Laxatives & Purgatives

Laxatives and Purgatives

1. Definitions, terminology & scope

• Laxatives are drugs that promote evacuation of the bowels; an umbrella term covering a spectrum of intensity of action (KDT 8e Ch.49). The synonyms aperients, purgatives, cathartics and evacuants are often used interchangeably, but a graded distinction exists (G&G 14e Ch.54; KDT 8e Ch.49).
  • Laxative / aperient — milder action; elimination of soft but formed stool (KDT 8e Ch.49).
  • Purgative / cathartic — stronger action; more fluid and forceful evacuation (KDT 8e Ch.49).
  • The distinction is dose-dependent and vague — many drugs act as a laxative in low dose and a purgative in higher dose (KDT 8e Ch.49).
• G&G draws the parallel physiological distinction: laxation = evacuation of formed faecal material from the rectum; catharsis = evacuation of unformed, watery material from the entire colon. Most clinical agents promote laxation; a few are cathartics that act as laxatives at low dose (G&G 14e Ch.54).
• Laxatives and purgatives sit within GI motility/water-flux pharmacology. Antidiarrhoeals are summarised in a companion section (§16) because they share the same water-flux and motility physiology (G&G 14e Ch.54; KDT 8e Ch.49).