Sustained release of isoniazid in vivo from a single implant of a biodegradable polymer

In order to solve the problem of poor patient compliance, attempts were made to prolong the bioavailability of antimycobacterial drugs after a single administration. A single implant of polylactic-co-glycolic acid (PLGA) co-polymer containing isoniazid ensured its sustained release up to 6 weeks. The levels are comparable with those obtained from daily doses. Homogenates of liver and lungs from animals killed at 6 weeks after a single implant showed high antimycobacterial activity against Mycobacterium tuberculosis. Sera from the implant and daily dose group animals showed no significant difference in renal, hepatic and haematological parameters. The implant caused no local or systemic toxicity.

Suppression of deferoxamine mesylate treatment-induced side effects by coadministration of isoniazid in a patient with Alzheimer's disease subject to aluminum removal by ionspecific chelation

Deferoxamine treatment may produce serious side effects that can be eliminated by modification of treatment and by control of deferoxamine metabolism. A patient suffering from dementia of the Alzheimer type with normal liver and kidney function who was treated with deferoxamine initially tolerated a dose of 7 mg/kg deferoxamine mesylate injected intramuscularly twice a day for a total of 5 days a week. After several months nausea and weight loss gradually developed in the patient that could be controlled initially by dose reduction, leading to levels inappropriate for aluminum chelation. HPLC analysis of blood and urine revealed several metabolites including, as a major component, a plasma monoamine oxidase (MAO) catalyzed end product MFO1. Coadministration of isoniazid, a plasma MAO inhibitor, with deferoxamine resulted in reduction of MFO1 from 81% to 8% accompanied by increases in the amounts of metabolite 2 (MFO2) from 2% to 24% and unmetabolized deferoxamine from 17% to 68% after 6 months of treatment. The side effects subsided, the patient regained weight, and treatment could be continued.

A comparison of a short half-life marker (low-dose isoniazid), a long half-life pharmacological indicator (low-dose phenobarbitone) and measurements of a controlled release 'therapeutic drug' (metoprolol, Metoros) in reflecting incomplete compliance by volunteers

1. Although, long half-life compounds appear to be more appropriate pharmacological indicators of compliance with treatment, short half-life markers or measurements of short half-life therapeutic drugs are frequently used. 2. We have compared the usefulness of low-dose phenobarbitone (a long half-life indicator), low dose isoniazid (a short half-life marker) and controlled release metoprolol (Metros) (a controlled release formulation of a short half-life 'therapeutic' drug) in seven volunteers with simulated partial (two thirds) compliance. 3. Detection of isoniazid metabolites in urine had an 83% sensitivity and 94% specificity for detecting ingestion within the previous 24 h and 100% sensitivity and 82% specificity for detecting ingestion within the past 6 h but gave no indication of the longer term pattern of compliance. 4. At 28 days (a time when steady-state would be obtained for all three drugs) phenobarbitone plasma levels were 70% (66-76%)--median and interquartile range--of the expected steady-state level if compliance had been complete. Corresponding figures for metoprolol were 82% (37-100%). 5. Measurement of phenobarbitone was much superior to isoniazid or metoprolol measurements in reflecting partial compliance over the previous 1 to 4 weeks.

Testing for isoniazid. An evaluation of the Arkansas method

To better treat and eliminate tuberculosis, patient compliance must be improved. Compliance can be evaluated by measuring a drug or its metabolite in the urine. In Arkansas, a simple colorimetric method of checking the urine for isoniazid (the Potts-Cozart test) has been used for many years, but it is relatively unknown outside that state and its reliability has not been confirmed. To evaluate this test, urine was blindly tested from patients from a tuberculosis clinic. Controls included urine from patients from a substance abuse clinic and Veterans Medical Center. In more than 200 urine samples tested, no false-positives were found. Urinalysis showed normal values for three patients who were supposed to be receiving antituberculosis medication, but it is likely that these patients were noncompliant. A peculiarity of the test was that the color change with positive tests varied. To investigate this variation, absorption spectroscopy of many substances was performed. Nicotine accounted for the different shade of blue associated with the positive test, but the color produced and the absorption spectroscopy were different from isoniazid, so it did not confuse the interpretation of the results. This test for isoniazid in the urine is simple, quick, inexpensive, easy to interpret, and reliable. It also can be used to detect nicotine and its metabolites.

Acetylation phenotyping of isoniazid using a simple and accurate high-performance liquid chromatography

A simple, specific, accurate and reproducible method for the analysis of isoniazid and its major metabolite, N-acetylisoniazid in urine using high-performance liquid chromatography (HPLC) is described. The assay is performed after extraction of isoniazid, N-acetylisoniazid and 5-(4-methylphenyl)-5-phenylhydantoin (internal standard) from urine using a mixture of chloroform:isopropanol (70:30, v/v) and eluted from a 5 microns C-18 reversed phase column at ambient temperature with a mobile phase consisting of 10 mM sodium acetate:methanol:acetonitrile (40:40:20, v/v) containing 10 mM dioctylsulphosuccinate sodium and adjusted to pH 2.9 with sulphuric acid (less than 1 ml), at a flow rate of 1 ml/min with u.v. detection at 266 nm. Quantification was achieved by the measurement of the peak height ratio, and the absolute recoveries ranged from 94 to 99%. Within-day coefficients of variation ranged from 2.81 to 4.54% for isoniazid and from 2.37 to 3.75% for N-acetylisoniazid. Between-day CVs varied from 3.27 to 5.62% and from 2.5 to 4.91% for isoniazid and N-acetylisoniazid, respectively. Preliminary stability tests using a urine sample from a subject showed an increase in mean isoniazid concentration of about 25% after 1 month storage at -20 degrees C. The method was used for acetylation phenotyping of five individuals.

High frequency of the rapid isoniazid acetylator phenotype in Lagos (Nigeria)

The metabolism of isoniazid was investigated in 323 unrelated and healthy Nigerians in Lagos using a simple dosage and urinalysis procedure. The distribution was bimodal and the population frequency of rapid acetylators was 61.92%, a value higher than that for most Caucasian populations. Males and females were equally affected by the traits. Analysis of both the population and pedigree data showed that the slow acetylator phenotype is a recessive trait, and the gene frequency of the recessive allele as computed by maximum likelihood methods is 0.6175 +/- 0.022. The clinical implications of these findings are discussed.

Effect of deoxyfructoserotonin (DFS) on lepromatous leprosy

To examine the anti-leprosy effect of deoxyfructoserotonin the drug was given in a dose of 10 mg/kg for 6 months to 6 patients with active lepromatous leprosy, in accordance with the WHO-THELEP protocol. Clinical and histological assessment and mouse foot-pad studies suggest that the drug has some anti-leprosy effect.

On phenotyping with isoniazid: the use of urinary acetylation ratio and the uniqueness of antimodes. Study of two Amerindian populations

Various conventions have been used to express the activity of polymorphic hepatic N-acetyltransferase of isoniazid. Among them, two of the most common are the "percentage of acetylisoniazid" and the "inactivation index." A third alternative convention is proposed, the "molar acetylation ratio," which showed the most clear-cut bimodal distribution when applied to the results obtained for Cuna and Teribe Amerindians living in Panama. Through this method a unique antimode was assigned to each Amerindian group and the same frequency of slow acetylators (24% to 29%) was found, unlike the results obtained by conventional approaches and antimodes derived from white populations.

Acute isoniazid toxicity--report of 2 cases and review of literature

Accidental or intentional isoniazid (INH) overdose is not uncommon. Two patients suffering from pulmonary tuberculosis ingested INH (9 g and 12 g respectively) intentionally following acute personal stress. One patient presented with oliguria and coma whereas seizures were the dominant feature in the second case. Serum levels of INH were high in both cases. Satisfactory clinical recovery followed after the administration of intravenous pyridoxine. Literature on the subject was reviewed and the manifestations and recommendations for the management of acute INH toxicity are highlighted.

Effect of rifampin, phenobarbital pretreatment, and acetylator phenotype on acetylisoniazid metabolism in the rabbit

The metabolism of [14C]acetylisoniazid was studied in male New Zealand White rabbits. Pretreatment of the rabbits with the microsomal enzyme inducers rifampin and phenobarbital had little effect on acetylisoniazid metabolism. Rifampin appears to produce some inhibition of acetylation of the metabolite acetylhydrazine to diacetylhydrazine. Acetylation phenotype was an important factor. Covalent binding of 14C to hepatic protein increased as the acetylation rate decreased. In plasma and urine acetylhydrazine levels were negatively correlated with acetylation rate and diacetylhydrazine levels were positively correlated as one would expect. It was concluded that in the rabbit covalent binding to hepatic protein was more dependent on the acetylation rate than on induction of microsomal oxidase.

Increased urinary excretion of toxic hydrazino metabolites of isoniazid by slow acetylators. Effect of a slow-release preparation of isoniazid

To test the hypothesis that slow acetylators, who may have a greater risk of developing isoniazid hepatitis than rapid acetylators, are exposed to more acetylhydrazine and hydrazine, two toxic metabolites of isoniazid, the urinary excretion of hydrazino metabolites of isoniazid was measured following the ingestion of 300 mg isoniazid. Slow acetylators (n = 7) excreted significantly more isoniazid (32.4 vs 9.2% dose), acetylhydrazine (3.1 vs 1.6% dose), and hydrazine (1.0 vs 0.4% dose) in 24 h than rapid acetylators (n = 5), whereas the excretion of acetylisoniazid and diacetylhydrazine was significantly lower. As the acetylation (i.e. detoxification) of acetylhydrazine is inhibited in the presence of high concentrations of isoniazid, a study was also made of the effect of a slow-release preparation that results in lower plasma concentrations of isoniazid on the production of hydrazino metabolites. The ratio of acetylisoniazid to isoniazid in urine was significantly increased in slow acetylators from 0.84 to 1.02 following administration of the slow release preparation, indicating increased acetylation of isoniazid. However, the excretion of diacetylhydrazine relative to the excretion of acetylhydrazine and hydrazine did not change. It is concluded that exposure to toxic metabolites of isoniazid is increased in slow acetylators. Detoxification of the toxic metabolites was not enhanced by a slow-release preparation of isoniazid.

The bioavailability of isoniazid, rifampin, and pyrazinamide in two commercially available combined formulations designed for use in the short-course treatment of tuberculosis

The bioavailability of isoniazid, rifampin, and pyrazinamide in 2 combined formulations of the 3 drugs (Rifater) for use primarily in the short-course chemotherapy of tuberculosis has been studied in Chinese patients in Singapore and Hong Kong. One formulation, containing 50 mg isoniazid, 120 mg rifampin, and 300 mg pyrazinamide per tablet is suitable for daily use, whereas the other, containing higher proportions of isoniazid and pyrazinamide, is designed for intermittent treatment, each tablet containing 125 mg isoniazid, 100 mg rifampin, and 375 mg pyrazinamide. Appropriate dosages for the Chinese patients, whose average weight was approximately 50 kg, were 5 and 6 tablets, respectively. Plasma concentrations of the 3 drugs after giving such dosages of the 2 combined formulations were compared in 16 patients, 8 in Singapore and 8 in Hong Kong, by means of a crossover study, with the concentrations obtained when identical doses of the 3 drugs were given using standard separate drug formulations. The concomitant urinary excretions of the drugs and their major metabolites were also estimated. Very similar results were obtained whether the drugs were given as the combined preparations or in their standard separate formulations, demonstrating the excellent bioavailability of all 3 drugs in each of the 2 combined formulations.

[Isoniazid acetylation in Gilbert's syndrome]

Phenotyping of isoniazid acetylators in 19 Caucasoid patients with Gilbert's syndrome was achieved by evaluating the percentual of acetylisoniazid in the urine. The proportion of slow acetylators among the patients with Gilbert's syndrome was similar to those found among Caucasoids of control group. The conclusion was that Gilbert's syndrome doesn't interfere in the hepatic capacity of isoniazid acetylation.

Urinary metabolic profile of isoniazid in patients who develop isoniazid-related liver damage

The urinary metabolite profile of isoniazid has been studied in patients receiving the drug as therapy for tuberculosis and the profile in patients suffering liver damage due to isoniazid compared with that in control patients. There were no consistent differences between control patients and those suffering liver damage in the excretion of isoniazid metabolites. It may be that susceptibility to the hepatotoxicity of isoniazid is not due to metabolic differences, although a number of other possible explanations are discussed. It is not at present possible to predict which patients will be susceptible from metabolic studies.