Source

Directive 2010/63/EU, Annex VIII

Administration of substances by subcutaneous, intramuscular, intraperitoneal routes, gavage and intravenously via superficial blood vessels, where the substance has no more than mild impact on the animal, and the volumes are within appropriate limits for the size and species of the animal.

Frequent application of test substances which produce moderate clinical effects, and withdrawal of blood samples (> 10 % of circulating volume) in a conscious animal within a few days without volume replacement.

Home Office (2014 a)

Injection by conventional routes, i.e. subcutaneous, intravenous, intraperitoneal or intramuscular (assuming competence of the person performing the procedure and that best practice guidelines for volume, pH, needle size, etc. are followed). Multiple injections by these routes may remain in the mild category if there are no cumulative effects.

Federal Food Safety and Veterinary Office FSVO (2018)

Single injection of small volumes s.c. and i.v. (species-specific), including repeated injections at long intervals (at least 24 hours).

I.v. or i.p. injections in sedated animals by catheter or tube and substances introduced into the body such as enemas. Implants and permanent accesses that can be created and used by means of a minimally invasive (superficial) procedure.
Examples: Repeated iv or sc injection of small volumes (species-specific). Insertion of cannulae into peripheral blood vessels. Subcutaneous injection of tumour tissue. Single subcutaneous implantations of osmotic minipumps and transponders. Subcutaneously channelled venous catheters.

Repeated injections at short intervals (several times within 24 hours). Implants and permanent accesses that have to be created by means of a deep surgical procedure or causing mild long-term constraint on an animal.
Examples: Chronic iv catheters. Duodenal infusion cannula. Hepatic portal vein catheter. Gastric tube or chronic intragastric infusion cannula. Intraperitoneal or intravenous osmotic minipumps. Gavage. Telemetry transmitters. Implanted iv catheters with pumps in a jacket worn by dogs. Implantation of indwelling catheters in ventricles of the brain, or of electrodes in the brain, if the animals retain their freedom of movement. Attachment of implants on the intact locomotor apparatus which do not cause any restriction of movement. 

Implants and permanent accesses that have to be created by means of a deep surgical procedure and causing severe long-term strain on an animal.
Examples: Attachment of implants on the locomotor apparatus or other large implants that restrict movement (e.g. dorsal skinfold chamber in mice). Implantation of catheters in the abdominal aorta or bile duct. Implantation of an arterial blood-pressure catheter in the aortic arch via the left carotid artery or in the abdominal aorta via the femoral artery. Implantation of a combination of a venous and arterial catheter.

Working Group of Berlin Animal Welfare Officers (2010)*

* With multiple applications, time must be taken into consideration!

Substance applications with short-term compulsory measures and not combined with other procedures. The substance may inflict only mild stress on the animal. Oral treatment (except gavage tubes for large animals). Intracerebral, intubation (under anaesthesia only). Local and external application at the eye, on the skin, on the mucosa.

Substance applications with short-term compulsory measures and not combined with other procedures. The substance may inflict only moderate stress on the animal. Oral treatment of large animals with use of gavage tubes. Intracardial, orbital sinus (under anaesthesia only).

Substance applications with severe restrictions on motion and not combined with other procedures.