Determination of macrolides in biological matrices by high-performance liquid chromatography with electrochemical detection

A liquid chromatographic method for the determination of macrolide antibiotics is described using a cyanopropyl column which proved to be as efficient or superior to the normally used apolar reversed-phase columns. The recovery of the macrolides from water and plasma was 80-90%. Using 0.5 ml of plasma, 30 ng/ml of clarithromycin, 50 ng/ml of roxithromycin and 10 ng/ml of azithromycin could be determined with acceptable precision and accuracy. The method has been employed in pharmacokinetic studies in humans for the determination of roxithromycin, clarithromycin and azithromycin in plasma, serum and other biological matrices. The particular selectivity of the cyanopropyl phase may also allow the simultaneous determination of erythromycin and its prodrug esters.

Bioavailability of cefpodoxime proxetil with co-administered acetylcysteine

In a cross-over study on twelve healthy volunteers cefpodoxime proxetil (CAS 87239-81-4) and acetylcysteine (CAS 616-91-1) were evaluated for possible pharmacokinetic interactions. After a standardized breakfast, the subjects received p.o. either 200 mg cefpodoxime administered as cefpodoxime proxetil (reference) or 200 mg cefpodoxime and 200 mg acetylcysteine (test). To determine the pharmacokinetic profile of cefpodoxime the plasma concentrations were determined by HPLC. The plasma concentration-time curve of cefpodoxime was very similar after both regimens, and with respect to cefpodoxime bioequivalence has been proven. The narrow range of 90% confidence intervals for the quotient test/reference for Cmax and AUC indicate reliable bioavailability of cefpodoxime proxetil independent of co-administered acetylcysteine.

Serum and cellular pharmacokinetics of clarithromycin 500 mg q.d. and 250 mg b.i.d. in volunteers

In an open-label, randomized, crossover study 12 healthy volunteers were given clarithromycin orally 250 mg twice daily (b.i.d.) and 500 mg once a day (q.d.). Blood and saliva samples were collected on study days 1 and 5 to determine the pharmacokinetics of clarithromycin and its 14-hydroxy metabolite in plasma and saliva, and to measure concentrations of clarithromycin in mononuclear cells (MNCs) and polymorphonuclear leucocytes (PMNs). The mean peak levels of clarithromycin on day 5 of therapy in serum (2.3 vs. 1.2 mg/l), saliva (1.1 vs. 0.3 mg/l) and blood cells 60 vs. 26 mg/l in MNCs and 29 vs. 14 mg/l in PMNs) were at least doubled, the trough levels were lower with 500 mg q.d. vs. 250 mg b.i.d. (0.09 vs. 0.28 mg/l in serum; 0.06 vs. 0.13 mg/l in saliva; < 1 vs. 6.8 mg/l in MNCs; 0.8 vs. 2.8 mg/l in PMNs). The mean relative peak serum concentrations of the 14-hydroxy metabolite were somewhat lower with the 500 mg dosage (0.78 vs. 0.46 mg/l). The peak concentrations of clarithromycin and its 14-hydroxy metabolite in saliva were 25-40% and 50-80% of the maximum serum concentrations with both dosage regimens. Clarithromycin exhibits good and rapid penetration into intracellular as well as into extravasal extracellular body compartments. Clarithromycin 500 mg q.d. compares favourably with 250 mg b.i.d., as far as peak serum levels and bioavailability are concerned, but trough levels are lower at the end of the 24-hour dosing interval.