A client is prescribed metformin for type 2 diabetes mellitus. The nurse instructs the client to take the medication with meals. What is the rationale for this instruction?

A) Incorrect. Metformin does not cause hypoglycemia, as it does not stimulate insulin secretion. It lowers blood glucose levels by decreasing hepatic glucose production and increasing insulin sensitivity.

B) Incorrect. Metformin absorption is not affected by food intake. The medication can be taken with or without food, but taking it with meals can help reduce gastrointestinal side effects.

C) Correct. Metformin can cause gastrointestinal upset, such as nausea, diarrhea, and abdominal pain. Taking it with meals can help minimize these effects by slowing down the transit of the medication through the digestive tract.

D) Incorrect. Metformin effectiveness is not influenced by food intake. The medication works by improving glucose metabolism and insulin action.

A) Incorrect. Acetaminophen is a non-opioid analgesic that can be used safely with phenytoin. However, the nurse should advise the client to limit their intake of acetaminophen to no more than 4 g per day, as higher doses can cause liver toxicity.

B) Incorrect. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that can be used safely with phenytoin. However, the nurse should advise the client to monitor for signs of bleeding, such as bruising, petechiae, and hematuria, as NSAIDs can inhibit platelet aggregation and increase the risk of bleeding.

C) Incorrect. Diphenhydramine is an antihistamine that can be used safely with phenytoin. However, the nurse should advise the client to avoid driving or operating machinery while taking diphenhydramine, as it can cause drowsiness and impair mental alertness.

D) Correct. Ginkgo biloba is an herbal supplement that can interact with phenytoin and reduce its effectiveness. Ginkgo biloba can induce hepatic enzymes that increase the metabolism and clearance of phenytoin, leading to subtherapeutic levels and increased risk of seizures.