What is the appropriate dosage and administration of glycerin (osmotic laxative) suppositories for an adult patient with constipation, considering their medical history and potential for adverse effects?

How to Prescribe Glycerin Suppositories for Adult Constipation

For adult patients with constipation, prescribe a single glycerin suppository (2-3 grams for adults) inserted rectally as needed, after ruling out fecal impaction and bowel obstruction through digital rectal examination. 1

Critical Pre-Treatment Assessment

Before prescribing any glycerin suppository, you must:

• Perform a digital rectal examination to rule out fecal impaction and assess for possible bowel obstruction 2, 1
• Check for contraindications including neutropenia, thrombocytopenia, recent colorectal surgery, anal trauma, or severe colitis 2, 1
• Evaluate for other causes of constipation: hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus, or constipating medications 1
• Ensure the patient does not have symptoms of intestinal obstruction before administering the suppository 1

Common pitfall: Do not prescribe oral laxatives alone if fecal impaction is present on rectal exam—the physical mass must be mechanically disrupted first with suppositories or enemas 3

When Glycerin Suppositories Are Indicated

Glycerin suppositories are appropriate when:

• Constipation has persisted for several days despite conservative measures (increased fluids, dietary fiber, exercise) 1
• The rectum is full on digital rectal examination 3
• First-line prophylactic measures (stimulant laxatives like senna or polyethylene glycol) have been insufficient 2

Dosing and Administration Instructions

Adult dose: One glycerin suppository (2-3 grams) inserted rectally as needed 1

Administration technique:

• Insert the suppository into the rectum beyond the anal sphincter 4
• The suppository should be retained for 15-30 minutes if possible to maximize effectiveness 3
• Glycerin works through local rectal irritation and by drawing water into the rectum, which softens stool and facilitates evacuation 1, 3

For more complete resolution: Consider combining the glycerin suppository with a mineral oil retention enema 1

If Constipation Persists After Glycerin Suppository

When the glycerin suppository is insufficient:

• Reassess for cause and severity of constipation; rule out bowel obstruction again 2, 1
• Add other agents such as bisacodyl suppository (2-3 tablets or suppository daily), polyethylene glycol (one capful in 8 oz water daily), lactulose (30-60 mL daily), or magnesium hydroxide (30-60 mL daily) 2, 1
• Consider sodium phosphate, saline, or tap water enema to dilate the bowel, stimulate peristalsis, and lubricate stool 2
• Avoid sodium phosphate enemas in patients at risk for renal dysfunction; limit to maximum once daily 2

Maintenance Therapy to Prevent Recurrence

After acute resolution with glycerin suppository:

• Prescribe a prophylactic stimulant laxative (senna) or polyethylene glycol (17 grams in 8 oz water twice daily) for ongoing prevention 2
• Do not prescribe docusate as prophylaxis—it has not shown benefit and is not recommended 2
• Maintain adequate fluid intake and dietary fiber (though supplemental medicinal fiber like psyllium is ineffective and may worsen constipation) 2
• Encourage exercise if feasible 2, 1