Final answer:
Close monitoring for drug toxicity is necessary when a client receives medication with a narrow therapeutic index or that tends to accumulate in the body, such as diuretics affecting the loop of Henle. The dosage of these medications must be determined with careful consideration of patient-specific factors to avoid toxicity.
Step-by-step explanation:
The nurse should observe most closely for drug toxicity when a client receives a medication that has the characteristic of a narrow therapeutic index or when the medication is known to accumulate in the body leading to potentially toxic levels. This is especially important in drugs that are cleared by the kidneys, such as drugs that cause diuresis (increased urination). Diuretic drugs, like those affecting the loop of Henle and inhibiting the reabsorption of Na+ and Cl-, can lead to significant alterations in fluid and electrolyte balance, which can subsequently result in drug toxicity if not monitored closely.
Factors to consider when determining the dosage of a drug include the patient's age, body mass, liver and kidney function, and potential drug-drug interactions. These factors are critical in avoiding toxicity. Furthermore, after a drug has been marketed, ongoing pharmacovigilance is essential to monitor its long-term safety and its effect on specific subgroups of patients, ensuring any signs of toxicity are promptly addressed.