DOC for drug (phenothiazine) induced parkinsonism: March 2013
**Core Concept**
Phenothiazine-induced parkinsonism is a form of drug-induced parkinsonism caused by the blockade of dopamine receptors in the basal ganglia, leading to an imbalance between dopamine and acetylcholine. This results in the characteristic symptoms of parkinsonism, including tremors, rigidity, bradykinesia, and postural instability.
**Why the Correct Answer is Right**
The dopamine agonists, such as bromocriptine, are effective in treating phenothiazine-induced parkinsonism by stimulating dopamine receptors in the basal ganglia, thereby counteracting the blocking effect of phenothiazines. Bromocriptine works by activating dopamine D2 receptors, which leads to an increase in dopamine release and a subsequent reduction in acetylcholine levels, thereby alleviating the symptoms of parkinsonism. The use of dopamine agonists is preferred in drug-induced parkinsonism as they do not carry the risk of exacerbating the underlying cause of the disorder.
**Why Each Wrong Option is Incorrect**
**Option A:** Levodopa is a precursor to dopamine and is used in the treatment of Parkinson's disease, but it is not the first-line treatment for phenothiazine-induced parkinsonism. Levodopa is more effective when used in combination with carbidopa, which inhibits the peripheral conversion of levodopa to dopamine, allowing more levodopa to cross the blood-brain barrier.
**Option B:** Anticholinergics, such as trihexyphenidyl, are used in the treatment of Parkinson's disease, but they are not the first-line treatment for phenothiazine-induced parkinsonism. Anticholinergics work by blocking the action of acetylcholine, but they can have significant side effects, including dry mouth, constipation, and confusion.
**Option C:** Amantadine is a dopamine agonist that is used in the treatment of Parkinson's disease, but it is not the first-line treatment for phenothiazine-induced parkinsonism. Amantadine has a more complex mechanism of action, involving the blockade of N-methyl-D-aspartate (NMDA) receptors and the inhibition of the reuptake of dopamine and norepinephrine.
**Clinical Pearl / High-Yield Fact**
Dopamine agonists are preferred in the treatment of drug-induced parkinsonism as they do not carry the risk of exacerbating the underlying cause of the disorder. This is in contrast to levodopa, which can worsen the symptoms of drug-induced parkinsonism in some cases.
**Correct Answer: C. Amantadine is a dopamine agonist that is used in the treatment of Parkinson's disease, but it is not the first-line treatment for phenothiazine-induced parkinsonism.