Bioadhesive Gel Ensures Drug Sticks to the Problem

HARROGATE, United Kingdom -- A new type of drug delivery formulation could improve treatment of a variety of conditions, the British Pharmaceutical Conference heard this week.

Scientists at Queen's University Belfast have developed a bioadhesive gel that sticks to the site of application and then releases drug over a prolonged period. One promising use for the delivery system is antibiotic treatment of periodontal disease. In this common gum disease, infected pockets develop between the teeth and the gum, leading eventually to destruction of the bone that supports the teeth. Periodontal disease is a major cause of tooth loss in adults.

Conventional treatment can involve applying the antibiotic tetracycline, from gels or tapes, to the gum pocket. However, the antibiotic tends to be washed out by the inflammatory fluid within the gum pocket. The Belfast researchers have developed a way of ensuring that the tetracycline is not washed out. They have been working for a number of years on the development of gels that stick to the hard tissues within the pocket.

Professor David Jones, from the Belfast group, explained, "Our aim is to lock the delivery system to the place where the drug needs to be delivered. The beauty of a bioadhesive system is the prolonged contact between the drug and the site of application."

In laboratory experiments, the gel releases drug over 24 hours. But this in vitro model is designed to measure pharmaceutically how the drug is released from the gel, rather than to predict what happens clinically. From other work, the researchers estimate that one application could lead to drug release over several weeks.

The idea is that treatment would be used to cleanse the pocket of pathogenic bacteria. When that has occurred, and the pocket starts to close, treatment could be continued with conventional mouthwashes.

The research involved developing polymers with the required physicochemical properties. As well as having good bioadhesion, the formulation needed to be fluid enough to be injected but then to harden when in place in the pocket.

The optimum formulation was found to be a mix of two polymers -- poly methylvinylether-co-malaeic anhydride and polyvinyl pyrrolidone. Each of these on its own is poorly bioadhesive. However, when mixed together they form a complex with good adhesive properties.

The next stage will be to move from the laboratory to test the gel in clinical trials. The same copolymer system can be manipulated for other types of treatment and the Conference heard that another area under investigation in Belfast is delivery of antifungal drugs for treating fungal infections in the mouth. Such infections are routinely treated with gels, lozenges or solutions but the new system offers the potential of greater retention of drug at the site of infection. A bioadhesive gel containing the antifungal drug nystatin has been developed. Fungal mouth infection can be a problem in children with diabetes, in immunosuppressed patients (for example, those receiving cancer treatment) and, particularly, in patients with AIDS.

Source: British Pharmaceutical Conference

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