Calcium: Decreased; Potassium: Decreased; Sodium: Decreased

Are you sure? You are right about potassium and sodium levels. Remember that thiazide diuretics work on the distal convoluted tubule, which results in excretion of sodium and potassium in the urine, thus leading to decreased levels in the plasma. Conversely, the levels of calcium in the blood are increased due to reduced excretion of this electrolyte in the urine. 

Further Development

Mr. Hill is treated accordingly for anaphylactic shock. He recovers well and is advised to return to his General Practitioner so that his anti-hypertensive medication can be adjusted accordingly. 

Which drug should Mr. Hill be prescribed?