Clinical Pharmacology

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This division was known as Pharmacology until 27 June 2013.

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Browsing Clinical Pharmacology by Subject "Aminosalicylic acid"

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    Pharmacokinetics of twice-daily versus once-daily dosing with granular slow-release para-aminosalicylic acid in adults on second-line anti-tuberculosis and antiretroviral treatment
    (Stellenbosch : Stellenbosch University, 2013-12) De Kock, Lizanne; Rosenkranz, B.; Diacon, A. H.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Medicine. Clinical Pharmacology.
    ENGLISH ABSTRACT: Background: Para-aminosalicylic acid (PAS) is one of the first effective anti-tuberculosis agents and has become one of the principal second-line drugs to treat patients with an extended resistance spectrum. Despite being one of the oldest anti-tuberculosis drugs, little data is available regarding its pharmacokinetics, drug interactions, genetic factors and dosing regimens, especially for the relative new granular slow release PAS (GSR-PAS) preparation. Objectives The aim of the study was to investigate the pharmacokinetics, tolerability and safety of a single 8 g once- or 4 g twice-daily GSR-PAS dose in a multidrug- or extensively drug resistant tuberculosis (M/XDR-TB) population, in which some subjects were also co-infected with the human immunodeficiency virus (HIV). An additional objective was to investigate the potential covariates (i.e. genetic factors and drug interactions) that can alter the pharmacokinetics of PAS. Study design and methodology A randomised, two-period, open-label cross-over study was conducted in 32 adults (≥18 years old) with M/XDR-TB admitted at Brooklyn Chest Hospital, Cape Town, South Africa and treated for drug resistant tuberculosis with a multidrug regimen containing GSR-PAS. The subjects were randomised to follow a single 8 g once-daily GSR-PAS regimen or a 4 g twice-daily GSR-PAS regimen for 8 days. On the eighth day blood samples were obtained at 0, 1, 2, 3, 4, 6, 8, 12 and 24 hours. After the 24-hour sample (Day 9) the regimens were crossed-over. The tolerability and safety of the two regimens were determined using Visual Analogue Scales and interviews. PAS plasma concentrations were determined by a developed HPLC-MS/MS method. N-acetyltransferase (NAT1 and NAT2) genotyping was performed. The data of this study together with unpublished data of a previous study in a very similar population were used in a pharmacometric analysis to determine the PK parameters and any subject covariates. Results and Discussion In comparison to the 4 g twice-daily GSR-PAS dose, the single 8 g once-daily GSR-PAS dose generated a pharmacokinetic profile with a significantly higher maximum concentration (Cmax), concentration at 12 hours (C12) and area under the curve 0 to 12 hours (AUC12). The concentrations of all subjects on the twice-daily regimen were maintained above a minimum inhibitory concentration (MIC) throughout a 12-hour interval, while the single 8 g dose was able to sustain the PAS plasma concentrations above the MIC in 18 out of 29 subjects (62.1%) for the entire 24-hour dosing interval. Both regimens were reasonably well tolerated but most subjects preferred the twice-daily dosing. The clearance of PAS was increased by 45% in HIV positive subjects prescribed antiretroviral treatment (ART), possibly due to interaction with efavirenz (EFV). No significant associations were found for any of the individual NAT1 or NAT2 genotypes, but a difference between mean concentrations of the different genotypic groups was reported. Conclusions The 8 g once-daily dose has the potential to be included in future regimens. The higher peak concentrations achieved can be expected to increase the bactericidal effect of GSR-PAS without significant loss of bacteriostatic effect, i.e. time over MIC. The 8 g once-daily dose has a reasonable tolerability and is potentially easier to supervise in an outpatient setting. Since antiretrovirals (ARVs) increase PAS clearance and decrease PAS exposure in HIV co-infected subjects on ART, the 8 g once-daily dose will be less suitable for maintaining bacteriostasis in these patients (inadequate PAS exposure). Therefore, PAS and ARV interactions need to be clarified before the 8 g once-daily dose can be recommended for the HIV co-infected patients on ART.