From the Guidelines
For a 41-year-old female schizophrenic patient experiencing constipation while on fluoxetine, carbamazepine, benztropine, and Lybalvi, I recommend first addressing benztropine as the likely culprit due to its strong anticholinergic properties, as suggested by the most recent guideline from the American Psychiatric Association 1. Consider discontinuing benztropine if extrapyramidal symptoms are not present, or reducing the dose if possible. Lybalvi (olanzapine/samidorphan) can also cause constipation, so dose reduction might be considered if clinically appropriate. For immediate management, recommend:
- Increased fluid intake to 2-3 liters daily
- Dietary fiber of 25-30g daily
- Regular physical activity Start with an osmotic laxative like polyethylene glycol (MiraLAX) 17g daily for 1-2 weeks, as recommended by recent studies on opioid-induced constipation 1. If ineffective, add a stimulant laxative such as bisacodyl 5-10mg daily as needed. For severe cases, consider adding docusate sodium 100mg twice daily. These medications cause constipation through anticholinergic effects that decrease gut motility and intestinal secretions. Benztropine has particularly strong anticholinergic properties, while antipsychotics like olanzapine (in Lybalvi) and some antidepressants can also contribute to this side effect through various receptor interactions affecting gastrointestinal function. It's also important to note that peripherally acting μ-opioid receptor antagonists (PAMORAs) such as methylnaltrexone may be effective in treating opioid-induced constipation, but their use may be limited by insurance coverage and should be considered on a case-by-case basis 1.
From the Research
Medication Changes and Treatments for Constipation
The patient is currently taking fluoxetine, carbamazepine, benztropine, and Lybalvi (olanzapine and samidorphan) for schizophrenia and is experiencing constipation.
- The patient's medication regimen should be reviewed to identify potential causes of constipation, such as antipsychotic-induced gastrointestinal hypomotility 2.
- Antipsychotic agents differ in their liability to induce constipation, and some, like clozapine, have a higher risk of serious complications 3, 4, 2, 5.
- Laxatives may be prescribed to treat constipation, but there is limited evidence on their effectiveness and safety in patients with antipsychotic-related constipation 3.
- A study comparing mannitol, an osmotic laxative, with rhubarb soda or phenolphthalein found that mannitol was more effective in relieving constipation within 24 hours of treatment, but the evidence was of very low quality and had a high risk of bias 3.
- Other treatments, such as glycerol suppositories, tuina massage, and acupuncture, have been studied, but the evidence is limited and of poor quality 3.
- Clinicians should be aware of the potential risks and benefits of off-label prescribing of newer medications for the treatment of antipsychotic-induced constipation 4.
- Active screening, monitoring, and treatment of constipation are recommended, as it can lead to serious consequences if left untreated 2, 5.
Considerations for Treatment
- The patient's medication regimen should be simplified, and unnecessary or potentially dangerous medications should be eliminated 6.
- The patient's pharmacist can be an excellent resource for determining appropriate dosages, potential for interaction, and overlapping drugs 6.
- Clinicians should be alert to possible adverse reactions and have a clearer understanding of the patient's medication therapy 6.