**Core Concept**
A highly ionized drug has a high degree of solubility in water but low lipid solubility, which affects its pharmacokinetic properties. This is due to the high degree of dissociation of the drug in the blood, making it less lipophilic and more hydrophilic. As a result, the drug's ability to cross cellular membranes and be absorbed, distributed, metabolized, and excreted is altered.

**Why the Correct Answer is Right**
The correct answer is A because highly ionized drugs are mainly excreted by the kidneys through the process of glomerular filtration. Since these drugs are highly water-soluble, they are readily filtered by the glomeruli and excreted in the urine. This is in contrast to non-ionized or lipophilic drugs, which are primarily metabolized by the liver or excreted through the biliary system. The kidneys' ability to filter and excrete highly ionized drugs makes them a crucial organ for the elimination of these substances from the body. The renal tubules, particularly the proximal convoluted tubules, play a significant role in the reabsorption and secretion of these drugs, further affecting their elimination.

**Why Each Wrong Option is Incorrect**
**Option B:** Highly ionized drugs do not easily cross the placental barrier due to their hydrophilic nature. The placental barrier is a lipid-rich structure, and polar molecules like highly ionized drugs have difficulty crossing this barrier.

**Option C:** Highly ionized drugs are not well absorbed from the intestine due to their poor lipid solubility and high degree of dissociation in the gastrointestinal tract. This makes it difficult for these drugs to cross the lipid-rich intestinal epithelial cells and be absorbed into the bloodstream.

**Option D:** Highly ionized drugs do not accumulate in cellular lipids because they are hydrophilic and have a high degree of solubility in water. As a result, they tend to distribute in the extracellular fluid rather than accumulating in cellular lipids.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that the ionization state of a drug can significantly affect its pharmacokinetic properties, including absorption, distribution, metabolism, and excretion. Understanding the ionization state of a drug can help predict its behavior in the body and inform clinical decisions regarding dosing and administration.

**✓ Correct Answer: A. Is excreted mainly by kidney**