Saliva and plasma concentrations of isoniazid and acetylisoniazid in man

Genetic Variants and Drug Efficacy in Tuberculosis: A Step toward Personalized Therapy

Tuberculosis (TB) continues to be a major infectious disease affecting individuals worldwide. Current TB treatment strategy recommends the standard short-course chemotherapy regimen containing first-line drug, i.e., isoniazid, rifampicin, pyrazinamide, and ethambutol to treat patients suffering from drug-susceptible TB. Although Mycobacterium tuberculosis, the causing agent, is susceptible to drugs, some patients do not respond to the treatment or treatment may result in serious adverse reactions. Many studies revealed that anti-TB drug-related toxicity is associated with genetic variations, and these variations may also influence attaining maximum drug concentration. Thus, inter-individual diversities play a characteristic role by influencing the genes involved in drug metabolism pathways. The development of pharmacogenomics could bring a revolution in the field of treatment, and the understanding of germline variants may give rise to optimized targeted treatments and refine the response to standard therapy. In this review, we briefly introduced the field of pharmacogenomics with the evolution in genetics and discussed the pharmacogenetic impact of genetic variations on genes involved in the activities, such as anti-TB drug transportation, metabolism, and gene regulation.

PBPK Analysis to Study the Impact of Genetic Polymorphism of NAT2 on Drug-Drug Interaction Potential of Isoniazid

PURPOSE

Isoniazid (INH) is prescribed both for the prophylaxis as well as the treatment of tuberculosis. It is primarily metabolized through acetylation by a highly polymorphic enzyme, N-acetyl transferase 2 (NAT2), owing to which significant variable systemic drug levels have been reported among slow and rapid acetylators. Furthermore, many drugs, like phenytoin, diazepam, triazolam, etc., are known to show toxic manifestation when co-administered with INH and it happens prominently among slow acetylators. Additionally, it is revealed in in vitro inhibition studies that INH carries noteworthy potential to inhibit CYP2C19 and CYP3A4 enzymes. However, CYP inhibitory effect of INH gets masked by opposite enzyme-inducing effect of rifampicin, when used in combination. Thus, distinct objective of this study was to fill the knowledge gaps related to gene-drug-drug interactions (DDI) potential of INH when given alone for prophylactic purpose.

METHODS

Whole body-PBPK models of INH were developed and verified for both slow and fast acetylators. The same were then utilized to carry out prospective DDI studies with CYP2C19 and CYP3A4 substrates in both acetylator types.

RESULTS

The results highlighted likelihood of significant higher blood levels of CYP2C19 and CYP3A4 substrate drugs in subjects receiving INH pre-treatment. It was also re-established that interaction was more likely in slow acetylators, as compared to rapid acetylators.

CONCLUSION

The novel outcome of the present study is the indication that prescribers should give careful consideration while advising CYP2C19 and CYP3A4 substrate drugs to subjects who are on prophylaxis INH therapy, and are slow to metabolic acetylation.

A Systematic Review and Meta-analysis of Isoniazid Pharmacokinetics in Healthy Volunteers and Patients with Tuberculosis

PURPOSE

This systematic review and meta-analysis assesses the pharmacokinetic (PK) summary estimates of isoniazid (INH) between healthy volunteers and patients with tuberculosis (TB), evaluates whether the current INH dose regimen is appropriate in patients with TB, and evaluates the impact of N-acetyl-transferase-2 (NAT2) status on the PK properties of INH.

METHODS

A systematic approach was conducted to find studies with relevant INH PK data published in the English language up to February 2018. The PK properties of INH were extracted with their respective INH dosages and were dose normalized to allow a fair comparison between healthy volunteers and patients with TB. Meta-analysis was then performed for the C_max and AUC estimates for all INH dosages.

FINDINGS

Ninety studies were included in this systematic review. TB status significantly affected the INH C_max and AUC estimates. In healthy volunteers, the dose-normalized INH C_max and AUC were statistically higher than those of patients with TB. No significant differences were found in dose-normalized C_max and AUC between adults with TB and adults with TB/HIV; however, the AUC in pediatric patients was significantly different between patients with TB and patients with TB/HIV. In addition, no significance was observed comparing the dose-normalized C_max and AUC of pediatric patients with TB and TB/HIV with their respective adult counterparts. Dose-normalized INH C_max and AUC in patients with fast and intermediate NAT2 were significantly lower than in patients with slow NAT2.

IMPLICATIONS

The current recommended dosages of INH were found to produce less drug exposure in patients with TB when compared with healthy volunteers. NAT2 polymorphism greatly impacts the PK properties of INH; hence, testing for acetylator status is highly recommended, and therapeutic drug monitoring would help reduce INH toxicity.

Systematic Review of Salivary Versus Blood Concentrations of Antituberculosis Drugs and Their Potential for Salivary Therapeutic Drug Monitoring

BACKGROUND

Therapeutic drug monitoring is useful in the treatment of tuberculosis to assure adequate exposure, minimize antibiotic resistance, and reduce toxicity. Salivary therapeutic drug monitoring could reduce the risks, burden, and costs of blood-based therapeutic drug monitoring. This systematic review compared human pharmacokinetics of antituberculosis drugs in saliva and blood to determine if salivary therapeutic drug monitoring could be a promising alternative.

METHODS

On December 2, 2016, PubMed and the Institute for Scientific Information Web of Knowledge were searched for pharmacokinetic studies reporting human salivary and blood concentrations of antituberculosis drugs. Data on study population, study design, analytical method, salivary Cmax, salivary area under the time-concentration curve, plasma/serum Cmax, plasma/serum area under the time-concentration curve, and saliva-plasma or saliva-serum ratio were extracted. All included articles were assessed for risk of bias.

RESULTS

In total, 42 studies were included in this systematic review. For the majority of antituberculosis drugs, including the first-line drugs ethambutol and pyrazinamide, no pharmacokinetic studies in saliva were found. For amikacin, pharmacokinetic studies without saliva-plasma or saliva-serum ratios were found.

CONCLUSIONS

For gatifloxacin and linezolid, salivary therapeutic drug monitoring is likely possible due to a narrow range of saliva-plasma and saliva-serum ratios. For isoniazid, rifampicin, moxifloxacin, ofloxacin, and clarithromycin, salivary therapeutic drug monitoring might be possible; however, a large variability in saliva-plasma and saliva-serum ratios was observed. Unfortunately, salivary therapeutic drug monitoring is probably not possible for doripenem and amoxicillin/clavulanate, as a result of very low salivary drug concentrations.

Isoniazid metabolism and hepatotoxicity

Isoniazid (INH) is highly effective for the management of tuberculosis. However, it can cause liver injury and even liver failure. INH metabolism has been thought to be associated with INH-induced liver injury. This review summarized the metabolic pathways of INH and discussed their associations with INH-induced liver injury.

pH-Responsive Isoniazid-Loaded Nanoparticles Markedly Improve Tuberculosis Treatment in Mice

Tuberculosis is a major global health problem for which improved therapeutics are needed to shorten the course of treatment and combat emergence of drug resistance. Mycobacterium tuberculosis, the etiologic agent of tuberculosis, is an intracellular pathogen of mononuclear phagocytes. As such, it is an ideal pathogen for nanotherapeutics because macrophages avidly ingest nanoparticles even without specific targeting molecules. Hence, a nanoparticle drug delivery system has the potential to target and deliver high concentrations of drug directly into M. tuberculosis-infected cells-greatly enhancing efficacy while avoiding off-target toxicities. Stimulus-responsive mesoporous silica nanoparticles of two different sizes, 100 and 50 nm, are developed as carriers for the major anti-tuberculosis drug isoniazid in a prodrug configuration. The drug is captured by the aldehyde-functionalized nanoparticle via hydrazone bond formation and coated with poly(ethylene imine)-poly(ethylene glycol) (PEI-PEG). The drug is released from the nanoparticles in response to acidic pH at levels that naturally occur within acidified endolysosomes. It is demonstrated that isoniazid-loaded PEI-PEG-coated nanoparticles are avidly ingested by M. tuberculosis-infected human macrophages and kill the intracellular bacteria in a dose-dependent manner. It is further demonstrated in a mouse model of pulmonary tuberculosis that the nanoparticles are well tolerated and much more efficacious than an equivalent amount of free drug.

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.

A single sample saliva test to determine acetylator phenotype

A comparison was made between the results of acetylator phenotyping by determination of the acetylisoniazid to isoniazid (AcINH/INH) concentration ratio in plasma and in saliva 3 h after oral administration of isoniazid (200mg). In the 154 subjects studied, 68 (44%) were fast acetylators (AcINH/INH ratio > 1.5) using the plasma ratio. In all subjects the saliva AcINH/INH ratio was also > 1.5. Eighty-five of the eighty-six remaining subjects had saliva and plasma AcINH/INH ratios < 1.5 in the 3 h sample. Thus, with one exception there was complete agreement between the acetylator status determined by measurement of saliva or plasma AcINH/INH ratio in a single 3 h sample. Saliva measurement may provide a simple non-invasive alternative to plasma collection in assessing acetylator status.

Clinical pharmacokinetics of antibiotics in patients with impaired renal function

Many antibiotics are eliminated renally and dosage adjustments are commonly made in patients with renal insufficiency. This is a critical review of antibiotic pharmacokinetics in patients with various degrees of renal function. Detailed information regarding pharmacokinetic alterations with specific antibiotics or antibiotic classes has been compiled and tabulated. From pharmacokinetic evidence, recommendations for dosage adjustments of antibiotics are supplied. The criteria used for assigning rating levels to specific pharmacokinetic articles as well as the grading system for dosage adjustments are outlined. In addition, a basic review of pharmacokinetic alterations in renal failure and factors affecting the removal of drugs by haemodialysis is included.

Salivary levels of isoniazid and rifampicin in tuberculous patients

Concentrations of isoniazid and rifampicin were determined in time-matched samples of saliva and serum from 30 tuberculous patients (18 with pulmonary tuberculosis and 12 with intestinal tuberculosis), comprising 18 slow and 12 rapid acetylators of isoniazid, following administration of isoniazid 300 mg and rifampicin 12 mg/kg. The diffusion of isoniazid into saliva was quite rapid and the salivary concentrations were similar to those in serum, suggesting that saliva could be used in place of serum for all pharmacokinetic studies with isoniazid. The salivary concentrations of rifampicin were much lower than those in serum, the mean peak concentrations being 0.9 and 8.5 microgram/ml, respectively. Further, there was evidence of a significant delay in the diffusion of rifampicin from serum to saliva.

Drug acetylation in breast cancer

The acetylator phenotype was determined in 100 patients with breast cancer and 100 control female subjects using isoniazid. The proportion of fast acetylators in the breast cancer patients (43%) was not significantly different from the control group (43%). We conclude that acetylator phenotype is unlikely to be an important determinant of the risk of developing breast cancer.