Naïve-pooled pharmacokinetic analysis of pyrazinamide, isoniazid and rifampicin in plasma and cerebrospinal fluid of Vietnamese children with tuberculous meningitis

BACKGROUND

Among the various forms of TB, tuberculous meningitis (TBM) is the most severe, with about 30% mortality and 50% of survivors left with neurological sequelae. Children suffer more frequently from TBM than adults and outcomes are often poor due to difficulties in making the diagnosis and uncertainty regarding the best anti-tuberculosis drug regimen. The aim of this prospective study was to describe the pharmacokinetics of pyrazinamide, isoniazid and rifampicin in plasma and cerebrospinal fluid of children with tuberculous meningitis treated with the standard TBM regimen.

METHODS

We performed a prospective observational study of 100 consecutively treated children (≤ 15 years of age) with tuberculous meningitis in Ho Chi Minh City, Vietnam. Children were treated according to the 2006 WHO recommended pediatric treatment regimen consisting of isoniazid (5 mg/kg), rifampicin (10 mg/kg) and ethambutol (15 mg/kg) for 8 months, with the addition of pyrazinamide (25 mg/kg) for the first 3 months and streptomycin (15 mg/kg) for the first 2 months. Pyrazinamide, isoniazid and rifampicin concentrations were measured in plasma at day 14 and in cerebrospinal fluid (CSF) at 1 month by HPLC-UV. A naïve-pooled non-compartmental data analysis was used to describe the pharmacokinetic properties of drugs in the two-age groups of children ≤ 4 years or > 4 years of age.

RESULTS

Younger children, when compared to older children, presented a higher body weight-normalized clearance and volume of distribution, and lower median total plasma exposures for the three studied drugs with -14%, -22% and -16% for Pyrazinamide, Isoniazid and Rifampicin, respectively. In CSF, individual concentrations of isoniazid and pyrazinamide were comparable to that in plasma in both age groups; but rifampicin concentrations were lower than the minimum inhibitory concentration of susceptible bacteria in all but two children.

CONCLUSIONS

There is an age-dependent variation in the plasma and cerebrospinal fluid pharmacokinetics of rifampicin, isoniazid and pyrazinamide. The safety and efficacy of higher doses of rifampicin should be investigated for the treatment of childhood tuberculous meningitis.

Effect of Isoniazid on the Pharmacodynamics of Cefazolin-Induced Seizures in Rats

Both isoniazid (INH) and cefazolin (CEZ) can have serious adverse effects on the central nervous system (CNS), causing seizures. In this study, we investigated the effect of INH on the pharmacodynamics of CEZ-induced seizures in rats. Male Wistar rats pretreated with INH (150 mg/kg i.p.) or saline received an intravenous infusion of CEZ at 3.2 g/h/rat until the onset of seizures, then samples of cerebrospinal fluid (CSF), blood (for serum), and brain were obtained immediately. The administration of INH was associated with a reduction in the total dose of CEZ required to produce seizures. The concentrations of CEZ in serum, brain, and CSF in INH-treated rats at the onset of seizures were significantly lower than those in control rats. In rats coadministered with pyridoxine (150 mg/kg s.c.), the concentration of CEZ in CSF at the onset of seizures was significantly higher than that in rats administered INH only. These results suggest that INH potentiates the sensitivity of the CNS to CEZ-induced seizures, and that the increased sensitivity is associated with the inhibition of vitamin B(6) metabolism by INH.

Therapeutic monitoring of antituberculosis drugs by direct in-line extraction on a high-performance liquid chromatography system

A direct in-line pre-column extraction technique in which guanidinium and ammonium sulfate are used, followed by column switching, was employed to analyze serum, plasma and cerebrospinal fluid samples of patients treated for tuberculous meningitis. Resolution of a wide range of polar to non-polar xenobiotics was obtained on a C8 silica column by using a linear gradient from a binary system consisting of solvent A (0.05 M KH2PO4) and solvent B (acetonitrile-isopropanol, 4:1, v/v). Apart from the antituberculosis drugs (isoniazid, pyrazinamide, ethionamide and rifampicin) the patients received up to sixteen different medicines for prevention of complications and the treatment of symptoms. Qualitative resolution of all the drugs was obtained by the chromatographic system. Quantitation of pyrazinamide and ethionamide was achieved with high precision and low inter-sample variation.

Cerebrospinal fluid drug concentrations and the treatment of tuberculous meningitis

Tuberculous meningitis is a very serious form of tuberculosis. In the absence of randomized controlled trials of alternative treatment regimens, its management depends on employing potent drugs that penetrate well into the cerebrospinal fluid (CSF). The penetration of isoniazid, rifampin, and streptomycin into the CSF of 27 Chinese patients was studied using fluorimetric and microbiologic procedures. Isoniazid rapidly diffused into the CSF, peak concentrations in excess of 3 mg/L, or over 30 times its minimal inhibitory concentration (MIC) against Mycobacterium tuberculosis being attained within 4 hr. In contrast, rifampin and streptomycin penetrated very slowly across the meninges, and CSF levels only slightly in excess of their MICs against M. tuberculosis were achieved. The penetration of the drugs into the CSF correlated poorly with differences in their partitioning between octanol/water and cyclohexane/water but could be predicted using a simple model based on their renal clearance rates and plasma protein binding. It is recommended that patients with tuberculous meningitis should be treated for at least 9 months with a combination of isoniazid, rifampin, and pyrazinamide, which may be supplemented in the first 2 mo with streptomycin.

Cerebrospinal fluid isoniazid concentrations in children with tuberculous meningitis: the influence of dosage and acetylation status

Cerebrospinal fluid (CSF) and plasma isoniazid (INH) concentrations were determined on 96 occasions in 38 children (median age 1.5 years) with tuberculous meningitis, and the effects of INH elimination status and test dosages of 10 mg/kg body weight and 20 mg/kg body weight was studied. Maximum cerebrospinal fluid INH concentrations were reached during the period 2 to 4 hours after dosing and cerebrospinal fluid and plasma INH concentrations did not differ significantly during this period. Cerebrospinal fluid INH concentrations following a dosage of 10 mg/kg (4.6 +/- 2.4 micrograms/mL) were, however, significantly lower than those following a dosage of 20 mg/kg (11.6 +/- 2.7 micrograms/mL). Cerebrospinal fluid INH concentrations in faster acetylators at a dosage of 10 mg/kg (3.2 +/- 1.1 micrograms/mL) were significantly lower than in slower acetylators (7.7 +/- 1.3 micrograms/mL), as was the case with a dosage of 20 mg/kg, where faster acetylators had cerebrospinal fluid INH concentrations of 10.5 +/- 2.5 micrograms/mL compared with 14.1 +/- 1.4 microgram/mL in slower acetylators. Following dosages of both 10 mg/kg and 20 mg/kg, INH concentrations in excess of the minimal inhibitory concentration for Mycobacterium tuberculosis persisted in the CSF 12 to 14 hours later. Despite the patients' being young and frequently malnourished, suffering from advanced forms of tuberculous meningitis, and receiving high dosages of INH, rifampicin, and pyrazinamide, none developed any clinical signs of hepatotoxicity and in only one child did the serum bilirubin level rise to 19 micrograms/mL.

Simultaneous assay for isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid in the rabbit

A simple procedure for the simultaneous determination of isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid in the rabbit is described. The assay involves organic extraction before and after derivatization of the two compounds and the internal standard, phenelzine. The extract of the derivatized compounds was evaporated to dryness at 40 degrees C and the residue redissolved in the mobile phase (50 microliters). A 25-microliters aliquot was injected into the liquid chromatograph and eluted with acetonitrile-water-triethylamine (70:30:0.4, v/v) containing 5 mM heptanesulphonic acid on a 30-microns C8 precolumn linked to a 10-microns C18 microBondapak column at ambient temperature (25 +/- 1 degree C). The eluate was detected by ultraviolet detection at 320 nm.

The pharmacokinetics of isoniazid and hydrazine metabolite in plasma and cerebrospinal fluid of rabbits

The pharmacokinetics of isoniazid (INH) and hydrazine metabolite (HYD) in plasma and cerebrospinal fluid (CSF) of ten rabbits was studied after separate intravenous (i.v.) and oral (p.o.) administration in a crossover study. The concentrations of INH and HYD in the biological fluids were determined by high performance liquid chromatography (HPLC). There was no difference in the area under plasma concentration-time curves, indicating that oral absorption was complete. The mean apparent volume of distribution after i.v. (3.02 +/- 0.55 L) was smaller (p less than 0.01) than that after p.o. (4.29 +/- 1.25 L) dosing. The elimination t1/2 of INH in CSF was longer (p less than 0.005) than that in plasma after either route of administration. There was no significant barrier to the penetration of INH into the CSF from the general circulation. The HYD plasma concentrations were similar after either route. HYD was eliminated at a slower rate (Ke = 0.17 h-1) than INH (Ke = 0.59 h-1). There was prolonged exposure of the body to HYD (greater than 6 h - above 0.1 micrograms/ml).

Kinetics of isoniazid transfer into cerebrospinal fluid in patients with tuberculous meningitis

For the pharmacokinetic analysis of isoniazid transfer into CSF, steady-state isoniazid concentrations of plasma and CSF were measured in eleven tuberculous meningitis patients confirmed with findings of CSF and neuroimazing. Peak plasma levels (4.17-21.5 micrograms/mL) were achieved at 0.25 to 3 hours after multiple isoniazid dose (600 mg/day). Terminal half-life, total clearance (CI/F) and volume of distribution (Vd/F) were 1.42 +/- 0.41 hr, 0.47 +/- 0.22 L/kg/hr and 0.93 +/- 0.48 L/kg, respectively. Isoniazid concentrations in CSF collected intermittently were highest at 3 hr (Mean, 4.18 micrograms/mL) and were 0.54 +/- 0.21 micrograms/mL at 12 hrs after the last dose of isoniazid 10 mg/kg/day. CSF/plasma partitioning of isoniazid and equilibration rate were estimated using modified pharmacokinetic/pharmacodynamic model. Disposition rate constant from CSF to plasma and CSF/plasma partitioning ratio of isoniazid were estimated to be 0.39 h-1 and 1.17, respectively.

Isoniazid therapy in Parkinson's disease

The effect of isoniazid on levodopa-induced dyskinesias has been evaluated in 20 patients with Parkinson's disease, following a serendipitous observation that choreic dyskinesias induced by levodopa in one parkinsonian patient were markedly reduced during treatment with isoniazid for tuberculous infection. A mean average isoniazid dose of 290 mg was given without any change in current antiparkinsonian treatment. "Benefit of dose" choreic dyskinesias were markedly reduced in 18 patients within the first few weeks of treatment. This effect was accompanied by an intolerable worsening of parkinsonian signs. All patients returned to their basal situation after isoniazid interferes with the therapeutic action of levodopa and dopamine agonists. The precise mechanism by which this action occurred is not known, but several possible explanations are discussed.

[Isoniazid therapy and monitoring plasma levels]

Plasma levels of isoniazid (INH) have been monitored in fifteen children, aged 1 to 13 years, who were under chronic therapy with INH plus rifampin for tuberculosis. The pharmacokinetic parameters of children were not significantly different from those found in adults by other authors. It is necessary to check two plasma concentrations at the 3rd h. versus different doses (5 mg/kg and 10 mg/kg) of INH, in order to determine the optimal dose to be given. In subjects with external ventricular drainage, the concentrations of INH in cerebro-spinal fluid are lower than in plasma. The latter finding should be stressed for its importance in the therapy of tuberculous meningitis.