SGLT2 Inhibitors Drug-Drug Interaction Table

Why SGLT2 Inhibitor DDIs Are Mostly Pharmacodynamic

SGLT2 inhibitors bypass the cytochrome P450 system almost entirely. Empagliflozin, dapagliflozin, and ertugliflozin are conjugated primarily by UGT1A3, UGT1A8, UGT1A9, and UGT2B7, producing inactive glucuronide metabolites that are renally cleared [1]. Because no single CYP isoform accounts for more than a minor fraction of metabolism, traditional CYP-based inhibitor/inducer tables are largely irrelevant for this class.

Pharmacokinetic Profile

Canagliflozin is the partial exception. It inhibits UGT1A9 and UGT2B4 in vitro and has been shown to raise the AUC of co-administered UGT1A9 substrates by up to 20% [2]. In practice, this magnitude rarely triggers a dose adjustment, but it can matter when stacking multiple UGT1A9 substrates (e.g., certain NSAIDs).

Clinical Relevance

The interactions that matter most are pharmacodynamic. SGLT2 inhibitors cause glycosuria, osmotic diuresis, and a mild natriuresis. Any drug that independently lowers blood glucose, reduces intravascular volume, or alters renal electrolyte handling can amplify these effects. The table below organizes every clinically relevant interaction by the co-prescribed drug and assigns a severity tier.

Master DDI Table

The table uses a three-tier severity system: High (dose adjustment or enhanced monitoring required), Moderate (monitor and adjust if symptomatic), and Low (awareness only, no routine change).

| Co-Prescribed Drug | Interaction Type | Mechanism | Severity | Clinical Action | |---|---|---|---|---| | Insulin (all forms) | Pharmacodynamic | Additive hypoglycemia | High | Reduce insulin dose by 15-20% at SGLT2i initiation; titrate by SMBG/CGM [3] | | Sulfonylureas (glipizide, glimepiride, glyburide) | Pharmacodynamic | Additive hypoglycemia | High | Consider halving the sulfonylurea dose; monitor fasting glucose weekly for 4 weeks [3] | | Loop diuretics (furosemide, bumetanide, torsemide) | Pharmacodynamic | Additive volume depletion, natriuresis | High | Assess volume status before starting; hold or reduce loop diuretic if signs of dehydration; check creatinine at 1-2 weeks [4] | | Thiazide diuretics (HCTZ, chlorthalidone) | Pharmacodynamic | Additive volume depletion, hyponatremia risk | Moderate | Monitor electrolytes at 2-4 weeks; counsel on hydration and orthostatic symptoms | | Lithium | Pharmacodynamic / PK | SGLT2i-induced diuresis may concentrate or dilute lithium levels unpredictably | High | Check lithium trough 5-7 days after SGLT2i start and after any diuretic change; adjust lithium dose to target 0.6-0.8 mEq/L [5] | | ACE inhibitors / ARBs | Pharmacodynamic | Additive reduction in intraglomerular pressure | Moderate | Expect an initial eGFR dip of 3-5 mL/min/1.73 m²; do not discontinue unless eGFR falls >30% [6] | | NSAIDs (ibuprofen, naproxen, diclofenac) | Pharmacodynamic + PK (canagliflozin) | Reduced renal perfusion; canagliflozin inhibits UGT1A9 metabolism of some NSAIDs | Moderate | Avoid chronic NSAID use; if unavoidable, recheck creatinine and potassium at 1-2 weeks | | Digoxin | Pharmacokinetic | Canagliflozin increases digoxin AUC by ~20% via P-gp modulation [2] | Moderate | Monitor digoxin trough when adding canagliflozin; no adjustment needed with empagliflozin or dapagliflozin | | Phenytoin / Rifampin (UGT inducers) | Pharmacokinetic | UGT induction lowers SGLT2i exposure by 30-35% | Moderate | Consider using the higher approved dose of the SGLT2i; monitor HbA1c response at 3 months [1] | | Ritonavir / Mefenamic acid (UGT inhibitors) | Pharmacokinetic | UGT inhibition raises SGLT2i exposure modestly (~25%) | Low | No routine dose adjustment; watch for volume-depletion symptoms | | Metformin | Pharmacodynamic | Mild additive glucose-lowering; no PK interaction | Low | Standard combination; no dose adjustment required [3] | | DPP-4 inhibitors (sitagliptin, linagliptin) | Pharmacodynamic | Complementary glucose-lowering with low hypoglycemia risk | Low | No dose adjustment; FDA-approved fixed-dose combinations exist | | GLP-1 receptor agonists | Pharmacodynamic | Additive weight loss, mild additive glucose-lowering | Low | No dose adjustment; growing evidence base from DURATION, SUSTAIN, and EMPA-REG trials supports combination [7] | | Warfarin | None significant | No CYP2C9 or PK interaction demonstrated | Low | No INR adjustment needed at SGLT2i initiation | | Statins (atorvastatin, rosuvastatin) | None significant | No clinically meaningful PK interaction | Low | No dose adjustment | | Levothyroxine | None significant | Separate absorption windows; no known interaction | Low | No adjustment; continue standard AM dosing separation |

High-Risk Combinations in Detail

Three drug pairings with SGLT2 inhibitors generate the most adverse-event reports and deserve expanded discussion.

Insulin and Sulfonylureas

The EMPA-REG OUTCOME trial (N=7,020) permitted concomitant insulin in over 48% of participants. Hypoglycemia rates in the empagliflozin plus insulin subgroup were 28% vs. 20.5% in the placebo plus insulin subgroup [8]. The CREDENCE trial (N=4,401) with canagliflozin reported a similar signal among patients on background sulfonylureas [9]. ADA Standards of Care 2024 recommend a preemptive 15-20% insulin dose reduction when adding any SGLT2 inhibitor [3].

Loop Diuretics

The DAPA-HF trial (N=4,744) enrolled patients already on loop diuretics (93% of participants). Investigators did not mandate diuretic dose reductions, and volume depletion events occurred in 7.5% of the dapagliflozin arm vs. 6.8% placebo [10]. The EMPEROR-Reduced trial (N=3,730) showed similar tolerability [11]. In clinical practice outside trial conditions, dehydration rates tend to be higher in older adults and patients on high-dose furosemide (>80 mg/day). A practical approach: hold or halve the loop diuretic for 48-72 hours if the patient is euvolemic at the time of SGLT2i initiation.

Lithium

No large RCT has studied SGLT2 inhibitors with lithium. Case reports and pharmacovigilance data from the FDA Adverse Event Reporting System (FAERS) describe both lithium toxicity (due to volume contraction concentrating lithium) and sub-therapeutic lithium levels (due to increased renal lithium clearance from osmotic diuresis) [5]. The direction of the shift depends on the patient's hydration, sodium intake, and concurrent diuretic use. Checking a lithium trough at 5-7 days post-initiation is the safest path.

ACE Inhibitor and ARB Overlap

SGLT2 inhibitors reduce intraglomerular pressure by constricting the afferent arteriole via tubuloglomerular feedback. ACE inhibitors and ARBs dilate the efferent arteriole. The combination produces a predictable initial eGFR dip of 3-5 mL/min/1.73 m², which stabilizes by week 4-6 and is considered hemodynamic (not structural) [6].

When to Hold vs. Continue

KDIGO 2024 CKD guidelines explicitly recommend continuing SGLT2 inhibitors through this initial dip unless eGFR falls by more than 30% from baseline or the patient develops symptomatic hypotension [6]. "The acute eGFR change with SGLT2 inhibitors reflects a reduction in hyperfiltration, not nephrotoxicity," the KDIGO work group states in the 2024 guideline update [6].

Triple Therapy Caution

Combining an SGLT2 inhibitor, an ACE inhibitor or ARB, and a loop diuretic creates a triple hit on intravascular volume and renal perfusion. Monitor creatinine and potassium at 1 week, 4 weeks, and 3 months. Patients over 75 or with baseline eGFR 25-45 mL/min/1.73 m² need the closest surveillance.

UGT Inducer and Inhibitor Effects

Because SGLT2 inhibitors rely on UGT-mediated glucuronidation, strong UGT inducers can lower plasma levels meaningfully.

UGT Inducers

Rifampin reduced the AUC of canagliflozin by approximately 51% and empagliflozin by approximately 35% in dedicated PK studies [1][2]. Phenytoin and carbamazepine carry a similar induction profile. For patients on chronic rifampin (e.g., tuberculosis treatment), prescribers should use the higher approved SGLT2i dose and re-check HbA1c at 12 weeks.

UGT Inhibitors

Mefenamic acid and probenecid inhibit UGT1A9 and can raise SGLT2i exposure by 20-25%. Ritonavir-boosted HIV regimens also carry modest UGT inhibitory activity. These increases fall within the therapeutic window for all four approved SGLT2 inhibitors and do not require dose reduction, but the clinician should maintain awareness of additive volume-depletion risk [1].

Canagliflozin-Specific Interactions

Canagliflozin stands apart from the other three SGLT2 inhibitors in two respects. It inhibits P-glycoprotein (P-gp) and UGT1A9 at clinically relevant concentrations.

Digoxin

A dedicated PK study showed canagliflozin 300 mg increased digoxin AUC by 20% and Cmax by 36% [2]. For patients on narrow-therapeutic-index digoxin (target trough 0.5-0.9 ng/mL per ACC/AHA heart failure guidelines), a follow-up digoxin level 7-10 days after canagliflozin initiation is warranted. Empagliflozin, dapagliflozin, and ertugliflozin do not share this P-gp effect.

Practical Switching Note

If a patient on digoxin needs an SGLT2 inhibitor and the prescriber wants to avoid the P-gp interaction entirely, switching from canagliflozin to empagliflozin or dapagliflozin eliminates the concern without losing the class benefit for HbA1c, heart failure, or CKD outcomes [7][8][11].

Monitoring Protocol After Adding an SGLT2 Inhibitor

| Timepoint | Labs / Assessments | |---|---| | Baseline | BMP (creatinine, potassium, sodium, bicarbonate), eGFR, HbA1c, urinalysis, volume status | | 1-2 weeks | Creatinine, potassium, volume status assessment (orthostatics if on diuretics or ACEi/ARB) | | 4 weeks | BMP, eGFR; lithium trough if applicable; digoxin trough if on canagliflozin | | 3 months | HbA1c, BMP, eGFR; reassess diuretic dosing | | Every 6-12 months | HbA1c, BMP, eGFR, urinalysis; annual lipid panel; reassess concomitant drug doses |

Adjust this schedule more frequently for patients over 75, eGFR <45, or those on three or more volume-active drugs.

Special Populations and DDI Nuances

Older Adults (Age 75+)

The osmotic diuresis effect of SGLT2 inhibitors is amplified in older adults with reduced thirst perception and lower baseline intravascular volume. When an older patient takes an SGLT2 inhibitor alongside a thiazide or loop diuretic, the combined volume loss may precipitate orthostatic hypotension and falls. The DELIVER trial (N=6,263) included patients with a mean age of 72 and showed manageable safety, though volume depletion was numerically higher in participants over 75 [12].

Chronic Kidney Disease (eGFR 20-45)

DAPA-CKD (N=4,304) and EMPA-KIDNEY (N=6,609) established SGLT2i benefit down to eGFR 20 [13][14]. At lower eGFR, glycosuric and diuretic effects diminish, which actually reduces DDI severity for hypoglycemia and volume depletion. The more relevant interaction in this range is with RAS blockers: the additive eGFR dip may trigger alarm in the clinician, but KDIGO recommends continuing unless the drop exceeds 30% [6].

Perioperative Setting

SGLT2 inhibitors should be held 3-4 days before major surgery to minimize euglycemic diabetic ketoacidosis (euDKA) risk. This hold also eliminates any additive volume-depletion interaction with perioperative fluid restriction or concurrent diuretics. The ADA and Endocrine Society recommend resuming postoperatively only when the patient is eating and well-hydrated [3].

Quick-Reference Decision Algorithm

1. Identify the co-prescribed drug from the DDI table above.
2. Check the severity tier. High-severity pairings require a preemptive dose change or enhanced lab monitoring before the first SGLT2i dose.
3. Assess the patient's baseline volume status. Orthostatic vitals plus BMP are the minimum.
4. Schedule follow-up labs. Use the monitoring table: creatinine and potassium at 1-2 weeks for any High-severity pairing.
5. Re-evaluate at 3 months. If the patient is stable on the combination, transition to routine 6-12 month monitoring.

Patients on three or more volume-active drugs (SGLT2i + loop diuretic + ACEi/ARB) should have creatinine checked at 1 week after any dose change in any of the three agents.