Volume of distribution, time of ingestion, half life of medication, was it taken orally or parenterally, etc, etc, would need to be known.

Also whether this was dose 1 or if there were multiple doses.

But the equations only apply to live people. After death, considerable changes can occur - Some drug concentrations go up, some go down, it’s not exactly predictable.

That being said, I haven’t really used pharmacokinetics and pharmacodynamics for years. Did you ask the person who performed the autopsy?