Cyanide toxicity of sodium nitroprusside in therapeutic use with and without sodium thiosulphate

Considering Adverse Effects of Common Antihypertensive Medications in the ED

PURPOSE OF REVIEW

To evaluate the adverse effects of common antihypertensive agents utilized or encountered in the Emergency Department.

RECENT FINDINGS

All categories of antihypertensive agents may manifest adverse effects, inclusive of adverse drug reactions (ADRs), drug-to-drug interactions, or accidental overdose. Adverse effects, and specifically ADRs, may be stratified into the organ systems affected, might require specific time-sensitive interventions, could pose particular risks to vulnerable populations, and may result in significant morbidity, and potential mortality. Adverse effects of common antihypertensive agents may be encountered in the ED, necessitating that ED systems of care are poised to prevent, recognize, and intervene when adverse effects arise.

Nitroprusside and metal nitroprusside nano analogues for cancer therapy

Sodium nitroprusside (SNP), U.S approved drug has been used in clinical emergency as a hypertensive drug for more than a decade. It is well established for its various biomedical applications such as angiogenesis, wound healing, neurological disorders including anti-microbial applications etc. Apart from that, SNP have been considered as excellent biomedical materials for its use as anti-cancer agent because of its behavior as NO-donor. Recent reports suggest that incorporation of metals in SNP/encapsulation of SNP in metal nanoparticles (metal nitroprusside analogues) shows better therapeutic anti-cancer activity. Although there are numerous reports available regarding the biological applications of SNP and metal-based SNP analogue nanoparticles, unfortunately there is not a single comprehensive review which highlights the anti-cancer activity of SNP and its derivative metal analogues in detail along with the future perspective. To this end, the present review article focuses the recent development of anti-cancer activity of SNP and metal-based SNP analogues, their plausible mechanism of action, current status. Furthermore, the future perspectives and challenges of these biomedical materials are also discussed. Overall, this review article represents a new perspective in the area of cancer nanomedicine that will attract a wider spectrum of scientific community.

Recent Developments in Nitric Oxide Donors and Delivery for Antimicrobial and Anti-Biofilm Applications

The use of nitric oxide (NO) is emerging as a promising, novel approach for the treatment of antibiotic resistant bacteria and biofilm infections. Depending on the concentration, NO can induce biofilm dispersal, increase bacteria susceptibility to antibiotic treatment, and induce cell damage or cell death via the formation of reactive oxygen or reactive nitrogen species. The use of NO is, however, limited by its reactivity, which can affect NO delivery to its target site and result in off-target effects. To overcome these issues, and enable spatial or temporal control over NO release, various strategies for the design of NO-releasing materials, including the incorporation of photo-activable, charge-switchable, or bacteria-targeting groups, have been developed. Other strategies have focused on increased NO storage and delivery by encapsulation or conjugation of NO donors within a single polymeric framework. This review compiles recent developments in NO drugs and NO-releasing materials designed for applications in antimicrobial or anti-biofilm treatment and discusses limitations and variability in biological responses in response to the use of NO for bacterial eradiation.

Evaluation of the health risks related to the presence of cyanogenic glycosides in foods other than raw apricot kernels

In 2016, the EFSA Panel on Contaminants in the Food Chain (CONTAM) published a scientific opinion on the acute health risks related to the presence of cyanogenic glycosides (CNGs) in raw apricot kernels in which an acute reference dose (ARfD) of 20 μg/kg body weight (bw) was established for cyanide (CN). In the present opinion, the CONTAM Panel concluded that this ARfD is applicable for acute effects of CN regardless the dietary source. To account for differences in cyanide bioavailability after ingestion of certain food items, specific factors were used. Estimated mean acute dietary exposures to cyanide from foods containing CNGs did not exceed the ARfD in any age group. At the 95th percentile, the ARfD was exceeded up to about 2.5‐fold in some surveys for children and adolescent age groups. The main contributors to exposures were biscuits, juice or nectar and pastries and cakes that could potentially contain CNGs. Taking into account the conservatism in the exposure assessment and in derivation of the ARfD, it is unlikely that this estimated exceedance would result in adverse effects. The limited data from animal and human studies do not allow the derivation of a chronic health‐based guidance value (HBGV) for cyanide, and thus, chronic risks could not be assessed.

This publication is linked to the following EFSA Supporting Publications article: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2019.EN-1601/full

On the volatilisation and decomposition of cyanide contaminations from gold mining

Cyanide leaching is the predominant process of gold extraction in large scale mining. Current initiatives for reducing the use of mercury in small scale and artisanal mining tend towards the cyanide technology as the only feasible alternative. Thus, the deliberate handling in consideration of the hazardous nature of cyanide compounds is an issue of particular importance. The hydrogen cyanide volatilised during the leaching process and from the tailings solutions after the gold extraction is reported to be destroyed by oxidation and photolysis from the surrounding atmosphere of gold mines and the sunlight. Cyanide solutions, drained into the surrounding waterbodies are stated to volatilise at a high rate, thus detoxifying them and releasing hydrogen cyanide to the air. In this study laboratory experiments and field tests were conducted to deliver basic data for the volatilisation and destruction of cyanide in the environment. In our laboratory tests we observed neither oxidation by the oxygen of air nor photolysis by UV-irradiation of cyanides after volatilisation from water. The whole amount of volatilised cyanide was found in the exhaust gas after absorption in a strong basic solution. Field experiments in Segovia (Colombia) could confirm these findings. Cyanide concentrations in a range 17 to 30mg/L were measured in a local creek. Hydrogen cyanide amounts of 5ppm were found in the atmosphere surrounding cyanide leaching facilities. With the findings of this study we want to point out that the concentrations of cyanide in the surrounding of cyanide leaching facilities exceed uncritical limits and a destruction via oxidation and photolysis is not detectable. These conclusions should result in initiatives to protect workers and the surrounding population of gold mines from contaminations of cyanide treatments.

Biomonitoring Equivalents for cyanide

Exposure to cyanide is widespread in human populations due to a variety of natural and anthropogenic sources. The potential health risks of excess cyanide exposure are dose-dependent and include effects on the thyroid, the male reproductive system, developmental effects, neuropathies and death. Many organizations have derived exposure guideline values for cyanide, which represent maximum recommended exposure levels for inhalation and oral routes of exposure. Biomonitoring Equivalents (BEs) are estimates of the average biomarker concentrations that correspond to these reference doses. Here, we determine BE values for cyanide. The literature on the pharmacokinetics of cyanide was reviewed to identify a biomarker of exposure. Despite issues with biomarker specificity, thiocyanate (SCN-) in the urine or plasma was identified as the most practical biomarker. BE values were produced that correspond to previously published critical effect levels. These BE values range from 0.0008 to 0.8 mg/L and 0.0005-2.5 mg/L for SCN- in urine and plasma, respectively. Confidence in these BE values varies, depending on route of exposure, biomarker, and health endpoint of interest. We anticipate that these BE values will be useful for lower tier (screening level) chemical risk assessment; however due to issues with biomarker specificity and uncertainty in background levels of SCN-, this approach requires refinement to be useful at higher tiers.

Does diathermy smoke contaminate processed salvaged blood in cardiac surgery?

INTRODUCTION

A cell salvage device is used in cardiac surgery with the aim of reducing allogeneic blood transfusion. Suction of blood from the operating field used for the device is often accompanied by diathermy smoke. There is limited published research to know if this blood is then contaminated with clinically significant levels of harmful chemicals from this smoke. Postoperative cardiac surgery patients are already physiologically vulnerable, making the optimization of salvaged blood worth considering.

METHODS

Ten patients who had cardiac surgery using a cell salvage device from a single institution had samples taken from the processed blood just prior to transfusion. Samples were tested for carbon monoxide (CO), cyanide and benzene. Results were compared to preoperative co-oximetry results and normal adult laboratory reference ranges. Demographic data about the patients was collected, including the type of operation, gender, age, body mass index, smoking status and amount of salvaged blood collected and processed.

RESULTS

Primary surgery was coronary artery bypass grafting (CABG) in three patients, mitral valve repair or replacement in three patients and one each of aortic valve replacement (AVR)/CABG, AVR/plication of the aorta, CABG/external wrapping of the aorta and valve-sparing root replacement. None were smokers. Neither the blood CO level prior to surgery nor in the processed salvaged blood was above the normal limit of 2% for non-smokers. There was no processed blood benzene found. Cyanide levels in the processed blood ranged from 1.8 to 44.1 μmol/l (where <8 μmol/l is considered within the normal adult laboratory limit).

CONCLUSION

Despite the obvious limitations of the current study, it shows that cyanide levels can be found many times the normal level in processed salvaged blood. Whilst the total dose of cyanide is small, the potential impact may be clinically significant due to cyanide's effect on mitochondrial metabolism in the heart and brain.

Thiocyanate Accumulation in Critically Ill Patients Receiving Nitroprusside Infusions

PURPOSE

This study evaluated thiocyanate concentrations and factors associated with thiocyanate accumulation in intensive care unit patients receiving nitroprusside with and without sodium thiosulfate coadministration.

MATERIALS AND METHODS

This retrospective study evaluated critically ill adults who received nitroprusside infusions and had at least one thiocyanate concentration. Patients with thiocyanate accumulation (concentrations ≥30 µg/mL) were compared to patients without accumulation. Factors associated with accumulation were determined by Spearman correlation and multivariate regression.

RESULTS

Thiocyanate concentrations (n = 192) were obtained from 87 patients. Fourteen of the 87 (16%) patients experienced thiocyanate accumulation with a mean (SD) thiocyanate concentration of 44 ± 11 µg/mL. Patients with accumulation had received greater cumulative nitroprusside doses (28 vs 8.2 mg/kg, P < .01), greater cumulative sodium thiosulfate doses (16.8 vs 10.1 mg/kg, P < .01), and longer infusion durations (10.9 vs 6.0 days, P < .01), compared to patients without accumulation. Sodium thiosulfate coadministration resulted in greater thiocyanate concentrations (22.8 ± 16.7 vs 16.8 ± 14.9 μg/mL, P = .01), despite utilization of lower cumulative nitroprusside doses (10.2 vs 14.6 mg/kg, P = .03). Cumulative nitroprusside dose ( r² .44, P < .001) and cumulative sodium thiosulfate dose ( r² .32, P < .001) demonstrated a significant correlation with measured thiocyanate concentrations. Thiocyanate accumulation was independently associated with cumulative nitroprusside dose in mg/kg (regression coefficient 0.75, 95% CI 0.63-0.89; P < .01). No clinically significant adverse effects of cyanide or thiocyanate toxicity were observed.

CONCLUSIONS

Cumulative nitroprusside dose was independently associated with thiocyanate accumulation. Despite elevated thiocyanate levels in 16% of patients, there was no clinical evidence of cyanide or thiocyanate toxicity. Routine monitoring of thiocyanate concentrations appears most warranted in patients receiving higher cumulative doses of nitroprusside.

Bioavailability of cyanide after consumption of a single meal of foods containing high levels of cyanogenic glycosides: a crossover study in humans

The acute toxicity of cyanide is determined by its peak levels reached in the body. Compared to the ingestion of free cyanide, lower peak levels may be expected after consumption of foods containing cyanogenic glycosides with the same equivalent dose of cyanide. This is due to possible delayed and/or incomplete release of cyanide from the cyanogenic glycosides depending on many factors. Data on bioavailability of cyanide after consumption of foods containing high levels of cyanogenic glycosides as presented herein were necessary to allow a meaningful risk assessment for these foods. A crossover study was carried out in 12 healthy adults who consumed persipan paste (equivalent total cyanide: 68 mg/kg), linseed (220 mg/kg), bitter apricot kernels (about 3250 mg/kg), and fresh cassava roots (76-150 mg/kg), with each "meal" containing equivalents of 6.8 mg cyanide. Cyanide levels were determined in whole blood using a GC-MS method with K(13)C(15)N as internal standard. Mean levels of cyanide at the different time points were highest after consumption of cassava (15.4 µM, after 37.5 min) and bitter apricot kernels (14.3 µM, after 20 min), followed by linseed (5.7 µM, after 40 min) and 100 g persipan (1.3 µM, after 105 min). The double dose of 13.6 mg cyanide eaten with 200 g persipan paste resulted in a mean peak level of 2.9 µM (after 150 min). An acute reference dose of 0.075 mg/kg body weight was derived being valid for a single application/meal of cyanides or hydrocyanic acid as well as of unprocessed foods with cyanogenic glycosides also containing the accompanying intact β-glucosidase. For some of these foods, this approach may be overly conservative due to delayed release of cyanide, as demonstrated for linseed. In case of missing or inactivated β-glucosidase, the hazard potential is much lower.

Effects of nitric oxide and its congeners on sickle red blood cell deformability

BACKGROUND

Sickle cell disease (SCD) is characterized by hemoglobin polymerization upon deoxygenation. Polymerization causes the sickle cells to become rigid and misshapen (sickling). Red blood cell (RBC) dehydration greatly increases polymerization. Cycles of sickling and unsickling cause an influx of calcium that leads to loss of potassium via the calcium-activated Gardos channel, which dehydrates the cells leading to increased polymerization. In this study the effects of nitric oxide (NO) and its congeners on RBC deformability were examined, focusing on sickle RBCs (sRBCs).

STUDY DESIGN AND METHODS

RBCs from patients with SCD and from nonpatients were exposed to various compounds that release NO or its congeners. Intracellular calcium was increased using a calcium ionophore or cycling of oxygen tension for sRBCs. Deformability was measured by laser-assisted osmotic gradient ektacytometry.

RESULTS

Consistent with a previous report, sodium nitroprusside (SNP) was found to protect against calcium-induced loss of deformability in normal RBCs, but (contrary to some previous reports) no effect of any NO donors was observed when calcium influx was not induced. Importantly, in studies of deoxygenation-induced dehydration of sRBCs, SNP resulted in substantial improvements in deformability (p = 0.036) and hydration (p = 0.024). Sodium nitrite showed similar trends. SNP was shown to have no effect on calcium influx, but reduced potassium efflux.

CONCLUSION

These data suggest that SNP and perhaps certain nitrogen oxides (like nitrite) inhibit the Gardos channel and may be able to protect sickle cells from dehydration and thereby improve outcome in the disease.

Review article: management of cyanide poisoning

Cyanide poisoning is uncommon, but generates interest because of the presumed utility of an antidote immediately available in those areas with a high risk of cyanide exposure. As part of its regular review of guidelines, the Australian Resuscitation Council conducted a systematic review of the human evidence for the use of various proposed cyanide antidotes, and a narrative review of the relevant pharmacological and animal studies. There have been no relevant comparative or placebo-controlled human trials. Nine case series were identified. Treatment with hydroxocobalamin was reported in a total of 361 cases. No serious adverse effects of hydroxocobalamin were reported, and many patients with otherwise presumably fatal poisoning survived. Sodium thiosulphate use was reported in two case series, similarly with no adverse effects. Treatment with a combination of sodium nitrite, amyl nitrite and sodium thiosulphate was reported in 74 patients, with results indistinguishable from those of hydroxocobalamin and sodium thiosulphate. No case series using dicobalt edetate or 4-dimethylaminophenol were identified, but successful use in single cases has been reported. Hydroxocobalamin and sodium thiosulphate differ from alternatives in having negligible adverse effects, and on the basis of current evidence are the antidotes of choice. The indications for the use of an antidote, the requirements for supportive care and a recommended approach for workplaces where there is a risk of cyanide poisoning are presented.

Stability of Sodium Nitroprusside and Sodium Thiosulfate 1:10 Intravenous Admixture

PURPOSE: Thiosulfate has been shown to reduce the risk of cyanide toxicity during nitroprusside administration. Admixtures containing both agents may provide a safe and effective alternative to more expensive agents used to reduce blood pressure in the critically ill patient. This study determined the physical and chemical stability of a 1:10 nitroprusside:thiosulfate admixture, stored up to 48 hours. The economic consequences of a shift toward using thiosulfate and nitroprusside, and away from higher cost alternatives, are considered. METHODS: Seven samples of 50 mg nitroprusside and 500 mg thiosulfate were prepared and stored away from light, at room temperature, and in a refrigerator prepared in D5W and NS. Each sample was analyzed via a novel high-performance liquid chromatographic (HPLC) method at time 0, 8, 24, and 48 hours. The method was tested and passed specifications for linearity, reproducibility, and accuracy. A visual inspection by 9 licensed pharmacists was used to demonstrate physical stability. A cost evaluation comparing nitroprusside and thiosulfate to alternative agents was completed. RESULTS: The concentration of both nitroprusside and thiosulfate remain greater than 95% of the initial concentration through 48 hours. Physical compatibility was confirmed in all samples tested through 72 hours. CONCLUSION: The combination of nitroprusside and thiosulfate is chemically and physically stable as a single compounded dose for up to 48 hours when stored at room temperature and protected from light. The admixture represents an inexpensive option to other higher cost alternatives such as nicardipine or clevidipine.

Adverse drug reactions in patients with phaeochromocytoma: incidence, prevention and management

The dangers of phaeochromocytomas are mainly due to the capability of these neuroendocrine tumours to secrete large quantities of vasoactive catecholamines, thereby increasing blood pressure and causing other related adverse events or complications. Phaeochromocytomas are often missed, sometimes only becoming apparent during therapeutic interventions that provoke release or interfere with the disposition of catecholamines produced by the tumours. Because phaeochromocytomas are rare, evidence contraindicating use of specific drugs is largely anecdotal or based on case reports. The heterogeneous nature of the tumours also makes adverse reactions highly variable among patients. Some drugs, such as dopamine D(2) receptor antagonists (e.g. metoclopramide, veralipride) and beta-adrenergic receptor antagonists (beta-blockers) clearly carry high potential for adverse reactions, while others such as tricyclic antidepressants seem more inconsistent in producing complications. Other drugs capable of causing adverse reactions include monoamine oxidase inhibitors, sympathomimetics (e.g. ephedrine) and certain peptide and corticosteroid hormones (e.g. corticotropin, glucagon and glucocorticoids). Risks associated with contraindicated medications are easily minimised by adoption of appropriate safeguards (e.g. adrenoceptor blockade). Without such precautions, the state of cardiovascular vulnerability makes some drugs and manipulations employed during surgical anaesthesia particularly dangerous. Problems arise most often when drugs or therapeutic procedures are employed in patients in whom the tumour is not suspected. In such cases, it is extremely important for the clinician to recognise the possibility of an underlying catecholamine-producing tumour and to take the most appropriate steps to manage and treat adverse events and clinical complications.

Role of nitric oxide in chick embryonic organogenesis and dysmorphogenesis

BACKGROUND

Nitric oxide (NO), produced by the nitric oxide synthase family of enzymes, mediates multiple signaling functions, and when unchecked, NO causes pathological damage. Exposure of embryos to a variety of teratogens, including carbon monoxide (CO), has been shown to increase reactive intermediates, such as NO, and recent work showed that either the excess or absence of NO caused morphological defects. While endogenous NO is known to regulate many adult tissues, its role during embryonic organogenesis and/or in mediating responses to teratogen exposure has not been explored.

METHODS

We have examined here the presence of NO during normal chick embryonic organogenesis, and investigated the teratogenicity of NO through the application of sodium nitroprusside (SNP), which mimics NO overproduction, and NG-monomethyl-L-arginine (L-NMMA), which inhibits endogenous NOS activity.

RESULTS

Topical treatment with SNP or L-NMMA for 18 h resulted in morphological defects, specifically in the neural tube and somites, which corresponded to sites of altered apoptosis. The location of NO was histochemically correlated with the observed morphological defects. Coadministration of SNP or L-NMMA with CO showed functional coregulation and interaction between NO and CO in chick embryonic development.

CONCLUSIONS

Our results showed that regulation of NO is essential for normal axial development, that sites of altered NO expression correlate to those of altered apoptosis and dysmorphogenesis, and that CO coadministration resulted in a rectification of normal NO expression. Collectively, these results suggest that alteration in endogenous NO/CO signaling is responsible, at least in part, for the observed NO-induced teratogenesis.

The role of oximes in the management of organophosphorus pesticide poisoning

The number of intoxications with organophosphorus pesticides (OPs) is estimated at some 3,000,000 per year, and the number of deaths and casualties some 300,000 per year. OPs act primarily by inhibiting acetylcholinesterase (AChE), thereby allowing acetylcholine to accumulate at cholinergic synapses, disturbing transmission at parasympathetic nerve endings, sympathetic ganglia, neuromuscular endplates and certain CNS regions. Atropine is the mainstay of treatment of effects mediated by muscarine sensitive receptors; however, atropine is ineffective at the nicotine sensitive synapses. At both receptor types, reactivation of inhibited AChE may improve the clinical picture. The value of oximes, however, is still a matter of controversy. Enthusiastic reports of outstanding antidotal effectiveness, substantiated by laboratory findings of reactivated AChE and improved neuromuscular transmission, contrast with many reports of disappointing results. In vitro studies with human erythrocyte AChE, which is derived from the same single gene as synaptic AChE, revealed marked differences in the potency and efficacy of pralidoxime, obidoxime, HI 6 and HLö 7, the latter two oximes being considered particularly effective in nerve agent poisoning. Moreover, remarkable species differences in the susceptibility to oximes were revealed, requiring caution when animal data are extrapolated to humans. These studies impressively demonstrated that any generalisation regarding an effective oxime concentration is inappropriate. Hence, the 4 mg/L concept should be dismissed. To antagonise the toxic effects of the most frequently used OPs, pralidoxime plasma concentrations of around 80 mumol/L (13.8 mg/L pralidoxime chloride) should be attained while obidoxime plasma concentrations of 10 mumol/L (3.6 mg/L obidoxime chloride) may be sufficient. These concentrations should be maintained as long as circulating poison is expected to be present, which may require oxime therapy for up to 10 days. Various dosage regimens exist to reach this goal. The most appropriate consists of a bolus short infusion followed by a maintenance dosage. For pralidoxime chloride, a 1 g bolus over 30 minutes followed by an infusion of 0.5 g/h appears appropriate to maintain the target concentrtion of about 13 mg/L (70 kg person). For obidoxime chloride, the appropriate dosage is a 0.25 g bolus followed by an infusion of 0.75 g/24 h. These concentrations are well tolerated and keep a good portion of AChE in the active state, thereby retarding the AChE aging rate. AChE aging is particularly rapid with dimethyl phosphoryl compounds and may thwart the effective reactivation by oximes, particularly in suicidal poisoning with excessive doses. In contrast, patients with diethyl OP poisoning may particularly benefit from oxime therapy, even if no improvement is seen during the first days when the poison load is high. The low propensity to aging with diethyl OP poisoning may allow reactivation after several days, when the poison concentration drops. Rigorous testing of the benefits of oximes is only possible in randomised controlled trials with clear stratification according to the class of pesticides involved, time elapsed between exposure and treatment and severity of cholinergic symptoms on admission.

Exposure to cyanide following a meal of cassava food

Exposure to cyanide from gari, a popular cassava food in West Africa, is implicated in the causation of ataxic polyneuropathy and amblyopia, but this has been questioned because cyanide was not detected in gari in a study. This study was carried out to determine if gari is a source of exposure to cyanide. Gari (150 g) containing cyanohydrin, from which 128 micromol of cyanide ions could be released, was dissolved in 500 ml of cold water for each of the 12 healthy subjects to drink. Concentrations of cyanide in plasma and erythrocytes were determined at baseline and following the meal at 30 min, 1 h, hourly for 4 h and two hourly for 12 h. The mean concentrations of cyanide in the plasma were 6 micromol/l (95% CI 2-10) at baseline, 12 micromol/l (95% CI 6-17) at peak and 6 micromol/l (95% CI 2-10) on return to baseline. The mean amount of cyanide absorbed into the plasma was 13 micromol (S.D. 12), while the transit time of absorbed cyanide was 7.3 h (S.D. 2.1). This study shows that exposure to cyanide follows consumption of gari, but the amount of cyanide absorbed into the plasma from a single meal is small and unlikely to cause acute intoxication. The long transit time of absorbed cyanide in the plasma suggests that frequent intake of gari could cause cyanide to accumulate in the plasma.

Involvement of nitric oxide in nitroprusside-induced hepatocyte cytotoxicity

Sodium nitroprusside (SNP) cytotoxicity towards rat hepatocytes was accompanied by peroxynitrite formation, lipid peroxidation, inhibition of glycolysis, cyanide (CN) release, partial inhibition of hepatocyte respiration, and ATP depletion. Antioxidants and desferoxamine prevented both cytotoxicity and lipid peroxidation induced by SNP. The CN antidote thiosulfate or the CN trapping agents dihydroxyacetone and glyceraldehyde increased SNP metabolism, SNP-induced peroxynitrite formation, cytotoxicity, and lipid peroxidation. On the other hand, addition of non-toxic concentrations of CN to hepatocytes prevented SNP metabolism and SNP-induced lipid peroxidation and cytotoxicity. SNP depleted hepatocyte GSH immediately upon addition, and GSH-depleted hepatocytes were more susceptible to SNP. The results of this study suggest that nitric oxide rather than CN mediates SNP cytotoxicity in isolated cells.

Sodium nitroprusside: twenty years and counting

SNP remains an effective, reliable, and commonly used drug for the rapid reduction of significant arterial hypertension regardless of the etiology, for afterload reduction in the face of low CO when blood volume is normal or increased, and for intraoperative induced hypotension. After establishing indwelling arterial monitoring, an initial infusion rate of 0.3-0.5 micrograms.kg-1.min-1 is begun with titration as needed up to 2.0 micrograms.kg-1.min-1. Higher rates for brief periods of time (10 min) are acceptable. The use of alternative drugs to reduce the dose or shorten the duration of infusion should be considered when the 2.0 micrograms.kg-1.min-1 range is exceeded (Table 1). SNP should not be used by individuals unfamiliar with its potency and metabolic pathways, as the many reports of adverse reactions testify. Careful attention to infusion rates, particularly in patients at risk for depleted thiosulfate stores, is mandatory, and the use of other drugs in conjunction with or instead of SNP should always be considered. As with many therapeutic interventions, SNP requires careful administration to appropriately selected patients by a clinician who knows its inherent hazards. Despite its toxicity, SNP is popular because it is often the most (in some cases, the only) effective drug in some difficult clinical circumstances.

Fenoldopam, but not nitroprusside, improves renal function in severely hypertensive patients with impaired renal function

PURPOSE

Patients with hypertensive crises often experience reduced renal function that may worsen as the elevated blood pressure is treated. Fenoldopam, a novel, peripherally acting dopamine-1 agonist, lowers blood pressure through arteriolar vasodilation, with particularly prominent effects on the renal vascular bed. This study was conducted to examine the effects of fenoldopam on blood pressure and renal function compared to those of sodium nitroprusside in severely hypertensive patients with impaired renal function.

PATIENTS AND METHODS

Renal function and systemic hemodynamics were studied in 19 severely hypertensive patients (diastolic blood pressure greater than or equal to 120 mm Hg) with impaired renal function (creatinine clearance less than or equal to 70 mL/min) enrolled in clinical trials of fenoldopam and sodium nitroprusside. For comparison, an additional 22 severely hypertensive patients with nonimpaired renal function were studied under the same conditions. Blood pressure and heart rate were measured at baseline before treatment and periodically during treatment. Renal function was determined before and during drug infusion by collection of timed urine specimens and blood samples. Creatinine clearance, urine flow rate, and sodium and potassium excretions were measured and compared.

RESULTS

In patients with impaired renal function, blood pressure (mean +/- SEM) was reduced successfully in both groups (fenoldopam: 214 +/- 8/139 +/- 6 mm Hg to 176 +/- 8/107 +/- 3 mm Hg, p < 0.001 for systolic and diastolic comparisons; nitroprusside: 226 +/- 4/145 +/- 5 mm Hg to 171 +/- 6/108 +/- 2 mm Hg, p < 0.001 for systolic and diastolic comparisons). Results of renal function studies showed significant increases in creatinine clearance (from 39 +/- 7 mL/min to 75 +/- 16 mL/min, p < 0.05), urine flow (from 119 +/- 37 mL/h to 275 +/- 84 mL/h, p < 0.01), and sodium excretion (from 75 +/- 22 microEq/min to 227 +/- 60 microEq/min, p < 0.01) in patients with impaired renal function treated with fenoldopam. No significant changes were seen in patients treated with nitroprusside. In patients with nonimpaired renal function, blood pressure was reduced by both agents, but only patients who received fenoldopam experienced significant increases in creatinine clearance, urine flow rate, and sodium excretion.

CONCLUSION

Fenoldopam, but not nitroprusside, improved renal function in severely hypertensive patients at all levels of baseline renal function while lowering blood pressure. Because of these effects, fenoldopam may be particularly useful in treating severely hypertensive patients with impaired renal function.

Cyanide toxicity from sodium nitroprusside: risks and management

OBJECTIVE

To review the risks, manifestations, and treatment of cyanide toxicity from nitroprusside therapy.

DATA SOURCES

All English case reports identified in Index Medicus (MEDLINE) of cyanide intoxication related to nitroprusside from 1970 to the present were reviewed. In addition, literature regarding the incidence, risks, and treatment of cyanide toxicity from nitroprusside is presented.

CONCLUSIONS

Numerous cases of cyanide toxicity associated with nitroprusside have been reported. The overall incidence appears to be infrequent; however, certain patients may be at high risk. Risk factors may include hypoalbuminemia, cardiopulmonary bypass procedures, or the administration of moderate to high doses of nitroprusside. Treatment of cyanide toxicity requires the cessation of nitroprusside and, for severe toxicity, use of the cyanide antidote kit. Cyanide toxicity from nitroprusside may be prevented by concomitant administration of sodium thiosulfate infusions.

The antidotal action of sodium nitrite and sodium thiosulfate against cyanide poisoning

The combination of sodium thiosulfate and sodium nitrite has been used in the United States since the 1930s as the primary antidote for cyanide intoxication. Although this combination was shown to exhibit much greater efficacy than either ingredient alone, the two compounds could not be used prophylactically because each exhibits a number of side effects. This review discusses the pharmacodynamics, pharmacokinetics, and toxicology of the individual agents, and their combination.

Thiosulphate and hydroxocobalamin prophylaxis in progressive cyanide poisoning in guinea-pigs

The duration of action of the cyanide antidotes sodium thiosulphate and hydroxocobalamin was investigated in guinea-pigs after prophylactic administration before a long-term infusion of NaCN. The parameter for the diminution of the antidote action was the point of time at which the concentration of HCN in the exhaled air of the animals exceeded 100 nmol/kg per min. The time taken to reach this threshold level in the control animals was 12 min. While the threshold level could be extended only to 35 min with hydroxocobalamin (300 mg/kg i.v.) the protective action of sodium thiosulphate (100, 500 and 1000 mg/kg i.v.) persisted dose dependently for about 1, 2 and 4 h, respectively. Additionally we found a plasma half-life of sodium thiosulphate in guinea-pigs of 26 min. This value corresponds approximately to the plasma half-life of sodium thiosulphate in humans given in the literature. Because of the large injection volume necessary, sodium thiosulphate is not suitable for prophylactic use in man.

Cyanide-induced neurotoxicity: mechanisms of attenuation by chlorpromazine

Chlorpromazine (CPZ) is an effective cyanide antidote, with its greatest efficacy displayed when combined with the antidotes, sodium nitrite and sodium thiosulfate. Since the central nervous system is a primary target organ in cyanide toxicity, the objective of the present study was to determine the mechanisms by which CPZ prevents cyanide-induced damage in neural systems. KCN (10 mM) increased cytosolic free calcium in rat pheochromocytoma (PC12) cells as indicated by the fluorescent dye quin 2. This was blocked by addition of CPZ (0.1 mM) to the cells 15 min prior to addition of KCN. Incubation of cells with KCN (0.1 mM) increased the levels of lipid conjugated dienes and this was blocked by addition of CPZ (1 microM). Peroxidation of brain lipids in mice administered KCN (7-15 mg/kg, sc) was also attenuated by pretreatment with CPZ. Furthermore, production of lipid peroxidation in fresh mouse brain slices, following incubation with 0.1 mM KCN, was blocked by simultaneous addition of CPZ. These observations indicate CPZ prevents cyanide-induced calcium influx and decreases peroxidation of membrane lipids. Thus the antidotal activity of CPZ in cyanide toxicity appears to be related to maintenance of cellular calcium homeostasis and membrane integrity.

Pharmacokinetics of intravenous potassium cyanide

The pharmacokinetics of intravenously injected potassium cyanide have been studied in Beagle bitches. In the period up to about 80 min after dosing, blood levels fell in a manner consistent with first-order elimination kinetics. Thereafter blood cyanide concentrations fell at a slower rate, indicating that a second phase of slower elimination had been entered.

Sodium nitroprusside: pharmacological aspects of its interaction with hydroxocobalamin and thiosulphate

Hydroxocobalamin (HOCb), when mixed with sodium nitroprusside (SNP) in a 10:1 or 1:1 molar ratio and injected (i.v.) into the anaesthetized rat, prolonged the depressor response to SNP by 25-50%, but did not affect the degree of blood pressure lowering. Both the 'onset' and 'offset' components of the response were prolonged. Injecting [14C]SNP along with a 10-fold molar excess of HOCb resulted in a 2- to 3-fold elevation of plasma radioactivity which was maintained during the first 10 min of a 40 min experimental period. These effects of HOCb on the pharmacodynamics and pharmacokinetics of SNP are probably due to complex formation between the two compounds. Sodium thiosulphate (ST) added to SNP (12:1 molar ratio) had no effect on the depressor response to SNP. This mixing of ST and SNP had a less-marked influence on the plasma [14C] SNP-derived radioactivity than occurred with HOCb. There was no initial elevation of radioactivity, but the levels were raised by 50-60% at 4, 6 and 10 min. Since the depressor response to SNP was unaffected by ST, it is presumed that the higher concentrations of radioactivity were due to inactive degradation products rather than the active species itself.

Detoxification of cyanide in a new-born child

A well-developed male baby was given infusions of 2-5 microgram/kg/min of sodium nitroprusside (SNP) in the first few days after birth on account of high arterial blood pressure. After 30 h of treatment, cyanide accumulation was found to have reached a life-threatening level. IV administration of 100 mg/kg of sodium thiosulphate promptly lowered the cyanide level. The mixed infusion of SNP together with thiosulphate, used in the subsequent course, was no longer toxic.