Here in Australia, an oncologist is currently being accused of (although not prosecuted for) possibly killing some of his patients at one of Sydney's most well-respected hospitals and elsewhere, by deliberate under-dosing of the chemicals to be administered in Chemotherapy treatments .

Of course. What Paracelsus had to say is now a truism. Too much iron, oxygen, water, potassium, salt, and so on are all toxic. So are not enough. Most drugs have toxic blood levels. For some drugs, (Lithium is one) the margin between therapeutic and toxic blood levels is very narrow. Some drugs are entirely and necessarily toxic -- like platinum based drugs for cancer. One hopes to kill more cancer cells that healthy cells. Kill too many healthy cells, and the drug is a failure. The monoclonal antibody drugs (whose names end in '-mab' like Retuximab) can be exceedingly harsh too, in ways quite different from straight poisons.

The right dose of the right medicine at the right time for the right patient...

The pharmacopeia is bigger now than it was 50 or 100 years ago, and the medicines are potentially more lethal than before, because they attempt to intimately interfere with the finely tuned machinery inside the cell.