It was three different doses, 0.3, 1, and 3 mg/kg per day

It was also delivered via subcutaneous pump, which is usually done with a mind towards a gradual dosing rather than a single push of the total amount all at once.

The kind of pump listed in the article previously linked was an osmotic pump.

Here's an excerpt from a different paper describing the various methods for substance delivery:

Osmotic pumps are internally implanted devices that use an osmotic displacement system to infuse a preloaded substance into an animal. Use of these pumps permits constant dosing without the need to handle an animal after the initial implant surgery. Extracellular fluid is absorbed at a constant rate by an osmotic salt layer immediately beneath the permeable outer membrane. As the osmotic layer absorbs fluid, it swells and puts pressure on an impermeable reservoir in the center of the pump. The reservoir then expels the loaded substance from the pump at a constant rate through a flow moderator. The outflow can pass directly into the tissue surrounding the pump, or a cannula can be attached to the pump to direct the flow into a blood vessel or specific tissue.

Osmotic pumps are cylindrical in shape and come in sizes small enough for mice. These devices are surgically implanted either subcutaneously or intraperitoneally. The flow rate is fixed, and the duration of action varies from 3 d to 6 wk, depending on the size of the pump and the delivery rate selected. Pumps cannot be refilled but can be implanted sequentially to prolong dosing.

I'm not up on the dosing levels in humans, So I I don't have the ability to know offhand if 3mg/kg spread over the day is unusually high (pun partially intended) or not. There's a section I can't find easily (I'm actually dyslexic so it takes me a while to get through this kind of dense and complicated writing) where they mentioned having a higher dose as a point of comparison.