Using an original high-pressure liquid chromatographic assay, we measured serum levels of metoclopramide and defined a concentration-response relationship for metoclopramide control of cisplatin-induced emesis. Using a metoclopramide regimen of 2 mg/kg body weight intravenously every 2 hours for four doses, we found that serum levels greater than 850 ng/mL immediately before the third dose were associated with complete control of emesis (less than three episodes) in 78% of patients and partial control (three to five episodes) in 18%. No patient with levels less than 850 ng/mL had complete control of emesis; only 42% had partial control (p less than 0.001). Increases in dosage for patients with low levels and poor responses improved control in four of five patients. Elderly patients had drug levels similar to those of young patients but had fewer episodes of emesis (p = 0.044), suggesting that elderly patients have increased sensitivity to this drug. The metoclopramide dose can be raised up to 2.75 mg/kg with an improvement in emetic control in patients who have an inadequate response to doses of 2 mg/kg and no toxicity.
To better understand the use of narcotic analgesics, the hydromorphone concentration was measured in serum samples from 43 patients with chronic severe pain who were receiving this drug. At the time of blood sampling, pain intensity, mood, and cognitive performance were assessed. There was large individual variation in the dose-drug level relationship. Seven patients with bone or soft tissue pain and drug levels of greater than or equal to 4 ng/ml had good pain control, whereas 10 did not. None of 15 patients with levels less than 4 ng/ml had pain control, despite drug doses similar to those given patients with higher levels. Thus 60% of the patients without control of their pain had hydromorphone levels below the lowest level that produced pain control. No patient with pain from nerve infiltration or compression had good pain control, irrespective of the drug level or dose. Poor mood correlated with high pain intensity and low drug level. Impaired cognitive performance was not related to drug level. Knowing that there is a low concentration of narcotic in the blood of a patient with chronic severe pain who is receiving high drug doses and who shows lack of both efficacy and side effects may reassure health care professionals that further narcotic dosage escalation is appropriate.
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