Intervening acts — third party's conduct (novus actus)

A doctor negligently prescribes a drug to a patient, causing the patient to be admitted to hospital with internal bleeding. While in hospital and recovering well, the patient is treated by a second doctor who, acting in a way that no competent doctor could possibly justify, administers a grossly excessive and plainly contraindicated dose of an unrelated medication. That second act causes a fresh and serious injury — kidney failure — which was wholly unconnected with the original bleeding and would not otherwise have occurred. The patient sues the first doctor in respect of the kidney failure.