ABSTRACT
BACKGROUND: Despite several decades of use of calcium channel blockers, the side effect of edema persists as a class effect, and its mechanism is unresolved. Amlodipine has effects on hemorheology (HR), and its hemodilutory property may partly contribute to its antihypertensive action. This aspect is not well studied, and the literature is sparse in this regard. OBJECTIVE: This experiment was planned to determine effect of a single-dose administration of amlodipine on HR parameters in normal human volunteers. METHODS AND RESULTS: Amlodipine (5 mg) or S (-) amlodipine (2.5 mg) was administered to 27 normal human volunteers. Whole-blood viscosity (WBV) at different shear rates, plasma viscosity (PV), red cell rigidity (RCR), red cell aggregation (RCA), hematocrit (Hct), plasma hemoglobin, along with plasma drug concentration were determined at time intervals, t = 0, 4, 8, 12, and 24 h. Statistically significant reductions were observed at tmax = 4 h in WBV at shear rates of 0.512 s-1 (p < 0.005), WBV at shear rates of 5.26 s-1 (p < 0.01), PV (p < 0.05), and Hct (p < 0.01). At t = 8 h, as drug concentration reduced, some of the changes persisted and later slowly decreased with the decreasing drug concentration till t = 24 h. Red blood cell-related parameters such as RCA and RCR remained unaltered. WBV values at all shear rates, when corrected for Hct = 0.45, did not show deviation from their original values at any time. CONCLUSIONS: Amlodipine causes a reduction in Hct and blood viscosity, along with hemodilution. These effects persist as long as the drug remains in plasma. Edema resulting from chronic dosing may be explained by the aforementioned effects. It is possible that antihypertensive action of the drug may be due to a combination of vasodilatation and an improvement in the HR properties.
Subject(s)
Amlodipine/administration & dosage , Blood Viscosity/drug effects , Edema/blood , Erythrocyte Aggregation/drug effects , Hypertension/drug therapy , Calcium Channel Blockers/administration & dosage , Dose-Response Relationship, Drug , Edema/drug therapy , Edema/etiology , Healthy Volunteers , Hematocrit , Humans , Hypertension/blood , Hypertension/complications , Male , Single-Blind Method , Treatment Outcome , Young AdultABSTRACT
OBJECTIVE: To assess the bioavailability of rifampicin (RMP) in three brands of combination formulations of anti-tuberculosis drugs. DESIGN: A three-way double-blind, cross-over bioavailability study of RMP and isoniazid (INH), consisting of a comparison of a two-drug combination of tablets of RMP and INH each separately (reference brand R) and a tablet of RMP + INH (brand N), and a capsule of RMP + INH (brand L) was carried out in 12 healthy male volunteers. Coded plasma samples were analysed for levels of RMP as well as INH and acetylisoniazid (ACINH) by two high performance liquid chromatography (HPLC) methods. RESULTS: The mean values of RMP in brand N (Cmax 6.49+/-0.52 microg/mL, Tmax 2.33+/-0.18 h, AUC(0-24h) 39.83+/-3.44 microg/mL.h) were comparable with those obtained with brand R (Cmax 5.22+/-0.59 microg/mL, Tmax 2.50+/-0.12 h, AUC(0-24h) 33.33+/-3.47 microg/mL.h). The mean values of RMP in brand L (Cmax 3.05+/-0.52 microg/ mL, Tmax 3.79+/-0.57 h and AUC(0-24h) 21.78+/-3.67 microg/ mL.h) were significantly different from those in brand R. Nevertheless, all of the pharmacokinetic parameters obtained for INH and ACINH in all three brands were comparable. CONCLUSION: Using brand R as a comparison, brand N was bioequivalent and brand L was not bioequivalent.
Subject(s)
Antibiotics, Antitubercular/pharmacokinetics , Antitubercular Agents/pharmacokinetics , Isoniazid/pharmacokinetics , Rifampin/pharmacokinetics , Adolescent , Adult , Antibiotics, Antitubercular/administration & dosage , Antibiotics, Antitubercular/blood , Antitubercular Agents/administration & dosage , Antitubercular Agents/blood , Area Under Curve , Biological Availability , Chromatography, High Pressure Liquid , Cross-Over Studies , Double-Blind Method , Drug Administration Schedule , Drug Combinations , Drug Therapy, Combination , Humans , Isoniazid/administration & dosage , Isoniazid/blood , Male , Reference Values , Rifampin/administration & dosage , Rifampin/blood , Therapeutic EquivalencyABSTRACT
Bioavailability (BA) of rifampicin (RMP) is a critical factor in successful treatment of tuberculosis. The BA of RMP can be reduced by pharmaceutical factors, patient factors and drug interactions. Failure of treatment and development of drug resistance are potential consequences of reduction in BA and it is necessary to understand and control the factors influencing BA of RMP.
