A 48-year-old man presents to general practice for a routine check and is found to have fasting plasma glucose 8.4 mmol/L on two occasions and HbA1c 7.6% (60 mmol/mol). He has BMI 32 kg/m², blood pressure 138/86 mmHg and eGFR 80 mL/min/1.73 m². According to the RACGP diabetes handbook, what is the most appropriate initial pharmacological management?