A double-blind clinical trial of isoniazid in Huntington disease

Isoniazid (INH) was given to nine patients with Huntington disease (HD) in a double-blind, placebo-controlled crossover trial. In an earlier open trial, three of six patients had improved, and one of them remained improved after 7 years on INH. Only one patient benefited in the present trial. All patients excreted small amounts of hydrazine in their urine while taking INH, and it is this INH metabolic that elevates GABA content in brain. GABA concentrations were markedly increased in CSF during INH therapy. Lack of clinical improvement in most HD patients despite elevation of brain GABA content suggests that in the minority who are benefited, INH may be acting by some mechanism other than increase of GABAergic neuronal function.

Acetylator phenotype and metabolic disposition of isoniazid in Japanese patients with systemic lupus erythematosus

Acetylator phenotype and metabolic disposition of isoniazid (INH) were studied in 19 Japanese (a population shown to be 11.5% slow acetylators) patients with spontaneous systemic lupus erythematosus (SLE) and 19 healthy controls. Subjects with the elimination half-life (t1/2) of INH of 2.0 hours or less were considered rapid and those of 2.2 hours or more were slow acetylators. Results of phenotyping showed that 17 of 19 SLE patients were rapid, 1 slow, and 1 indeterminate, whereas 18 of the controls were rapid and 1 indeterminate. When phenotyped according to another reported antimode (107 or 110 minutes), 3 of the patients and 2 of the controls were slow and the remainder were all rapid acetylators. The distribution of INH t1/2, acetyl INH to INH ratios in urine and plasma, and hydrazine compounds in urine measured with gas chromatography mass spectrometry was similar between the two groups, except for 1 patient who was definitely classified as a slow acetylator. The relationship between phenotype distribution and possible pathoetiologic factors is discussed.

Monitoring regularity of drug intake in tuberculous patients by means of simple urine tests

A study was undertaken to evaluate simple, reliable urine spot tests suitable for detection of the major anti-tuberculosis (TB) drugs rifampicin, isoniazid and pyrazinamide. The discrepancy between the actual ingestion of anti-TB tablets and prescribed medication was investigated in 234 hospitalized male and female patients as well as in 85 male and female outpatients with pulmonary tuberculosis. Several factors implicated in patient non-compliance are discussed, namely the degree of supervision, the independent administration of rifampicin before the other TB medication, and patient preference for certain TB medicines because of tablet size.

Noneffect of isoniazid on urine glucose tests

Isoniazid has been shown by in vitro study to reduce Clinitest tablets. The effect of isoniazid on urine glucose tests was investigated in 30 patients by comparing commonly used glucose oxidase methods to Clinitest. Study results indicate that isoniazid does not cause clinically significant interference with the copper reduction method for urine glucose determination.

Clinical pharmacokinetics of isoniazid

The pharmacokinetics of isoniazid in man are described. Pronounced interindividual variation in circulating isoniazid concentration and clearance which occur after dosing with the drug are associated with hereditary differences in the acetylator status. The variations in rate of isoniazid inactivation and elimination in different (rapid and slow) acetylator phenotypes are primarily due to differences in the rate of acetylation of isoniazid by a genetically controlled polymorphic N-acetyltransferase in liver and small intestine. An appreciable 'first-pass' effect is observed following oral isoniazid administration, particularly in the rapid acetylator phenotype. Liver disease can cause a significant prolongation in the clearance of isoniazid; in the acutely ill patient, the prolongation correlates most closely with serum bilirubin elevation, although the degree of prolongation is less important than the intrinsic genetic difference between acetylator phenotypes. The effect of renal impairment on isoniazid excretion is relatively unimportant, even in slow acetylators. Methods for monitoring blood and urine concentrations of isoniazid and for acetylator phenotype determination which are convenient for the patient and clinician are available. Implications of phenotype differences in acetylator status for the optimal management of tuberculosis with isoniazid are considered. Attempts to devise new isoniazid formulations for this purpose are being evaluated.

Pharmacodynamic interference between rifampicin and isoniazid

This study includes 30 children below the age of 3 years, distributed in three groups of 10 children each. One group received 15 mg/kg/day of rifampicin (RAMP), the other received 15 mg/kg/day of isoniazid (INH) and the third received both drugs (RAMP + INH) at the same doses. Plasma levels of RAMP and INH were determined. At the same time, some hepatic function parameters were analyzed: bilirubin, transaminases, alkaline phosphatases and prothrombin. Plasma levels of INH administered alone show significantly higher levels on the 7th day with respect to the 1st day, thus demonstrating a marked tendency towards the accumulation of successive doses. Very significant differences exist between initial and final values of transaminases in the RAMP + INH group. There are no significant differences in the other two groups. These data suggest a hepatic overload when both drugs are simultaneously administered.

Determination of hydrazine metabolites of isoniazid in human urine by gas chromatography

A method is described for the determination of isoniazid, acetylisoniazid, acetylhydrazine, diacetylhydrazine and hydrazine in urine. Isoniazid, acetylhydrazine and hydrazine are reacted in aqueous solution with p-chlorobenzaldehyde to form hydrazones. Following the addition of appropriate internal standards, these hydrazones are then extracted into an organic solvent and determined by gas chromatography using a nitrogen-sensitive detector. Acetylisoniazid and diacetylhydrazine are determined similarly after hydrolysis to isoniazid and acetylhydrazine, respectively.

Liquid chromatography in pharmaceutical analysis VIII: determination of isoniazid and acetyl derivative in plasma and urine samples

Parameters are described for the qualitative and quantitative analysis of a mixture of isoniazid and its acetyl derivative. The compounds are chromatographed on an octadecylsilane column, using absolute methanol-distilled water (60:40) at pH 2.5 containing 0.01 M dioctyl sodium sulfosuccinate. The flow rate was 2.0 ml/min (2500 psig). The separation and quantification are applicable to plasma and urine samples. The determination in each biological fluid can be achieved in approximately 90 min with percentage accuracies for isoniazid of 5.25 and 7.45 and for the acetyl derivative of 4.47 and 1.56 in plasma and urine, respectively.

Controlled clinical trial of four 6-month regimens of chemotherapy for pulmonary tuberculosis. Second report. Second East African/British Medical Research Council Study

A comparison has been made of the relapse rates between 7 and 30 months for four 6-month regimens. Streptomycin plus isoniazid plus rifampicin had a relapse rate of 2 per cent of 171 patients; isoniazid plus rifampicin had a relapse rate of 7 per cent of 164. An initial 2 months of streptomycin, isoniazid, rifampicin, and pyrazinamide, when followed by thiacetazone plus isoniazid, had a relapse rate of 7 per cent of 179, and when followed by streptomycin plus isoniazid plus pyrazinamide twice a week the relapse rate was 4 per cent of 159 patients. Of the 36 relapses, 32 occurred in the first 6 months after stopping chemotherapy and 35 were with drug-susceptible organisms. The difference between the relapse rate on the streptomycin plus isoniazid plus rifampicin regimen and the isoniazid plus rifampicin and thiacetazone plus isoniazid regimens approached significance (P =0.06 for both comparisons).

Failure of commercially prepared isoniazid diet to produce isoniazid serum concentrations in rhesus monkeys

A comparison was made of serum isoniazid concentrations and the time course of isoniazid elimination in rhesus monkeys given the drug im, orally on sugar cubes, or in a commercially medicated diet. When the drug was administered orally on sugar cubes or im, peak serum concentrations were usually reached within 2 hr. A threefold individual variation in the rate of elimination was noted, and in most animals the serum concentration at 6 hr approached zero. Isoniazid was not detected in the serum of any animal receiving the commercially medicated diet. Others using this medicated food in their tuberculosis prophylaxis programs should be aware that the diet probably does not provide therapeutically effective dosage to the animals.

Determination of the acetylator phenotype using matrix isoniazid

The development of a simple method for classifying subjects as slow or rapid acetylators is reported. The method is based on determining the ratio of acetylisoniazid to acid-labile isoniazid in the urine 23-24 hours after an oral dose of a slow-release isoniazid formulation. The results obtained when this method was applied to phenotype over 200 East African tuberculosis patients are described. It is suggested that the method would be particularly suitable for classifying tuberculosis out-patients.

The use of isoniazid as a marker to monitor the self-administration of medicaments

1. Isoniazid was used as a marker to monitor the regularity of drug self-administration in a trial of chemoprophylaxis against natural influenza infection. Two hundred and sixty-two volunteers were treated for five weeks with a synthetic isoquinoline compound (U.K. 2371) or a matching placebo. 2. Five marker tablets containing isoniazid (150 mg) were incorporated into each regimen and their ingestion monitored by testing for acetylisoniazid in the urine. 3. Positive evidence of marker tablet consumption was obtained on 75% of the occasions on which urine samples were requested. The results obtained among the volunteers from each treatment group who returned urine specimens as requested (92%) indicated that they had swallowed at least 81% of their prescribed tablets. 4. The findings of the study suggest that when used in this way isoniazid is a very suitable compound for use on a few occasions for monitoring the self-administration of drugs in clinical trials.

Treatment of acute isoniazid toxicity

The clinical symptoms and treatment of acute isoniazid toxicity are presented. The use of supportive measures and chemotherapy are discussed in detail. The pharmacology and biochemistry underlying the symptons of isoniazid poisoning are aslo presented. It is concluded that diazepam in combination with pyridoxine is the treatment of choice for the management of convulsions associated with isoniazid toxicity. Pyridoxine should be administered intravenously in amounts equal to the estimated quantity of isoniazid ingested, even if seizures have not occurred.