Simple Methods for the Spectrophotometric Determination of Carvedilol

Two simple spectrophotometric methods are described for the determination of carvedilol (CAR). Method A is the condensation reaction of CAR with p-dimethylaminobenzaldehyde (PDAB), and the reaction mixture exhibits maximum absorbance at 601？nm. Method B is based on the charge transfer complex formation of CAR with p-chloranil; the color developed is measured at 662？nm. The calibration graphs are found to be linear over 50.00–250.00 and 20.00–100.0？μg mL？1 with molar absorptivity values of and ？L mol？1cm？1 for CAR-PDAB and CAR-p-chloranil, respectively. Statistical comparisons of the results are performed with regard to accuracy and precision using Student’s t-test and F-test at 95% confidence level. The methods are successfully employed for the determination of CAR in pharmaceutical preparations, and the results agree favorably with the reference and proposed methods. 1. Introduction Carvedilol (1-(9H-carbazol-4-yloxy)-3-[2-(2-methoxyphenoxy)ethylamino]propan-2-ol) belongs to a group of medicines called beta-adrenergic blocking agents, that are indicated for the treatment of hypertension, angina pectoris, and heart failure. Beta-blockers work by affecting the response to some nerve impulses in certain parts of the body. As a result, they decrease the heart’s need for blood and oxygen by reducing its workload. They also help the heart to beat more regularly. CAR is used for treating high blood pressure and congestive heart failure. By blocking the receptors, CAR reduces the heart’s rate and force of contraction and thereby reduces the work of the heart. CAR also blocks adrenergic receptors on arteries and causes the arteries to relax and the blood pressure to fall. The drop in blood pressure further reduces the work of the heart since it is easier to pump blood against a lower pressure. The FDA first approved CAR in 1995 [1]. Many methods have been used for the determination of carvedilol such as HPLC [2–7], capillary electrophoresis [8], fluorometry [9], and differential pulse voltammetry [10]. Recently a second polymorph of carvedilol has also been reported [11]. The two spectrophotometric methods [12, 13] reported earlier for the determination of CAR are in the UV region, and it is well known that UV-spectrophotometry is not a selective method, and therefore excipients can interfere with the method. The other three methods [14, 15] involve reaction of CAR with reagents like bromocresol green, ninhydrin, acetaldehyde, and nitroprusside. A comparison of the performance characteristics of the reported methods and proposed methods is given in Table 1.