Thesis (M.Sc. in Pharmacy)--Chulalongkorn University, 1990

This research study was proposed to compare the rate and extent of absorption of the local manufactured brands of 100 mg doxycycline capsules relative to the original brand, VibramycinR, according to both the in vitro and in vivo results. The disintegration time and dissolution rare of doxycycline capsules were determined from the in vitro studies. All eight brands studied met the United State Pharmacopoeia XXI specification. Four brands of doxycycline capsules which showed the differences in their dissolution rate constants were selected for bioequivalent study in 20 Thai healthy male volunteers, age ranged from 18 to 24 years. The 100 mg single dose of doxycycline capsule from four selected brands was administered to individual overnight fasted volunteer following a complete crossover design. Blood samples of every subject were collected before the administration of a drug and immediately after drug administration up to 33 hours. Plasma samples were separated and doxycycline levels were determined using a high performance liquid chromatographic technique. The innovator’s product (brand A) significantly (p < 0.05) showed the lower of extent of doxycycline absorption than those from the local manufactured products (band B, C, D) while the rate of drug absorbed into the body was not different. There were no statistically significant linear correlation between the disintegration time and the dissolution rate constants. Also no correlation between the in vitro and the in vivo parameters (AUC o t, AUC o ∞ and Cpmax) were observed (p > 0.05). The mean peak plasma doxycycline concentrations were ranged from 1.53 to 2.15 µg/ml and the time to peak level ranged from 1.55 to 2.25 hours. The mean biological half-life of doxycycline in Thai male was 15.09 (12.88-16.67) hours which was similar to the other previously reported.