to adult dose
Adults: 1250 mg 1–4 times a day
Children 6–12 yr: 625 mg 1–4 times a day
Adults and children older than 12 yr: 50–500 mg/day
Children 6–12 yr: 40–120 mg/day (All doses taken with a full glass of water)
Adults: 10–15 mg (tablets) or 10-mg suppository once daily
Children: 5-mg tablet or 5-mg suppository once daily
Adults: 2 tablets once or twice a day
Children 6–12 yr: 1 tablet once or twice a day
Adults: 15–30 mL daily, increased to 60 mL if needed
Children 6 mo–1 yr: 40 mg/kg PO daily
Children 2–5 yr: 400–1200 mg PO daily
Children 6–11 yr: 1200–2400 mg PO daily
Children >12 yr: 2400–4800 mg PO daily
Adults: 15–45 mL daily; may take in divided doses
Children: 5–45 mL daily; may take in divided doses
The surfactants (e.g., docusate sodium) are group III laxatives: they produce a soft stool several days after the onset of treatment. Surfactants alter stool consistency by lowering surface tension, which facilitates penetration of water into the feces. The surfactants may also act on the intestinal wall to (1) inhibit fluid absorption and (2) stimulate secretion of water and electrolytes into the intestinal lumen. In this respect, surfactants resemble the stimulant laxatives (see later).
Preparations, Dosage, and Administration
The surfactant family consists of two docusate salts: docusate sodium and docusate calcium. The dosage for docusate sodium [Colace], the prototype surfactant, is shown in Table 63.4. Administration should be accompanied by a full glass of water.
The stimulant laxatives (e.g., bisacodyl, senna, castor oil) have two effects on the bowel. First, they stimulate intestinal motility—hence their name. Second, they increase the amount of water and electrolytes within the intestinal lumen by increasing secretion of water and ions into the intestine and by reducing water and electrolyte absorption. Most stimulant laxatives are group II agents: they act on the colon to produce a semifluid stool within 6 to 12 hours.
Stimulant laxatives are widely used—and abused—by the general public and are of concern for this reason. They have few legitimate applications. Two applications that are legitimate are (1) treatment of opioid-induced constipation and (2) treatment of constipation resulting from slow intestinal transit. Properties of individual agents are discussed next.
Bisacodyl [Correctol, Dulcolax] is unique among the stimulant laxatives in that it can be administered by rectal suppository as well as by mouth. Oral bisacodyl acts within 6 to 12 hours. Hence tablets may be given at bedtime to produce a response the following morning. Bisacodyl suppositories act rapidly (in 15–60 minutes). Dosages for bisacodyl are shown in Table 63.4.
Bisacodyl tablets are enteric coated to prevent gastric irritation. Accordingly, patients should be advised to swallow them intact, without chewing or crushing. Because milk and antacids accelerate dissolution of the enteric coating, the tablets should be administered no sooner than 1 hour after ingesting these substances.
Bisacodyl suppositories may cause a burning sensation and, with continued use, proctitis may develop. Accordingly, long-term use should be discouraged.
Senna [Senokot, Ex-Lax] is a plant-derived laxative that contains anthraquinones as active ingredients. The actions and applications of senna are similar to those of bisacodyl. Anthraquinones act on the colon to produce a soft or semifluid stool in 6 to 12 hours. Systemic absorption followed by renal secretion may impart a harmless yellow-brown or pink color to the urine. Dosages are presented in Table 63.4.
Castor oil is the only stimulant laxative that acts on the small intestine. As a result, the drug acts quickly (in 2–6 hours) to produce a watery stool. Hence, unlike other stimulant laxatives, which are all group II agents, castor oil belongs to group I. Use of castor oil is limited to situations in which rapid and thorough evacuation of the bowel is desired (e.g., preparation for radiologic procedures). The drug is far too powerful for routine treatment of constipation. Because of its relatively prompt action, castor oil should not be administered at bedtime. The drug has an unpleasant taste that can be improved by chilling and mixing with fruit juice.
The laxative salts (e.g., sodium phosphate, magnesium hydroxide) are poorly absorbed salts whose osmotic action draws water into the intestinal lumen. Accumulation of water causes the fecal mass to soften and swell, thereby stretching the intestinal wall, which stimulates peristalsis. When administered in low doses, the osmotic laxatives produce a soft or semifluid stool in 6 to 12 hours. In high doses, these agents act rapidly (in 2–6 hours) to cause a fluid evacuation of the bowel. High-dose therapy is employed to empty the bowel in preparation for diagnostic and surgical procedures. High doses are also employed to purge the bowel of ingested poisons and to evacuate dead parasites after anthelmintic therapy.
We have two groups of laxative salts: (1) magnesium salts (magnesium hydroxide, magnesium citrate, and magnesium sulfate) and (2) one sodium salt (sodium phosphate). Dosages for magnesium hydroxide solution (also known as milk of magnesia) and sodium phosphate are shown in Table 63.4.