Drug concentrations are not routinely required for management except in specific circumstances (see below).
In patients who are cooperative, appear to have a low suicidal intent and give a clear history, it is not necessary to do any drug concentrations (including paracetamol) of drugs they do not state they have ingested.
However, in patients who are uncooperative, have high suicidality or are unconscious it is useful to do paracetamol concentrations.
Patients who are apparently alcohol intoxicated should have a breath alcohol if possible or have blood taken for a blood alcohol concentration. Blood alcohol generally does not need to be done urgently, but it is useful to document for the drug and alcohol team. It should be done urgently if alcohol is assumed the cause of the unconsciousness. Note that alcohol generally only causes unconsciousness with concentrations greater than 150 mg/dl (0.15 mg%). An alternate cause for coma should be actively pursued if concentrations are less than this. If there is an osmolal gap blood alcohol should be measured and included in the calculated osmolality as mmol/L or mg/dL/4.3. The osmolal gap should then be recalculated after the addition of ethanol to determine whether other more toxic alcohols are also likely to be present.
Patients who present having ingested the following toxins should have concentrations done
Digoxin is the only drug for which it may be worth testing urgently in this setting. Hyperkalaemia, underlying atrial fibrillation, and coexisting tachyarrhythmias make the diagnosis more likely.