Hepatitis B virus (HBV) is a partially double-stranded deoxyribonucleic acid (DNA) virus belonging to the Hepadnaviridae family that infects hepatocytes and maintains a stable nuclear reservoir of covalently closed circular DNA (cccDNA) that persists despite antiviral therapy. This intranuclear reservoir is the fundamental pharmacological barrier to HBV cure and the basis for the distinction between suppression and eradication.
The HBV replication cycle proceeds through several pharmacologically targetable steps. After attachment to the sodium-taurocholate co-transporting polypeptide (NTCP) receptor on the hepatocyte surface, the viral nucleocapsid releases the partially double-stranded DNA into the nucleus where it is converted by host polymerases to cccDNA. The cccDNA functions as a minichromosome that directs transcription of pregenomic RNA (pgRNA) and all viral messenger ribonucleic acids (mRNAs). The pgRNA is packaged with the viral polymerase into new nucleocapsids, within which the HBV reverse transcriptase converts pgRNA first to a single-stranded negative-sense DNA and then to a relaxed circular DNA (rcDNA) through its DNA-dependent DNA polymerase activity. The complete nucleocapsid is either enveloped and secreted as a mature virion or recycled to the nucleus to amplify the cccDNA pool. Current antiviral therapy targets the reverse transcriptase step; no approved agent directly degrades cccDNA, which is why HBV therapy is indefinite in most patients rather than curative.1
Serological markers provide both a roadmap of infection phase and endpoints for treatment monitoring. Hepatitis B surface antigen (HBsAg) is present in all phases of active infection; its loss (HBsAg clearance) with or without development of hepatitis B surface antibody (anti-HBs) represents functional cure and the highest achievable therapeutic endpoint, occurring spontaneously in fewer than 1% of chronically infected adults per year and rarely in response to antiviral therapy. Hepatitis B e antigen (HBeAg) is a secreted protein derived from the precore region of the HBV genome; its presence indicates high-level viral replication and high infectivity, while seroconversion to anti-HBe marks a transition to lower-replication phases in many patients. HBV DNA quantification by polymerase chain reaction (PCR) is the primary measure of viral replication and treatment response, with treatment targets of undetectable or below the lower limit of quantification (generally below 10 to 20 international units per milliliter (IU/mL) depending on assay). Hepatitis B core antibody (anti-HBc) IgM indicates acute infection; anti-HBc IgG persists lifelong and marks past or current HBV exposure.2
HBV infection phases determine treatment eligibility. The immune-tolerant phase, seen predominantly in perinatally infected patients, features high HBV DNA (often above 10 million IU/mL), HBeAg positivity, normal alanine aminotransferase (ALT), and minimal hepatic inflammation — antiviral therapy is generally not indicated in this phase because immune-mediated hepatocyte injury is absent and treatment response is poor. The immune-active phase (HBeAg-positive or HBeAg-negative) features elevated ALT, active hepatic inflammation, and variable HBV DNA levels — treatment is indicated. HBeAg-negative chronic hepatitis B, which predominates in Mediterranean and Asian regions due to precore mutant strains, features low-to-intermediate HBV DNA with fluctuating ALT and absent HBeAg; it represents a distinct treatment-requiring phase. The inactive carrier state features low or undetectable HBV DNA, normal ALT, and anti-HBe positivity — treatment is not indicated but monitoring is required given the risk of reactivation, particularly with immunosuppression.2
HBV reactivation occurs when immunosuppression allows amplification of the cccDNA reservoir, producing a sudden surge in HBV DNA, hepatitis, and occasionally acute liver failure. Risk is highest with anti-CD20 therapy (rituximab), systemic corticosteroids, and cytotoxic chemotherapy; moderate with TNF inhibitors and tyrosine kinase inhibitors. All patients receiving immunosuppression should be screened for HBsAg and anti-HBc before initiation. HBsAg-positive patients require prophylactic antiviral therapy (tenofovir or entecavir) starting one to two weeks before immunosuppression and continuing for at least six to twelve months after completion. Anti-HBc-positive/HBsAg-negative patients require monitoring or prophylaxis depending on immunosuppression intensity.
Treatment indications for chronic HBV are based on a combination of HBV DNA level, ALT elevation, HBeAg status, and the degree of hepatic fibrosis assessed by liver biopsy or non-invasive methods (transient elastography, serum fibrosis markers). Most guidelines recommend treatment for all patients with compensated or decompensated cirrhosis regardless of HBV DNA level or ALT, for patients with HBV DNA above 2,000 IU/mL and ALT above the upper limit of normal, and for patients with significant fibrosis (METAVIR F2 or above) regardless of HBV DNA or ALT. Treatment endpoints differ by regimen: finite therapy with peginterferon alfa aims for HBeAg seroconversion or HBsAg loss; oral nucleos(t)ide analogue therapy aims for sustained viral suppression, which is maintained indefinitely in most patients because cccDNA persists and HBV DNA rebounds upon discontinuation in the majority.2
The pharmacological treatment of chronic hepatitis B virus (HBV) has been transformed by the development of high-barrier nucleos(t)ide analogues (NAs) with potent HBV reverse transcriptase inhibitory activity and minimal resistance selection. Tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF) are now the preferred first-line agents for most patients; entecavir is an alternative with an equally high resistance barrier.
Tenofovir disoproxil fumarate and tenofovir alafenamide are acyclic phosphonate nucleotide analogues that inhibit HBV reverse transcriptase after intracellular conversion to tenofovir diphosphate (TFV-DP). TFV-DP acts as a chain terminator after incorporation into nascent HBV deoxyribonucleic acid (DNA) strands, lacking the 3-prime hydroxyl group required for chain elongation. TDF has been the standard of care for HBV for over a decade and the only nucleos(t)ide analogue (NA) with demonstrated efficacy in decompensated cirrhosis; it achieves undetectable HBV DNA in approximately 70 to 80% of treatment-naive HBeAg-positive and 90% of HBeAg-negative patients by week 48. TAF, the same prodrug technology that reduced tenofovir-related renal and bone toxicity in human immunodeficiency virus (HIV) treatment, produces equivalent HBV suppression at one-quarter the dose of TDF with significantly better renal and bone safety parameters in phase 3 trials — a meaningful advantage given the long-term, often lifelong nature of HBV therapy. Neither TDF nor TAF has yielded any confirmed resistance mutations in treatment-naive patients through 8 years of follow-up in clinical trials, establishing the highest resistance barrier of any anti-HBV agent.3
Entecavir (ETV) is a guanosine nucleoside analogue that requires phosphorylation to entecavir triphosphate; it inhibits three distinct steps of HBV reverse transcription: base priming, reverse transcription of pgRNA, and synthesis of positive-strand HBV DNA. Its triple mechanism of action contributes to its high resistance barrier: fewer than 1% of treatment-naive patients develop entecavir resistance through 5 years of therapy. However, a critical caveat applies: entecavir resistance is substantially higher in patients with pre-existing lamivudine resistance mutations (rtM204I/V plus rtL180M), because these mutations, which reduce entecavir binding affinity, are present at the start of entecavir therapy and require only one or two additional substitutions for high-level entecavir resistance. Entecavir should therefore not be used in patients with known lamivudine or telbivudine resistance; TDF or TAF are the preferred alternatives in this setting. Entecavir has minimal antiviral activity against HIV and was initially thought safe to use as HBV monotherapy in HIV-co-infected patients; however, subsequent evidence demonstrated that entecavir has sufficient anti-HIV activity to select for the methionine-to-valine substitution at codon 184 (M184V) resistance mutation in HIV when used without a fully suppressive antiretroviral (ARV) regimen. This pharmacological reality mandates that HIV-positive patients receiving entecavir must also be on a fully suppressive ARV regimen.4
Lamivudine (3TC), adefovir dipivoxil (ADV), and telbivudine (LdT) are older HBV agents with low resistance barriers and have been largely superseded by tenofovir and entecavir in resource-rich settings. Lamivudine selects for the rtM204I/V mutation (tyrosine-methionine-aspartate-aspartate, YMDD motif mutations) in up to 70% of patients after 4 years of therapy, producing high-level lamivudine resistance and cross-resistance to telbivudine. Adefovir selects for rtN236T and rtA181V/T mutations after prolonged use; it also has dose-limiting nephrotoxicity at higher doses and slower viral suppression kinetics than tenofovir. These agents are no longer recommended as initial therapy by major guidelines but remain clinically encountered as legacies of prior treatment, and understanding their resistance mutation profiles is essential for interpreting genotypic resistance testing in treatment-experienced patients.2
Peginterferon alfa (pegIFN-alfa) is the only immune-based therapy approved for chronic HBV and the only agent capable of inducing durable off-treatment responses, including HBeAg seroconversion and, rarely, HBsAg loss. Peginterferon alfa-2a at 180 micrograms subcutaneously weekly for 48 weeks achieves HBeAg seroconversion in approximately 27 to 32% of HBeAg-positive patients and sustained HBV DNA suppression in approximately 19% of HBeAg-negative patients at 24 weeks post-treatment. The mechanism involves both direct antiviral activity (upregulation of interferon-stimulated genes inhibiting HBV replication) and immune modulatory effects (restoration of HBV-specific T-cell responses). Predictors of favorable response include HBV genotype A or B (versus C or D), high baseline ALT (suggesting active immune activation), low baseline HBV DNA, and HBsAg decline on treatment. Peginterferon is contraindicated in decompensated cirrhosis, autoimmune hepatitis, and psychiatric disorders; adverse effects are substantial and include flu-like symptoms, cytopenias, neuropsychiatric effects, and thyroid dysfunction requiring monitoring.4
| Agent | Mechanism | Resistance Barrier | Key Resistance Mutations | Preferred Use |
|---|---|---|---|---|
| TDF | Nucleotide analogue RT inhibitor | Very high | None confirmed in 8-year trials | First-line; decompensated cirrhosis; HIV/HBV |
| TAF | Nucleotide analogue RT inhibitor | Very high | None confirmed | First-line; preferred if CKD or osteoporosis risk |
| Entecavir | Guanosine analogue (3-step inhibition) | Very high (naive) | rtI169T, rtT184G, rtS202I, rtM250V (on LAM-R background) | First-line; avoid if lamivudine-resistant |
| Lamivudine | Cytidine analogue RT inhibitor | Low | rtM204I/V (YMDD); rtL180M | Not recommended first-line; HIV backbone use only |
| Peginterferon alfa-2a | Immune modulation + antiviral ISG induction | N/A | N/A (immune-based) | Finite therapy goal; HBeAg-positive; genotype A/B preferred |
Hepatitis C virus (HCV) is a positive-sense single-stranded ribonucleic acid (RNA) virus of the Flaviviridae family. Unlike hepatitis B virus (HBV), HCV does not integrate into the host genome and lacks a nuclear cccDNA reservoir, making pharmacological cure achievable with finite antiviral therapy. Current direct-acting antiviral (DAA) regimens achieve sustained virological response at 12 weeks post-treatment (SVR12) — defined as undetectable HCV RNA at 12 weeks after completing therapy and operationally equivalent to cure — in more than 95% of treatment-naive patients across all genotypes.
The HCV genome encodes a large polyprotein that is cleaved by host and viral proteases into structural proteins (core, envelope 1 and 2) and non-structural proteins (nonstructural protein 2 (NS2), nonstructural protein 3 (NS3), nonstructural protein 4A (NS4A), nonstructural protein 4B (NS4B), nonstructural protein 5A (NS5A), nonstructural protein 5B (NS5B)). Three non-structural proteins are the targets of all approved direct-acting antivirals (DAAs). NS3/4A (nonstructural protein 3/4A) is a serine protease that cleaves the HCV polyprotein at four sites; its inhibition blocks polyprotein processing and halts viral replication. NS5A is a multifunctional phosphoprotein essential for viral ribonucleic acid (RNA) replication, virion assembly, and modulation of host cell signaling; its precise enzymatic function is not fully characterized, but its inhibition at picomolar to femtomolar concentrations makes it the most potent target in the HCV drug armamentarium. NS5B is the RNA-dependent RNA polymerase (RdRp) responsible for copying the HCV genome; it is targeted by two mechanistically distinct drug classes: nucleotide analogues (which act as obligate chain terminators after incorporation) and non-nucleoside inhibitors (which bind allosteric sites on the RdRp and alter its conformation).5
HCV exists in seven major genotypes (GT1 through GT7) with multiple subtypes, which differ in their geographic distribution, treatment response, and the activity of genotype-specific DAAs. Genotype 1 (GT1) is the most prevalent worldwide, particularly in North America and Europe; genotype 1a (GT1a, where GT denotes genotype) and genotype 1b (GT1b) are the clinically relevant subtypes with different resistance profiles for NS3 inhibitors. Genotype 2 (GT2) is sensitive to sofosbuvir-based therapy and historically the most treatment-responsive genotype. Genotype 3 (GT3) is associated with higher rates of steatohepatitis, more rapid fibrosis progression, and lower sustained virological response (SVR) rates with some older regimens. Genotype 4 (GT4) predominates in Africa and the Middle East; genotype 5 (GT5) and genotype 6 (GT6) are geographically restricted. The advent of pangenotypic DAA regimens — those active against all genotypes — has substantially simplified treatment by obviating genotype testing before therapy in most clinical settings, though genotype knowledge remains important for sequencing after treatment failure and in resource-limited settings where genotype-specific regimens may be preferred on cost grounds.6
The pharmacological basis of HCV cure with finite therapy rests on four properties of current DAA regimens: extremely high antiviral potency (reducing HCV RNA by 4 to 6 log10 within days of initiation), combinational targeting of three non-overlapping mechanisms (preventing resistance emergence through single mutations), high barrier to resistance for newer agents (particularly sofosbuvir, for which resistance requires multiple simultaneous mutations), and the absence of a persistent nuclear reservoir (unlike HBV cccDNA, HCV RNA is entirely cytoplasmic and is lost when viral replication is suppressed). SVR12 is considered durable and equivalent to cure because HCV RNA levels do not rebound after sustained suppression in the absence of reinfection, unlike HBV where the cccDNA reservoir allows viral rebound when therapy is discontinued. The transition from interferon-based therapy, which required 48 to 72 weeks of treatment with significant toxicity, to 8 to 12-week all-oral DAA regimens with minimal adverse effects represents one of the most dramatic pharmacological advances in the treatment of chronic viral infections.6
Undetectable HCV RNA 12 weeks after completing therapy (SVR12) represents durable eradication of HCV infection in the vast majority of patients. Large prospective cohort studies demonstrate that fewer than 1% of patients with SVR12 experience viral relapse, and relapse must be distinguished from reinfection in persons with ongoing exposure risk. SVR12 is associated with regression of hepatic fibrosis, reduced risk of hepatocellular carcinoma (though not elimination of risk in patients with advanced cirrhosis), and in compensated cirrhosis a significant reduction in liver-related mortality. Patients with advanced fibrosis or cirrhosis who achieve SVR12 require continued hepatocellular carcinoma surveillance by ultrasound every 6 months indefinitely, as residual risk persists despite cure.
The current landscape of hepatitis C virus (HCV) therapy is defined by three pangenotypic regimens — sofosbuvir/velpatasvir, glecaprevir/pibrentasvir, and sofosbuvir/velpatasvir/voxilaprevir — alongside retained genotype-specific regimens for specific clinical indications. Treatment selection is driven by genotype (where known), presence of cirrhosis, prior treatment history, renal function, and the direct-acting antiviral (DAA) interaction profile of concurrent medications.
Sofosbuvir (SOF) is a uridine nucleotide analogue prodrug that, after intracellular activation to sofosbuvir triphosphate (SOF-TP), acts as a chain terminator at the nonstructural protein 5B (NS5B) active site. Sofosbuvir has an essentially absolute genetic resistance barrier: resistance requires substitution of serine at NS5B position 282 (S282T), which produces a severe fitness cost and has never been documented to emerge during clinical treatment. Sofosbuvir is a P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) substrate; inducers of these transporters (rifampin, carbamazepine, St. John's Wort) reduce sofosbuvir plasma concentrations substantially and are contraindicated. Sofosbuvir is renally eliminated (80% of the inactive metabolite GS-331007 excreted renally) and is not recommended in patients with estimated glomerular filtration rate (eGFR) below 30 mL/min/1.73m² due to accumulation of metabolites; pharmacokinetic data for sofosbuvir in dialysis patients are limited and safety uncertain.6
Sofosbuvir/velpatasvir (SOF/VEL, Epclusa) is a pangenotypic fixed-dose combination pairing sofosbuvir with velpatasvir, a second-generation nonstructural protein 5A (NS5A) inhibitor with activity across all genotypes including genotype 3 (GT3). It is administered as one tablet daily for 12 weeks in treatment-naive and treatment-experienced patients without cirrhosis or with compensated cirrhosis, achieving sustained virological response at 12 weeks (SVR12) rates above 95% in the registrational ASTRAL (A Sofosbuvir and Velpatasvir Combination) trials across all genotypes. The addition of the nonstructural protein 3/4A (NS3/4A) protease inhibitor voxilaprevir to sofosbuvir/velpatasvir produces sofosbuvir/velpatasvir/voxilaprevir (SOF/VEL/VOX, Vosevi), a pangenotypic triple combination used for 8 weeks in treatment-naive patients without cirrhosis (GT1-GT6) and for 12 weeks in treatment-experienced patients with prior NS5A inhibitor exposure. Velpatasvir is metabolized by cytochrome P450 3A4 (CYP3A4), cytochrome P450 2C8 (CYP2C8), and P-gp; acid-suppressing agents raise gastric pH and reduce velpatasvir absorption, requiring that proton pump inhibitors (PPIs) not exceed omeprazole-equivalent 20 mg and be taken simultaneously with SOF/VEL (not at other times of day).6
Glecaprevir/pibrentasvir (GLE/PIB, Mavyret) is a fixed-dose combination of a pangenotypic NS3/4A protease inhibitor (glecaprevir) and a pangenotypic NS5A inhibitor (pibrentasvir). Its defining pharmacological advantage is an abbreviated treatment duration: 8 weeks in treatment-naive patients without cirrhosis regardless of genotype, making it the shortest approved HCV treatment. Glecaprevir/pibrentasvir is also the preferred regimen in severe renal impairment, including dialysis, because neither component is renally eliminated (both are primarily biliary-excreted), avoiding the accumulation concerns of sofosbuvir in this population. Glecaprevir is both a CYP3A4 substrate and a P-gp/BCRP inhibitor; it inhibits organic anion transporting polypeptide 1B1 (OATP1B1) and organic anion transporting polypeptide 1B3 (OATP1B3) transporters, raising statin plasma concentrations — rosuvastatin is contraindicated with glecaprevir/pibrentasvir, and other statins require dose limitation. Atazanavir substantially raises glecaprevir plasma concentrations and is contraindicated; efavirenz reduces both glecaprevir and pibrentasvir levels and is also contraindicated.7
Ledipasvir/sofosbuvir (LDV/SOF, Harvoni) was the first once-daily fixed-dose combination DAA and remains in use for genotype 1 (GT1), genotype 4 (GT4), genotype 5 (GT5), and genotype 6 (GT6) infection. Ledipasvir is a first-generation NS5A inhibitor with limited activity against genotype 2 (GT2) and GT3. It has no significant drug-metabolizing enzyme interactions but does require gastric acidity for absorption; PPIs reduce ledipasvir exposure and should be used at doses not exceeding omeprazole 20 mg, taken simultaneously. Elbasvir/grazoprevir (EBR/GZR, Zepatier) pairs a NS5A inhibitor (elbasvir) with a NS3/4A protease inhibitor (grazoprevir) active against GT1 and GT4. Its key clinical feature is safety in severe renal impairment and dialysis, as grazoprevir and elbasvir are both hepatically eliminated with minimal renal excretion. Elbasvir/grazoprevir requires nonstructural protein 5A resistance-associated substitution (RAS) testing in patients with genotype 1a infection before prescribing, as baseline NS5A RAS reduce treatment duration-adjusted sustained virological response (SVR) rates with this combination; nonstructural protein 3 (NS3) RAS testing is not routinely required.7
| Regimen | Targets | Genotypes | Duration | Key Interactions / Notes |
|---|---|---|---|---|
| SOF/VEL (Epclusa) | NS5B + NS5A | Pangenotypic | 12 wks | PPIs: simultaneous, max omeprazole 20 mg; avoid rifampin/carbamazepine |
| GLE/PIB (Mavyret) | NS3/4A + NS5A | Pangenotypic | 8 wks (naive, no cirrhosis) | Preferred in dialysis; rosuvastatin contraindicated; avoid ATV, EFV |
| SOF/VEL/VOX (Vosevi) | NS5B + NS5A + NS3/4A | Pangenotypic | 8 wks (naive) / 12 wks (NS5A-experienced) | Same interactions as SOF/VEL + VOX statin/OATP effects |
| LDV/SOF (Harvoni) | NS5A + NS5B | GT1, GT4-6 | 8–12 wks | PPI max omeprazole 20 mg simultaneous; avoid rifampin |
| EBR/GZR (Zepatier) | NS5A + NS3/4A | GT1, GT4 | 12–16 wks | GT1a: NS5A RAS testing required; safe in dialysis; avoid CYP3A4 inducers/strong inhibitors |
Direct-acting antiviral therapy achieves high sustained virological response at 12 weeks (SVR12) rates across most patient populations, but cirrhosis, advanced renal impairment, human immunodeficiency virus (HIV) co-infection, prior direct-acting antiviral (DAA) experience, and baseline resistance-associated substitutions (RASs) require tailored regimen selection and, in some cases, extended treatment duration or combination adjustment.
Compensated cirrhosis (Child-Pugh A) does not substantially reduce SVR12 rates with pangenotypic regimens, but does influence treatment duration and ribavirin use. Glecaprevir/pibrentasvir for 12 weeks (rather than 8 weeks) is used in treatment-naive patients with compensated cirrhosis; sofosbuvir/velpatasvir for 12 weeks is similarly used. Genotype 3 (GT3)-infected patients with cirrhosis represent the most challenging treatment scenario in contemporary hepatitis C virus (HCV) practice: SVR12 rates with sofosbuvir/velpatasvir are approximately 88 to 91% in GT3 cirrhotic patients, below the greater-than-95% threshold achieved in other populations; sofosbuvir/velpatasvir/voxilaprevir for 12 weeks is the preferred approach in nonstructural protein 5A (NS5A)-inhibitor-naive GT3 cirrhotic patients where available. Decompensated cirrhosis (Child-Pugh B or C) is a contraindication to nonstructural protein 3/4A (NS3/4A) protease inhibitor-containing regimens (including glecaprevir, voxilaprevir, grazoprevir, and ledipasvir/sofosbuvir is acceptable but protease inhibitor-containing combinations are not) because protease inhibitor concentrations increase dramatically in hepatic impairment, increasing toxicity. Sofosbuvir/velpatasvir with or without ribavirin for 12 to 24 weeks is the preferred approach in decompensated cirrhosis, with liver transplantation evaluation proceeding in parallel.8
Severe renal impairment (eGFR below 30 mL/min/1.73m²) requires careful DAA selection because sofosbuvir accumulation is not well characterised at low eGFR levels. The preferred regimen in this setting is glecaprevir/pibrentasvir, which has no renal elimination pathway and is approved at standard doses for all genotypes including in patients on hemodialysis; SVR12 rates above 98% have been demonstrated in this population. Elbasvir/grazoprevir is an alternative for genotype 1 (GT1) and genotype 4 (GT4) patients on dialysis. Ledipasvir/sofosbuvir has been used in dialysis patients in observational studies with acceptable sustained virological response (SVR) rates but carries regulatory uncertainty regarding sofosbuvir metabolite accumulation; it is not the preferred choice when glecaprevir/pibrentasvir is available. Ribavirin, which is renally eliminated, requires dose modification or avoidance in renal impairment and is generally not used in patients on dialysis due to hemolytic anemia risk in this population.8
Human immunodeficiency virus/hepatitis C virus (HIV/HCV) co-infection was historically associated with accelerated hepatic fibrosis progression, reduced interferon response rates, and higher liver-related mortality than HCV monoinfection. With DAA therapy, SVR12 rates in HIV/HCV co-infected patients are equivalent to those in HCV monoinfected patients across all approved regimens, provided that HIV is virologically suppressed and the antiretroviral (ARV) regimen is compatible with the chosen DAA. Drug interactions between DAAs and ARVs require systematic evaluation before treatment initiation. NS3/4A protease inhibitors (glecaprevir, voxilaprevir, grazoprevir) are sensitive cytochrome P450 3A4 (CYP3A4) substrates; ritonavir- and cobicistat-boosted ARV regimens raise NS3/4A inhibitor concentrations substantially — atazanavir/ritonavir raises glecaprevir exposure approximately 6-fold and is contraindicated; lopinavir/ritonavir similarly raises glecaprevir to unsafe levels. Sofosbuvir/velpatasvir has favorable interaction profiles with most INSTIs and NNRTIs, though efavirenz reduces sofosbuvir and velpatasvir exposure and is not recommended without careful assessment. Dolutegravir, raltegravir, and rilpivirine have minimal interactions with sofosbuvir/velpatasvir and are preferred HIV backbone options during HCV treatment.9
HCV reinfection following SVR12 is clinically distinct from relapse and is an increasingly recognized phenomenon in populations with ongoing exposure risk, particularly people who inject drugs (PWID) and men who have sex with men (MSM) with high-risk sexual behaviors. Reinfection does not alter the SVR12 achieved from the first treatment episode and does not reflect treatment failure. Annual HCV ribonucleic acid (RNA) testing is recommended for persons with ongoing risk behaviors. Retreatment of reinfection follows the same principles as treatment-naive therapy, as reinfection almost always involves a genetically distinct strain; RAStesting before retreatment for reinfection is not required unless the same genotype is identified, in which case nonstructural protein 5A (NS5A) resistance-associated substitution (RAS) testing is prudent.9
Resistance-associated substitutions at NS5A and nonstructural protein 3 (NS3) positions can reduce SVR12 rates with specific regimens when present at baseline. NS5A RASs are particularly clinically relevant because NS5A inhibitors have a lower genetic resistance barrier than sofosbuvir; common NS5A RAS positions include L28 (leucine 28), Q30 (glutamine 30), L31 (leucine 31), H58 (histidine 58), and Y93 (tyrosine 93). Baseline NS5A RAS testing is recommended before elbasvir/grazoprevir in genotype 1a-infected patients (where RASs at positions 28, 30, 31, or 93 predict reduced efficacy and mandate 16-week treatment with ribavirin), before sofosbuvir/velpatasvir/voxilaprevir in genotype 1a treatment-experienced patients, and before retreatment after prior DAA failure involving NS5A inhibitors. Sofosbuvir nonstructural protein 5B (NS5B) serine-282-threonine substitution (S282T) resistance is extremely rare clinically; NS3 protease inhibitor RASs are clinically important after protease inhibitor treatment failure but do not substantially affect pangenotypic regimen SVR rates in treatment-naive patients.9
Hepatitis B virus/hepatitis C virus (HBV/HCV) co-infection, HBV reactivation during HCV direct-acting antiviral (DAA) therapy, and the long-term management obligations that persist after sustained virological response at 12 weeks (SVR12) represent the synthesis of hepatitis B and C pharmacology as it applies in clinical practice. Understanding these intersections is essential for clinicians managing patients with viral hepatitis across diverse contexts.
HBV/HCV co-infection occurs in geographic regions where both viruses are endemic and among persons with shared risk factors for parenteral transmission. In HBV/HCV co-infected patients, HCV typically dominates virologically, suppressing HBV replication through interferon-mediated mechanisms; as a result, HBV deoxyribonucleic acid (DNA) is often low or undetectable during active HCV infection. Paradoxically, this viral suppression can be unmasked during HCV DAA therapy: as HCV is eliminated, the interferon-stimulated gene (ISG) signaling that suppressed HBV replication dissipates, allowing HBV reactivation in patients who were not receiving HBV-active therapy. HBV reactivation during DAA therapy occurs in 1 to 2% of HBV surface antigen (HBsAg)-positive patients and up to 5% in some cohorts, with rare cases of acute liver failure documented. All patients initiating HCV DAA therapy must be screened for HBsAg and anti-HBc before starting treatment; HBsAg-positive patients should receive concomitant HBV-active antiviral therapy (TDF or TAF) throughout HCV DAA therapy and for several months after completion.10
Monitoring during and after HCV DAA therapy follows a streamlined protocol given the favorable safety profiles of modern regimens. HCV ribonucleic acid (RNA) should be measured at baseline, at the end of treatment (to confirm on-treatment suppression), and at 12 weeks after completing treatment (to establish SVR12). Routine alanine aminotransferase (ALT) and complete blood count (CBC) monitoring during treatment is not mandatory for most patients but is appropriate in cirrhotic patients and those on ribavirin. Hepatic function should be monitored in patients with decompensated cirrhosis given the risk of hepatic decompensation during HCV DAA therapy — though DAA therapy typically improves hepatic function, acute hepatic decompensation has been reported, particularly in patients with very advanced liver disease. Renal function monitoring is appropriate in patients receiving sofosbuvir-containing regimens who have baseline renal impairment. After SVR12, patients with advanced fibrosis or cirrhosis require hepatocellular carcinoma (HCC) surveillance by liver ultrasound every 6 months indefinitely, even after cure, because the risk of HCC is reduced but not eliminated by viral eradication in the setting of established cirrhosis.1011
Treatment sequencing in human immunodeficiency virus/hepatitis B virus/hepatitis C virus (HIV/HBV/HCV) triply infected patients — a situation encountered in clinical practice, particularly in people who inject drugs — requires systematic prioritization. In patients with advanced immunodeficiency (cluster of differentiation 4 (CD4) count below 200 cells/mm³), antiretroviral (ARV) therapy for HIV should be optimized and immune reconstitution allowed before HCV DAA initiation, given that immune reconstitution itself improves HCV outcomes and reduces HCV-related liver disease progression. Once HIV is suppressed, HCV DAA therapy can be initiated; the ARV regimen should be reviewed for DAA interactions and adjusted where needed before HCV treatment starts. HBV must be covered throughout: the preferred ARV backbone (TDF/FTC or TAF/FTC) suppresses HBV simultaneously, simplifying management. After achieving SVR12 for HCV, the HBV-active ARV backbone should be continued indefinitely to maintain HBV suppression; the most dangerous scenario is achieving HCV cure and then switching to an HBV-inactive ARV regimen, which can precipitate catastrophic HBV reactivation and hepatic decompensation in the setting of hepatitis B virus/human immunodeficiency virus (HBV/HIV) co-infection.911
HBV reactivation during HCV DAA treatment can produce acute liver failure in HBsAg-positive patients who are not receiving HBV-active therapy. The mechanism is loss of HCV-driven ISG signaling that suppressed HBV. All patients initiating HCV DAA therapy must have HBsAg and anti-HBc checked before treatment. HBsAg-positive patients without HBV-active therapy must start TDF or TAF simultaneously with or before HCV DAA initiation and continue for at least 12 weeks after completing HCV treatment. Anti-HBc-positive, HBsAg-negative patients require monitoring of HBV DNA during and after HCV therapy. Do not treat HCV in an HBsAg-positive patient without a clear HBV management plan in place.
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