[Loading-doses of carbamazepine and diphenylhydantoin: use in high-risk patients]

Rapid Oral Loading of Carbamazepine in the Emergency Department

STUDY OBJECTIVE

This study evaluates the safety and efficacy of rapid oral loading of carbamazepine in the emergency department (ED).

METHODS

Adult patients receiving maintenance carbamazepine who presented with negligible levels received an oral load of carbamazepine suspension, with a dose of 8 mg/kg.

RESULTS

Forty-two oral loads among 36 patients were studied. Mean subject age was 36 years; 61% of the sample were male patients. The actual load administered ranged from 7.9 to 8.6 mg/kg. The mean 3-hour carbamazepine level (therapeutic 4 to 12 microg/mL) was 6.5 microg/mL (SD 2.0 microg/mL). Three patients had subtherapeutic levels after loading (successful loading rate 93%). Adverse effects occurred in 58% of patients, most commonly drowsiness (26%) and nausea (23%). Other adverse effects included dizziness, nystagmus, abdominal pain, vomiting, ataxia, and double vision. Two patients were treated for vomiting. All other adverse effects were mild and self-limited.

CONCLUSION

Rapid oral loading of carbamazepine in the ED in this cohort, although effective, was associated with a high rate of adverse effects. Given a sample size of 36, 95% confidence intervals suggest that the rate of serious adverse effects may be as high as 9.7% and that the rate of successful loading may be as low as 76.9%.

Carbamazepine kinetics in cardiac patients before and during amiodarone

Carbamazepine and amiodarone may often be used together, especially in countries where cardiomyopathies are common. In this study single doses of carbamazepine (400 mg) were given to patients with cardiac disease before and after one month of therapy with amiodarone, 400 mg daily. The kinetic profile of carbamazepine, its free fraction, and serum amiodarone, were measured at the two occasions. There was no statistically significant change in carbamazepine kinetics or free fraction, before and after the introduction of amiodarone. The concentrations of amiodarone after one month of therapy were low. It is suggested that the possible interaction in the hepatic metabolism was not demonstrated because amiodarone concentrations were not enough to inhibit carbamazepine metabolism.

Acute oral loading of carbamazepine-CR and phenytoin in a double-blind randomized study of patients at risk of seizures

The serum levels and side effects of an acute oral loading dose-schedule of carbamazepine (CBZ) divitabs [CBZ controlled release (CR)] and phenytoin (PHT) were assessed in patients at risk of seizures. CBZ-CR and PHT were administered to 42 adult patients (21 each) at a dosage of 20 mg/kg with a minimum and maximum dosage of 1,200 and 1,600 mg in patients weighting < 60 and > 80 kg, respectively. CBZ-CR was given as single loading dose; PHT was split, with two thirds of the dose administered at 0 h and one third administered 2 h later. The 24- and 36-h doses were assessed according to the nystagmus status at 24 h. Mean CBZ serum levels (percentage of subjects with level > 4 micrograms/ml shown in parentheses) were 0.0 (0%), 5.2 (62%), 6.7 (81%), 6.8 (95%), and 6.1 micrograms/ml (95%) at 0, 4, 8, 24, and 48 h after loading, respectively, and mean PHT levels (percentage of subjects with PHT level > 10 micrograms/ml in parentheses) were 0.1 (0%), 13.2 (86%), 16.3 (100%), 16.3 (100%), and 15.4 micrograms/ml (82%). One subject in the CBZ group and 3 in the PHT group vomited. Clinical effects did not differ significantly between treatment groups and are reported. Acute doses of CBZ-CR 20 mg/kg and PHT 20 mg/kg (two-thirds at 0 h and one-third at 2 h) provided therapeutic levels in most patients in < or = 4 h and were well tolerated.