Excess fatality from desipramine in children and adolescents

OBJECTIVE

To compare the case fatality rate (CFR) from desipramine ingestion in children and adolescents with that of other tricyclic antidepressants.

METHOD

All mentions of desipramine, amitriptyline, imipramine, nortriptyline, and doxepin in children and adolescents recorded in the American Association of Poison Control Centers Toxic Exposure Surveillance System from 1983 to 2002 were analyzed. The CFR for each drug was defined as the ratio of the number of deaths/number of mentioned exposures.

RESULTS

There were 24 fatalities in children younger than 6 years old (desipramine, n=10; amitriptyline, n=7; doxepin, n=3; imipramine, n=3; nortriptyline, n=1) and 144 fatalities in older children and adolescents (desipramine, n=56; amitriptyline, n=30; doxepin, n=16; imipramine, n=31; nortriptyline, n=11). The CFR from desipramine was significantly higher compared with the other tricyclic antidepressants in children younger than 6 years old (chi=36, p<.001) and in older children and adolescents (chi=155, p<.001). The CFR from desipramine exceeded that of amitriptyline, doxepin, imipramine, and nortriptyline by 7- to 8-, 4-, 6- to 12-, and 7- to 10-fold, respectively.

CONCLUSIONS

The excess CFR from desipramine in children and adolescents and the reports of sudden death in children treated with therapeutic doses call for caution in prescribing desipramine to children and adolescents.

Excess fatality from desipramine and dosage recommendations

Higher case fatality rates (CFR) were previously reported from desipramine than for 3 other tricyclic antidepressants (TCAs): amitriptyline, nortriptyline, and imipramine. The database of the American Association of Poison Control Centers (AAPCC) Toxic Exposure Surveillance System (TESS) for the 20 years 1983-2002 was used to evaluate the CFR of desipramine and the other TCAs. The CFR of desipramine was 2.25-, 2.31-, and 2.62-fold the CFR for amitriptyline, nortriptyline, and imipramine, respectively (P < 0.001). Mechanisms of desipramine toxicity and its dosage recommendations are discussed. Desipramine and nortriptyline have higher distribution volumes and erythrocyte/plasma ratios than their parent compounds imipramine and amitriptyline. This implies lower therapeutic plasma levels and reduced doses for desipramine and nortriptyline compared with their parent compounds. Such adjustments have been done for nortriptyline, but not for desipramine. The authors suggest that the high CFR of desipramine might be reduced by lowering its dose, therapeutic plasma level, and maximal pill content.

Inhibition of endothelial cell proliferation and bFGF-induced phenotypic modulation by nitric oxide

S-nitroso-N-acetyl-D,L-acetylpenicillamine (SNAP), a chemical donor of NO, inhibited serum- and basic fibroblast growth factor (bFGF)-stimulated cultured endothelial cell (EC) proliferation in a dose-dependent manner. The inhibitory effect of NO was reversible after washoff of SNAP-containing media. Measurement of nitrate and nitrite in the media of SNAP-treated EC indicated that decomposition of SNAP into NO reached a stable level at or before 24 h; proliferation of EC was significantly inhibited for another 48 h and recovered thereafter if no additional SNAP was added. The level of NO produced by inhibitory concentrations of SNAP was comparable to NO levels produced by the induction of inducible nitric oxide synthase (iNOS) in smooth muscle cells or retinal pigmented epithelial cells. The growth-inhibitory effect of NO was unlikely to be due to cytotoxicity since 1) cells never completely lost their proliferative capacity even after 10 days of exposure to repeated additions of SNAP, 2) the inhibitory effect was reversible upon removal of NO and with the passage of time, and 3) NO did not reduce the number of cells that were growth-arrested with TGF-beta 1. In addition to its mitogenic effect, bFGF induced pronounced phenotypic changes, including suppression of contact inhibition, altered cell morphology, and scattering of the cells, in BPAEC cultures, whereas cells treated simultaneously with bFGF and NO did not exhibit these changes. These observations suggest that NO contributes to the regulation of angiogenesis and reendothelialization, processes that require EC proliferation, migration, and differentiation.

Glucose-6-phosphate dehydrogenase deficiency severely restricts the biotransformation of daunorubicin in human erythrocytes

Recognition and analysis of distinct mechanisms by which primaquine and other hemolytic drugs activate the hexose monophosphate shunt (HMS) have suggested a hitherto unsuspected pharmacogenetic interaction between daunorubicin metabolism and glucose-6-phosphate dehydrogenase (G6PD) deficiency. Because this deficiency is very common, and because anthracyclines are indispensable antitumor antibiotics that are biotransformed mainly by carbonyl reductase, we have compared the reductase-mediated conversion of daunorubicin to daunorubicinol and the conversion of doxorubicin to doxorubicinol in G6PD-deficient and nondeficient erythrocytes. We found that even without G6PD deficiency, the HMS dehydrogenases selectively limited daunorubicin metabolism, as contrasted with that of doxorubicin. The milder GdA- variety of G6PD deficiency restricted the biotransformation of daunorubicin at therapeutic levels, in hemolysates and intact erythrocytes, within 15 minutes, for at least 24 hours. The bioconversion defect was even more severe in Gd Mediterranean G6PD deficiency. Primaquine aldehyde competed with daunorubicin as a substrate for carbonyl reductase. These studies show that HMS dehydrogenase activity controls carbonyl reductase-dependent biotransformation. New issues arise concerning possible effects of G6PD deficiency on the oncolytic and toxic properties of anthracyclines that are effective substrates for carbonyl reductase and also on non-xenobiotic reactions catalyzed by this enzyme.

Glutathione, cell proliferation, and 1,3-bis-(2-chloroethyl)-1-nitrosourea in K562 leukemia

We have pursued our findings of glutathione reductase (GSSG-R) deficiency and disturbed glutathione in cancer patients treated with 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU), by investigating how thiol metabolism, cell proliferation, and the nitrosourea interact in human K562 leukemia. Fasting cells arrested in G greatly increased their reduced glutathione (GSH) in response to growth factors. The rise in thiol began after several hours, peaked before DNA synthesis, and resulted from increased production. BCNU inactivated GSSG-R rapidly, and later retarded, doubled, and greatly prolonged GSH formation before stopping DNA synthesis. Pretreatment unlike post treatment with buthionine-S-R-sulfoximine (BSO) diminished BCNU's ability to block GSSG-R. Enzyme inhibition decreased with falling cellular GSH. In the leukemia system as in vivo, sequential BCNU-induced thiol alterations heralded delayed antiproliferative effects. Drug timing markedly affected both thiol and DNA syntheses. By destroying GSSG-R and delaying the upregulation of thiol synthesis while escalating GSH utilization and requirements, the nitrosourea created a striking and previously unrecognized window of vulnerability for GSH-dependent processes. During this period, altered GSH metabolism could contribute indirectly to BCNU's pleiotropic effects by interfering with DNA alkylation repair, glucose decarboxylation, deoxyribose formation, and possibly by influencing other aspects of proliferation. Acquired GSSG-R deficiency was also an early and sensitive marker for prodrug breakdown and activation.

Distribution of amitriptyline and nortriptyline in blood: role of alpha-1-glycoprotein

To interpret blood levels of tricyclic antidepressants, we studied the distributions of amitriptyline and nortriptyline in human blood and explored their control by plasma factors. Each compound (300 ng/ml) was added to whole adult blood and to cord blood with decreased alpha-1-glycoprotein (AGP). Drugs (250 ng/ml) were also added to washed erythrocytes (RBCs) resuspended in autologous plasma or saline (hematocrit = 0.4) with or without AGP, albumin, or tris(2-butoxyethyl) phosphate (TBEP), used to displace AGP-bound drugs. Plasma AGP was determined in all adult blood donors (n = 17). With adult blood, plasma amitriptyline was 393 +/- 52 ng/ml, RBC amitriptyline was 184 +/- 33 ng/ml. Plasma and RBC nortriptyline were 199 +/- 28 and 288 +/- 39 ng/ml, respectively. With saline, cellular amitriptyline and nortriptyline were 81 +/- 10 and 88 +/- 6%, respectively. With plasma, cellular amitriptyline and nortriptyline were 25 +/- 8 and 49 +/- 10%, respectively. The corresponding cord blood values were 52 +/- 12 and 62 +/- 6%. Graded increments of AGP in saline reproduced the distribution pattern seen with increasing concentrations of plasma. Albumin did not influence drug distribution. TBEP markedly increased erythrocyte amitriptyline in adult but not in cord blood. Plasma AGP correlated positively (p = 0.031) with the RBC/plasma ratio of amitriptyline. Amitriptyline is predominantly distributed in plasma, nortriptyline in RBCs. This differential distribution is dose dependent and reflects the higher binding of amitriptyline to AGP when compared with nortriptyline. Interpretation of tricyclic antidepressant blood levels is clarified by obtaining assays from RBCs and plasma.

Tricyclic antidepressants in red cells and plasma: correlation with impaired intraventricular conduction in acute overdose

OBJECTIVE

Tricyclic antidepressant levels in red blood cells and plasma in acute overdose and their association with cardiotoxicity were studied.

METHODS

This was a prospective study in 15 patients with acute tricyclic antidepressant overdose. Tricyclic antidepressant parent compounds and metabolites were measured in red blood cells and plasma, and tricyclic antidepressant levels were correlated with ECG indexes of toxicity.

RESULTS

Plasma levels of the parent compounds were higher than their red blood cell levels on admission (mean +/- SD, 691 +/- 409 and 337 +/- 220 ng/ml, respectively). Admission metabolite levels were higher in red blood cells than in plasma (264 +/- 180 and 190 +/- 164 ng/ml, respectively). QRS duration and the red blood cell levels of the metabolites were significantly correlated at the time of admission (r = 0.77, p < 0.01), as well as at 6 to 10 hours (r = 0.74, p < 0.01).

CONCLUSIONS

In acute overdose, a shift of tricyclic antidepressants from plasma to red blood cells and increased levels of red blood cell metabolites reflect tissue redistribution of the drug. Tricyclic antidepressant red blood cell metabolites are the best markers for impaired intraventricular conduction.

Red cell and plasma concentrations of fluoxetine and norfluoxetine

To study the distribution of fluoxetine and norfluoxetine in blood compartments we determined their concentrations in red cells and plasma after the addition of 500 ng/ml of each compound to human blood in vitro. Red cell and plasma fluoxetine concentrations were 493 +/- 79 ng/ml and 454 +/- 53 ng/ml, respectively (P > 0.1). To assess the potential implications of this distribution on routine monitoring of these compounds in plasma, we determined fluoxetine and norfluoxetine concentrations in red cells and plasma in 6 patients receiving various doses of fluoxetine. While in 4 patients the concentrations of fluoxetine and norfluoxetine in red cells and plasma were comparable, 2 patients had higher concentrations of both compounds in red cells. Variations in the distribution of fluoxetine and norfluoxetine in blood compartments are relatively small. Plasma levels may reflect the drug concentration in whole blood more reliably for fluoxetine and norfluoxetine than for tricyclic antidepressants.

Visualization of ingested medications in the stomach by ultrasound

The authors describe a potential application of ultrasound in detection of pills in the stomach, and report the first case of its use in a patient. Thirty pills were studied in vitro by ultrasound. All were clearly detected, with better imaging compared with plain radiography. Four pills with slow disintegration (sustained release or enteric coated) and two with fast disintegration (immediate release) were further studied by ultrasound, following their ingestion by human volunteers. All four pills with slow disintegration were clearly visualized in the stomach, while detection of the other two pills was inconsistent. A sustained-release phenytoin capsule was detected by ultrasound in the stomach of a patient 3 hours after its ingestion. Ultrasound is a potential diagnostic tool in detection of pills in the stomach following acute ingestion. Its use, however, seems to be limited to sustained-release or enteric-coated preparations.

The conversion of primaquine into primaquine-aldehyde, primaquine-alcohol, and carboxyprimaquine, a major plasma metabolite

Although efficacy and toxicity of primaquine (PQ) depend on bioconversion, the process is poorly understood, even for carboxyprimaquine (CPQ), the major plasma metabolite. Earlier work to clarify drug metabolism showed that PQ could be converted quantitatively into CPQ, in vitro, with human erythroleukemic K562 cells or nonleukemic bone marrow supplemented with calf serum. We have now found--using systems with serum only, as well as with K562, bone marrow, and adult or embryonic liver cells--that the bioconversion of the side chain of PQ involves a branched pathway with at least three separate enzymes and two derivatives other than CPQ. An oxidase activity in serum converted PQ first into a novel side chain aldehyde (Y). Aldehyde dehydrogenase transformed PQ-aldehyde into CPQ in cell-free systems and in K562, bone marrow, and adult liver cells. Embryonic hepatocytes or bone marrow treated with 1,3-bis(2-chloroethyl)-1-nitrosourea did not produce CPQ; instead, they made a metabolite (Xc) that we could synthetize via PQ-aldehyde and identify as PQ-alcohol. PQ-alcohol replaced CPQ as the final product whenever alcohol-dehydrogenase prevailed over aldehyde dehydrogenase. These enzymes operated in intact cells and controlled the biotransformation of PQ absolutely. Unless both dehydrogenase were absent, inhibited, or deprived of coenzyme, potentially cytotoxic PQ-aldehyde intermediate did not accumulate. Some of the unique tissues schizonticidal and gametocidal effects of PQ may depend on the distribution pattern and relative activities of PQ oxidase, aldehyde dehydrogenase, and alcohol dehydrogenase in human subjects and in parasites.

Defenses against oxidation in human erythrocytes: role of glutathione reductase in the activation of glucose decarboxylation by hemolytic drugs

We have used 1,3-bis(2-chloroethyl)-1-nitrosourea, a selective inhibitor of oxidized glutathione reductase (GSSG-R), to examine the role of this enzyme in regulating the hexose monophosphate shunt (HMS) and to explore how a variety of agents influence glucose decarboxylation in intact human red blood cells (RBCs). Substances tested included primaquine and several other drugs that are specially hemolytic and methemoglobinemic in glucose-6-phosphate dehydrogenase (G6PD) deficiency and related disorders. The results allowed us to distinguish and quantitate contrasting modes of HMS stimulation and to clarify how RBCs respond to different classes of oxidants. Some agents like methylene blue (MB), phenazine methosulfate, and pyrroline carboxylate do not require GSSG-R to increase CO2 production; they activate G6PD and 6-phosphogluconic dehydrogenase by directly oxidizing reduced nicotinamide adenine dinucleotide phosphate (NADPH) to oxidized nicotinamide adenine dinucleotide phosphate (NADP). Other compounds, like ascorbate, nitrofurantoin, and doxorubicin, oxidize GSH primarily; CO2 increases indirectly only when GSSG-R, activated by glutathione disulfide (GSSG), raises the level of NADP. Chemicals like primaquine, daunorubicin, and methylphenylazoformate trigger the HMS by independently oxidizing both NADPH and GSH. Unlike MB, most drugs that are hemolytic in G6PD deficiency activate the HMS in a manner that depends to a variable extent on GSSG-R. This variability may explain hitherto puzzling clinical and pharmacogenetic differences between primaquine and diaminodiphenylsulfone-induced hemolysis.

Distribution of primaquine in human blood: drug-binding to alpha 1-glycoprotein

To clarify the distribution of the antimalarial primaquine in human blood, we measured the drug separately in the liquid, cellular, and ultrafiltrate phases. Washed red cells resuspended at a hematocrit of 0.4 were exposed to a submaximal therapeutic level of 250 ng/ml of carbon 14-labeled primaquine. The tracer was recovered quantitatively in separated plasma and red cells. Over 75% of the total labeled drug was found in red cells suspended in saline solution, but only 10% to 30% in red cells suspended in plasma. The plasma effect was not mediated by albumin. Studies with alpha 1-acid glycoprotein (AGP), tris(2-butoxyethyl)phosphate, an agent that displaces AGP-bound drugs, and cord blood known to have decreased AGP established that primaquine binds to physiologic amounts of the glycoprotein in plasma. Red cell primaquine concentration increased linearly as AGP level fell and as the free drug fraction rose. We suggest that clinical blood levels of primaquine include the red cell fraction or whole blood level because (1) erythrocytic primaquine is a sizable and highly variable component of the total drug in blood; (2) this component reflects directly the free drug in plasma, and inversely the extent of binding to AGP; (3) the amount of free primaquine may influence drug transport into specific tissues in vivo; and (4) fluctuations of AGP, an acute-phase reactant that increases greatly in patients with malaria and other infections, markedly affect the partition of primaquine in blood. Because AGP binds many basic drugs, unrecognized primaquine-drug interactions may exist.

Comparison of intestine and bone marrow radiosensitivity of the BALB/c and the C57BL/6 mouse strains and their B6CF1 offspring

The radiosensitivity as measured by LD50/6 or LD50/30 of the F1 hybrid B6CF1 (C57BL/6 X BALB/c) is similar to that of C57BL/6 mice but markedly different from BALB/c. The LD50/6 for BALB/c mice was about 8.8 Gy compared to 16.4 Gy for the B6CF1. The difference in LD50/6 between the parent strains or between BALB/c and the F1 hybrid could not be explained by any differences in crypt cell number, cell cycle time, or transit time. Likewise, the observed differences in the LD50/6 do not appear to result from marked differences in the radiosensitivity of marrow stem cells (CFU-S) since the D0's for the three genotypes of mice were similar. Also, there were no apparent differences in the red blood cell contents of several enzymes associated with antioxidant defenses. The microcolony assay was used to determine the D0 for the crypt clonogenic cells and the D0 values for 60Co gamma rays were about 0.8 Gy for BALB/c mice and 1.4 Gy for B6CF1 mice. However, the D0 values for JANUS fission neutrons were similar; 0.6 Gy for the BALB/c mice and 0.5 for the B6CF1 mice. A comparison of clonogenic cell kinetics, using prolonged colcemid block to distinguish between slowly and rapidly cycling cells suggest that, normally, the stem cells are slowly cycling in both the BALB/c and the B6CF1 hybrid. However, the stem cells of the B6CF1 appear to go into rapid cell cycle more rapidly than those of the BALB/c following irradiation or prolonged colcemid treatment. The more rapid recovery in intestinal epihelial cell production in the B6CF1 hybrid after irradiation may provide an increased mucosal barrier and may, in part, explain the difference in the response to radiation compared to that in the BALB/c.

Consequences of erythrocytic glutathione reductase deficiency

We have used 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) as a selective and irreversible inhibitor of oxidized glutathione reductase (GSSG-R) to determine how human erythrocytes with various degrees of GSSG-R deficiency recover their reduced glutathione (GSH) after exposure to acetylphenylhydrazine or diamide. Pentose phosphate dehydrogenases and glutathione synthesis were not inhibited, de novo glutathione synthesis was negligible within the experimental time frame, and the reappearance of GSH was strictly under the control of GSSG-R. Results obtained with acetylphenylhydrazine or diamide were concordant. In red cells stressed by these reagents, GSSG-R deficiency began to impair the regeneration of GSH only after greater than 80% of the normal enzyme activity had been abolished. Thereafter GSH recovery deteriorated as drug-induced GSSG-R depression increased. Only erythrocytes that had been rendered almost totally GSSG-R deficient, that is, had lost greater than 90% of baseline activity, became functionally equivalent to GdA- glucose-6-phosphate dehydrogenase-deficient cells. The reserve capacity of GSSG-R in human erythrocytes is extremely large. Of all types of isolated GSSG-R "deficiencies" reported so far, only two can be considered pathogenically significant: the homozygous genetic defect found in a single family, and much more commonly, the acute pharmacologic phenocopy induced by BCNU.

Biotransformation of primaquine in vitro with human K562 and bone marrow cells

Although the antimalarial activity, hemolytic and methemoglobinemic side effects, and detoxification of primaquine are all thought to depend on various biotransformation products of the drug, their site and mechanism of formation and degradation are unknown and their specific biologic effects remain very poorly understood, particularly in humans. We have therefore explored the feasibility of studying primaquine metabolism in cultured human cells. We found that the biotransformation of primaquine can be investigated in vitro in serum-supplemented liquid cultures of partially synchronized and exponentially growing human erythroleukemic K562 cells. Further, these cells can be replaced by cells present in normal bone marrow. Primaquine is rapidly and predominantly converted in vitro into carboxyprimaquine (CPQ) in a quantitative manner and without further modification. In addition to CPQ, a compound Xc that is not 6-methoxy-8-aminoquinoline, and is not derived from CPQ, appears in minor amounts in a delayed fashion. With the K562 as well as with the bone marrow cells the formation of CPQ from primaquine can be totally blocked by large concentrations of the nitrosourea, 1,3-bis-(2-chloroethyl)-nitrosourea (BCNU). With bone marrow, increasing blockade of CPQ formation by BCNU leads invariably to a progressive and striking accumulation of Xc. The availability of reproducible, quantitative, and practical new tools for the study of primaquine metabolism in vitro raises a number of challenging questions and may improve understanding of the mode of action, toxicology, and pharmacogenetics of 8-aminoquinolines.

Association of red cell spherocytosis with deletion of the short arm of chromosome 8

Congenital spherocytic anemia is a common disorder, but in most cases the nature of the underlying membrane lesion is unknown and the genetic defect has not yet been unequivocally mapped to a chromosome. We studied two dysmorphic siblings with neurologic findings and hemolytic anemia. Clinical and laboratory findings in these two siblings were consistent with the diagnosis of congenital spherocytosis whereas both parents and two unaffected siblings were normal. The two affected children had an abnormal chromosomal complement as a result of a deletion of the short arm of chromosome 8 [(46,XX,del(8)(p11.1p21.1)]. These results suggest that a gene whose deletion results in a congenital spherocytic anemia phenotype resides on this region on the short arm of chromosome 8.

Active site-specific inhibition by 1,3-bis(2-chloroethyl)-1-nitrosourea of two genetically homologous flavoenzymes: glutathione reductase and lipoamide dehydrogenase

We extended our previous studies of the selectivity and mechanism of action as an enzyme inhibitor of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an antitumor drug now widely used to inactivate glutathione reductase (GSSG-R) experimentally. In contrast to other enzymes examined so far, lipoamide dehydrogenase (LSSLNH2-D) was, like its genetic relative GSSG-R, also strongly inhibited by BCNU. The drug concentration needed to inactivate GSSG-R and LSSLNH2-D was much smaller than that affecting the least resistant of five other flavoenzymes tested. When oxidized, both GSSG-R and LSSLNH2-D were resistant to BCNU, and to be effective, the drug had to interact directly with enzyme protein reduced by its specific pyridine nucleotide. In intact human erythrocytes, GSSG-R was mostly reduced and LSSLNH2-D activity undetectable. The partial genetic homology of GSSG-R and LSSLNH2-D and their special sensitivity to BCNU provided a unique opportunity to define more exactly the site of drug-enzyme interaction through comparative coenzyme studies combined with direct and reciprocal substrate competition experiments. The results, together with earlier data on the prevention of BCNU inhibition by cysteine, indicate that the nitrosourea achieves its relative selectivity against the two related flavoenzymes by interacting with at least one of the two reduced cysteinyls located within their oxidoredox active site. For GSSG-R, the attacked cysteinyl is most probably Cys-58.

Glutathione reductase deficiency and platelet dysfunction induced by 1,3-bis(2-chloroethyl)-1-nitrosourea

Human platelets exposed in vitro to increasing amounts of BCNU rapidly develop a progressive, relatively selective, and almost complete deficiency of GSSG-R activity. Several other enzymes are not inhibited when intact platelets are exposed to the nitrosourea; lipoamide dehydrogenase was investigated because of the remarkable similarity of the structure of its active site with that of GSSG-R. BCNU inhibits lipoamide dehydrogenase and GSSG-R only when they are in the reduced state; in the intact platelet, lipoamide dehydrogenase (unlike GSSG-R) is oxidized and is therefore unaffected. This is the first documentation of lipoamide dehydrogenase activity in platelets. After BCNU exposure, there is a reduced release of 14C-serotonin in response to collagen; the cells become incapable of aggregating in response to even large doses of epinephrine, ADP, collagen, or arachidonic acid, with loss of both primary and secondary waves of aggregation. At higher doses of BCNU, there is also a diminished PF-3 activity of intact platelets; sonication of drug-treated platelets normalizes coagulant activity. The drug-induced functional abnormalities occur despite preservation of the number of platelets, their electron microscopic appearance, and their capacity to take up 14C-serotonin. BCNU induced GSSG-R deficiency precedes the development of the earliest evidence of platelet dysfunction, and almost all of the enzyme's activity must be abolished before any functional abnormality becomes detectable. A small fraction of GSSG-R activity is essential for platelet function, and BCNU provides a powerful new tool to investigate the role of the enzymatic reduction of glutathione in platelet physiology and pathology.

Toxicology of the 8-aminoquinolines and genetic factors associated with their toxicity in man

In vitro studies on primaquine have been carried out to examine its ability to stimulate the oxidative pathway of glucose metabolism in human erythrocytes and in vivo studies were carried out after ingestion of the drug to determine plasma levels and to investigate the formation of metabolites and the effects of the drug on human erythrocytes. These investigations showed that:1) Two mechanisms are involved in the stimulation of the oxidative pathway. This was demonstrated by comparing the effects of methylene blue, ascorbic acid, primaquine, and other drugs on normal, glutathione-reductase-deficient, and G6PD-deficient erythrocytes. A start was made towards classifying drugs according to the mechanism by which they stimulate CO(2) production.2) Following oral ingestion of primaquine, three as yet unidentified metabolites were present, two in the plasma and one in the urine. The rapid disappearance of primaquine from the plasma (within 24 hours) was confirmed.3) Two factors that stimulate glucose oxidation in human erythrocytes were found in plasma; one occurred only in fresh plasma, when EDTA was present, and the other occurred in all plasma and serum samples studied.4) The erythrocytes of blood drawn 24 hours after the ingestion of primaquine (after primaquine had disappeared from the plasma) showed increased ability to oxidize glucose.It is not yet known whether serum or plasma prepared from blood drawn 24 hours after ingestion of primaquine has the ability to increase the oxidation of glucose.

Mechanical fragility of erythrocytes in multiple sclerosis

Erythrocyte fragility was measured by mechanical shaking in 82 normal individuals and 19 patients with multiple sclerosis (MS). On the average, fragility was significantly higher in the MS patients, although this increase did not correlate with the presence of serum neuroelectric blocking factors.

The influence of acetylator phenotype on the response to sulfalene in individuals with chloroquine-resistant falciparum malaria

The disposition of sulfalene was studied in eight individuals before and during an infection with a chloroquine-resistant strain of Plasmodium falciparum. Isoniazid acetylator phenotype was determined in each individual prior to the administration of sulfalene. Following the administration of sulfalene before infection with malaria, a significant difference in half-life of non-acetylated sulfalene and percent acetylation of sulfalene in plasma was observed between rapid and slow acetylators. When sulfalene was administered during malaria, this difference was no longer apparent. Individuals who did not respond to the therapeutic administration of sulfalene alone were treated with a combination of sulfalene and pyrimethamine. Three individuals were cured by sulfalene without pyrimethamine and one was cured by the drug combination. Three of the four individuals who were not cured by any dose of sulfalene or the drug combination were slow acetylators. There was no distinct correlation between clinical response and maximum levels or half-life of nonacetylated sulfalene. These findings suggest that acetylator phenotype does not influence the therapeutic response of individuals infected with falciparum malaria to sulfalene or to the combination of sulfalene and pyrimethamine. Further information is presented, however, to confirm the importance of an as yet unidentified host factor(s) in determining therapeutic response to these agents.

Severe generalized glutathione reductase deficiency after antitumor chemotherapy with BCNU" [1,3-bis(chloroethyl)-1-nitrosourea]

Patients receiving BCNU [1,3-bis(2 chloroethyl)-1-nitrosourea] acquire a profound deficiency of erythrocytic oxidized glutathione reductase (GSSG-R) within minutes after the first intravenous injection of a single therapeutic dose (75 mg/M.2) of the drug. This effect is not accompanied by changes in the activites of 19 additional erythrocytic enzymes tested, is reproducible in vitro in a dose-related manner, and is not caused by the antitumor agents administered concurrently with the nitrosourea. The inactivation of erythrocytic GSSG-R results in decreased levels of reduced glutathione (GSH), marked GSH instability and disturbed hydrogen peroxide removal with a positibe ascorbate cyanide test and leads to increased susceptibility to oxidative hemolysis, particularly in glucose-6-phosphate dehydrogenase (G-6-D)-deficient patients. BCNU inhibits GSSG-R irreversibly, probably through alkylation rather than carbamylation, and the reappearance of enzyme activity in vivo after each chemotherapy pulse depends on the capacity of the marrow to release erythrocytes with normal activity formed during the drug-free interval. BCNU inhibits GSSG-R not only in erythrocytes but also in human leukocytes and platelets, as well as in yeast, monkey erythrocytes, and all the organs tested in the mouse. This generalized, severe, and specific GSSG-R deficiency caused by therapeutic doses of BCNU may enhance or mediate the toxic and antitumor effects of the nitrosourea and provides a simple yet sensitive biochemical means of monitoring bone marrow reserve in patients receiving multiple courses of chemotherapy with this agent.

Erythrocytic glutathione reductase deficiency in a hospital population in the United States

In the USA, erythrocytic glutathione reductase (GSSG-R) deficiency is significantly more common, and can be considerably more pronounced in hospitalized patients (118/3198) than in outpatients (37/1639) or in apparently healthy persons (12/849). Retrospective analysis of illnesses found in 118 inpatients with erythrocytic GSSG-R deficiency revealed a striking and previously unsuspected association of the enzyme deficiency with a variety of chemotherapeutically treated hematological or nonhematological malignancies (51/118 patients, 43.2%, or 51/170 diagnoses, 30.0%). The prevalence of erythrocytic GSSG-R deficiency also increased in malnutrition, liver disease, and sepsis. Drugs of the nitrosourea class, particularly BCNU [1, 3-bis(2-chloroethyl)-1-nitrosourea] are causally implicated in the association of GSSG-R deficiency with malignancies. Severe of complete GSSG-R deficiency may handicap host response to infections.

Quinine disposition during malaria and during induced fever

Quinine disposition was studied in 5 subjects before and during an experimentally induced infection with a chloroquine-resistant strain of Plasmodium falciparum and in 2 individuals before and during artificially induced fever. Plasma quinine levels were determined by both a benzene extraction method (QB), which measures principally unmetabolized quinine, and a metaphosphoric acid precipitation method (QMPA), which measures quinine and quinine metabolites. The ratio QB/QMPA in plasma was used to estimate the extent of metabolism of quinine. In all individuals plasma levels of quinien and QB/QMPA ratios were increased during malaria, suggesting impaired hepatic metabolism of quinine. The changes observed during malaria were not due to altered renal excretion of quinine. In 2 subjects in whom fever was artificially induced there were similar changes in quinine metabolism. These observations suggest that quinine dosage should be modified during the initial period of treatment, when symptoms and fever are greatest, in acute falciparum malaria.

Mefloquine (WR 142,490) in the treatment of human malaria

Mefloquine hydrochloride, a new 4-quinolinemethanol, was administered as a single oral dose to 47 volunteers infected with malaria. Treatment resulted in rapid clearence of fever and parasitemia. No recrudescence of parasites was observed after treatment of chloroquine-sensitive infections of Plasmodium falciparum. More significantly, in nonimmune persons with chloroquine-resistant infections, 1 gram of mefloquine cured 10 of 12 patients and 1.5 grams cured all 8 patients who received this dose of the drug. The marked activity of a single dose of mefloquine against chloroquine-resistant strains of Plasmodium falciparum suggests that this agent may be more useful than currently available drugs are for the treatment of drug-resistant malaria.

Acetylator phenotype and response of individuals infected with a chloroquine-resistant strain of Plasmodium falciparum to sulfalene and pyrimethamine

Acetylator phenotype was determined in 33 volunteers who were infected with a chloroquine-resistant strain of Plasmodium falciparum and who received, for cure, 2 g of sulfalene and 50 mg of pyrimethamine. This drug combination did not cure 5 of 14 rapid acetylators and 3 of 19 slow acetylators. This difference is not significant. Plasma levels of non-acetylated sulfalene, acetylated sulfalene, acetylation, and biologic half-life of non-acetylated sulfalene after administration of the combination did not differ importantly between the two groups. Acetylator phenotype does not appear to influence the response to sulfalene and pyrimethamine of individuals infected with chloroquine-resistant falciparum malaria.

Hemoglobin E, an oxidatively unstable mutation

When bloods from 3,159 individuals from the United States, Iran, Ethiopia, and South Vietnam were examined for erythrocytic enzyme deficiencies with a new test utilizing the visible reduction of 2,6-dichlorophenolindophenol by glutathione, gross turbidity was observed in 81 samples. All were from Southeast Asia and 78 contained hemoglobin E. The precipitation rates of various hemoglogins in hemolysates incubated with dichlorophenolindophenol were: Hb EE greater than Hb AE greater than other hemoglobins (A, S, C, D, A2, F, O-Arabia, Rush). Hemoglobin E is an oxidatively unstable hemoglobin, possibly with weakened alpha 1 beta 1 contact; it may result in increased susceptibility to oxidative hemolysis and can be simply detected and differentiated from both Hb C and Hb O-Arabia.

Host failure in treatment of malaria with sulfalene and pyrimethamine

An individual infected with a multidrug-resistant strain of Plasmodium falciparum failed to respond to treatment with sulfalene and pyrimethamine. Subinoculation studies showed that parasite resistance to the drug combination was not present. Plasma levels of sulfalene and pyrimethamine in this individual were similar to those of three individuals, subinoculated from him, who were cured by the drug combination. Erythrocyte levels of sulfalene in this individual were similar to those in an individual, subinoculated from him, who was cured by the drug combination. After treatment with the drug combination, in vitro tests showed similar antimalarial activity in the serum of this individual in comparison with the serum of this individual in comparison with the serum of an individual subinoculated from him. The failure of this individual to respond to treatment with sulfalene and pyrimethamine is attributed to an undefined host factor (or factors) that appear(s) to be present in his erythrocytes.

A method for the determination of amodiaquine

A new fluorometric method for analysis of amodiaquine in serum, plasma, or red cells is described. Amodiaquine is extracted from alkalinized biological fluid into 1,2-dichloroethane and is then re-extracted into 0.1 N hydrochloric acid. Borate buffer is added to the acid solution and the resultant solution is heated for 30 min in boiling water. Heating the buffered solution produces a marked increase in the fluorescence of amodiaquine, which may then be measured. Standard curves prepared in serum and red cells were linear between 50 and 3 000 mug/litre. Reproducibility of the assay and recovery of amodiaquine from serum and red cells were satisfactory. The specificity of the assay and the nature of the induced fluorophor are not known. The paper indicates representative serum and red cell levels of amodiaquine after the administration to 5 subjects of 10 mg of amodiaquine base per kg of body weight.

Prophylactic activity of mefloquine hydrochloride (WR 142490) in drug-resistant malaria

In preliminary studies with mefloquine (WR 142 490) a single dose exerted prolonged suppressive activity against a drug-resistant strain of Plasmodium falciparum. Development of patent parasitaemia was prevented when nonimmune persons were exposed to infected mosquitos 2 weeks after medication, and it was delayed when exposure occurred 3 weeks after drug administration.

NAD(P) glycohydrolase deficiency in human erythrocytes and alteration of cytosol NADH-methemoglobin diaphorase by membrane NAD-glycohydrolase activity

Erythrocytic NADH methemoglobin diaphorase acquires NADH-dichlorophenolindophenol diaphorase activity when enzyme-associated NAD is removed. This transformation is reversible and can be mediated by membrane NAD glycohydrolase (EC 3.2.2.5) in hemolysates as well as in intact cells exposed to hydrogen peroxide. It is abolished either in NADH methemoglobin diaphorase deficiency or in NAD(P) glycohydrolase (EC 3.2.2.6) deficiency which is common in Afro-American but not in European-American adults. Activities of erythrocytic NADP glycohydrolase and NAD glycohydrolase appear to depend on a single membrane enzyme.