Last updated: September 1, 2026
Merck’s fixed-dose combination of doravirine, lamivudine and tenofovir disoproxil fumarate, marketed as Delstrigo, is a durable but strategically secondary HIV product. Its commercial position benefits from once-daily dosing, doravirine’s relatively favorable drug-interaction profile and Merck’s established HIV infrastructure. It competes against stronger integrase inhibitor-based regimens, particularly Gilead’s Biktarvy and Dovato from ViiV Healthcare.
Merck reports Delstrigo together with Pifeltro, the doravirine single-tablet product. The combined franchise generated approximately $1.0 billion in 2022, $1.1 billion in 2023 and $1.2 billion in 2024, based on Merck’s annual product-sales disclosures. The revenue trajectory has been positive, but growth is slowing as HIV prescribing continues to shift toward integrase strand transfer inhibitor, or INSTI, regimens and as generic alternatives become available for the older nucleoside components. [1-3]
What is Delstrigo and how does the regimen work?
Delstrigo is a once-daily, three-drug antiretroviral tablet containing:
| Component |
Drug class |
Role in regimen |
| Doravirine |
Non-nucleoside reverse transcriptase inhibitor, or NNRTI |
Inhibits HIV-1 reverse transcriptase |
| Lamivudine |
Nucleoside reverse transcriptase inhibitor, or NRTI |
Backbone agent |
| Tenofovir disoproxil fumarate |
Nucleotide reverse transcriptase inhibitor, or NtRTI |
Backbone agent |
The FDA approved Delstrigo on August 30, 2018, for treatment of HIV-1 infection in adults with no prior antiretroviral treatment or in patients replacing a stable antiretroviral regimen with no history of treatment failure and no known resistance to the three components. [4]
Doravirine differentiates the product from older NNRTI-based regimens through lower central nervous system adverse-effect burden than efavirenz and a comparatively limited interaction profile. The product remains vulnerable to class-level resistance considerations and does not have the broad first-line guideline preference of bictegravir- or dolutegravir-based treatment.
How has Delstrigo revenue changed over time?
Merck does not separately disclose Delstrigo revenue from Pifeltro. The combined disclosure makes it impossible to calculate Delstrigo’s standalone net sales without third-party prescription or channel data.
| Fiscal year |
Merck-reported Pifeltro/Delstrigo sales |
Approximate year-over-year change |
| 2021 |
Approximately $0.8 billion |
Not comparable to prior disclosed base |
| 2022 |
Approximately $1.0 billion |
Low-to-mid teens growth |
| 2023 |
Approximately $1.1 billion |
High-single-digit growth |
| 2024 |
Approximately $1.2 billion |
High-single-digit growth |
Sources: Merck annual reports and Form 10-K filings. [1-3]
The revenue pattern reflects several factors:
- Continued adoption of doravirine-containing regimens in treatment-experienced patients and selected first-line patients.
- Price increases and gross-to-net management in the U.S.
- Growth outside the United States through national reimbursement systems.
- Merck’s ability to sell Pifeltro and Delstrigo as a doravirine franchise rather than as isolated products.
- A relatively small competitive base within the NNRTI segment.
The sales trajectory is commercially meaningful for Merck but remains modest compared with large HIV franchises. Biktarvy generated several billion dollars annually for Gilead and remains the principal benchmark for market access, physician preference and treatment volume. [5]
What is the current market position of doravirine, lamivudine and tenofovir disoproxil fumarate?
Delstrigo occupies a differentiated but non-leading position in the HIV market.
Clinical positioning
The regimen is most commercially defensible in patients for whom:
- A once-daily, single-tablet regimen is preferred.
- Avoidance of an INSTI is clinically or operationally desirable.
- Doravirine’s interaction profile is advantageous.
- The patient has no resistance to doravirine, lamivudine or tenofovir.
- The prescriber accepts the renal and bone monitoring requirements associated with TDF.
The main clinical limitation is the use of TDF rather than tenofovir alafenamide, or TAF. TDF generally has greater renal and bone toxicity potential than TAF, although it remains effective, widely used and available at lower cost through generic products.
U.S. guidelines generally prioritize bictegravir- or dolutegravir-based regimens for most adults. Doravirine-based treatment remains an alternative rather than the dominant standard of care. [6]
Competitive comparison
| Product |
Company |
Core regimen |
Primary competitive strength |
Principal risk to Delstrigo |
| Biktarvy |
Gilead |
Bictegravir/emtricitabine/TAF |
Strong guideline position and broad prescriber adoption |
Captures new starts and switches |
| Dovato |
ViiV |
Dolutegravir/lamivudine |
Two-drug regimen and reduced NRTI exposure |
Competes for simplified treatment |
| Triumeq |
ViiV |
Dolutegravir/abacavir/lamivudine |
Established INSTI efficacy |
Declining preference because of abacavir restrictions |
| Juluca |
ViiV |
Dolutegravir/rilpivirine |
Two-drug maintenance regimen |
Competes in stable suppressed patients |
| Delstrigo |
Merck |
Doravirine/3TC/TDF |
Doravirine tolerability and once-daily formulation |
Lower guideline priority and TDF profile |
| Generic 3TC/TDF combinations |
Multiple manufacturers |
Lamivudine/TDF |
Low acquisition cost |
Enables low-cost multi-tablet regimens |
The market is divided between treatment initiation, maintenance switching, public-sector procurement and commercial insurance. Delstrigo’s growth is therefore influenced less by epidemiological expansion than by formulary placement, rebate levels, treatment guidelines and switching patterns.
When does Delstrigo lose exclusivity?
Delstrigo faces a layered exclusivity profile because it combines two widely available generic backbone agents with the newer active ingredient doravirine.
Regulatory exclusivity
The FDA approved Delstrigo in 2018. New chemical entity exclusivity associated with doravirine has expired, while the commercial protection of the product depends primarily on patents and the absence of an approved doravirine generic.
Lamivudine and tenofovir disoproxil fumarate are long-established active ingredients with extensive generic competition. Their inclusion in Delstrigo does not independently preserve the commercial value of the combination.
Patent protection
The principal U.S. patent estate is directed to doravirine and related antiviral chemistry. The Orange Book has listed doravirine-related patents associated with Delstrigo and Pifeltro, including U.S. Patent No. 9,266,850. The key protection is generally understood to extend into the early 2030s after applicable patent-term adjustments and extensions. [7]
| Protection layer |
Commercial relevance |
| Doravirine composition and compound patents |
Main barrier to a fully substitutable doravirine generic |
| Doravirine formulation patents |
May delay or complicate single-tablet competition |
| Fixed-dose combination patents |
Potentially relevant to Delstrigo-specific substitution |
| Lamivudine and TDF patents |
Limited current value because generic products are established |
| Pediatric exclusivity |
Can add six months where applicable, subject to FDA conditions |
The practical generic-entry date is more important than the nominal expiration of any one patent. A generic manufacturer may challenge listed patents before expiry through an ANDA Paragraph IV certification or wait for patent expiry and file with a later effective date.
How strong is the Delstrigo patent estate?
The estate is commercially meaningful but narrower than the patent position of a newly launched, composition-of-matter-protected product.
Its strengths are:
- Doravirine is the only component without long-standing generic substitution.
- The doravirine patent family can block a fully substitutable product even though the backbone agents are generic.
- Merck can defend both Pifeltro and Delstrigo through overlapping doravirine rights.
- Combination and formulation claims may create additional litigation leverage.
Its weaknesses are:
- Lamivudine and TDF can be sourced generically.
- Physicians and payers can switch patients to unrelated INSTI-based products without infringing Delstrigo patents.
- A generic doravirine product could be used with generic lamivudine and TDF in a multi-tablet regimen, reducing the need for a generic version of the exact Delstrigo tablet.
- The principal commercial exposure is concentrated in the doravirine patent estate rather than distributed across three equally protected ingredients.
The estate is stronger against direct pharmaceutical substitution than against therapeutic substitution. Merck can potentially prevent a generic Delstrigo tablet before core doravirine patents expire, but it cannot prevent payers and prescribers from moving patients to Biktarvy, Dovato or generic multi-tablet regimens.
What Paragraph IV challenges and litigation affect Delstrigo?
Publicly identified litigation risk should be assessed at the doravirine level, including both Delstrigo and Pifeltro. A Paragraph IV filing against a listed doravirine patent could trigger a 30-month stay of FDA approval for the challenged ANDA, subject to statutory conditions and litigation outcomes. [8]
No major, broadly reported final judgment establishing immediate generic entry for Delstrigo has defined the market through the latest Merck disclosures cited here. The absence of a reported final judgment does not eliminate future Paragraph IV risk. The relevant scenarios are:
| Scenario |
Likely commercial outcome |
| No Paragraph IV challenge |
Merck retains the market until patent expiry or settlement |
| Paragraph IV challenge settled with delayed entry |
Revenue declines gradually before full generic launch |
| Merck wins litigation |
Delstrigo protection remains intact until patent expiry |
| Generic prevails |
Rapid erosion in U.S. prescription volume and net price |
| Generic doravirine launches without identical FDC |
Partial erosion through multi-tablet substitution |
Settlement agreements are particularly important because a delayed-entry date can preserve material value even when a patent challenge is filed. Merck’s public financial reporting does not provide a product-specific summary of any Delstrigo settlement economics.
What is the FDA and Orange Book status of Delstrigo?
Delstrigo is FDA approved as a prescription, once-daily, fixed-dose oral tablet. The FDA label includes warnings and precautions relating to renal function, bone mineral density, hepatitis B infection and immune reconstitution inflammatory syndrome. [4]
The Orange Book status is commercially important because:
- It identifies patents and regulatory exclusivities listed for the approved product.
- It informs ANDA applicants which patents may require certification.
- It distinguishes the branded combination from generic versions of individual components.
- It does not prevent substitution with therapeutically different HIV products.
No biosimilar pathway applies to Delstrigo. It is a small-molecule drug, so competitive entry would occur through an ANDA or another small-molecule regulatory pathway, not through a 351(k) biosimilar application.
What generic entry risks exist for Delstrigo?
The main risk is a two-stage erosion process.
Stage one: backbone commoditization
Generic lamivudine and TDF already reduce the economic value of two-thirds of the active-ingredient content. Payers can compare Delstrigo against low-cost generic combinations, even when those alternatives require multiple tablets.
Stage two: doravirine competition
A generic doravirine product would create the largest direct threat. The market impact would depend on whether the competitor launches:
- As a direct fixed-dose combination.
- As doravirine alone, paired with generic lamivudine and TDF.
- Through a limited channel, such as Medicaid or government procurement.
- With an authorized-generic or settlement-based launch date.
A fully substitutable generic tablet would likely produce the steepest price and volume decline. A standalone generic doravirine product could still erode Delstrigo by allowing pharmacy and payer substitution at the ingredient level.
How do manufacturing and supply-chain factors affect the product?
The active ingredients use established small-molecule manufacturing processes. Manufacturing complexity is therefore lower than for biologics, long-acting injectables or cell and gene therapies.
The relevant barriers are:
- Doravirine active pharmaceutical ingredient qualification.
- Control of polymorph, impurity and stability specifications.
- Demonstration of bioequivalence for the fixed-dose tablet.
- Reliable sourcing of three active ingredients.
- Regulatory validation of the combination manufacturing process.
- Compliance with HIV-product procurement standards in public programs.
Manufacturing is unlikely to be the principal long-term barrier to generic entry. Patent rights, bioequivalence requirements and commercial access are more important.
What licensing deals affect Delstrigo?
Delstrigo is a Merck-developed and Merck-marketed product. There is no major publicly disclosed co-commercialization or external licensing transaction that defines its current revenue model.
Merck’s relevant commercial advantage is internal portfolio leverage. The company markets both Delstrigo and Pifeltro, allowing one doravirine development and manufacturing platform to support two products:
| Product |
Formulation |
Strategic role |
| Pifeltro |
Doravirine single-agent tablet |
Enables combination with selected backbone regimens |
| Delstrigo |
Doravirine/lamivudine/TDF fixed-dose tablet |
Provides a complete once-daily regimen |
This portfolio structure supports prescriber retention but also exposes both products to the same doravirine patent and generic-entry risks.
What is the revenue exposure if doravirine loses exclusivity?
The direct revenue exposure is the combined Pifeltro/Delstrigo franchise, which reached approximately $1.2 billion in 2024 according to Merck’s product-sales reporting. [3]
A generic event would not necessarily eliminate all revenue immediately. The erosion curve would depend on:
- The number of approved competitors.
- U.S. versus international entry timing.
- Whether the first entrant is authorized for direct substitution.
- Rebate and formulary responses.
- The degree of switching to INSTI regimens.
- Merck’s ability to preserve Pifeltro use in selected patients.
A reasonable commercial framework is:
| Event |
Expected effect |
| First Paragraph IV filing |
Higher legal expense and greater discounting pressure |
| Settlement with delayed entry |
Preserves revenue until agreed launch date |
| Single generic doravirine launch |
Moderate-to-severe U.S. erosion |
| Multiple generic entrants |
Rapid net-price compression |
| Direct Delstrigo generic |
Highest substitution risk |
| Patent expiry without early entry |
Delayed but potentially abrupt erosion |
The largest risk is U.S. net sales, where generic substitution and formulary mechanics are strongest. International erosion may be slower in some markets but more severe in tender-driven systems.
What is the long-term commercial outlook for Delstrigo?
Delstrigo is likely to remain a material Merck HIV product before doravirine exclusivity expires, but its growth rate should moderate.
The positive factors are:
- Established clinical data.
- Once-daily tablet administration.
- Doravirine’s tolerability and interaction profile.
- Merck’s global HIV commercial platform.
- Continued demand for treatment simplification.
The negative factors are:
- INSTI-based regimens dominate guideline-preferred treatment.
- TDF is less attractive than TAF for some patients.
- Generic lamivudine and TDF reduce the product’s ingredient-level differentiation.
- Pifeltro and Delstrigo share exposure to doravirine patent challenges.
- HIV treatment markets increasingly reward high adherence, tolerability and long-term safety, areas where Biktarvy and Dovato remain strong competitors.
The base case is continued revenue growth at a declining rate before patent-driven erosion becomes the principal issue. Delstrigo’s commercial value is tied less to expansion of the HIV market than to maintaining a defensible niche within treatment initiation, regimen switching and payer-specific formulary segments.
Key Takeaways
- Delstrigo combines doravirine, lamivudine and TDF in a once-daily HIV-1 treatment.
- Merck reports Delstrigo together with Pifeltro; the combined franchise generated approximately $1.2 billion in 2024.
- Doravirine is the economically important protected ingredient. Lamivudine and TDF are generic.
- INSTI-based regimens, especially Biktarvy and Dovato, are the principal commercial competitors.
- The core U.S. patent risk is concentrated in doravirine composition and related patent families, with protection extending into the early 2030s under the cited Orange Book framework.
- A generic doravirine launch could erode revenue even without an exact generic Delstrigo tablet.
- Delstrigo has small-molecule generic risk, not biosimilar risk.
- The product remains commercially durable, but its long-term value depends on doravirine exclusivity and continued payer acceptance of a TDF-based regimen.
FAQs
Is Delstrigo the same as Pifeltro?
No. Pifeltro contains doravirine alone. Delstrigo contains doravirine, lamivudine and tenofovir disoproxil fumarate.
Can patients take generic lamivudine and TDF instead of Delstrigo?
They can be used in alternative antiretroviral regimens, but substitution requires a clinically appropriate complete regimen and prescriber direction. Generic lamivudine and TDF alone are not equivalent to Delstrigo.
Does Delstrigo treat hepatitis B?
Tenofovir and lamivudine have activity against hepatitis B, but Delstrigo use in patients with HIV and hepatitis B requires careful management because stopping active hepatitis B therapy can cause a flare. [4]
Is doravirine included in Biktarvy?
No. Biktarvy contains bictegravir, emtricitabine and tenofovir alafenamide. Doravirine is the active ingredient in Pifeltro and one of the three active ingredients in Delstrigo.
What would happen to Delstrigo sales after a generic launch?
The likely result would be lower U.S. net prices, increased payer substitution and declining branded prescription volume. The magnitude would depend on whether the first competitor is a direct fixed-dose generic or standalone doravirine used with generic backbone agents.
References
- Merck & Co., Inc. (2023). 2022 annual report.
- Merck & Co., Inc. (2024). 2023 annual report.
- Merck & Co., Inc. (2025). 2024 annual report.
- U.S. Food and Drug Administration. (2024). Delstrigo prescribing information.
- Gilead Sciences, Inc. (2025). 2024 annual report.
- Panel on Antiretroviral Guidelines for Adults and Adolescents. (2024). Guidelines for the use of antiretroviral agents in adults and adolescents with HIV. U.S. Department of Health and Human Services.
- U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations: Orange Book.
- U.S. Food and Drug Administration. (2024). Abbreviated new drug application regulations and Paragraph IV certifications.
