Previous studies have shown controversial results on whether acetylator status causes
isoniazid-induced hepatotoxicity (IIH). Moreover, the contribution of CYP2E1, a hepatic
enzyme implicated in the formation of hepatotoxins, to the risk of developing IIH
remains unclear. The objectives of this study were (i) to assess the quantitative
relationship between the level of isoniazid serum concentration and the incidence
of IIH and (ii) to evaluate the extent of implication of the N-acetyltransferase-2
(NAT2) and CYP2E1 polymorphisms genes to induce this disorder. Seventy-one patients
with tuberculosis receiving a conventional antituberculosis regimen were included.
NAT2 and CYP2E1 genotypes were determined using polymerase chain reaction. Three restriction
enzymes, RsaI, PstI and DraI were used to detect CYP2E1 RFLP and four different restriction
enzymes, KpnI, TaqI, BamHI and Ddel were used to determine NAT2 acetylator status.
Therapeutic drug monitoring (TDM) of isoniazid (serum concentration performed 3 h
after the morning dose: C3) was performed. Cases of isoniazid-induced hepatotoxicity
were diagnosed according to Benichou et al. Receiver Operating Characteristics curve
analysis was used to evaluate the relationship between risk factors and the incidence
of IIH. Eleven (15.4%) patients have developed IIH. Demographic factors, including
age, weight and gender were not associated with the incidence of hepatotoxicity. High
serum concentration of isoniazid (C3) was found to be a risk factor of IIH (area under
the curve: 0.74, P=0.007, 95% confidence interval (95% CI): 0.56-0.93), with a cutoff
value at 3.69 mg l-1 (odds ratio (OR): 13.2, P=0.0007, 95% CI: 2.9-59). Multivariate
analysis showed that only a C3 over 3.69 mg l-1 remains a risk factor of IIH. NAT2
and CYP2E1 variants were not found to increase the risk of IIH when analyzed separately.
However, combined analysis of the NAT2/CYP2E1 gene polymorphisms showed that patients
with both DraI C/D and slow acetylator have an increased risk of IIH compared with
other combined NAT2/CYP2E1 genotype profiles (OR: 8.41, P=0.01, 95% CI: 1.54-45.76).
Our results suggest that a serum concentration of isoniazid over 3.69 mg l-1 and a
combined genotype CYP2E1 DraI(C/D)/slow acetylator are major risk factors for IIH.
Therefore, TDM of isoniazid and the determination of both NAT2 and CYP2E1 genotypes
could be useful for the prediction and prevention of IIH in Tunisian tuberculosis
patients.