COX-2 inhibition may be of benefit in the treatment of tuberculosis (TB) through a number of pathways including efflux pump inhibition (increasing intracellular TB drug levels) and diverse effects on inflammation and the immune response. We investigated celecoxib (a COX-2 inhibitor) alone and with standard anti-tuberculosis drugs in the whole-blood bactericidal activity (WBA) model. Healthy volunteers took a single dose of celecoxib (400 mg), followed (after 1 week) by a single dose of either rifampicin (10 mg/kg) or pyrazinamide (25 mg/kg), followed (after 2 or 7 days respectively) by the same anti-tuberculosis drug with celecoxib. WBA was measured at intervals until 8 hours post-dose (by inoculating blood samples with Mycobacterium tuberculosis and estimating the change in bacterial colony forming units after 72 hours incubation). Celecoxib had no activity alone in the WBA assay (cumulative WBA over 8 hours post-dose: 0.03 ± 0.01ΔlogCFU, p = 1.00 versus zero). Celecoxib did not increase cumulative WBA of standard TB drugs (mean cumulative WBA −0.10 ± 0.13ΔlogCFU versus −0.10 ± 0.12ΔlogCFU for TB drugs alone versus TB drugs and celecoxib; mean difference −0.01, 95% CI −0.02 to 0.00; p = 0.16). The lack of benefit of celecoxib suggests that efflux pump inhibition or eicosanoid pathway-related responses are of limited importance in mycobacterial killing in the WBA assay.

Coadministering pyrazinamide (PZA) with the xanthine oxidase inhibitor allopurinol increases systemic levels of the active metabolite, pyrazinoic acid (POA), but the effects on bactericidal activity against tuberculosis are unknown. We randomized healthy volunteers to take a single dose of PZA (either 10 or 25 mg/kg of body weight) at the first visit and the same dose 7 days later, coadministered with allopurinol (100 mg daily; 2 days before to 1 day after the PZA dose). Blood was drawn at intervals until 48 h after each PZA dose, and drug levels were measured using liquid chromatography-tandem mass spectrometry. Whole-blood bactericidal activity (WBA) was measured by inoculating blood samples with and estimating the change in bacterial CFU after 72 h of incubation. Allopurinol increased the POA area under the concentration-time curve from 0 to 8 h (AUC) (18.32 h · μg/ml versus 24.63 h · μg/ml for PZA alone versus PZA plus allopurinol) ( < 0.001) and its peak plasma concentration () (2.81 μg/ml versus 4.00 μg/ml) ( < 0.001). There was no effect of allopurinol on mean cumulative WBA (0.01 ± 0.02 ΔlogCFU versus 0.00 ± 0.02 ΔlogCFU for PZA alone versus PZA plus allopurinol) ( = 0.49). Higher systemic POA levels were associated with greater WBA levels ( < 0.001), but the relationship was evident only at low POA concentrations. The lack of an effect of allopurinol on WBA despite a significant increase in blood POA levels suggests that host-generated POA may be less effective than POA generated inside bacteria. Coadministration of allopurinol does not appear to be a useful strategy for increasing the efficacy of PZA in clinical practice. (This study has been registered at ClinicalTrials.gov under registration no. NCT02700347.).

We investigated the contribution of host immune cells to bacterial killing in a whole-blood bactericidal activity (WBA) assay, an ex vivo model used to test efficacy of drugs against mycobacterium tuberculosis (Mtb). We performed WBA assays with immuno-magnetic depletion of specific cell types, in the presence or absence of rifampicin. Innate immune cells decreased Mtb growth in absence of drug, but appeared to diminish the cidal activity of rifampicin, possibly attributable to intracellular bacterial sequestration. Adaptive immune cells had no effect with or without drug. The WBA assay may have potential for testing adjunctive host-directed therapies acting on phagocytic cells.

Objectives: High-dose rifampicin improved bactericidal activity and culture conversion in early-phase trials, done mainly in Africa. We performed a Whole Blood Bactericidal Activity (WBA) study to determine whether the effects of high-dose rifampicin differ across globally-relevant strains; and whether effects are similar in dormant bacilli that will be required for enhancing cure. Methods: Whole blood from healthy volunteers was spiked with rifampicin (range 0.63-60mg/L) and incubated with one of 4 Mycobacterium tuberculosis (Mtb) clinical strains (Haarlem, Latin American-Mediterranean [LAM], East African-Indian [EAI] and Beijing lineages) or a dormant strain (Streptomycin-Starved Mtb 18b strain [ss18b]). Change in bacterial cfu was estimated after inoculation of WBA cultures in MGIT. Results: WBA increased with higher concentrations of rifampicin in all strains. At rifampicin concentrations up to 5mg/L the rate of increase in WBA per unit increase in rifampicin concentration was similar in all 4 clinical strains (p>0.51). Above 5mg/L, EAI (p<0.001) and Beijing (p=0.007) strains showed greater increase in WBA than did LAM; Haarlem was similar to LAM. The dormant strain showed a lower rate of increase in WBA than clinical strains at rifampicin concentrations up to 5mg/L; above 5mg/L the rate of increase was similar to LAM, Beijing and Haarlem strains. Conclusions: Increasing rifampicin concentration enhanced WBA in all strains; the greatest effects were seen in strains common in Asia, suggesting that early-phase trial findings may be generalizable beyond Africa. Similar effects of high concentrations of rifampicin on the dormant strain support the concept that this intervention may enhance sterilizing activity.