US FDA wants to reclassify co-crystals to ease regulatory burden

By Gareth Macdonald

- Last updated on GMT

Image: iStock/v_alex
Image: iStock/v_alex

Related tags Good manufacturing practice Current good manufacturing Pharmaceutical drug Pharmacology Fda

The US FDA wants to reclassify pharmaceutical co-crystals as solvates rather than intermediates to reduce the regulatory burden on manufacturers that work with them.

Pharmaceutical co-crystals are composed of two or more different molecules, typically an active pharmaceutical ingredient (API) and an excipient.

Under current guidelines​ – introduced in April 2013 - such mixtures are defined as product intermediates or in-process materials.

cGMP requirements

In theory, the non-API component of a co-crystal can be modified to tweak drug process-ability, stability or bioavailability.

However, according to the US Food and Drug Administration (FDA), drug companies have been reluctant to work with them as a result of the strict current good manufacturing practice (cGMP) requirements that must be met when working with in-process materials.

In a commercial setting, co-crystals are typically manufactured in drug substance facilities. However, when classified as a drug product intermediate, additional current good manufacturing practice requirements (CGMPs) apply to co-crystals.

As a result of this classification”​ the agency continued, adding that “the [current] guidance was not conducive to the development of co-crystals by industry.”


To address this, the US Food and Drug Administration (FDA) said it wants to reclassify co-crystals as a special class of solvates in which the second component is non-volatile.

The idea – detailed in new draft guidelines​ this week – would free manufacturers of the additional cGMP requirements applied to intermediates and instead mean they have to meet those applied to API polymorphs according to the FDA.

It said “A co-crystal with a pharmaceutically acceptable conformer…can be considered to be a pharmaceutical co-crystal and has a regulatory classification similar to that of a polymorph of the API.

Specifically, it is not regarded as a new API. From a regulatory perspective, drug products that are designed to contain a new co-crystal are considered analogous to a new polymorph of the API.

It added that: “A co-crystal that is composed of two or more APIs (with or without additional inactive coformers) will be treated as a fixed-dose combination product and not a new API.”

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