Optimizing Moxifloxacin Dose in MDR-TB Participants with or without Efavirenz Coadministration Using Population Pharmacokinetic Modeling

Moxifloxacin is included in some treatment regimens for drug-sensitive tuberculosis (TB) and multidrug-resistant TB (MDR-TB). Aiming to optimize dosing, we described moxifloxacin pharmacokinetic and MIC distribution in participants with MDR-TB. Participants enrolled at two TB hospitals in South Africa underwent intensive pharmacokinetic sampling approximately 1 to 6 weeks after treatment initiation. Plasma drug concentrations and clinical data were analyzed using nonlinear mixed-effects modeling with simulations to evaluate doses for different scenarios. We enrolled 131 participants (54 females), with median age of 35.7 (interquartile range, 28.5 to 43.5) years, median weight of 47 (42.0 to 54.0) kg, and median fat-free mass of 40.1 (32.3 to 44.7) kg; 79 were HIV positive, 29 of whom were on efavirenz-based antiretroviral therapy. Moxifloxacin pharmacokinetics were described with a 2-compartment model, transit absorption, and elimination via a liver compartment. We included allometry based on fat-free mass to estimate disposition parameters. We estimated an oral clearance for a typical patient to be 17.6 L/h. Participants treated with efavirenz had increased clearance, resulting in a 44% reduction in moxifloxacin exposure. Simulations predicted that, even at a median MIC of 0.25 (0.06 to 16) mg/L, the standard daily dose of 400 mg has a low probability of attaining the ratio of the area under the unbound concentration-time curve from 0 to 24 h to the MIC (fAUC_0-24)/MIC target of >53, particularly in heavier participants. The high-dose WHO regimen (600 to 800 mg) yielded higher, more balanced exposures across the weight ranges, with better target attainment. When coadministered with efavirenz, moxifloxacin doses of up to 1,000 mg are needed to match these exposures. The safety of higher moxifloxacin doses in clinical settings should be confirmed.

Effect of tablet crushing on drug exposure in the treatment of multidrug-resistant tuberculosis

SETTING: Treatment outcomes in multidrug-resistant tuberculosis (MDR-TB) are poor. Due to drug toxicity and a long treatment duration, approximately half of patients are treated successfully. Medication is often crushed for patients who have difficulty swallowing whole tablets. Whether crushing tablets affects drug exposure in MDR-TB treatment is not known.OBJECTIVE AND DESIGN: We performed a sequential pharmacokinetic study in patients aged >18 years on MDR-TB treatment at two hospitals in Cape Town, South Africa. We compared the bioavailability of pyrazinamide, moxifloxacin, isoniazid (INH), ethambutol and terizidone when the tablets were crushed and mixed with water before administration vs. swallowed whole. We sampled blood at six time points over 10 h under each condition separated by 2 weeks. Non-compartmental analysis was used to derive the key pharmacokinetic measurements.RESULTS: Twenty participants completed the study: 15 were men, and the median age was 31.5 years. There was a 42% reduction in the area under the curve AUC0-10 of INH when the tablets were crushed compared with whole tablets (geometric mean ratio 58%; 90%CI 47-73). Crushing tablets of pyrazinamide, moxifloxacin, ethambutol and terizidone did not affect the bioavailability significantly.CONCLUSION: We recommend that crushing of INH tablets in the MDR-TB treatment regimen be avoided. Paediatric INH formulations may be a viable alternative if the crushing of INH tablets is indicated.

Quality assurance of rifampicin-containing fixed-drug combinations in South Africa: dosing implications

SETTING:

Rifampicin (RMP) drives treatment response in drug-susceptible tuberculosis. Low RMP concentrations increase the risk of poor outcomes, and drug quality needs to be excluded as a contributor to low RMP exposure.

OBJECTIVES AND DESIGN:

We performed an open-label, three-way cross-over study of three licensed RMP-containing formulations widely used in South Africa to evaluate the bioavailability of RMP in a two-drug fixed-dose combination tablet (2FDC) and a four-drug FDC (4FDC) against a single-drug reference. RMP dosed at 600 mg was administered 2 weeks apart in random sequence. Plasma RMP concentrations were measured pre-dose and 1, 2, 3, 4, 6, 8 and 12 h post-dose. The area under the concentration-time curve (AUC_0–12) of the FDCs was compared to the single drug reference. Simulations were used to predict the impact of our findings.

RESULTS:

Twenty healthy volunteers (median age 22.8 years, body mass index 24.2 kg/m²) completed the study. The AUC_0–12 of the 4FDC/reference (geometric mean ratio [GMR] 78%, 90%CI 69–89) indicated an average 20% reduction in RMP bioavailability in the 4FDC. The 2FDC/reference (GMR 104%, 90%CI 97–111) was bioequivalent. Simulations suggested dose adjustments to compensate for the poor bioavailability of RMP with the 4FDC, and revised weight-band doses to prevent systematic underdosing of low-weight patients.

CONCLUSION:

Post-marketing surveillance of in vivo bioavailability of RMP and improved weight band-based dosing are recommended.

Effect of lidocaine on kanamycin injection-site pain in patients with multidrug-resistant tuberculosis

SETTING

Reducing pain from intramuscular injection of kanamycin (KM) could improve the tolerability of multidrug-resistant tuberculosis (MDR-TB) treatment. Lidocaine has been shown to be an effective anaesthetic diluent for some intramuscular injections, but has not been investigated with KM in the treatment of adult patients with MDR-TB.

OBJECTIVE AND DESIGN

We performed a randomised single-blinded crossover study to determine if lidocaine reduces KM injection-site pain. We recruited patients aged 18 years on MDR-TB treatment at two TB hospitals in Cape Town, South Africa. KM pharmacokinetic parameters and a validated numeric pain scale were used at intervals over 10 h following the injection of KM with and without lidocaine on two separate occasions.

RESULTS

Twenty participants completed the study: 11 were males, the median age was 36 years, 11 were HIV-infected, and the median body mass index was 17.5 kg/m2. The highest pain scores occurred early, and the median pain score was 0 by 30 min. The use of lidocaine with KM significantly reduced pain at the time of injection and 15 min post-dose. On multiple regression analysis, lidocaine halved pain scores (adjusted OR 0.5, 95%CI 0.3-0.9). The area under the curve at 0-10 h of KM with and without lidocaine was respectively 147.7 and 143.6 μg·h/ml.

CONCLUSION

Lidocaine significantly reduces early injection-site pain and has no effect on KM pharmacokinetics.