Pharmacokinetics: Permeation of physiological membranes
(Absorption, distribution)
. Plasma protein binding
. Volume of distribution
Pharmacodynamics: Target recognition
. Target affinity
. Target specificity
The aim of the present study is to determine the distribution coefficient of the given drug in different pH mediums.
MATERIALS AND METHODS:
Apparatus: 10 ml volumetric flasks, beaker, pipette (10 ml), spatula.
Chemicals: 0.2 M Sodium hydroxide, 0.2 M boric acid, 0.2 M potassium hydrogen phthalate, 0.2 M hydrochloric acid, 0.2 M potassium chloride, distilled water, test drug.
Instruments: Weighing Balance, JASCO UV-Visible Spectrophotometer, pH meter.
PREPARATION OF AQUEOUS PHASES:
20 ml of different pH media of pH 1.2, 4.8, 7.4 and 10 were prepared.
Hydrochloric Acid Buffer: Place 50.0 ml of the 0.2 M potassium chloride in a 200-ml volumetric flask, add the specified volume of 0.2 M hydrochloric acid and then add water to volume.
Neutralised Phthalate Buffer; Phthalate Buffer: Place 50.0 ml of 0.2 M potassium hydrogen phthalate in a 200-ml volumetric flask, add the specified volume of 0.2 M sodium hydroxide and then add water to volume
Phosphate Buffer: Place 50.0 ml of 0.2 M potassium dihydrogen phosphate in a 200-ml volumetric flask, add the specified volume of 0.2 M sodium hydroxide and then add water to volume.
Alkaline Borate Buffer: Place 50.0 ml of 0.2 M boric acid and potassium chloride in a 200-ml volumetric flask, add the specified volume of 0.2 M sodium hydroxide (Table 3) and then add water to volume.
Preparation of pre-saturated liquid system:
Four Biphasic systems were prepared in with chloroform and the above-mentioned pH media. They were prepared by taking equal volumes (10 ml) of the aqueous and non-aqueous phases. They were kept for presaturation for 24 hrs on a rotary flask shaker.
Preparation of Primary Stock:
30 mg of drug was accurately weighed and dissolved in 10 ml of methanol:water (7:3) to get a concentration of 3mg/ml stock solution.
Preparation of drug solution in different pH media:
- 1 ml from the stock solution was added in the aqueous phase of each system .
- Absorbances were noted down after proper dilutions at the wavelength of 296 nm.
- Again both the aqueous and non-aqueous phases were mixed and kept for 24 hrs on rotary flask shaker.
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At 24th hour the aqueous and the non-aqueous phases were seperated
- The absorbances were taken for aqueous phase.
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The concentration in the non-aqueous was calculated using CO – C24 where CO and C24 are the concentration of the drug in aqueous phase at 0 and 24 hours respectively.
- All the concentrations were back calculated using the calibration equation.
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The distributon coefficient was calculated using D= CO – Ct/Ct where CO and Ct are concentration of the drug in aqueous phase at zero and time t hours respectively.
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Log D was calculated and a graph was plotted taking pH on x-axis and log D on y-axis.
Calibration Curve at 296 nm. (Conc. and Mean Absorbance)
Regression equation y=0.026x + 0.027
RESULTS & DISCUSSION:-
Concentrations at different pH were back calculated from the calibration curve equation and multiplied with the corresponding dilution factor to get the actual concentration.
The value of log D was found to be maximum (0.598) at a pH of 1.2.
At physiological pH, the value of log D was found to be 0.048.