Differential Diagnosis

The patient's symptoms of mild constipation, occasional inability to completely empty the bladder, bladder distention, and mild confusion can be caused by various medications. Here's a differential diagnosis based on the provided categories:

• Single most likely diagnosis

  • Anticholinergics (e.g., diphenhydramine): These medications are commonly found in over-the-counter (OTC) drugs, such as those used for allergies, sleep aids, or cold and flu relief. Anticholinergics can cause urinary retention, constipation, and confusion, especially in elderly patients, due to their antimuscarinic effects.

• Other Likely diagnoses

  • Opioids: Opioid medications, whether prescription or OTC (in some combination products), can cause constipation and urinary retention. The patient's age and the fact that she takes OTC medications frequently increase the likelihood.
  • Calcium channel blockers: Certain calcium channel blockers can cause constipation and may contribute to urinary retention, although this is less common.

• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)

  • Antipsychotics: Although less likely given the context of OTC medications, antipsychotics can have significant anticholinergic side effects. In elderly patients, they can also increase the risk of stroke and mortality.
  • Diuretics (if prescribed): While diuretics are not typically OTC, if the patient is taking them, they could contribute to dehydration, which might exacerbate constipation and confusion.

• Rare diagnoses

  • Iron supplements: Iron can cause constipation, but it's less likely to cause significant urinary retention or confusion unless taken in very high doses.
  • Antihistamines (first-generation): Similar to anticholinergics, first-generation antihistamines can have anticholinergic effects, but they are less likely to be the primary cause unless the patient is taking them in high doses or has predisposing factors.