Pharmacokinetic study of anti-tb drug para-aminosalicylic acid and its metabolites: a possible relationship with the development of toxicity

Abstract

Background Para-aminosalicylic acid (PAS) is a bacteriostatic anti-tuberculosis (anti-TB) drug, used in the treatment of multi-drug resistant (MDR) and extensively drug-resistant (XDR) tuberculosis (TB). While PAS has shown great efficacy, it is notorious for its association with gastrointestinal (GI) intolerance. The intolerance was considered to be due to the dosing strategy, which therefore caused clinicians to opt for divided doses as opposed to a single large dose daily, but no evidence of improvement has been reported. It has thus been proposed that the rate of absorption and/or metabolism of PAS could possibly be responsible for poor tolerability of the drug. Aims The aim of the study was to investigate the potential association between the plasma concentrations of the main metabolites, acetyl-PAS (APAS) and glycine-PAS (GPAS), and the occurrence of GI intolerance, after the administration of a granular slow release PAS (GSR-PAS) formulation. Study design and methodology A two-period study of PAS and its metabolites was conducted in 29 adult patients (≥ 18 years old) MDR- and XDR-TB, at the Brooklyn Chest Hospital, Cape Town, South Africa. These patients were assigned to a 4g twice-daily GSR-PAS regimen for 1 week followed by another week given 8g once-daily GSR-PAS. Whole blood was collected in EDTA-containing tubes at 1, 2, 3, 4, 6, 8, 12 and 24 hours post dose, at the end of each week. PAS plasma concentrations were determined using an ultra high performance liquid chromatography system coupled to a tandem mass spectrometer, (UHPLC-MS/MS) of which the assay was developed and partially validated according to the Food and Drug Administration (FDA) criteria. Thereafter, pharmacokinetic analysis was performed for the metabolites and parent drug of which pharmacokinetic parameters Cmax, AUC0-24 and Tmax were determined by non-compartmental analysis, using Winnonlin software version 8.0. The tolerability of PAS was evaluated using a 10-point visual analogue scale (VAS) rating the severity of the adverse effects (AE’s) experienced, with the most left indicating no symptoms and the most right indicating severe symptoms. The patients completed the evaluation on a daily basis after dosing. The AE’s evaluated included nausea, bloating, diarrhoea, vomiting, and abdominal pain and cramps. A correlation analysis using STATA software version 15.1 was used to measure the association between each AE and the median Cmax of PAS, APAS and GPAS using the Spearman’s rank correlation. Statistical significant was set at a P value less than 0.05. Results: The developed method proved successful in the assay of APAS, GPAS and PAS in a single run of 4 minutes. A large inter-individual variability was observed in the Cmax ranging from 40.42 to 102.41 mg/L for PAS, and 10.00 to 22.36 mg/L and 3.90 to 9.45 mg/L for APAS and GPAS, respectively. The VAS data reported that 26 patients had evidence of GI intolerance, but the majority of these scores were clustered around zero. Abdominal pain and cramps were found to be statistically more frequent in the 4g twice-daily than 8g once-daily regime [0.14(0 – 0.59) versus 0(0 – 0.08); median (IQR); p= 0.018]. Statistically significant inverse associations were observed between APAS concentrations and bloating (rho= -0.448; p= 0.025) and diarrhoea (rho= -0.407; p= 0.044), respectively, for the twice-daily dose. The same inverse association was found for GPAS concentrations and diarrhoea (rho= -0.412; p= 0.041). Conclusions: Plasma concentrations of metabolites APAS and GPAS did not correlate with the occurrence of AE’s. On the contrary, the data showed that higher plasma concentrations of APAS and GPAS were associated with lower scores of AE’s, which were statistically significant relationships but considered clinically negligible. Further work with a larger population size may be needed to determine the true effect of metabolite formation on the presence of GI discomfort when treated with PAS.

Agtergrond Para-aminosalisielsuur (PAS) is ʼn bakteriostatiese anti-tuberkulosemedisyne wat in die behandeling van middelweerstandige (MDR) en uiters middelweerstandige (XDR) tuberkulose (TB) gebruik word. Alhoewel PAS aanmerklike doeltreffendheid toon, is dit bekend vir ʼn verband met gastro-intestinale (GI) intoleransie. Die intoleransie word aan die doseringstrategie verbind, wat dus meebring dat klinikusse verdeelde dosisse verkies teenoor ʼn enkele groot daaglikse dosis, maar geen bewyse van verbetering is egter gerapporteer nie. Daar is dus voorgestel dat die tempo van absorpsie en/of metabolisme van PAS moontlik vir swak toleransie van die medisyne verantwoordelik is. Doelwitte Die doel van die studie was om ondersoek in te stel na die moontlike verband tussen die plasmakonsentrasies van die hoofmetaboliete, asetiel-PAS (APAS) en glisien-PAS (GPAS), en die voorkoms van GI-intoleransie ná toediening van ʼn formulering van ʼn granulêre stadigvrystellende PAS (GSR-PAS). Studie-ontwerp en -metodologie ʼn Tweetydperk-studie van PAS en sy metaboliete is uitgevoer onder 29 volwasse MDR- en XDR-TB-pasiënte (≥ 18 jaar oud) by die Brooklyn Chest Hospitaal in Kaapstad, Suid-Afrika. Hierdie pasiënte is ingedeel vir ʼn GSR-PAS-regimen van 4 g twee keer per dag vir een week, gevolg deur nog ʼn week waarin hulle een keer per dag 8 g GSR-PAS ontvang het. Heelbloed is in EDTA-bevattende buise teen 1, 2, 3, 4, 6, 8, 12 en 24 ure ná toediening van die dosis aan die einde van elke week geneem. PAS-plasmakonsentrasies is bepaal met behulp van ʼn ultrahoëverrigting-vloeistofchromatografiestelsel gekoppel aan ʼn tandem-massaspektrometer, waarvan die toets volgens kriteria van die Amerikaanse Voedsel- en Medisyne-administrasie ontwikkel en bekragtig is. Daarna is farmakokinetiese ontleding vir die metaboliete en moedermedikasie uitgevoer, waarvan farmakokinetiese parameters Cmax, AUC0-24 en Tmax deur niekompartementele ontleding bepaal is met gebruik van Winnonlinsagteware weergawe 8.0. Toleransie van PAS is met behulp van ʼn tienpunt- visuele analoë skaal (VAS) geëvalueer, wat die erns van die negatiewe gevolge (NG’s) wat ervaar is, gerangeer het, met heel links wat geen simptome aantoon en heel regs wat ernstige simptome aantoon. Die pasiënte het die evaluering daagliks ná dosering voltooi. Die NG’s wat geëvalueer is, het naarheid, opgeblaasdheid, diarree, vomering en maagpyn en -krampe ingesluit. ʼn Korrelasie-ontleding met behulp van STATA-sagteware weergawe 15.1 is gebruik om die verband tussen elke NG en die mediaan Cmax van PAS, APAS en GPAS aan die hand van die Spearman-rangkorrelasie te meet. Statisties betekenisvol is gestel as ʼn Pwaarde onder 0.05. Resultate: Die ontwikkelde metode het sukses getoon in die toets van APAS, GPAS en PAS in ʼn enkellopie van 4 minute. ʼn Groter interindividuele veranderlikheid is waargeneem in die Cmax, wat gewissel het van 40.42 tot 102.41 mg/L vir PAS, en 10.00 tot 22.36 mg/L en 3.90 tot 9.45 mg/L vir onderskeidelik APAS en GPAS. Die VAS-data het getoon dat 26 pasiënte bewyse van GI-intoleransie getoon het, maar die meerderheid van hierdie tellings het trosvorming om nul getoon. Maagpyn en -krampe is gevind om statisties meer gereeld voor te kom by die regimen van 4 g twee keer per dag as dié van 8 g een keer per dag [0.14(0 – 0.59) teenoor 0(0 – 0.08); mediaan (IQR); p = 0.018]. Statisties betekenisvolle inverse verbande is waargeneem tussen onderskeidelik APASkonsentrasies en opgeblaasdheid (rho = -0.448; p = 0.025) en diarree (rho = -0.407; p = 0.044) vir die dosis wat twee keer per dag toegedien is. Dieselfde inverse verband is gevind vir GPAS-konsentrasies en diarree (rho = -0.412; p = 0.041). Gevolgtrekkings: Plasmakonsentrasies van metaboliete APAS en GPAS het nie ʼn verband getoon met die voorkoms van NG’s nie. In teendeel, die data het getoon dat hoër plasmakonsentrasies van APAS en GPAS verband gehou het met laer tellings NG’s, wat statisties betekenisvolle verhoudings was, maar as klinies onbeduidend geag is. Verdere studie met ʼn groot populasiegrootte is moontlik nodig om die ware uitwerking van metabolietvorming op die teenwoordigheid van GI-ongemak tydens behandeling met PAS te bepaal.