A patient who has been taking opioids for several weeks tells the nurse, "The medication doesn't seem to work as well anymore." The nurse recognizes this as a sign of:

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: Vasoconstriction is the desired therapeutic effect of phenylephrine in this context. Phenylephrine is a medication that stimulates the alpha1 receptors on the blood vessels, causing them to constrict or narrow. This increases the resistance to blood flow and raises the blood pressure. Phenylephrine is used as a vasopressor to treat hypotension, which is a condition of low blood pressure that can cause dizziness, fainting, or organ damage. The nurse should monitor the blood pressure and the peripheral pulses of the patient after administering phenylephrine.

Choice B reason: Bronchodilation is not the desired therapeutic effect of phenylephrine in this context. Phenylephrine is a medication that stimulates the alpha1 receptors on the blood vessels, causing them to constrict or narrow. It has no effect on the beta2 receptors on the bronchial smooth muscle, which are responsible for bronchodilation or widening of the airways. Phenylephrine is not used to treat respiratory conditions, such as asthma or chronic obstructive pulmonary disease, that cause bronchoconstriction or narrowing of the airways. The nurse should assess the respiratory rate and the breath sounds of the patient after administering phenylephrine.

Choice C reason: Diuresis is not the desired therapeutic effect of phenylephrine in this context. Phenylephrine is a medication that stimulates the alpha1 receptors on the blood vessels, causing them to constrict or narrow. It has no effect on the kidney function or the urine output. Phenylephrine is not used to treat fluid retention or edema, which are conditions of excess fluid in the body that can cause swelling, weight gain, or heart failure. The nurse should measure the urine output and the specific gravity of the patient after administering phenylephrine.

Choice D reason: Decreased heart rate is not the desired therapeutic effect of phenylephrine in this context. Phenylephrine is a medication that stimulates the alpha1 receptors on the blood vessels, causing them to constrict or narrow. It has little or no effect on the beta1 receptors on the heart, which are responsible for increasing the heart rate and the contractility. Phenylephrine may actually cause a reflex bradycardia, which is a slow heart rate that occurs when the baroreceptors in the blood vessels sense an increase in blood pressure and send signals to the brain to lower the heart rate. Phenylephrine is not used to treat tachycardia, which is a fast heart rate that can cause palpitations, chest pain, or arrhythmias. The nurse should monitor the electrocardiogram and the heart rate of the patient after administering phenylephrine.