Patient/caregiver was instructed upon therapeutic uses and mechanism of action of Carbidopa-Levodopa as follows:
- Carbidopa-Levodopa is a medication that is a combination of two drugs, levodopa and carbidopa.
- This combination therapy of levodopa and carbidopa is used in the treatment of symptoms of parkinson’s disease, which is caused by low levels of the neurotransmitter, dopamine, in the brain and nervous tissues.
- Blood-brain barrier is a highly selective membrane barrier, rich in lipid, around the brain, helping to prevent harmful chemicals and drugs gaining access to the brain. This helps with preventing any damage to the brain and nerve tissues from harmful chemicals. Being a highly selective membrane, blood-brain barrier will allow certain medications to pass through and reach the brain and will prohibit some others from reaching the brain. Lipid solubility is one major factor that determines the ability of a drug to cross the blood-brain barrier and enter the brain and nervous tissues.
- Levodopa, which is a part of Carbidopa-Levodopa, is a medication that crosses the blood-brain barrier and gains access into the brain and nervous tissues. After gaining access into the brain, levodopa is converted into dopamine, by the action of an enzyme, dopa decarboxylase. Thus, levodopa acts as a precursor to dopamine in the brain.
- A part of the levodopa taken could be acted upon by the enzyme dopa decarboxylase, in the peripheral blood, outside of the brain and nervous tissues, converting it to dopamine. But, dopamine by itself cannot cross the blood-brain barrier and gain access to brain and nervous tissues and so, cannot help with relief from symptoms of parkinson’s disease. As some portion of levodopa, due to conversion to dopamine in the peripheral blood, is getting wasted, levodopa has to be taken in high doses to cover for this wastage, if it were the only medication taken for relief of symptoms of parkinson’s disease. To avoid this intake of high dose of levodopa, it is combined with carbidopa and taken as Carbidopa-Levodopa, a combination therapy.
- Carbidopa is a medication that inhibits the enzyme dopa decarboxylase in the peripheral blood. Carbidopa cannot cross the blood-brain barrier and so, has no action on dopa decarboxylase in the brain and nervous tissues. This contributes to higher levels of levodopa in the peripheral blood, as conversion to dopamine is blocked, due to inhibition of the enzyme dopa decarboxylase by carbidopa. This helps with more levodopa available to cross the blood-brain barrier, which results in more precursor availability, and consequently, leads to production of more dopamine. Carbidopa, in other words, reduces the need for higher doses of levodopa.
- Increased production of dopamine in the brain and nervous tissues, secondary to Carbidopa-Levodopa use, can help with relief and management of symptoms of parkinson’s disease.
- Also, exposure to carbon monoxide intoxication and manganese intoxication can result in damage to the dopaminergic neurons, leading to symptoms of parkinson’s. Carbidopa-Levodopa can also be used in these cases of dopamine deficiency, to provide relief from the symptoms.
