Toxicity  of purgatives:

    A purgative is a drug which caused marked intensification of intestinal activity & results in the expulsion of intestinal contents from the colon and rectum. Primarly indicated for the t/t of constipation. Certain drugs act as luxative in low doses and in higher doses as purgatives.

They are of various types:

Bulk purgatives: It includes dietary Fibres ( undigested polysaccharide vegetable, fruits, grains, bran, pectin) ,Methyl cellulose, Carboxymethyl cellulose (CMC)) , Synthetic non absorbed resins (Calcium polycarbophil).

Mode of action: Increase the bulk of intestinal contents by water absorption

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                        Increase mechanical pressure on the walls of intestine

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                          stimulation of stretch receptors

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                                      Increase peristalsis.

Side effects:

• Bloating
• Malabsorption syndrome, abdominal distention
• Interfere with other drug absorption e.g. iron, calcium and cardiac glycosides.

Osmotic purgatives:

1. Organic/ Sugar purgative ( Lactulose, Polyethylene glycol (PEG)).

 Mechanism of action: Metabolized by colic bacteria into fructose and galactose.These sugars are fermented into lactic acid and acetic acid that function as osmotic purgatives.

Side effects/ Toxic effects.

• Abdominal Cramps and flatulence.
• Electrolyte disturbance
• Dizziness or light headedness.

1. Non-organic/Saline purgatives (Magnesium sulfate, Magnesium hydroxide, Sodium sulfate, Sod. Phosphate, Sod. Pot. Tartrate)

Mechanism of Action: Non organic purgatives are poorly absorbed salts.They remain in the bowel and retain water by osmosis thereby increasing the volume of feces which increase peristalsis and evacuation of watery stool.

Toxic effects/ Side effects

• Intravascular volume depletion
• Electrolyte fluctuations: severe in children
• Irregular heartbeat
• Unusual tiredness and weaknenss.

Irritant purgatives:

Castor oil , cascara and aloe vera

Mechanism of action: These act via. direct stimulation of enteric nervous system which leads to  peristalsis & purgation.

Clinical signs:

• Abdominal Cramps.
• Prolonged use leads to dependence & destruction of myenteric plexus and atonic colon.
• Confusion
• Dizziness and fatigue
• Yellow to brown coloration of acid urine ( for cascara, and/or senna only.

Diagnosis of purgative toxicity:

• History
• Clinical Signs
• Toxicological analysis of serum, urine and stool.
• Collapse and frequent diarrhoea
• Laboratory test.

o Blood and Urine test

o Stool test

• Purgatives containing Mg cause serious electrolyte and heart rhythm disturbances.

 Treatment:

• I/V fluid administration with close attention paid to electrolyte balance.
• Antidiarrheals (loperamide; 4mg orally after 1st stool then 2mg orally after each unformed stool , bismuth subsalicylate; 542 mg orally every 30 to 60 mins. and not to exceed 4 doses in 24 hrs.) are given to reduce symptomatic discomfort and inconvenience of frequent bowel movements.
• Activated charcoal reduces the efficacy of laxatives/ purgatives.

 Differential diagnosis:

• Food allergies
• Food poisoning/ bacterial toxins
• Diarrhoea

• Malabsorption