Stimulating Laxatives
Two therapeutic effects
What is the best laxative for constipation treatments? One of them may be the stimulating laxatives. Fiber and osmotic laxatives act by increasing water content, improving consistency, softening the stool and allowing quicker passaage. Prokinetic agents send chemical signals to receptors in the gut which cause it to contract with greater frequency and force.
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In contrast so-called stimulating or stimulant laxatives increase mucosal release, as well as stimulate the myenteric plexus which leads to increased propulsive (or pushing) activity in the gut.
Therefore, stimulating laxatives actually have two therapeutic effects, overlapping with bulking laxatives. The result is increased smooth muscle activity which helps propel the stool through the intestinal lumen, alleviating chronic constipation. The major chemical groups are the anthraquinones, available under the generic name sennoside, and the diphenylmethane-derived agents, available under the generic name bisacodyl. Patients looking for the best laxative for themselves should check out this class of constipation medication.
Time to take effect
How long does it take for a stimulating laxative to take effect? Usually within 6 to 12 hours, patients can expect to begin having bowel movements.
Anthraquinones
Interestingly, the anthraquinones have no stimulating effect in the original chemical form, and must instead by activated by bacterial colonizing the gut (or enteric bacteria). In large doses, there may be cramping side effects. However, three worries plague patients who take anthraquinones, though none should be a cause of concern. The first is a fear that anthraquinones cause cancer, but there have been several studies that show no association of increased incidence in cancer and anthraquinone intake. The second is a condition known as melanosis, in which anthraquinone ingestion leads to discoloration of urine and colonic mucosa. However, this discoloration has been shown to be completely benign. Finally, the third is the fear that taking anthraquinones for long periods can lead to enteric (or intestinal) nerve damage. However, studies again show that the association between the two is insignificant.
Sennoside, an anthraquinone
The generic product sennoside is an anthraquinone, often touted as a completely natural constipation treatment. It is a highly effective laxative but unclear if it is the best laxative should there such a thing. There are no indications that the natural form is any better than industrially produced forms.
Bisacodyl
The bisacodyl class of stimulating laxative compounds is also activated by enzymes from gut bacteria. These medications are available in tablet form for ingestion, but can also be obtained in a suppository form for direct treatment of the rectum. Bisacodyls have been studied as to whether there are adverse effects from treatment. Of chief worry amongst these adverse is the claim that bisacodyls can lead to carcinogenesis and subsequently cancer in the colon. However, controlled studies show no such association.
For acute constipation and not chronic constipation?
The stimulating class of laxatives are usually used for acute constipation, or constipations that occur suddenly and disappear in a relatively short time. This is in contrast to chronic constipation that lasts weeks or months. The reason for caution in using sennoside and bisacodyl so often is that overuse can lead to electrolyte imbalance. However, reports have been written up on bisacodyl use in paraplegic and tetraplegic patients over very long periods of years to decades. In these cases, careful management of constipation medication shows that long-term use can be tolerated.
Sources:
Muller-Lissner et al, Myths and Misconceptions about Constipation, American Journal of Gastroenterology, 2005, 100:232-242