Psyllium

Psyllium (ispaghula husk) is a soluble, gel-forming bulk laxative made from the seed husk of Plantago ovata. It increases stool bulk and softens stool, and is used for chronic constipation, constipation-predominant irritable bowel syndrome, mild faecal incontinence and as an adjunct for lowering cholesterol.

Classification. Bulk-forming laxative; soluble dietary fibre.

Mechanism. The husk absorbs water to form a viscous gel that resists fermentation and adds mass to stool, stimulating peristalsis. It binds bile acids, increasing their faecal loss and lowering LDL cholesterol modestly.

Pharmacodynamics. Effect takes 12 to 72 hours and builds over 1 to 2 weeks. It is least effective in constipation from slow-transit or opioid effect.

Pharmacokinetics. Not absorbed. Fermented only partly by colonic bacteria.

Adult doses unless stated. Take with plenty of fluid.

Constipation and irritable bowel syndrome (constipation-predominant).

• 3.5 to 5 g (about 1 teaspoon or one sachet) once to three times daily mixed in at least 240 mL of water.

• Start at once daily and increase gradually over 1 to 2 weeks.

• Usual maximum about 30 g daily.

Adjunct for raised LDL cholesterol. About 10 g daily in two divided doses with meals, with diet.

Mild faecal incontinence and loose stool. 5 g once to twice daily to bulk stool.

Children. Age 6 to 11 years: half the adult dose, 2.5 g once to three times daily. Not advised under 6 years.

Kidney and liver adjustment. No dose adjustment. Check the potassium and sodium content of products in advanced kidney disease.

Contraindications. Intestinal obstruction; faecal impaction; colonic atony or megacolon; difficulty swallowing or oesophageal stricture; undiagnosed abdominal pain; hypersensitivity (including occupational allergy to the powder).

Common adverse effects. Flatulence, bloating and abdominal distension, usually settling over 1 to 2 weeks.

Serious adverse effects.

• Oesophageal or intestinal obstruction if taken dry or with too little fluid.

• Allergic reactions, including anaphylaxis and asthma, particularly with repeated inhalation of powder.

• Faecal impaction in dehydrated or immobile patients.

Major interactions. Psyllium can bind drugs and delay absorption. Separate other oral medicines by at least 2 hours.

• Digoxin, lithium, carbamazepine, warfarin, iron, calcium and levothyroxine: reduced absorption.

• Antidiabetic drugs: glucose-lowering effect may increase; monitor.

• Opioids: reduce transit and increase obstruction risk.

Special groups.

• Pregnancy: first-line, not absorbed; compatible.

• Breastfeeding: compatible.

• Children: half adult dose from 6 years.

• Older adults and bed-bound patients: risk of impaction; ensure fluid intake and mobility.

• Diabetes: lowers post-meal glucose; use sugar-free products.

• Phenylketonuria: some flavoured products contain aspartame.

• Kidney impairment: no adjustment, but check electrolyte content.

• Liver impairment: no adjustment.

Formulations. Powder or granules 3.5 g sachets; capsules; wafers.

Administration. Mix a dose in at least 240 mL of water or juice, stir and drink at once before it thickens. Follow with another glass of fluid. Do not take immediately before going to bed.

Baseline. Cause of constipation; exclusion of obstruction; fluid intake; medicines that need separating.

Monitoring.

• Stool frequency and consistency, bloating and abdominal pain.

• Fluid intake.

• LDL cholesterol at 6 to 8 weeks if used for lipid lowering.

Therapeutic drug monitoring. Not applicable.

Stopping. No taper is needed. Stop for worsening distension, vomiting or no benefit after 2 to 4 weeks.

Referral and escalation. Seek urgent review for severe abdominal pain, vomiting, distension or inability to pass flatus (obstruction). Investigate red flags: weight loss, rectal bleeding, iron deficiency anaemia or change in bowel habit over age 50.