Pharmacokinetic study of doxycycline polyphosphate (PPD), hydrochloride (CHD) and base (DB)

Six healthy volunteers received the same oral dose of doxycycline, base (200 mg). Each received two of the three preparations at two-week intervals. Experimental results were interpreted on the basis of one or two-compartment models. The three preparations gave the elimination constants of the same order of magnitude (0.045 h-1 to 0.051 h-1). The plasma half-life t 1/2 beta was 14.143 h for DP, 15.400 h for DHC and 13.588 h for DB. Vd is higher for DB (91.955 L) than for DPP (73.401 L) and DHC (64.827 L). Total plasma clearance is 52.767 ml/min for DPP, 48.728 ml/min for DHC and 60.174 ml/min for DB. Urinary elimination 72 hours after administration is 29.24% for DPP, 35.60% and 28.15% for DB. Fluorimetric analysis of some of the samples confirmed the values obtained, with the exception of a few parameters such as Vd and clearance, which were lower. This may result from the fact that this method of determination is more broadly responsive, and is not limited to the evaluation of the active fraction. Relative bioavailability of the capsule form of DPP is 111.15% of that of DHC.