Amantadine for chronic hepatitis C: a magic bullet or yet another dead duck?
Authors: Antonio Craxı̀, Oreste Lo Iacono
Journal: Journal of Hepatology (2001)

Dissatisfaction with the results of antiviral therapy for chronic hepatitis C fuels continuous research for more effective and tolerable regimens. Debate has recently been focused on the possible use of amantadine (AMA), an agent with direct activity against RNA viruses, to enhance the effects of interferons. Two papers [27Caronia S Bassendine M.F Barry R Mills P Naoumov N.V Fox R et al.Interferon plus amantadine versus interferon alone in the treatment of naı̈ve patients with chronic hepatitis C: a UK multicentre study.J Hepatol. 2001; 35: 512-516Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 28Tabone M Laudi C Delmastro B Biglino A Andreoni M Chieppa F et al.Interferon and amantadine in combination as initial treatment for chronic hepatitis C patients.J Hepatology. 2001; 35: 517-521Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar] add to the controversy. AMA (1-aminoadamantan), a tricyclic amine, and its related analogue rimantadine (RIMA) have antiviral activity against toga, myxo, arena, flavi, and coronaviruses [1De Clercq E Antiviral drugs: current state of the art.J Clin Virol. 2001; 22: 73-89Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar, 2Wintermeyer S.M Nahata M.C Rimantadine: a clinical perspective.Ann Pharmacother. 1995; 29: 299-310PubMed Google Scholar]. Inhibition of influenza A virus replication obtained with these drugs has been exploited clinically to prevent and to cure flu. Known mechanisms of action of AMA include inhibition of an early step in viral replication, most likely viral uncoating and interaction with the influenza A viral matrix protein (M2), which is important in virion budding [1De Clercq E Antiviral drugs: current state of the art.J Clin Virol. 2001; 22: 73-89Abstract Full Text Full Text PDF PubMed Scopus (246) Google Scholar]. In 1997, J.P. Smith reported, in a pilot study of 22 patients with chronic hepatitis C who had failed previous monotherapy with α-interferon (IFN) [3Smith J.P Treatment of chronic hepatitis C with amantadine.Dig Dis Sci. 1997; 42: 1681-1687Crossref PubMed Scopus (153) Google Scholar], that AMA was effective in reducing necroinflammation, with 64% of patients having a decrease in aminotransferases on therapy. Six patients had normal alanine aminotransferase (ALT) and negative hepatitis C virus (HCV)-RNA at the end of therapy, and four had a sustained response (SR) [4Smith J.P Hepatitis C treatment with amantadine-HCl in non-responders to alpha-interferon.Arq Gastroenterol. 1999; 36: 61-62PubMed Google Scholar]. The effectiveness of these tricyclic amines as antiviral agents against HCV was challenged by subsequent trials of AMA [5Tabone M Ercole E Zaffino C Sallio Bruno F Pera A Bonino F Amantadine hydrochloride decreases serum ALT activity without effects on serum HCV-RNA in chronic hepatitis C patients.Ital J Gastroenterol Hepatol. 1998; 30: 611-613PubMed Google Scholar, 6Hubert I.F Lunel F Cadranel J.F Oberti F Cales P Treatment of chronic hepatitis C with amantadine.Am J Gastroenterol. 1999; 94: 2316-2317Crossref PubMed Scopus (8) Google Scholar, 7Parolin M.B Lacerda M.A Lopes R.W Amantadine-HCl in the treatment of chronic hepatitis C in non-responders to alpha-interferon. Effect on ALT serum levels and viral load.Arq Gastroenterol. 1999; 36: 63-67PubMed Google Scholar, 8Andant C Lamoril J Deybach J.C Jouet P Soule J.C Amantadine for chronic hepatitis C: pilot study in 14 patients.Eur J Gastroenterol Hepatol. 2000; 12: 1319-1322Crossref PubMed Scopus (16) Google Scholar, 9Goff J.S Reveille R.M Johnson A Treatment of chronic hepatitis C with amantadine.J Dig Dis Sci. 2000; 45: 1389-1391Crossref PubMed Scopus (26) Google Scholar, 10Senturk H Mert A Akdogan M Tabak F Basaran G Turkoglu S et al.Amantadine monotherapy of chronic hepatitis C patients infected with genotype 1b.Scand J Infect Dis. 2000; 32: 575-576Crossref PubMed Scopus (17) Google Scholar, 11Di Martino V Boudjema H Delacour T Cazier A Caron C Coutarel P et al.Treatment of chronic hepatitis C with amantadine hydrochloride in patients who had not responded to previous treatment with interferon-alpha and/or ribavirin.Clin Infect Dis. 2001; 32: 830-831Crossref PubMed Scopus (15) Google Scholar] and of RIMA [12Fong T.L Fried M.W Clarke-Platt J A pilot study of rimantadine for patients with chronic hepatitis C unresponsive to interferon therapy.Am J Gastroenterol. 1999; 94: 990-993Crossref PubMed Google Scholar], both in non-responders to IFN and in naı̈ve patients. These studies have shown almost uniformly some reduction of ALT, ranging from 0 to 58% of patients while on therapy, but no consistent effects on HCV-RNA. SR to AMA monotherapy has never been reported after the original study [3Smith J.P Treatment of chronic hepatitis C with amantadine.Dig Dis Sci. 1997; 42: 1681-1687Crossref PubMed Scopus (153) Google Scholar]. The behaviour of AMA is similar to ribavirin, which, in monotherapy, often improves liver biochemistry [13Reichard O Andersson J Schvarcz R et al.Ribavirin treatment for chronic hepatitis C.Lancet. 1991; 337: 1058-1061Abstract PubMed Scopus (278) Google Scholar] but does not significantly reduce the HCV viral load [14Reichard O Yun Z.B Sonnerborg A Weiland O Hepatitis C viral RNA titers in serum prior to, during, and after oral treatment with ribavirin for chronic hepatitis C.J Med Virol. 1993; 41: 99-102Crossref PubMed Scopus (94) Google Scholar]. The absence of suitable cellular models of HCV replication has hampered the in vitro evaluation of AMA and RIMA. Indirect assessment of their effects on HCV protease, helicase, ATPase, RNA-dependent RNA polymerase, and HCV internal ribosomal entry site (IRES) translation has been performed by in vitro biochemical assays [15Jubin R Murray M.G Howe A.Y Butkiewicz N Hong Z Lau J.Y Amantadine and rimantadine have no direct inhibitory effects against hepatitis C viral protease, helicase, ATPase, polymerase, and internal ribosomal entry site-mediated translation.J Infect Dis. 2000; 181: 331-334Crossref PubMed Scopus (39) Google Scholar]. No inhibition (>15%) was observed with concentrations up to 400 μg/ml. IRES-specific inhibition was not seen at clinically relevant concentrations. Cap and IRES reporter genes were suppressed at higher levels, possibly by non-specific translation inhibition. These experiments allowed to conclude that AMA and RIMA have no direct specific inhibitory effect against HCV non-structural proteins and IRES in vitro. A mammalian binary expression system able to synthesize positive and negative strand HCV-RNA [16Chung A et al.Hepatology. 1999; 30: 354AGoogle Scholar] has recently been used to determine whether IFN, ribavirin, and AMA directly inhibit HCV replication. In this replicon system, rIFN-α-2b induced a dose-responsive inhibition of HCV (−) strand synthesis without affecting actin and β-galactosidase mRNA levels. The same doses produced complete inhibition of HCV protein synthesis. Ribavirin and AMA, at doses above pharmacological concentrations, had no effect on HCV (−) RNA levels. Thus, while IFN acts directly as an anti-HCV agent, ribavirin and AMA actions against HCV are likely to be indirect. Like ribavirin, AMA and RIMA may act also on the immune system. The effects of AMA and rIFN-α-2b alone and combined have been studied in cultured PBMC from 15 chronic hepatitis C patients and ten controls [17Martin J Navas S Fernandez M Rico M Pardo M Quiroga J.A et al.In vitro effect of amantadine and interferon alpha-2a on hepatitis C virus markers in cultured peripheral blood mononuclear cells from hepatitis C virus-infected patients.Antiviral Res. 1999; 42: 59-70Crossref PubMed Scopus (41) Google Scholar]. Four patients (27%) had HCV core and NS3-specific proliferative responses. AMA suppressed these responses in all cases with an antiproliferative effect greater than IFN. All PBMC cultures from patients were HCV-RNA positive. AMA, alone or combined with IFN, dose-dependently reduced the HCV-RNA content. With AMA alone, IFN alone and their combination, 7, 13 and 20% of PBMC cultures became HCV-RNA negative, respectively. In contrast to IFN, AMA did not modify the expression of 2′,5′-OAS or the spontaneous or mitogen-stimulated production of γ-IFN and interleukin 10. AMA and RIMA are thus very weak antivirals providing some anti-inflammatory activity. The lack of more potent direct inhibitors of HCV replication suitable for clinical use has nonetheless stimulated studies aimed at evaluating the potential of combination therapy between IFN and AMA, both in non-responders to IFN or IFN and ribavirin [18Brillanti S Foli M Di Tomaso M Gramantieri L Masci C Bolondi L Pilot study of triple antiviral therapy for chronic hepatitis C in interferon alpha non-responders.Ital J Gastroenterol Hepatol. 1999; 31: 130-134PubMed Google Scholar, 19Carlsson T Lindahl K Schvarcz R Wejstal R Uhno I Shev S et al.HCV RNA levels during therapy with amantadine in addition to interferon and ribavirin in chronic hepatitis C patients with previous nonresponse or response/relapse to interferon and ribavirin.J Viral Hepat. 2000; 7: 409-413Crossref PubMed Scopus (26) Google Scholar, 20Brillanti S Levantesi F Masi L Foli M Bolondi L Triple antiviral therapy as a new option for patients with interferon nonresponsive chronic hepatitis C.Hepatology. 2000; 3: 630-634Crossref Scopus (157) Google Scholar, 21Khalili M Denham C Perrillo R Interferon and ribavirin versus interferon and amantadine in interferon nonresponders with chronic hepatitis C.Am J Gastroenterol. 2000; 95: 1284-1289Crossref PubMed Google Scholar, 22Berg T Naumann U Wiedenmann B Hopf U Pilot study of interferon-alpha high-dose induction therapy in combination with ribavirin plus amantadine for nonresponder patients with chronic hepatitis C.Z Gastroenterol. 2001; 39: 145-151Crossref PubMed Scopus (21) Google Scholar, 23Younossi Z.M Mullen K.D Zakko W Hodnick S Brand E Barnes D.S et al.A randomized, double-blind controlled trial of interferon alpha-2b and ribavirin vs. interferon alpha-2b and amantadine for treatment of chronic hepatitis C non-responder to interferon monotherapy.J Hepatol. 2001; 34: 128-133Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar] and in naı̈ve patients [24Zeuzem S Teuber G Naumann U Berg T Raedle J Hartmann S et al.Randomized, double-blind, placebo-controlled trial of interferon alfa2a with and without amantadine as initial treatment for chronic hepatitis C.Hepatology. 2000; 32: 835-841Crossref PubMed Scopus (83) Google Scholar, 25Mangia A Minerva N Annese M Leandro G Villani M.R Santoro R et al.A randomized trial of amantadine and interferon versus interferon alone as initial treatment for chronic hepatitis C.Hepatology. 2001; 33: 989-993Crossref PubMed Scopus (60) Google Scholar]. Many other controlled and uncontrolled trials are in progress. Two recently reported trials have reached contrasting results. Zeuzem and colleagues [24Zeuzem S Teuber G Naumann U Berg T Raedle J Hartmann S et al.Randomized, double-blind, placebo-controlled trial of interferon alfa2a with and without amantadine as initial treatment for chronic hepatitis C.Hepatology. 2000; 32: 835-841Crossref PubMed Scopus (83) Google Scholar] studied 119 naı̈ve subjects with chronic hepatitis C, randomly allocating them to IFN-α-2a at 6 MU t.i.w. for 24 weeks, then 3 MU t.i.w. for another 24 weeks plus AMA sulphate at 100 mg twice daily p.o. for 48 weeks, or to the same IFN regimen plus placebo. A virological, end-of-treatment response (ETR) was observed in 34% of patients treated with the combination therapy and in 33% on monotherapy, while a SR occurred in 10 and 22%, respectively. Mangia and colleagues [25Mangia A Minerva N Annese M Leandro G Villani M.R Santoro R et al.A randomized trial of amantadine and interferon versus interferon alone as initial treatment for chronic hepatitis C.Hepatology. 2001; 33: 989-993Crossref PubMed Scopus (60) Google Scholar], who enrolled 200 naı̈ve patients and randomized them to 48 weeks of treatment with IFN-α-2a at 6 MU t.i.w. for 48 weeks with or without AMA hydrochloride at 100 mg twice daily, reported more optimistic findings. The rate of ETR in their study was 45.5% for combination and 28.7% for monotherapy, and more importantly, that of SR was 29.3 vs. 16.8%, respectively. Interestingly, in both studies, the addition of AMA did not affect the safety and tolerability profile of IFN. The health-related quality of life [26Fried M.W Shiffman M.L Reddy R.K et al.Pegylated (40 kDa) interferon alfa-2a (Pegasys®) in combination with ribavirin: efficacy and safety results from a phase III, randomized, actively-controlled, multicenter study.Gastroenterology. 2001; 120: A55Abstract Google Scholar] was seemingly improved, in terms of fatigue and vigour scores by the antidepressant action of AMA. Even accounting for some differences among the trials in the IFN schedule, the distribution of HCV genotypes and the rate of advanced fibrosis, a strong determinant of low responsiveness to IFN, it is difficult to reconcile the discordant results of these trials. Scarce information can be derived from the other studies, many with confoundingly small sample sizes and reported only in abstract. Two large studies [27Caronia S Bassendine M.F Barry R Mills P Naoumov N.V Fox R et al.Interferon plus amantadine versus interferon alone in the treatment of naı̈ve patients with chronic hepatitis C: a UK multicentre study.J Hepatol. 2001; 35: 512-516Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 28Tabone M Laudi C Delmastro B Biglino A Andreoni M Chieppa F et al.Interferon and amantadine in combination as initial treatment for chronic hepatitis C patients.J Hepatology. 2001; 35: 517-521Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar] add some relevant elements to the pattern. In the first, ref. [27Caronia S Bassendine M.F Barry R Mills P Naoumov N.V Fox R et al.Interferon plus amantadine versus interferon alone in the treatment of naı̈ve patients with chronic hepatitis C: a UK multicentre study.J Hepatol. 2001; 35: 512-516Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar], produced by a cooperative UK group after a small pilot trial at one of the centres involved, a total of 179 naı̈ve patients (pilot+multicentre studies), 9% with cirrhosis and an unusually low 32% of genotype 1, were randomized to receive IFN-α-2a at 4.5 MU t.i.w. for 48 weeks with or without AMA hydrochloride at 100 mg twice daily. ETR rates were 31% for combination and 19% for monotherapy, and SR rates were 23 and 17%, respectively. In the other study [28Tabone M Laudi C Delmastro B Biglino A Andreoni M Chieppa F et al.Interferon and amantadine in combination as initial treatment for chronic hepatitis C patients.J Hepatology. 2001; 35: 517-521Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar], a multicentre Italian trial, 180 naı̈ves without cirrhosis were randomized to IFN-α-2a at 6 MU t.i.w. for 24 weeks, then 3 MU t.i.w. for another 24 weeks with or without AMA hydrochloride at 100 mg twice daily for 48 weeks. The results were again uninspiring, with an ETR of 47% for the combination and 37% for monotherapy and an SR of 24 vs. 17%. A negative effect of genotype 1 on responsiveness was seen in the two studies, reiterating the findings by Zeuzem and Mangia. Is then AMA another failed promise? Possibly, but the case is still open. An interesting finding in both studies [27Caronia S Bassendine M.F Barry R Mills P Naoumov N.V Fox R et al.Interferon plus amantadine versus interferon alone in the treatment of naı̈ve patients with chronic hepatitis C: a UK multicentre study.J Hepatol. 2001; 35: 512-516Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 28Tabone M Laudi C Delmastro B Biglino A Andreoni M Chieppa F et al.Interferon and amantadine in combination as initial treatment for chronic hepatitis C patients.J Hepatology. 2001; 35: 517-521Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar] is that at 3 months of treatment, patients on the combination are significantly more likely to be HCV-RNA negative (62 vs. 47% in the UK study, 61 vs. 46% in the Italian study). These figures, which are consistently higher than the ETR, suggest that an initial additive effect of AMA exists, and helps to reduce temporarily the viral load to undetectable levels. This weak effect is then lost, possibly by viral escape mutations, while still on treatment, thus bringing the final result down to the level of IFN monotherapy. In a similar trial still underway, we have observed the same phenomenon, and found a reduction in the heterogeneity of the re-emerging quasispecies of subjects with a breakthrough (Di Marco, unpublished data). AMA thus probably has some anti-HCV effect, but readily induces viral resistance leading to a loss of efficacy. Should we discard the feeble antiviral activity of AMA and RIMA? In naı̈ve patients, AMA is already a loser when, in combination with IFN, it is compared with the standard IFN–ribavirin schedule with its 41% rate of SR [29Reichard O Norkrans G Fryden A Braconier J.H Sonnerborg A Weiland O Swedish Study GroupRandomised, double-blind, placebo-controlled trial of interferon α-2b with and without ribavirin for chronic hepatitis C.Lancet. 1998; 351: 83-87Abstract Full Text Full Text PDF PubMed Scopus (663) Google Scholar]. Pegylated IFNs, whose rate of success in naı̈ves goes from 54 [30Manns M.P McHutchison J.G Gordon S et al.PEG interferon alfa-2b plus ribavirin compared to interferon alfa-2b plus ribavirin for the treatment of chronic hepatitis C: 24 week treatment analysis of a multicenter, multinational phase III randomized controlled trial.Hepatology. 2000; 32: 297ACrossref PubMed Scopus (54) Google Scholar] to 56% [26Fried M.W Shiffman M.L Reddy R.K et al.Pegylated (40 kDa) interferon alfa-2a (Pegasys®) in combination with ribavirin: efficacy and safety results from a phase III, randomized, actively-controlled, multicenter study.Gastroenterology. 2001; 120: A55Abstract Google Scholar], are even more ahead on the course. Adding AMA to combination regimens with standard IFNs is probably unsuccessful in naı̈ves. In fact, an interim analysis at 26 weeks of induction therapy with daily, high-dose IFN-α-2a in combination with ribavirin and AMA in 168 naı̈ves has not shown any increase of the response rate [31Engler S.H Stremmel W Kallinowski B.I Interferon alpha-2a induction therapy in combination with ribavirin and amantadine in naive patients with chronic HCV infection.J Hepatol. 2001; 34: S177Google Scholar]. The issue of three-drug combination regimens could be more promising in non-responders to IFN or to IFN plus ribavirin. Brillanti recently published [20Brillanti S Levantesi F Masi L Foli M Bolondi L Triple antiviral therapy as a new option for patients with interferon nonresponsive chronic hepatitis C.Hepatology. 2000; 3: 630-634Crossref Scopus (157) Google Scholar] a randomized controlled trial including 60 patients with chronic hepatitis C, non-responders to previous courses of IFN. Forty received IFN-α-2b at a dose of 5 MU on alternate days, ribavirin (800–1000 mg daily) and AMA (200 mg daily) for 12 months, and 20 had the same treatment without AMA. After 6 months of follow-up, 57 (23/40) and 10% (2/10) of patients treated with a triple or a double therapy had achieved SR. Conversely, Teuber and colleagues [32Teuber G Berg T Lafrenz M Weidenbach H Schoelmerich J Wietze-Braun P et al.Randomized, controlled trial with interferon-alpha combined with amantadine sulfate in primary IFN-alpha non-responsive patients with chronic hepatitis C.J Hepatol. 2001; 34: S23Google Scholar] have just reported negative results in a German multicentre study evaluating the efficacy of triple therapy vs. the IFN/ribavirin combination in 134 IFN non-responders. IFN was given as the induction at 5 MU daily for the first 4 weeks, followed by 5 MU t.i.w. for 20 weeks, and then 3 MU t.i.w. for 24 weeks. The SR rates were not significantly higher in patients receiving triple therapy than in those on IFN/ribavirin (23.4 vs. 17.1%). Other studies of triple therapy with or without IFN induction [33Berg T Naumann U Wiedenmann B Hopf U Pilot study of interferon-alpha high-dose induction therapy in combination with ribavirin plus amantadine for nonresponder patients with chronic hepatitis C.Z Gastroenterol. 2001; 39: 145-151Crossref PubMed Scopus (21) Google Scholar, 34Carlsson T Lindahl K Schvarcz R Wejstal R Uhnoo I Shev S et al.HCV RNA levels during therapy with amantadine in addition to interferon and ribavirin in chronic hepatitis C patients with previous nonresponse or response/relapse to interferon and ribavirin.J Viral Hepat. 2000; 7: 409-413Crossref PubMed Scopus (27) Google Scholar, 35Kulling U Porst H Wise M Herrmann A Sundermann U Oesen U et al.High daily dosing interferon alpha in monotherapy, double and triple therapy of hepatitis C non responders patients.J Hepatol. 2000; 32: S112Abstract Full Text PDF PubMed Google Scholar, 36Adinolfi L Marracino M Tonziello A Utili R Andreana A Giordano M et al.Interferon induction plus ribavirin and amantadine as a novel approach for treatment non responders chronic hepatitis C patients.Hepatology. 2000; 32: 352AAbstract Full Text Full Text PDF Scopus (59) Google Scholar] in smaller series of non-responders or relapsers to IFN monotherapy would suggest that adding AMA does not recover a significant amount of sustained responsiveness. It is unknown whether the slight advantage observed for AMA in viral clearance rates at 3 months in naı̈ves [27Caronia S Bassendine M.F Barry R Mills P Naoumov N.V Fox R et al.Interferon plus amantadine versus interferon alone in the treatment of naı̈ve patients with chronic hepatitis C: a UK multicentre study.J Hepatol. 2001; 35: 512-516Abstract Full Text Full Text PDF PubMed Scopus (30) Google Scholar, 28Tabone M Laudi C Delmastro B Biglino A Andreoni M Chieppa F et al.Interferon and amantadine in combination as initial treatment for chronic hepatitis C patients.J Hepatology. 2001; 35: 517-521Abstract Full Text Full Text PDF PubMed Scopus (34) Google Scholar] also exists in non-responders. Again, it is difficult to explain why these studies differ in their conclusions. Besides intrinsic differences in the schedules and in the selection of patients, it should be reminded that the definition of non-response to IFN monotherapy is not as clear-cut as that of response: 'partial responders' and breakthrough patients, who are intrinsically interferon sensitive, may have been included at different rates in these trials. Moreover, it would be relevant now to know if AMA helps to re-treat non-responders to IFN/ribavirin, who are likely to be much tougher clients. If pegylated IFNs (PEG) are going to be the future standard, we need information on their combination with AMA. Data on the early kinetics of response to PEG+AMA have just been provided for naı̈ve patients [37DiBisceglie A.M Bernstein D.E Rustgi V.R Gitlin N Jeffers L.J Simons D et al.Pegylated (40 kDa) interferon alfa-2a (Pegasys) in new combination therapies: a report of a randomized, multicenter efficacy and safety study.J Hepatol. 2001; 34: S143Google Scholar], for relapsers (Herrine et al., Digestive Disease Week, Atlanta, GA, 2001) and for non-responders (Afdahl et al., Digestive Disease Week, Atlanta, GA, 2001) to IFN/ribavirin. At 24 weeks, PEG+AMA had cleared HCV-RNA in 69% of naı̈ve, in 32% of relapsers and in 18% of non-responder patients, while PEG+RIBA had induced clearance in 69% of relapsers and 30% of non-responders. Triple therapy (PEG+RIBA+AMA) was apparently more effective, obtaining negativization of HCV-RNA in 81% of relapsers and 39% of non-responder patients. Thus, in proportion to the patient's sensitivity to IFN, AMA seems to enhance the effects of the combination of PEG and ribavirin, albeit being scarcely effective by itself. Finally, some more question marks remain. First of all, even if most randomized studies have essentially negative results in terms of SR, most show a non-significant trend favouring AMA. The study sample size may be inadequate to exclude a type β (false negative) error. Pooling of individual patient data among some of these trials is underway in order to perform a meta-analysis to conclusively solve this issue. All trials have used a fixed dose of AMA, which was seemingly derived from its use in neurology rather than from any evidence of antiviral activity. Dose-finding trials could be useful in exploring the possibility of underdosing, which theoretically could have affected the effectiveness of the drug in trials performed in populations with a higher mean body mass index. The HCV replicon model could also be helpful in sorting out in vitro the right amount of drug. The formulation of AMA used could be relevant: all studies reporting some positive results have used AMA hydrochloride, while the negative German trials were performed with AMA sulphate. Are the bioavailability, pharmacokinetic and pharmacodynamic properties of AMA hydrochloride and sulphate equivalent? And, on the same line, is the much less exploited RIMA equivalent to AMA? To sum up, this low-cost and highly tolerable drug has somehow defeated its initial promises of efficacy against HCV. Part of the disappointment may be due to the relatively high level of efficacy reached by the current combination schedule. Given the current shortage of promising alternatives, before giving up AMA, it would be wise to re-explore its clinical potential in combination with pegylated IFNs and ribavirin in non-responders, using cohorts of patients sufficiently large to analyze predictors of effectiveness. The search for better antiviral drugs is still on!