Carbamazepine clearance in hemodialysis and hemoperfusion

A 47-year-old woman with endstage renal disease and dialysis-induced encephalopathy was being treated with carbamazepine for myoclonus. Her carbamazepine serum concentration appeared to be therapeutic at 5.1 micrograms/ml. She experienced a seizure while on hemodialysis/hemoperfusion that was possibly related to the removal of carbamazepine during dialysis. The elimination of carbamazepine on a dialysis day was compared with elimination on a nondialysis day. The half-life and apparent clearance were the same for each day, indicating that hemodialysis/hemoperfusion had little effect on the overall removal of carbamazepine from the body. The possible reasons for this lack of effect are discussed.

The effect of total parenteral nutrition-induced cholestasis on theophylline clearance in neonates

The effect of total parenteral nutrition (TPN) induced cholestasis on theophylline clearance was examined in premature neonates. Thirty-six neonates receiving TPN and theophylline concurrently were reviewed. Aminophylline was administered according to a standard protocol of 6 mg/kg loading dose, followed by a maintenance dose of 2.5-5 mg/kg every 12 h. Of the 36 neonates reviewed, 18 developed cholestasis (direct bilirubin greater than or equal to 1 mg/100 ml and direct bilirubin greater than or equal to 60% of total bilirubin). The remaining 18 did not develop cholestasis. The two groups were closely matched for gestational age, 5-min apgar score, and sex. The neonates with cholestasis had a mean maximum direct bilirubin of 5.19 mg/100 ml (range 1-13.8 mg/100 ml) as compared to the patients without cholestasis who had a mean maximum direct bilirubin of 0.54 mg/100 ml (range 0.3-0.8 mg/100 ml). Steady-state theophylline clearance was determined at least once a week for at least 4 separate weeks. The study lasted a minimum of 8 weeks, and if more than one theophylline clearance was determined in any given week, the mean of these clearances was used. Both groups demonstrated a significant increase in mean theophylline clearance over time (from 16.09 and 18.60 ml/h/kg to 28.65 and 24.73 ml/h/kg for the cholestatic and noncholestatic groups, respectively). The mean slope, an indicator of the average rate of change of theophylline clearance, was 1.4 for the noncholestatic group and 2.5 for the cholestatic group, indicating that the theophylline clearance for neonates with cholestasis was not significantly different from that for neonates with normal liver function (p = 0.61) over time.

Therapeutic drug monitoring in neonates: problems and issues

Therapeutic drug monitoring has been applied in several patient populations to promote safer, more effective use of drugs. The development of therapeutic ranges allows clinicians to aim for a plasma drug concentration that is usually safe and effective, and calculation of specific pharmacokinetic parameters allows selection of doses that will achieve the desired plasma concentration. This concept certainly holds true in the intensive care nursery; however, the intensity of monitoring in this setting provides opportunities for far broader applications of the information obtained from drug concentration monitoring. This review provides an overview of the complexity of and potential applications for therapeutic drug monitoring in neonates based on literature and clinical experience.

Valproic acid efficacy, toxicity, and pharmacokinetics in neonates with intractable seizures

Six neonates with prolonged, intractable seizures were treated with valproic acid (VPA). Each patient had received maximum doses of phenobarbital (greater than 40 micrograms/ml), and five patients received at least two additional anticonvulsants, without success. Seizure activity was controlled in five of six (83%) cases. In four cases, all other anticonvulsants could be withdrawn, and seizures were controlled on VPA monotherapy. VPA was discontinued in three patients because of VPA-induced hyperammonemia. VPA pharmacokinetic measurements were as follows: for total VPA, volume of distribution (V) = 0.40 l/kg (range, 0.36 to 0.47 l/kg), serum clearance (Cl) = 14.4 ml/h/kg (5.5 to 18.2 ml/h/kg), half-life (T1/2) = 26.4 hours (8.6 to 48.5); for unbound VPA, V = 2.02 l/kg (1.14 to 2.44 l/kg), Cl = 108.9 ml/h/kg (42.0 to 252.0 ml/h/kg). T1/2 = 17.6 hours (6.7 to 34.2). VPA free fraction ranged from 11.3 to 31.6% (mean, 19.2%).

Heparin dosage adjustment in patients with deep-vein thrombosis using heparin concentrations rather than activated partial thromboplastin time

In patients with deep-vein thrombosis, heparin dosage adjustment based on measurement of heparin concentrations in whole blood was compared with conventional dosage adjustment based solely on activated partial thromboplastin time (APTT) measurement. Initially, all patients were given i.v. bolus doses of heparin sodium 70 units/kg followed by continuous infusion of 16 units/kg/hr. Seventeen patients (group 1) had their initial heparin dosages adjusted according to the results of the APTT value four hours after the start of heparin therapy; subsequent adjustments were made to maintain APTT values within the therapeutic range of 1.5 to 2.5 times the patient's baseline control. Fifteen patients (group 2) had heparin dosage adjusted four hours after the start of heparin infusion, based on apparent heparin clearance using the two-point method of Chiou et al., to maintain whole-blood heparin concentrations of 0.3 to 0.6 units/mL. APTT values less than 1.5 times control occurred in about 12% of group 1 patients at 8, 12, and 24 hours and in 11 of 17 (65%) for at least one value during the study. In group 2 patients, no APTT values were less than 1.5 times control. The patients in group 2 had faster symptomatic improvement and shorter hospital stays. Heparin dosing based on measurement of whole-blood heparin concentrations and application of a practical two-point pharmacokinetic model was superior to dosing based on APTT values.

Peritoneal transport of cefonicid

The pharmacokinetic characteristics of cefonicid, a highly protein-bound expanded-spectrum cephalosporin, were examined in six noninfected, clinically stable patients undergoing continuous ambulatory peritoneal dialysis. After a 1.0-g intravenous dose of cefonicid, the mean concentrations in serum were 105 +/- 25 and 35.6 +/- 14.4 micrograms/ml at 3 and 72 h, respectively. Despite a prolonged half-life in serum of 49.7 +/- 18 h, the penetration into peritoneal fluid was low. The average concentration in dialysate over the 72-h study period was 2.7 micrograms/ml. The serum clearance was 2.6 +/- 1.0 ml/min, and the distribution volume was 0.14 +/- 0.02 liter/kg. Dosage recommendations and clinical considerations for cefonicid use in continuous ambulatory peritoneal dialysis patients are discussed.

Use of antiepileptic drugs in the elderly population

Medical records for 572 patients in two extended care facilities were reviewed to study seizure disorders and antiepileptic drug use. Seventy patients (12.2 percent) were receiving antiepileptic drugs. Of this group, 43 patients (61.4 percent) had a diagnosis of epilepsy or documented seizures, 2 were being treated for neuralgia, and 25 (35.7 percent) had no reason given for antiepileptic use. The most common cause was cerebrovascular accident (38.9 percent), and no associated etiology was found in 29.2 percent. Phenytoin was the most commonly used agent. Thirty-two (45.7 percent) were taking two or more antiepileptic drugs. Thirteen patients had had no serum concentration monitoring in the last year. Thirty-seven patients (52.9 percent) had had at least one serum concentration outside of the therapeutic range.

The effect of oral cimetidine on total and unbound serum lidocaine concentrations in patients with suspected myocardial infarction

In this study, we prospectively evaluated the effect of oral cimetidine on serum lidocaine concentrations in 6 patients with suspected myocardial infarction. Compared to baseline lidocaine levels, total lidocaine concentrations increased by 8.2 +/- 7.8% at 6 hours, 16.4 +/- 9.0% at 12 hours and 27.9 +/- 9.4% at 24 hours after two doses of oral cimetidine. Unbound lidocaine concentrations increased by 14.3 +/- 4.1% at 6 hours, and 18.3 +/- 10.3% at 24 hours after cimetidine. In patients with myocardial infarction (3), total lidocaine concentrations increased by 24.2 +/- 10.4%, whereas unbound lidocaine increased by 8.9 +/- 10.2% at 24 hours. Therefore, increases in total lidocaine concentrations after cimetidine administration were considerably less than those previously reported and empiric dosage reductions of lidocaine in patients receiving cimetidine may not be appropriate.

Interference with oral theophylline absorption by continuous nasogastric feedings

Continuous enteral feedings through a nasogastric tube is the preferred route of nutritional support for malnourished patients with inadequate spontaneous oral intake. However, in patients also receiving oral medications, the use of continuous nasogastric feedings may cause malabsorption of the drugs and consequently increase the risk of an inadequate clinical response. We report a case of an elderly patient with subtherapeutic theophylline serum concentrations and recurrent bronchospasm while receiving oral theophylline and continuous enteral feedings.

Inadequacy of FDA dosing guidelines for theophylline use in neonates

The efficacy of the FDA guidelines for theophylline dosing in newborns was evaluated retrospectively in 224 patients who had clearance data available. Mean projected post loading dose serum concentration was 4.1 +/- 1.0 mg/L in 160 patients. Mean projected steady-state concentration was 4.8 +/- 1.6 mg/L in 189 patients receiving intravenous aminophylline and 4.2 +/- 1.3 mg/L in 35 patients on oral therapy. Projected serum concentrations were subtherapeutic (less than 6.0 mg/L) in 181 of the 224 patients analyzed. There was a statistically significant difference in serum concentrations between asphyxiated and nonasphyxiated patients (p less than 0.001). There was no significant difference in mean projected serum concentrations between patients age 26-41 weeks (postconceptional age). This study suggests that the FDA dosing guidelines for theophylline in infants is inadequate and results in subtherapeutic (less than 6.0 mg/L) serum concentrations in the majority of newborns.

Effect of pharmacist intervention on control of resistant hypertension

The effect of a pharmacist's clinical intervention on blood pressure control in ambulatory adults with resistant hypertension was studied. Twenty patients of an internal medicine clinic who had diastolic blood pressures greater than 96 mm Hg on two consecutive visits and antihypertensive regimens consisting of two or more agents were entered in the study between November 1, 1980, and February 1, 1981. After asking each patient 15 questions about hypertension and its treatment, the pharmacist counseled the patient about antihypertensive therapy, obtained a medication history, and discussed diet. The patient's blood pressure was measured, and the pharmacist evaluated the appropriateness of the patient's antihypertensive regimen (based on compliance, adverse reactions, and regimen complexity) and possible reasons for the poor response to treatment. The pharmacist then recommended drug therapy to the physician; stepped care including hydrochlorothiazide, reserpine, and hydralazine was used when possible. Patients' mean age was 56 years. Most did not know the names of their medications or understand their dosage schedules. Eight patients had severe hypertension (193/124 +/- 23/4 mm Hg), five had moderate hypertension (161/109 +/- 20/2 mm Hg), and seven had mild hypertension (171/100 +/- 29/0 mm Hg). Factors contributing to poor blood pressure control were noncompliance and adverse drug effects. After five to eight months of follow-up, mean blood pressures for patients with severe, moderate, and mild hypertension were, respectively, 140/92 +/- 23/10 mm Hg, 131/92 +/- 8/6 mm Hg, and 137/88 +/- 26/3 mm Hg; the mean for each group was significantly different from baseline. In this study, pharmacists intervened successfully with patients and physicians to enhance blood pressure control through drug therapy.

Physicians' opinions of the accuracy, accessibility, and frequency of use of ten sources of new drug information

We surveyed internists, surgeons, and general practitioners in a six-county area of North Carolina to determine how accurate and accessible they believed ten sources of new drug information to be and how frequently they used each of the sources. Evaluable questionnaires were returned by 119 of the 336 physicians. The majority indicated that all sources were accessible. Commercial sources were thought to be less accurate than noncommercial sources, but were used more frequently (P less than .0002), especially by physicians who had practiced more than 15 years (P less than .02). Written sources were thought to be more accurate (P less than .0001) and were preferred over oral sources of new drug information (P less than .0004). Pharmacists and pharmacology textbooks were believed to be both accurate and accessible, but were relatively infrequently used.

Factors influencing theophylline disposition in 179 newborns

The pharmacokinetics of intravenous theophylline were prospectively studied in 179 premature babies. Interrelated variables were analyzed for their influence on theophylline serum clearance. Gestational age, gender, duration of treatment, body weight, and Apgar scores were not found to correlate significantly with theophylline clearance. Weak but statistically significant correlations were found between serum clearance and postnatal (p less than 0.005) and postconceptional age (p less than 0.01). No significant difference in mean serum clearance (Cls) values was found between small-for-gestational-age (SGA) patients (Cls = 17.9 +/- 5.3 ml/kg/h) and appropriate-for-gestational-age (AGA) patients (Cls = 18.8 +/- 5.8 ml/kg/h). Conversely, asphyxiated patients had significantly lower mean clearance values than nonasphyxiated patients (16.4 +/- 5.3 ml/kg/h vs. 20.2 +/- 5.4 ml/kg/h, respectively, p less than 0.001). Volume of distribution for theophylline (n = 147) was 0.77 +/- 0.17 L/kg; there was no significant difference in distribution volumes between asphyxiated and nonasphyxiated patients or between SGA and AGA patients. Step-wise multiple regression analysis revealed postnatal age as the most important determinant of theophylline clearance among the variables analyzed (p less than 0.01). Postconceptional age had a statistically significant association with theophylline clearance in the entire group (n = 179, p less than 0.05). Duration of treatment had a small and statistically borderline effect (p less than 0.10) on theophylline clearance among nonasphyxiated infants when age factors were considered. Analysis of covariance confirmed the statistical effects of both postnatal age and asphyxia on theophylline serum clearance.

Carbamazepine and carbamazepine-epoxide serum protein binding in newborn infants

To evaluate the serum protein binding of carbamazepine (CBZ) and its active metabolite carbamazepine-10, 11-epoxide (CBZ-E) in newborns, cord serum was obtained from 20 infants at the time of birth. Each of the samples was spiked to concentrations of CBZ 12 + CBZ-E 3 micrograms/ml, and CBZ 4 + CBZ-E 1 micrograms/ml and then subjected to analysis for total and free drug concentrations. Total drug concentrations were determined by high pressure liquid chromatography (HPLC), and free drug concentrations were determined by ultrafiltration and subsequent HPLC. The mean percentage of CBZ unbound, calculated as (free drug concentration divided by total drug concentration) X 100, was 30.6 and 29.8% at the high and low concentrations, respectively. Results for CBZ-E were 52.0 and 47.5% at the high and low concentrations, respectively. Compared with previously published values for protein binding in older children and adults, neonates appear to bind CBZ to a lesser degree and CBZ-E to the same degree. The lower binding of CBZ suggests that the therapeutic range of total CBZ in neonates may differ from that in older patients; however, this will have to be determined through clinical study. As previously demonstrated in older patients, CBZ and CBZ-E binding was variable. Monitoring of free CBZ serum concentrations in neonates appears advisable because of this variability.

Anticonvulsant therapy after neonatal seizures--how long should it be continued? I. A case for early discontinuation of anticonvulsants

The risk of epilepsy or afebrile seizures after convulsions in the neonatal period is compared with the benefits and risks of chronic use of anticonvulsants in infants. The best predictor of later seizures appears to be the presence of moderate to severe neurologic damage. In the absence of such deficits, the risk is below 10%, but increases to 50-70% when damage is severe. A comparison of reports indicates no difference in seizure recurrence rates when anticonvulsants are stopped early in the neonatal period or when treatment is longer, even in the high-risk group. After phenobarbital is discontinued and the plasma concentration falls below the therapeutic range, seizures usually recur within a few days or not for several months. Only 50% of these seizure types are expected to be controlled with phenobarbital. Long-term phenobarbital use is associated with impaired cognitive function in infants and toddlers, and retarded brain growth in rodent studies.

Hospital charges for antibiotics

Hospital charges for intravenous antibiotics were obtained in a survey of 71 hospitals in 25 U.S. cities. Only 56.3% of the hospitals used their actual drug acquisition cost to calculate patient charges; the remainder used a base price derived from one of the wholesale price guides, which often seriously overstate the cost of antibiotics. Sixty-eight percent added a markup, averaging 134.5%, and 63.4% added a dispensing fee, averaging $5.47. A relatively high-dose, single-antibiotic regimen costs patients $50-$150 per day, independent of dose-preparation charges (average, $9.09 per dose) for a piggyback-type system or intravenous line-related charges. Antibiotics were least expensive in large hospitals and in those located in the northeastern United States. Charges for antibiotics are often inconsistently calculated, vary enormously among hospitals, and may be unfair to patients and confusing to physicians. Cost-conscious prescribing of antibiotics by physicians would be facilitated by a more consistent relationship between charges and true costs.

Neonatal seizure recurrence following discontinuation of phenobarbital

The recurrence of seizures in neonates following discontinuation of phenobarbital was studied. All neonates treated for seizures in the intensive care nursery over a period of four years were followed for seizure recurrence after discharge from the hospital. Of 64 neonates treated for seizures, 50 were followed until they were at least 12 months of age. Their charts were reviewed for birth date, birth weight, gestational age, Apgar scores, age at seizure onset, seizure type, seizure etiology, duration of anticonvulsant therapy, and any neurologic deficits. Information on seizure activity and neurologic and developmental status was obtained through clinic observation or telephone interviews with parents and pediatricians. Anticonvulsant therapy was continued for 4 to 97 days; however, 85% of patients were treated less than three weeks. Those treated longer than three weeks either could not be withdrawn from anticonvulsants or were premature infants who had prolonged, severe illness. The length of follow-up ranged from 12 to 47 months, the average follow-up age being 24 months. Six patients were found to require long-term anticonvulsants because of persistent or recurring seizures. The severity of neurologic damage was a good predictor of seizure recurrence. The duration of anticonvulsant therapy in neonates should be limited to the period when the neonate is acutely ill.