What counts as a medical device
A product is a medical device when it serves a medical purpose without achieving its principal intended action by pharmacological, immunological or metabolic means. Once it is a device, its risk class decides how demanding its route to market is and which documents have to be submitted.
The definition of a medical device
The Medical Device Regulation defines a medical device as an instrument, apparatus, appliance, software or material that does not achieve its primary intended action in or on the human body by pharmacological, immunological or metabolic means, but which may be assisted in its intended function by such means. In 2017 the term referred to any instrument, apparatus, software, implant, reagent, material or other article intended to be used for medical purposes that does not achieve its principal intended action by pharmacological means.
Some devices do exert a pharmacological effect, as a drug-eluting vascular stent does, but what matters for their classification is that this is not their principal mode of action.
Active medical devices are an important subclass: they depend on a source of energy or power for their action, usually electrical, such as the battery in a cardiac pacemaker.
Medical devices are a diverse group of products, from small to large, from simple to complex, and from products used every day to highly specialised and highly invasive ones. A device can be anything from a simple syringe to a new hip implant. Examples include plasters, blood bags, catheters, sutures, surgical instruments, bone cements, hip implants, stents, heart valves, CT scanners and hospital laboratory equipment.
The US definition and intended use
The FDA distinguishes medical devices from drugs: a product whose primary intended use is achieved through chemical action or by being metabolised by the body is usually a drug. Medical devices encompass nearly every medical product that does not achieve its intended purpose in either of these ways. They range from the simple, such as tongue depressors and bedpans, to the complex, such as magnetic resonance imaging machines and laser surgical devices, and from the safe, such as stethoscopes and thermometers, to the risky, such as automated implantable cardioverter defibrillators and intra-aortic balloon pumps. They include in vitro diagnostic products such as general-purpose laboratory equipment and test kits, including monoclonal antibody technology; electronic radiation-emitting products such as diagnostic ultrasound and medical lasers; and drug–device combinations such as drug-eluting coronary stents. The FDA also regulates specific mobile applications, software programs and smartphone accessories, known as software as a medical device.
A product that is labelled, promoted or used in a manner that meets the definition in section 201(h) of the Federal Food, Drug, and Cosmetic Act is regulated as a medical device. That section defines a medical device as an instrument, apparatus, implement, machine, contrivance, implant, in vitro reagent or other similar or related article, including a component, part or accessory, that is recognised in the official National Formulary or the United States Pharmacopoeia or any supplement to them, or is intended for use in the diagnosis of disease or other conditions or in the cure, mitigation, treatment or prevention of disease in man or other animals, or is intended to affect the structure or any function of the body of man or other animals, and that does not achieve its primary intended purposes through chemical action within or on the body and is not dependent on being metabolised to achieve them. The definition repeats the word intended often, emphasising that intentions cannot be underestimated in navigating the complexity of medical devices.
Unlike drug classifications, medical device classifications rely almost exclusively on the claims, or labelling, made for a product's intended use. Whether those claims are implicit or explicit, a product they label or promote in any manner that meets the definition is regulated as a medical device. So a ballpoint pen, which does not achieve its primary intended purpose through chemical action and does not depend on being metabolised, meets the definition of a medical device if its manufacturer or supplier implicitly intends it to be used as a surgical tool for leaving a mark, and it is then subject to the FDA's pre- and postmarketing controls.
Risk classes
Given the heterogeneity of medical devices on the EU single market, subjecting all of them to the same level of scrutiny during a conformity assessment is not considered practical or cost-effective, so they are stratified by a risk-based classification system that considers the vulnerability of the human body and the potential risks associated with the device. Because the dangers of devices as different as a pair of surgical scissors and an implantable heart valve are very different, four risk classes have been established: class I for low risk, class IIa for low to medium, class IIb for medium to high and class III for high. Class I represents the lowest perceived risk and class III the highest, and an implantable heart valve is a class III device. Devices are classified by a rule-based system that considers criteria such as the duration of contact, invasiveness, local against systemic effects, and the part of the body affected by the device.
The approval pathway of a device depends on its risk class and becomes increasingly demanding as the risk rises: in 2017, for class I devices scientific data were commonly not needed, while, with a few exceptions, information from clinical research studies was essential for class III devices. The risk class of a device also determines which documents must be submitted.
The four classes are also labelled low, medium, higher and highest risk. Examples of class I devices are sticking plasters, tongue depressors, thermometers, wheelchairs, corrective glasses and stethoscopes; of class IIa, endotracheal tubes, dental filling material, infusion pump syringes, devices intended for storing and transporting organs for transplant, fridges specifically intended for storing blood, surgical gloves, hearing aids and diagnostic ultrasound machines; of class IIb, x-ray machines, peripheral vascular stents, long-term corrective contact lenses, dressings for severe burns or ulcerated wounds, surgical lasers and incubators for babies; and of class III, artificial heart valves, coronary stents, cardiovascular catheters, aneurysm clips, breast implants and hip replacement systems.
One regulatory writer describes a scheme of three classes of increasing risk: class I, low risk, such as forceps and bandages; class II, moderate risk, devices that can pose a risk to human health through illness or injury, such as powered wheelchairs and hydrogel dressings; and class III, high risk, such as indwelling catheters and cardiac monitors, which are permanently implanted and whose failure can directly harm the patient.