Comparison of intraosseous versus intravenous loading of phenytoin in pigs and effect on bone marrow

Review article: phenytoin use and efficacy in the ED

This article reviews the evidence regarding the use of phenytoin in adult and paediatric patients experiencing seizures in the ED in Australasia, including relevant pharmacokinetics, dosage, therapeutic drug monitoring and methods of administration. It summarizes current evidence regarding the use of phenytoin in a number of seizure types commonly seen in ED. A search of Medline, Embase and Cochrane was performed using appropriate keyword and MeSH headings. A loading dose of phenytoin should be given to phenytoin naïve patients for the emergency treatment of seizures; parenteral administration results in therapeutic concentration sooner than oral administration but is associated with more frequent and significant adverse effects. Diluting phenytoin is safe but there is limited evidence regarding adverse effects of diluted phenytoin; a filter is probably not needed. Free phenytoin concentrations correlate best with antiseizure efficacy. Phenytoin is used in the treatment of status epilepticus although evidence here is limited; it may also be given to prevent early post-traumatic seizures. It should not be given to treat or prevent eclamptic or alcohol-related seizures. There is insufficient evidence regarding its use in preventing febrile convulsions, treating or preventing seizures due to space occupying lesions or intracerebral haemorrhage and thrombosis. In conclusion, phenytoin is appropriate for treatment of some seizures seen in the ED; it is associated with significant adverse effects; trials are ongoing regarding the use of other anticonvulsants in the treatment of status epilepticus.

Comparison of plasma levels and pharmacodynamics after intraosseous and intravenous administration of fosphenytoin and phenytoin in piglets

OBJECTIVE: To compare plasma drug levels and pharmacodynamics of fosphenytoin or phenytoin when given intraosseously or intravenously in doses relevant to children. DESIGN: Prospective controlled randomized study. SETTING: University hospital animal laboratory. SUBJECTS: A total of 40 mixed-breed piglets (age, 4-6 months; weight, 20-40 kg). INTERVENTIONS: The animals were anesthetized, after which they underwent intubation, instrumentation, and mechanical ventilation. A central venous catheter and an arterial catheter were placed for monitoring and blood sampling. A peripheral intravenous catheter with a 15-gauge intraosseous needle was inserted for drug infusion. A total of 40 animals (ten per group) were randomly assigned to receive intravenous or intraosseous phenytoin or fosphenytoin infusions. Phenytoin (20 mg/kg) was infused over 20 mins, and fosphenytoin (20 mg phenytoin equivalent kg) was infused over 7 mins. All infusions were followed by the administration of a 5-mL normal saline flush. MEASUREMENTS AND MAIN RESULTS: Blood samples (3 mL) were drawn for use in determining drug levels before infusions (baseline) and 0, 5, 10, 15, 20, 30, 40, 50, 60, and 75 mins after the infusion had been completed. Repeated measures of analysis of variance were used to evaluate statistical significance (p <.05). Phenytoin levels were undetected at baseline. Free (10 to 20 &mgr;g/mL) and total (80 to 110 &mgr;g/mL) phenytoin levels were well above the therapeutic range (free, 1 to 2 &mgr;g/mL; total, 10 to 20 &mgr;g/mL) after infusion in the animals that received fosphenytoin. Significant differences in values were seen in free phenytoin levels at 0 to 10 mins (p <.05) and in total phenytoin levels at 0 to 20 mins (p <.05) between intraosseous phenytoin or fosphenytoin administration. Similar differences were also seen when piglets that received intravenous phenytoin were compared with those that received intravenous fosphenytoin. From 20 to 75 mins, all groups had free and total levels within the therapeutic range. There were no significant differences among heart rate and blood pressure in the groups. CONCLUSION: There is no need to adjust standard drug doses of phenytoin when given intraosseously. The initial high levels of phenytoin in the fosphenytoin groups are of concern because neurologic toxic effects may occur in humans at those levels. Slower infusion rates of fosphenytoin may be needed to avoid toxic levels.

Pediatric use of intravenous and intramuscular phenytoin: lessons learned

First developed in 1950, parenterally administered phenytoin offered substantial advantages over parenterally administered phenobarbital and paraldehyde, which were the treatments for status epilepticus until the 1960s. During the 1950s, clinical research established the pediatric dosage of parenteral phenytoin for the treatment of seizures, which was based on the adult dosage adjusted to each child's weight. Studies in the late 1970s and early 1980s established more appropriate dosing for neonates and children on a milligram-per-kilogram basis. Scientifically derived dosing guidelines have been available only for the past 12 years. Side effects associated with parenteral phenytoin, caused primarily by its high pH level and the propylene glycol content needed to increase its solubility, were frequently reported during the 1970s and 1980s, after 25 years of clinical use. Intravenous administration of phenytoin caused burning at the infusion site and was associated with severe local cutaneous reactions following infiltration into surrounding tissue, leading to a recommendation that intravenous phenytoin be avoided in young children and the elderly. The propylene glycol solvent was linked to seizures, arrhythmia, asystole, and hepatic and renal damage. When administered intramuscularly, phenytoin is poorly absorbed and can cause hemorrhagic necrosis of the soft tissues at the injection site. Many of these side effects can be avoided in children with the use of fosphenytoin.

Status epilepticus in children. The acute management

Status epilepticus is a common pediatric emergency that may result in significant morbidity and mortality. This article provides a clinical update on generalized tonic-clonic status epilepticus in children and a practical approach to their initial stabilization and pharmacologic management. Only an organized approach to the initial stabilization and management of the child in status epilepticus will help prevent unnecessary complications and death.

Long-term local effects of intraosseous infusion on tibial bone marrow in the weanling pig model

The weanling pig model was used to determine the long-term local effects, if any, on tibial bone marrow after intraosseous (IO) infusion of resuscitation fluid and drugs at standard dosages. One of six IO treatments (two normal saline boluses [20 mL/kg]; bolus sodium bicarbonate [1 mEq/kg]; 10% sodium bicarbonate infusion at a maintenance rate for 1 hour; bolus 1:10,000 epinephrine [0.01 mg/kg]; 1:10,000 epinephrine solution infusion, 1 microgram/kg/min for 1 hour; or dopamine infusion, 10 micrograms/kg/min for 1 hour) was randomly administered via the left tibia to 18 pigs at 4 weeks of age. The animals were subsequently followed for 3 months, after which marrow from the same space and peripheral blood were examined. Marrow from the right tibia of each animal served as control; untreated historic controls were also used for comparison. Examination of the marrow revealed normal cell differentials in all limbs in all groups. Overall cellularity was somewhat decreased in the experimental limbs of the normal saline bolus group when compared with same-animal control limbs, perhaps due to the pressure effect from rapid injection. Peripheral blood counts and differentials in these and all other animals were normal. The authors conclude that IO administration of commonly used resuscitative medications does not result in significant adverse effects in the tibial bone marrow in this model.

Intraosseous administration of antibiotics: same-dose comparison with intravenous administration in the weanling pig

STUDY OBJECTIVES

To assess the reliability of the intraosseous route of administration for delivery of a loading dose of broad-spectrum antibiotics in a pediatric animal model.

DESIGN

Serum levels achieved within 90 minutes of equivalent intraosseous (IO) and IV bolus dosing of ceftriaxone, cefotaxime, and a combination of ampicillin and gentamicin were compared in the weanling pig.

SUBJECTS

Twelve female weanling pigs were studied in the Animal Facilities Laboratory at the University of Mississippi Medical Center.

INTERVENTIONS

Through a proximal tibial IO catheter, each anesthetized animal received one of the following: 50 mg/kg ceftriaxone, 50 mg/kg cefotaxime, or 300 mg/kg ampicillin followed immediately by 2.5 mg/kg gentamicin. Venous blood was obtained for antibiotic assay at 15, 30, 45, 60, and 90 minutes after IO injection. The animals were allowed to recover, and, after a one-week washout period, each received the same antibiotic and dose as before through a peripheral IV. Levels were assayed at the same intervals and IO versus IV were compared.

MEASUREMENTS AND MAIN RESULTS

Comparable serum levels of all four antibiotics were achieved by the two routes. Gentamicin levels were statistically indistinguishable IO versus IV at all assay intervals. Ampicillin and cefotaxime levels achieved by the two routes were equivalent within one hour of dosing. Serum levels of ceftriaxone after IO administration paralleled those after IV dosing but remained significantly lower at all time intervals.

CONCLUSIONS

In the weanling pig model, the IO route was used to deliver serum levels of broad-spectrum antibiotics comparable to those attained after IV administration. The data support the use of standard parenteral doses for IO administration. To overcome potential avid protein binding of ceftriaxone in the bone marrow, we recommend using ceftriaxone at its highest recommended IO loading dose. Consistent with many other medications that have been similarly tested, these data indicate that initial or empiric antibiotic coverage in hypodynamic and shock states in infants and young children need not await the establishment of traditional IV access.