AIM: To further evaluate the relationship between BSA and the effects of lamivudine in a greater number of cases and over a longer period of observation than in our previous evaluation.

METHODS: We evaluated 249 patients with chronic hepatitis B. The effects of treatment for one year (n = 249), two years (n = 147), and three years (n = 72) were evaluated from the levels of serum ALT and HBV-DNA, as biological and virological effects (undetectable levels by PCR), respectively. Moreover, several variables that could influence the response to treatment, including ALT, albumin, bilirubin, platelet counts, BSA, HBV-DNA, and HBeAg were analyzed.

RESULTS: For 1-year treatment, multivariate analysis revealed that BSA (P = 0.0002) was the only factor for the biological effect, and that ALT (P = 0.0017), HBV-DNA (P = 0.0004), and HBeAg (P = 0.0021) were independent factors for the virological effect. For 2-year treatment, multivariate analysis again showed that BSA (P = 0.0147) was the only factor for the biological effect, and that ALT (P = 0.0192) and HBeAg (P = 0.0428) were independent factors for the virological effect. For 3-year treatment, multivariate analysis, however, could not reveal BSA (P = 0.0730) as a factor for the normalization of ALT levels.

CONCLUSION: BSA is a significant predictor for the normalizing the effect of lamivudine therapy on ALT for an initial 2-year period, suggesting that lamivudine dosage should be based on the individual BSA.

Chronic hepatitis B is an important cause of morbidity and mortality resulting from cirrhosis-related liver failure and hepatocellular carcinoma (HCC)[1-3]. Lamivudine is an oral nucleoside analog approved for the treatment of chronic hepatitis B. It inhibits viral DNA replication by means of chain termination, and competitively inhibits viral polymerase. A daily dosage of lamivudine of 100 mg has been accepted worldwide for the treatment for chronic hepatitis B, since early studies showed that there was no significant difference in the effect of lamivudine at doses of 100 and 300 mg[4,5]. However, to establish ideal dosages in those studies, efficacy was mainly evaluated by measuring hepatitis B virus (HBV)-DNA, and the assay used was much less sensitive than the polymerase chain reaction (PCR) assay. Studies in which HBV-DNA was measured by PCR assay reported an additional viral suppressive activity with high doses (300 mg) of lamivudine for 24 wk[6]. In addition to the limits imposed by the assay methods that were used, the observation periods in the studies on lamivudine doses of 100-300 mg were limited to a period of 12[4] or 24 wk[5]. Although the effect of doses greater than 100 mg on the emergence of YMDD mutants has not been evaluated, baseline body mass index has been reported to be significantly related to the emergence of HBV mutants during lamivudine treatment in patients co-infected with HBV and human immunodeficiency virus-1 (HIV-1)[7]. In a previous study of 134 patients treated for 23.1 mo(mean observation period), body surface area (BSA) was shown to be an independent factor contributing to the effects of lamivudine treatment[8]. In the present study, to further confirm these results, we evaluated the relationship between BSA and the effects of lamivudine effects in a greater number of patients and for longer observation periods than those in the previous report.

The effects of lamivudine for 1 year were analyzed in a total of 249 patients (Table 1), of which 150 (60.2%) were identified as SR-ALT and 99 (39.8%) as NR-ALT, and 183 (73.5%) were identified as SR-DNA and 66 (26.5%) as NR-ALT (Table 1). To evaluate the contribution of the variables to the effect of treatment, univariate and multivariate logistic analyses were performed. In the univariate logistic analysis, BSA and ALT in the biological evaluation, and ALT, albumin, bilirubin, platelet count, BSA, HBV-DNA, and HBeAg in the virological evaluation, had χ² values of more than 1.0 (Table 2). Therefore, we used these factors as variables for multivariate logistic analysis. The results of multivariate analysis revealed that BSA was the only significant factor for the improvement of ALT levels (χ² = 14.3, P = 0.0002), and ALT, albumin, HBV-DNA and HBeAg were independent factors for the disappearance of serum HBV-DNA (ALT: χ² = 9.8, P = 0.0017; albumin: χ² = 5.1, P = 0.0238; HBV-DNA: χ² = 12.6, P = 0.0004; and HBeAg: χ² = 9.5, P = 0.0021) (Table 3).

The effects of 2-year therapy were evaluated in 147 patients (Table 4). Of these patients, 75 (51.0%) were identified as SR-ALT and 72 (49.0%) as NR-ALT, while 85 (57.8%) were identified as SR-DNA and 62 (42.2%) as NR-ALT (Table 5). In the univariate logistic analysis, bilirubin, platelet count and BSA in the biological evaluation, and ALT, bilirubin, platelet, BSA and HBeAg in the virological evaluation, were selected (χ²>1.0) (Table 5). Multivariate analysis revealed that BSA was the only significant factor in the biological effects (χ² = 5.6, P = 0.0147), and ALT and HBeAg were independent factors in the virological effects (ALT: χ² = 5.5, P = 0.0192; and HBeAg: χ² = 4.1, P = 0.0428) (Table 6).

Finally, the effects of 3-year therapy were evaluated in 72 patients (Table 7). Of these patients, 33 (45.8%) were identified as SR-ALT and 39 (54.2%) as NR-ALT, while 38 (52.8%) were identified as SR-DNA and 34 (47.2%) as NR-DNA (Table 8). In the univariate logistic analysis, albumin, platelet count, BSA, and HBeAg in the biological evaluation, and no variables in the virological evaluation, were selected (χ²>1.0) (Table 8). Multivariate analysis did not reveal BSA as a factor for predicting the biological efficacy of lamivudine therapy χ² = 3.2, P = 0.0730) (Table 9).

In this present study, we found that BSA was a significant factor that could contribute to the normalization of serum ALT (biological response) after the treatment with lamivudine for an initial 2-year period. Body weight was also a significant factor contributing to the effects of lamivudine treatment (data not shown). Because χ² values of BSA were higher than those of body weight and BSA is determined with body weight and height, we used BSA as a variable for statistical analysis. We initially reported that BSA was an independent factor contributing to both the biological and virological responses[8]. The difference in the contribution to the virological response between the present and the previous study might be attributed to the differences in the criteria used to evaluate treatment effects. In our previous study, we used a third category in addition to SR and NR transient responder (TR) which included patients with serum ALT levels that initially decreased to less than 30 U/L but increased to more than 30 U/L during the subsequent observation period (TR-ALT), and the patients in whom serum HBV-DNA initially decreased to undetectable levels (<2.6 log copies/mL) but became positive again during the subsequent observation period (TR-DNA). Regardless of the differences in evaluation criteria, both studies clearly demonstrated that BSA independently contributed to the normalization of ALT in the patients treated with lamivudine for an initial 2-year period. Because the pharmacokinetics of lamivudine correlate with body weight, as is the case with many other drugs[9], it is reasonable to conclude that patients with lower BSA would have achieved higher blood concentrations of lamivudine, although we did not actually monitor the concentration of lamivudine. Recent reports suggest that the baseline body mass index is significantly related to the emergence of HBV mutation during lamivudine treatment (300 mg/d, >6 mo) in patients co-infected with HBV and HIV-1[7]. Therefore, the results of our studies again question whether a lamivudine dosage of 100 mg/d is adequate, particularly for long-term treatment.

The standard lamivudine dose of 100 mg daily was based on early studies in which doses of 25, 100, and 300 mg were compared for 12[4] or 24 wk[5]. Because there were no significant differences reported in the rates of non-detection of HBV-DNA and normalization of ALT levels between the 100 and 300 mg doses, the dose of 100 mg has become a well-accepted therapeutic standard[4,5]. However, several factors should be considered when evaluating the results of these studies, including the number of patients, duration of treatment, emergence of lamivudine-resistant mutants over long-term treatment, and detection limits for HBV-DNA.

In the present study, we found that there was a significant difference in the contribution of BSA to the biological effect, although the differences in the mean values of BSA between SR-ALT and NR-ALT were relatively small. Therefore, it is possible that previous studies failed to detect a significant contribution of BSA to the effects of lamivudine because of the smaller number of patients examined. The major drawback of lamivudine monotherapy is the emergence of resistant HBV with mutations of the tyrosine-methionine-aspartate-aspartate (YMDD) motif. The incidence of these mutants rises from 15-20% in the first year of therapy to 40% by the second year, and to 67% by the fourth year[10]. In some cases, fatal liver failure subsequent to the emergence of the mutant was reported[11]. Therefore, observation periods of 24 wk may not be adequate for detecting the emergence of lamivudine-resistant mutants. In our evaluation of HBV-DNA, the rates of NR-DNA were found to be 26.5%, 42.2%, and 57.2% in patients who were positive for HBV-DNA (>2.6 log copies/mL) by the first, second, and third year, respectively. Although we did not confirm YMDD mutation in all cases of NR-DNA, the increase in NR-DNA ratio might be attributable to the emergence of mutants. Concomitant with the increases in HBV-DNA seen over the 3-year period, the NR-ALT ratio rose from 39.8% in the first year to 49.0% by the second year and to 54.8% by the third year in the present study, suggesting that the emergence of mutants could abolish the contribution of BSA to biological effects in the third year. Further studies will be needed to confirm whether BSA affects the incidence of YMDD mutants.

In previous studies that showed no difference in the effects of 100 and 300 mg lamivudine on HBV-DNA levels (as aforementioned)[4,5], HBV-DNA was measured quantitatively by liquid hybridization assay (Abbott Laboratories), which has a detection limit of 10⁷ geq/mL[12]. Honkoop et al[6] studied the efficacy of 100 and 300 mg lamivudine in viral suppression for 24 wk using a semi-quantitative PCR method with a detection limit of 10²-10³ geq/mL. In the present study, we used a Roche Monitor kit, which has detection limit of 2.6 log copies/mL, and could not find a significant relationship between BSA and the virological effect of lamivudine. Chun et al[13], reported that there was no significant correlation between viral replication and liver damage in chronic hepatitis B. Hence, it seems reasonable that we did not find a contribution of BSA to the virological effects of treatment. Further study will be needed to evaluate dose-dependent lamivudine effects on viral suppression including the emergence of mutants which could directly affect the viral load.

In conclusion, we have shown that BSA is a statistically significant and potentially important factor for predicting the efficacy of lamivudine therapy for chronic hepatitis B. A noteworthy finding in our study was that small differences in BSA might significantly influence the effect of lamivudine treatment, suggesting that a small increase in lamivudine dose might markedly increase its therapeutic efficacy. We believe that a long-term clinical trial with higher-dose lamivudine treatment in a large number of cases is warranted, since lamivudine will continue to be a first-line treatment for HBV.