siRNA Lipid Therapeutics Drug-Drug Interaction Table

What Is the siRNA Lipid Therapeutics Drug Class?

SiRNA lipid therapeutics are oligonucleotide drugs packaged in lipid nanoparticle (LNP) or GalNAc-conjugate delivery systems that use RNA interference (RNAi) to silence specific messenger RNA transcripts in the liver. Once inside hepatocytes, the short interfering RNA strand loads into the RNA-induced silencing complex (RISC) and directs sequence-specific cleavage of its target mRNA, suppressing protein synthesis at the source rather than blocking a receptor or enzyme downstream.

Approved Agents and Their Targets

Three siRNA-based medicines are currently FDA-approved for lipid or protein-related conditions:

• Inclisiran (Leqvio) targets PCSK9 mRNA. Approved December 2021 for adults with heterozygous familial hypercholesterolemia (HeFH) or clinical ASCVD requiring additional LDL-C lowering. Administered by a healthcare provider as a 284 mg subcutaneous injection.
• Patisiran (Onpattro) targets transthyretin (TTR) mRNA. Approved August 2018 for adult-onset polyneuropathy caused by hereditary TTR-mediated amyloidosis (hATTR).
• Vutrisiran (Amvuttra) is a GalNAc-conjugated TTR-targeting siRNA. Approved June 2022 as a 25 mg SC injection every 3 months for hATTR polyneuropathy, superseding patisiran for many patients because it eliminates the need for premedication.

Why This Class Exists

Statins and ezetimibe reduce hepatic LDL-receptor clearance indirectly by lowering intracellular cholesterol. PCSK9 inhibits that receptor. Inclisiran bypasses both downstream mechanisms and silences PCSK9 production entirely, producing LDL-C reductions comparable to monoclonal anti-PCSK9 antibodies (evolocumab, alirocumab) but with a twice-yearly dosing schedule that addresses the adherence gap seen with biweekly self-injections. A 2022 analysis in the Journal of the American College of Cardiology estimated that 50% of patients prescribed biweekly PCSK9 inhibitors were non-adherent at 12 months, compared with adherence rates above 90% in inclisiran clinical trials where dosing is provider-administered.

Pharmacokinetics: Why the DDI Risk Is Low

Understanding why siRNA lipid therapeutics carry minimal DDI risk requires a brief look at each pharmacokinetic (PK) phase.

Absorption and Distribution

Inclisiran is administered subcutaneously. It reaches peak plasma concentration (Cmax) within 4 hours, then distributes rapidly from plasma into the liver. Plasma concentrations drop more than 97% within 48 hours of injection. After that two-day window, the active drug resides almost entirely in hepatocytes where RISC-loaded siRNA continues to cleave PCSK9 mRNA for months. Patisiran is delivered as a 30-minute IV infusion in LNPs that passively accumulate in the liver via ApoE-mediated uptake. Vutrisiran uses triantennary N-acetylgalactosamine (GalNAc) conjugation, which binds the asialoglycoprotein receptor on hepatocytes with high affinity, achieving liver uptake without the LNP vehicle or premedication.

Metabolism

None of the three approved agents are substrates of cytochrome P450 enzymes. They are degraded by nucleases into short oligonucleotide fragments and then to individual nucleotides, which are recycled through normal nucleotide salvage pathways. The FDA prescribing information for inclisiran confirms no CYP, UGT, or transporter-mediated DDIs were identified in in vitro or clinical studies.

Excretion

Renal excretion accounts for approximately 16% of an inclisiran dose as intact drug within 24 hours; the remainder exits as nucleotide metabolites. This low intact-drug renal clearance is why dose modification is not required across most renal function categories. Patisiran is cleared primarily by hepatic metabolism; vutrisiran shows a similar hepatic-predominant elimination pattern.

Transporter Interaction Profile

In vitro studies evaluated inclisiran against P-glycoprotein (P-gp), BCRP, OATP1B1, OATP1B3, OAT1, OAT3, OCT1, OCT2, MATE1, and MATE2-K. No clinically significant inhibition or induction was detected at therapeutic concentrations. This profile contrasts sharply with small-molecule lipid agents such as gemfibrozil, which inhibits OATP1B1 and CYP2C8, creating a well-characterized DDI with statins.

Drug-Drug Interaction Table: siRNA Lipid Therapeutics

The table below covers the concomitant drug categories most commonly encountered in the cardiovascular and metabolic medicine clinic. Because inclisiran is the agent prescribed most often alongside other lipid-lowering drugs, it receives the most detailed entries.

| Concomitant Drug / Class | Mechanism of Concern | DDI Evidence | Clinical Verdict | Action Required | |---|---|---|---|---| | Statins (atorvastatin, rosuvastatin, simvastatin) | CYP3A4 / OATP1B1 substrates; no overlap with siRNA PK | None in ORION trials (N>3,500 combined); PK sub-studies negative | No interaction | No dose change | | Ezetimibe | NPC1L1 inhibitor; renally cleared glucuronide | No shared pathway | No interaction | No dose change | | PCSK9 monoclonal antibodies (evolocumab, alirocumab) | Same biological target (PCSK9); additive LDL-C reduction possible | Not formally studied in combination RCT; mechanistic overlap expected | Theoretical additive benefit; no safety signal | Prescriber discretion; combination not standard of care | | Fibrates (fenofibrate, gemfibrozil) | Gemfibrozil inhibits OATP1B1 and CYP2C8; fenofibrate does not | No siRNA transporter overlap in FDA review | No interaction with siRNA agents | No dose change; gemfibrozil-statin DDI still applies | | Niacin (extended-release) | Hepatic flux effects; HCAR2 agonism | No shared metabolic pathway | No interaction | No dose change | | Warfarin | CYP2C9 substrate; narrow therapeutic index | Patisiran labeling notes INR monitoring recommended due to TTR reduction altering vitamin K-dependent factor levels indirectly | Monitor INR at patisiran initiation | Check INR at baseline and after first two doses; adjust warfarin PRN | | Direct oral anticoagulants (apixaban, rivaroxaban, edoxaban) | P-gp / CYP3A4 substrates | No siRNA interaction with P-gp or CYP3A4 | No interaction | No dose change | | Amiodarone | CYP2D6 / CYP3A4 inhibitor; P-gp inhibitor | No siRNA pathway overlap | No interaction for inclisiran/vutrisiran | No dose change | | Cyclosporine | OATP1B1 inhibitor; P-gp inhibitor | No siRNA OATP/P-gp substrate activity | No interaction | No dose change; cyclosporine-statin DDI still applies independently | | Tacrolimus / sirolimus | CYP3A4 substrates; calcineurin / mTOR inhibitors | No shared PK pathway | No interaction | No dose change | | Metformin | OCT1/OCT2 renal substrate | No siRNA transporter overlap; renal clearance of intact siRNA is low | No interaction | No dose change | | Levothyroxine | Narrow therapeutic index; thyroid binding globulin affected by amyloid in TTR disease | Vutrisiran/patisiran: TTR reduction may alter thyroid transport proteins over time | Monitor TSH every 6 months in hATTR patients on levothyroxine | Adjust levothyroxine dose if TSH drifts | | Vitamin A supplements | Patisiran LNP contains DLin-MC3-DMA and PEG-lipid; vitamin A co-delivery was studied in early LNP platforms | No clinical DDI; patisiran LNP delivers vitamin A incidentally but no supplementation interaction documented | Monitor vitamin A levels annually in patisiran-treated patients (labeling recommendation) | Avoid additional high-dose vitamin A supplementation | | Oral contraceptives (estrogen / progestin) | CYP3A4 substrates | No siRNA CYP3A4 interaction | No interaction | No dose change | | GLP-1 receptor agonists (semaglutide, liraglutide, tirzepatide) | Hepatic lipid flux changes with weight loss; no shared PK pathway | No PK interaction; LDL-C may fall further with weight loss, creating pharmacodynamic additive effect | Monitor LDL-C at 3 months if starting both simultaneously | Consider dose review of statin background therapy if LDL-C overshoots goal |

Clinical Efficacy Data Supporting Combined Use with Standard-of-Care Therapy

The ORION program enrolled patients already on maximally tolerated statin therapy, providing real-world-analog data on combined use.

ORION-10

ORION-10 (N=1,561) randomized patients with ASCVD on maximally tolerated statin therapy to inclisiran 284 mg SC or placebo at day 1, month 3, and then every 6 months. At 510 days, inclisiran reduced LDL-C by 52.3% from baseline vs. A 0.5% increase with placebo (P<0.0001). Rates of adverse events were similar between arms. No statin DDI signals appeared in safety sub-analyses.

ORION-9

ORION-9 (N=482) enrolled patients with HeFH. Inclisiran reduced LDL-C by 39.7% at day 510 vs. Placebo, with 74% of treated patients achieving LDL-C below 1.8 mmol/L when combined with background statin or ezetimibe. No hepatotoxicity signal was reported.

HELIOS-A (Vutrisiran)

In HELIOS-A (N=164), vutrisiran 25 mg SC every 3 months reduced serum TTR by 83% at 9 months vs. 3% with placebo (P<0.001), and the modified Neuropathy Impairment Score improved by 2.2 points vs. A 5.0-point worsening with placebo. Concomitant use of tafamidis or diflunisal (TTR stabilizers) was allowed per protocol; no PK interaction was identified.

APOLLO-B (Patisiran in Cardiomyopathy)

The APOLLO-B trial (N=360) demonstrated that patisiran 0.3 mg/kg IV every 3 weeks reduced TTR protein by 87% and improved 6-minute walk distance by 14.7 meters vs. Placebo at 12 months (P=0.0152) in patients with TTR amyloid cardiomyopathy. Patients on tafamidis were eligible; no PK signals emerged from that co-administration.

Renal and Hepatic Dose Adjustments

Inclisiran Renal Dosing

Inclisiran does not require dose adjustment for mild (CrCl 60-89 mL/min), moderate (CrCl 30-59 mL/min), or severe (CrCl 15-29 mL/min) renal impairment. Patients with CrCl <15 mL/min or on dialysis were excluded from Phase III trials; use in this population should be individualized. The FDA label confirms this guidance.

Inclisiran Hepatic Dosing

Mild and moderate hepatic impairment (Child-Pugh A and B) do not require dose adjustment. Severe hepatic impairment (Child-Pugh C) was not studied; use caution given the liver as the primary site of drug action and degradation.

Patisiran and Vutrisiran Hepatic Considerations

Patisiran trials excluded patients with ALT or AST more than 2 times the upper limit of normal. Vutrisiran trials used the same cutoff. Neither agent should be initiated during acute hepatic decompensation. The prescribing information for vutrisiran specifies this restriction.

Injection-Site Reactions and Monitoring Protocol

Injection-site reactions (ISRs) are the most common adverse event with inclisiran and vutrisiran. In ORION-10, ISRs occurred in 8.2% of inclisiran-treated patients vs. 1.8% placebo. They were almost all mild or moderate in severity and did not lead to discontinuation. No systemic hypersensitivity reactions meeting anaphylaxis criteria were reported in Phase III. Patisiran, delivered by IV, carries a higher infusion-related reaction rate (18% vs. 9% placebo in APOLLO); premedication with dexamethasone, oral acetaminophen, and an H1/H2 blocker is required.

HealthRX Monitoring Framework for siRNA Lipid Therapeutics

The following schedule applies to most outpatient prescribers initiating inclisiran as add-on therapy:

1. Baseline (before dose 1): Fasting lipid panel, ALT/AST, CrCl or eGFR, pregnancy test if applicable.
2. Month 3 (before dose 2): Fasting LDL-C to confirm response; no PK monitoring needed.
3. Month 6 (after dose 2): Fasting lipid panel, ALT/AST. LDL-C nadir is typically reached here.
4. Every 6 months (ongoing): Fasting lipid panel before each provider-administered injection. Review concomitant medications for any newly initiated agents with narrow therapeutic index.
5. For patisiran patients only: Vitamin A level annually; INR at initiation and after doses 1-2 if on warfarin; TSH every 6 months if on levothyroxine.
6. For vutrisiran patients: TSH every 6 months if on levothyroxine; no vitamin A monitoring required per current labeling.

Special Populations

Pregnancy and Lactation

Inclisiran is contraindicated in pregnancy. The FDA label states that animal reproduction studies showed fetal toxicity at doses producing exposures below those expected at the 284 mg human dose. Cholesterol is required for fetal development; PCSK9 silencing during pregnancy carries uncharacterized fetal risk. Women of childbearing potential should use effective contraception. No lactation data exist; avoidance during breastfeeding is recommended.

Patisiran and vutrisiran carry similar warnings given the absence of human pregnancy data and theoretical risk from TTR silencing, which may alter retinol transport (patisiran's LNP carries vitamin A as an excipient component in the LNP formulation design history).

Pediatric Use

None of the three agents are approved for patients under age 18. HeFH trials in pediatric populations are ongoing for inclisiran; the adult label does not extend to this group.

Older Adults (Age >75)

No dose adjustment is required for age alone. ORION-10 included patients up to age 80; PK did not differ meaningfully from younger cohorts in sub-group analyses. Renal function should be assessed individually.

Interaction with Lipid-Lowering Combination Therapy

Cardiologists frequently ask whether combining inclisiran with high-intensity statin therapy plus ezetimibe is safe and whether any pharmacodynamic ceiling effect applies.

The short answer: no PK or safety ceiling has been identified. The ORION-11 trial (N=1,617, European ASCVD or HeFH population) placed 89% of participants on background statin therapy. At day 510, inclisiran reduced LDL-C by 49.9% from baseline vs. A 1.0% increase with placebo, regardless of statin type or intensity. Adding ezetimibe does not alter inclisiran PK; the two mechanisms are pharmacodynamically independent and additive in LDL-C lowering.

The ACC/AHA 2022 Guideline on the Management of Blood Cholesterol states: "For patients with clinical ASCVD not at LDL-C goal on maximally tolerated statin plus ezetimibe, a PCSK9 inhibitor is recommended (Class I, LOE A)." Inclisiran received a Class IIb recommendation in the same guideline update as an alternative when the patient-specific preference is for less-frequent dosing. Full guideline text is available from the American Heart Association.

Comparison with PCSK9 Monoclonal Antibodies for DDI Purposes

Prescribers sometimes ask how inclisiran's DDI profile compares with evolocumab (Repatha) and alirocumab (Praluent), both monoclonal antibodies targeting the PCSK9 protein rather than its mRNA.

All three share a clean DDI profile relative to small molecules. Monoclonal antibodies are not CYP substrates; they are catabolized to amino acids. Inclisiran's nucleotide degradation path is equally benign. The practical difference: monoclonal antibodies act within days, while inclisiran requires approximately 14 days to show LDL-C reduction as PCSK9 protein levels fall in response to mRNA silencing. Neither class interacts with anticoagulants, immunosuppressants, or antimicrobials through PK mechanisms.

A 2021 review in JAMA Cardiology summarized the RNAi therapeutic mechanism and noted that the GalNAc-siRNA conjugate platform used by inclisiran and vutrisiran achieves hepatocyte selectivity that fundamentally limits systemic off-target effects, making the DDI profile structurally different from small molecules at the design level.

Formulary and Prior Authorization Context

In the United States, inclisiran is covered under Medicare Part B (administered in the office) rather than Part D (self-administered pharmacy benefit). This classification means that prior authorization workflows differ from those for evolocumab and alirocumab. Most commercial payers require documentation of maximally tolerated statin therapy and an LDL-C at or above the plan's threshold (commonly 70 mg/dL for ASCVD or 100 mg/dL for primary prevention HeFH) before approving inclisiran. Prescribers should document concomitant statin dose and duration in the prior authorization letter; the clean DDI profile and provider-administered schedule are commonly cited in medical necessity narratives.