A nurse is completing a medical interview with a client who has elevated cholesterol levels and takes warfarin. The nurse should recognize that which of the following actions by the client can potentiate the effects of warfarin?

Choice A reason: A headache is not likely due to the anxiety about the chest pain, as anxiety usually causes other symptoms, such as palpitations, sweating, or trembling. A headache is more likely related to the vasodilating action of nitroglycerin, which causes increased blood flow to the brain.

Choice B reason: A headache does not indicate tolerance to the medication, as tolerance usually manifests as a reduced effect of the medication on relieving chest pain. A headache is more likely a sign of the medication's potency, as it indicates that the nitroglycerin is reaching the systemic circulation.

Choice C reason: A headache is an expected adverse effect of the medication, as nitroglycerin causes vasodilation of the cerebral vessels, which can result in increased intracranial pressure and pain. A headache is usually mild and transient, and can be relieved by taking analgesics, such as acetaminophen.

Choice D reason: A headache is not an indication of an allergy to the medication, as an allergic reaction usually causes other symptoms, such as rash, itching, swelling, or difficulty breathing. A headache is more likely a pharmacological effect of the medication, rather than an immunological response.

Choice A reason: Taking the medication in the morning is not the correct instruction. Simvastatin is a statin drug that lowers cholesterol levels by inhibiting the enzyme that produces cholesterol in the liver. The liver produces more cholesterol at night, so simvastatin is more effective when taken in the evening or at bedtime.

Choice B reason: Avoiding grapefruit juice is the correct instruction. Grapefruit juice can increase the blood levels of simvastatin and cause serious side effects such as muscle damage, liver damage, and kidney failure. Grapefruit juice inhibits the enzyme that metabolizes simvastatin in the intestine, leading to higher concentrations of the drug in the bloodstream.

Choice C reason: Monitoring for ringing in the ears is not the correct instruction. Ringing in the ears, or tinnitus, is not a common or serious side effect of simvastatin. However, some other medications that lower cholesterol, such as niacin and gemfibrozil, can cause tinnitus. The client should report any unusual or persistent symptoms to the prescriber.

Choice D reason: Expecting brown-colored urine is not the correct instruction. Brown-colored urine, or hematuria, is not a normal or expected side effect of simvastatin. However, it may indicate a serious condition such as rhabdomyolysis, which is a rare but life-threatening complication of statin therapy. Rhabdomyolysis is the breakdown of muscle tissue that releases a protein called myoglobin into the bloodstream. Myoglobin can damage the kidneys and cause brown-colored urine. The client should seek immediate medical attention if they notice any signs of rhabdomyolysis, such as muscle pain, weakness, fever, or dark urine.