An in vitro study of the quality of essential drugs available on the rwandan market

II.5 Paracetamol formulations

II.5.1 Material and equipment

Material

· Cetamol 500 mg tablets (Regal pharmaceuticals, Kenya)

· Panadol 500 mg tablets (SmithKline Beecham, Kenya)

· Saramol 500 mg tablets (S&R Pharmaceuticals, Rwanda)

· Paracetamol (Ludeco, Belgium)

· Potassium dihydrogen phosphate (Vel, Belgium)

· Sodium hydroxide (Acros Organics, Belgium)

· Methanol-HPLC quality (Biosolve B, The Netherlands)

All chemicals and reagents were at least of analytical grade.

Equipment

· Incubator: U-60 (Memmert, Analis, Namen, Belgium)

· Column: Lichrospher 100 RP-C 18 e (5um), 250X4 mm

(Merck-Hitachi, Darmstadt, Germany)

· Detector: L-7400 UV detector (Merck-Hitachi, Darmstadt, Germany)

· Pump: L-7100 pump (Merck-Hitachi, Darmstadt, Germany)

· Integrator: D-7000 integrator (Merck-Hitachi, Darmstadt, Germany)

· Software Package `HPLC System Manager'

(Merck-Hitachi, Darmstadt, Germany)

· Lambda 12 UV/VIS Spectrophotometer

(Perkin Elmer UV/VIS, Perkin Elmer, Norwalk, USA)

· Dissolution equipment (VK 7000, Vankel Technology, Cary, NC, USA)

II.5.2 Quantitative drug analysis

5.2.1 Methods

The amount of paracetamol and the dissolution rate for each formulation was determined using the method described in USP 24.

· Mobile phase

A degassed mixture of distilled water and methanol (75:25) was used as mobile phase.

· Standard preparation

An accurately weighed quantity of paracetamol (100 mg) was dissolved in mobile phase to make a 100 ml solution having a concentration of 1 mg/ml. From that solution 200 ul was diluted to 20.0 ml, and a resulting solution (0.01 mg/ml) was used as standard solution.

· Sample preparation

From each formulation, 10 tablets were weighed and finely powdered. An accurately weighed portion of powder, equivalent to 100 mg of paracetamol was diluted with mobile phase to make 100 ml of mixture, which was filtered through a 0.2um cellulose acetate filter (Sartorius, Goettingen, Germany). From the filtrate 1 ml was diluted to 100.0 ml with mobile phase.

· Chromatographic conditions

Flow rate : 1.5 ml/min

Detection wavelength : 243 nm

Injection volume : 20 ul

Temperature : Room temperature

· Calibration curve

A calibration curve (peak area vs. concentration) y = 94199 (1687) x - 16441 (2852) with a correlation coefficient (R²) of 0.9998 (0.0002) (n = 3) was constructed using standard solutions from 4 to 40 mg/l.

The precision of the method was determined by calculating the relative standard deviation (within a day and within three days) of the peak area responses after repeated injections (n =3) of a paracetamol standard solution (20 mg/l).

· Procedure

Equal volumes of standard and assay preparations were separately injected, the chromatograms were recorded, and the major peak integrated.

The drug quantity, Q, (in mg of paracetamol in the portion of tablets taken) were calculated by the formula:

Q = 10.000C( r_u/r_s)

Whereby C is the concentration (mg/l) of the standard preparation, r_u and r_s are the paracetamol peak responses obtained from the assay preparation and the standard preparation, respectively.

· Stability testing

A part of the tablets was stored in a sealed box above a saturated solution of sodium chloride (RH 75 5 %). This box was placed in an incubator maintained at 40 2°C. After 3 and 6 months, tablets were withdrawn from the incubator and evaluated for dissolution rate and their content in active ingredient.