Thimerosal exposure in infants and developmental disorders: a retrospective cohort study in the United kingdom does not support a causal association

OBJECTIVE

After concerns about the possible toxicity of thimerosal-containing vaccines in the United States, this study was designed to investigate whether there is a relationship between the amount of thimerosal that an infant receives via diphtheria-tetanus-whole-cell pertussis (DTP) or diphtheria-tetanus (DT) vaccination at a young age and subsequent neurodevelopmental disorders.

METHODS

A retrospective cohort study was performed using 109 863 children who were born from 1988 to 1997 and were registered in general practices in the United Kingdom that contributed to a research database. The disorders investigated were general developmental disorders, language or speech delay, tics, attention-deficit disorder, autism, unspecified developmental delays, behavior problems, encopresis, and enuresis. Exposure was defined according to the number of DTP/DT doses received by 3 and 4 months of age and also the cumulative age-specific DTP/DT exposure by 6 months. Each DTP/DT dose of vaccine contains 50 microg of thimerosal (25 microg of ethyl mercury). Hazard ratios (HRs) for the disorders were calculated per dose of DTP/DT vaccine or per unit of cumulative DTP/DT exposure.

RESULTS

Only in 1 analysis for tics was there some evidence of a higher risk with increasing doses (Cox's HR: 1.50 per dose at 4 months; 95% confidence interval [CI]: 1.02-2.20). Statistically significant negative associations with increasing doses at 4 months were found for general developmental disorders (HR: 0.87; 95% CI: 0.81-0.93), unspecified developmental delay (HR: 0.80; 95% CI: 0.69-0.92), and attention-deficit disorder (HR: 0.79; 95% CI: 0.64-0.98). For the other disorders, there was no evidence of an association with thimerosal exposure.

CONCLUSIONS

With the possible exception of tics, there was no evidence that thimerosal exposure via DTP/DT vaccines causes neurodevelopmental disorders.

Intérêt d’une nouvelle formulation de diclofénac sans conservateur pour la surface oculaire

AIM

To compare the ocular tolerance of nonpreserved diclofenac versus thiomersal-preserved diclofenac in healthy volunteers.

MATERIALS AND METHODS

Forty healthy volunteers instilled Dicloabak in the randomised eye and thiomersal-preserved diclofenac in the other eye, according to a strictly identical dosing regimen, for 28 days. Each volunteer thus served as his or her own control. The dose regimen was five drops/day for 7 days followed by three drops/day for 20 days. Ocular tolerance was assessed by the discomfort upon instillation (measured on a visual analogue scale [VAS]), subjective ocular symptoms following instillation (irritation/burning/stinging, eye dryness and foreign body sensation) and finally by an objective examination of the ocular surface. These criteria were evaluated on days 0, 14, 21 and 28.

RESULTS

The subjective ocular symptoms following instillation were significantly lower in the nonpreserved group at Day 7 and nearly significantly lower until the end of the study. The biomicroscopy exam confirmed that there was better tolerance without thiomersal. There was less follicular-papillary conjunctivitis and a significantly better lissamine green score in the Dicloabak group.

CONCLUSION

The results of this study demonstrate that the nonpreserved formulation of diclofenac is better tolerated by the ocular surface and thus constitutes a therapeutic benefit.

Dose–response study of thimerosal-induced murine systemic autoimmunity

The organic compound ethylmercurithiosalicylate (thimerosal), which is primarily present in the tissues as ethylmercury, has caused illness and several deaths due to erroneous handling when used as a disinfectant or as a preservative in medical preparations. Lately, possible health effects of thimerosal in childhood vaccines have been much discussed. Thimerosal is a well-known sensitizing agent, although usually of no clinical relevance. In rare cases, thimerosal has caused systemic immune reactions including acrodynia. We have studied if thimerosal might induce the systemic autoimmune condition observed in genetically susceptible mice after exposure to inorganic mercury. A.SW mice were exposed to 1.25-40 mg thimerosal/l drinking water for 70 days. Antinucleolar antibodies, targeting the 34-kDa protein fibrillarin, developed in a dose-related pattern and first appeared after 10 days in the two highest dose groups. The lowest observed adverse effect level (LOAEL) for antifibrillarin antibodies was 2.5 mg thimerosal/l, corresponding to an absorbed dose of 147 microg Hg/kg bw and a concentration of 21 and 1.9 microg Hg/g in the kidney and lymph nodes, respectively. The same LOAEL was found for tissue immune-complex deposits. The total serum concentration of IgE, IgG1, and IgG2a showed a significant dose-related increase in thimerosal-treated mice, with a LOAEL of 5 mg thimerosal/l for IgG1 and IgE, and 20 mg thimerosal/l for IgG2a. The polyclonal B-cell activation showed a significant dose-response relationship with a LOAEL of 10 mg thimerosal/l. Therefore, thimerosal induces in genetically susceptible mice a systemic autoimmune syndrome very similar to that seen after treatment with inorganic mercury, although a higher absorbed dose of Hg is needed using thimerosal. The autoimmune syndrome induced by thimerosal is different from the weaker and more restricted autoimmune reaction observed after treatment with an equipotent dose of methylmercury.

The thiol reagent, thimerosal, irreversibly inhibits meiosis reinitiation in mouse oocyte when applied during a very early and narrow temporal window: a pharmacological analysis

The effect of the sulfhydryl reagent, thimerosal (TMS) on meiosis resumption in germinal vesicle (GV)-stage denuded mouse oocytes was studied. It irreversibly inhibits both GV breakdown (GVBD) and the first polar body (pb1) extrusion in concentration- and time-dependent manners, the most striking result being the very early and narrow temporal window during which denuded primary oocytes released from their follicle are susceptible to a pulse of the drug. This inhibition is bypassed by dithiothreitol (DTT) with an efficiency declining with time, while thiosalicylic acid (TA), an analog of TMS devoid of the mercury atom, has no effect on meiosis reinitiation. These results strongly suggest that the inhibitory effect of TMS is a consequence of its sulfhydryl group oxidising activity. The molecular target(s) of this inhibitory oxidation should however be identified. In contrast to DTT, okadaic acid (OA), known to bypass the inhibitory effect of drugs interfering with protein kinase activities, only induces chromatin condensation and GVBD in TMS-pulsed oocytes with a delay of about 8 hr as compared to the control situation. This confirms that a very early thiol oxidation induced by TMS exerts a much more dramatic effect on resumption on meiosis than any pharmacological manipulation of protein kinase activities leading to activation of MPF.

Thiomersal enhances the binding of histamine to the H1 receptor, but not histamine-stimulated inositol phosphate formation

Thiomersal (thimerosal) was a weak inhibitor of the binding of [(3)H]mepyramine to histamine H(1) receptors in guinea-pig cerebellar membranes (11 +/- 1% inhibition at 10 microM, 32 +/- 3% inhibition at 300 microM). However, in the concentration range 3-30 microM, thiomersal enhanced the binding of histamine to the H(1) receptor, as reflected by the displacement of curves of histamine inhibition of [(3)H]mepyramine binding to lower concentrations, without any change in the Hill coefficient. The ratio of the IC50 values (the concentration giving 50% inhibition) in the absence and presence of thiomersal increased from 1.8 with 3 microM to 3.6 with 30 microM thiomersal. There was no consistent effect of thiomersal at concentrations of 30 microM and below on curves of mepyramine inhibition of [(3)H]mepyramine binding. In the presence of 10 microM thiomersal histamine-induced accumulation of inositol phosphates in U373 MG astrocytoma cells was partially inhibited (37 +/- 8% inhibition of the maximum response), without any significant change in the EC50 (the concentration giving the half maximal response) for histamine. Thus although histamine binding was potentiated by thiomersal, there was no potentiation of an H(1) receptor-mediated functional response.

Allergic contact dermatitis from mercury antiseptics and derivatives: study protocol of tolerance to intramuscular injections of thimerosal

BACKGROUND

Mercury derivatives are frequent contact allergens and their cross-reactivity is not constant. Thimerosal is an organic mercurial used as an antiseptic and as a preservative in most vaccines.

OBJECTIVE

To evaluate cross-reactivity, exposure factors, and tolerance to vaccines containing thimerosal in patients sensitized to mercury derivatives.

METHODS

DESIGN

Observational study (cross-sectional);

PATIENTS

125 patients were recruited for the study, 72 women and girls and 53 boys and men, average age 18.7 years old, range 3 to 65, with positive patch tests to mercury derivatives and/or thimerosal;

INTERVENTIONS

All patients were studied by means of enquiry, patch tests, intradermal tests, and intramuscular challenge with thimerosal.

RESULTS

A sensitization to thimerosal was observed in 57 patients. Twenty-four of these 125 patients presented a positive intradermal reaction. Ammoniated mercury seems to be a good marker of mercury sensitization eliciting positive reaction in 78% of all patients and merbromin in 66%. In most cases, (100/125) cross-reactivity was found among mercury derivatives. The intramuscular injection of thimerosal induced a mild local reaction in only 5 patients (4% of the total, 9% of thimerosal positive reactions). Childhood vaccinations, merbromin used as an antiseptic, broken thermometers, and the use of drops were the main sources of exposure.

CONCLUSIONS

The majority of the patients showed positive tests to both organic and inorganic mercury derivatives. Vaccination with thimerosal is relatively safe, even for individuals with delayed type hypersensitivity to this chemical, since more than 90% of allergic patients tolerated intramuscular challenge tests with thimerosal. A simplified protocol of patch tests to study mercury derivatives is proposed. It would be advisable to restrict the use of mercurial antiseptics and mercury thermometers.

Iatrogenic exposure to mercury after hepatitis B vaccination in preterm infants

Thimerosal, a derivative of mercury, is used as a preservative in hepatitis B vaccines. We measured total mercury levels before and after the administration of this vaccine in 15 preterm and 5 term infants. Comparison of pre- and post-vaccination mercury levels showed a significant increase in both preterm and term infants after vaccination. Additionally, post-vaccination mercury levels were significantly higher in preterm infants as compared with term infants. Because mercury is known to be a potential neurotoxin to infants, further study of its pharmacodynamics is warranted.

Preserved solid lipid nanoparticles (SLN) at low concentrations do cause neither direct nor indirect cytotoxic effects in peritoneal macrophages

In order to investigate the interaction of preserved solid lipid nanoparticles (SLN) with murine peritoneal macrophages (Mpsi), cytotoxicity and proinflammatory effects of two different solid lipid nanoparticles (SLN) preparations consisting of either compritol (CO) or cetyl palmitate (CP) preserved with thiomersal were analyzed. Concentration-dependent cytotoxic effects were observed using the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyl-tetrazolium bromide (MTT) assay. Secretion of interleukin-6 by Mpsi following incubation with CO and CP SLN did not differ from secretion by untreated cells; proinflammatory cytokines interleukin-12 and tumor-necrosis-factor-alpha as further indicators of immunomodulatory effects were not detectable. These findings paralleled our previous findings that unpreserved CO and CP SLN did not induce immunomodulatory effects but cytotoxicity at higher concentrations. There were no synergistic cytotoxic effects of preservative and SLN. Thus, preservation of SLN using thiomersal does not appear to cause increased cytotoxicity and immunomodulatory effects following incubation with Mpsi.

Preservative-free influenza vaccine

OBJECTIVE

To investigate the immunogenicity of and tolerance towards the preservative-free inactivated influenza vaccine Begrivac.

METHODS

In this prospective, single-centre, non-controlled study, efficacy was evaluated by the change in influenza antibody titre from baseline to 21 days following vaccination. The safety variables included post-injection reactions and adverse events. Blood samples were taken on day 21 and the antibody titre assayed by haemagglutination inhibition test.

RESULTS

All three of the European efficacy requirements for influenza vaccines are satisfied by the new preservative-free vaccine described in this report. The mean geometric increase in titre and the proportion of vaccination responders were greater in patients of the adult group than in the elderly. Thus for strain A/Beijing/262/95 66% of subjects seroconverted and 28% showed a significant increase in antibody titre (total 94%), compared to a total of 45 patients (76%) in the elderly group. For strain A/Sydney/5/97 the corresponding figures were total 55 (90%) adult and 47 (80%) elderly, and for B/Beijing/184/93 46 (75%) adult and 31 (53%) elderly. Sixty four subjects (53%) reported adverse events, mainly local reactions at the injection site such as pain, erythema and induration, and systemic reactions such as headache and fatigue.

CONCLUSIONS

The absence of preservative in this novel vaccine preparation does not have any detectable impact on its efficacy or safety and tolerability profile.

Thimerosal-induced Ca2+ mobilization in isolated guinea pig cochlear outer hair cells

Intracellular calcium mobilization of isolated guinea pig cochlear outer hair cells (OHCs) was investigated using thimerosal, a -SH group oxidizing agent, and fura-2 fluorescence ratio imaging microscopy. In the presence of thimerosal, intracellular Ca2+ concentrations ([Ca2+]i) of OHCs were elevated in a dose-dependent manner. Even in Ca(2+)-free medium, Ca2+ response was still induced. The effects of thimerosal on [Ca2+]i were completely blocked and reversed by dithiothreiotol (DTT). Neither 1-100 microM ryanodine nor 5-20 mM caffeine altered the effects of thimerosal. Pretreatment with pertussis toxin (PTX) for 30 min did not affect the thimerosal-induced increase in [Ca2+]i. The increase in [Ca2+]i when Ca2+ was added during thimerosal application in Ca(2+)-free medium was almost completely blocked by 500 microM LaCl3, while nifedipine did not inhibit further increase in [Ca2+]i caused by thimerosal. Thus, oxidation of the -SH group of the OHC membrane can induce a Ca2+ release from intracellular Ca2+ stores, which are ryanodine- and caffeine-insensitive, and Ca2+ influx through non-specific Ca2+ channels, but not the nifedipine-sensitive Ca2+ channels. The possible oxidation of -SH group gated Ca2+ channels in OHCs is worthy of further study.

Thimerosal positivities: the role of organomercury alkyl compounds

Contact allergy to thimerosal (TH) has not been considered a marker for mercury allergy, since there is a low degree of cross-sensitivity to inorganic as well as to organic mercury salts. 40 subjects, who previously gave a positive patch test reaction only to thimerosal 0.1% pet. (Hermal), when simultaneously repatch-tested to solutions containing TH, mersalyl acid, p-amino-phenylmercuric acid, mercuric acetate and thiosalicylic acid, respectively, gave positive reactions only to TH. 36 out of 40 subjects were divided into 2 groups of 18 subjects and simultaneously repatch-tested to solutions containing TH, methylmercury chloride (MeHgCl), thiosalicylic acid, and, ethylmercury chloride (EtHgCl), respectively. EtHgCl was tested in the 1st group at 0.031% and in the 2nd group at 0.015%. The results showed that all subjects gave concomitant positive reactions to TH, EtHgCl and MeHgCl. EtHgCl 0.031% gave a higher number of reactions than EtHgCl 0.015%, underlining the rôle of the solvent in these reactions. Patch test results in 300 consecutive patients to a standard series, to which MeHgCl was added, showed that MeHgCl and TH were never able to give isolated positive reactions, and that the concomitant positive reactions occurred in only 3.6% of subjects. In conclusion, our data seem to suggest that the positive reactions to TH found in our patients were due to EtHgCl, and that the structural similarities with MeHgCl were so close that the skin reacted against each as if they were identical.

Clinical course of severe poisoning with thiomersal

CASE REPORT

A 44-year-old man ingested 83 mg/kg Thiomersal. He developed gastritis, renal tubular failure, dermatitis, gingivitis, delirium, coma, polyneuropathy and respiratory failure. Treatment was symptomatic plus gastric lavage and the oral chelating agents dimercaptopropane sulfonate and dimercaptosuccinic acid. The patient recovered completely. Maximum mercury concentrations were blood 14 mg/L, serum 1.7 mg/L, urine 10.7 mg/L, and cerebrospinal fluid 0.025 mg/L. Mercury concentration in blood declined with two velocities: first with half-time 2.2 days, then with half-time 40.5 days. The decline of mercury concentration in blood, urinary mercury excretion, and renal mercury clearance were not substantially influenced by chelation therapy.

[Otomycosis and topical application of thimerosal: study of 152 cases]

PURPOSE

To evaluate the effectiveness of the topical application of Timerosal (merthilate tintura) in mycosis involving the external auditory canal.

PATIENTS AND METHODS

The study includes 152 patients with the clinical, otoscopic and microscopic diagnosis of otomycosis. Results were assessed 72 hours and 10 days after the application.

RESULTS

Bacteriological study was performed in 83 patients, finding Aspergilly niger in 54.0% of the cases, Candida albicans in 25.4%, Aspergillus fumigatus in 15.8% and Penicillium in 4.8%. Improvement at 72 h. was found in 66.4% and at 10 days in 93.4% of the patients. Bacteriological contamination was found in 6.6% of the total.

COMMENTS

In most of the patients, the otomycosis healed after cleaning of the external auditory canal and topical application of timerosal. This method is easy to apply, fast, effective, of low cost and few side effects.

Minimum eliciting patch test concentration of thimerosal

Positive patch test reactions to thimerosal 0.1% pet. (40/690 subjects: 5.8%) were more common in younger age groups, in the allergic contact dermatitis group and in subjects who had used contact lens solutions. In the 40 thimerosal-positive patients, the minimum eliciting quantity of preservative was evaluated using different test concentrations: 0.05% and 0.01% pet. (patch testing) and 1:10,000 in saline (intradermal testing). Cross-reactions between thimerosal and other mercury compounds and sensitivity to thiosalicylic acid were also examined. The results of the investigation demonstrate that many of the reactions to 0.1% thimerosal are probably irritant, because only half the subjects studied had positive patch tests when allergen concentrations 5 to 10x lower than that conventionally used for patch testing, were utilized. In these subjects, the average strength of patch test reactions was higher, intradermal testing was more often positive and cross-reactions between mercurials more frequent. These data indicate that the optimal eliciting patch test concentration for studying thimerosal sensitivity is 0.05% pet.

Effect of thimerosal concentration on the efficacy of inactivated Newcastle disease oil-emulsion vaccines

Different quantities of the preservative thimerosal in inactivated Newcastle disease oil-emulsion vaccines were tested to determine the influence on the hemagglutination-inhibition (HI) response of broilers. The effect of thimerosal was measured in vaccines that had been stored for 1, 21, and 52 weeks; HI serology was conducted at 2, 4, and 6 weeks after vaccination. Mean HI titers 4 weeks after vaccination decreased at a significant rate (P less than or equal to 0.001) with increasing concentrations of thimerosal. HI titers 4 weeks after vaccination with 1-week-old vaccine were significantly (P less than or equal to 0.05) higher than those after vaccination with 52-week-old vaccine at all thimerosal concentrations tested. Titers were also significantly higher (P less than or equal to 0.05) after vaccination with 1-week-old vaccine than after vaccination with 21-week-old vaccine at all thimerosal concentrations below about 8.25 mg/ml of antigen. Thimerosal at the levels recommended in commercial vaccines does not significantly decrease vaccine efficacy.