The document discusses the various types of laxatives and purgatives, categorized by their action and mechanism, including bulk forming agents, stool softeners, stimulant purgatives, and osmotic purgatives. It details the effects of dietary fibers and specific chemical compounds, their classifications, and mechanisms of action on the intestines. Additionally, it provides information on dosages, formulations, and potential side effects associated with different laxative agents.

1. Pharmacology
By-
Dr. Mrunal R. Akre

2. Laxatives (Aperients,
Purgatives, Cathartics)

3.  These are drugs that promote evacuation of bowels. A
distinction is sometimes made according to the intensity of
action.
◦ (a) Laxative or aperient: milder action, elimination of soft but
formed stools.
◦ (b) Purgative or cathartic: stronger action resulting in more fluid
evacuation. Many drugs in low doses act as laxative and in larger
doses as purgative.
 CLASSIFICATION
◦ 1. Bulk forming
 Dietary fibre: Bran, Psyllium (Plantago) Ispaghula, Methylcellulose
◦ 2. Stool softener
 Docusates (DOSS), Liquid paraffin
◦ 3. Stimulant purgatives
 (a) Diphenylmethanes Phenolphthalein, Bisacodyl, Sodium picosulfate
 (b) Anthraquinones (Emodins) Senna, Cascara sagrada
 (c) 5-HT4 agonist Prucalopride
 (d) Fixed oil- Castor oil
◦ 4. Osmotic purgatives
 Magnesium salts: sulfate, hydroxide Sodium salts: sulfate, phosphate
Sod. pot. Tartrate Lactulose

4.  MECHANISM OF ACTION
◦ All purgatives increase the water content of the
faeces by:
 (a) A hydrophilic or osmotic action, retaining water and
electrolytes in the intestinal lumen—increase volume of
colonic content and make it easily propelled.
 (b) Acting on intestinal mucosa, decrease net absorption of
water and electrolyte; intestinal transit is enhanced indirectly
by the fluid bulk.
 (c) Increasing propulsive activity as primary action—allowing
less time for absorption of salt and water as a secondary
effect
◦ Laxatives modify the fluid dynamics of the mucosal
cell and may cause fluid accumulation in gut lumen
by one or more of following mechanisms:
◦ (a) Inhibiting Na+K+ATPase of villous cells— impairing
electrolyte and water absorption.
 (b) Stimulating adenylyl cyclase in crypt cells— increasing
water and electrolyte secretion.
 (c) Enhancing PG synthesis in mucosa which increases
secretion.
 (d) Increasing NO synthesis which enhances secretion and

5.  BULK PURGATIVES
◦ Dietary fibre: bran Dietary fibre consists of
unabsorbable cell wall and other constituents of
vegetable food—cellulose, lignins, gums, pectins,
glycoproteins and other polysaccharides.
◦ Bran is the residual product of flour industry which
consists of ~40% dietary fibre.
◦ It absorbs water in the intestines, swells, increases
water content of faeces—softens it and facilitates
colonic transit.
◦ Psyllium (Plantago) and Ispaghula
 They contain natural colloidal mucilage which forms a
gelatinous mass by absorbing water.
 It is largely fermented in colon: increases bacterial mass and
softens the faeces.
 Ispaghula husk (refined): ISOGEL (27 g/ 30 g), NATURE
CURE (49 g/100 g), FYBOGEL (3.5 g/5.4 g) powder FIBRIL
(3.4 g/11 g) powder;
 Psyllium hydrophilic mucilloid: ISOVAC (65 g/100 g) granules.
◦ Methylcellulose
 A semi-synthetic, colloidal, hydrophilic derivative of
cellulose that remains largely unfermented in colon.

6.  STOOL SOFTENER
◦ Docusates (Dioctyl sodium sulfosuccinate: DOSS)
 It is an anionic detergent, softens the stools by net water accumulation in the lumen by
an action on the intestinal mucosa.
 It emulsifies the colonic contents and increases penetration of water into the faeces.
 Dose: 100–400 mg/day; acts in 1–3 days.
 TM- CELLUBRIL 100 mg cap; LAXICON 100 mg tab, DOSLAX 150 mg cap. As enema
50–150 mg in 50–100 ml; LAXICON 125 mg in 50 ml enema.
◦ Liquid paraffin It is a viscous liquid;
 a mixture of petroleum hydrocarbons
 STIMULANT PURGATIVES
◦ They are powerful purgatives: often produce griping.
◦ They irritate intestinal mucosa and thus were thought to primarily stimulate
motor activity
◦ Diphenylmethanes
 Phenolphthalein is a litmus-like indicator which is in use as purgative from the
beginning of the 20th century. It turns urine pink if alkaline.
 Bisacodyl is a later addition and is more popular. They are partly absorbed and
reexcreted in bile.
 Phenolphthalein 60–130 mg: LAXIL 130 mg tab. To be taken at bedtime (tab. not to be
chewed).
 Bisacodyl 5–15 mg: DULCOLAX 5 mg tab; 10 mg (adult), 5 mg (child) suppository:
CONLAX 5 mg, 10 mg suppository, BIDLAX-5 5 mg tab.
◦ Sodium picosulfate:
 Another diphenylmethane related to bisacodyl.
 It is hydrolysed by colonic bacteria to the active form, which then acts locally to irritate
the mucosa and activate myenteric neurones
 Dose: 5–10 mg at bed time. Indications and side effects are similar to bisacodyl.
 TM- CREMALAX, LAXICARE 10 mg tab; PICOFIT 5 mg/5 ml syr.

7.  Anthraquinones
◦ These are plant products used in household/ traditional medicine for
centuries. Senna is obtained from leaves and pods of certain Cassia sp.,
while Cascara sagrada is the powdered bark of the buck-thorn tree.
◦ These and a number of other plant purgatives contain anthraquinone
glycosides, also called emodins Regular use for 4–12 months causes
colonic atony and mucosal pigmentation (melanosis). Sennosides (Cal.
salt):
◦ TM- GLAXENNA 11.5 mg tab; PURSENNID 18 mg tab; SOFSENA 12 mg
tab.
◦ Castor oil
 It is one of the oldest purgatives. Castor oil is a bland vegetable oil obtained from the
seeds of Ricinus communis. It mainly contains triglyceride of ricinoleic acid which is a
polar longchain fatty acid.
 OSMOTIC PURGATIVES
◦ Solutes that are not absorbed in the intestine retain water osmotically and
distend the bowel— increasing peristalsis indirectly. Mag. sulfate (Epsom
salt): 5–15 g; bitter in taste, may nauseate.
 • Mag. hydroxide (as 8% W/W suspension—milk of magnesia) 30 ml; bland in taste,
also used as antacid.
 • Sod. sulfate (Glauber’s salt): 10–15 g; bad in taste.
 • Sod. phosphate: 6–12 g, taste not unpleasant.
 • Sod. pot. tartrate (Rochelle salt): 8–15 g, relatively pleasant tasting.
 The salts taken in above mentioned doses, dissolved in 150–200 ml of water, produce
1–2 fluid evacuations within 1–3 hours with mild cramping; cause nearly complete
emptying of bowels
◦ Lactulose
 It is a semisynthetic disaccharide of fructose and lactose which is neither digested nor

8. To be continued…………