Ticarcillin-clavulanic acid pharmacokinetics in preterm neonates with presumed sepsis

The objective of the reported study was to characterize the pharmacokinetics of ticarcillin and clavulanic acid in premature low-birth-weight (less than 2,200 g) neonates with presumed sepsis. Eleven infants received 12 courses of ticarcillin-clavulanic acid at 75 mg/kg of body weight intravenously every 12 h. Blood samples were collected at 0.5, 1.5, 4, and 8 h following the infusion of the initial dose. The concentrations of ticarcillin and clavulanic acid were determined by a microbiologic assay. Median (interpatient coefficients of variation) values for the volume of the central compartment, total steady-state volume, distributional clearance, total clearance, and terminal elimination half-life for ticarcillin were 0.030 liter/kg (21%), 0.26 liter/kg (48%), 0.41 liter/h/kg (47%), 0.047 liter/h/kg (47%), and 4.2 h (45%), respectively. For clavulanic acid the parameters were 0.28 liter/kg (32%), 0.36 liter/kg (34%), 11 liters/h/kg (36%), 0.12 liters/h/kg (72%), and 1.95 h (40%), respectively. Our results suggest that the current dosing recommendations of 75 mg/kg every 12 h risk subtherapeutic clavulanic acid concentrations and that 50 mg/kg every 6 h is a more rational dosing strategy.

The role of inhaled steroids in the treatment of bronchopulmonary dysplasia

Bronchopulmonary dysplasia has been well described in premature infants requiring mechanical ventilation. Systemic steroids are one of many treatment modalities used in the management of these infants, but these agents have been associated with a number of adverse effects. Aerosolized therapy has been proposed as an alternative in order to minimize the systemic complications that occur with the parenteral route. The initial reports of inhaled steroids, although limited, have shown promising results with minimal side effects. This article addresses the mechanism of action, the role in therapy, and potential complications associated with the use of inhaled steroids in the treatment of bronchopulmonary dysplasia.

Rapid determination of maintenance heparin infusion rates with the use of non-steady-state heparin concentrations

OBJECTIVE

To compare heparin dosage adjustment using only activated partial thromboplastin time (APTT) with a method using non-steady-state heparin concentrations (HCs) to rapidly achieve and maintain an APTT ratio greater than or equal to 1.5 times baseline throughout the first 24 hours of therapy.

DESIGN

Randomized, blind, parallel comparison of an empiric dosing method based only on APTT with a dosing method based on the calculation of heparin clearance using non-steady-state HCs.

SETTING

A private community teaching hospital. The patient, physician, nurses, and investigators were blinded to the dosing method. Only the clinical staff pharmacist, who received the consult and made all dosage adjustments, was not blinded.

PATIENTS

All patients requiring heparin for the treatment of thromboembolic disease were evaluated for potential inclusion in the study. Patients were enrolled in the study if they had a clinical diagnosis of deep venous thrombosis confirmed by objective means such as venography or ultrasonography. Patients were excluded if they had active bleeding, platelet dysfunction, thrombocytopenia, severe hepatic disease (total bilirubin > 25.7 mumol/L), renal disease, or evidence of stroke. Patients were also excluded if they were receiving heparin prior to enrollment.

MAIN OUTCOME MEASURE

Maintenance of an APTT ratio greater than or equal to 1.5 times baseline throughout the first 24 hours of heparin therapy.

RESULTS

Thirty-four patients were enrolled in the study; 17 in each group. The groups were not significantly different with regard to gender, age, baseline APTT, or mean loading dose (p > 0.5). Mean initial infusion rates for the control and HC groups were 1042 +/- 194 and 1071 +/- 143 units/h, respectively (p > 0.5). After the first rate adjustment at 4 hours, the difference achieved significance at 1032 +/- 232 and 1367 +/- 317 units/h for the control and HC groups, respectively (p < 0.01). At 12 hours, 18.8 percent of the patients in the control group were subtherapeutic; by 24 hours, 33.3 percent were subtherapeutic. No patients became subtherapeutic in the HCs group during the first 24 hours.

CONCLUSIONS

This study demonstrates that, in contrast to standard heparin dosing methods, the use of non-steady-state HCs allows patients with deep venous thrombosis to rapidly achieve and maintain therapeutic APTT ratios throughout the critical first 24 hours of therapy.

Drug disposition in neonates with patent ductus arteriosus

OBJECTIVE

To review the literature on the physiologic changes created by neonatal patent ductus arteriosus (PDA) and the potential impact on drug disposition in these infants.

DATA SOURCES

An Index Medicus and bibliographic search of the English-language literature pertaining to neonatal PDA and drug usage in newborns.

DATA SYNTHESIS

PDA in premature infants is associated with a variety of physiologic changes that could alter drug disposition. Perfusion of drug-elimination organs (i.e., liver and kidney) may be diminished, resulting in decreased drug elimination. Further, the general fluid overload state associated with PDA may result in larger volumes of distribution (Vd), and dilutional effects for many drugs. Drug absorption, Vd, tissue penetration, and clearance may be affected by the physiologic changes incurred by a PDA. Although the pharmacokinetics of several categories of therapeutic agents may be affected by a PDA, disposition changes with the aminoglycosides and indomethacin have been the best documented. The most reliable pharmacokinetic change appears to be related to drug Vd. The interpretation of many of these studies is confounded by a potential drug interaction with the concurrent administration of indomethacin for PDA closure.

CONCLUSIONS

Close therapeutic drug monitoring is indicated in newborns with PDAs as abrupt changes in drug disposition can occur with PDA closure. PDA-induced changes in specific pharmacokinetic parameters of agents such as the aminoglycosides, indomethacin, and perhaps vancomycin may prove to be a valuable diagnostic adjunct for the identification of babies with undiagnosed PDA. More research into this pharmacophysiologic aspect of pharmacokinetics is warranted.

Pharmacotherapy specialty certification examination. IV. 1992 results and process modifications, including recertification. The 1992 Specialty Council on Pharmacotherapy, Board of Pharmaceutical Specialties

Certification of pharmacotherapy specialists is proceeding smoothly. Modifications to the examination process, which include reapportioning domains, offering the examination at several sites, and establishing the recertification process, have occurred. The guidelines for petitioners and structure of specialization continue to receive the attention and interest of prospective candidates, pharmacy organizations, and the BPS. To date, 674 specialists have been certified in the approved specialties: 175 nuclear pharmacists, 236 nutrition pharmacists, and 263 pharmacotherapy specialists.

Comparison of intranasal versus intravenous verapamil bioavailability

Intranasal verapamil administration may limit intrasubject variability encountered due to the metabolism differences of the d and l-isomers. We simultaneously measured verapamil/norverapamil concentrations, PR interval, heart rate (HR), and mean arterial pressure (MAP) in six healthy volunteers receiving verapamil 5 mg intranasally and intravenously on two separate occasions. Two subjects achieved measurable verapamil concentrations after intranasal administration with a mean bioavailability of 16.1%. Intranasal bioavailability was limited secondary to instillation volume. No relationship between HR, MAP and verapamil concentration was noted. A relationship between mean intravenous verapamil concentration and mean PR interval was observed; however, extensive interpatient variability existed: two subjects demonstrated enough counterclockwise hysteresis to skew mean data. Mean data may falsely represent the verapamil concentration-effect relationship. Intranasal verapamil administration is limited by instillation volume. Development of a concentrated dosage form is necessary to assess bioavailability. Concentration-effect relationships are more accurately described using individual, rather than mean data.

Altered heparin pharmacodynamics in patients with pulmonary embolism

Heparin clearance and pharmacodynamic response were examined in 12 patients being treated for deep venous thrombosis (DVT, 6 patients) or pulmonary embolism (PE, 6 patients). A loading dose of 70 units/kg was administered to DVT patients and 100 units/kg to PE patients followed by an initial infusion rate of 15 or 25 units/kg/h for DVT or PE patients, respectively. Heparin clearance was determined at 4, 12, and 24 h after initiating heparin therapy. The mean heparin clearance in the DVT group was 2,164 +/- 1,024 ml/h at 4 h, 2,591 +/- 1,239 ml/h at 12 h, and 2,795 +/- 1,863 m/h at 24 h. The PE patients had clearances of 1,775 +/- 494, 2,004 +/- 321, and 2,843 +/- 1,000 ml/h at 4, 12, and 24 h, respectively. The difference between the two groups was not statistically significant (p greater than 0.50). The activated partial thromboplastin time (aPTT) was used as a measure of heparin effect. The maximum effect (EMAX) and concentration required to attain 50% of the maximum effect (EC50) were determined for each group using the Lineweaver-Burke linearization method. The mean EMAX and EC50 for the DVT patients were 130 +/- 40.99 s and 1.01 +/- 0.70 units/ml, respectively. For the PE patients, the mean EMAX was 418 +/- 200 s and the mean EC50 was 4.32 +/- 2.81 units/ml. The difference between both groups for each parameter was statistically significant (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant human complement subcomponent C1s lacking beta-hydroxyasparagine, sialic acid, and one of its two carbohydrate chains still reassembles with C1q and C1r to form a functional C1 complex

In contrast to the human serum protein which is approximately one-half erythro-beta-hydroxyasparagine at asparagine 134 [Theilens et al. (1990) Biochemistry 29, 3570-3578], recombinant C1s expressed by insect cells after infection with recombinant baculovirus entirely lacks posttranslational modification at asparagine 134. It is also incompletely glycosylated, lacking, at least, sialic acid. Site-directed mutagenesis of one of the two sites of carbohydrate attachment (Asn 159 to Gln 159) yields a faster migrating recombinant C1s still abundantly secreted. Furthermore, the mutated protein displays good hemolytic activity when reassembled with C1q and either human serum or recombinant C1r, demonstrating that these posttranslational modifications are not critical for any of the multiple interactions between C1s and C1q, C1r, C2, and C4 required for reassembly of the C1 complex, activation, and initiation of the classical complement pathway. The 4.0S recombinant C1s dimerizes to yield 5.6S C1s2 in the presence of Ca2+ and forms the 9.1S C1s-C1r-C1r-C1s tetramer upon the addition of human serum C1r and the 15.6S C1 complex upon the addition of C1q to the tetramer. The recombinant C1s and human serum C1s have identical N-terminal amino acid sequences, indicating proper recognition by the insect signal peptidase. The recombinant C1s is secreted and isolated as the unactivated zymogen, and it may be activated by human serum C1r which cleaves at Arg422-Ile423 to yield the characteristic heavy and light chains. A very tight complex is formed between C1-inhibitor and the light chain of recombinant C1s.(ABSTRACT TRUNCATED AT 250 WORDS)

Neonatal thrombosis: treatment with heparin and thrombolytics

Thrombotic events are a serious and potentially fatal complication during the neonatal period. Despite clinically serious thromboses in up to one percent of neonates and less severe complications (e.g., catheter malfunction secondary to clots) in a much higher percentage, well-designed studies on prevention and treatment of thromboses are lacking. Treatment approaches are largely anecdotal and involve the use of heparin and, occasionally, thrombolytics. Proper monitoring of anticoagulant and thrombolytic effects is difficult because of the limited blood volumes available from neonates and the relatively large sample volumes needed for most coagulation studies. Activated clotting times (ACTs) are preferred because they use low blood volume and are a rapid bedside test. Heparin should be administered with an initial loading dose of 50-100 units/kg followed by a continuous infusion of 20 units/kg/h. Further doses should then be adjusted based on the ACT, targeting a value of 1.5-2.5 times the control. Thrombolytics also have been used in several case reports and are guided by both clinical response and serial D-dimer values. We prefer urokinase 100 units/kg/h for local infusion to the thrombus and urokinase 1000-10,000 units/kg/h for systemic therapy.

The impact of changing ventilator parameters on availability of nebulized drugs in an in vitro neonatal lung system

An in vitro model was developed to assess nebulized drug delivery. The model simulated the intubated neonate and examined the effect of changes in a variety of parameters commonly confronted in the clinical setting. Theophylline was nebulized for 15 minutes and captured in an artificial lung system (a 1000-mL intravenous bag). Variables were: peak pressure (20, 24, 28 cm H2O), ventilator rate (40, 60, 80 breaths/min), nebulizer flow rate (5, 7, 10 L/min), endotracheal tube size (2.5, 3.0, 3.5 mm), and ventilator type (Servo 900C, Bourns BP 200, Bear Cub BP 2001). The amount of drug actually captured in the bag ranged from 0.009 to 12.59 percent (mean 2.08). A multivariate analysis showed that only nebulizer flow rate had a statistically significant effect on drug delivery with 10 L/min delivering the most drug. All factors combined only accounted for 11.5 percent of the variability in drug delivery. In light of the wide and unpredictable amounts of drug delivered through ventilators, dosing to pharmacologic effect rather than staying within narrow dosing guidelines may be more rational in patients responding poorly to standard doses.

Indomethacin pharmacokinetics in neonates: the value of volume of distribution as a marker of permanent patent ductus arteriosus closure

Indomethacin (INDO) pharmacokinetics were examined in 18 neonates on 19 occasions, before and after patent ductus arteriosus (PDA) closure. Patients received INDO as an initial dose of 0.25 mg/kg intravenously, and INDO serum concentrations were measured 2 and 8 h after the dose. Subsequent doses were individualized based on clinical response, toxicity, and INDO pharmacokinetics. PDA status was confirmed echocardiographically at the start and end of therapy. INDO pharmacokinetic parameters varied from dose-to-dose within the same patient, and wide interpatient variability was also observed. Pre- and post-PDA closure, only INDO volume of distribution differed significantly (p less than 0.001) with mean values of 0.36 (+/- 0.06) L/kg and 0.26 (+/- 0.08) L/kg. The reason for this occurrence remains unclear. However, a new application for pharmacokinetics as a probe of physiology is demonstrated.

The effect of hemodialysis and hemoperfusion on serum valproic acid concentration

We report a patient with dialysis-induced encephalopathy who was taking divalproex sodium for a seizure disorder. Her serum valproic acid concentration appeared to be in the low therapeutic range at 54 mg/l yet she continued to have seizure activity. The elimination half-life and apparent clearance of valproic acid were the same for both a dialysis and nondialysis day, indicating that hemodialysis/hemoperfusion has little effect on the overall removal of valproic acid from the body.

Gentamicin in neonates: the need for loading doses

One hundred eighty-four neonates had gentamicin serum concentrations measured twice after an initial loading dose of 5 mg/kg infused over 1 hour. Gentamicin concentrations immediately postinfusion were calculated using a one-compartment pharmacokinetic model. The extrapolated peak gentamicin concentrations achieved with the 5 mg/kg loading dose was optimal (between 5 and 12 micrograms/ml) in 94% of cases. Had an initial dose of 2.5 mg/kg been given as suggested in most references, peak concentrations 5 mg/kg or higher would only have been achieved in 5% of neonates less than 28 weeks' gestation, 10% of neonates 28 to 30 weeks' gestation, 11% of neonates 31 to 34 weeks' gestation, and 36% of neonates more than 34 weeks' gestation. Our data support the need for greater loading doses of gentamicin in newborns. Our recommendation of 5 mg/kg achieves gentamicin concentrations known to be safe and effective.

Indomethacin for patent ductus arteriosus closure. Application of serum concentrations and pharmacodynamics to improve response

Indomethacin dosing for patent ductus arteriosus closure has been standardized despite wide interpatient variability in indomethacin pharmacokinetics. We compared a novel indomethacin dosing approach using individual pharmacokinetic and pharmacodynamic information (group A) with a control group from our institution (group B) and a level 3 university-based intensive care nursery (group C) who were dosed using current dosing guidelines. Permanent patent ductus arteriosus closure was achieved in 27 of 28 (96.4%) group A patients, 10 of 16 (62.5%) group B patients, and 7 of 13 (52.8%) group C patients. Success rates were significantly higher in group A than Groups B and C (P less than .02). Renal toxicity was the only toxicity reported in any group. The major manifestations of renal toxicity, ie, urine output below 1 mL/kg/h or increased serum creatinine by greater than or equal to 0.5 mg/dL, occurred in none of the group A patients but in seven (43.8%) group B and eight (61.5%) group C patients. Renal toxicity was significantly greater in groups B and C than group A (P less than .02). A pharmacodynamic concentration versus response curve was developed and proved predictive of patent ductus arteriosus closure rates in previous studies where indomethacin concentration versus response data were available. Serum concentration monitoring is a valuable adjunct to indomethacin therapy for patent ductus arteriosus closure, especially when a pharmacodynamic approach is used.

Effect of phenobarbital administration on theophylline clearance in premature neonates

The effect of phenobarbital administration on theophylline clearance was studied in 24 premature neonates. 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/12 h. Of the 24 neonates studied, 12 received a mean phenobarbital dose of 26.34 mg/kg/d (ranging from 2 mg every 24 h to 25 mg every 12 h) and the mean phenobarbital concentration was 56.12 micrograms/ml (range 22-112 micrograms/ml). The remaining 12 patients did not require phenobarbital therapy but did receive aminophylline alone. The two groups were closely matched for gestational age, 5-min Apgar scores, and sex (p greater than 0.2). Steady-state theophylline clearance was determined at least once a week for four or more separate weeks. The study lasted a minimum of 8 wk and if more than one theophylline clearance was determined in any given week, the mean of these clearances was used. Both groups demonstrated an increase in mean theophylline clearance over time (from 15.75 and 16.67 ml/h/kg to 30.33 and 35.42 ml/h/kg for the aminophylline and aminophylline plus phenobarbital groups, respectively). The mean slope, an indicator of the average change in theophylline clearance, was 2.19 for the aminophylline group and 3.27 for the aminophylline plus phenobarbital group (p greater than 0.2), indicating that the theophylline clearance for neonates receiving phenobarbital was not significantly different from that for neonates receiving aminophylline alone. Based on this information, aminophylline does not need to be adjusted solely based on concomitant phenobarbital administration; however, theophylline concentrations should be monitored since theophylline clearance can change rapidly and unpredictably in neonates.

Heparin pharmacokinetics during hemodialysis

The disposition of heparin was studied in 21 chronic hemodialysis patients. Heparin was administered as a bolus injection in doses of 3,000-12,000 U. Combined zero and first-order elimination was demonstrated, with heparin half-life declining by 74% over 3.5 h during dialysis. Assumption of a first-order pharmacokinetic model of elimination resulted in a mean difference of 0.001 U/ml between actual and predicted heparin concentrations. Mean first-order pharmacokinetic parameters were: half-life, 117 min; heparin volume of distribution (V), 68 ml/kg; clearance, 28 ml/min. A high degree of interpatient variability was also observed. A comparison of V and plasma volume (PV) revealed V to be significantly greater than PV (p less than 0.001), indicating distribution outside the plasma compartment. When compared to blood volume, there was no significant difference (p greater than 0.1), indicating that blood volume may be used to approximate V. The nonlinear component of the elimination process is not clinically significant within the range of therapeutic plasma concentrations used during hemodialysis, but the high degree of interpatient variability indicates that dosage individualization may be useful.

Rapid sequential phenobarbital treatment of neonatal seizures

The optimal serum concentration of phenobarbital in newborns and its safety at high doses are not well established. The dose response relationship of rapid sequential phenobarbital loading in the newborn was examined and the efficacy of high-dose monotherapy was compared with the addition of a second anticonvulsant for persistent seizure activity. A single loading dose of phenobarbital 15 to 20 mg/kg was initially administered to 120 newborns. Nonresponders received sequential bolus doses of 5 to 10 mg/kg until seizures ceased or a serum concentration of 40 micrograms/mL was obtained. Infants with refractory seizures received additional phenobarbital to a maximum serum concentration of 100 micrograms/mL. The seizures of 48 babies (40%) were controlled after initial loading and 37 of the remaining 72 subjects (51%) responded at serum concentrations of as great as 40 micrograms/mL. The seizures of only seven subjects were controlled at greater concentrations. A second anticonvulsant controlled seizures in 13 of the 28 subjects (46%) whose seizures were refractory to phenobarbital. A gestational age of less than 32 weeks was associated with a significantly better response to phenobarbital. Serum phenobarbital concentrations greater than 50 micrograms/mL produced only occasional feeding difficulty and sedation. It was concluded that sequentially administered IV phenobarbital controls seizures in both term and preterm newborns (77%). This therapeutic effect is dose dependent but plateaus at a serum concentration of 40 micrograms/mL. At greater serum concentrations, unresponsive patients should receive a second antiepileptic agent.