A nurse is preparing to administer phenylephrine as a vasopressor to treat a patient for hypotension. The desired therapeutic effect of phenylephrine in this context is:

Choice A reason: Peak level is the correct term to describe the highest concentration of a drug in the blood after it is administered. Peak level is also known as peak plasma concentration or Cmax, and it reflects the rate and extent of drug absorption. Peak level is influenced by factors such as the route of administration, the dose, the formulation, and the bioavailability of the drug. Peak level is important to monitor for drugs that have a narrow therapeutic range, meaning that there is a small difference between the effective and toxic doses. The nurse should measure the peak level at the appropriate time after the drug administration, and adjust the dose or the frequency as needed to achieve the desired therapeutic effect and avoid adverse effects .

Choice B reason: Halflife is not the correct term to describe the highest concentration of a drug in the blood after it is administered. Halflife is the time it takes for the concentration of a drug in the blood to decrease by 50%. Halflife reflects the rate of drug elimination, which depends on factors such as the metabolism and excretion of the drug. Halflife is important to determine the dosing interval and the time to reach steady state. The nurse should consider the halflife of the drug when prescribing or administering the drug, and avoid drug accumulation or subtherapeutic levels .

Choice C reason: Trough level is not the correct term to describe the highest concentration of a drug in the blood after it is administered. Trough level is the lowest concentration of a drug in the blood before the next dose is given. Trough level reflects the balance between drug absorption and elimination, and it indicates the minimum effective concentration of the drug. Trough level is important to monitor for drugs that have a narrow therapeutic range, meaning that there is a small difference between the effective and toxic doses. The nurse should measure the trough level just before the next dose of the drug, and adjust the dose or the frequency as needed to achieve the desired therapeutic effect and avoid adverse effects .

Choice D reason: Steady state is not the correct term to describe the highest concentration of a drug in the blood after it is administered. Steady state is the condition when the rate of drug administration is equal to the rate of drug elimination, and the concentration of the drug in the blood remains constant. Steady state is usually reached after four to five halflives of the drug, and it reflects the optimal therapeutic level of the drug. Steady state is important to maintain for drugs that have a long halflife or a narrow therapeutic range, meaning that there is a small difference between the effective and toxic doses. The nurse should ensure that the drug is administered at regular intervals and at the appropriate dose to achieve and maintain steady state.

Choice A reason: Tinnitus is a rare side effect of Flexeril, which is a medication that relaxes the muscles and relieves pain and stiffness¹. Tinnitus is a ringing or buzzing sound in the ears that can be caused by various factors, such as ear infections, noise exposure, or certain medications. Flexeril does not affect the auditory system directly, but it can cause confusion or dizziness, which may worsen the perception of tinnitus.

Choice B reason: Drowsiness is the most common side effect of Flexeril, which is a medication that relaxes the muscles and relieves pain and stiffness¹. Drowsiness occurs because Flexeril has sedative and anticholinergic properties, which means that it blocks the action of acetylcholine, a neurotransmitter that regulates arousal and alertness. Flexeril can impair the mental and physical abilities, especially in elderly patients or those who take other medications that cause drowsiness¹. The nurse should educate the patient about the risk of drowsiness and advise them to avoid driving or operating machinery while taking Flexeril.

Choice C reason: Diarrhea is not a common side effect of Flexeril, which is a medication that relaxes the muscles and relieves pain and stiffness¹. Diarrhea is a condition that causes loose or watery stools, which can be caused by various factors, such as infections, food intolerance, or certain medications. Flexeril does not affect the gastrointestinal system directly, but it can cause dry mouth, nausea, or constipation, which may alter the bowel movements¹.

Choice D reason: Palpitations are not a common side effect of Flexeril, which is a medication that relaxes the muscles and relieves pain and stiffness¹. Palpitations are a sensation of rapid or irregular heartbeat, which can be caused by various factors, such as stress, anxiety, caffeine, or certain medications. Flexeril does not affect the cardiac system directly, but it can lower the blood pressure or interact with other medications that affect the heart rate, such as betablockers or antidepressants¹.