Carbidopa/levodopa (Sinemet) is used for managing motor symptoms of Parkinson’s Disease (PD). Levodopa is a dopamine precursor used to replenish depleted dopamine levels associated with PD. Unfortunately, levodopa isn’t effective alone as it is broken down before making it across the blood-brain barrier. Therefore, carbidopa is added to levodopa formulations to prevent its breakdown and allow it to penetrate the brain. The majority of patients are dosed anywhere between 1-3 tablets 3 times daily, though it varies depending on individual response, tolerability, and formulation. In practice, I’ve seen Sinemet dosed up to 6-8 times per day to help manage symptoms as the disease progresses. This post addresses common Sinemet clinical pearls encountered in everyday practice.
Food Interactions – Take With Or Without Food?
Carbidopa/levodopa is ideally taken on an empty stomach 1 hour before a meal for optimal absorption. This isn’t always practical or possible especially when you consider patients who need to take the medication several times per day. Dietary protein competes for the same transporters as levodopa, consuming meals high in protein can significantly decrease the absorption and efficacy of levodopa. Consistency and clinical monitoring are important for the management of the carbidopa/levodopa and protein interaction. If you are looking for a nice reference guide on drug-food interactions, look no further!
Side Effects – Sinemet Clinical Pearls
Some patients may experience nausea after taking carbidopa/levodopa on an empty stomach. If this occurs, high protein foods should still be minimized but it may be taken with bread, crackers, banana, or another non-protein product.
Though carbidopa/levodopa can reduce tremor, stiffness, and rigidity associated with PD, overdosing can induce worsening movement or dyskinesia. Compared to dystonia, dyskinesia is usually painless and presents as dance-like motions. Dystonia is generally associated with pain and is more typically seen in underdosed states. Usually, dystonia would relate to untreated symptoms of PD itself. Development of dyskinetic movement doesn’t warrant treatment unless bothersome. If these movements significantly interfere with daily activities, dose reduction is usually the first-line consideration though this comes at the risk of worsening stiffness and mobility issues.
Psychiatric concerns such as hallucinations are also a potential adverse effect of carbidopa/levodopa. Much like other adverse effects, this is a dose-dependent effect. Dose reduction is the usual first step in alleviating this adverse effect. In rare cases, low-dose antipsychotics (with lower EPS risk such as quetiapine) may be considered if dose reductions cause substantial Parkinson’s symptoms.
Carbidopa/levodopa is available in a variety of dosage forms, though immediate-release (IR) tablets are the most frequently used formulation. Controlled-release formulations require less frequent administration, but they are more expensive and undergo erratic absorption. Their delayed onset can also prolong “off” time or periods of motor symptoms. The major disadvantage of IR tablets is their frequent dosing requirements. Dose adjustments can be made to promote adherence and should be guided by “on” and “off” times. Since carbidopa/levodopa is only intended for symptomatic control as opposed to prevention of disease progression, it should be used to optimize patient quality of life.
Carbidopa/levodopa remains the gold standard for symptomatic control of PD. It is effective for improving mobility and functionality for individuals experiencing muscle rigidity, stiffness, and potentially tremor. Frequent administration and potential food interactions pose challenges to its administration, though adjustments can be to help alleviate these issues. Over time, symptoms of PD can worsen as the body losses its ability to produce endogenous dopamine and therefore may require higher doses of carbidopa/levodopa. Additionally, some may wish to live a more active lifestyle and require more intense treatment whereas others can function normally with mild symptoms. Regardless, symptoms must be monitored regularly to optimize quality of life and functionality. This Sinemet podcast episode is a no-brainer if you are looking for more Sinemet clinical pearls!
Written by Alyssa Butterfield, PharmD Candidate in collaboration with Eric Christianson, PharmD, BCPS, BCGP