Final answer:
An oliguric drug used to treat hypertension by working on the loop of Henle and inhibiting the reabsorption of Na+ and Cl- can cause an increase in urination frequency.
Step-by-step explanation:
The drug that can cause an increase in urination frequency is most likely an oliguric used to treat hypertension. The oliguric is likely working on the loop of Henle and inhibiting the reabsorption of Na+ and Cl-. This inhibits the concentration of urine, leading to increased urination frequency.