Pharmacokinetics of continuous infusion fentanyl in newborns

Although fentanyl administration by continuous infusion in newborns during ventilatory support has increased, pharmacokinetic data are lacking. Our objective was to determine the pharmacokinetics of fentanyl continuous infusions for sedation/analgesia in newborns who had undergone mechanical ventilation. Fentanyl was administered per routine care in seven newborns who had undergone mechanical ventilation and had normal hepatic, renal, and cardiac function. Five blood samples were collected from each newborn's umbilical artery catheter. Sample 1 was obtained at > or = 36 hours after constant fentanyl was infused, and sample 2 was collected 12 hours later. Fentanyl was then discontinued and meperidine given. Additional samples were obtained 6, 12, and 24 hours after fentanyl was discontinued. Decanted plasma was stored at -20 degrees C until gas chromatography analysis was performed. Total body clearance (TBC), elimination half-life, and volume of distribution at steady state were determined. Patient weights were 1.88 +/- 1.12 kg (mean +/- SD) with postnatal age 16 +/- 9 days; the mean gestational age was 32 +/- 4 weeks. Mean final fentanyl dosage was 1.28 +/- 0.58 microgram/kg/hr (range 0.53 to 1.9 micrograms/kg/hr). Mean elimination half-life was 9.5 +/- 2.6 hours (range 5.7 to 12.7 hours), and volume of distribution at steady state was 17 +/- 9 L/kg (range 10.1 to 30.3 L/kg). Mean TBC was 1154 +/- 494 ml/kg/hr (range 565 to 2000 ml/kg/hr). Significant correlation between postnatal age and TBC occurred (r = 0.80; p = 0.03). Newborns were hemodynamically stable during the sampling period. We found an increased volume of distribution at steady state and prolonged elimination half-life compared with single-dose administration in newborns. TBC was similar to reported values for infants and young children but was higher than for older patients.

Phenoxybenzamine placental transfer during the third trimester

OBJECTIVE

To report phenoxybenzamine placental transfer in the treatment of maternal hypertension secondary to pheochromocytoma.

CASE SUMMARY

A 22-year-old woman diagnosed with pheochromocytoma was medically managed at 33 weeks gestation with oral phenoxybenzamine and labetalol until delivery 26 days later. To determine phenoxybenzamine placental passage, at the time of cesarean section simultaneous samples were obtained from the cord blood, maternal blood, and amniotic fluid. Additional blood samples were obtained from the newborn at 32 and 80 hours of life. Mean concentrations of phenoxybenzamine from cord and maternal plasma and in amniotic fluid were 103.3, 66, and 79.3 ng/mL, respectively; the newborn's plasma concentration at 32 hours of life was 22.3 ng/mL. At the time of delivery, the 2475-g male infant exhibited perinatal depression; mild transient hypotension was also noted for the first few days of life.

DISCUSSION

The fetal-maternal plasma accumulation ratio of 1.6:1 indicates that at this gestational age after 26 days of therapy, the placental transfer of phenoxybenzamine occurs and is accompanied by accumulation in the fetal blood.

CONCLUSIONS

Because of the placental transfer of phenoxybenzamine, mild perinatal depression and transient hypotension may occur in newborns of mothers receiving this medication. These newborns must be closely monitored during the first few days of life for respiratory depression and hypotension.

Guidelines for continuous infusion medications in the neonatal intensive care unit

OBJECTIVE

To present practical guidelines in tabular form for dosage, calculation, preparation, and monitoring of common medications administered by continuous infusion to neonatal intensive care patients.

DATA SOURCES

Review articles and clinical trials were identified through a computer literature search with subsequent bibliography scanning.

STUDY SELECTION

Articles selected for review were considered important contributions.

DATA EXTRACTION

Data from human studies and review articles published in the English language were evaluated.

DATA SYNTHESIS

In emergency situations, physicians and other healthcare providers caring for critically ill newborns often perform rapid calculations to determine the dosage and rate of continuous intravenous medication infusions. Because of the crisis situation, there is the potential for calculation errors. We compiled a concise table designed to provide a standardized method for the administration of emergency medications to neonatal intensive care patients. This table must be used in conjunction with clinical judgment and each medication infusion rate must be adjusted to the patient's clinical response and individual parameters.

CONCLUSIONS

These guidelines help to minimize the volume of fluid needed for medication administration and facilitate the calculation, preparation, and timely administration of these medications, thus preventing errors that might occur in an emergency situation.

Cocaine and indomethacin: fetal anuria, neonatal edema, and gastrointestinal bleeding

A case is reported in which exposure to cocaine and indomethacin was associated with development of fetal anuria, anasarca, and neonatal gastrointestinal hemorrhage. Cocaine and indomethacin may act synergistically to adversely affect renal, cardiovascular, and platelet function. It may be prudent to obtain a drug history and urine screen for cocaine before instituting indomethacin therapy for preterm labor or polyhydramnios.