Medications as a Contributing Factor
The amount of disability experienced by the patient will determine the start of dopamine therapy. A hand tremor that is disabling to an executive may not be the same experience for a retiree. Once started, levadopa can be titrated to best efficacy, considering motor fluctuations and dyskinesias. The dose can be modified, the interval between dosing can be changed, or another product can be added as an adjunct. This includes catechol-O-methyl transferase inhibitors (entacapone, talcapone), dopamine agonists (ropinirole and pramipexole), and monoamine oxidase-b inhibitors.
Antipsychotics may interact with dopamine, decreasing its effectiveness. Of the antipsychotics available, Quetiapine fumarate is preferred over clozapine because of agranulocytosis, a reduction in white blood cells.
In addition to PD's physical impairments, drugs frequently prescribed to PD patients have adverse effects that can be a contributing factor for constipation. Nortryptylline is often used for depression. Anticholinergics such as oxybutynin for overactive bladder and scopolamine for increased saliva can also exacerbate the symptoms of constipation.
Diuretics used to treat hypertension, hypokalemia induced by diuretics, opioids, calcium to treat osteoporosis, iron supplements to treat anemia, calcium channel blockers, and nonsteroidal anti-inflammatories are all cited as confounding factors that multiply the problem of constipation.
The effect of levadopa in early-stage PD gastrointestinal dysfunction was explored. Levadopa/carbidopa 200/20 mg administered 2 times a day for 3 months was found to lessen paradoxical sphincter contraction and improve anorectal constipation. There was no change in CTT. There was less resistance of paradoxical sphincter contraction (significant), lessened postdefecation residuals, and lessened amplitude of abdominal strain.