A single sample saliva test to determine acetylator phenotype

Clinical standards for the dosing and management of TB drugs

BACKGROUND: Optimal drug dosing is important to ensure adequate response to treatment, prevent development of drug resistance and reduce drug toxicity. The aim of these clinical standards is to provide guidance on 'best practice´ for dosing and management of TB drugs.METHODS: A panel of 57 global experts in the fields of microbiology, pharmacology and TB care were identified; 51 participated in a Delphi process. A 5-point Likert scale was used to score draft standards. The final document represents the broad consensus and was approved by all participants.RESULTS: Six clinical standards were defined: Standard 1, defining the most appropriate initial dose for TB treatment; Standard 2, identifying patients who may be at risk of sub-optimal drug exposure; Standard 3, identifying patients at risk of developing drug-related toxicity and how best to manage this risk; Standard 4, identifying patients who can benefit from therapeutic drug monitoring (TDM); Standard 5, highlighting education and counselling that should be provided to people initiating TB treatment; and Standard 6, providing essential education for healthcare professionals. In addition, consensus research priorities were identified.CONCLUSION: This is the first consensus-based Clinical Standards for the dosing and management of TB drugs to guide clinicians and programme managers in planning and implementation of locally appropriate measures for optimal person-centred treatment to improve patient care.

Isoniazid Therapeutic Drug Monitoring in Tunisian Patients With Tuberculosis

A regular therapeutic drug monitoring (TDM) of isoniazid could be useful to predict the acetylation profile and to prescribe doses associated with optimal efficacy and safety. We aimed to assess the usefulness of isoniazid TDM in the Tunisian population, to describe the acetylation profile distribution in this population, and to investigate the influence of certain parameters on acetylation phenotype. We performed a retrospective study including Tunisian patients with tuberculosis underwent an isoniazid TDM. Isoniazid concentrations were measured 3 hours after drug intake (C₃ ). Subsequent isoniazid doses were adjusted to maintain the C₃ within the recommended target (1-2 µg/mL). Patients were qualified as slow acetylators (SAs) or rapid acetylators (RAs) according to their acetylation index. Among the 255 patients, 58% were SAs and 42% were RAs. Of all patients, only 30.6% had a C₃ value within the target range. A dose adjustment has been performed for patients with C₃ outside the target range. C₃ was controlled in 77 patients. It became within the target range in 39 patients (50.6%). The median recommended isoniazid weight doses for SAs and RAs were 2.1 ± 0.7 mg/kg and 4.2 ± 1.4 mg/kg, respectively. The multivariate analysis showed that body weight, C_3, and C₃ /isoniazid dose were found to be significantly different between the 2 acetylation groups. In the pediatric group, only 9 had a C₃ value within the target range, and all of them were RAs. The irrevocable interest of isoniazid TDM has been shown in Tunisian patients with tuberculosis, in both adult and pediatric patients, as isoniazid demonstrates an unpredictable pharmacokinetic profile.

The Effect of pyrazinamide and rifampicin on isoniazid metabolism in rats

Hepatotoxicity is the main concern during tuberculosis chemotherapy with the first-line drugs isoniazid (INH), rifampicin (RMP) and pyrazinamide (PYR). Since these hepatotoxic events have been associated with INH metabolites, the study aimed to measure the area under curve (AUC) parameter for INH and its metabolites acetylisoniazid (AcINH), hydrazine (Hz) and acetylhydrazine (AcHz), when groups of rats were pre-treated for 21 days with INH alone or in combination with RMP and/or PYR, in the following amounts per kg body weight: INH 100 mg; INH 100 mg + RMP 100 mg; INH 100 mg + PYR 350 mg; INH 100 mg + PYR 350 mg + RMP 100 mg. It was found that co-administration of RMP, PYR and RMP + PYR caused a significant decrease in the AUC for INH. Co-administration of PYR was the only treatment that caused a significant increase in the AUC for Hz and a decrease in the AUC for its acetylated product AcHz. The AUC for AcINH was not significantly altered in any experimental group. In conclusion, the increased metabolism of INH in all the drug combinations and the significantly higher production of Hz in the group INH + PYR might be linked with exacerbated hepatotoxic effects of these drug associations.

The effects of acute ethanol intake on isoniazid pharmacokinetics

AIM

To assess effects of acute ethanol intake on the pharmacokinetics of isoniazid in healthy male volunteers.

METHODS

Sixteen healthy male, drug-free subjects were studied. Each received in the fasting state, on two occasions separated by at least 1 week, isoniazid (200 mg orally). On one occasion (assigned randomly), subjects received ethanol 0.73 g/kg, 1 h before isoniazid, followed by 0.11 g/kg ethanol orally every hour thereafter for 7 h. Plasma isoniazid and acetylisoniazid concentrations were measured by means of high-performance liquid chromatography. Blood ethanol concentrations were measured hourly by breath analysis. Plasma concentrations of isoniazid and acetylisoniazid were analysed using TOPFIT software.

RESULTS

Peak concentrations of isoniazid were reached within 90 min, in both the ethanol-treated and control groups. The ethanol dosage regimen used resulted in peak blood ethanol concentrations between 78 mg/l and 103 mg/l. There was no significant difference in area under the curve, half-life of elimination or the ratio of acetylisoniazid to isoniazid (AcINH/INH) in the sample withdrawn 3 h after isoniazid dose. Acetylator phenotype for patients was the same in both phases, whether assessed by half-life of isoniazid or the AcINH/INH ratio at 3 h.

CONCLUSIONS

Acute ethanol intake at this dose is unlikely to affect results of acetylation studies in which isoniazid is used as a substrate, whether the half-life of isoniazid or the AcINH /INH ratio at 3 h is used to phenotype patients.