What is peak and trough in medical terms?

What is peak and trough in medical terms?
Peak and trough are methods used to establish the effectiveness of a drug. Peak is drawing the serum blood levels after the drug is administered as it distributes rapidly and reaches its peak in therapeutic range.Trough is drawing the serum blood levels right before the next dose. Trough is the lowest drug level that is needed to reach therapeutic range. If trough is > than normal, the patient is at risk for adverse effects. Therefore, the doctor should expand the time interval before ordering the next dose or decrease drug dose.In general, a trough is usually drawn one hour prior to start infusion and the peak about one hour after the infusion finished. The are times when the physician orders the trough drawn immediately prior to an infusion (ie Vancomycin).