EFFECTS OF CHLORPHENIRAMINE ON THE PHARMACOKINETICS OF ASCORBIC ACID IN HEALTHY MALE VOLUNTEERS

ABSTRACT

Ascorbic acid is a vitamin commonly used in the treatment of common cold and scurvy. It interacts with some drugs during absorption from the gastrointestinal tract, in the systemic circulation or during metabolism in the liver. However, interaction between ascorbic acid and chlorpheniramine has hitherto not been reported.

Six healthy adult male volunteers took part in this research. The average age of the volunteers is

24.33 ± 0.71 years and average weight of 64.83 ± 1.08 kg. The six healthy male volunteers were given 200 mg oral ascorbic acid only, during the control study. They received 200 mg ascorbic acid and 4 mg chlorpheniramine after a wash out period of two weeks through the same route. Urine samples collected in a plastic covered tube were analyzed for ascorbic acid levels by colorimetric method. A standard calibration curve was prepared by making five different concentrations of standard ascorbic acid each made to a total volume of 2mL. The concentrations were 0.01, 0.02, 0.03, 0.04, and 0.05 mg/mL. Absorbance was obtained using a colorimeter set at 520 nm. A plot of absorbance against standard ascorbic acid concentration resulted in a straight line with correlation coefficient of 0.98.    The concentrations of the tests samples were obtained by interpolation of the calibration curve.

The pharmacokinetics parameters were generated from the urine levels of ascorbic acid excreted against time curve and rates of ascorbic acid excretion against average time intervals profile.

The apparent volume of distribution Vd, and total body clearance CLT decreased significantly (p<0.05) in the tests when compared with the controls. However, the area under the curve AUC0-

∞ increased significantly from values obtained in the control. In fact, the increase in AUC0-∞ was about 2-3 fold. The elimination half life t1/2(b) similarly increased (p< 0.05). There was little but

statistically insignificant increase in renal clearance CLR, fraction of drug excreted fe, and bioavailability fraction F.

In conclusion, it was observed that chlorpheniramine co-administration altered the volume of distribution, total body clearance, area under the curve, and elimination half- life of ascorbic acid tablet. The results from this study, implies that chlorpheniramine reduced the amount of ascorbic acid available to the body tissues for utilization and storage. Such concurrent administration should therefore be discouraged.