond |
| What happens with activation of H2 receptors? |
1. inc gastric acid secretion --> inc GI ulcers, 2. inc SA nodal rate --> positive inotropy (contractility) and automaticity |
| What is the mechanism of H1 antagonist drugs? |
competitive antagonists of histamine and therefore may be ineffective at high levels of histamine |
| Where are H1 antagonists metabolized? |
in liver |
| Can H1 antagonists cross the placental barrier? |
yes. |
| What are anti-histamines (H1) used for? |
1. allergic rxns, 2. motion sickness, 3. N and V in pregnancy, 4. preoperative sedation, 5. OTC sleep aid and cold medication |
| What are the adverse side effects of H1 antagonists? |
M block and sedation (additive with other CNS depressants), GI distress, allergic rxns |
| What is diphenhydramine? |
Widely used OTC anti-H1. M block, sedation, anti-motion |
| What is promethazine? |
Anti-H1 (histamine). M block, some a block, sedation, local anesthetic, anti motion. |
| What is chlorpheniramine? |
antihistamine (H1); M block and antimotion; CNS stimulation |
| What is meclizine? |
highly effective in antimotion; anti-histamine (H1) |
| What is hydroxyzine? |
Anti-histamine (H1). M block, sedation, anti-motion. Commonly used as sedative. |
| What is loratadine? |
anti-histamine (H1). M block. No CNS entry. |
| What is Fexofenadine? |
anti-histamine (H1). M block. No CNS entry. |
| What drugs would you use in GI dysfxn? |
H2 antagonists like cimetidine and ranitidine |
| How do H2-antagonists work? |
1. block H2 receptor. Suppress secretory responses to food stimulation & nocturnal secretion of gastric acid via ability to indirectly decrease activity of proton pump. 2. partially antagonize HCl secretion caused by vagal stimulation or by gastrin. |
| Do H2-antagonists affect gastric emptying time? |
no |
| What would you use H2 antagonists for? |
1. Acid peptic disease (less effective than PPI's), 2. GERD, 3. Zollinger-Ellison Syndrome |
| What is Zollinger-Ellison Syndrome? |
increased levels of gastrin produced --> excess HCl released in stomach --> peptic ulcers (95%). Often cause is tumor (gastrinoma) of duodenum or pancreas |
| Adverse effects of H2-antagonists |
1. GI distress, 2. dizziness, 3. somnolence. Elderly: slurred speech and delirium. |
| How does cimetidine affect the CYP450 system? |
H2 antagonist. inhibits CYP450 --> inc effects of quinidine, phenytoin, TCA's and warfarin. |
| How does cimetidine affect androgens? |
H2 antagonist. dec androgens --> gynecomastia and dec libido! |
| "prazoles" are what type of drugs? |
PPI's |
| What is the mechanism of PPI's? |
inhibit the K+/H+ antiporter in the parietal cell |
| What would you use PPI's for? |
1. peptic ulcer disease, 2. GERD, 3. Zollinger-Ellison syndrome |
| What are adverse effects of PPI's? |
dec bioavailability of drugs that require acidity for oral absorption (because PPI's decrease acidity) -- e.g. drugs like fluoroquinolones and ketoconazole. |
| How do PPI's affect the CYP450 system? |
inhibits CYP450 --> dec elimination of diazepam (BZ, seizures and muscle relaxation), phenytoin (anticonvulsant, blocks fast Na channels), warfarin. |
| What is misoprostol |
PGE1 analog, used for NSAID-induced GI ulcers |
| What is the mechanism of misoprostol |
PGE1 analog --> cytoprotective --> inc mucus and HCO3- secretion |
| What is sucralfate? |
Polymerizes on GI luminal surface to form protective gel-like coating of ulcer beds |
| When would you use sucralfate? |
increase healing and decrease recurrence of ulcers |
| Why shouldn't you prescribe sucralfate with antacids? |
Sucralfate polymerizes to protect ulcers. It requires acidic environment so antacids would interfere. |
| What is the mechanism of antacids? |
Antacids are combo of Ca, Mg, and Al hydroxides that neutralize H+ in the gut lumen. |
| What are adverse side fx of antacids? |
because decrease acidic environment in stomach, dec oral absorption of weak bases (e.eg. Quinidine), weak acids (e.g. warfarin), "azoles" (PPI's), fluoroquinilones (anti-microbial), and TCA's (via chelation) |
| What are adverse side fx of the antacid, Al(OH)3? |
1. hyPO-phosphate, 2. osteodystrophy, 3. dementia |
| What are adverse side fx of the antacid, CaCO3? |
HyPERcalcemia |
| What are adverse side fx of the antacid, Mg(OH)2? |
1. HyPER-Mg --> lose deep tendon reflexes, 2. resp paralysis |
| What are adverse side fx of the antacid, NaHCO3? |
"Gas" |
| What is MgSO4? |
Laxative. Retains water --> inc intraluminal P |
| What is bisacodyl? |
Laxative. Directly stimulates intestinal wall. |
| What is methylcellulose? |
Laxative. Collects water and swells --> inc bulk in stool |
| What is docusate? |
Laxative. Detergent --> stool softener |
| Why would you want to give mineral oil to a constipated patient? |
lubricant - works as a laxative |
| What is lactulose? |
Laxative. hyperosmotic (also indicated for systemic encephalopathy) |
