Emetics (15 marks)

Classification

1. Composition

• ★ Ipecac is the dried root of Cephaelis ipecacuanha. Syrup of ipecac contains the alkaloids cephaeline and emetine. (Goodman & Gilman's The Pharmacological Basis of Therapeutics, section on GI decontamination.)
• ★ Syrup of ipecac is a standardised extract in a glycerin and syrup base (about 7% ipecac extract, from my own knowledge, not the library).
• ★ Do not confuse it with "fluid extract of ipecac". That is 14 times stronger and has caused deaths.

2. Mechanism of action

• ★ Mixed action. Locally, it irritates the GI mucosa and activates peripheral sensory receptors. Centrally, it stimulates the CTZ in the area postrema of the medulla, which triggers the vomiting centre. (Goodman & Gilman's; The Essentials of Forensic Medicine and Toxicology, 36th ed., section "Treatment of Poisoning".)
• ★ Onset is 20 to 30 minutes. Vomiting usually continues for 1 to 2 hours.
• The only other method is mechanical: touching the back of the throat. It is usually ineffective.

3. Dose and route

• ★ Follow each dose with several glasses of water. Adults take 200 to 300 mL.
• ★ Repeat the dose once if vomiting has not occurred in 20 to 30 minutes.
• ★ It induces vomiting in 90 to 95% of patients.
• The patient should lie on their side with the head lower than the body.
• Other emetics (Parikh's Textbook of Medical Jurisprudence, Forensic Medicine and Toxicology, section "Removal of Unabsorbed Poison"):
  • Apomorphine 6 mg subcutaneously (SC), followed by naloxone 5 to 10 mg IM or IV. It acts within 3 to 5 minutes.
  • Mustard 15 g, or common salt 2 tablespoons in 200 mL of tepid water.

4. Indications

• Early management of oral poisoning in a conscious, cooperative patient, ideally within 1 hour, when a stomach tube is not available or cannot be used. (The Essentials of Forensic Medicine and Toxicology, 36th ed.)
• ★ Current status: ipecac is no longer manufactured in the US and its use is not recommended. It was used in only 0.003% of poisonings in 2019. Some authors call it obsolete. Gastric lavage and activated charcoal are preferred. (Goodman & Gilman's)
• Apomorphine and copper sulfate, zinc sulfate and tartar emetic are obsolete.

5. Contraindications

• Altered state of consciousness: coma, drowsiness, absent gag reflex, or a patient likely to deteriorate.
• Convulsions or convulsant poisons (e.g. strychnine), and CNS stimulants.
• Corrosives (acid or alkali), because of the risk of perforation and re-injury.
• Petroleum distillates, kerosene and hydrocarbons, because of aspiration pneumonitis.
• Severe heart or lung disease, and advanced pregnancy.
• Hemorrhagic diathesis, esophageal varices, and recent GI surgery.
• ★ Infants younger than 6 months.
• ★ Prior vomiting, or prior use of antiemetics.
• ★ Cardiac patients, because of emetine cardiotoxicity.
• Ingested sharp objects.
• Poisoning more than 1 hour earlier (useless).
• Eating disorders (bulimia).

6. Drug interactions

• ★ Activated charcoal adsorbs ipecac and blocks emesis. Give charcoal only after vomiting has stopped.
• ★ Antiemetics (phenothiazines, ondansetron, metoclopramide) abolish the effect.
• ★ Milk and carbonated drinks are said to reduce or delay the effect.
• CNS depressants increase the risk of aspiration.
• Other cardiotoxic drugs add to emetine toxicity.
• For comparison, apomorphine should not be used with 5-HT3 antagonists, because of severe hypotension. (Katzung's Basic and Clinical Pharmacology, 16th ed., "Apomorphine".)

7. Side effects (common, minor)

• Nausea, abdominal cramps and protracted vomiting.
• ★ Diarrhea.
• ★ Drowsiness, lethargy and irritability, especially in children.
• ★ Vomiting delays the use of activated charcoal and oral antidotes.

8. Adverse effects (serious)

• Aspiration pneumonia and laryngospasm.
• Mallory-Weiss tear, hematemesis, and esophageal or gastric rupture.
• Pneumomediastinum.
• ★ Fatal hypernatremia after excess salt-water emetics, which is not an ipecac effect.
• For apomorphine: CNS and respiratory depression, which is reversed with naloxone. Other effects are hypotension, bradycardia, drowsiness and syncope. (Katzung's; Parikh's.)

9. Toxicity

• Abuse by patients with bulimia or anorexia nervosa.
• Munchausen syndrome by proxy.
• Cause: accumulation of emetine.
• ★ Cardiotoxicity: cardiomyopathy, arrhythmias, hypotension, T-wave changes, and heart failure.
• ★ Skeletal myopathy: proximal muscle weakness.
• Management: stop the drug, give supportive care, and monitor with ECG and cardiac enzymes.

10. Role of the nurse

• Check consent, the time of ingestion, the substance, and the patient's consciousness.
• Confirm that none of the contraindications apply.
• Keep suction, oxygen and an airway tray ready.
• Collect the first vomitus as a specimen.
• Check with the doctor before giving charcoal.

• Position the patient on the left side with the head lower than the body.
• Give the drug orally, followed by fluids.
• Observe for onset of vomiting within 20 to 30 minutes.
• Keep an intake and output chart.
• Check vitals.

• Watch for aspiration, bleeding, dehydration and electrolyte imbalance. Give fluids as ordered.
• Do oral care.
• Send the vomitus to the lab for analysis and keep it as medico-legal evidence.
• ★ Do not give activated charcoal until vomiting has ended.
• Educate the family to keep medicines and poisons away from children and not to use ipecac at home without advice from a poison centre.
• Document the dose, time, response and outcome.

Quick recap: points unique to ipecac

Laxatives and Purgatives (15 marks)

• Laxatives (aperients) are drugs that promote defecation. They give a soft, formed stool with mild action.
• Purgatives (cathartics) are drugs that act strongly. They give a fluid or semifluid stool with colicky pain.
• The two overlap, because most drugs act as a laxative at a low dose and as a purgative at a high dose.

1. Classification, composition and dose

2. Mechanism of action

• Bulk-forming: they are not digested. They absorb water, increase stool volume and softness, and stimulate peristalsis. They need adequate fluid. (Katzung's)
• ★ Saline osmotic (magnesium and phosphate): they are poorly absorbed and hold water in the lumen. Stool becomes fluid and cholecystokinin (CCK) release increases secretion and motility.
• ★ Lactulose: the colon bacteria ferment it to lactic and acetic acids. This acidifies the gut, which draws in water and traps ammonia as NH4+.
• ★ PEG: it is an isotonic, non-fermentable osmotic agent. It causes no net fluid or electrolyte shift.
• Stimulant (anthraquinones, bisacodyl): they irritate the mucosa and the myenteric plexus. They increase motility and secretion and decrease water absorption. The colon activates the glycosides (anthraquinones are activated by colonic bacteria).
• ★ Castor oil: the small-bowel lipase converts it to ricinoleic acid. This acts on the small intestine and so differs from other stimulants, which act on the colon.
• Stool softeners: surfactant action lets water and fat penetrate the stool. Liquid paraffin coats and lubricates it.
• ★ Lubiprostone, linaclotide and plecanatide: they stimulate chloride secretion into the lumen, and water follows.
• ★ Prucalopride: it stimulates high-amplitude proximal colonic contractions.

3. Indications

• Simple constipation: all classes.
• Prevent straining: after MI, hernia repair, hemorrhoids, anal fissure, and after surgery. Use softeners and bulk agents.
• Bowel preparation before colonoscopy, surgery or radiology: PEG solutions, senna, bisacodyl, sodium picosulfate.
• ★ Hepatic encephalopathy: lactulose.
• Removal of poisons: saline cathartics after activated charcoal. Goodman & Gilman's say cathartics alone are no longer used for GI decontamination.
• Opioid-induced constipation: a laxative plus peripheral μ-opioid antagonists. (Katzung's)
• Drug-induced constipation: treat as for simple constipation.
• Expulsion of worms: after anthelmintics. The usual choice is magnesium sulfate. Do not use castor oil with fat-soluble anthelmintics.
• Chronic idiopathic constipation or IBS-C: ★ the secretagogues and prucalopride.

4. Contraindications

• Intestinal obstruction or ileus.
• Acute abdomen of undiagnosed cause (appendicitis).
• Fecal impaction (for bulk agents), megacolon, and active inflammatory bowel disease.
• Dehydration and electrolyte imbalance.

• ★ Magnesium salts: renal failure (hypermagnesemia). Take care in children. (Rosen's)
• ★ Sodium phosphate: renal insufficiency, heart failure, and elderly patients.
• ★ Bulk agents: dysphagia, esophageal narrowing, and difficulty swallowing.
• ★ Liquid paraffin: the elderly, small children, pregnancy, bedridden patients and anyone prone to aspiration.
• ★ Castor oil: pregnancy (it is an oxytocic) and fat-soluble poisons such as phosphorus.
• ★ Anthraquinones: pregnancy and breastfeeding (dose-related).
• ★ Lactulose: galactosemia.

5. Drug interactions

• ★ Magnesium salts chelate tetracyclines, fluoroquinolones, iron, bisphosphonates and reduce their absorption.
• ★ Bulk-forming agents reduce the absorption of digoxin, warfarin, iron and lithium. Separate the doses by 2 hours.
• Stimulant laxatives with diuretics or corticosteroids cause hypokalemia. This worsens digoxin toxicity and arrhythmias.
• ★ Liquid paraffin reduces absorption of fat-soluble vitamins A, D, E and K and the oral contraceptive. With docusate, it is absorbed more and can reach the tissues.
• ★ Bisacodyl tablets are enteric coated. Antacids, milk, or PPIs dissolve the coating early and cause gastric irritation.
• ★ Lactulose has reduced action with antibiotics (neomycin) and antacids.
• ★ Phosphate enemas with ACE inhibitors, ARBs, NSAIDs and diuretics raise the risk of acute kidney injury (phosphate nephropathy).

6. Side effects

• Abdominal cramps and colic (stimulants, castor oil, saline).
• Diarrhea, nausea and flatulence.
• ★ Bloating and gas: bulk agents and lactulose.
• ★ Sweetness and flatulence with lactulose.
• ★ Anal seepage and pruritus: liquid paraffin.
• ★ Rectal irritation: suppositories.
• ★ Discoloured urine: senna.

7. Adverse effects

• Dehydration, hypokalemia and metabolic alkalosis or acidosis.
• ★ Hypermagnesemia: magnesium salts in renal failure.
• ★ Hyperphosphatemia, hypocalcemia, and acute phosphate nephropathy: sodium phosphate.
• ★ Melanosis coli: pigmentation of the colon by anthraquinones. Reversible. (Swanson's Family Medicine Review)
• ★ Dermatitis, photosensitivity and Stevens-Johnson syndrome: phenolphthalein and some stimulants. Phenolphthalein has been withdrawn.
• ★ Lipoid pneumonia: liquid paraffin is aspirated.
• ★ Fat-soluble vitamin deficiency: liquid paraffin.
• ★ Esophageal or intestinal obstruction: bulk agents taken with too little water.
• Dependence and atonic colon (cathartic colon): habitual use of stimulants. The colon loses tone.
• ★ Hepatitis: old stimulant oxyphenisatin.
• ★ Ischemic colitis: alosetron. (Katzung's)

8. Toxicity (acute and chronic)

• Chronic overuse (laxative abuse): typically in patients with eating disorders, who purge. It causes chronic diarrhea, hypokalemia, dehydration, metabolic acidosis, secondary hyperaldosteronism, steatorrhea, protein-losing enteropathy, osteomalacia and kidney stones. Laxative abuse is detected from stool tests for laxatives. (Henry's Clinical Diagnosis; Tietz Textbook)
• ★ Magnesium toxicity: hypotension, loss of reflexes, respiratory depression, cardiac arrest. Treat with IV calcium gluconate, fluids and dialysis.
• ★ Phosphate toxicity: tetany, arrhythmias and renal failure.
• ★ Castor oil overdose: severe colic and dehydration.
• Management of toxicity: stop the drug, give IV fluids and potassium or other electrolytes, and monitor ECG and renal function.

9. Role of the nurse

• Take a bowel history: frequency, stool type, pain and previous laxative use.
• Check the abdomen for distension, bowel sounds and tenderness. Report an acute abdomen to the doctor before giving anything.
• Check fluid intake, hydration and electrolytes, and renal function (important for magnesium and phosphate).

• Check the order, the contraindications and the drug history.
• Give bulk agents with 200 to 250 mL of water.
• Give stimulants at night so that they act in the morning.
• Do not crush enteric-coated bisacodyl.
• Give suppositories and enemas with privacy, in the left lateral position.
• Give PEG bowel prep in divided doses with the patient staying near a toilet.
• Give lactulose in juice, and titrate it to 2 or 3 soft stools a day in hepatic encephalopathy.

• Record frequency and consistency of stools, abdominal pain, and fluid balance on an intake and output chart.
• Watch for signs of dehydration and hypokalemia (weakness, cramps, arrhythmias), and for signs of magnesium excess.
• Prevent falls if the patient urgently needs the toilet.

• Use laxatives for the shortest time, and avoid regular use of stimulants.
• Eat a high-fibre diet (fruit, vegetables, whole grain), drink 2 to 3 L of fluid daily, exercise, and keep a regular toilet routine. Do not ignore the urge to defecate.
• Do not use laxatives for weight loss.
• Do not use laxatives for abdominal pain or when you have nausea or vomiting.
• Report any bleeding, or no stool for several days.
• Explain that paraffin should not be used at bedtime.

Quick recap: points unique to individual drugs

• Psyllium: needs a lot of water. Slowest onset, 12 to 72 h.
• Lactulose: hepatic encephalopathy, ammonia trapping.
• PEG: bowel prep, no electrolyte shift.
• Magnesium salts: renal failure causes hypermagnesemia. They chelate tetracyclines.
• Sodium phosphate: acute phosphate nephropathy.
• Senna and cascara: melanosis coli.
• Bisacodyl: do not take with antacids or milk. The suppository acts in 15 to 60 min.
• Castor oil: works on the small bowel and is an oxytocic.
• Liquid paraffin: lipoid pneumonia, anal seepage, vitamin loss.
• Docusate: softener, slow action, max 500 mg/day.
• Peripheral opioid antagonists: for opioid constipation, do not reverse analgesia.

Recent evidence check

Laxatives and Purgatives: Easy Notes

1. Meaning

• Laxative: a mild drug that gives a soft, formed stool.
• Purgative (cathartic): a strong drug that gives a watery stool, often with cramps.
• A low dose acts as a laxative. A high dose acts as a purgative.

2. Types, examples and dose

3. How they work (simple)

• Bulk-forming: they swell with water, make the stool bigger and softer, and push the gut to move.
• Softeners: they let water into hard stool or coat it so it slides out.
• Osmotic: they pull water into the bowel, so the stool becomes loose.
• Stimulant: they irritate the bowel lining, so the gut moves faster and absorbs less water.
• Newer drugs: they push fluid into the gut or speed up bowel movement.

4. Uses (indications)

• Constipation.
• Avoiding straining after a heart attack, surgery, hemorrhoids or anal fissure.
• Cleaning the bowel before colonoscopy or surgery.
• Constipation caused by opioids.
• Removing poison from the gut (as an add-on).

5. Do not give in (contraindications)

• Intestinal obstruction.
• Undiagnosed abdominal pain, such as possible appendicitis.
• Severe dehydration.
• Inflammatory bowel disease with a very swollen colon.

6. Side effects

• Abdominal cramps and colic.
• Diarrhea.
• Gas and bloating.
• Nausea.

7. Serious adverse effects

• Dehydration and low potassium.
• Dependence: the bowel stops working without the drug ("lazy bowel").
• Electrolyte disturbance with long use.

8. Toxicity (overdose or misuse)

• Habitual misuse, often by people with eating disorders, causes chronic diarrhea, dehydration, low potassium and weakness.
• Treatment: stop the drug, give IV fluids, and replace potassium and other electrolytes.

9. Drug interactions

• Laxatives with diuretics or steroids lower potassium even more. This is dangerous with digoxin.
• Laxatives can lower absorption of other drugs, so keep medicines 2 hours apart.

10. Points that apply to only one drug

11. Nurse's role

• Ask about bowel pattern, abdominal pain and past laxative use.
• Examine the abdomen. Call the doctor if there is severe pain, vomiting or a hard abdomen.
• Check fluid intake and kidney function.

• Give psyllium with a full glass of water.
• Give stimulants at night.
• Do not crush enteric-coated tablets.
• Give suppositories or enemas gently, in the left side lying position, and keep the patient's privacy.
• Keep a toilet or commode close by.

• Record stool frequency and type.
• Watch for dehydration (dry mouth, dizziness) and low potassium (weakness, cramps).
• Keep an intake and output chart.

• Eat more fiber: fruit, vegetables, whole grains.
• Drink 2 to 3 litres of water a day.
• Exercise and keep a regular toilet routine.
• Do not ignore the urge to pass stool.
• Avoid long-term use of laxatives. Do not use them for weight loss.

12. Quick memory line