Pharmacological Stimulants: Oral and Rectal Laxatives

Oral and rectal laxatives used in current neurogenic bowel management can include stool softeners, osmotic laxatives, and stimulant laxatives:

Stool softeners: Promote stool passage by increasing the water in stool via lowering the surface tension at the oil-water surface interface (e.g., Docusate sodium) (Johns et al. 2021)

Osmotic laxatives: Promote stool passage by increasing the water in stool via osmosis, (e.g., Polyethylene glycol, magnesium hydroxide, docusate sodium, lactulose) (Johns et al. 2021)

Stimulant laxatives: Promote colonic transit by activating contractions of the intestinal walls (e.g., Bisacodyl, sennosides) (Johns et al. 2021)

Oral laxatives are commonly used to treat constipation, but studies typically investigate rectal administration and/or prescription grade laxatives in neurogenic bowel management with SCI. Pharmacological rectal stimulants (suppositories and enemas) are a common component of a successful bowel management program, used by up to 60% of individuals with UMN bowel dysfunction (Coggrave et al. 2009). The two most commonly used are the glycerin suppository, which provides a mild local stimulus and lubrication, and the bisacodyl (dulcolax) suppository, which provides a dose of stimulant laxative directly to the colonic mucosa producing peristalsis throughout the colon. Other options include polyethylene glycol suppository, sennosides suppository, sodium hydrogen carbonate suppositories, sodium citrate and glycerol micro-enema and docusate sodium micro-enema (Johns et al. 2021).

Discussion

Pharmacological rectal agents (suppositories or enemas) are commonly used by individuals with SCI to stimulate reflex evacuation at the time chosen for bowel care. They are an essential element of a bowel program for many individuals with upper motor neuron bowel though there is little evidence to support most of the suppositories and enemas used. However, the effectiveness of the HVB bisacodyl suppositories compared to the PGB suppositories has been examined. The total bowel care time with the PGB suppository is significantly less (Stiens et al. 1998; Frisbie 1997; Dunn & Galka 1994) compared to HVB suppository. House and Stiens (1997) compared the effectiveness of HVB, PGB and docusate glycerin (mini-enema) in participants with upper motor neuron lesions. Results showed a significant decrease in bowel care time using the PGB suppository and the mini-enema as compared with the HVB suppositories.

In documenting the use of laxatives and opioids in people with SCI and their effects on bowel outcomes, Round et al. (2021) found that the number of people using laxatives and opioids significantly decreased between admission and discharge (p=0.004 and p=0.001, respectively). Findings showed that laxatives were positively correlated with fecal incontinence frequency at discharge, but not at admission. Also, the average dose of opioids demonstrated a constipating effect with higher dosages at discharge (p=0.009). There is little evidence on opioid-induced constipation and narcotic agonists in the SCI population (Johns et al. 2021), but the American Gastroenterological Association (AGA) Guidelines recommend laxatives as first line treatment, followed by narcotic antagonists (PAMORA drugs) such as naloxegol, methylnaltrexone, and naldemedine. Johns et al. (2021) also identified the oral opioid antagonist lubiprostone which is currently used in NBD.

Based on the poor evidence and the myriad of potential side effects, opioids may be considered in neuropathic pain treatment only as add-on therapy to anticonvulsants, always considering the risk-benefit ratio, particularly re: someone’s bowels, and opioids are not suggested at all as a singular therapy for SCI related neuropathic pain (Franz et al. 2019).

Conclusion

There is level 1 evidence (from systematic review; Yi et al. 2014) to support PGB suppositories for bowel management. There is a clinically significant decrease in the total bowel care time, time to flatus and defecation period.

There is evidence from one systematic review (Johns et al. 2021) that PGB bisacodyl suppositories demonstrate a higher efficacy than HVB bisacodyl suppositories in most studies, although findings show HVB bisacodyl is more commonly used due to lower costs and higher availability.

There is level 1 evidence from one RCT (House & Stiens, 1997) that bowel care time decreases with the use of PGB bisacodyl suppositories or docusate sodium mini-enemas in comparison to HVB bisacodyl suppositories. PGB bisacodyl suppositories and docusate sodium mini-enemas demonstrated similar effects on bowel care in comparison to each other.

There is level 2 evidence (Stiens 1998) that found PGB bisacodyl suppositories significantly reduce total time of bowel care and time of defecation when compared to HVB bisacodyl suppositories.

There is level 2 evidence (Frisbie 1997) that bowel care time reduces by half with the use of PGB bisacodyl suppositories in comparison to HVB bisacodyl suppositories.

There is level 4 evidence (Dunn & Galka, 1994) that mean evacuation time significantly decreases with the use of Therevac SB “mini-enema” in comparison to bisacodyl suppositories.

There is level 4 evidence (Round et al. 2021) that the use of opioids decreases bowel movement frequency and has a constipating effect. Laxative use was associated with higher fecal incontinence at discharge.