Use of vitamin B12 in the treatment and prevention of nitroprusside-induced cyanide toxicity

OBJECTIVE

To review the mechanism of action, safety, and efficacy of hydroxocobalamin in the treatment and prevention of nitroprusside-induced cyanide toxicity.

DATA SOURCES

English and foreign-language journal articles and reference texts identified from Index Medicus. Both animal and human studies were included.

DATA SYNTHESIS

High-dose or prolonged therapy with nitroprusside in patients with hepatic or renal dysfunction increases the risk for nitroprusside-induced cyanide or thiocyanate toxicity, respectively. Hydroxocobalamin has been shown to significantly reduce RBC and plasma cyanide concentrations in animals and surgical patients without producing clinically important adverse effects or toxic metabolites. Thiosulfate infusions also decrease cyanide toxicity but can cause accumulation of thiocyanate resulting in clinical toxicity. Cyanocobalamin cannot effectively remove cyanide due to poor binding.

CONCLUSIONS

Hydroxocobalamin is a safe and effective agent in the prevention and treatment of nitroprusside-induced cyanide toxicity. Prolonged or high-dose infusions of nitroprusside should be minimized in critically ill patients, especially if hepatic and/or renal dysfunction is present.

Biochemical diagnosis and outcome of 2 years treatment in a patient with combined methylmalonic aciduria and homocystinuria

We describe a patient with methylmalonic aciduria and homocystinuria due to a defect in cobalamin metabolism of the Cbl-C type mutant (McKusick 277400). Our case was diagnosed within the first 2 months of life by amino acid analysis (ion-exchange chromatography) and by biochemical studies in cultured fibroblasts ([14C]propionate incorporation, methionine and serine formation). We discuss the clinical course and the biochemical evolution after 2 years of hydroxycobalamin treatment that led to an improvement in general clinical condition and neurological performance.

[Do antidotes have a future? The example of 4-methylpyrazole and hydroxocobalamin]

In all probability the future progress in the "molecular" approach of therapy in acute poisoning within the next 20 years or so will be more rapid than the "mechanistic" approach, which undoubtedly has brought considerable improvements in the overall survival of these patients in the past. Principally molecular antidotes can act on three different levels, a) prior to the cellular targets (e.g. through modifications of toxokinetics), b) at specific cellular receptors through competition for binding (e.g. naloxone and flumazenil), and c) after the receptor sites through unspecific counteraction of toxic effects (e.g. betablockers for intoxications with theophylline). Immune-antidotes act prior to cellular receptors. Examples are the digoxin antibodies and the anti-venoms as well as the very recently developed and not yet clinically tested antibodies against antidepressive drugs and against colchicine. Two newer antidotes, the 4-methylpyrazole and the hydroxocobalamin, act also prior the cellular targets of the corresponding toxic compounds. Thus, 4-Methylpyrazole decreases the degradation of ethylene-glycol by inhibiting alcohol dehydrogenase, which results in a higher excretion of unchanged ethylene-glycol in urine. Hydroxycobalamin complexes with cyanides to form the physiologic vitamin B12. In order to allow an equimolar neutralization of ingested cyanides a concentrated preparation containing 5 g of hydroxycobalamin was developed, the pharmacokinetic properties of which are discussed.

Bitter cassava poisoning in eight children: a case report

Bitter cassava poisoning in 8 children is reported. The incidence of bright cherry-red blood is emphasized. These patients were in bad condition, but they survived although they received different therapies. Four of them were treated with sodium nitrite and thiosulfate and the remainder with hydroxocobalamin alone. This latter drug may be useful in less severe circumstances.

Enzymologic studies on patients with methylmalonic aciduria: basis for a clinical trial of deoxyadenosylcobalamin in a hydroxocobalamin-unresponsive patient

Eleven patients with methylmalonic aciduria have been classified on the basis of detailed enzymology on cultured skin fibroblasts. Nine were classified as mutase deficiencies and were unresponsive to hydroxocobalamin in vivo or in vitro. One was classified as a Cbl A variant and was responsive to hydroxocobalamin therapy in vitro and in vivo. Patient 11 was classified as having deoxyadenosyltransferase deficiency (Cbl B). However, a clinical therapeutic trial of deoxyadenosylcobalamin resulted in no clinical or biochemical improvement. Further studies on the patient's cultured fibroblasts suggested that deoxyadenosylcobalamin fails to reach the mitochondria in an intact form. These studies show that detailed enzymologic classification is essential for the reliable evaluation of the response to therapeutic maneuvers; complementation studies alone may be inadequate to completely classify these patients. Therapy with deoxyadenosylcobalamin offers no advantages over the use of hydroxocobalamin in the treatment of patients with methylmalonic aciduria.

Vitamin B-12 abnormalities in HIV-infected patients

A prospective study of 60 consecutively admitted patients with HIV infection was performed to document the prevalence, etiology and manifestations of low serum vitamin B-12 in such patients. Low serum B-12 levels were found in 10 patients (16.7%). In 6, vitamin B-12 absorption was impaired and hog intrinsic factor addition did not improve it. Patients with low vitamin B-12 levels showed lower hemoglobin, leukocytes, lymphocytes, CD4 lymphocytes and CD4/CD8 lymphocyte ratio than HIV patients with physiological serum vitamin B-12 levels. However, bone marrow megaloblastosis was found in only 3 low vitamin B-12 patients and the deoxyuridine suppression test was pathological in only 1 case. In 7 patients, parenteral treatment was begun with variable response despite serum vitamin B-12 correction. In conclusion, low serum vitamin B-12 is often found in HIV-infected patients and it could be related to malabsorption, but clear megaloblastic abnormalities and treatment response could not be demonstrated. A decreased concentration of the serum binders due to disturbances in the leukocytes and related immunocompetent cell may play an additional role.

Effects of hydroxocobalamin on rat cardiac papillary muscle

Hydroxocobalamin is a rapid and powerful antidote in acute cyanide poisoning. The effects of hydroxocobalamin (0.1, 0.3, and 1 mM) on intrinsic myocardial contractility were studied on isolated rat cardiac papillary muscles (n = 10). Whatever the concentration, hydroxocobalamin did not modify the active isometric force and a slight increase in maximum unloaded shortening velocity was noted at 1 mM. Only 0.3 mM significantly impaired contraction-relaxation coupling under low load, suggesting a slight decrease in sarcoplasmic reticulum function. No changes in contraction-relaxation coupling under heavy load were noted, suggesting the lack of modification of myofilament calcium sensitivity. These results suggest that hydroxocobalamin does not induce noticeable changes in intrinsic myocardial contractility. An indirect mechanism might be involved in the previously reported decrease in cardiac function at supratherapeutic concentrations of hydroxocobalamin.

Function of vitamin B12 in the central nervous system as revealed by congenital defects

The 13 cases of methylcobalamin (MeCbl) deficiency presenting in early infancy have all been developmentally delayed, and the majority have had seizures, hypotonia, lethargy, and microcephaly. The CNS injury appears to occur during the first 6 months of postnatal life. The same symptoms are seen in acquired cobalamin (Cbl) deficiency in the same age group. MRI performed at age 18-19 months and after 13-14 months of large amounts of Cbl, in two cases showed delayed myelination, most pronounced in the cerebrum. Isolated MeCbl deficiency is the consequence of cblE and G mutations where the lesion is of a single Cbl-dependent enzyme, the methyltransferase. One effect of a deficiency of MeCbl, and of the associated failure of the methionine synthase reaction, is, therefore, an impairment of myelination of the brain of the newborn. The slow, but usually incomplete, improvement in psychomotor status after years of treatment with Cbl may be related to the eventual myelination. However, the hypotonia, lethargy, and impaired responsiveness react to treatment with Cbl within 24-48 hours, which suggests an expression of MeCbl deficiency on the CNS distinct from the delayed myelination. Although there is much to be learned, it is now clear that a normally functioning Cbl-dependent methyl transferase is required for development and function of the human brain.

Leber's hereditary optic atrophy: an atypical case with response to hydroxycobalamine therapy

A 15-year old Chinese boy was diagnosed to have Leber's hereditary optic neuropathy (LHOA), having manifested with typical findings of bilateral severe visual loss and telangiectasia at the optic disc. However, no family history was elicited and an interval of more than 5 years separated visual loss in the two eyes. The latter is an extremely uncommon finding. Visual improvement was rapid and marked after instituting intramuscular hydroxycobalamine 5 mg weekly. Bilateral improvement of Snellen acuity to 6/9 was achieved within 6 months. This is also unusual in that visual prognosis is generally poor in LHOA, although spontaneous remissions have occasionally been recorded. In addition, the eye with a longer history of poor vision responded to therapy first.

Vitamin B-12b as an antidote for over-sedation

Several observations have led the author to conclude that massive injections of vitamin B-12b (hydroxocobalamin) will prove an excellent antidote for patients overdosed with sedatives/tranquilizers and/or alcohol.

Vitamin B-12: placebo or neglected therapeutic tool?

Patients with normal serum vitamin B-12 levels were given injections of hydroxocobalamin (vitamin B-12b) interspersed with injections of sterile water. Those who felt better with B-12b had additional injections to establish the amount of B-12b that gave the maximum feeling of well-being. Serum vitamin B-12 tests were performed to record the level at which the patients felt best. On the same day they took a Multiphasic Personality Inventory (MMPI), an objective computerized psychological test. Hydroxocobalamin injections were then discontinued for 5 to 7 days. The patients took another serum vitamin B-12 test and another MMPI. With the higher vitamin B-12 levels, the MMPI patterns were at or closer to normal. With lower serum vitamin B-12 levels, MMPI patterns showed much more emotional distress. The author suspects that vitamin B-12 dependency disorders are common and are neglected by the medical profession.

Iron deficiency in pernicious anaemia: a neglected diagnosis

In 114 patients (52 males and 62 females) with long-standing pernicious anaemia, hypoferritinaemia was found in 27 (23.7%) and hypochromic microcytic anaemia in 19 (16.6%). Our findings indicate that iron deficiency is a common yet neglected complication of long-standing pernicious anaemia and warrants greater diagnostic and therapeutic attention.

Cyanide poisoning from propionitrile exposure

A 55-year-old worker was exposed to propionitrile by both the inhalational and dermal routes. He rapidly lost consciousness and developed metabolic acidosis consistent with cyanide poisoning. Treatment with hydroxycobalamin and sodium thiosulfate produced complete symptom resolution within an hour. Serial blood cyanide and thiocyanate levels documented a rapid decrease in cyanide and concomitant increase in thiocyanate. Serious cyanide poisoning can occur from propionitrile exposure. Treatment with hydroxycobalamin and sodium thiosulfate can produce rapid clinical improvement.

[A case of recurrence of pernicious anemia]

A case of pernicious anaemia recurring after 14 years in a patient who had suspended parenteral vitamin B12 treatment two months after the first hospitalisation is described. The earliest haematological signs of vitamin B12 deficiency are examined and the apparent failure to absorb the vitamin B12 regularly taken with the diet when no longer administered parenterally is discussed.

Hydroxycobalamin/sodium thiosulfate as a cyanide antidote

Severe, acute cyanide poisoning is uncommon and can be very difficult to diagnose if a history of exposure is unavailable. Victims of smoke inhalation may have significant cyanide poisoning as well as carbon monoxide toxicity. The Lilly Cyanide Antidote Kit currently available in America unfortunately has its own inherent toxicity. An efficacious antidote lacking toxicity is desirable, especially in cases where the diagnosis of cyanide poisoning cannot be made with certainty. Hydroxycobalamin/sodium thiosulfate has been used in France since 1970. Both components have been shown to be safe and efficacious in animal studies. Case reports of human cyanide poisoning treated with hydroxycobalamin/sodium thiosulfate have been published only in French. Animal and human data on the use of this antidotal combination are reviewed. Hydroxycobalamin/sodium thiosulfate is an efficacious cyanide antidote with little inherent toxicity.

Clinical heterogeneity in cobalamin C variant of combined homocystinuria and methylmalonic aciduria

We describe two patients with methylmalonic aciduria and homocystinuria (Cbl C). The disorder was not diagnosed in patient 1 until 4 1/2 years of age; he had a history of fatigue, anorexia, delirium, and spasticity. Moderate megaloblastic bone marrow changes were observed, and there was hyperreflexia of the lower limbs. His condition improved clinically with hydroxycobalamin therapy. Patient 2 was hospitalized at 6 weeks of age because of lethargy and poor feeding. She was found to have macrocytosis. Despite an initial good clinical response to hydroxycobalamin, she developed a striking pigmentary retinopathy. Methylmalonic aciduria persisted in both patients, and homocystinuria persisted in patient 1 despite therapy. The diagnosis of Cbl C disease has been confirmed in both patients by biochemical studies of cultured fibroblasts, including complementation studies. The differences in age of onset and clinical findings together with the similar biochemical findings in these two patients demonstrate the heterogeneity of phenotypic expression in patients with apparently identical abnormalities of vitamin B12 metabolism.

Homozygous transcobalamin II deficiency maintained on oral hydroxocobalamin

A case of transcobalamin II (TCII) deficiency in which a total absence of TCII was demonstrated both functionally and immunologically is reported. Unlike previously described patients, this child has been maintained on oral hydroxocobalamin, 2 mg daily, without any parenteral supplementation for the last five years. At the age of six years her development is normal and her health is good. Plasma cobalamin levels are in the range of 3,000 ng/L and most of this appears to be bound to a molecule, which on gel filtration, elutes with albumin. In an extended family study, a clear separation of heterozygotes from both the propositus and from normal subjects suggests that the underlying defect in this condition is confined to a single gene.

Depletion of extracellular cysteine with hydroxocobalamin and ascorbate in experimental murine cancer chemotherapy

Treatment of mice bearing P388 lymphocytic leukemia with combined hydroxocobalamin (0.1 mmol/kg) and sodium ascorbate (1.0 mmol/kg) for 10 consecutive days resulted in 70% increase in survival. Treatment with dehydroascorbate (1.0 mmol/kg) similarly increased survival. The extended treatment for 15 days posttumor inoculation failed to improve survival as did lowering the tumor inocula from 10(6) to 10(4) cells in similarly treated mice. P388 cells in primary culture with cystine as a source of cysteine require exogenous thiols or disulfides for growth and also grow with cysteine but only when trace copper is sequestered with bathocuproine sulfonate. This is due to the copper catalyzed oxidation of cysteine to cystine, which these cells cannot utilize. Cells grew in medium preincubated for 8 h with cysteine and bathocuproine sulfonate, but lysed when the preincubated medium included hydroxocobalamin (10 microM) and sodium ascorbate (100 microM). This defect was corrected by resupplementation with cysteine or cystine plus bishydroxyethyl disulfide after addition of the cells. Further support for cysteine depletion as a factor in therapy is obtained by therapeutic interference with 4-thiamethionine (25 mumol/kg). This mixed disulfide of cysteine and methyl mercaptan enters cells as a methionine analogue, is reduced to supply cysteine, and thus withstands the oxidative environment that limits the utilization of cysteine as a nutrient. These results suggest that dehydroascorbate is generated from combined hydroxocobalamin and ascorbate and accounts for the thiol-prive activity of combined hydroxocobalamin and ascorbate therapy. The ultimate failure of therapy by thiol oxidation may be due to the increased availability of cysteine produced by host tissues, possibly infiltrating macrophages, that occurs independently of extended treatment and the size of the tumor inoculum.

Lymphocyte subpopulations in patients with hydroxocobalamin responsive megaloblastic anaemia

Lymphocyte subpopulations and intrinsic factor and gastric parietal cell antibodies have been measured in 23 patients with megaloblastic anaemia who responded to treatment with hydroxocobalamin. The ratio of helper (OKT4) to suppressor (OKT8) lymphocytes was significantly increased in patients with intrinsic factor antibody compared with those who lacked the antibody. No such correlation was found for gastric parietal cell antibody. Alterations in the lymphocyte helper to suppressor (OKT4:OKT8) ratio may be associated with pernicious anaemia.

Acute organic psychosis caused by thyrotoxicosis and vitamin B12 deficiency: case report

A 64-year-old woman developed an acute organic psychosis secondary to thyrotoxicosis and B12 deficiency, without the overt clinical features of pernicious anemia. The psychosis resolved with B12 and thyroid hormone replacement. The patient relapsed after an erroneous iatrogenic tripling of the levothyroxine dosage, but her condition normalized after dosage correction.