Comprehensive coverage of type 2 diabetes pharmacotherapy — mechanism of action, pharmacokinetics, cardiovascular and renal outcomes evidence, key drug interactions, and ADA/EASD algorithm positioning for metformin, SGLT2 inhibitors, GLP-1 receptor agonists, DPP-4 inhibitors, and insulin formulations.
Metformin (Glucophage) remains the cornerstone first-line agent in type 2 diabetes for most patients. Its primary action is reduction of hepatic gluconeogenesis via inhibition of mitochondrial complex I → elevated AMP:ATP ratio → AMPK activation → reduced PEPCK and G6Pase expression. Secondary actions include improved peripheral insulin sensitivity and — increasingly recognised — beneficial gut microbiome modulation (↑Akkermansia muciniphila).
PK: oral bioavailability ~50–60% (absorbed in small intestine, saturable transporter); renal elimination unchanged (no hepatic metabolism); t½ ~5 hours; not protein-bound. Dose: 500 mg BD–850 mg TDS with meals (reduces GI side effects); maximum 2,550–3,000 mg/day in divided doses. Extended-release (XR) formulation improves GI tolerability.
Renal monitoring: reduce dose at eGFR 30–45 mL/min/1.73m²; stop at eGFR <30 (risk of lactic acidosis). Withhold 48 hours before/after IV iodinated contrast in patients with eGFR <60. Vitamin B12 levels should be monitored annually (metformin reduces B12 absorption via ileal calcium-dependent mechanism — see metformin B12 warning update and drug-induced nutrient depletion guide).
SGLT2 inhibitors block the sodium-glucose co-transporter 2 in the proximal renal tubule, which is responsible for ~90% of filtered glucose reabsorption. This results in glucosuria of ~70 g/day, caloric loss of ~280 kcal/day, and modest weight reduction (2–4 kg). Their benefits extend far beyond HbA1c reduction.
| Drug | CV outcome trial | Key benefit | eGFR threshold |
|---|---|---|---|
| Empagliflozin | EMPA-REG OUTCOME | ↓CV death 38%, ↓HHF 35% | eGFR ≥20 (CKD) |
| Dapagliflozin | DAPA-HF / DELIVER / DAPA-CKD | HFrEF + HFpEF + CKD | eGFR ≥25 |
| Canagliflozin | CANVAS / CREDENCE | ↓CKD progression | eGFR ≥20 |
Farxiga heart failure approval: Dapagliflozin (Farxiga) received FDA approval for heart failure across the full spectrum of ejection fractions — both HFrEF (DAPA-HF trial) and HFpEF (DELIVER trial) — making it one of the first SGLT2 inhibitors approved for heart failure regardless of diabetes status. The DailyMed dapagliflozin label ↗ now includes heart failure and CKD as approved indications independent of glycaemic control. Empagliflozin (Jardiance) has similar cardiorenal approvals via the EMPEROR-Reduced and EMPEROR-Preserved trials.
Key safety signals: euglycaemic DKA (withhold 3–4 days perioperatively); genital mycotic infections (5–15%); volume depletion (especially with loop diuretics — monitor renal function and BP); canagliflozin: ↑lower limb amputation risk, ↑fracture risk. See also: SGLT2i paediatric HF approval.
Fournier's gangrene (necrotising fasciitis of the perineum): The FDA issued a Boxed Warning for all SGLT2 inhibitors regarding the rare but serious risk of Fournier's gangrene — a rapidly progressing necrotising soft-tissue infection of the genital and perineal area. Although extremely rare (estimated <1 per 10,000 patient-years), cases with SGLT2 inhibitors have been disproportionately reported compared to other diabetes medications. The mechanism is thought to relate to glucosuria providing a favourable environment for bacterial growth in the perineal region. Patients should be counselled to seek immediate medical attention for perineal pain, tenderness, erythema, or swelling. Treatment requires urgent surgical debridement and broad-spectrum antibiotics. The risk applies to dapagliflozin, empagliflozin, canagliflozin, and ertugliflozin. See the FDA SGLT2 Fournier's gangrene safety communication ↗ and label update.
GLP-1 receptor agonists mimic the actions of native GLP-1 (glucagon-like peptide-1), an incretin hormone secreted by intestinal L-cells in response to food. They stimulate glucose-dependent insulin secretion, suppress glucagon, slow gastric emptying, and reduce appetite via central GLP-1 receptors.
| Drug | Type | Frequency | Weight loss | CV trial |
|---|---|---|---|---|
| Semaglutide SC | GLP-1 RA | Weekly (Ozempic 0.5–2 mg) | ~5–7% | SUSTAIN-6 (−26% MACE) |
| Semaglutide PO | GLP-1 RA | Daily (Rybelsus 7–14 mg) | ~4% | SOUL trial |
| Tirzepatide | GLP-1/GIP dual | Weekly (2.5–15 mg) | ~15–21% | SURPASS-CVOT |
| Liraglutide | GLP-1 RA | Daily (0.6–1.8 mg) | ~4–6% | LEADER (−13% MACE) |
| Dulaglutide | GLP-1 RA | Weekly (0.75–4.5 mg) | ~3–5% | REWIND (−12% MACE) |
Gastroparesis warning (Nov 2026): FDA updated all GLP-1 RA labels to formally add gastroparesis as a recognised adverse effect. Delayed gastric emptying affects absorption of co-administered oral drugs — particularly levothyroxine, digoxin, oral contraceptives. See GLP-1 gastroparesis label update and drug interactions guide. Pancreatitis: rare but serious — check lipase if abdominal pain occurs; discontinue if confirmed.
DPP-4 inhibitors (sitagliptin, vildagliptin, saxagliptin, alogliptin, linagliptin) block dipeptidyl peptidase-4, the enzyme that rapidly degrades native GLP-1 and GIP. By extending the action of endogenous incretins, they provide modest glucose-lowering (~0.5–0.7% HbA1c reduction) without weight gain or hypoglycaemia (monotherapy).
PK differences: Linagliptin is the only DPP-4i not renally eliminated (hepatic/biliary excretion) — no dose adjustment required in renal impairment. Sitagliptin, alogliptin, and saxagliptin require dose reduction in moderate–severe CKD. Saxagliptin is a CYP3A4 substrate — dose cap 2.5 mg when co-prescribed with strong CYP3A4 inhibitors (ketoconazole, clarithromycin).
Safety note: saxagliptin and alogliptin showed an unexpected signal for increased heart failure hospitalisation (SAVOR-TIMI 53, EXAMINE trials) — avoid in patients with high HF risk; prefer empagliflozin or dapagliflozin in this group. DPP-4i are associated with a rare risk of bullous pemphigoid with long-term use.
Insulin formulations are characterised by onset, peak, and duration of action — which determines clinical use (prandial vs basal coverage). All subcutaneous insulin is absorbed from a depot into the bloodstream; absorption rate is modified by formulation design and injection site.
| Type | Example | Onset | Peak | Duration |
|---|---|---|---|---|
| Ultra-rapid | Fiasp, Lyumjev | ~5 min | 30–70 min | 3–5 h |
| Rapid analogue | Aspart, Lispro, Glulisine | 10–20 min | 1–3 h | 3–5 h |
| Regular (soluble) | Actrapid, Humulin R | 30–60 min | 2–4 h | 5–8 h |
| NPH | Insulatard, Humulin N | 1–4 h | 4–8 h | 12–18 h |
| Long-acting analogue | Glargine (U100/U300), Detemir, Degludec | 2–4 h | None/flat | 20–42 h |
Key principle: only regular (soluble) insulin is safe for IV administration — insulin analogues should not be given intravenously. Degludec (Tresiba) has the most prolonged action (~42 hours) and lowest day-to-day variability — beneficial in patients with frequent hypoglycaemia on glargine. See full insulin therapy guide.
Mounjaro (tirzepatide), a dual GLP-1/GIP receptor agonist, has shown emerging evidence of benefit in patients with chronic kidney disease (CKD). The SURPASS-4 trial demonstrated reductions in eGFR decline and albuminuria in patients with T2D and high cardiovascular risk, suggesting potential nephroprotective effects beyond glucose lowering. While tirzepatide does not currently have an FDA-approved CKD indication (unlike dapagliflozin and empagliflozin), clinical data support its use in patients with CKD who require weight management and glucose control. No dose adjustment is required for renal impairment per the DailyMed tirzepatide label ↗, but GI side effects (nausea, vomiting) may cause dehydration and acute kidney injury in patients with pre-existing renal impairment — monitor renal function closely. See also our tirzepatide CKD label update.
The 2023 ADA/EASD consensus approach prioritises individualised treatment based on patient characteristics rather than a rigid step-up approach:
Interactions relevant to diabetes pharmacotherapy:
See drug interactions guide and CYP450 guide for full interaction principles.
Metformin primarily inhibits hepatic gluconeogenesis via mitochondrial complex I inhibition → AMPK activation → reduced PEPCK/G6Pase expression. It does not stimulate insulin secretion, so does not cause hypoglycaemia as monotherapy. Renal elimination — stop at eGFR <30; reduce at 30–45. Hold 48 hours around IV iodinated contrast (eGFR <60). Monitor vitamin B12 annually — metformin reduces ileal B12 absorption.
SGLT2i reduce MACE, CV death, and HF hospitalisation in T2D patients with established CVD (EMPA-REG, CANVAS, DECLARE-TIMI 58). Empagliflozin/dapagliflozin benefit HFrEF and HFpEF regardless of diabetes status (DAPA-HF, DELIVER, EMPEROR-Reduced). Dapagliflozin reduces CKD progression (DAPA-CKD). Mechanisms: diuresis/natriuresis (preload), cardiac ketone utilisation, erythropoietin stimulation, tubuloglomerular feedback (nephroprotection).
Insulin is required when: HbA1c target cannot be reached on ≥2 agents; very high HbA1c at presentation (>86 mmol/mol); acute illness/surgery (sick-day protocol); eGFR <30 (most oral agents contraindicated); pregnancy (insulin + metformin only). Start basal insulin 10 units bedtime; titrate fasting glucose. Intensify to basal-bolus when postprandial control is insufficient.
Nausea (20–40%), vomiting (10–20%), diarrhoea (10–15%) are dose-related and GLP-1R mediated. Manage with: slow dose escalation; taking with food; small frequent low-fat meals. Clinically significant gastroparesis (persistent vomiting, >10% weight loss) requires dose reduction or cessation per FDA Nov 2026 label update. Important interaction: delayed absorption of levothyroxine, oral contraceptives — separate by ≥4 hours. Pancreatitis: rare, discontinue if confirmed.
Fournier's gangrene (necrotising fasciitis of the perineum) is a rare but serious FDA Boxed Warning risk for all SGLT2 inhibitors including dapagliflozin, empagliflozin, and canagliflozin. The estimated incidence is <1 per 10,000 patient-years, but cases are disproportionately reported with SGLT2i vs other diabetes drugs. Glucosuria may promote bacterial growth in the perineal region. Patients should seek immediate medical attention for perineal pain, tenderness, erythema, or swelling. Treatment requires urgent surgical debridement and antibiotics.
Yes. Metformin reduces vitamin B12 absorption via inhibition of calcium-dependent ileal cubilin receptor uptake. Approximately 10–30% of long-term metformin users develop low B12 levels. The ADA Standards of Care (2024) and updated FDA metformin labelling recommend periodic B12 monitoring in patients on long-term metformin, especially those with peripheral neuropathy or anaemia. Serum B12 should be checked at baseline and annually. Supplementation with oral cyanocobalamin 1,000–2,000 mcg/day is effective.