Comparative bioavailability and in-vitro antimicrobial activity of two different brands of rifampicin

Pharmacokinetics of rifampicin in adult TB patients and healthy volunteers: a systematic review and meta-analysis

Objectives

The objectives of this study were to explore inter-study heterogeneity in the pharmacokinetics (PK) of orally administered rifampicin, to derive summary estimates of rifampicin PK parameters at standard dosages and to compare these with summary estimates for higher dosages.

Methods

A systematic search was performed for studies of rifampicin PK published in the English language up to May 2017. Data describing the C_max and AUC were extracted. Meta-analysis provided summary estimates for PK parameter estimates at standard rifampicin dosages. Heterogeneity was assessed by estimation of the I² statistic and visual inspection of forest plots. Summary AUC estimates at standard and higher dosages were compared graphically and contextualized using preclinical pharmacodynamic (PD) data.

Results

Substantial heterogeneity in PK parameters was evident and upheld in meta-regression. Treatment duration had a significant impact on the summary estimates for rifampicin PK parameters, with C_max 8.98 mg/L (SEM 2.19) after a single dose and 5.79 mg/L (SEM 2.14) at steady-state dosing, and AUC 72.56 mg·h/L (SEM 2.60) and 38.73 mg·h/L (SEM 4.33) after single and steady-state dosing, respectively. Rifampicin dosages of at least 25 mg/kg are required to achieve plasma PK/PD targets defined in preclinical studies.

Conclusions

Vast inter-study heterogeneity exists in rifampicin PK parameter estimates. This is not explained by the available modifying variables. The recommended dosage of rifampicin should be increased to improve efficacy. This study provides an important point of reference for understanding rifampicin PK at standard dosages as efforts to explore higher dosing strategies continue in this field.

Stability of rifampicin in dissolution medium in presence of isoniazid

Rifampicin (RIF) hydrolyzes in acidic medium to form insoluble and poorly absorbed 3-Formyl rifamycin SV (3-FRSV). This study describes development of two principally different methods, Dual Wavelength UV-Vis. spectrophotometry (DW spectrophotometry) and HPTLC, to determine 3-FRSV in presence of RIF. Using DW spectrophotometry, RIF was estimated by using wavelengths 475.0 and 507.0 nm and 3-FRSV was estimated using 457.0 and 492.0 nm. In HPTLC method, a mixture of chloroform:methanol:water (80:20:2.5 v/v) was used as the mobile phase to resolve 3-FRSV from RIF and 3-FRSV was quantified at 333 nm. The linearity range for 3-FRSV was 2-10 microg/ml and 50-250 ng/spot for DW spectrophotometric method and HPTLC method, respectively, and 5-50 microg/ml for RIF using DW spectrophotometric method. Both the methods were found to be specific, accurate and reproducible. The proposed methods were successfully applied to determine the rate of degradation of RIF to 3-FRSV in dissolution medium (0.1 N HCl) and also in presence of isoniazid (INH). The rate of degradation of RIF in presence of INH was almost two times more than that of RIF alone. These methods were utilized to study the stability of RIF in market formulations of RIF and RIF with INH in dissolution medium. It has been observed that RIF degrades by 12.4% to form 3-FRSV (RIF formulations) while in presence of INH the degradation is catalyzed to about 21.5% (RIF+INH formulations), in 45 min. Thus, lower concentration of RIF may be available for absorption leading to poor bioavailability of RIF from combination dosage forms (RIF+INH) as compared to formulations containing only RIF. It is proposed that specific analytical method should be used to measure RIF in presence of 3-FRSV in a dissolution study.

Comparative bioavailability of three different preparations of rifampicin

OBJECTIVE

To study the relative bioavailabilities of two generic rifampicin preparations with Rimactane.

METHOD

Each of nineteen healthy volunteers received a single oral dose of 600 mg of rifampicin in an open cross-over randomised three-way single-dose design with a washout period of 7 days between each doses. Plasma concentrations of rifampicin were determined by HPLC. In vitro dissolution profiles of the same drugs were determined and compared with human bioavailability study results.

RESULTS

No statistically significant difference was found in main bioavailability parameters between Rimactane and generic preparations studied. Both generic preparations also fulfilled the bioequivalence criteria based on the 90% confidence intervals. There was a good correlation between in vivo and in vitro results: faster dissolution time corresponded to the lower Tmax value; lower percentage of released compound to the lower AUC value. Significant intersubject variations were found in main bioavailability parameters; significant negative correlation was found between average AUC values and body weight of the volunteer.

CONCLUSION

All three products were bioequivalent. Our results also suggest the suitability of one-compartmental model with lag time, first order input and first order output to describe the kinetics of rifampicin.

Pharmacokinetic study of the interaction between rifampin and delavirdine mesylate

OBJECTIVE

To study the effect of rifampin (INN, rifampicin), a potent inducer of cytochrome P450, on the steady-state pharmacokinetics of delavirdine.

METHODS

Twelve patients who were positive for human immunodeficiency virus, with CD4 counts ranging from 110 to 483/mm3, were randomized to two groups and studied in parallel. Both the control group (n = 5) and the rifampin group (n = 7) received 400 mg delavirdine mesylate every 8 hours for 30 days; subjects in the rifampin group took a 600 mg once-daily dose of rifampin on days 16 through 30. Harvested plasma from serial blood samples collected after dosing on days 15, 16, and 30 was assayed for delavirdine and its N-desalkyl metabolite concentrations with a reversed-phase HPLC method. Blood samples obtained on days 16 and 30 were also assayed for rifampin by HPLC.

RESULTS

Delavirdine mesylate alone and in combination with rifampin was well tolerated. On day 30, statistically significant differences between groups were observed for all delavirdine pharmacokinetic parameters (p < 0.049). In the rifampin group, delavirdine oral clearance increased by about 27-fold (p = 0.022), resulting in virtually negligible (< 0.09 mumol/L) steady-state through drug concentrations in all patients after 2 weeks of concurrent dosing of delavirdine mesylate and rifampin. The ratio of metabolite formation to elimination clearance for desalkyldelavirdine was significantly higher (3.9 +/- 1.2 versus 0.23 +/- 0.10) and delavirdine elimination half-life was significantly shorter (1.7 +/- 1.4 versus 4.3 +/- 1.3 hours) when delavirdine mesylate was taken with rifampin. Rifampin pharmacokinetic parameters on days 16 and 30 were similar to those previously reported for normal volunteers.

CONCLUSIONS

The findings of this study indicate that rifampin induces the metabolism of delavirdine. Therefore therapy with rifampin is contraindicated in patients receiving delavirdine mesylate.