**Core Concept**
Hemoperfusion with charcoal is a medical treatment that uses a filter to remove toxins from the blood. It is particularly useful for treating patients with severe poisoning from substances that are poorly metabolized by the liver or that have a high volume of distribution.

**Why the Correct Answer is Right**
Hemoperfusion with charcoal is effective for removing substances like phenobarbital, carbamazepine, and theophylline from the bloodstream. The charcoal adsorbs these substances, allowing for their removal from the body. This is particularly useful in cases of overdose or severe poisoning, where other treatments may not be effective. The charcoal used in hemoperfusion is designed to have a high surface area, allowing it to effectively adsorb a wide range of toxins.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because hemoperfusion with charcoal is not typically used for treating heavy metal poisoning, which often requires chelation therapy.

**Option B:** This option is incorrect because hemodialysis is a more effective treatment for removing water-soluble substances like urea and creatinine from the blood, rather than charcoal adsorption.

**Option C:** This option is incorrect because activated charcoal is not effective for removing substances that are highly protein-bound, such as warfarin.

**Clinical Pearl / High-Yield Fact**
One important consideration when using hemoperfusion with charcoal is that it should only be used in cases of severe poisoning, as it can be a complex and resource-intensive treatment.

**Correct Answer: C. Theophylline**