الفهرس 
abstractOnly 14 pages are availabe for public view
 |  | from | 317 |  |  |
| | | from | 317 | | |
Abstract
Abstract
Binding of small molecule drugs to plasma proteins has a major clinical significance in-vivo for both the pharmacokinetics and pharmacodynamics of the drug. If drug exhibits low binding to serum proteins, its tissue distribution may be limited. This relationship is especially relevant to poorly hydrosoluble ligands, where binding to serum proteins enhances their solubilization and subsequent tissue distribution. However, when a drug binds to plasma proteins, the level of free drug (pharmacologically active form) may never reach the therapeutic concentration. Therefore, adjustment of dosage regimen should be considered. The binding equilibrium is often described by an association constant. Such information is useful in establishing a proper dosage regimen. The binding to human serum albumin of a new drug should be examined since competitive binding between both exogenous and endogenous substances for serum protein has been shown to be of particular significance.
Propranolol hydrochloride and diltiazem hydrochloride are two antihypertensive drugs widely used in Egypt. The work in this thesis deals with the binding of these drugs to bovine serum albumin, as well as, factors that affect the binding process. Also binding of these drugs to bovine serum albumin in the presence of competing drugs was investigated. The release of these drugs from drug-protein complex was also studied.
Hence this thesis is divided into two parts
Part I: Binding of propranolol hydrochloride to bovine serum albumin.
Part II: Binding of diltiazem hydrochloride to bovine serum albumin.
Part I
Binding of Propranolol Hydrochloride to Bovine Serum Albumin:
The experimental work in this part includes:
A) Binding of propranolol hydrochloride to bovine serum albumin
B) Release of propranolol hydrochloride from the formed drug-protein complex.
C) Binding of propranolol hydrochloride to bovine serum albumin in the presence of competing drugs
A) Binding of Propranolol Hydrochloride to Bovine Serum Albumin:
Binding of propranolol hydrochloride to bovine serum albumin was studied in isotonic Sorensen’s phosphate buffer of pH 7.4 at 25 0C using equilibrium dialysis technique. The concentration of bovine serum albumin was 2.98 x 10-4 M and that of the drug ranged from 1 x 10-5 M to 20 x 10-5 M. The results showed that equilibrium was attained after 4 hours. The equilibrium dialysis data were plotted according to Scatchard, Klotz, Scott, and Sandberg-Rosenthal plots.
Propranolol hydrochloride was found to be strongly bound to bovine serum albumin as indicated by high value of the primary association constant (K1). All plots were curved indicating the presence of more than one class of binding sites on the albumin molecule for propranolol hydrochloride. At fixed protein concentration the percentage bound drug to bovine serum albumin was inversely proportional to the concentration of the drug; increasing the drug concentration decreased the percent of bound drug. The effect of the following factors on the binding of the drug to bovine serum albumin was investigated:
1- Albumin Concentration:
Binding of the drug to bovine serum albumin was studied at different albumin concentrations namely; 1.49 x 10-4 M, 2.98 x 10-4 M, and 5.96 x 10-4 M. Isotonic Sorensen’s phosphate buffer of pH 7.4 was used to prepare the solutions of both bovine serum albumin and the drug. The binding constants K1 and K2 were found to be increased as the albumin concentration increased. Linear relation was obtained between the percentage of bound drug and the logarithm of albumin concentration.
2- pH of the buffer solution:
Binding of propranolol hydrochloride to bovine serum albumin was studied in isotonic Sorensen’s phosphate solutions of different pH values namely; 6.2, 6.6, 7, 7.4 and 8. Bovine serum albumin concentration was 2.98 x 10-4 M and that of the drug ranged from 1 x 10-5 M to 20 x 10-5 M. The binding parameters were found to be unaffected by the pH change.
3- Temperature:
Binding of the drug to bovine serum albumin was investigated at three different levels of temperatures namely; 25 0C, 30 0C, and 37 0C. The binding was found to be decreased as the temperature decreases.
4- Buffer system:
Different buffer systems namely; Walpole’s acetate buffer and Gomori’s tris buffer were used instead of Sorensen’s phosphate buffer to investigate the effect of buffer systems on the binding of the drug to bovine serum albumin. The binding parameters K1, n1, K2, and n2 were found to be affected by changing the buffering system.
5- Buffer species:
The effect of buffer species on the binding of the drug to bovine serum albumin was investigated using two acids namely; citric acid, and tartaric acid. Each of these acids was added to the external solution. It was found that the presence of either citric or tartaric acid did not affect the binding of the drug to bovine serum