What is the recommended dosing of senna (generic name) for a typical adult patient with constipation, considering factors such as age and impaired renal (kidney) or hepatic (liver) function?

Senna Dosing for Adult Constipation

Start senna at 8.6-17.2 mg (one to two standard tablets of 8.6 mg each) once daily at bedtime, and titrate upward only if there is no response after several days. 1, 2

Standard Adult Dosing

• Initial dose: 8.6-17.2 mg orally once daily at bedtime 1, 2
• Maximum dose: 17.2 mg twice daily (34.4 mg total per day) 3
• Most commercial senna tablets contain 8.6-9 mg of sennosides per tablet 1
• The FDA-approved liquid formulation allows 10-15 mL once daily (maximum 15 mL twice daily) for adults 3

Critical dosing caveat: Clinical trials used 1 gram (1000 mg) daily, which is 10-12 times higher than standard commercial tablets, and 83% of trial participants reduced their dose due to side effects. 1, 2 This means the evidence base used excessive dosing, making the lower starting dose even more appropriate in real-world practice.

Titration Strategy

• Goal of therapy: Achieve one non-forced bowel movement every 1-2 days 1, 2
• If no response after several days at the starting dose, increase by one tablet (8.6 mg) 1
• Monitor for abdominal cramping and diarrhea, which indicate the need for dose reduction 1, 2
• In palliative care settings with weeks-to-days life expectancy, doses can be increased to 2-3 tablets (17.2-25.8 mg) two to three times daily 1, 2

Renal and Hepatic Impairment

• Renal impairment: No dose adjustment needed—over 90% of sennosides and metabolites are excreted in feces, making senna safe in chronic kidney disease 1, 4
• Hepatic impairment: No specific dose adjustment data available, but fecal excretion route suggests safety 1
• Senna is preferred over magnesium-based laxatives in CKD patients due to the risk of hypermagnesemia with magnesium products 2, 4

Mechanism and Onset of Action

• Sennosides are metabolized by gut bacteria to active metabolites (rheinanthrone and rhein) that stimulate prostaglandin E2 production and chloride secretion, enhancing colonic peristalsis 1, 4
• Onset: Typically 6-12 hours when taken orally 1
• Important interaction: Antibiotics may reduce senna efficacy by affecting colonic bacteria needed for activation 1, 2

Duration of Therapy

• The American Gastroenterological Association conditionally recommends senna with low certainty evidence 1, 5
• While clinical trials lasted only 4 weeks, longer-term use is probably appropriate, though data on tolerance and long-term side effects are limited 1
• No evidence of tolerance development has been found in pediatric or adult literature 6

Common Side Effects and Management

• Most common: Abdominal pain, cramping, and diarrhea—all dose-dependent 1
• Side effects typically occur in the first week of treatment 1
• Rare but notable: Perineal blistering can occur with high doses (≥60 mg/day) combined with prolonged stool-to-skin contact, particularly with nighttime accidents 6

Contraindications

• Intestinal obstruction or ileus 1, 2
• Severe dehydration 1, 2
• Acute inflammatory bowel conditions 1, 2

When to Escalate Beyond Senna

If senna fails at maximum tolerated doses: 2

• Add polyethylene glycol (PEG) 17 grams once daily as first-line combination therapy 2, 5
• Consider bisacodyl 5-10 mg for short-term or rescue therapy 1, 5
• Rule out fecal impaction with physical examination 1
• Rule out mechanical obstruction with abdominal imaging if clinically indicated 1
• Consider prescription secretagogues (linaclotide, plecanatide, prucalopride) for refractory cases 1, 5