Incidence and predictors of treatment-related mortality in paediatric acute leukaemia in El Salvador.

Survival rates among children with leukaemia in low-income countries are lower than those in high-income countries. This has been attributed in part to higher treatment-related mortality (TRM). We examined the demographics, treatment, and outcomes of paediatric patients in El Salvador with acute lymphoblastic leukaemia (ALL) or acute myeloid leukaemia (AML) to determine the incidence, causes, and risk factors for TRM. Two trained data managers collected data prospectively; no patients were excluded. Biological, socioeconomic and nutritional predictors were examined. A total of 469 patients with ALL and 78 patients with AML were included. The 2-year cumulative incidence of TRM was significantly higher among children with AML (35.4+/-6.4%) than those with ALL (12.5+/-1.7%; P<0.0001). However, the proportion of deaths attributable to the toxicity of treatment did not differ significantly between AML (25/47, 53.2%) and ALL (55/107, 51.4%; P=0.98). Among children with ALL, low monthly income (P=0.04) and low parental education (P=0.02) significantly increased the risk of TRM. Among children with AML, biological, socioeconomic, and nutritional variables were not associated with TRM. In this low-income country, toxic death significantly contributes to mortality in both ALL and AML. A better understanding of the effect of socioeconomic status on TRM may suggest specific strategies for patients with ALL.

Erythropoietic and reticuloendothelial function in bone marrow in dogs.

Erythropoietic and reticuloendothelial functions in bone marrow were found to be identically distributed between various bones and within individual bones in the dog.

Vaccine protection of chimpanzees against challenge with HIV-1-infected peripheral blood mononuclear cells.

Because human immunodeficiency virus (HIV) can be transmitted as cell-free virus or as infected cells (cell-associated virus), vaccines must protect against infection by both viral forms. Vaccine-mediated protection of nonhuman primates against low doses of cell-free HIV-1, HIV-2, or simian immunodeficiency virus (SIV) has been demonstrated. It is now shown that multiple immunizations of chimpanzees with HIV-1 antigens protected against infection with cell-associated virus. Protection can persist for extended periods (one animal had not been exposed to viral antigens for 1 year before challenge). These results show that it is possible to elicit long-lasting protective immunity against cell-associated HIV-1.

3,3',5-triiodothyronine administration in vivo modulates the hormone-sensitive adenylate cyclase system of rat hepatocytes.

The ability of 10 muM epinephrine or isoproterenol to stimulate cyclic AMP accumulation was decreased in hepatocytes isolated from hyperthyroid (triiodothyronine treated) as compared to euthyroid rats. In the presence of methylisobutylxanthine, epinephrine or isoproterenol-stimulated cyclic AMP accumulation was approximately 65% lower in hyperthyroid as compared with euthyroid rat hepatocytes. The ability of glucagon to stimulate a cyclic AMP response was also decreased in the hyperthyroid state, when assayed in either the absence or presence of a methyl xanthine. The character of the catecholamine-stimulated cyclic AMP response was beta adrenergic in both the hyperand euthyroid states. No evidence for an alpha(2) adrenergic mediated component of catecholamine action on cyclic AMP levels was noted. Cyclic AMP phosphodiesterase activity of hepatocyte homogenates was not altered in the hyperthyroid state. Hormone-stimulated, guanine nucleotide- and fluoride-activatable adenylate cyclase activity was reduced in subcellular fractions obtained from hyperthyroid as compared with euthyroid rat hepatocytes. Beta adrenergic receptor binding was reduced approximately 35% and glucagon receptor binding reduced approximately 50% in the hyperthyroid as compared with euthyroid rat hepatocyte membrane fractions. The status of the regulatory components of adenylate cyclase were examined by in vitro treatment of subcellular fractions with cholera toxin. The ability of cholera toxin to modulate adenylate cyclase was not altered by hyperthyroidism. Cholera toxin catalyzed AD[(32)P]ribosylation of hyperthyroid and euthyroid rat hepatocyte proteins separated electrophoretically displayed nearly identical autoradiograms. Studies of the reconstitution of adenylate cyclase activity of S49 mouse lymphoma cyc(-) mutant membranes by detergent extracts from rat hepatocyte membranes, indicated that hyperthyroidism was associated with a reduced capacity of regulatory components to confer fluoride, but not guanine nucleotide activatability to catalytic cyclase. Thyroid hormones regulate the hormone-sensitive adenylate cyclase system of rat hepatocytes at several distinct loci of the system.

Induction of stress proteins in cultured myogenic cells. Molecular signals for the activation of heat shock transcription factor during ischemia.

Expression of major stress proteins is induced rapidly in ischemic tissues, a response that may protect cells from ischemic injury. We have shown previously that transcriptional induction of heat-shock protein 70 by hypoxia results from activation of DNA binding of a preexisting, but inactive, pool of heat shock factor (HSF). To determine the intracellular signals generated in hypoxic or ischemic cells that trigger HSF activation, we examined the effects of glucose deprivation and the metabolic inhibitor rotenone on DNA-binding activity of HSF in cultured C2 myogenic cells grown under normoxic conditions. Whole-cell extracts were examined in gel mobility shift assays using a 39-bp synthetic oligonucleotide containing a consensus heat-shock element as probe. ATP pools were determined by high-pressure liquid chromatography and intracellular pH (pHi) was measured using a fluorescent indicator. Glucose deprivation alone reduced the cellular ATP pool to 50% of control levels but failed to activate HSF. However, 2 x 10(-4) M rotenone induced DNA binding of HSF within 30 min, in association with a fall in ATP to 30% of control levels, and a fall in pHi from 7.3 to 6.9. Maneuvers (sodium propionate and amiloride) that lowered pHi to 6.7 without ATP depletion failed to activate HSF. Conversely, in studies that lowered ATP stores at normal pH (high K+/nigericin) we found induction of HSF-DNA binding activity. Our data indicate that the effects of ATP depletion alone are sufficient to induce the DNA binding of HSF when oxidative metabolism is impaired, and are consistent with a model proposed recently for transcriptional regulation of stress protein genes during ischemia.

Serial controlled N-of-1 trials of topical vitamin E as prophylaxis for chemotherapy-induced oral mucositis in paediatric patients.

The objectives were (1) to determine whether in children undergoing doxorubicin-containing chemotherapy, topical vitamin E decreases an objective measurement of oral mucositis compared to placebo, and (2) to assess the feasibility of an innovative trial design in paediatric cancer, combining N-of-1 trials using Bayesian meta-analysis. We conducted a series of N-of-1, double-blinded, randomised controlled trials in children > or = 6 years of age receiving repeated cycles of identical doxorubicin-containing chemotherapy. Each study cycle was followed by topical vitamin E (800 mg) or placebo. We enroled 16 children and 45 post chemotherapy cycles were randomised to vitamin E (N=22) or placebo (N=23). There was no difference in objective mucositis scores with a mean score of 0.2 with vitamin E and 0.3 with placebo. Topical vitamin E does not reduce doxorubicin-induced oral mucositis in children. The use of N-of-1 studies and Bayesian meta-analysis may facilitate the study of some therapies in paediatric oncology.

Evolution of genotypic and phenotypic resistance during chronic treatment with the fusion inhibitor T-1249.

T-1249 is a peptide HIV fusion inhibitor (FI) previously under development for use in FI-naive and experienced patients. Here we present prospectively planned longitudinal analyses of FI resistance during 48 weeks of T-1249 dosing in patients with extensive prior FI exposure. T1249-105 was a single-arm rollover study in patients with prior resistance to enfuvirtide (ENF) and 10 days of T-1249 functional monotherapy exposure. The phenotype and genotype of plasma virus envelopes were analyzed at baseline and at study weeks 8, 16, and 48. At study entry, viruses had a geometric mean decrease in susceptibility to ENF of 51.8-fold but to T-1249 of 1.8-fold; extensive genotypic resistance to ENF was observed. A median viral load response of - 1.5 log(10) copies/ml was observed at week 2 that was partially sustained (- 0.5 log(10) copies/ml) through 48 weeks. Resistance to T-1249 gradually increased to a geometric mean 92.7-fold decrease from FI-naive baseline; this occurred concomitant with further evolution of gp41 amino acids 36-45, most commonly the G36D (n = 6, 16%) or N43K (n = 9, 24%) substitutions. A novel substitution, A50V (n = 12, 32%), was also common, as were the N126K and S138A substitutions in heptad-repeat 2 (HR-2). These data point toward a primary role for the gp41 36-45 locus in modulating FI binding and suggest that residues in HR-2 may contribute in a more limited manner to development of peptide FI resistance. These data also point toward a substantial genetic barrier and fitness cost to development of resistance to next-generation fusion inhibitors.

Inositol regulates phosphatidylglycerolphosphate synthase expression in Saccharomyces cerevisiae.

The enzyme phosphatidylglycerolphosphate synthase (PGPS; CDPdiacylglycerol-glycerol-3-phosphate 3-phosphatidyltransferase; EC 2.7.8.5) catalyzes the committed step in the synthesis of cardiolipin, a phospholipid found predominantly in the mitochondrial inner membrane. To determine whether PGPS is regulated by cross-pathway control, we analyzed PGPS expression under conditions in which the regulation of general phospholipid synthesis could be examined. The addition of inositol resulted in a three- to fivefold reduction in PGPS expression in wild-type cells in the presence or absence of exogenous choline. The reduction in enzyme activity in response to inositol was seen in minutes, suggesting that inactivation or degradation of the enzyme plays an important role in inositol-mediated repression of PGPS. In cho2 and opi3 mutants, which are blocked in phosphatidylcholine synthesis, inositol-mediated repression of PGPS did not occur unless choline was added to the media. Three previously identified genes that regulate general phospholipid synthesis, INO2, INO4, and OP11, did not affect PGPS expression. Thus, ino2 and ino4 mutants, which are unable to derepress biosynthetic enzymes involved in general phospholipid synthesis, expressed wild-type levels of PGPS activity under derepressing conditions. PGPS expression in the opi1 mutant, which exhibits constitutive synthesis of general phospholipid biosynthetic enzymes, was fully repressed in the presence of inositol and partially repressed even in the absence of inositol. These results demonstrate for the first time that an enzymatic step in cardiolipin synthesis is coordinately controlled with general phospholipid synthesis but that this control is not mediated by the same genetic regulatory circuit.

New positive and negative regulators for general control of amino acid biosynthesis in Saccharomyces cerevisiae.

The biosynthesis of most amino acids in Saccharomyces cerevisiae is coregulated. Starvation for a single amino acid results in the derepression of amino acid biosynthetic enzymes in many unrelated pathways. This phenomenon, known as general control, is mediated by both positive (GCN) and negative (GCD) regulatory genes. In this paper we describe the identification and characterization of several new regulatory genes for this system, GCN6, GCN7, GCN8, GCN9, and GCD5. A mutation in the negative regulator GCD5 was isolated on the basis of its suppression of a gcn2 mutation. The effect of gcd5 is a posttranscriptional increase in histidine biosynthetic enzyme activity. Suppressors of gcd5 which are deficient in derepression were in turn isolated. Eight such mutations, defining four new positive regulatory genes (GCN6 through GCN9), were obtained. These mutations are recessive, confer sensitivity to multiple amino acid analogs, and result in decreased mRNA levels for genes under general control. The GCN6 and GCN7 gene products were shown to be positive regulators for transcription of the GCN4 gene, the most direct-acting positive regulator thus far identified. The interaction of GCN6 and GCN7 with GCN4 is fundamentally different from that of previously isolated GCN genes. It should also be noted that these gcn selections gave a completely different nonoverlapping set of mutations from earlier selections which relied on analog sensitivity. Thus, we may have identified a new class of GCN genes which are functionally distinct from GCN1 through GCN5.

Negative regulatory gene for general control of amino acid biosynthesis in Saccharomyces cerevisiae.

In Saccharomyces cerevisiae, many amino acid biosynthetic pathways are coregulated by a complex general control system: starvation for a single amino acid results in the derepression of amino acid biosynthetic genes in multiple pathways. Derepression of these genes is mediated by positive (GCN) and negative (GCD) regulatory genes. In this paper we describe the isolation and characterization of a previously unreported negative regulatory gene, GCD3. A gcd3 mutation is recessive to wild type, confers resistance to multiple amino acid analogs, and results in overproduction and partially constitutive elevation of mRNA levels for amino acid biosynthetic genes. Furthermore, a gcd3 mutation can overcome the derepression-deficient phenotype of mutations in the positive regulatory GCN1, GCN2, and GCN3 genes. However, the gcd3 mutation cannot overcome the derepression-deficient phenotype of a gcn4 mutation, suggesting that GCD3 acts as a negative regulator of the important GCN4 gene. Northern blot analysis confirmed this conclusion, in that the steady-state levels of GCN4 mRNA are greatly increased in a gcd3 mutant. Thus, the negative regulatory gene GCD3 plays a central role in derepression of amino acid biosynthetic genes.

Characterization of envelope glycoprotein gp41 genotype and phenotypic susceptibility to enfuvirtide at baseline and on treatment in the phase III clinical trials TORO-1 and TORO-2.

Enfuvirtide (T-20) is the first entry inhibitor approved for treatment of HIV infection and acts by inhibiting conformational changes in the viral envelope protein gp41 that are necessary for fusion of the virus and host cell membranes. Here we present genotypic and phenotypic data on viral envelopes obtained at baseline (n = 627) and after 48 weeks of enfuvirtide treatment (n = 302) from patients in the TORO (T-20 versus Optimized Regimen Only)-1 and -2 phase III pivotal studies. The amino acid sequence at residues 36-45 of gp41 was highly conserved at baseline except for polymorphism of approximately 16% at position 42. Substitutions within gp41 residues 36-45 on treatment were observed in virus from 92.7% of patients who met protocol defined virological failure criteria and occurred in nearly all cases (98.8%) when decreases in susceptibility to enfuvirtide from baseline of greater than 4-fold were observed. Consistent with previous observations, a wide range of baseline susceptibilities (spanning 3 logs) was observed; however, lower in vitro baseline susceptibility was not significantly associated with a decreased virological response in vivo. Virological response was also independent of baseline coreceptor tropism and viral subtype.

Effect in vivo of multiple injections of purified murine and recombinant human macrophage colony-stimulating factor to mice.

Hematopoietic efficacy in vivo of multiple injections of purified murine L-cell and recombinant human macrophage colony-stimulating factors (M-CSF; specific activity, greater than 2 x 10(7) units/mg) was assessed in mice. Injections i.v. of sterile saline or 20,000 units of M-CSF were administered once (at 0 h), twice (at 0 and 12 h), or three times (at 0, 12, and 24 h) to C57BL/6 x DBA/2 F1 mice. Numbers and cycling rates of marrow and spleen granulocyte-macrophage, erythroid, and multipotential progenitor cells were assessed 32-36 h after the first injection. Marrow, spleen, and peripheral blood cellularity was assessed at intervals of up to 105 h. Progenitor cell cycling rates were significantly increased after one and two injections of M-CSF but were reduced to a slow or noncycling state after three injections. For marrow cells, the third injection resulted in a significant suppression of hematopoietic progenitor cell cycling compared to the control group. No significant changes were noted for number of progenitors per femur or spleen, for marrow, spleen, or peripheral blood cellularity, or for differential cell counts in these organs after any of the M-CSF treatment schedules. Suppression of progenitor cell proliferation noted after three injections of M-CSF may at least partially explain why repeated injections of 20,000 units of M-CSF fails to increase bone marrow, spleen, or blood cellularity even though one injection of M-CSF increases cycling rates of the hematopoietic progenitors.

NDPK-D (NM23-H4)-mediated externalization of cardiolipin enables elimination of depolarized mitochondria by mitophagy.

Mitophagy is critical for cell homeostasis. Externalization of the inner mitochondrial membrane phospholipid, cardiolipin (CL), to the surface of the outer mitochondrial membrane (OMM) was identified as a mitophageal signal recognized by the microtubule-associated protein 1 light chain 3. However, the CL-translocating machinery remains unknown. Here we demonstrate that a hexameric intermembrane space protein, NDPK-D (or NM23-H4), binds CL and facilitates its redistribution to the OMM. We found that mitophagy induced by a protonophoric uncoupler, carbonyl cyanide m-chlorophenylhydrazone (CCCP), caused externalization of CL to the surface of mitochondria in murine lung epithelial MLE-12 cells and human cervical adenocarcinoma HeLa cells. RNAi knockdown of endogenous NDPK-D decreased CCCP-induced CL externalization and mitochondrial degradation. A R90D NDPK-D mutant that does not bind CL was inactive in promoting mitophagy. Similarly, rotenone and 6-hydroxydopamine triggered mitophagy in SH-SY5Y cells was also suppressed by knocking down of NDPK-D. In situ proximity ligation assay (PLA) showed that mitophagy-inducing CL-transfer activity of NDPK-D is closely associated with the dynamin-like GTPase OPA1, implicating fission-fusion dynamics in mitophagy regulation.

Phosphatidylglycerophosphate synthase from yeast.

The phospholipid cardiolipin, or diphosphatidylglycerol, is ubiquitous in eucaryotes. It is unique in structure, subcellular localization, and potential function. Because it is found predominantly in the mitochondrial inner membrane, it is an excellent marker for mitochondrial biogenesis. Cardiolipin is required for activity of several mitochondrial enzymes and possibly also for import of proteins into the mitochondrion. To understand the role of cardiolipin in these cellular events, it is necessary to characterize the enzymes of the cardiolipin pathway, as well as the genes that control the expression of these enzymes. To date, the structural genes encoding the cardiolipin biosynthetic enzymes have not been identified in any eucaryotic organism. However, considerable information is available regarding the regulation of this pathway in yeast. The activity and regulation of the first enzyme of the pathway, CDP-diacylglycerol:sn-glycerol-3-phosphate 3-phosphatidyltransferase (phosphatidylglycerophosphate (PGP) synthase, EC 2.7.8.5), has been characterized in two evolutionarily divergent yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe. In contrast to the second and third enzymes of the pathway, this enzyme is highly regulated, both by cross-pathway control and by factors affecting mitochondrial development. PGP synthase from S. pombe (and cardiolipin synthase from S. cerevisiae) have been purified to homogeneity. The amino acid sequences of these enzymes, combined with the availability of the complete genome sequence from S. cerevisiae will simplify the cloning of these genes in the near future.

Cardiolipin synthase from yeast.

Cardiolipin synthase catalyzes the synthesis of the mitochondrial phospholipid cardiolipin. Cardiolipin synthase is a unique membrane-bound enzyme in that it utilizes two phospholipids, both insoluble in water, as substrates. Kinetic analysis suggests that the enzyme forms a ternary complex with the two lipid substrates, and that a divalent metal ion directly associates with cardiolipin synthase to form the active enzyme. While little is known about the regulation of cardiolipin synthase in yeast, activity is reduced in mutants in which the mitochondrial genome is deleted, and in mutants with defective respiratory complexes. In p0 mutants, which contain no mitochondrial DNA and are defective in the assembly of many mitochondrial membrane protein complexes, cardiolipin synthase activity is reduced by 50%. Mutants defective in respiratory complexes, particularly those incapable of cytochrome oxidase assembly, also have reduced cardiolipin synthase activity. Thus it is likely that respiration and cardiolipin formation are interdependent. The enzyme was recently purified from the budding yeast Saccharomyces cerevisiae. Enzyme activity was associated with a 25-30-kDa protein. The amino acid sequence of this protein, combined with the availability of the complete yeast genome sequence, will hopefully lead to the identification of the structural gene for this enzyme in the near future.

Characterization and regulation of phosphatidylglycerolphosphate phosphatase in Saccharomyces cerevisiae.

Phosphatidylglycerophosphatase (EC 3.1.3.27) activity was characterized in mitochondrial extracts from Saccharomyces cerevisiae. The enzyme has a pH optimum of 5.5. Maximum activity occurs in the presence of Triton X-100 (5 mM) and cobalt or magnesium ions (5 mM). The apparent Km for PGP is 14.6 microM. The temperature optimum is between 50 degrees C and 60 degrees C. The enzyme is labile above 50 degrees C. The presence of inositol in growth media results in a slight but reproducible increase in PGPase activity in mitochondrial extracts from glucose-grown cells but not glycerol-grown cells. The inositol effect is not seen in crude cell extracts. Carbon source does not affect PGPase activity in mitochondrial extracts or in crude cell extracts.

Biochemical characterization and regulation of cardiolipin synthase in Saccharomyces cerevisiae.

Cardiolipin (CL) synthase activity was characterized in mitochondrial extracts of the yeast Saccharomyces cerevisiae and was shown for the first time to utilize CDP-diacylglycerol as a substrate. CL synthase exhibited a pH optimum of 9.0. Maximal activity was obtained in the presence of 20 mM magnesium with a Triton X-100: phospholipid ratio of 1:1. The apparent Km values for phosphatidylglycerol and CDP-diacylglycerol were 1 mM and 36 microM, respectively. CL synthase activity was maximal at 45 degrees C and heat inactivation studies showed that the enzyme retained greater than 75% of its activity at temperatures up to 55 degrees C. To study the regulation of CL synthase, the enzyme was assayed in cells grown under conditions known to affect general phospholipid synthesis. Unlike many phospholipid biosynthetic enzymes including PGP synthase, which catalyzes the initial step in CL biosynthesis, CL synthase was not repressed in cells grown in the presence of the phospholipid precursor inositol. Detailed procedures for the enzymatic synthesis of 32P-labelled substrates are described.

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.

Improvement of canine pancreas-allograft survival with diagnosis of rejection by fine-needle aspiration biopsy.

Early diagnosis of rejection in pancreas-allograft transplantation remains a clinical challenge. The aim of this study was to assess the ability of antirejection therapy to reverse rejection when the diagnosis was based on either fine-needle aspiration biopsy (FNAB) or urinary amylase (UA). Sixteen dogs received a total-pancreas allograft with exocrine drainage into the bladder. Initially, a deliberately low dose of cyclosporin was given. Monitoring included percutaneous FNAB with ultrasound guidance and fasting spot measurements of UA. The diagnosis of rejection was made in alternate dogs when UA fell to less than 5000 IU/L (group A) or when the total corrected increment (TCI) of aspirated infiltrating cells was greater than 2.6 (group B). Antirejection therapy consisted of 10 mg.kg-1.day-1 i.v. methylprednisolone for 5 days and an increased dose of cyclosporin (25 mg.kg-1.day-1). The median allograft survival was 9 days (range 8-19) in group A and 32 days (range 10-63) in group B (P = .01). A fall in UA permitted the successful reversal of rejection in only one of six grafts, whereas five of seven grafts were successfully treated when rejection diagnosis was based on FNAB. In conclusion, early diagnosis of rejection was achieved by FNAB, improving the ability of antirejection therapy to reverse pancreas-allograft rejection and prolong survival.

Relation between amiodarone and desethylamiodarone plasma concentrations and electrophysiologic effects, efficacy and toxicity.

Because the value of monitoring amiodarone plasma concentrations remains undefined, this study was performed to evaluate its role during the management of patients receiving amiodarone. The early electrophysiologic effects of amiodarone were assessed in 40 consecutive patients with coronary artery disease and sustained ventricular tachycardia or fibrillation who underwent electrophysiologic studies and measurement of amiodarone plasma concentration before and 29 +/- 15 (mean +/- SD) days after initiation of therapy. Amiodarone and desethylamiodarone plasma levels did not correlate with changes in either sinus cycle length, QTc interval, ventricular effective refractory period, AH and HV intervals or ventricular tachycardia cycle length. Amiodarone and desethylamiodarone plasma concentrations and the effects of the drug on conduction intervals or right ventricular effective refractory periods were not related to suppression of arrhythmia induction by ventricular stimulation after 1 month of therapy. The relation between amiodarone plasma concentrations and both toxicity and efficacy during long-term therapy were prospectively assessed in a larger series of 114 consecutive patients with either symptomatic supraventricular or ventricular arrhythmias who were followed up on long-term amiodarone therapy for 26 +/- 15 months. Sixty-three patients (55%) had one or more adverse effects attributed to amiodarone. By life-table analysis, 40, 69 and 80% of patients had experienced an adverse reaction after 1, 2 and 3 years of therapy, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)