Once-daily and twice-daily dosing of p-aminosalicylic acid granules.

The study objective was to determine the minimum frequency of dosing for standard 4-g doses of p-aminosalicylic acid (PAS) granules. Two sequential six-patient pharmacokinetic studies are described, followed by clinical data from 40 subsequent patients. All patients had multidrug-resistant tuberculosis (MDR-TB). Serum was collected at two to three time points after dosing, and assayed by a validated high performance liquid chromatography (HPLC) assay. Data were analyzed using noncompartmental methods. In six patients, twice-daily dosing produced median serum concentrations at 4, 8, and 12 h post-dose of 25.8, 23.2, and 16.4 microgram/ml. In six patients, once-daily dosing produced median serum concentrations at 6, 12, and 24 h post-dose of 23.4, 3.7, and 0 microgram/ml. In 40 patients, twice-daily dosing produced median serum concentrations at 4 to 8 and 9 to 12 h post-dose of 24.8 and 20.6 microgram/ml. Unlike once-daily dosing, twice-daily PAS maintained serum concentrations in excess of 1 microgram/ml, the typical minimal inhibitory concentration against Mycobacterium tuberculosis, for the entire dosing interval. We now use twice-daily PAS granules for our patients with MDR-TB.