Rifampicin causes false-positive immunoassay results for urine opiates

The treatment of tuberculosis usually includes the antibiotic rifampicin, especially in patients with concomitant human immunodeficiency virus infection. Some of these patients are in withdrawal therapy for drug abuse. When opiate screening is carried out in patients receiving rifampicin, false positive results are detected with the kinetic interaction of microparticles in solution method. We evaluated this interference in a Cobas-Integra analyzer and found a 12% cross-reactivity of rifampicin for antibiotic concentrations ranging from 0.19 to 6.08 mumol/l (156 to 5000 micrograms/l). This effect is not explained by the colour of the rifampicin solutions. Calculations assuming first order kinetics of elimination show that more than 18 hours after a single oral dose of 600 mg of rifampicin, a false positive result for opiates could be obtained. This indicates that the risk of a false positive result must always be considered when urine samples from these patients are analyzed.

Treatment of enterococcal pyelonephritis with trovafloxacin and rifampin: in vitro-in vivo contrast

The in vitro bactericidal interaction of trovafloxacin and rifampin against Enterococcus spp. has indicated that antagonism occurs between these two antimicrobial agents. This drug combination was examined in vivo in rats with experimental pyelonephritis. The rats received trovafloxacin, rifampin, or both drugs. On the basis of the mean log10 CFU of Enterococcus faecalis from the kidneys, there was no evidence that trovafloxacin and rifampin were antagonistic in vivo.

Attendance versus compliance with tuberculosis treatment in an occupational setting--a pilot study

AIM

To determine the prevalence of non-compliance with tuberculosis treatment at Freegold Mines.

OBJECTIVES

1. To establish the rates of attendance and collection of anti-tuberculosis drugs. 2. To determine prevalence of non-compliance by means of urine tests.

DESIGN

A cross-sectional study conducted over 2 weeks at mine medical stations.

METHOD

Urine samples were collected from tuberculosis patients 3 hours after drug ingestion. Non-compliance was established by testing these samples for rifampicin and/or isoniazid (INH) metabolites. Non-compliance was defined as a negative urine test result for these drugs in participants whose treatment regimens included one or both. Daily attendance and collection of drugs statistics are recorded in the medical station tuberculosis register. The patient rate of adherence was calculated as the observed number of days on which medication had been collected over the expected treatment days in a given period.

RESULTS

Urine test results showed an overall prevalence of non-compliance of 14.6 +/- 3.3%. The study showed that non-compliance with tuberculosis treatment was underestimated by the surveillance data. The rate of non-adherence with treatment established from the formal surveillance procedure was 0.2%. The poor response rate of patients was found to be a major problem and fewer than 40% per day returned to bring urine specimens. The mean prevalences of non-compliance established by rifampicin and INH tests were 19.5 +/- 5.3% and 9.8 +/- 3.9%, respectively, and these were significantly different (Chi 2 = 7.44; P < 0.05). The proportion of false-positive results for INH and rifampicin urine tests were 21% (11/53) and 35% (17/48), respectively, showing that some patients were taking the wrong treatment.

CONCLUSIONS

It is clear that attendance at the clinics does not accurately reflect compliance. Both programme compliance (dispensing of the correct treatment) and patient compliance need to be improved. This has important implications for the new national tuberculosis control policy adopted by the South African government that stresses the importance of directly observed therapy, short-course (DOTS) and a patient-centred approach.

Effect of activated charcoal on rifampicin absorption in man

The effect of activated charcoal (AC) on rifampicin excretion was investigated in six healthy volunteers. On three occasions, at weekly intervals, each subject received a 600 mg rifampicin with 350 ml of water; b+c one and two weeks later, 600 mg of rifampicin plus 7.5 and 15 g AC, respectively, in 350 ml of water as a charcoal slurry. Urinary levels of rifampicin were measured form 1-36 hr after ingestion. Treatment with AC led to 1.2 per cent urinary recovery of rifampicin; decreased excretion rate; and a much lower plateau indicative of reduced absorption.

Plasma and saliva concentrations of rifampicin in man after oral administration

The saliva and plasma concentrations of rifampicin were determined following oral administration of 600 mg of the drug to healthy human subjects. Rifampicin is a zwitterion with PKa's of 1.7 and 7.9. The saliva-plasma concentration ratios calculated on the basis of the PKa of 1.7 was 1.6346. The saliva concentrations were much higher than the MICs of a variety of organisms, indicating the possible usefulness of rifampicin in the treatment of susceptible oropharyngeal and nasopharyngeal pathogens. After 24 hrs, when rifampicin was completely absent in the urine, the saliva and plasma concentrations also had fallen almost to zero.

Profiles of non-compliance with antituberculous therapy

Treatment compliance was assessed by testing multiple urine samples for rifampicin in 113 consecutive patients taking a rifampicin containing regimen for tuberculosis. Nineteen (16.8%) patients had at least one negative urine sample after chromatographic analysis and these patients were more likely to be from social classes IV and V, to be Asian, and to have defaulted from at least one clinic appointment without good reason. A questionnaire was completed by 70 of the patients and four (6%) admitted to having omitted at least one treatment weekly; two of these also had at least one negative urine test. Physicians were only partly successful in identifying non-compliers. The relevance of these findings is discussed.

Microbiological assay versus spectrophotometry for determination of rifampicin in urine

A comparative study on the microbiological and spectrophotometric methods for estimation of rifampicin in urine was carried out in 15 individuals. The urinary levels of rifampicin were determined on 2nd, 8th and 15th days at 3 hour, 6 hour and 24 hour samples by the above methods after administration of 600 mg rifampicin. The results suggest that the microbiological assay is more sensitive than spectrophotometric method. The difference was highly significant in all the cases by paired t-test. Incidentally it was also noticed that urinary excretion of rifampicin was comparatively more on 15th day.

[Pharmacokinetics of rifampicin administered intravenously to pulmonary tuberculosis patients]

Pharmacokinetics of rifampicin studied in 15 patients after its intravenous administration in a dose of 10 mg/kg was described by a two-compartment model. The drug levels in serum and urine were determined with a chemical method. At the moment of the infusion discontinuation the maximum drug levels in serum averaged to 14.05 micrograms/ml. The mean values of the total clearance, distribution of the kinetic volume and half-lives were 93.2 ml/(h X kg), 1016.1 ml/kg and 8.1 h respectively. Cumulative excretion of the total rifampicin within 24 hours amounted to 19.4 per cent of the administered dose, the proportions of the main metabolite (25-O-desacetyl rifampicin) and intact rifampicin being equal to 29 and 71 per cent respectively. The renal and nonrenal clearance of rifampicin amounted to 14.2 and 79 ml/(h X kg) respectively.

The influence of enzyme induction on polymorphic sparteine oxidation

The effects of antipyrine (1200 mg day-1), phenobarbitone (100 mg day-1) and rifampicin (600 mg and 1200 mg day-1, respectively) administration for 7 days on sparteine metabolism and 6 beta-hydroxycortisol excretion were studied in panels of extensive (EM) and poor metaboliser (PM) subjects. Drug metabolism was induced in both EM and PM subjects by antipyrine and rifampicin pretreatment as indicated by increased excretion of 6 beta-hydroxycortisol. A 30% increase in metabolic clearance of sparteine was observed in EM subjects following rifampicin administration whereas in PM subjects no effect on the overall elimination of the drug was seen. The data indicate that the regulation of cytochrome P-450 isozyme involved in polymorphic debrisoquine/sparteine metabolism is predominantly under genetic control and that enzyme induction exerts only a marginal effect.

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.

[The pharmacokinetics of rifampicin in the intermittent treatment of patients with pulmonary tuberculosis. 1. Excretion of rifampicin in the urine]

With a rifampicin (RMP) range of 600 to 1800 mg, 12.5% of the administered dose are on an average secreted in urine. In spite of this minimal portion the course of pharmacokinetic processes can distinctly be learned from its alterations. Analyses in 84 patients revealed that the age will influence the induction and the sex-specific differences of the pharmacokinetics. Compared to male subjects, an increased RMP secretion in urine can be recorded in young female subjects, whereas in older male ones an induction-reduced RMP elimination in urine becomes more obviously. Considering these multiform processes, the determination of the bioavailability of RMP preparations by means of the RMP secretion in urine is taken to be manipulatable and uncertainly. More evident results can be gained by the determination of the RMP concentration in serum or by the calculation of the AUC.

Effect of probenecid on serum rifampicin levels

Serum Rifampicin levels were determined by a microbiological assay using Staphylococcus aureus in 22 cases of leprosy after administering the drug with and without probenecid. Most of the patients showed higher serum rifampicin levels when probenecid was given along with rifampicin. Six patients showed statistically significant increase in the serum levels of the drug when given in the dose of 300 mg along with 1 g of probenecid one hour before breakfast and these levels were comparable with those obtained following administration of 450 mg of rifampicin alone two hours after breakfast. Thus administration of probenecid preceding rifampicin may be employed to reduce cost of drug as well as hepatotoxicity in patients requiring rifampicin for long duration.

Non-compliance with antituberculous drugs

A case of inadvertent 'total' non-compliance with a course of antituberculous drugs is described. Subsequently the value of routine urine testing for rifampicin in a chest clinic was assessed. The butanol extraction test was found to be a simple and rapid guide to the identification of defaulting patients.

[Urinary excretion of rifampicin in kidney failure when administered alone or together with isoniazid]

Rifampicin excretion with urine and its plasma levels were studied in 46 patients with nephrophthisis treated with rifampicin alone or in combination with isoniazid in doses of 8--10 mg/kg bw with regard to the degree of renal insufficiency. It was shown that excretion of rifampicin with urine decreased with progression of renal insufficiency and had no effect on its plasma levels. The combined use of isoniazid and rifampicin in a single dose was accompanied by a decrease in the latter's excretion with urine and different changes in its plasma concentration. The use of the two drugs for 4--6 weeks resulted in a further decrease in rifampicin excretion with urine not dependent on renal function and in decreased plasma levels of the antibiotic in 1/3 of patients. The findings indicate that the use of rifampicin in a dose less than 10 mg/kg of the body weight in patients with chronic renal insufficiency is not advisable. The absence of rifampicin in the urine specimens collected during the first hours on the 2nd day after its single use or its use for 4--6 weeks indicate that rifampicin does not accumulate in patients with renal insufficiency.

Drug interactions -- the influence of rifampicin and clofazimine on the urinary excretion of DDS

Indication of an enhancing effect of Rifampicin on the urinary excretion of DDs has already been reported from this institution. Further observations on this aspect in 25 cases of lepromatous leprosy treated with a 15 day schedule of Rifampicin at a dose of 600 mg daily along with DDS are presented. The earlier findings that Rifampicin in the initial phase of administration enhance the urinary output of DDS are confirmed. An estimation of Rifampicin Creatinine levels in urine done concurrently also showed a quicker elimination of the drug in the earlier phase compared to later phases of the drug administration. As part of the study of drug interactions, the influence of Clofazimine administration on DDS metabolism was also studied. The findings indicate that Clofazimine does not exert any influence on DDs excretion by leprosy patients. The findings and their implications are 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.