Researchers from the University of Nottingham and spin-out company Critical Pharmaceuticals have described a new method of coating drugs that involve dissolving the polymer coatings in supercritical carbon dioxide (sCO

) which then encapsulates the drugs.

The methods were described during a presentation at the British Association for the Advancement of Science Conference in York, UK last week by Professor Steve Howdle of the University of Nottingham and chief scientific officer for Critical Pharmaceuticals.

Conventional methods of coating drugs often use high temperatures and harsh solvents which can damage delicate active biopharmaceuticals and reduce their potency.

"Many very potent new drugs based on proteins are being discovered all the time. But a major problem the pharmaceutical industry faces is that they have to be wrapped up in plastic to be delivered to the patient, so that there is controlled release of the drug over time," said Prof. Howdle.

"Many of these new proteins are fragile and are damaged by high temperatures and harsh solvents used in conventional processes."

Traces of solvents, often chloroform or benzene, can remain in the product even after drying and these can be toxic to both the patient and the environment.

In addition, these solvents require special disposal and recycling measures to prevent them escaping into the environment - adding to process costs.

The new method, removes the need for traditional solvents by using sCO

to dissolve the polymer coating used to coat the drugs.

CO

enters a state known as the 'supercritical fluid state' at modest pressures and close to room temperature. Supercritical fluids possess physical properties that lie between those of a gas and a liquid, but once the pressure is removed the fluid turns back to a gas and evaporates.

"Our process works in sCO

at close to room temperatures so the molecule is not damaged by the mixing process, and we don't use normal solvents we don't have toxic residues left behind in the product and potentially ending up in the patient," said Prof. Howdle.

Due to the low temperatures used by the technique proteins and other biologicals can be safely encapsulated into the bio-degradable polymer that is based on lactic acid, commonly used in dissolvable stitches, to encapsulate the drugs.

The polymer slowly dissolves in the body at a controlled rate and prolongs the length of time over which the pharmaceutical is released at the delivery site.

This gradual process means that the release of the drug can be controlled to continue over several weeks reducing the frequent dosing frequency which is often a drawback for biologicals that are generally administered by painful injections.

"The process allows for gradual, controlled release of a drug, reducing side effects and improving quality of life. For the patient, it could mean the end of twice-daily injections - in favour of an injection once a week," said Howdle.