BASIC - GASTROINTESTINAL & HAEMATOLOGY Flashcards
Names of bulk-forming laxatives?
Ispaghula husk, methylcellulose, sterculia
Indications of bulk-forming laxatives?
- Constipation (patients who can’t increase dietary fibre)
- Mild chronic diarrhoea
Mechanism of bulk-forming laxatives?
- Hydrophilic substance (polysaccharide or cellulose), not absorbed or broken down in gut
- Attracts water into stool and increases its mass
- Increased stool bulk stimulates peristalsis to help relieve constipation
- Need adequate fluid intake
Side effects of bulk-forming laxatives?
- Mild abdominal distension and flatulence
- Rarely, faecal impaction and GI obstruction
Contraindications of bulk-forming laxatives?
- Colonic Atony
- Intestinal obstruction
- Faecal impaction
- Undiagnosed rectal bleeding
Prescription of bulk-forming laxatives?
- Oral granules, powder to be dissolved in water or tablets (methylcellulose)
- Dose to be taken with at least 150ml liquid
- Preferably after meals, morning and evening – e.g. 1 sachet BDS
Names of stimulant laxatives?
Senna, Bisacodyl, glycerol suppositories
Indications of stimulant laxatives?
Constipation
As suppositories for faecal impaction
Mechanism of stimulant laxatives?
- Stimulant laxatives increase water and electrolyte secretion from the colonic mucosa
- Increasing volume of colonic content and stimulating peristalsis
- Direct pro-peristaltic action, although the exact mechanism differs between agents
o Bacterial metabolism of Senna in intestine produces metabolites that have a direct action on the enteric nervous system, stimulating peristalsis
o Rectal administration of glycerol suppositories, provokes a similar but more localised effect and can be useful to treat faecal impaction
o Docusate sodium has both stimulant and faecal softening actions
Side effects of stimulant laxatives?
- Abdominal pain/cramps
- Diarrhoea
- Prolonged use
o Melanosis coli (reversible pigmentation of intestinal wall)
Contraindications of stimulant laxatives?
- Contraindications for Senna
o Intestinal Obstruction
o Atony
o Undiagnosed abdominal pain - Contraindications for glycerol suppositories
o Avoid in haemorrhoids or anal fissures - Avoid during pregnancy
Prescription of stimulant laxatives?
- Regular oral administration, usually BDS
- When rectal, PRN or once only
Prescription in palliative care?
Prescribe a softener and stimulant (Movicol, co-danthrosate)
Names of osmotic laxatives?
Lactulose, Macrogol (Movicol), phosphate enema
Indications of osmotic laxatives?
Constipation and faecal impaction – 1st line Movicol in paediatrics
Bowel preparation prior to surgery or endoscopy
Hepatic encephalopathy – lactulose
Mechanism of osmotic laxatives?
- Osmotically active substances (sugars/alcohol) that remain in gut lumen
- Hold water in stool
- Maintain volume and stimulate peristalsis
- Lactulose
o Reduces ammonia absorption by increasing gut transit rate and acidifying stool
o Inhibits proliferation of ammonia-producing bacteria
o Useful in hepatic encephalopathy
Side effects of osmotic laxatives?
- Flatulence
- Abdominal cramps
- Nausea
- Diarrhoea
- Phosphate enema
o Local irritation, electrolyte disturbances
Interactions of osmotic laxatives?
- Effects of warfarin may be slightly increased
Contraindications of osmotic laxatives?
- Contraindications
o Intestinal obstruction (risk of perforation)
o Severe IBD
o Toxic Megacolon - Contraindications for lactulose
o Galactosaemia
Caution of phosphate enema?
o Heart failure, ascites, electrolyte disturbances
Prescription of osmotic laxatives?
- Orally used prescribed regularly
- May take a few days for an effect to be seen, as need to pass through GI tract
- Phosphate enema PRN or once only
- Taken with or without food
Name of antimotility drugs?
Loperamide
Indications of loperamide?
- Symptomatic treatment of diarrhoea
- Chronic diarrhoea
- Faecal incontinence
Mechanism of loperamide?
- Opioid similar to pethidine however does not penetrate CNS
- Agonist of opioid u-receptors in GI tract
- Reduces peristaltic contractions of gut smooth muscle
- Transit of bowel contents is slowed and anal sphincter tone is increased
Side effects of loperamide?
- Constipation
- Abdominal cramping
- Flatulence
Cautions of loperamide?
- Acute ulcerative colitis – risk of perforation and megacolon
- C.diff colitis
- Acute bloody dysentery
- Children <12 years old
Prescription of loperamide?
- Purchased OTC – 4mg followed by 2mg following each loose stool to maximum of 8mg per day
- Usually tablets or capsules
Names of antacids?
Gaviscon, Peptac
Indications of antacids?
- Mild GORD
- Dyspepsia
Mechanisms of antacids?
- Usually an alginate with one or more antacids (sodium bicarbonate, calcium carbonate, magnesium or aluminium salts)
- Antacids – buffer stomach acids
- Alginates – increase viscosity of stomach contents, reducing reflux
- Form a floating raft, separating gastric contents from GOJ
Side effects of antacids?
- Diarrhoea (magnesium), constipation (aluminium)
Interactions of antacids?
- Divalent cations bind to other drugs and reduce absorption
o ACEi, cephalosporins, ciprofloxacin, tetracyclines, bisphosphonates, digoxin, levothyroxine, PPIs - Increase alkalinity of urine – increase excretion of aspirin and lithium
Contraindications of antacids?
- Caution in fluid overload or hyperkalaemia (sodium or potassium containing preparations)
Prescription of antacids?
- Oral suspensions or chewable tablets
- Take following meals, before bedtime and/or symptomatically
Communications to have in antacids?
- Discuss lifestyle measures to reduce GORD
o Smaller meals, avoiding food and drink triggers, stop smoking, raising head of bed - Leave a gap of >2 hours when taking medications that interact
- Come back if symptoms of bleeding, vomiting, dysphagia and weight loss
Names of H2RA?
Ranitidine
Indications of ranitidine?
- Peptic ulcer disease (2nd line)
- GORD
- Dyspepsia
- Gastric acid reduction in obstetrics
Mechanism of ranitidine?
- H2 receptor antagonists reduce gastric acid secretion
- Acid usually produced by proton pump of gastric parietal cell
- Proton pump can be stimulated by other things than histamine so cannot completely suppress gastric acid production
Side effects of ranitidine?
- Diarrhoea, Constipation
- Headache
- Dizziness
Caution of ranitidine?
- Can mask symptoms of gastric cancer
Dose change in renal impairment in ranitidine?
- Reduce dose if eGFR<50 – excreted by kidneys
Prescription of ranitidine?
- Can be purchased short-term OTC
- Typical dose 150mg BDS
Names of PPIs?
Lanzoprazole, Omeprazole, esomeprazole, pantoprazole
Indications of PPIs?
- H.pylori eradication
- Peptic Ulcer
- GORD
- Dyspepsia
Mechanism of PPIs?
- Irreversibly inhibit H/K/ATPase in gastric parietal cells
- Suppress gastric acid secretion completely
Side effects of PPIs?
- GI upset
- Headache
- High doses can increase risk of fractures
- Prolonged – hypomagnesaemia – tetany or ventricular arrhythmias
Interactions of PPIs?
- Omeprazole inhibits CYP450 enzymes
Caution of PPIs?
- Mask symptoms of gastric cancer
- Increased risk of fractures – adequate intake of Vit D and Ca
- Risk of GI infections
Max dose in hepatic impairment in PPIs?
- Max dose 20mg
Prescription of PPIs?
- Oral usually – best taken in morning
- 20mg OD omeprazole
- Lowest dose for shortest period possible
Monitoring of PPIs?
- Before – check serum magnesium
- Prolonged use (>1 year) – check serum magnesium
Name of antispasmodic?
Hyoscine butylbromide (Buscopan)
Indications of hyoscine?
- IBS
- Colicky pain in cancer
- Palliative care - Reduce copious respiratory secretions (death rattle)
Mechanism of hyoscine?
- Competitive inhibitor of Ach
- Blocks the parasympathetic ‘rest and digest’ effects so:
o Increase HR and conduction
o Reduces smooth muscle tone
o Reduces peristaltic contraction
o Relax pupillary constrictor and ciliary muscles preventing accommodation
Side effects of hyoscine?
- Tachycardia
- Dry mouth
- Constipation
- Urinary retention
- Blurred vision
Caution of hyoscine?
- Angle-closure glaucoma
Contraindications of hyoscine?
- GI obstruction
- Myasthenia gravis
- Paralytic ileus
- Prostatic enlargement
- Urinary retention
- Arrhythmias
Interactions of hyoscine?
- Adverse effects enhanced with other antimuscarinics e.g. TCAs
Prescription of hyoscine?
- Buscopan 10mg 8-hourly – available without prescription
Names of dopamine receptor antagonists antiemetics?
Metoclopramide, domperidone
Indications of dopamine receptor antagonists antiemetics?
- Prophylaxis and treatment of nausea and vomiting in reduced gut motility
- N&V associated with migraine
- Radiotherapy and chemotherapy induced N&V
- Prevention of PONV
- Palliative care – Nausea and vomiting due to gastric stasis and irritation, hiccups
Mechanism of dopamine receptor antagonists antiemetics?
- D2 receptor is main receptor in chemoreceptor trigger zone (CTZ)
- Dopamine promotes relaxation of stomach and LOS and inhibits gastroduodenal coordination
- Blocking D2 has prokinetic effect
Side effects of dopamine receptor antagonists antiemetics?
- Diarrhoea, drowsiness, hypotension, menstrual irregularities
- Metoclopramide
o Extrapyramidal syndromes – acute dystonic reaction (facial and skeletal muscle spasms)
o Galactorrhoea, gynaecomastia - Domperidone does not cross BBB
o Dry mouth
Contraindications of dopamine receptor antagonists antiemetics?
- Phaeocytochroma
- Gastrointestinal obstruction/perforation, 3-4 days after GI surgery
- Cardiac disease – domperidone
Caution of dopamine receptor antagonists antiemetics?
- Young adults
- Asthma
- Bradycardia
- Parkinson’s (Metoclopramide)
Dose changes in renal/hepatic impairment of dopamine receptor antagonists antiemetics?
Hepatic Impairment
- Caution in severe
- Dose reduction of 50% in severe
Renal Impairment
- Avoid in renal impairment
Interactions of dopamine receptor antagonists antiemetics?
- Risk of EPSE increased with antipsychotics
- Do not combine with dopaminergic agents for Parkinson’s - antagonise
Prescription of metoclopramide?
o Short term use – 5 days
o Dose 10mg up to TDS
o Metoclopramide available IV/IM and orally
Name of iron supplements?
Ferrous Fumarate, Ferrous Sulphate
Indications of iron?
- Treatment of iron deficiency anaemia
- Prophylaxis of iron deficiency anaemia in patients with risk factors:
o Poor diet, malabsorption, menorrhagia, gastrectomy, haemodialysis
Mechanism of iron?
- Replenish iron stores
o Iron needed for erythropoiesis – synthesise haem component of haemoglobin - Iron best absorbed in Fe2+ state – in duodenum and jejunum
- Absorption increased by stomach acid and ascorbic acid (Vit C)
- Once in blood, iron bound by transferrin for either bone marrow for erythropoiesis or stored as ferritin in liver, bone marrow, spleen and skeletal muscle
Side effects of iron?
- Nausea, epigastric pain
- Constipation, diarrhoea
- Bowel motions turn black
- IV iron – irritation and hypersensitivity reactions
Contraindications of iron?
- May exacerbate bowel symptoms in intestinal disease (IBD, diverticular disease, strictures)
Interactions of iron?
- Reduce absorption of other drugs
o Levothyroxine, bisphosphonates
o Take at least 2 hours before oral iron
Prescription of iron?
- Ferrous fumerate – 210mg tablets 1-2 times a day
- Once Fe returned to normal, continue for 3 months to replenish iron stores
Communication to patients of iron?
- Taking with food helps reduce GI side effects
- May turn stools black
- Iron treatment stopped 7 days before colonoscopy
Monitoring of iron?
- FBC until haemoglobin returned to normal
- Should rise by 20g/L per month
Name if vitamin B12 supplement?
Hydroxocobalamin
Indications of hydroxocobalamin?
- Treatment of macrocytic anaemias and subacute combined demyelination of cord in B12 deficiency
- Pernicious anaemia
Mechanism of hydroxocobalamin?
- Addition vitamin B12 replenishes stores
Side effects of hydroxocobalamin?
- Diarrhoea, headache, nausea
Contraindications of hydroxocobalamin?
- If both Vitamin B12 and folic acid deficiency:
o Replace both simultaneously
Prescription of hydroxocobalamin?
- Hydroxocobalamin given by IM injection
o If prophylaxis of macrocytic anaemia – 1mg every 2-3 months
o If macrocytic anaemia without neurological complications – 1mg three times a week for 2 weeks and then 1mg every 2-3 months
o If macrocytic anaemia with neurological involvement – 1mg OD on alternate days until no improvement then 1mg every 2 months
Monitoring of hydroxocobalamin?
- FBC before and during treatment
Indications of folic acid?
- Folate-deficient megaloblastic anaemia
- Prevention of neural tube defects
- Methotrexate treatments
Mechanism of folic acid?
- Synthetic form of Vitamin B9 or folate
- Replaces stores
- Reduces risk of neural tube defects
Side effects of folic acid?
- Abdominal distention
- Decreased appetite
- Flatulence
- Nausea
Contraindications of folic acid?
- If both Vitamin B12 and folic acid deficiency:
o Replace both simultaneously
Prescription of folic acid?
- Folate-deficiency – 5mg OD for 4 months
- Prevention of neural tube defects
o Low risk - 400 micrograms OD, before conception to 12 weeks
o High risk – 5mg OD, before conception to 12 weeks
o Sickle Cell – 5mg OD throughout pregnancy - Methotrexate treatment – 5mg once weekly to be take on different day to methotrexate dose
Monitoring of folic acid?
- FBC before and during treatment
Name of vitamin K replacement?
Phytomenadione
Indications for vitamin K?
- All newborn babies to prevent vitamin K deficiency bleeding
- Reverse anticoagulant effect of warfarin
Mechanism of vitamin K?
- Reverses warfarin by providing fresh supply of Vitamin K for synthesis of Vitamin-K dependent clotting factors (Factor 2, 7, 9, 10)
- Effect apparent 12-24 hours after administration
Cautions of vitamin K?
- Give IV injections very slowly – risk of vascular collapse
Interactions of vitamin K?
- May alter warfarin dosing requirements after treatment
Prescription of vitamin K?
- Neonates – 1mg IM as single dose at birth
- To treat high INR – low dose (1mg oral or IV) given
- Major bleeding – 10mg IV