Chapter 58-Laxatives Flashcards
Laxatives (cathartic drugs)-Overview
Laxative, or cathartic, drugs are indicated for:
The short-term relief of constipation
To prevent straining when it is clinically undesirable (such as after surgery, myocardial infarction [MI], or obstetrical delivery)
To evacuate the bowel for diagnostic procedures
To remove ingested poisons from the lower GI tract
As an adjunct in anthelmintic therapy when it is desirable to flush helminths from the GI tract
Most laxatives are available in OTC preparations, and they are often abused.
Laxatives-Subtypes
Chemical stimulants- Chemically irritate the lining of the GI tract
Bulk stimulants- Cause fecal matter to increase in bulk
Osmotic laxatives- Pull more solute and/or water into the GI tract
Lubricants- Help the intestinal contents stay softer and more slippery
Laxatives, Chemical Stimulants- Generic Medications
Bisacodyl (Dulcolax)
Cascara
Castor oil
Senna (Senokot)
Laxatives, Chemical Stimulants-MOA
Directly stimulate the nerve plexus in the intestinal wall, causing increased movement and the stimulation of local reflexes.
Begin working at the beginning of the small intestine and increase motility throughout the rest of the GI tract by irritating the nerve plexus.
Castor oil, an old standby, is used when a thorough evacuation of the intestine is desirable.
Because castor oil blocks absorption of fats (including fat-soluble vitamins) and may lead to constipation from GI tract exhaustion when there is no stimulus to movement, its frequent use is not desirable
Bisacodyl acts in a similar manner but is somewhat milder in effect; it can also be given in a water enema to stimulate the activity in the lower GI tract.
Cascara is somewhat milder than castor oil and is often used when effects are needed overnight.
Laxatives, Chemical stimulants- ADME
Most of these agents are only minimally absorbed and exert their therapeutic effects directly in the GI tract.
Castor oil has an onset of action of 2 to 6 hours; the remaining chemical stimulants have an onset of action of 6 to 8 hours, making them preferable if one wants the drug to work overnight and result in effects in the morning.
Laxatives, Chemical stimulants-Contraindications & cautions
Contraindicated in acute abdominal disorders, including appendicitis, diverticulitis, and ulcerative colitis, when increased motility could lead to rupture or further exacerbation of the inflammation.
Laxatives should be used with caution in heart block, coronary artery disease (CAD), or debilitation, which could be affected by the decrease in absorption and changes in electrolyte levels that can occur.
Use with great caution during pregnancy and lactation because, in some cases, stimulation of the GI tract can precipitate labor, and many of these agents cross the placenta and are excreted in breast milk.
Magnesium laxatives can cause diarrhea in the neonate if used during lactation.
Laxatives, Chemical stimulants-Adverse effects
The adverse effects most commonly associated with chemical stimulant laxatives are GI effects such as diarrhea, abdominal cramping, and nausea.
A common adverse effect that is seen with frequent laxative use or laxative abuse is cathartic dependence. This reaction occurs when patients use laxatives over a long period of time and the GI tract becomes dependent on vigorous stimulation of the laxative. Without this stimulation, the GI tract does not move for a period of time (i.e., several days), which could lead to constipation, drying of the stool, and ultimately impaction.
Cascara, though a reliable agent, may have a slow, steady effect or may cause severe cramping and rapid evacuation of the contents of the large intestine.
Laxatives, Chemical stimulants-Drug to drug interactions
Because laxatives increase the motility of the GI tract and some interfere with the timing or process of absorption, it is advisable to not take laxatives with other prescribed medications.
The administration of laxatives and other medications should be separated by at least 30 minutes.
