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# System prepended metadata

title: Pharm block V GI

---

# Pharm block V GI
## anti-emetics
* Ondansetron
  * Antagonizes 5-HT3-R
    * vagal (-)
    * central anti-emetic
  * Adverse
    * QT prolong => torsades
    * serotonin syndrome
* M1 R
  * Scopolamine
    * M1R antagonist
    * Tx: motion sickness
* H1 R
  * Gq
  * Diphenhydramine, meclizine
    * 第一代 H1R blocker
    * cause sedation, anti-muscarinic
    * Tx: motion sicknes
* Metoclopramide
  * D2 receptor antagonist
  * (+) resting tone, contractility, LES tone, motility
  * Tx: chemotherapy induced vomiting, delayed gastric emptying (upper GI prokinetic)
  * Contraindic.: small bowel obstruction, Parkinson (D2R already blocked), pre-existing elongated QT interval
  * Adverse: 
    * diarrhea, 
    * drowsiness & depression (central D2 block), 
    * extrapyramidal (dystonia, akathisia, parkinsonian [central D2 blockade]), 
    * tardive dyskinesia (跟 chronic use 有關, 不自主重複運動), 
    * neuroleptic (-leptic: acting on) malignant syndrome (發燒、僵直、意識改變、自主神經系統不穩定、橫紋肌溶解)
    * (+) prolactin level => galactorrhea, impotence, gynecomastia (男性女乳), menstrual disorders
    * torsades
* NK1 (neurokinin 1) receptor (activated by substance P)
  * Aprepritant (Emend)
    * blocks NK1 receptor
    * Tx: chemotherapy induced vomiting

## Gastroesophageal refund
* H2 R (Gs) => parietal cells on basolateral membrane
* M3 R => parietal cells (H+ secretion)
* Cimetidine, ranitidine, famotidine, nizatidine
  * H2 receptor antagonist, (-) H+ secretion by parietal cells
  * Tx: **nocturnal** secretion of acid, GERD & peptic ulcers (PPI as first line)
  * Adverse: 
    * inhibitor of CYP450 (multidrug interaction), 
    * 混亂、頭暈、頭痛 (cross BBB), 
    * anti-androgenic
    * cimentidine, ranitidine => (-) renal creatinine excretion
* Ome**prazole**, lansoprazole, esomeprazole, pantoprazole, dexlansoprazole
  * PPI irreversibly inhibit H/K-ATPase pump (H secretion)
  * Tx: nocturnal & meal-stimulated scretion of acid, Zollinger-Ellison  syndrome (gastrinoma causing hypersecretion)
  * Adverse: 
    * *C*. *difficile*, pneumonia, 
    * (-) absorption of 二價陽離子 => (+) osteoporosis, hypomagnesemia

* Octreotide
  * long-acting somatostatin analog
  * Tx: 
    * gastrinoma 當 PPI 沒用時
    * Secretary diarrhea (VIPoma & carcinoid syndrome)

* *H*. *pylori*
  * triple therapy: ppi, clarithromycin, amoxicillin/metronidazole

## Relaxatives
* laxatives vs. pro-kinetic agents
  * change consistency of feces vs. direct stimulation of GI (metoclopramide, erythromycin)
* Magnesium hydroxide, magnesium citrate
  * Osmotic laxatives: draw water in GI => distension & peristalsis
* Polyethylene glycol (PEG), lactulose, sorbital
  * 不可吸收的 sugar osmotic laxative
  * 被腸道菌代謝造成 severe flatulence and cramps
  * lactulose tx: hepatic encephalopathy ([+] ammonia [NH3] following cirrhosis, metabolized into acidic metabolites, which convert NH3 to NH4+ (trapped in intestinal lumen and excreted), rifaximin [antibiotic] 殺製造ammonia的細菌)
* Psyllium
  * bulk-forming laxative
* Stool softeners: surfactant agents
  * Docusate
* Senna
  * Cathartic agent (stimulant) => enteric nervous system (+) colonic secretion
* Opiod agonists
  * Diphenoxylate, loperamide
  * (+) μ-opioid receptor
  * Tx: diarrhea
  * Loperamide doesn't cross BBB, no analgesia (止痛) nor addiction
  * Diphenoxylate cross BBB, w/ atropine => 預防 abuse
  * Adverse: (+) colonic transit time ([+] segmentation contractions [跟會推大便的 peristaltic contraction 不同]) = constipation
  * Contraindic.: bloody diarrhea & fever

* VIPoma => VIP => secretary diarrhea
* Carcinoid tumor => serotonin => secretary diarrhea

## GI
* Misoprostol: PGE1 analog
  * (+) gastric mucus, (-) acid production
  * Tx: 
    * NSAID-induced peptic ulcer
    * ripens cervix, induction of labor (promotes uterine contraction
  * Adverse: abortifacient, diarrhea (所以少用)
* Sulfasalazine: sulfapyridine (anti-bacterial) & 5-aminosalicylic acid (anti-inflammatory)
  * 受腸道菌激活
  * Tx: ulcerative colitis & Crohn disease
  * Adverse: oligospermia (寡精), sulfanamide toxicity
* Metoclopramide
  * D2R antagonist
  * (+) resting tone, contractility, LES tone
  * Tx: 糖尿病/手術相關 gastroparesis
## Antacids
* Adverse: hypokalemia
* Aluminum hydroxide
  * Adverse: constipation, proximal muscle weakness & seizures, hypophosphatemia & osteodystrophy
* Magnesium hydroxide
  * Adverse: diarrhea
* Calcium carbonate
  * Adverse: hypercalcemia => (+) gastrin => acid rebound
* Bismuth, sucralfate
  * physical protection
  * Tx: travelers diarrhea
## Weight loss
* Orlistat
  * Adverse: steatorrhea, (-) absorption of fat-soluble vitamins
  * (-) pancreatic lipase => (-) breakdown of fatty acid and (-) absorption
* Ursodeoxycholic acid (ursodiol)
  * non-toxic bile acid, (+) bile, (-) cholesterol secretion => gallstones 分解 (dissolution of gallstones) & 提高 cholesterol saturate bile salts 的 threshold
  * Tx: primary biliary cirrhosis (bile acid induce hepatocyte apoptosis, ursodiol => EGFR & MAPK => survival signals), biliary stasis in cystic fibrosis
  * Adverse: increase the risk of cirrhosis

## Cholestatic drugs
* Obeticholic acid
  * semisyntetic bile acid, (+) farnesoid X receptor => (-) cholesterol-7-hydroxylase (bile acid synthesis)
  * Tx: primary biliary cholangitis
  * Adverse: itching, serious liver injury (incorrect dosing)
