What are the common prescription writings for antidiabetic drugs in a patient with type 2 diabetes mellitus, considering potential contraindications such as impaired renal function?

Common Prescription Writings for Antidiabetic Drugs

For patients with type 2 diabetes, initiate metformin and an SGLT2 inhibitor together as first-line therapy, with metformin dosed at 500 mg once daily with the evening meal, titrated by 500 mg weekly to a target of 1500-2000 mg daily, adjusting for renal function. 1, 2

First-Line Therapy: Metformin + SGLT2 Inhibitor

Metformin Dosing Protocol

Immediate-Release Formulation:

• Initial dose: 500 mg or 850 mg once daily with meals 1
• Titration: Increase by 500 mg or 850 mg every 7 days 1, 2
• Target dose: 1500-2000 mg daily for optimal glycemic control and weight loss 2
• Frequency: Can be divided into twice or three times daily dosing with meals 3

Extended-Release Formulation:

• Initial dose: 500 mg once daily with the evening meal 1, 2
• Titration: Increase by 500 mg every 7 days 1, 2
• Target dose: 1500-2000 mg once daily 2
• Advantage: Better GI tolerability and once-daily dosing improves adherence 4

Critical Renal Function-Based Dosing Adjustments

eGFR ≥60 mL/min/1.73 m²:

• Continue full dose up to 2000 mg daily 1, 2
• Monitor eGFR annually 1, 2

eGFR 45-59 mL/min/1.73 m²:

• Consider dose reduction in high-risk patients 1, 2
• Maximum 1000 mg daily recommended 2
• Monitor eGFR every 3-6 months 1, 2

eGFR 30-44 mL/min/1.73 m²:

• Halve the current dose 1
• Do not initiate or increase dose 2
• Monitor eGFR every 3-6 months 1, 2

eGFR <30 mL/min/1.73 m²:

• Stop metformin immediately; do not initiate 1, 2
• Risk of lactic acidosis 2

SGLT2 Inhibitor Dosing

Common SGLT2 Inhibitors (examples):

• Empagliflozin: 10 mg once daily, may increase to 25 mg daily 1
• Dapagliflozin: 5 mg once daily, may increase to 10 mg daily 1
• Canagliflozin: 100 mg once daily before first meal, may increase to 300 mg daily 1

Renal considerations:

• Continue if eGFR ≥20 mL/min/1.73 m² 5
• Can continue even if eGFR falls below 20 mL/min/1.73 m² unless not tolerated 5

Second-Line Therapy: GLP-1 Receptor Agonists

When to add: If glycemic targets not achieved with metformin + SGLT2i, or if SGLT2i contraindicated/not tolerated 1, 5

Long-Acting GLP-1 RA Dosing (Preferred Agents with CV Benefit)

Liraglutide (Victoza):

• Initial dose: 0.6 mg subcutaneous once daily 1, 6
• Titration: After 1 week, increase to 1.2 mg once daily 1, 6
• Maximum dose: 1.8 mg once daily for glycemic control 1, 6
• Administration: Any time of day, with or without meals 1

Semaglutide (Ozempic):

• Initial dose: 0.25 mg subcutaneous once weekly for 4 weeks (not therapeutic, for GI tolerability) 1
• Maintenance dose: 0.5 mg once weekly 1
• Maximum dose: Can increase to 1 mg or 2 mg once weekly if needed 1
• Administration: Any time of day, any day of week 1

Dulaglutide (Trulicity):

• Initial dose: 0.75 mg subcutaneous once weekly 1
• Maintenance dose: 1.5 mg once weekly for most patients 1
• Maximum dose: Can increase to 3 mg or 4.5 mg weekly if needed 1

Exenatide Extended-Release (Bydureon):

• Dose: 2 mg subcutaneous once weekly 1
• Administration: Any time of day 1

Renal considerations for GLP-1 RAs:

• No dose adjustment required for most agents down to eGFR ≥15 mL/min/1.73 m² 1
• Preferred for patients with eGFR <30 mL/min/1.73 m² when additional therapy needed 1, 5

Third-Line and Alternative Agents

DPP-4 Inhibitors

When to use: Alternative to GLP-1 RA based on patient preference, cost, or contraindications 1

Sitagliptin (Januvia):

• Standard dose: 100 mg once daily 1
• eGFR 30-44: 50 mg once daily 1
• eGFR <30: 25 mg once daily 1

Linagliptin (Tradjenta):

• Dose: 5 mg once daily 1
• Advantage: No renal dose adjustment required 1

Insulin Therapy

When to initiate: Evidence of catabolism, severe hyperglycemia (glucose >300 mg/dL or A1C >10%), or eGFR <30 mL/min/1.73 m² when oral agents insufficient 1

Basal Insulin (examples):

• Insulin glargine (Lantus, Basaglar): Start 10 units subcutaneous once daily at bedtime, titrate by 2 units every 3 days based on fasting glucose 1
• Insulin detemir (Levemir): Start 10 units subcutaneous once or twice daily 1
• Insulin degludec (Tresiba): Start 10 units subcutaneous once daily, any time 1

Sulfonylureas

When to use: Cost-driven choice or when other agents contraindicated; higher hypoglycemia risk 1

Glipizide:

• Initial dose: 5 mg once daily before breakfast 1
• Maximum dose: 20 mg daily (can divide into twice daily) 1
• Caution: Reduce dose in renal impairment 1

Glimepiride:

• Initial dose: 1-2 mg once daily with breakfast 1
• Maximum dose: 8 mg daily 1

Thiazolidinediones (TZDs)

When to use: Alternative agent; avoid in heart failure 1

Pioglitazone:

• Initial dose: 15-30 mg once daily 1
• Maximum dose: 45 mg daily 1
• Contraindication: Active heart failure 1

Essential Monitoring Requirements

For All Patients on Metformin:

• eGFR monitoring: Annually if ≥60 mL/min/1.73 m²; every 3-6 months if <60 mL/min/1.73 m² 1, 2
• Vitamin B12 levels: Check after 4 years of continuous use, or earlier if anemia or peripheral neuropathy develops 1, 2

For Patients on SGLT2 Inhibitors:

• Monitor for genital mycotic infections and volume depletion 1
• Educate on diabetic ketoacidosis risk, even with normal glucose levels 1

For Patients on GLP-1 RAs:

• Monitor for GI side effects (nausea, vomiting, diarrhea) especially during titration 1, 6
• Educate on pancreatitis symptoms 6

Common Pitfalls to Avoid

Metformin-specific:

• Never continue metformin with eGFR <30 mL/min/1.73 m² due to lactic acidosis risk 1, 2
• Hold metformin 48 hours before and after contrast procedures in patients with eGFR <60 mL/min/1.73 m² 1
• Start with low dose and titrate slowly to minimize GI side effects 2

SGLT2 inhibitor-specific:

• Do not withhold in patients with declining eGFR; continue for renal protection even if glycemic benefit diminishes 5
• Educate patients to stop during acute illness to prevent ketoacidosis 1

GLP-1 RA-specific:

• Titrate slowly to minimize nausea; the initial dose is not therapeutic 1
• Never share pens between patients due to infection risk 6