Pharmacology
Experimental pharmacology
The effects of Senna Leaves are due primarily to the hydroxyanthracene glucosides, especially sennosides A and B. These _-linked glucosides are secretagogues that increase net secretion of fluids and specifically influence colonic motility and enhance colonic transit. They are not absorbed in the upper intestinal tract; they are converted by the bacteria of the large intestine into
the active derivatives (rhein-anthrone). The mechanism of action is twofold:
(1) Effect on the motility of the large intestine (stimulation of peristaltic contractions and inhibition of local contractions), resulting in an accelerated colonic transit, thereby reducing fluid absorption.
(2) An influence on fluid and electrolyte absorption and secretion by the colon (stimulation of mucus and active chloride secretion), increasing fluid secretion
Clinical pharmacology
The time of action of senna is usually 8–10 hours, and thus the dose should be taken at night. The action of the sennosides augments, without disrupting, the response to the physiological stimuli of food and physical activity. The sennosides abolish the severe constipation of patients suffering from severe irritable bowel syndrome. In therapeutic doses, the sennosides do not disrupt the usual pattern of defecation times and markedly soften the stool. Sennosides significantly increase the rate of colonic transit and increase colonic peristalsis, which in turn increase both faecal weight and dry bacterial mass. Due to their colonic specificity, the Sennosides are poorly absorbed in the upper gastrointestinal tract.
Toxicity
The major symptoms of overdose are griping and severe diarrhoea with consequent losses of fluid and electrolytes. Treatment should be supportive with generous amounts of fluid. Electrolytes, particularly potassium, should be monitored, especially in children and the elderly.
Contraindications
As with other stimulant laxatives, the drug is contraindicated in persons with ileus, intestinal obstruction, and stenosis, atony, undiagnosed abdominal symptoms, inflammatory colonopathies, appendicitis, abdominal pains of unknown cause, severe dehydration states with water and electrolyte depletion, or chronic constipation. Senna Leaves should not be used in children under the age of 10 years.
Warnings
Stimulant laxative products should not be used when abdominal pain, nausea, or vomiting are present. Rectal bleeding or failure to have a bowel movement after use of a laxative may indicate a serious condition. Chronic abuse, with diarrhoea and consequent fluid electrolyte losses, may cause dependence and need for increased dosages, disturbance of the water and electrolyte balance (e.g. hypokalaemia), atonic colon with impaired function, albuminuria and haematuria The use of stimulant laxatives for more than 2 weeks requires medical supervision. Chronic use may lead to pseudomelanosis coli (harmless). Hypokalaemia may re