Apomorphine is a potent medication used in the management of Parkinson’s disease. Despite the similarity in name, apomorphine contains no morphine and is not an opioid or a pain-relieving medication. Its function is specifically tied to the motor symptoms associated with Parkinson’s, and it is prescribed to address specific challenges that arise during the course of the disease.
What Apomorphine Treats
Apomorphine is indicated for the acute, intermittent treatment of “off” episodes in people with advanced Parkinson’s disease. These episodes are periods when a patient’s regular maintenance medications, like levodopa, are not working optimally. During an “off” period, the motor symptoms of Parkinson’s return, sometimes suddenly and unpredictably. This can include the re-emergence of tremor, stiffness, and significant difficulty with movement and coordination.
These periods of hypomobility can be disruptive, impacting a person’s ability to perform daily tasks. “Off” episodes can manifest as “wearing-off,” where symptoms return before the next scheduled dose of medication is due, or dose failure, where a dose provides no noticeable effect. Apomorphine is not a routine treatment but is instead used as an on-demand, or “rescue,” therapy.
Its purpose is to provide rapid relief from these specific episodes, helping to restore a state of mobility, referred to as an “on” state. Studies have shown that its use can significantly reduce daily “off” time and improve motor function as measured by clinical scales.
How Apomorphine Is Administered
The delivery methods for apomorphine are designed for rapid action to counteract “off” episodes as they occur. Because the drug is not effectively absorbed when taken orally, it must be administered through routes that bypass the digestive system. This ensures the medication reaches the bloodstream and brain quickly, with symptom relief often occurring within minutes.
One primary method of administration is subcutaneous injection, delivered into the fatty layer of tissue just under the skin. Patients and caregivers are trained to give these injections using a portable, pen-like auto-injector device. This method allows for precise dosing and is effective for providing relief, with an onset of action that can range from four to twelve minutes. Common injection sites include the abdomen or the thigh.
A second form of administration is a sublingual film, which is placed under the tongue. This thin film dissolves in the mouth in about three minutes, allowing the medication to be absorbed directly into the bloodstream. Patients are instructed to moisten their mouth with water before placing the entire film as far back under the tongue as possible and allowing it to dissolve completely. Both the injection and the sublingual film require an initial dose titration supervised by a healthcare provider to find the effective and tolerable dose.
Mechanism of Action
The motor symptoms of Parkinson’s disease are caused by the progressive loss of brain cells that produce dopamine, a neurotransmitter that regulates movement and coordination. This dopamine deficiency disrupts the brain’s ability to send signals that control muscle function. Apomorphine works as a potent dopamine agonist, meaning it directly stimulates the brain’s dopamine receptors. It effectively mimics the action of natural dopamine.
By binding to and activating specific dopamine receptors, particularly the D1 and D2 subtypes, apomorphine helps to compensate for the lack of dopamine in the brain. This action can be visualized like a key fitting into a lock; the dopamine receptors are the “locks,” and apomorphine acts as a “key” that turns them on.
This direct stimulation of postsynaptic dopamine receptors in brain regions like the striatum is what allows for the rapid reversal of “off” episode symptoms. The clinical response to apomorphine is comparable in effect to levodopa, the standard treatment for Parkinson’s, but with a much faster onset.
Side Effects and Safety Considerations
The use of apomorphine is associated with a range of potential side effects, with severe nausea and vomiting being among the most common. Because of this, treatment is initiated along with an anti-nausea medication, such as trimethobenzamide. This is started three days prior to the first apomorphine dose and continued for up to two months.
Other frequent side effects include:
- Drowsiness or sudden sleepiness
- Dizziness
- Yawning
- Swelling in the arms or legs
Apomorphine can cause a drop in blood pressure (hypotension) when changing positions from sitting to standing, which increases the risk of falls. A dangerous interaction can occur when apomorphine is used with a class of anti-nausea drugs known as 5-HT3 antagonists, such as ondansetron. The combination is contraindicated because it can lead to profound hypotension and loss of consciousness.
Other serious potential effects include hallucinations or psychotic-like behaviors, which may involve seeing things that are not there or feeling agitated. Some individuals may develop intense, uncontrollable urges, such as compulsive gambling or shopping. For the injectable form, reactions at the injection site like bruising, swelling, and itching are common. In rare cases, more serious issues like blood clots can occur if the medication is accidentally injected into a vein.