Various methods can be used for the release studies of drugs from suppositories, including beaker method, basket method, membrane diffusion method, dialysis method and flow-through cell method [1]. Among those the pharmacopoeial (Ph. Eur.) flow-through cell is probably the most useful although published data on its feasibility are rather scarce.

The aim of this study was to investigate the influence of lecithin on the release rate of paracetamol from suppositories.

The suppository was placed in the cell with a temperature sensor, the apparatus was thermostated at 37 ± 0.1 °C, the flow rate of an acceptor medium (phosphate buffer pH 7.3) was 1.7 ml/min. Samples were collected at: 0.5; 1; 1.5; 2; 3; 4 and 5 h. The concentration of drug in the dissolution medium was analysed using spectrophotometry and first derivate spectrophotometry.

The test was carried out on six suppositories from each formulation. The preliminary test was performed for two commercially available products, with and without lecithin. Much slower paracetamol release was found from the product A containing lecithin than from the product B containing another surfactant: after 4 h the dose released was 16 % and 98 %, respectively. In the second step of investigation comparison between two different formulations containing 125 and 500 mg of paracetamol confirmed that the addition of 2% lecithin decreased the rate of drug release from suppositories. It was observed that for the suppositories containing 500 mg paracetamol, with and without Lipoid S-100, after 4 h the release of the drug was 37 % and 97 %, respectively. For 125 mg paracetamol the dose released after 0.5 h was 24 % (with lecithin) and 45 % (without lecithin).

The flow-through cell method shows the differences in release profiles of paracetamol depending on the presence of lecithin, an excipients often used in commercial preparations. It is demonstrated that lecithin significantly decreases drug release rate from fatty base suppositories.

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