A 28-year-old primigravida at 16 weeks of gestation presents to the antenatal clinic with complaints of severe headaches and elevated blood pressure (160/110 mmHg). She has a history of chronic hypertension managed with enalapril for the past 3 years. On examination, she appears anxious but has no focal neurological deficits. Urinalysis shows 2+ proteinuria. The obstetrician decides to switch her antihypertensive medication immediately. Which of the following is the most appropriate replacement drug?