Metobromuron/metolachlor ingestion with late onset methemoglobinemia in a pregnant woman successfully treated with methylene blue

Rare Case of Methemoglobinemia Complicating Pregnancy

A patient at 38 weeks of gestation when taken for emergency cesarean section had her oxygen saturation of 66 to 70% (by saturation probe on monitor) in operation theatre. She was otherwise asymptomatic but her oxygen saturation was persistently low on the monitors. Her arterial blood gas analysis showed all parameters to be normal. Her electrocardiography was normal. Her surgery was imperative but due to her reduced oxygen saturation she became a high-risk case. In presence of senior consultants of anesthesia and gynecology and under high-risk consent she had an uneventful cesarean delivery. Physician and cardiologist opinions were sought thereafter. The outcomes and the results of our efforts to find the etiology of her reduced saturation on monitors despite being clinically asymptomatic lead to the disclosure of this rare hemoglobinopathy. Mother and baby had uneventful course after delivery and were discharged well.

Poisoning due to Urea Herbicides

Urea herbicides, which act by inhibiting photosynthesis, were introduced in 1952 and are now used as pre- and post-emergence herbicides for general weed control in agricultural and non-agricultural practices. Urea herbicides are generally of low acute toxicity and severe poisoning is only likely following ingestion when nausea, vomiting, diarrhoea and abdominal pain may occur. As urea herbicides are metabolised to aniline derivatives, which are potent oxidants of haemoglobin, methaemoglobinaemia (18-80%) has been documented, as well as haemolysis. Treatment is supportive and symptomatic. Methylthioninium chloride (methylene blue) 1-2mg (the dose depending on the severity of features) should be administered intravenously over 5-10 minutes if there are symptoms consistent with methaemoglobinaemia and/or a methaemoglobin concentration >30%.

Methylene blue

Methylene blue finds its major utilization in toxicology in the treatment of methemoglobinemia at a dose of 1 to 2 mg/kg intravenously. By interacting with methemoglobin and the erythrocyte's enzyme systems to reduce back to hemoglobin, methylene blue is a generally safe drug with dose-related hemolytic effects. People with G-6-PD deficiency, along with patients exposed to aniline dyes and dapsone, may present with special risks in the treatment of methemoglobinemia.

The fetal safety and clinical efficacy of gastrointestinal endoscopy during pregnancy

More than 12,000 pregnant patients in the United States per annum have conditions that are normally evaluated by EGD. More than 6000 pregnant patients in the United States per annum have conditions that are normally evaluated by sigmoidoscopy or colonoscopy. About one thousand more have symptomatic choledocholithiasis during pregnancy, which is a strong indication for endoscopic sphincterotomy in nonpregnant patients. Endoscopy during pregnancy raises the unique issue of fetal safety. Endoscopic medications comprise a significant component of fetal endoscopic risks. Safety of EGD during pregnancy has been examined in a case-controlled study of 83 patients, a mailed survey of 73 patients, and 28 case reports. Safety of sigmoidoscopy during pregnancy has been examined in a case-controlled study of 46 patients, a mailed survey of 13 patients, and 10 case reports. Safety of therapeutic ERCP during pregnancy has been analyzed in studies of 23, 10, 6, and 5 patients, and in 32 case reports. These studies suggested that EGD, sigmoidoscopy, and ERCP should be performed when strongly indicated: EGD for significant upper gastrointestinal bleeding, sigmoidoscopy for nonhemorrhoidal rectal bleeding, and ERCP for symptomatic choledocholithiasis when sphincterotomy is contemplated. PEG and colonoscopy are currently considered experimental during pregnancy because of insufficient data on fetal safety. Several cases of PEG and colonoscopy were successfully performed during pregnancy. Performance of endoscopy during pregnancy should increase with further technical refinements, and greater awareness of procedure safety.

Transplacental exposure to methylene blue initiates teratogenesis in the mouse: preliminary evidence for a mechanistic implication of cyclic GMP pathway disruption

BACKGROUND

The vital dye methylene blue (MB) has been shown to be teratogenic when injected into the amnion in the second trimester. On the other hand, the teratogenic potential of transplacental exposure to MB has not been determined.

METHODS

MB was administered subcutaneously to ICR (CD-1) mice at 0, 35, 50, 60, or 70 mg/kg on gestation day 8 (plug day = day 0). Teratological assessments were carried out at term gestation, on gestation day 18. Since MB inhibits soluble guanylate cyclase enzyme activity, zaprinast (ZPN), a selective cGMP-phosphodiesterase type V inhibitor, was administered to prevent developmental disorders initiated by MB at 50 mg/kg.

RESULTS

There was a dose-dependent increment of embryolethality. MB treatment also produced axial skeleton and neural tube defects. Coadministration of ZPN (20 mg/kg per three times) abolished completely MB-induced neural tube defects and reduced by one-half the incidence of fetuses exhibiting axial skeletal defects. ZPN did not provide protection against the embryocidal effects of MB.

CONCLUSIONS

This study showed that transplacental exposure to MB is teratogenic in the mouse. Coadministration of ZPN prevented partly MB-induced teratogenesis, which supports the hypothesis that imbalance of cGMP pathway accounts, in part, for the teratogenicity of MB.

Construction of artificial methemoglobin reduction systems in Hb vesicles

The hemoglobin vesicle (HbV) is a red cell substitute encapsulating purified concentrated Hb in a phospholipid vesicle. In order to suppress metHb formation for the long term maintenance of oxygen transporting capability in vivo, thiols (cysteine, Cys; homocysteine, Hcy) were studied as reductants of metHb. Hcy showed a suppressive effect on metHb formation, while Cys adversely accelerates metHb formation at the rate of twice the Hb solution without any reductants. The suppression of Cys-induced metHb formation by the addition of superoxide dismutase (SOD) and catalase indicated that Cys was easily oxidized by oxygen and simultaneously generated a large amount of active oxygens. The rate of metHb formation was influenced by PO2 and pH. Furthermore, the reducing systems (methylene blue (MB), NADH or ascorbic acid) were added to the outer aqueous phase of HbV, and the artificial reduction systems constructed through the bilayer membrane were evaluated.