AGS Beers Criteria Practice Test

Nitrofurantoin relies on kidney clearance to achieve high concentrations in the urine, which are necessary to treat lower urinary tract infections effectively. When creatinine clearance falls below a certain point, these urinary levels become unreliable and the drug may accumulate, raising the risk of toxicity without providing real benefit. The Beers Criteria specify avoiding nitrofurantoin when CrCl is below 30 mL/min because at or under this threshold the drug is neither effective nor safe for most older adults. The other values listed are not the cutoff used in this guideline. CrCl values like 60, 40, or 50 mL/min are higher than the threshold and do not mandate avoidance according to the Beers Criteria, whereas the critical caution is specifically at less than 30 mL/min.