|
Background
Chelation therapy is an established treatment for heavy metal poisoning. Heavy metals, which can not be metabolized, persist in the body and exert their toxic effects by combining with one or more reactive groups (ligands) essential for normal physiological functions. Chelating agents, also known as heavy metal antagonists, form complexes with toxic heavy metals rendering them physiologically inactive and enhancing their excretion in the urine. Specific chelating agents include edetate calcium disodium (EDTA), deferoxamine (Desferal), dimercaprol (BAL in oil) and penicillamine (Cuprimine, Depen).
Dimercaprol was developed as an antidote to lewisite, an arsenic-based war gas and was designated British anti-Lewisite or BAL. It is used principally to treat arsenic, gold and mercury poisoning and in combination with edetate calcium disodium, to treat lead poisoning. The main therapeutic use of edetate calcium disodium is in the treatment of metal intoxication, especially lead intoxication. Mercury poisoning does not respond to this drug. Penicillamine is used for treating copper, mercury, lead and arsenic poisoning, and cystinuria. It is the drug of choice for Wilson's disease (hepato-lenticular degeneration due to an excess of copper). Deferoxamine has a highly affinity for iron and is the drug of choice for acute or chronic iron intoxication.
Chelation therapy with appropriate chelating agents is established treatment for biliary cirrhosis, Cooley's anemia (thalassemia major), cystinuria, heavy metal (arsenic, cadmium, copper, gold, iron, mercury) poisoning, Wilson's disease, and sickle cell anemia, i.e., secondary hemachromatosis (iron overload from multiple transfusions).
The administration of the chelating agent calcium EDTA as a mobilization test (provocative chelation) to determine if chelation therapy is indicated is controversial. The provocative chelation test was developed to assess the total body lead burden and efficacy of chelation treatment. The tests involve obtaining a timed urine collection after administering a dose of calcium EDTA. In view of a paucity of relevant clinical outcome studies of provocative chelation, and in view of and animal studies suggesting that single doses of chelation might cause harm from mobilizing lead and redistributing to the central nervous system, the use of provocative chelation is not indicated.
Intravenous or oral chelation therapy is indicated in all children with acute lead intoxication, and in children with moderate to severe chronic lead intoxication (blood lead level of 45 mcg/dL or greater). For children with mild intoxication (blood level less than 45 mcg/dL), oral chelation (DMSA or D-penacillamine) is indicated for those with blood levels are between 20 and 44 mcg/dL). Chelation therapy is not necessary for children with blood levels of lead less than 20 mcg/dL.
For adults, intravenous or oral chelation therapy is recommended for those with acute lead toxicity, and for adults with blood lead levels greater than 80 mcg/dL. Chelation therapy is also indicated for adults with blood lead levels between 60 and 80 mcg/dL if they have lead-related symptoms. In addition, chelation therapy may be considered in adults with blood lead levels between 40 and 60 mcg/dL, if they have continued symptoms and elevated blood lead levels after 2 weeks of removal from exposure.
Treatment with chelators should be considered in persons with acute symptoms arising from the central nervous system due to confirmed mercury poisoning (e.g., via measurement of mercury in air, blood, or urine). The normal range of mercury concentrations in whole blood is 0 to 10 mcg/L. Early signs and symptoms may occur with concentrations greater than 35 mcg/L. Clinically significant poisoning from mercury is unlikely if blood and urine concentrations are below 100 µg/L.
A concentration greater than or equal to 50 mcg/L or 100 mcg of arsenic/g creatinine in the absence of recent fish or shellfish intake strongly suggests arsenic poisoning. Chelation indicated in symptomatic arsenic poisoning and in all patients whose speciated urine arsenic level exceeds 200 mcg/L. Patients who are minimally symptomatic and have chronic arsenic poisoning may be removed from the source of their exposure without chelation therapy. Chelation can be accomplished with oral penicillamine; IV dimercaprol can be used for person who can not take oral medications.
Chelation therapy with calcium EDTA may be indicated in acute cadmium toxicity. Blood levels of cadmium above 5 mcg/dL suggest acute cadmium toxicity. There is a lack of evidence of beneficial effects of chelating agents on cadmium toxicity after prolonged exposure. The literature on the influence of chelating agents on cadmium distribution and excretion is limited to animal studies, and is confined to the early period after acute cadmium exposure. Developing an effective chelation therapy for cadmium is difficult because cadmium is tightly bound to metallothionein in liver and kidney.
Gold is used in the treatment of rheumatoid arthritis (RA) and other rheumatic diseases. Chelation therapy may be used in persons with gold toxicity with severe reactions who are unresponsive to steroids. Moderate to high-dose steroid therapy may be beneficial in gold-induced thrombocytopenia, bone marrow toxicity, enterocolitis, and pulmonary infiltrates. Dimercaprol, penicillamine, N-acetylcysteine, and other chelating agents have been used to treat reactions unresponsive to glucocorticoids.
Chelation therapy may be indicated in copper toxicity. For copper toxicity due to ingesting grams of copper, prompt gastric lavage followed by daily intra-muscular injections of dimercaprol may prevent death. The oral chelating drug penicillamine binds copper, facilitating its excretion, and may promote excretion of copper absorbed from burned skin. Chronic oral chelation therapy may be necessary in persons with inherited chronic copper toxicity (Wilson's disease).
There is insufficient evidence to support the use of chelation therapy for prevention or treatment of cardiovascular disease. Chelation therapy for atherosclerosis involves the intravenous infusion of ethylene diaminetetraacetic acid, also known as edetate disodium, endrate or EDTA. It may involve as many as 20 to 40 infusions, each 3 to 4 hours long, administered 1 to 3 times weekly.
Used since the 1950s, the premise for EDTA chelation is the removal of calcium from the atherosclerotic lesion. Proponents claim that EDTA forms a chelated soluble complex with the calcium which is excreted in the urine. Calcium, however, is not a major constituent in the pathogenesis of atherosclerosis. The atherosclerotic lesion is highly cellular and contains smooth muscle, macrophages, lipid particles, and connective tissue. Within the lesion there are areas of necrotic debris, cholesterol crystal and calcification. Lesions are primarily fibrous overgrowths and calcium deposition is an insignificant part of the total lesion.
Proponents also champion EDTA as the original calcium-channel antagonist. However, there is no evidence that lowering serum, tissue and bone calcium with EDTA produces the same physiologic effects as the calcium-channel antagonists. These work by binding to calcium channel receptors to reduce calcium influx into the myofibril, therefore producing relaxation of smooth muscle without affecting the serum concentration of calcium.
Explanations for individual positive responses to chelation therapy include placebo effect (often seen in the controlled evaluation of therapies for angina pectoris), lifestyle changes and natural variations in the disease. There are case reports of symptomatic improvement with angiographically documented persistence of the lesion. Toxic effects may include death, renal failure, arrhythmias, tetany and hypocalcemia.
A systematic review of chelation therapy for cardiovascular disease (Villaruz et al, 2003) reached the following conclusions: "[a]t present, there is insufficient evidence to decide on the effectiveness or ineffectiveness of chelation therapy in improving clinical outcomes of patients with atherosclerotic cardiovascular disease. This decision must be preceded by conducting randomized controlled trials that would include endpoints that show the effects of chelation therapy on longevity and quality of life among patients with atherosclerotic cardiovascular disease."
The American Heart Association (2002) has concluded that there is "no scientific evidence to demonstrate any benefit from this form of therapy."
A assessment of chelation therapy by the West Midlands Health Technology Assessment Collaboration (Connock et al, 2002) concluded that “[c]urrently there is little objective evidence that CT [chelation therapy] is effective for CHD [coronary heart disease] or IC [intermittent claudication].”
The New Zealand Guidelines Group (2003) found that insufficient evidence to recommend chelation for the treatment of prevention of cardiovascular disease, stroke, or type 2 diabetes.
A Canadian Cardiovascular Society consensus conference statement on heart failure (2006) concluded that "[c]helation therapy should not be used as heart failure therapy."
The American College of Cardiology (Hirsch et al, 2005) stated that "[c]helation (e.g., ethylenediaminetetraacetic acid) is not indicated for treatment of intermittent claudication and may have harmful adverse effects." The Scottish Intercollegiate Guidelines Network (2006) explained: "[c]helation has been studied in only one robust trial of patients with intermittent claudication [citing van Rig et al, 1994], which showed no difference between experimental and placebo groups, leaving no evidence on which to base a recommendation. Adverse effects are potentially serious."
The American College of Physicians (Snow et al, 2004) concluded that chelation should not be used to prevent myocardial infarction (MI) or death or to reduce symptoms in patients with symptomatic chronic stable angina.
In August 2002, the National Center for Complementary and Alternative Medicine (NCCAM) and the National Heart, Lung, and Blood Institute (NHLBI) announced that they have launched the Trial to Assess Chelation Therapy (TACT), which is the first large-scale, multi-center study to find out if EDTA chelation therapy is safe and effective for people with coronary heart disease. This placebo-controlled, double-blind study will involve 2,372 participants aged 50 years and older with a history of MI. Recruitment for this study began in March 2003, and the study will take 5 years to complete.
In a randomized double-blind, placebo-controlled study (n = 47), Anderson et al (2003) reported that EDTA chelation therapy in combination with vitamins and minerals did not provide additional benefits on abnormal vasomotor responses in patients with coronary artery disease optimally treated with proven therapies for atherosclerotic risk factors.
Rose and colleagues (2010) stated that iron chelation therapy improves survival in thalassemia major but its beneficial effects on survival in patients with myelodysplastic syndrome (MDS) remain uncertain. These researchers analyzed, by multi-variate analysis, survival and causes of deaths in 97 low or intermediate 1 International Prognostic Scoring System (IPSS) patients regularly transfused as outpatients, chelated or not, who were included during a month period and followed for 2.5 years. A total of 44 (45 %) of patients were not chelated and 53 (55 %) received chelation therapy, mainly with deferoxamine, for at least 6 months (median duration of chelation of 36 months, range of 6 to 131+ months). During the follow-up period, 66 of the 97 patients died, including 51 % and 73 % of chelated and non-chelated patients, respectively. Median overall survival was 53 months and 124 months in non-chelated and in chelated patients, respectively (p < 0.0003). Causes of death did not significantly differ between the 2 groups (p = 0.51). In multi-variate Cox analysis, adequate chelation was the strongest independent factor associated with better overall survival. The authors concluded that iron chelation therapy appears to improve survival in heavily transfused lower risk MDS. Moreover, they stated that prospective randomized studies are needed to confirm these findings, and to determine more precisely the mechanisms of this potential survival benefit.
Zhang et al (2011) noted that oxidative stress plays a critical role in cataractogenesis, the leading cause of blindness worldwide. Since transition metals generate reactive oxygen species (ROS) formation, metal chelation therapy has been proposed for treatment of cataracts. However, the effectiveness of most chelators is limited by low tissue penetrability. This study was the first to demonstrate that the topically applied di-valent metal chelator EDTA combined with the carrier and permeability enhancer methyl sulfonyl methane (MSM) ameliorates both oxidation-induced lens opacification and the associated toxic accumulation of protein-4-hydroxynonenal (HNE) adducts. Both in vitro (rat lens culture) and in vivo (diabetic rats), EDTA-MSM (i) significantly reduced lens opacification by about 40 to 50 %, (ii) significantly diminished lens epithelial cell proliferation and fiber cell swelling in early stages of cataract formation in vivo, and (iii) notably decreased the levels of protein-HNE adducts. The authors stated that these findings have important implications specifically for the treatment of cataract and generally for other diseases in which oxidative stress plays a key pathogenic role.
Although chelation therapy has been cited as a potential treatment for autism and attention deficit hyperactivity disorder (ADHD) (e.g., Curtis and Patel, 2008), there is insufficient evidence to support its use for these indications. Well-designed clinical trials are needed to ascertain the clinical value, if any, of chelation therapy for autism and ADHD.
In a systematic review on novel and emerging treatments for autism spectrum disorders (ASD), Rossignol (2009) stated that currently only 1 medication (risperidone) is Food and Drug Administration (FDA)-approved for the treatment of ASD; and the use of novel, unconventional, and off-label treatments is common, with up to 74 % of children with ASD using these treatments. The author performed a systematic literature search of electronic scientific databases to identify studies of novel and emerging treatments for ASD, including nutritional supplements, diets, medications, and non-biological treatments. A grade of recommendation ("Grade") was then assigned to each treatment using a validated evidence-based guideline as outlined in this review: "Grade A": Supported by at least 2 prospective randomized controlled trials (RCTs) or 1 systematic review; "Grade B": Supported by at least 1 prospective RCT or 2 non-randomized controlled trials; "Grade C": Supported by at least 1 non-randomized controlled trial or 2 case series; and "Grade D": Troublingly inconsistent or inconclusive studies or studies reporting no improvements. Potential adverse effects for each treatment were also reviewed. Grade A treatments for ASD included melatonin, acetylcholinesterase inhibitors, naltrexone, and music therapy. Grade B treatments include carnitine, tetrahydrobiopterin, vitamin C, alpha-2 adrenergic agonists, hyperbaric oxygen treatment (HBOT), immunomodulation and anti-inflammatory treatments, oxytocin, and vision therapy. Grade C treatments for ASD include carnosine, multi-vitamin/mineral complex, piracetam, polyunsaturated fatty acids, vitamin B6/magnesium, elimination diets, chelation, cyproheptadine, famotidine, glutamate antagonists, acupuncture, auditory integration training, massage, and neurofeedback. The author concluded that the reviewed treatments for ASD are commonly used, and some are supported by prospective RCTs. Promising treatments include melatonin, antioxidants, acetylcholinesterase inhibitors, naltrexone, and music therapy. All of the reviewed treatments are currently considered off-label for ASD (i.e., not FDA-approved) and some have adverse effects. Further studies exploring these treatments are needed.
Furthermore, in a review on autism, Levy et al (2009) stated that popular biologically based treatments include anti-infectives, chelation medications, gastrointestinal medications, HBOT, and immunoglobulins. Non-biologically based treatments include auditory integration therapy, chiropractic therapy, cranio-sacral manipulation, interactive metronome, and transcranial stimulation. However, few studies have addressed the safety and effectiveness of most of these treatments.
Chelation therapy has been shown to be useful in treatment of aluminum toxicity in renal failure. Hernandez and Johnson (1990) noted that aluminum (AL) toxicity, common among individuals with chronic renal failure, is associated with disabling osteomalacia, encephalopathy, and anemia. The control of AL intake has included standards to limit the amount of AL in the dialysis fluid in addition to the use of non-AL containing phosphate binders. Deferoxamine (DFO) mesylate, a heavy metal chelating agent, is used to remove AL from the tissues of dialysis patients. Chelation therapy has resulted in improvements of clinical symptoms and bone histology. Ocular, auditory, and infectious adverse effects have occurred with the use of DFO. Day and Ackrill (1993) stated that DFO now finds extensive use in the treatment and diagnosis of AL-related diseases in renal patients. Moreover, the American Academy of Pediatrics' statement on Al toxicity in infants and children (1996) stated that intravenous DFO has been used successfully in treating Al toxicity in children.
Barata and colleagues (1996) reported that according to the recommendations proposed at the 1992 consensus conference on diagnosis and treatment of AL overload in end-stage renal failure patients, low-dose DFO treatment was applied for the first time in 41 acutely Al-intoxicated patients. DFO-related neurological/ophthalmological side-effects were observed in 9 of 11 patients with a post-DFO serum Al level greater than 300 ug/L and in 2 patients of 30 below this level after a single administration of a 5 mg/kg dose of the chelator in the conventional way (i.e., the last hour of a dialysis session). They were no longer observed after introducing an alternative DFO administration schedule (i.e., administration of the chelator 5 hours prior to the start of a hemodialysis session; group I: n = 14). A significant decrease in the serum Al levels as well as in the post-DFO serum Al increment (delta sAl) was observed during the first 6 months, course of low-dose DFO treatment in group I as well as group II (which consisted of patients receiving DFO in the conventional way; n = 27). Low-dose DFO treatment was accompanied by a significant increase in the mean +/- SD serum iPTH levels (group I: 174 +/- 245 up to 286 +/- 285 ng/L; group II: 206 +/- 272 up to 409 +/- 424 ng/L; p < 0.005) and the mean corpuscular volume (group I: 80 +/- 6.4 up to 85 +/- 3.7 fL, p < 0.005; group II: 76 +/- 5.0 up to 87 +/- 4.3 fL, (p < 0.0001). Serum ferritin levels significantly decreased in both groups. No further side-effects were observed during the DFO course. Patients in which DFO treatment could be stopped (i.e., subjects in which both serum Al and delta sAl were below 50 ug/L at two successive occasions) before the end of the 6 months' treatment course had a significantly greater residual diuresis (700 +/- 682 ml/min versus 84 +/- 109 ml/24 hours). Also, residual diuresis was found to protect against Al intoxication as reflected by the values noted in group I versus those in group II. The authors concluded that the 5 mg/kg DFO treatment provides a safe and adequate therapy for Al overload. In severely Al-intoxicated patients presenting post-DFO serum Al levels above 300 ug/L, DFO should be given once weekly 5 hours prior to high-extraction dialysis ensuring (i) maximal chelation of Al, (ii) limited exposure to circulating Al noxamine levels, and (iii) adequate removal of the latter compound.
Chappell (2007) stated that the recently reported increased risk of blood clots, resulting in MI and sudden death beginning 6 months after medicated stents were implanted in patients following percutaneous transluminal coronary angioplasty (PTCA), has left physicians pondering what course of action to take. The purpose of adding implanted medication to a stent is to prevent thrombin accumulation and re-stenosis. However, these stents may increase, rather than decrease, the risk. Although long-term treatment with clopidogrel plus aspirin for at least 12 months has been suggested as a preventive treatment, there is no evidence from randomized, controlled trials that this approach is effective for more than 6 months. Clopidogrel also increases the risk of major bleeding episodes. The author served as the primary investigator for a study that showed cardiovascular patients treated with EDTA chelation therapy had a lower rate of subsequent cardiac events, including MI and death, than those treated with cardiac medications, PTCA, or coronary artery bypass graft. The data also indicated chelation therapy might be effective in preventing thrombosis and cardiac events from stent implantation. There is evidence that EDTA chelation therapy might prevent hyper-coagulability resulting from the placement of stents, although not specifically medicated stents. Based on the limited data currently available, intravenous EDTA may be safe and effective for treating patients who have implanted medicated stents. The author noted that prospective clinical trials are needed, and EDTA should be included in those trials.
Whayne (2010) noted that a wide range of alternative medications with relevance or connection to cardiovascular (CV) disease have been considered. While many are worthless, others have definite benefit, and at least one, chelation therapy, is associated with definite harm, significant risk, no benefit, and enrichment of the practitioners who prescribe it. The issues concerning alternative therapies will likely never be studied with randomized clinical trials due to the lack of a profit motive on the part of pharmaceutical companies -- only rarely do other institutions, such as the National Institutes of Health, support medicinal studies. Basic knowledge of alternative therapies is essential for the CV specialist and other practicing physicians and other practitioners, since at least a few of their patients will take these medications regardless of medical advice. The result is that a number of these alternative medications will then interact with conventional CV medications, many times unfavorably.
In a review on current and future treatments of zygomycosis, Rogers (2008) noted that zygomycosis is a frequently lethal invasive infection in high-risk patients such as the immunocompromised (especially hematopoietic stem cell transplant (HSCT) recipients) and patients with type 2 diabetes mellitus. However, zygomycosis has also been reported in individuals without known risk factors. Zygomycosis can present clinically as rhinocerebral, pulmonary or disseminated disease which progresses rapidly. The management of cases is based on early diagnosis, surgical debridement when possible and aggressive anti-fungal therapy. Based on clinical experience, but without the benefit of comparative studies, liposomal amphotericin B has become the therapeutic agent of choice. Posaconazole is a new orally administered triazole anti-fungal and the first member of this class to have comparable in vitro activity to amphotericin B against most zygomycetes. Studies of salvage therapy of zygomycosis with posaconazole have yielded promising results and there are additional case reports of successful outcomes using these and other anti-fungal drugs as combination therapy. Moreover, adjunctive approaches that are showing promise but with limited clinical experience are iron chelation and immunotherapy.
Bolognin et al (2009) stated that available evidence suggests a central role for transition biometals in the pathogenesis of neurodegenerative diseases (ND). It has become increasingly evident that biometals and non-physiological aluminum are often involved in pathological onset and progression, either by affecting the conformation of specific proteins or by exacerbating local oxidative stress. The apparently critical role played by metal dishomeostasis in ND makes chelation therapy an attractive pharmacological option. However, classical metal chelation approaches, relying on potent metal ligands, turned out to be successful only in those rare cases where exceptional brain metal accumulation occurs due to specific defects in metal metabolism. In contrast, metal-targeted approaches using ligand of intermediate strength seem to be more appropriate in fighting the major ND, although their benefits are still questioned.
Hedge et al (2009) noted that a close association between brain metal dishomeostasis and the onset and/or progression of Alzheimer's disease (AD) has been established in a number of studies, although the underlying biochemical mechanisms remain obscure. This observation renders chelation therapy an attractive pharmacological option for the treatment of this disease. However, a number of requirements must be fulfilled in order to adapt chelation therapy to AD.
A Cochrane systematic evidence review found insufficient evidence for the use of chelation (metal protein attenuating compounds) in AD (Sampson et al, 2008). Metal protein attenuating compounds have great affinity for copper and zinc ions, preventing them from binding to beta amyloid, a protein strongly implicated in the development of AD. Chelation of these metal ions promotes dissolution of beta amyloid, thus presenting a potential therapeutic target for AD. The Cochrane systematic evidence review found 1 RCT (n = 36) of metal protein attenuating compounds in AD. That trial, of clioquinol (also known as PBT1) showed no statistically significant difference in cognition between active treatment and placebo groups at 36 weeks. The authors concluded that there is no current evidence that treatment with clioquinol (PBT1) has any significant effect on cognition (as measured by the ADAS-Cog scale) in patients with AD.
Garcia-Manero et al (2011) noted that myelodysplastic syndromes (MDS) are a very heterogeneous group of myeloid disorders characterized by peripheral blood cytopenias and increased risk of transformation to acute myelogenous leukemia (AML). Myelodysplastic syndromes occurs more frequently in older male and in individuals with prior exposure to cytotoxic therapy. Diagnosis of MDS is based on morphological evidence of dysplasia upon visual examination of a bone marrow aspirate and biopsy. Information obtained from additional studies such as karyotype, flow cytometry, or molecular genetics is complementary but not diagnostic. Therapy is selected based on risk, transfusion needs, percent of bone marrow blasts and more recently cytogenetic profile. Goals of therapy are different in lower risk patients than in higher risk. In lower risk, the goal is to decrease transfusion needs and transformation to higher risk disease or AML. In higher risk, the goal is to prolong survival. Current available therapies include growth factor support, lenalidomide, hypomethylating agents, intensive chemotherapy, and allogeneic stem cell transplantation. The use of lenalidomide has significant clinical activity in patients with lower risk disease, anemia, and a chromosome 5 alteration. 5-azacitidine and decitabine have activity in higher risk MDS. 5-azacitidine has been shown to improve survival in higher risk MDS. Additional supportive care measures may include the use of prophylactic antibiotics and iron chelation. At the present time, there are no approved interventions for patients with progressive or refractory disease particularly after hypomethylating based therapy. Options include cytarabine-based therapy, transplantation, and participation on a clinical trial.
In the National Comprehensive Cancer Network's clinical practice guidelines on MDS, Greenberg et al (2011) stated that 4 drugs have recently been approved by the FDA for treating specific subtypes of myelodysplastic syndromes (MDS): (i) lenalidomide for MDS patients with del(5q) cytogenetic abnormalities; (ii) azacytidine and (iii) decitabine for treating patients with higher-risk or non-responsive MDS; and (iv) deferasirox for iron chelation of iron overloaded patients with MDS.
Dental amalgam is a widely used restorative material containing 50 % elemental mercury that emits mercury vapor. Available evidence indicates that this low-level mercury exposure in children with dental amalgam is not associated with adverse health outcomes (Bellinger et al, 2006; DeRouen et al, 2006; and Shenker et al, 2008). Moreover, when chelation therapy is used to treat individuals who attribute their health problems to mercury from dental amalgam, there appears to be a strong placebo effect (Grandjean et al, 1997).
In a randomized study, Bellinger et al (2006) compared the neuropsychological and renal function of children whose dental caries were restored using amalgam or mercury-free materials. A total of 534 children aged 6 to 10 years at baseline with no prior amalgam restorations and 2 or more posterior teeth with caries were randomly assigned to receive dental restoration of baseline and incident caries during a 5-year follow-up period using either amalgam (n = 267) or resin composite (n = 267) materials. The primary neuropsychological outcome was 5-year change in full-scale IQ scores. Secondary outcomes included tests of memory and visuomotor ability. Renal glomerular function was measured by creatinine-adjusted albumin in urine. Children had a mean of 15 tooth surfaces (median, 14) restored during the 5-year period (range of 0 to 55). Assignment to the amalgam group was associated with a significantly higher mean urinary mercury level (0.9 versus 0.6 microg/g of creatinine at year 5, p < 0.001). After adjusting for randomization stratum and other covariates, no statistically significant differences were found between children in the amalgam and composite groups in 5-year change in full-scale IQ score (3.1 versus 2.1, p = 0.21). The difference in treatment group change scores was 1.0 (95 % confidence interval: -0.6 to 2.5) full-scale IQ score point. No statistically significant differences were found for 4-year change in the general memory index (8.1 versus 7.2, p = 0.34), 4-year change in visuomotor composite (3.8 versus 3.7, p = 0.93), or year 5 urinary albumin (median, 7.5 versus 7.4 mg/g of creatinine, p = 0.61). The authors concluded that there were no statistically significant differences in adverse neuropsychological or renal effects observed over the 5-year period in children whose caries were restored using dental amalgam or composite materials. Although it is possible that very small IQ effects cannot be ruled out, these findings suggested that the health effects of amalgam restorations in children need not be the basis of treatment decisions when choosing restorative dental materials.
In a randomized clinical trial, DeRouen et al (2006) evaluated the safety of dental amalgam restorations in children. A total of 507 children in Lisbon, Portugal, aged 8 to 10 years with at least 1 carious lesion on a permanent tooth, no previous exposure to amalgam, urinary mercury level less than 10 microg/L, blood lead level less than 15 microg/dL, Comprehensive Test of Nonverbal Intelligence IQ greater than or equal to 67, and with no interfering health conditions were included in this study. Routine, standard-of-care dental treatment was provided, with one group receiving amalgam restorations for posterior lesions (n = 253) and the other group receiving resin composite restorations instead of amalgam (n = 254). Main outcome measures were neurobehavioral assessments of memory, attention/concentration, and motor/visuomotor domains, as well as nerve conduction velocities. During the 7-year trial period, children had a mean of 18.7 tooth surfaces (median, 16) restored in the amalgam group and 21.3 (median, 18) restored in the composite group. Baseline mean creatinine-adjusted urinary mercury levels were 1.8 microg/g in the amalgam group and 1.9 microg/g in the composite group, but during follow-up were 1.0 to 1.5 microg/g higher in the amalgam group than in the composite group (p < 0.001). There were no statistically significant differences in measures of memory, attention, visuomotor function, or nerve conduction velocities (average z scores were very similar, near zero) for the amalgam and composite groups over all 7 years of follow-up, with no statistically significant differences observed at any time point (P values from 0.29 to 0.91). Starting at 5 years after initial treatment, the need for additional restorative treatment was approximately 50 % higher in the composite group. The authors concluded that children who received dental restorative treatment with amalgam did not, on average, have statistically significant differences in neurobehavioral assessments or in nerve conduction velocity when compared with children who received resin composite materials without amalgam. These findings, combined with the trend of higher treatment need later among those receiving composite, suggested that amalgam should remain a viable dental restorative option for children.
Shenker et al (2008) evaluated a subpopulation of the participants in the New England Children's Amalgam Trial for in-vitro manifestations of immunotoxic effects of dental amalgam. These investigators conducted a randomized clinical trial in which children requiring dental restorative treatment were randomly assigned to receive either amalgam for posterior restorations or resin-based composite restorations. They assessed 66 children, aged 6 to 10 years, for total white blood cell counts, specific lymphocyte (T-cell and B-cell) counts and lymphocyte, neutrophil and monocyte responsiveness across a 5-year period. Because of the small number of participants, the authors acknowledged that the study is exploratory in nature and has limited statistical power. The mean number of tooth surfaces restored during the 5-year period was 7.8 for the amalgam group and 10.1 for the composite group. In the amalgam group, there was a slight, but statistically insignificant, decline in responsiveness of T cells and monocytes at 5 to 7 days after treatment; these researchers consistently observed no differences at 6, 12 or 60 months. The authors concluded that these findings confirmed that treatment of children with amalgam restorations leads to increased, albeit low-level, exposure to mercury. In this exploratory analysis of immune function, amalgam exposure did not cause overt immune deficits, although small transient effects were observed 5 to 7 days after restoration placement. They stated that these findings suggested that immunotoxic effects of amalgam restorations are minimal and transient in children and most likely do not need to be of concern to practitioners considering the use of this restorative dental material.
Furthermore, an UpToDate review on “Epidemiology and toxicity of mercury” (Elinder, 2012) states that “The release of mercury from amalgam fillings is proportional to the number of fillings and the total amalgam surface area. It has been difficult to accurately estimate the release from amalgam fillings; however, an expert committee from the World Health Organization believes that the average exposure from dental amalgam is approximately 10 mcg/day. Measurements of urinary excretion of mercury have revealed that persons with a habit of tooth grinding release considerably more mercury from their dental fillings than those without this habit. Health studies have focused on identifying the early effects of mercury on the central nervous system. Overall, there is no evidence suggesting a link between exposure to mercury from amalgam fillings and degenerative changes of the nervous system. There is also little evidence to support the removal of existing fillings …. Treatment with chelators may be considered in patients with acute symptoms arising from the central nervous system due to confirmed mercury poisoning (e.g., via measurement of mercury in air, blood, or urine)”.
Grandjean et al (1997) stated that treatment of patients who attribute their environmental illness to mercury from amalgam fillings is largely experimental. On the Symptom Check List, overall distress, and somatization, obsessive-compulsive, depression, and anxiety symptom dimensions, were increased in 50 consecutive patients examined, and Eysenck Personality Questionnaire scores suggested less extroversion and increased degree of emotional liability. Succimer (meso-2, 3-dimercaptosuccinic acid) was given at a daily dose of 30 mg/kg for 5 days in a double-blind, randomized placebo-controlled trial. Urinary excretion of mercury and lead was considerably increased in the patients who received the chelator. Immediately after the treatment and 5 to 6 weeks later, most distress dimensions had improved considerably, but there was no difference between the succimer and placebo groups. The authors concluded that these findings suggested that some patients with environmental illness may substantially benefit from placebo.
Glotzer (1993) stated that 2,3-dimercaptosuccinic acid (DMSA) is an orally active chelating agent used in the treatment of lead and other heavy metal poisonings. In animals, DMSA chelates lead from soft tissues, including the brain, without clinically evident adverse effects or histopathological changes. In lead-poisoned children and adults, DMSA significantly increases urinary lead excretion, and, at least transiently, reduces the blood lead concentration. The safety profile of DMSA in both children and adults is encouraging, with few clinically apparent or biochemical adverse effects reported. However, clinical experience with DMSA is limited, and is not sufficient to exclude the possibility that other more serious drug-related adverse events including hypersensitivity or idiosyncratic reactions may occur. No data currently exist to determine whether drug-enhanced lead excretion with DMSA (or any other chelating agent) is beneficial in reducing lead-related neurotoxicity. The efficacy of DMSA in reducing neuropsychological morbidity, and additional safety data, are key areas requiring additional study before DMSA can be clearly recommended as the chelating agent of choice for the treatment of lead-poisoned children.
An UpToDate review on “Adult lead poisoning” (Goldman and Hu, 2012) states that “Provocative chelation is a mobilization test that has been proposed to give an indirect measure of lead body burden and thereby determine if chelation therapy is indicated. Some medical practices assess lead poisoning by provocative chelation with DMSA or CaEDTA, comparing urinary excretion to reference ranges for non-challenged urine specimens. Studies have failed to establish a valid correlation between prior metal exposure and post-challenge test values. The American College of Medical Toxicology (ACMT) does not support provocative chelation”. Furthermore, an UpToDate review on “Childhood lead poisoning: Management” (Hurwitz and Lee, 2012) states that “CaNa2EDTA mobilization tests, once used as indicators of potential response to chelation therapy in children with moderate lead intoxication, are no longer used by most centers that treat childhood lead poisoning. They are thought to be unnecessary because most patients with BLL [blood lead levels] greater than 40 microgram/dL (1.93 micromol/L) have an adequate response. In addition, they are expensive and difficult to administer”.
A report of the Advisory Committee on Childhood Lead Poisoning Prevention of the Centers for Disease Control and Prevention (2012) states that “There is no medical foundation for relying on the following methods to diagnose over-exposure to lead: gingival lead lines, testing of neurophysiologic function; evaluation of renal function (except during chelation with EDTA); testing of hair, teeth, packed red cells , saliva or fingernails for lead; radiographic imaging of long bones, nor is provocative chelation prior to measurement of lead in urine testing recommended. The widely accepted sequelae of BLLs less than 45 μg/dL are cognitive and behavioral impairment. Chelation of children with BLLs greater than or equal to 20 and less than or equal to 45 μg/dL has not been shown to offer therapeutic benefit for these outcomes”.
|
Close Window
