Contractile and relaxing mechanisms in pulmonary resistance arteries of the preterm fetal lamb.

Isolated pulmonary resistance arteries from term fetal lambs have nitric oxide (NO)- and prostaglandin-mediated relaxing mechanisms which are activated when PO(2) is raised from fetal to neonatal levels. The same vessels contract under hypoxia, and the contraction has been ascribed to endothelin-1 (ET-1). We have now studied these vasoeffector mechanisms before term (0.7 and 0.65 gestation) with the objective of determining whether their activity correlates with the development of susceptibility to oxygen changes. Experiments were carried out at neonatal PO(2), when expectedly relaxing mechanisms are maximally expressed, or under hypoxia. At either fetal age, the NO synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (100 microM), had no effect on basal tone, while indomethacin (2.8 microM) was a weak constrictor. Premature arteries did not contract when first exposed to hypoxia, but they responded marginally to a second exposure. The same arteries contracted strongly to a thromboxane A(2) analogue (ONO-11113, 0.1 microM) and ET-1 (10 nM), while their contraction to activating solution (5 mM Ca(2+) in K(+)-Krebs solution) was small and variable. At 0.7 gestation, bradykinin (0.1-100 nM), acetylcholine (0.01-10 microM), and sodium nitroprusside (0.1 nM to 10 microM) dose-dependently relaxed arteries precontracted with ONO-11113. Conversely, at 0.65 gestation the relaxation to bradykinin and acetylcholine was not dose-dependent and tended to be weaker. We conclude that preterm pulmonary arteries have viable effector mechanisms for contraction and relaxation. However, the capability for these mechanisms to be activated by PO(2) changes is markedly curtailed.

Assessment of systemic toxicity in children receiving chemotherapy with cyclosporine for sarcoma.

BACKGROUND: Overexpression of P-glycoprotein in malignant tumors has been associated with poor responses to chemotherapy. It appears biologically plausible that addition of the P-glycoprotein inhibitor cyclosporine (CsA) to standard chemotherapy may improve the outcome. The protective functions of P-glycoprotein in healthy tissues, however, have not been fully elucidated. Addition of CsA may lead to increased systemic chemotherapy toxicity, so we compared the rate and severity of chemotherapy-associated systemic toxicity in the presence and absence of CsA. PROCEDURE: Standard chemotherapy consisted of etoposide/ifosfamide (VP16/IFOS) cycles, alternating with vincristine/dactinomycin/cyclophosphamide (VAC) cycles. CsA was given at a median dose of 20 mg/kg with unaltered doses of the antineoplastic drugs. The analysis of toxicity was performed by comparing clinically significant toxicity events recorded during and after chemotherapy cycles with and without CsA. RESULTS: Toxicity-related hospital admissions occurred after 93% of VAC cycles with CsA compared to 40% of the cycles without CsA (P < 0. 0001); 29% of VP16/IFOS cycles with CsA led to admissions vs. 12% with non-CsA cycles (P = 0.04). Infections or fever and neutropenia were the main reasons for these admissions. Thirty-seven percent of the VAC cycles with CsA were complicated by culture-proved sepsis, which did not occur in cycles without CsA (P < 0.0001). Requirements for blood and platelet transfusions were greatly increased after VAC cycles with CsA compared to VAC cycles without CsA. CONCLUSIONS: The chemosensitizer CsA increases the systemic toxicity of VAC chemotherapy in patients with sarcomas. Future trials of chemotherapy with chemosensitizers will have to take into account a potential increase in systemic toxicity. Careful monitoring of chemotherapy-related toxicity becomes mandatory in such studies.

Rapid development of tolerance to dipyridamole-associated headaches.

AIMS: In the Second European Stroke Prevention Study headaches associated with dipyridamole frequently (8% of patients taking dipyridamole or dipyridamole plus acetylsalicylic acid (ASA) vs 2% of patients taking ASA or placebo) led to discontinuation of therapy. We have now used data from a recent trial comparing the bioequivalence of two formulations of the fixed combination of 200 mg dipyridamole in an extended release formulation and 25 mg ASA to explore predicting factors for headaches associated with this drug combination. METHODS: The bioequivalence trial employed a two-way crossover, randomised, open design. Trial medication was given for two periods of five days separated by a 72 h washout period. Statistical methods were employed to explore the prevalence, the time course, and the relation to individual pharmacokinetic parameters of treatment associated headaches. RESULTS: Headache episodes, being mostly mild and transient, rapidly declined from 67% of the volunteers on the first day of treatment to 3% on the final days of treatment (days 4-5 of the second period). During the first days the prevalence of the headaches peaked 2-3 h after the morning administration, which coincided with the peak of the plasma concentrations of dipyridamole. The occurrence of headaches was not related to interindividual differences of the pharmacokinetic parameters. CONCLUSIONS: The rapid decrease in the incidence of headaches over time implies that most patients quickly develop tolerance to dipyridamole-associated headaches. Appropriate information given to the patient when prescribing and dispensing dipyridamole/ASA may reduce early withdrawals from treatment and increase compliance.

Effect of endothelium removal on prostaglandin and nitric oxide function in pulmonary resistance arteries in the lamb.

We have recently shown that isolated pulmonary resistance arteries of the fetal lamb have prostaglandin (PG) I2 based and nitric oxide (NO) based relaxing mechanisms, which are activated by oxygen (at neonatal levels) and bradykinin. The present study was carried out to ascertain whether these mechanisms remain operational after removal of the endothelium. Endothelium-denuded vessels pre-equilibrated at a neonatal Po2 were not affected by indomethacin (2.8 microM), while they contracted weakly to NG-nitro-L-arginine methyl ester (L-NAME, 100 microM). However, the latter response did not reach significance and resembled that of intact vessels at fetal Po2. Bradykinin (0.1-100 nM) dose dependently (from 1-3 nM upwards) relaxed endothelium-denuded arteries that had been precontracted with a thromboxane (TX) A2 analog (ONO-11113, 0.1 microM) or excess potassium (5 mM Ca2+ in K(+)-Krebs) at a neonatal Po2. The response was the same under the two conditions, but it was smaller than that of intact arteries. Bradykinin relaxation of ONO-11113-contracted arteries was completely or nearly completely inhibited by indomethacin and L-NAME. We conclude that endothelium-denuded, pulmonary resistance arteries maintain PG (conceivably PGI2) mediated and NO-mediated relaxing mechanisms. These extra-endothelial mechanisms are activated by bradykinin but not by oxygen.

Efficacy of amlodipine in pediatric bone marrow transplant patients.

The calcium antagonist amlodipine may have the potential for expanded use in children owing to its physiochemistry and pharmacokinetic profile that facilitates once-daily dosing in a liquid formulation. Its safety and efficacy have not been previously evaluated in children. A retrospective analysis of 15 pediatric bone marrow transplant patients who had amlodipine incorporated into their antihypertensive drug regimen reveals significantly lower blood pressure as compared with baseline therapy (123.5+/-2.1 mmHg and 117.2+/-2.2 mmHg, systolic blood pressure before and during amlodipine, P<0.05; 81.5+/-1.8 mmHg and 75.5+/-2.6 mmHg, diastolic blood pressure before and during amlodipine, P<0.05). Amlodipine provided improved blood pressure control in this cohort and may provide a valuable pharmacologic alternative for treatment of pediatric hypertension.

Mechanism of anaphylactoid reactions: improper preparation of high-dose intravenous cyclosporine leads to bolus infusion of Cremophor EL and cyclosporine.

BACKGROUND: During a Phase I/II trial of high-dose intravenous cyclosporine, a high incidence of anaphylactoid reactions was observed. Epidemiologic investigations revealed that the occurrence of anaphylactoid reactions was significantly associated with improper mixing during preparation of the infusions. It was hypothesized that improper mixing during the preparation of the infusion may have caused initial bolus infusions of the vehicle, Cremophor EL. These inadvertent bolus infusions may have caused the anaphylactoid reactions. OBJECTIVE: To investigate the effect of different mixing techniques on the distribution of the components of cyclosporine concentrate for infusion: cyclosporine, Cremophor EL, and ethanol in the infusions administered to the patients. METHODS: Infusions were prepared in a similar fashion as those administered to study patients enrolled in a high-dose cyclosporine therapy protocol. Samples were collected at defined time points of the infusions. Concentrations of cyclosporine and Cremophor EL were spectrophotometrically determined; ethanol concentrations were measured enzymatically. RESULTS: Cyclosporine and Cremophor EL concentrations were up to ninefold higher than intended during the first 10 minutes of the infusions that were not appropriately mixed. In contrast, the concentrations of cyclosporine and Cremophor EL were similar to the intended concentrations in all of the well-mixed infusions. CONCLUSIONS: Inappropriate mixing of high-dose cyclosporine infusions can lead to initial bolus infusion of cyclosporine and Cremophor EL. Bolus infusions of Cremophor EL have been associated with anaphylactoid reactions. Thus, through mixing of high-dose cyclosporine infusions may be important to reduce the possibility of life-threatening anaphylactoid reactions.

Interactions of clobazam with conventional antiepileptics in children.

Clobazam is a 1,5-benzodiazepine effective in antiepileptic therapy of children and adults. Presently it is mainly used as adjuvant therapy for intractable seizures. Our objective was to evaluate the effect of clobazam on the apparent clearance of other antiepileptic drugs at steady state, and to determine the factors that determine the plasma levels of clobazam and its active metabolite N-desmethylclobazam. Patients were 74 children with intractable seizures who received treatment with clobazam at our institution as part of the Canadian Cooperative Clobazam Study Group during the years 1987 to 1991. Serum concentrations of clobazam, N-desmethylclobazam, and of concomitant antiepileptic drugs were monitored and prospectively collected. The effect of clobazam treatment on the apparent clearance steady state of the other antiepileptic drugs was determined by statistical comparison of the clearances of each drug before and after initiation of clobazam treatment using Wilcoxon's signed rank test. The effects of dosage, age, and concomitant antiepileptic therapy on the levels of clobazam and N-desmethylclobazam was assessed by multivariate analysis. Response to treatment and incidence of adverse effects were evaluated for each conventional antiepileptic drug to possibly identify favorable or unfavorable combinations with clobazam. Whereas the clearances of most conventional antiepileptics are not affected by cotherapy with clobazam, the apparent clearances of valproic acid and primidone are significantly reduced in the presence of clobazam. Serum concentrations of clobazam increased with dosage and age, and decreased with phenobarbital cotherapy. Serum concentrations of N-desmethylclobazam significantly correlated with clobazam serum levels, age, or clobazam dosage and were significantly increased by cotherapy with phenytoin or carbamazepine. None of the concomitantly used drugs were associated with increased or decreased rate of seizure control. Twelve patients experienced mild adverse drug effects that were not associated with particular cotherapy, clobazam dose, or plasma concentrations. When clobazam is added to a therapy regimen that includes valproic acid, the patient should be closely followed for possible adverse drug reactions caused by elevated valproic acid serum concentrations, and monitoring of valproate serum levels should be considered. When clobazam doses are gradually increased to achieve an optimal clinical effect, the interactions with phenobarbital, carbamazepine, and phenytoin do not necessitate therapeutic drug monitoring of clobazam or N-desmethylclobazam, because there is a large therapeutic window and a poor correlation between plasma concentrations and therapeutic efficacy.

Current management of the neonatal abstinence syndrome: a critical analysis of the evidence.

OBJECTIVE: To systematically and critically analyse and summarise the published evidence for the rational choice of pharmacologic treatment of the neonatal abstinence syndrome (NAS), a frequently observed condition in neonates born to mothers who are dependent on physically addicting drugs. DESIGN: Studies comparing different pharmacological agents for the treatment of NAS were identified utilising MEDLINE and additionally the references cited in pertinent articles. The identified studies were critically analysed regarding their study designs and outcome measures. The reported data for the comparative efficacy of the drugs were summarised and evaluated. RESULTS: Fourteen studies were identified, most of them comparing treatment of NAS with phenobarbital, paregoric or diazepam. However, none of these studies was conducted in a double-blind fashion. Frequently, treatment allocations were not properly randomised. Prenatal drug exposure varied and was often not sufficiently verified. Outcome measures and their evaluations differed widely. Due to the different study objectives and flaws in study design, a combined analysis of the published data in the form of a meta-analysis was not deemed possible. When attempting to compare efficacy, diazepam appears to be less efficacious in treating NAS than phenobarbital or paregoric. The relative efficacy of paregoric and phenobarbital appears to depend upon the antenatal exposure of the neonate and on the outcome measure of the study. Only two studies evaluate the efficacy of pure opioids, none of them in direct comparison to paregoric. It remains questionable whether paregoric, which contains the central stimulant camphor and a large amount of alcohol, should be the opioid of choice for the treatment of NAS. CONCLUSION: Most published studies were conducted prior to the development of clinical epidemiology and modern study design and thus yielded only very limited comparative data on the benefits of different treatment protocols. There is very little evidence regarding the efficacy of different pharmacological therapy regimens to treat NAS. More studies are required to produce the evidence needed to allow a rational choice between treatment modalities of NAS and thus to ensure optimal care of the neonates suffering from this condition.

Neurodevelopment of children exposed in utero to antidepressant drugs.

BACKGROUND: Many women of reproductive age have depression, necessitating therapy with either a tricyclic antidepressant drug or a drug, such as fluoxetine, that inhibits the reuptake of serotonin. Whether these drugs affect fetal neurodevelopment is not known. METHODS: We studied the children of 80 mothers who had received a tricyclic antidepressant drug during pregnancy, 55 children whose mothers had received fluoxetine during pregnancy, and 84 children whose mothers had not been exposed during pregnancy to any agent known to affect the fetus adversely. The children's global IQ and language development were assessed between 16 and 86 months of postnatal age by age-appropriate Bayley Scales of Infant Development or the McCarthy Scales of Children's Abilities (for IQ) and the Reynell Developmental Language Scales. RESULTS: The mean (+/-SD) global IQ scores were 118+/-17 in the children of mothers who received a tricyclic antidepressant drug, 117+/-17 in those whose mothers received fluoxetine, and 115+/-14 in those in the control group. The language scores were similar in all three groups. The results were similar in children exposed to a tricyclic antidepressant drug or fluoxetine during the first trimester and those exposed throughout pregnancy. There were also no significant differences in temperament, mood, arousability, activity level, distractibility, or behavior problems in the three groups of children. CONCLUSIONS: In utero exposure to either tricyclic antidepressant drugs or fluoxetine does not affect global IQ, language development, or behavioral development in preschool children.

ATP-gated potassium channel activity of pulmonary resistance vessels in the lamb.

There are conflicting reports on the role of ATP-gated potassium channels (KATP) in the perinatal pulmonary circulation. To investigate this issue, we have used isolated pulmonary resistance vessels from near-term fetal lambs and have tested levcromakalim and glybenclamide, respectively a KATP opener and blocker, on muscle tone at fetal and neonatal PO2, and under hypoxia. Levcromakalim (from 1 microM upwards) relaxed arteries and veins precontracted with a thromboxane A2 (TXA2) analogue (ONO-11113) at neonatal PO2. This effect was nearly completely inhibited by glybenclamide (10 microM) and NG-nitro-L-arginine methyl ester (L-NAME, 100 microM). Conversely, levcromakalim relaxed little arteries precontracted with activating solution (5 mM Ca2+ in K(+)-Krebs) or hypoxia. Equally modest was the response of endothelium-denuded, ONO-11113-contracted arteries. Glybenclamide (10 microM) by itself did not raise the basal tone of vessels, regardless of PO2. We conclude that fetal pulmonary resistance vessels have KATP channels. In the arteries, these channels are located in the endothelium, and their opening causes relaxation by promoting nitric oxide formation. However, this relaxing mechanism does not become active when PO2 is raised from fetal to neonatal levels, nor does its inhibition contribute to hypoxic vasoconstriction.

Anaphylactoid reactions in children receiving high-dose intravenous cyclosporine for reversal of tumor resistance: the causative role of improper dissolution of Cremophor EL.

PURPOSE: An unusually high incidence of anaphylactoid reactions was observed during a phase I/II trial of high-dose intravenous cyclosporine (CsA) therapy to attenuate tumor multidrug resistance (MDR). Five of 21 children experienced severe anaphylactoid reactions shortly after initiation of the first or second CsA infusion. We hypothesized that improper dissolution of the vehicle Cremophor EL may have been a cause for these anaphylactoid reactions. METHODS: All nurses who had administered intravenous CsA were interviewed regarding their technique of preparing the infusion and the occurrence of an anaphylactoid reaction. The responses were statistically analyzed. The effect of various mixing techniques on the distribution of Cremophor EL in the infusion was experimentally evaluated. Different mixing techniques were used to assess their effect on the distribution of Cremophor EL in the solution. RESULTS: Analysis of the preparation techniques of the CsA infusion showed significant correlation between suboptimal mixing of CsA by nurses and the occurrence of anaphylactoid reactions (P = .02). Experimental simulation showed that suboptimal mixing results in an uneven distribution of Cremophor EL, which subsequently sinks to the bottom of the vial. CONCLUSION: Improper mixing of high-dose CsA infusions causes nonsolubilized Cremophor EL to sink to the outflow area of the bottle. An initial bolus infusion of highly concentrated Cremophor EL may produce an anaphylactoid-like response. This mechanism of toxicity is important to recognize, because it is easily preventable by proper preparation of the infusion, thus reducing the incidence of potentially life-threatening anaphylactoid reactions.

Camphorated oil: still endangering the lives of Canadian children.

Camphor is a volatile, aromatic compound familiar to many people as a principal ingredient in topical home remedies for colds. It is highly toxic when ingested. Although camphorated oil in concentrations of 11% or greater is not longer sold in the United States, preparations containing concentrations of up to 20% are still sold over the counter in Canada. The authors describe two children who suffered severe poisoning after accidental ingestion of a small amount of camphorated oil. Both children exhibited generalized tonic-clonic seizures with subsequent respiratory depression. Treatment was symptomatic, consisting of seizure control and respiratory assistance. The authors argue that because camphorated oil is of questionable benefit and poses a danger to the public it should be removed from the market.

Binding characteristics of the new thromboxane A2/prostaglandin H2 receptor antagonist [3H]BAY U 3405 to washed human platelets and platelet membranes.

The new thromboxane A2 antagonist [3H]BAY U 3405 was characterized for its binding to washed human platelets and platelet membranes. In washed platelets the specific binding was reversible, selective and stereospecific, but not saturable. The dissociation constant (Kd) was 6 +/- 2.5 nM, the number of specific binding sites 1177 +/- 306 per platelet. Three structurally different thromboxane A2 (TXA2)/prostaglandin H2 (prostaglandin endoperoxide) (PGH2) receptor ligands completely inhibited the specific binding of [3H]BAY U 3405 in a concentration-dependent manner, indicating that the observed high affinity binding site is the TXA2/PGH2 receptor. In platelet membranes, however, specific [3H]BAY U 3405 binding showed saturability in addition to reversibility, selectivity, and stereospecifity. The Kd of the binding was 9.6 +/- 2.3 nM in kinetic studies and 8.7 +/- 3.7 nM in saturation studies, the inhibition constant (Ki) was 10 +/- 1.1 nM in displacement studies. The TXA2/PGH2 receptor agonists U 46619 and CTA2, and the antagonists Daltroban (BM 13505), I-PTA-OH and SQ 29548 all completely inhibited the specific binding of [3H]BAY U 3405 thus defining the observed binding site as the TXA2/PGH2 receptor. In conclusion, the data suggest that the previously reported TXA2 antagonism of BAY U 3405 is mediated by binding to a specific high affinity binding site of human platelets and platelet membranes that represents the TXA2/PGH2 receptor.

pH dependency of the binding of [3H]BAY U 3405 and various non-labelled ligands to the thromboxane A2/prostaglandin H2 receptor of human platelet membranes.

[3H]BAY U 3405 was used to characterize the effect of acidic and alkaline pH values on the binding of the thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor of human platelet membranes. The specific binding of [3H]BAY U 3405 largely increased upon acidification up to pH 5.8. Saturation binding studies revealed an increase in binding affinity without change in the number of binding sites. At pH 7.4 the Kd was 8.7 +/- 3.7 nM (Bmax = 6.6 +/- 0.6 pmol/mg protein) compared to 1.2 +/- 0.2 nM (Bmax = 6.1 +/- 0.6 pmol/mg protein) at pH 5.8. A more than 10-fold higher rate of association was observed at pH 5.8 compared to pH 7.4, while the rate of dissociation showed only minor changes. The kinetically derived dissociation constant was 1 nM (pH 5.8) and 9.6 nM (pH 7.4). The pH dependency of the binding of structurally different non-labelled ligands to the TXA2/PGH2 receptor was evaluated by inhibition studies at pH 5.8 and pH 7.4. BAY U 3405, daltroban, CTA2, and U 46619 showed significantly higher affinities at pH 5.8. In contrast, I-PTA-OH and GR 32191 had a higher affinity at pH 7.4. No significant difference was seen with SQ 29548 at the observed pH values. A second protonable group within the molecules I-PTA-OH, GR 32191, and SQ 29548 might be responsible for the observed differences.

pH-dependent binding of the TXA2/PGH2-receptor of human platelet membranes to various ligands.

[3H]-BAY U 3405 was used to characterize the pH-dependency of the binding of various ligands to the TXA2/PGH2-receptor of human platelet membranes. Maximum binding of [3H]-BAY U 3405 is achieved at pH 5.8. In inhibition studies the ligands Daltroban, CTA2, and U 46619 also show a higher affinity at pH 5.8 compared to pH 7.4. In contrast, the ligands I-PTA-OH and GR 32191 have a higher affinity at pH 7.4. No difference is seen with SQ 29548. The ligands I-PTA-OH, GR 32191, and SQ 29548 have a second protonable group in common, which is thought to be the reason for the different pH-dependent binding.