**Core Concept**
Infantile spasms, also known as West syndrome, is a severe form of epilepsy that affects infants. The condition is characterized by sudden, brief muscle contractions, often accompanied by developmental regression. Treatment of infantile spasms typically involves medications that can help control seizures and promote brain development.

**Why the Correct Answer is Right**
The first-line treatment for infantile spasms is adrenocorticotropic hormone (ACTH), which is derived from the pituitary gland. ACTH works by stimulating the adrenal glands to produce cortisol, a hormone that can help reduce inflammation in the brain and promote normal brain development. ACTH has been shown to be effective in controlling seizures and improving developmental outcomes in infants with infantile spasms.

**Why Each Wrong Option is Incorrect**
**Option A:** Vigabatrin is an antiepileptic medication that is sometimes used to treat infantile spasms, but it is not the first-line treatment. Vigabatrin can cause visual field defects and other side effects, making it a less desirable option for infants.
**Option B:** Topiramate is a broad-spectrum antiepileptic medication that can be used to treat a variety of seizure disorders, but it is not typically used to treat infantile spasms. Topiramate can cause side effects such as weight loss and cognitive impairment.
**Option C:** Phenobarbital is a barbiturate that can be used to treat seizures, but it is not the preferred treatment for infantile spasms. Phenobarbital can cause sedation, respiratory depression, and other side effects.

**Clinical Pearl / High-Yield Fact**
Infantile spasms are a medical emergency that requires prompt treatment to prevent long-term developmental consequences. Infants with infantile spasms should be evaluated by a pediatric neurologist or neonatologist as soon as possible to determine the best course of treatment.

**Correct Answer: C. Phenobarbital.**