[Corticosteroids: pharmacology and indications of short courses in pediatrics]

The principle of short courses of corticosteroids (SCC), ie, courses of less than 2 weeks, is to use the potent anti-inflammatory effect of corticosteroids. The pharmacological and pathophysiological basis of this anti-inflammatory effect are presented. Because they represent a very peculiar strategy of treatment, intravenous bolus dosages of methylprednisolone are not discussed. As compared to cortisol, the synthetic corticosteroids used in SCC (ie, mainly prednisone, prednisolone and betamethazone) have a more potent anti-inflammatory activity, a reduced mineralocorticoid effect and a longer biological half-life. The main indications of SCC are laryngitis and acute asthma. SCC are also indicated in bacterial meningitis, in addition to antibiotherapy. Other indications are Henoch-Schönlein purpura and intestinal inflammatory diseases. Adverse effects of SCC are uncommon. There are possible immunoallergic manifestations presenting mainly as skin reactions and sometimes as anaphylaxis. Abnormal psychological behaviour may be observed during the first 10 days of treatment. Few cases of ocular complications have been reported in adults, related to an increased intraocular pressure in patients with myopia or glaucoma. However, there is no evidence that SCC may cause gastric ulcer, nor that they may induce suppression of the adrenal function so that there is no need for a progressive decrease of the dosage when discontinuing the treatment.

Oxidative metabolism of lansoprazole by human liver cytochromes P450

The aim of this work was to identify the form(s) of human cytochrome P450 (P450) involved in the hepatic biotransformation of lansoprazole to its two main metabolites, i.e., the sulfone and the hydroxy derivative. In liver microsomes, the production of the sulfone of lansoprazole correlated with the level of P450 3A4, cyclosporin oxidase, and the production of the hydroxy derivative, as well as of omeprazole sulfone. The production of hydroxylansoprazole moderately correlated with the level of P450 3A4, cyclosporin oxidase, and (S)-mephenytoin 4'-hydroxylase. The production of the sulfone and of the hydroxy derivative of lansoprazole was significantly inhibited by anti-P450 3A4 antibodies, by cyclosporin and ketoconazole, and by tolbutamide. Anti-P450 2C8 and 2C3 antibodies moderately inhibited the biotransformation of lansoprazole, whereas they completely inhibited (S)-mephenytoin 4'-hydroxylase activity under the same conditions. In primary cultures of human hepatocytes, the biotransformation of lansoprazole and the oxidation of cyclosporin were strongly increased by rifampicin and phenobarbital, whereas (S)-mephenytoin 4'-hydroxylation was not. beta-Naphthoflavone did not induce the formation of the sulfones but stimulated the production of hydroxylansoprazole. Among several forms of cDNA-expressed human P450s, 3A4 generated significant amounts of the sulfones of lansoprazole and omeprazole and 2C18 was active for the production of hydroxylansoprazole but inactive in the 4'-hydroxylation of (S)-mephenytoin. We conclude that P450 3A4 is the major enzyme involved in the production of the sulfone of lansoprazole and that this P450, as well as P450 2C18 and/or another 2C-related form, could contribute to the production of hydroxylansoprazole.

Population pharmacokinetics of midazolam in neonates

OBJECTIVE

To describe the pharmacokinetics of midazolam, a water-soluble benzodiazepine with a short half-life, in critically ill neonates.

HYPOTHESIS

Midazolam clearance is reduced in neonates compared with clearance in children, and the doses currently in use, which are derived from pediatric studies, are excessive.

PATIENTS AND METHODS

This population study was conducted in 187 neonates requiring intravenous sedation for artificial ventilation. The 531 midazolam concentration measurements obtained were analyzed by use of NONMEM and a two-compartment model with four parameters: clearance (CL), central volume (Vc), peripheral volume (Vp), and intercompartmental clearance (Q). The influence of birth weight (range, 700 to 5200 gm), gestational age (range, 26 to 42 weeks), postnatal age (range, 0 to 10 days), and comedications were investigated.

RESULTS

CL and Vc (mean +/- SE) were found to be directly proportional to birth weight (CL = 0.070 +/- 0.013 L/kg/hr; VC = 0.591 +/- 0.065 L/kg). The CL was 1.6 times higher in neonates with a gestational age of more than 39 weeks. It was 0.7 times lower in neonates receiving inotropic support. The postnatal age had no apparent effect on midazolam kinetics. The Vp and Q (mean +/- SE; 0.42 +/- 0.11 L and 0.29 +/- 0.08 L/hr, respectively) were not influenced by any of the covariates studied. There was a large interindividual variability for the pharmacokinetic parameters.

CONCLUSION

The mean midazolam doses required for critically ill neonates are lower than those required for older infants.

DNA haplotype-dependent differences in the amino acid sequence of debrisoquine 4-hydroxylase (CYP2D6): evidence for two major allozymes in extensive metabolisers

The molecular basis for DNA haplotype-dependent debrisoquine 4-hydroxylase (CYP2D6) expression was explored by sequencing all of the nine exons of the CYP2D6 gene. Two distinct exon sequence frameworks of the CYP2D6 gene were found, each associated with specific BamHI-defined DNA haplotypes of the CYP2D cluster. They corresponded to Arg296/Cys296 and Ser486/Thr486 amino acid polymorphisms in the CYP2D6 enzyme, and occurred in almost equal frequency among the Caucasians examined. These two major allozymes with amino acid differences in the presumed substrate recognition region and in the vicinity of the heme binding site could be the source of the observed DNA haplotype-dependent variation in phenotypic expression.

Placebo-controlled trial of midazolam sedation in mechanically ventilated newborn babies

Although midazolam is used for sedation of mechanically ventilated newborn babies, this treatment has not been evaluated in a randomised trial. We have done a prospective placebo-controlled study of the effects of midazolam on haemodynamic variables and sedation as judged by a five-item behaviour score. 46 newborn babies on mechanical ventilation for respiratory distress syndrome were randomly assigned to receive midazolam (n = 24) or placebo (n = 22) as a continuous infusion. Doses of midazolam were calculated to obtain plasma concentrations between 200 and 1000 ng/mL within 24 h of starting treatment and to maintain these values throughout the study. Haemodynamic and ventilatory variables were noted every hour, as were complications and possible side-effects of treatment. Mean (SD) duration of inclusion was 78.7 (30.9) h. 1 patient in the treatment group and 7 in the placebo group were withdrawn because of inadequate sedation (p < 0.05). Midazolam gave a significantly better sedative effect than placebo, as estimated by the behaviour score (p < 0.05). Heart rate and blood pressure were reduced by treatment but remained within the normal range for gestational age and there was no effect on ventilatory indices. The incidence of complications was similar in the two groups. No midazolam-related side-effects were noted. Continuous infusion of midazolam at doses adapted to gestational age induces effective sedation in newborn babies on mechanical ventilation, with positive effects on haemodynamic variables. The course of the respiratory distress syndrome was not influenced by this treatment. Midazolam was given over only a few days and the limited effects on heart rate and blood pressure that we report should not encourage long-term administration.

Pharmacokinetics of intravenous omeprazole in children

This study was undertaken to define the pharmacokinetics of omeprazole in children and included 13 patients, heterogeneous in terms of age (0.3 to 19 years), underlying disease and biological constants, indication of omeprazole administration and associated therapy. The dose administered ranged from 36.9 to 139 mg.1.73 m-2. The pharmacokinetic parameters of omeprazole were: systemic clearance, 0.23 l.kg-1.h-1; volume of distribution, 0.45 l.kg-1; elimination half life 0.86 h; but were highly variable between individuals. Dosage, differences in hepatic and renal function and associated therapy may contribute to inter-individual variability. Within the range of doses administered, the pharmacokinetic parameters were similar to those reported in adults. The drug has been well tolerated in all children.

[Has the use of indomethacin during pregnancy consequences in newborn infants? Prospective study of 83 pregnant women and 115 newborn infants]

BACKGROUND

Prolonged exposure of pregnant women to indomethacin for tocolysis may have significant effects on the fetus or neonate, but their incidence is still debated.

POPULATION AND METHODS

From January 1990 to July 1991, 83 pregnant women were prospectively given indomethacin for treatment of premature labor, after ineffective course of salbutamol. The initial dose of indomethacin was 100 mg, then the daily dose was 50 mg while salbutamol was continued. Indomethacin was discontinued beyond the 33rd week of gestational age. Efficacy of indomethacin was judged upon the disappearance of uterine contractions and the increased duration of pregnancy from the onset of treatment until delivery. Adverse effects of treatment were evaluated in the neonates.

RESULTS

The mean duration of indomethacin administration was 16 days (range: 1-62 days); the mean total dose was 900 mg (range: 100-4500 mg). The reason for discontinuation of the treatment was its efficacy (41 patients), a gestational age of 33 weeks (12 patients), oligoamnios (21 patients), demonstration of fetal abnormalities (two patients). The mean interval between discontinuation of treatment and delivery was 5 weeks. Fourty three of the 58 patients who were given indomethacin before the 30rd week were delivered after the 33rd week. There was no adverse effect in the women and babies; all oligoamnios were spontaneously reversible. One hundred and fifteen babies were born including 12 who died during the first post-natal days. The rate of admission in an intensive care unit was similar to that of untreated pregnancies.

CONCLUSIONS

Indomethacin can be safely used for treatment of premature labor provided that its administration is carefully monitored.

Cyclosporine pharmacokinetics in nephrotic and kidney-transplanted children

The pharmacokinetic parameters of cyclosporine (CsA) were determined in 23 kidney transplant recipients and 19 children with nephrotic syndrome, after intravenous and oral administration. The mean bioavailability was 39%, blood clearance was 0.55 l.h-1.kg-1 and volume of distribution at steady-state was 2.77 l.kg-1. The absorption profile was monophasic (67%), biphasic (29%) or poor (4%). The maximum blood concentration of CsA was significantly higher in children with a monophasic profile than in children with a biphasic profile (550 vs 380 ng.ml-1). Blood clearance was significantly higher in the transplant recipients than in the patients with nephrotic syndrome (0.65 vs 0.43 l.h-1.kg-1. Although age, haematocrit, creatinine clearance, serum albumin and cholesterol differed between the two groups, only haematocrit and creatinine clearance were significantly (negatively) correlated with CsA clearance.

Thiopurine methyltransferase activity in a French population: h.p.l.c. assay conditions and effects of drugs and inhibitors

1. Thiopurine methyltransferase (TPMT) is a cytosolic enzyme involved in the catabolism of thiopurine drugs, which are used to treat cancer patients and organ transplant recipients. Because TPMT activity is polymorphic and under genetic control, large interindividual variations in the immunosuppressive activity and toxicity of these drugs may, at least in part, be inherited. 2. We have developed a specific h.p.l.c. method for measuring 6-methyl mercaptopurine formed from 6-mercaptopurine (6-MP) in red blood cell lysates during the TPMT assay procedure. In blinded assays of 55 samples from adult blood donors, the results of the h.p.l.c. method correlated with those of the radiochemical reference method (r = 0.83, P < 0.001). 3. Using this h.p.l.c. assay, we tested the effect of known inhibitors of TPMT activity (syringic acid, p-anisic acid and tropolone) in vitro and showed that they were highly inhibitory. We also found that drugs often administered concomitantly with 6-MP (prednisone, prednisolone, 6-methylprednisolone, cyclophosphamide, methotrexate, and trimethoprim-sulphamethoxazole) had little or no effect on TPMT activity in vitro. 4. In a group of 300 French individuals, TMPT activity was highly variable, ranging from 4.7 to 35.3 nmol h-1 ml-1 of packed red blood cells (nmol h-1 ml-1 PRBC) with a mean value of 19.3 +/- 4.9. TMPT activity was not influenced by sex. 5. This sensitive and reproducible h.p.l.c. assay for TPMT activity in red blood cells may prove useful for prospective clinical studies designed to optimise dosage regimens of thiopurine drugs (detection limit for 6-methyl mercaptopurine is 5 ng ml-1, intra- and inter-assay variations are 6.8 and 8.2%, respectively).

[Anaphylactic shock and low osmolarity contrast medium]

BACKGROUND

Low osmolality contrast media are generally better tolerated than those with high osmolality. This report describes a case of severe collapse after injecting a low osmolality contrast medium.

CASE REPORT

A 15 month-old girl with aortic arch abnormalities was admitted for investigation under general anesthesia. She had a history of allergy but had not previously been exposed to contrast medium. She was given ioxaglate (2 mg/kg) into an artery. The infusion immediately resulted in generalized erythema, tachycardia, hypotensive collapse and ECG abnormalities. The patient was immediately given adrenaline, vasopressive drugs, corticosteroids and plasma protein fraction, which led to a rapid recovery. The ductus arteriosus was ligated a few days later without complications despite the application of iodine to the skin and the use of anesthetic drugs.

CONCLUSION

An unpredictable adverse reaction to low osmolality contrast medium can occur. Risk factors must be identified and immediate arrangements made for resuscitation.

[Severe poisoning risk linked to intravenous administration of quinine]

BACKGROUND

High concentrations of quinine, the drug of choice for severe malaria, are toxic to the cardiovascular system, producing hypotension and abnormal myocardial conduction.

CASE REPORTS

Five children, aged 14 months to 13 years, were admitted because of fever that appeared a few days after their return from an area in which malaria was endemic. Examination of a thick blood film showed Plasmodium falciparum. They were given quinine intravenously. Four children developed a seizure that recurred in three of them; the fifth child suffered from headache, buzzing in the ears and vision anomalies. Four children rapidly developed hypotension followed by cardiac arrest. All children had abnormal ECG. Retrospective study of the instructions given for quinine administration showed that they were inexplicit and were responsible for incorrect dilution of the drug. Four of the five children recovered completely. The fifth child developed ventricular tachycardia followed by bradycardia that did not respond to resuscitation.

CONCLUSION

Major errors can be made in prescribing intravenous quinine. This type of treatment must be carefully monitored and is only indicated in severe forms of malaria, which our patients were not suffering from.

DNA haplotype dependency of debrisoquine 4-hydroxylase (CYP2D6) expression among extensive metabolisers

Deficient debrisoquine/sparteine type oxidation is inherited as an autosomal recessive trait. Of all Caucasians, 5-10% are poor metabolisers, due to the absence of cytochrome P4502D6. Extensive metabolisers (EMs) exhibit highly variable metabolic activity. We investigated the relationship between CYP2D6 activity and genotypes of the CYP2D locus in a large set of French Caucasian families. Genotypes concern both common mutations affecting the enzyme activity and linked BamHI polymorphisms of the locus. We found, like other authors, that in EMs part of the heterogeneity is explained by a subgroup of individuals heterozygous for a mutant allele. However, a second level of heterogeneity was detected among individuals not carrying mutations, and this was related to a polymorphic BamHI-defined DNA haplotype. Different combinations of haplotypes are associated with differences in CYP2D6 metabolic activity. This finding might help to clarify the conflicting data on the relation between CYP2D6 activity and susceptibility to lung cancer.

CYP2D6- and CYP3A-dependent metabolism of dextromethorphan in humans

The metabolism of dextromethorphan, a drug used to probe genetically determined CYP2D6 activity has been investigated in vivo and in vitro. In vitro, kinetic parameters were determined in adult microsomes: Km for the O-demethylation was much lower than for N-demethylation (7 versus 650 microM) but Vmax was comparable. Fetal liver microsomes actively catalysed the N-demethylation of dextromethorphan, with kinetic parameters (Vmax and Km) quite similar in fetal and adult microsomal preparations while the O-demethylation did not exceed 5% of adult activity. In microsomes, the N-demethylation was inhibited by antibodies raised against CYP3A subfamily members although fetal microsomes were much less sensitive to immunoinhibition than adult microsomes. In vivo, urinary excretion of dextromethorphan and its three demethylated metabolites was examined in 155 adult volunteers and compared between extensive (n = 144, 92.9%) and poor (n = 11, 7.1%) metabolizers. The O-demethylation to dextrorphan is the rate-limiting step of metabolism. In 2D6 poor metabolizers, the N-demethylation to 3-methoxymorphinan is slightly higher than in 2D6 extensive metabolizers but does not compensate defective O-demethylation. The frequency distribution histograms of dextromethorphan/dextrorphan and 3-methoxymorphinan/3-hydroxymorphinan metabolic ratios appeared bimodally distributed, reflecting the participation of CYP2D6 in the O-demethylation reaction. They clearly differed from the random distribution of dextromethorphan/3-methoxymorphinan, and dextrorphan/3-hydroxymorphinan ratios among the population. These data clearly suggest that the N-demethylation of dextromethorphan is dependent on CYP3A and that both CYP2D6 and CYP3A are involved in the overall metabolism of dextromethorphan.

[Atrioventricular block complicating the use of diphemanil (Prantal) in 2 premature newborn infants]

BACKGROUND

Diphemanil can be useful in some neonates presenting with bradycardia due to vagal hyperreflectivity. Paradoxically, this drug may induce atrio-ventricular (AV) block in premature babies.

CASE REPORTS

Case no 1. A premature neonate suffering from acute respiratory distress from birth required respiratory support, antibiotics and caffeine. Despite this treatment, he underwent many episodes of apnea, and bradycardia that appeared on day 4 and did not respond to IV doxapram (1 mg/kg/h). He was given diphemanil on day 9 (10 mg/kg/d) and permanent bradycardia with complete AV block and a normal QT interval appeared 2 days later. Cessation of diphemanil and administration of IV isoprenaline led to a normal sinusal rhythm, but there were bladder, intestinal and ocular signs of atropinic intoxication. A complete definitive recovery occurred 5 days after cessation of diphemanil. Case no 2. A premature neonate developed episodes of apnea 2 days after birth. These episodes persisted and were complicated by bradycardia on day 4 despite administration of caffeine. Vagal stimulation on day 7 was positive and the infant was then given diphemanil (10 mg/kg/d). Permanent bradycardia occurred 2 days later, with partial AV block and a normal QT interval. The child recovered a normal sinusal rhythm 2 days after cessation of diphemanil.

CONCLUSIONS

Anticholinergic therapy may cause permanent bradycardia due to AV block in premature infants. This therapy should not be given to premature infants without a prior ECG. Doses lower than those used in infants are recommended.

[Maternal and neonatal effects of indomethacin administrated during pregnancy. Apropos of 18 cases]

BACKGROUND

There have been several reports that prolonged exposure of pregnant women to indomethacin for tocolysis may have significant pharmacological effects on the fetus or newborn.

PATIENTS

Eighteen pregnant women were given indomethacin during the year 1989 for treatment of premature labor (n = 16) or polyhydramnios (n = 2). Treatment was started at gestational week 28.1 +/- 2.5 and was discontinued at gestational week 30.7 +/- 1.8. The mean age of the women at the onset of pregnancy was 30.6 +/- 5.3 years. The daily dose of indomethacin was initially 200 mg (2-3 mg/kg), then 107 +/- 59 mg. The cumulative dose was 1,820 +/- 2,370 mg. The duration of treatment was 18.1 +/- 16.4 days (less than 7 days in 8 women).

RESULTS

The term at delivery was 33.4 +/- 3.3 weeks (11 after 32 weeks). The mean interval between discontinuation of treatment and delivery was 19.0 +/- 18.7 days. Indomethacin was effective in 10 cases of premature labor, and gestation was prolonged by 52.6 +/- 19.2 days. Among the 23 live-born neonates, 5 developed renal insufficiency attributed to indomethacin (4 premature labor, 1 hydramnios). The kidney failure with early hyperkalemia was cured within about 7 days in 4 cases. The remaining neonate also suffered from severe prolonged hypoxia and died on day 4.

CONCLUSIONS

Administration of indomethacin for premature labor places the fetus at risk because of the short drug-free interval before birth. High daily or cumulative doses of indomethacin dit not result in adverse effects.

Endogenous digoxin-like immunoreactivity during pregnancy and at birth

1. We have measured endogenous digoxin-like immunoreactivity (EDLI), in mothers and infants, during normal/pathological pregnancies and at birth. 2. During pregnancy, EDLI was measured in 38 maternal-fetal pairs. At the time of fetal sampling, maternal age was 29 (s.d. 6) years and gestational age was 28 (s.d. 6) weeks. EDLI was present in 13 (34%) mothers and in 27 (71%) fetuses. There was no correlation between maternal and fetal concentrations or between maternal or fetal concentrations and gestational age. 3. EDLI was measured at birth in blood samples from 45 maternal-cord pairs. Maternal age was 29 (s.d. 5) years and gestational age was 39 (s.d. 2) weeks. EDLI was present in 11 (22%) maternal and in 44 (98%) cord samples. The concentrations were significantly higher in cord than in fetal or maternal samples (P < 0.001 in both cases). 4. High cord EDLI concentrations suggest acute synthesis during delivery. Thus, the placental transfer of digoxin calculated from maternal and cord digoxin concentrations at birth may be overestimated.

Molecular heterogeneity of the XbaI defined 44kb allele of the CYP2D locus within the Caucasian population

1. Cytochrome P450 debrisoquine (CYP2D6) activity is polymorphic and under genetic control. Most Caucasians are extensive metabolizers, but 5%-10% are poor metabolizers. 2. Restriction fragment length polymorphism analysis of the CYP2D6 locus identifies a 29kb XbaI fragment, either normal (D6-wt) or mutated, and three mutated XbaI alleles (44kb, 11.5kb and 16 + 9kb). The 44kb allele was initially considered as a poor metabolizer allele owing to a D6-B mutation, but cases of 44kb allele not carrying the D6-B, and therefore potentially functional, have been found. The degree of molecular heterogeneity of this allele was investigated by phenotype and genotype analysis of families. 3. Thirty-one French Caucasian families, representing 117 individuals, possessing at least one 44kb allele in each family were selected. Phenotypes were determined using dextromethorphan, and the XbaI, NcoI and BamH1 RFLPs of 42 independent chromosomes were analyzed. 4. 80% of the XbaI 44kb alleles carried the CYP2D6-B mutation and had an additional NcoI fragment (12.5kb or 4.8kb). The remaining 20% did not carry the CYP2D6-B or A mutations and had no extra NcoI fragment. 5. Information on three families demonstrated that 44kb alleles not carrying the CYP2D6-B mutation were associated with the extensive metabolizer phenotype. 6. We conclude that a substantial percentage of XbaI 44kb alleles is associated with a functional CYP2D gene, and therefore, that the XbaI 44kb allele is not consistently a poor metaboliser allele.

Polymorphism of dextromethorphan metabolism: relationships between phenotype, genotype and response to the administration of encainide in humans

The polymorphism of dextromethorphan and encainide metabolism is genetically determined and is related to the activity of hepatic CYP2D6. In order to examine the relations between CYP2D6 phenotype, genotype and the electrocardiographic response to the oral administration of encainide, 110 healthy subjects were studied. Metabolic ratios were calculated in urine after oral administration of 40 mg of dextromethorphan and in plasma obtained 2.5 h after oral administration of 50 mg of encainide. Encainide-induced electrocardiographic changes were measured 2.5 h after oral administration of the drug. Genotype was determined in 52 subjects. Results showed that phenotype, either extensive or poor metabolizer, for CYP2D6-dependent metabolism could be identified from the dextromethorphan metabolic ratio calculated in urine, from the encainide metabolic ratio calculated in plasma and from the genotype. However, despite the fact that the changes in atrioventricular (PR) and intraventricular (QRS) conduction times produced by encainide were different in extensive and poor metabolizer subjects and correlated with CYP2D6 activity, the electrocardiographic response was never 100% specific and sensitive for the identification of either phenotype. Moreover, genotypic identification of heterozygous and homozygous extensive metabolizer subjects did not predict CYP2D6 activity, as determined by dextromethorphan and encainide metabolic ratios, or encainide response, as determined by intraventricular and atrioventricular changes. Thus, CYP2D6 activity does not fully predict the electrocardiographic effects of encainide, and genotype, as determined in our study, cannot replace the determination of metabolic ratio in predicting CYP2D6 activity and encainide response in extensive metabolizer subjects.

Clinical and pharmacologic study of fetal supraventricular tachyarrhythmias

The purpose of this study was to evaluate the efficacy of maternal digoxin administration in 16 cases of fetal supraventricular tachyarrhythmia diagnosed by fetal echocardiography; cardiac anatomy was normal in all cases. The retrospective analysis included nine mothers who received digoxin orally in most cases, with control of the arrhythmia in two fetuses. The addition of amiodarone (five cases) and propranolol (two cases) yielded two successes with amiodarone. The therapeutic regimen of digoxin was then modified on the basis of poor response to orally administered digoxin. In the prospective study, digoxin was administered intravenously to seven mothers according to a standard protocol; high doses (1 to 2 mg intravenously) were prescribed for the first 24 hours and intravenous digoxin therapy was maintained for at least 5 days, depending on the fetal response. Digoxin pharmacokinetic studies of four mothers showed an increased plasma clearance and reduced elimination half-life. Digoxin controlled the five supraventricular tachycardias (with hydrops in four cases). Maternal flecainide therapy restored sinus rhythm in two cases of atrial flutter. Our prospective study emphasizes the efficacy and safety for the fetus and the mother of intravenously administered digoxin as a first-choice drug in the treatment of supraventricular tachyarrhythmias. Flecainide may be a promising second-choice drug but requires further clinical investigation. Amiodarone and propranolol seem to be ineffective.

[Kidney failure induced by administration of acyclovir. Apropos of 2 cases]

BACKGROUND

There have been several reports of acyclovir-induced renal failure, when the drug has been administered intravenously and/or associated with water restriction.

CASE REPORT

Case n. 1: A 14 year-old boy, was treated with intravenous acyclovir because of an acute encephalitis, possibly due to Herpes viral infection. The acyclovir dose was given erroneously high, 24 mg/kg, 3 times/day, with water restriction, 30 ml/kg/day. Creatininemia increased from 70 to 200 mumol/liter after 48 hours of treatment and was 426 mumol/liter after 5 days. It decreased within a few days after the acyclovir dose was reduced to 6 mg/kg/day and the water intake was increased to 80 ml/kg/day. Case n. 2: A 17 year-old girl was suffering from chronic renal failure due to bilateral kidney hypoplasia associated with hypertension (creatinine clearance: 40 ml/min/1.73 m2). She was given intravenous acyclovir, 20 mg/kg/day, with water restriction, 30 ml/kg/day, to treat acute meningoencephalitis, possibly due to Herpes infection. Creatininemia increased from 200 to 450 mumol/l within 8 days of treatment; it returned to initial values 5 days after cessation of acyclovir and rehydration.

CONCLUSION

These 2 cases confirm the risk of renal impairment when acyclovir is administered intravenously. The risk is greater after bolus injections and when high doses are used. Water restriction is an additional risk, as was the chronic renal insufficiency in our second patient. A scheme of acyclovir therapy based on initial values of creatininemia is mandatory.

Interspecies variations in caffeine metabolism related to cytochrome P4501A enzymes

1. Interspecies (including man, monkey, rabbit, rat and mouse) variations in caffeine metabolism by liver microsomes were studied. While N-3 demethylation was the major pathway in man (81% of total dimethylxanthines), N-7 demethylation was predominant in monkey (89%), and the three demethylation pathways were about equal in mouse, rabbit and rat. 2. Three monooxygenase activities (methoxyresorufin O-demethylase, phenacetin O-deethylase and acetanilide 4-hydroxylase) correlated significantly with the rate of metabolism of caffeine. 3. P4501A1 and 1A2 enzymes were immunodetected in different species. P4501A2 was the only isoform detected in liver of man, rat and mouse, while no polypeptide immunorelated to P4501A was detected in monkey and only a minor band of P4501A1 was detected in rat and rabbit. 4. All in vitro data indicate that paraxanthine formation is mediated mainly by P4501A2 in mammals while theophylline formation is mediated mainly by cytochromes P-450 other than those of the 1A family.

Relation between chloroguanide bioactivation to cycloguanil and the genetically determined metabolism of mephenytoin in humans

It has been suggested recently that the bioactivation of chloroguanide hydrochloride (proguanil) to its active antimalarial metabolite cycloguanil cosegregates with the genetically determined polymorphism of mephenytoin hydroxylation. We determined the chloroguanide to cycloguanil ratio in urine after oral administration of a single dose of 200 mg proguanil either alone or together with 100 mg racemic mephenytoin or 40 mg dextromethorphan in a randomized crossover study performed in 24 healthy subjects. The mephenytoin hydroxylation index was also determined after administration of 100 mg racemic mephenytoin either alone or together with 200 mg proguanil. Two subjects were poor metabolizers and one subject was an intermediate metabolizer of mephenytoin. These three subjects had chloroguanide to cycloguanil ratios of more than 50. The 21 subjects with the extensive metabolizer phenotype for mephenytoin hydroxylation had chloroguanide to cycloguanil ratios of less than 10. The chloroguanide to cycloguanil ratio was not significantly altered by mephenytoin or dextromethorphan coadministration. The trend toward a correlation between chloroguanide/cycloguanil ratio and log mephenytoin hydroxylation index did not reach statistical significance. Inclusion of the dextromethorphan metabolic ratio into the model did not improve the relationship. These findings confirm that the bioactivation of chloroguanide to cycloguanil cosegregates with the genetically determined activity of the CYP2C family. However, the chloroguanide to cycloguanil ratio and the mephenytoin hydroxylation index do not similarly reflect the variable activity of CYP2C.

Pharmacokinetics of midazolam during continuous infusion in critically ill neonates

Midazolam is a water soluble benzodiazepine, with a short elimination half-life in adults and children. An IV bolus (0.2 mg.kg-1) immediately followed by continuous infusion of 0.06 mg.kg-1.h-1 was administered to 15 critically ill neonates at a gestational age of 32.8 weeks, who required sedation for mechanical ventilation. Heart rate and blood pressure were closely monitored. Hypotension occurred in 4 patients after the bolus dose or during the continuous infusion. Three of them had also been given fentanyl. Individual pharmacokinetic parameters were calculated: plasma clearance was 3.9 ml.min-1, elimination half-life was 12.0 h. Because of its short half-life compared to diazepam, midazolam may be used during the neonatal period to achieve rapid, brief sedation. However, it should be administered cautiously to neonates, particularly in premature infants, or if fentanyl is also given.

Pharmacokinetics of ganciclovir in renal transplant children

Three cytomegalovirus (CMV)-seronegative children received renal transplants from CMV-seropositive donors and developed clinical symptoms of CMV infection between days 20 and 34 post transplantation. Ganciclovir (DHPG) was administered in a 1-h infusion, and the doses and dose intervals were adapted to the degree of renal insufficiency, according to the manufacturer's recommendations for adults. Individual pharmacokinetic parameters of DHPG were determined and were markedly altered. Plasma clearances were 0.4, 1.1 and 2.2 ml/min per kg and were related to individual creatinine clearances (20, 45 and 60 ml/min per 1.73 m2); the corresponding elimination half-lives were 23.7, 9.9 and 3.9 h. In two patients, the doses had to be further reduced in order to maintain plasma levels within the recommended values for peak and trough plasma concentrations. Therefore, monitoring of DHPG appears essential in adjusting dosage for optimal efficacy and minimal toxicity.

Expression of CYP2D6 in developing human liver

The CYP2D6 protein is a polymorphic isoenzyme involved in the biotransformation of several drugs including the probe drug dextromethorphan. The rise in the protein concentration, immunochemically determined with a specific antibody, was shown to occur within the first week following birth, whatever the gestational age at birth. In fetuses, the concentration of hepatic CYP2D6 protein was very low or undetectable in 70% of samples tested. In the remaining 30%, its concentration was comparable to that of newborns aged 1-7 days. This early rise was associated with spontaneous abortion in 70% of positive samples, whereas in fetuses with an intermediate CYP2D6 protein concentration, 80% were from induced abortions. The rise in CYP2D6 protein was associated with the developmental onset of dextromethorphan O-demethylation, but not N-demethylation, even if activity was lower in fetal than in neonatal and in adult liver microsomes. Lastly, the CYP2D6 RNA is detectable earlier than the protein and exhibits a peak of hepatic accumulation in newborns, before declining in adulthood. A positive correlation between RNA accumulation and protein concentration can be demonstrated only in the adult. This suggest that regulation is primarily at the transcriptional level, but cannot rule out the participation of post-transcriptional events in the regulation process throughout ontogenesis.

[Use of flecainide in the preventive treatment of tachycardia crisis of Wolff-Parkinson-White syndrome in 4 newborn infants]

Four neonates with Wolff-Parkinson-White syndrome developed supraventricular tachycardia and received flecainide orally after reduction of the arrhythmia. The initial doses were 5 mg/kg/day. They are increased according to clinical response and flecainide concentrations, with 5 and 10 mg/kg/24 h respectively, were in the therapeutic range of 200 to 1000 micrograms/l. Flecainide was effective and well tolerated in the 4 cases. Therefore, this drug may be an alternative to digoxine to prevent supraventricular tachycardias in the neonatal period.

Influence of amiodarone on genetically determined drug metabolism in humans

Amiodarone has been shown to interact with the nongenetically determined hepatic elimination of several drugs, including phenytoin and digoxin. Its influence on genetically determined metabolic pathways has not been studied in humans. We examined the effects of oral amiodarone therapy on the genetically determined metabolism of isoniazid (N-acetyltransferase), mephenytoin (cytochrome P450MEPH), and dextromethorphan (CYP2D6). Eight patients with arrhythmias were studied before and 76 +/- 16 days after amiodarone (loading dose of 1000 mg/day for 10 days followed by a maintenance dose of 200 to 400 mg/day). Genetically determined enzyme activity was assessed indirectly by calculating the metabolic ratio (parent drug/metabolite in 8-hour urine for CYP2D6 and P450MEPH and N-acetylisoniazid/isoniazid in plasma for N-acetyltransferase) after oral administration of the parent compounds. At the time of phenotyping, plasma concentrations of amiodarone and N-desethylamiodarone were 0.66 +/- 0.35 micrograms/ml and 0.65 +/- 0.26 micrograms/ml, respectively. Amiodarone increased the log(metabolic ratio) of dextromethorphan from a median of -2.5 (range, -2.9 to -2.0) to a median of -1.9 (range, -2.5 to -1.5; p less than 0.02) but did not alter the metabolic ratio of mephenytoin or isoniazid. The amount of dextromethorphan excreted in urine increased from a median of 0.084 mumol/8 hours (range, 0.041 to 0.161 mumol/8 hours) to a median of 0.205 mumol/8 hours (range, 0.064 to 0.288 mumol/8 hours; p less than 0.02) and the amount of its metabolite (dextrorphan) tended to decrease from a median of 26 mumol/8 hours (range, 15 to 37 mumol/8 hours) to a median of 20 mumol/8 hours (range, 7 to 27 mumol/8 hours; p less than 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of amiodarone on genetically determined drug metabolism in humans

Amiodarone has been shown to interact with the nongenetically determined hepatic elimination of several drugs, including phenytoin and digoxin. Its influence on genetically determined metabolic pathways has not been studied in humans. We examined the effects of oral amiodarone therapy on the genetically determined metabolism of isoniazid (N-acetyltransferase), mephenytoin (cytochrome P450MEPH), and dextromethorphan (CYP2D6). Eight patients with arrhythmias were studied before and 76 +/- 16 days after amiodarone (loading dose of 1000 mg/day for 10 days followed by a maintenance dose of 200 to 400 mg/day). Genetically determined enzyme activity was assessed indirectly by calculating the metabolic ratio (parent drug/metabolite in 8-hour urine for CYP2D6 and P450MEPH and N-acetylisoniazid/isoniazid in plasma for N-acetyltransferase) after oral administration of the parent compounds. At the time of phenotyping, plasma concentrations of amiodarone and N-desethylamiodarone were 0.66 +/- 0.35 micrograms/ml and 0.65 +/- 0.26 micrograms/ml, respectively. Amiodarone increased the log(metabolic ratio) of dextromethorphan from a median of -2.5 (range, -2.9 to -2.0) to a median of -1.9 (range, -2.5 to -1.5; p less than 0.02) but did not alter the metabolic ratio of mephenytoin or isoniazid. The amount of dextromethorphan excreted in urine increased from a median of 0.084 mumol/8 hours (range, 0.041 to 0.161 mumol/8 hours) to a median of 0.205 mumol/8 hours (range, 0.064 to 0.288 mumol/8 hours; p less than 0.02) and the amount of its metabolite (dextrorphan) tended to decrease from a median of 26 mumol/8 hours (range, 15 to 37 mumol/8 hours) to a median of 20 mumol/8 hours (range, 7 to 27 mumol/8 hours; p less than 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibody fluorescent polarisation immunoassay versus 125Iode labelled ligand radioimmunoassay for the measurement of cyclosporine concentrations in whole blood

Monoclonal antibody fluorescent polarisation immunoassay for cyclosporine in whole blood was first evaluated. Inter- and intra-assay CVs were less than 7%. We also compared concentrations measured by 125I-RIA and FPIA in specimens obtained from kidney and bone marrow transplanted patients. FPIA correlated well with 125I-RIA (slope = 1.03, r = 0.989, n = 58) over a wide range of concentrations (44-984 ng/ml). However, an additive bias estimated by the mean difference in cyclosporine concentrations between the 2 readings (44.1 +/- 44.3 ng/ml), led to overestimation of cyclosporine concentrations measured by FPIA. The monoclonal FPIA kit is therefore a rapid and reproductive method to monitor cyclosporine concentrations in whole blood. However, FPIA and 125I-RIA are not interchangeable and the therapeutic range of cyclosporine measured by FPIA should be defined.

Distinct phenotypes and genotypes of debrisoquine hydroxylation among Europeans and Chinese

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Cytochrome P450IID subfamily in non-human primates. Catalytical and immunological characterization

Interindividual variations of debrisoquine metabolism was recently identified in non-human primates tested in vivo. The catalytical and immunological characterization of cytochrome P450IID subfamily was undertaken in hepatic microsomes from extensive metabolizer primates. The NADPH/O2 mediated metabolism of debrisoquine, dextromethorphan and bufuralol was similar to the kinetics reported in humans. The CuOOH mediated metabolism of bufuralol suggested that at least two enzymes are responsible for bufuralol 1'-hydroxylation. Eleven compounds were tested for their capacity to modify P450IID function in vitro. Eight competitive inhibitors of P450IID6 in man were all and exclusively competitive inhibitor of P450IID subfamily in non-human primates. Quinidine, which is the strongest competitive inhibitor in man, exhibited the higher inhibitory potency in monkey (Ki = 0.75 microM). Anti-LKM antibody against P450IID subfamily cross-reacted with two proteins of 49 and 47 kDa, and sera containing anti-LKM antibody against these two proteins inhibited dextrorphan formation in vitro. These data provide evidence for catalytical and immunological similarities between human and monkey microsomes and indicate that the primate system could be a model for enzymatic studies of P450IID.

Pharmacokinetics of midazolam in critically ill neonates

Midazolam is a water soluble benzodiazepine, with a short elimination half-life in adults and children. An IV bolus of midazolam 0.2 mg.kg-1 was administered to 10 critically ill neonates receiving intensive care who required sedation. The plasma clearance was 6.85 ml.min-1 and the elimination half-life was 6.52 h. Midazolam was well tolerated during and after administration. Because of its short half-life compared to diazepam, midazolam could be used during the neonatal period to produce brief rapid sedation.

Genetic polymorphisms of drug metabolism. Possible implications during development

Genetic polymorphisms of drug metabolism can affect phase I and phase II reactions. Polymorphisms of cytochrome P450 activity or inducibility have been implicated in drug toxicity and in cancerogenesis. Polymorphisms of the detoxification processes may be important in the appearance of adverse responses to conventional doses of drugs. Pharmacogenetics now opens new ways to investigate the relations between genetic factors, xenobiotics and teratogenesis.

[Pharmacogenetics of oxidation reactions of drugs]

Drug oxidation reactions are performed by different isoenzymes of the cytochrome P450 family. A few enzymes exhibit genetically determined polymorphisms. The two main and independent polymorphisms are related to the 4 hydroxylation of debrisoquine and mephenytoin. Poor metabolizers of one of those test drugs are at high risk of developing adverse responses to conventional doses of drugs. Furthermore it is possible that oxidative polymorphisms may be important in the development of cancer of birth defects. The relations between genetic factors, xenobiotics and cancerogenesis/teratogenesis are now widely investigated. The advances in molecular biology will provide, in the near future, new ways of investigations in pharmacogenetics.

Pharmacokinetics of cefotaxime and desacetylcefotaxime in the newborn

A study of the pharmacokinetic parameters of cefotaxime (CTX) and desacetylcefotaxime (dCTX) in newborns was conducted; the former is commonly used for neonatal infections. The elimination half life of CTX correlated with gestational age (GA) and postnatal age (PNA). Elimination of dCTX was longer permitting a synergistic or additive effect with CTX against Gram-negative bacteria. CTX is indicated in the treatment of neonatal sepsis because of the increasing resistance of Escherichia coli to ampicillin and its good efficacy against group B streptococcus.