Methemoglobinemia: etiology, pharmacology, and clinical management

Methemoglobin (MHb) may arise from a variety of etiologies including genetic, dietary, idiopathic, and toxicologic sources. Symptoms vary from mild headache to coma/death and may not correlate with measured MHb concentrations. Toxin-induced MHb may be complicated by the drug's effect on other organ systems such as the liver or lungs. The existence of underlying heart, lung, or blood disease may exacerbate the toxicity of MHb. The diagnosis may be complicated by the effect of MHb on arterial blood gas and pulse oximeter oxygen saturation results. In addition, other dyshemoglobins may be confused with MHb. Treatment with methylene blue can be complicated by the presence of underlying enzyme deficiencies, including glucose-6-phosphate dehydrogenase deficiency. Experimental antidotes for MHb may provide alternative treatments in the future, but require further study.

Use of phenothiazines as sedatives in children: what are the risks?

Phenothiazines have been widely used for their antiemetic, antipsychotic and sedative properties for many years. The introduction of alternative agents for paediatric sedation has led to the re-evaluation of phenothiazines as paediatric sedatives. Newer agents, such as fentanyl and midazolam, have short half-lives and reversal agents are available. Therefore these agents may offer comparable therapeutic efficacy with a better safety profile in young children. Reports of sudden infant death syndrome in children receiving a phenothiazine-containing syrup for symptoms of upper respiratory infection means that the outpatient use of these compounds in very young infants is not recommended.

The distribution, determinants, and clinical correlates of vertebral osteophytosis: a population based survey

OBJECTIVE

Vertebral osteophytes are a characteristic feature of intervertebral disc degeneration. There are, however, few population data concerning the occurrence of and clinico-biological correlates of vertebral osteophytes in both the dorsal and lumbar spine. Our purpose was to determine the frequency and distribution of anterior osteophytes in the thoracic and lumbar spine, and their relationship with both various putative risk factors, including physical activity and obesity, and self-reported back pain.

METHODS

Men and women aged 50 years and over were recruited from primary care based registers in 5 UK centers. They were invited to attend for an interviewer administered lifestyle questionnaire, assessment of height and weight, and lateral spinal radiographs. Lateral spinal radiographs were evaluated by a single observer for the presence of osteophytes from T4 to L5 using a semiquantitative score (grade): 0 = none, 1 = doubtful, 2 = mild, 3 = moderate, 4 = severe. Based on these data 2 summary statistics were derived: the maximum osteophyte grade at any vertebral level (MAX), and the sum of the osteophyte grades at the individual vertebral levels (TOT).

RESULTS

In total, 681 women, mean age 63.3 years, and 499 men, mean age 63.7 years, were studied; 84% of men and 74% of women had at least one vertebral level with a grade 1 or higher osteophyte. Both the sum of the individual grades (TOT) and the proportion of subjects with MAX > or =2 were greater in men than in women in both the dorsal and lumbar spine, and both increased with age. The pattern of spinal involvement was similar in the sexes, with osteophytes occurring most frequently at T9-10 and L3. Increasing body mass index was associated with more frequent osteophytes at both dorsal and lumbar spine, although the relationship was stronger at the dorsal spine. Heavy physical activity, particularly in young adult life, was associated with osteophytosis in men. Self-reported back pain, both ever and in the past year, was linked with lumbar osteophytes in men.

CONCLUSION

The distribution within the spine in our study and the relationship with heavy physical activity points to mechanical factors being important in pathogenesis of vertebral osteophytosis. Prospective studies are needed to explore the types of physical activity that increase susceptibility to vertebral osteophytosis. In men, osteophytes affecting the lumbar spine are associated with back pain.

Effect of metoclopramide dose on preventing emesis after oral administration of N-acetylcysteine for acetaminophen overdose

OBJECTIVE

To determine the effect of the metoclopramide dose on the prevention of vomiting of N-acetylcysteine in acetaminophen overdose.

METHODS

Patients with acetaminophen ingestions receiving metoclopramide prior to emergency department administration of N-acetylcysteine were included. Emergency Department and poison center records were reviewed for administration of metoclopramide pre-N-acetylcysteine and incidence of subsequent vomiting. The treatment group was defined as patients receiving high-dose metoclopramide (20-50 mg intravenously) prior to the loading dose of N-acetylcysteine. Controls were patients receiving standard-dose (< 20 mg intravenously) metoclopramide prior to loading dose of N-acetylcysteine. Outcome was vomiting within 60 minutes of N-acetylcysteine administration.

RESULTS

Twelve of 19 patients (63%) receiving standard-dose metoclopramide vomited N-acetylcysteine. Only 5 of 23 patients (22%) receiving high-dose metoclopramide vomited N-acetylcysteine (crude odds ratio: 6.2; 95% CI [1.3-30.3]). After controlling for confounding in the logistic regression model, the effect of high-dose metoclopramide in preventing vomiting of N-acetylcysteine remained significant (adjusted odds ratio: 17.0; 95% CI [2.6-110.0]).

CONCLUSION

This study supports the efficacy of high-dose metoclopramide to prevent emesis after the oral loading dose of N-acetylcysteine.

Choice of NSAID and management strategy in rheumatoid arthritis and osteoarthritis. The impact on costs and outcomes in the UK

OBJECTIVE

Although nonsteroidal anti-inflammatory drugs (NSAIDs) are an effective therapy for rheumatoid arthritis, they are associated with significant adverse effects, the management of which imposes additional costs on the healthcare system. Prescribing NSAIDs which have a lower risk of major adverse effects as the first-line NSAID for patients with rheumatoid arthritis and osteoarthritis may be expected to lead to an improvement in clinical outcomes and reduce overall treatment costs. This analysis examines data from a published randomised controlled trial of 5 NSAIDs to explore these hypotheses.

DESIGN AND SETTING

Data from a clinical trial comparing 5 NSAIDs were combined with published cost data to construct 2 clinical decision models, reflecting alternative approaches to the management of major and minor adverse effects in the UK.

INTERVENTIONS

The 5 NSAIDs evaluated in the analysis were nabumetone, diclofenac, ibuprofen, piroxicam and naproxen, although only the results for ibuprofen and nabumetone are reported.

MAIN OUTCOME MEASURES AND RESULTS

The total cost of care per patient receiving nabumetone was estimated to be between 25 pounds sterling (Pound) and 41 Pounds more expensive than ibuprofen. In a hypothetical cohort of 100,000 patients, there were between 690 and 821 more major adverse effects using ibuprofen than nabumetone. The cost per life-year gained (LYG) from using nabumetone rather than ibuprofen ranged between 1880 Pounds and 2517 Pounds (1995 values), depending upon the management of adverse effects.

CONCLUSIONS

These results indicate that: (i) prescribing the newer, currently more expensive, NSAIDs will not necessarily lead to cost savings; (ii) the management of adverse effects can have a significant impact on costs; and (iii) the additional cost may be justifiable in terms of the mortality and morbidity gains associated with the new lower-risk NSAIDs.

Effect of iron deficiency anemia on lead distribution after intravenous dosing in rats

OBJECTIVE

To determine the effect of iron deficiency anemia on blood and tissue lead distribution.

METHODS

24 weanling rats were divided into 2 groups. One group received an iron replete diet (200 ppm); the other received a low iron diet (20 ppm). After 24 days, each group was further subdivided into two doses of lead (5 mg/kg and 10 mg/kg) which was administered intravenously. Rats were continued on their respective diets for 7 days post-lead injection to allow tissue distribution, then sacrificed and blood and tissue lead concentration measured.

RESULTS

Prior to lead administration, baseline blood lead concentrations were not significantly different between groups. At sacrifice, whole blood lead levels were significantly higher in iron deficient animals than in iron replete at both 5 and 10 mg/kg administered lead. Iron deficient animals had comparable lead concentrations to iron replete animals in brain, kidney and liver. Femur lead concentrations were higher at 10 mg/kg administered lead.

CONCLUSION

Iron deficiency alters lead distribution such as that increased lead is found in blood for a given exposure.

Baclofen overdose: drug experimentation in a group of adolescents

BACKGROUND

Baclofen, a lipophilic analog of gamma-aminobutyric acid, is clinically used to control spasticity. We report a mass exposure to baclofen in adolescents seeking intoxication; toxicokinetic data are included.

CASE SERIES

A group of adolescents became symptomatic after ingesting 3 to 30 20-mg tablets of baclofen during a party at a suburban Boys' Club. Several children were noted to be very lethargic by chaperones, ingestion was suspected, and paramedics were called. Some white tablets were found in a couch at the site of the party. The Massachusetts Poison Control Center was called, and the tablets were identified as baclofen (20 mg). Fourteen patients were taken to local hospitals; 9 required intubation. Eight adolescents were transferred to our institution. In these 8 patients, symptoms were noted within 1 to 2 hours after overdose. The most common clinical findings included coma (7), hypothermia (6), bradycardia (5), hypertension (4), and hyporeflexia (8). Mean length of mechanical ventilation was 40 hours. Three patients had unifocal premature ventricular contractions. Two patients had tonic-clonic seizures. A single dose of activated charcoal was given to all patients. Drugs administered included nifedipine (1), flumazenil (1), naloxone (1), lorazepam (2), and phosphenytion (2). All patients recovered and were discharged home within 5 days of ingestion. Serial serum baclofen levels were obtained in all intubated patients (range, 0.049 to 6.0; normal, 0.08 to .40 microgram/mL). Levels obtained 14 hours after ingestion showed a linear correlation with length of mechanical ventilation (R2 = 0.9863). Persistent symptoms were noted in some patients, despite nondetectable baclofen levels. Toxicologic screening for drugs of abuse was negative except in 2 patients with ethanol levels, both < 5 mg/dL.

CONCLUSION

Baclofen overdose may result in coma, apnea, autonomic disturbances, cardiac conduction abnormalities, and seizures. Levels obtained shortly after overdose correlate with length of mechanical ventilation.

N-acetylcysteine reduces methemoglobin in an in-vitro model of glucose-6-phosphate dehydrogenase deficiency

OBJECTIVE

To determine whether N-acetylcysteine (NAC) reduces methemoglobin (MHB) in an in-vitro model of glucose-6-phosphate dehydrogenase (G6PD) deficiency, given that methylene blue is an ineffective MHB antidote in G6PD deficiency.

METHODS

Five volunteers donated blood, which was divided equally into 2 test tubes, centrifuged, and washed with Tris-Mopps buffer (pH 7.4, 15 mmol/L glucose). Both tubes were incubated with epiandrosterone (EA) (400 micromol), a specific inhibitor of G6PD. After 75 microL of 0.18 mol hydroxylamine (HA) was added to induce MHB formation, 150 microL of NAC (20 mg/mL) was added to tube 1 and 150 microL of phosphate-buffered saline (PBS) was added to tube 2 as a volume control. Serial MHB levels are reported as a percentage of total hemoglobin (Hb). G6PD activity was measured at baseline, 15 minutes after EA, and at 5 hours.

RESULTS

Mean G6PD activity at baseline was 9.2+/-2.9 U/g Hb (normal >4.6 U/g Hb); 15 minutes after EA was 3.0+/-1.0 U/g Hb; and at experiment's end was 2.3+/-0.7 U/g Hb. The mean (+/-SD) areas under the concentration-time curves (AUCs) of NAC-EA-HA and PBS-EA-HA samples were compared using an unpaired t-test and were significantly different: PBS-EA-HA, 20,400+/-1,100 % min, vs NAC-EA-HA, 10,400+/-1,000 % min, respectively (p < 0.05).

CONCLUSION

In this in-vitro model of G6PD deficiency, NAC efficiently reduced MHB.

Smoking and nicotine addiction: a pediatric epidemic with sequelae in adulthood

Pediatric addiction to nicotine from cigarette smoking is a major public health problem, extracting a tremendous societal toll in terms of human suffering, a loss of future productivity, and the consumption of scarce health care resources. Teenagers smoke 1.1 billion packs of cigarettes yearly and will account for more than $200 billion in future health care costs. Recent behavioral studies confirm nicotine's ability to induce in adolescents both the tolerance and abstinence phenomena typical of other addicting substances. A range of adverse health effects, first detectable in adolescent cigarette smokers, extend into adulthood. Through the effects of environmental smoke or smoking during pregnancy, adolescent smokers affect not only their own health, but that of friends, family members, and even their own fetuses and children. Additional research into effective prevention and smoking cessation programs is urgently needed to forestall the ravaging of yet another generation by this preventable and deadly habit.

Osteoporosis: outstanding issues

Major advances have occurred in our knowledge of osteoporosis and its treatment in the past 10 years. This paper reviews aspects of the epidemiology, pathogenesis, and diagnosis of the disease that deserve further investigation. Although anti-resorption treatments such as hormone replacement therapy and bisphosphonates have been shown to reduce the incidence of osteoporotic fractures, there is room for improving available treatments. Today, there is no bone-forming agent that has been shown to decrease fracture rate, and several agents are under clinical investigation. The potential value of combined therapy will also be discussed.

On-site availability of selected antidotes: results of a survey of Massachusetts hospitals

Hospital pharmacies in Massachusetts were surveyed to determine their patterns of stocking antidotes. Mailed questionnaires were completed by hospital pharmacy directors at 82 of 93 acute care institutions (87% response rate). Results confirmed great variability in on-site accessibility of antidotes. Only 8 of the 82 hospitals (9.8%) stocked all of 14 common antidotes inventoried by the survey. Even fewer hospital pharmacies stocked specific antidotes (eg, Crotalid anti-venin, digoxin-specific Fab antibodies, pyridoxine) in an adequate quantity to treat one poisoned adult. Larger hospitals and those with a 24-hour pharmacy were more likely to have certain antidotes than smaller institutions. We conclude that Massachusetts hospitals do not carry complete inventories of 14 common antidotes. It is important that poisoned patients be referred to medical centers with adequate toxicological care. Improved guidelines for the accessibility of antidotes need to be developed and made available to hospital pharmacies and emergency departments.

N-acetylcysteine reduces methemoglobin in vitro

STUDY OBJECTIVE

To determine whether N-acetylcysteine (NAC reduces methemoglobin.

METHODS

We carried out an in vitro laboratory experiment in which five healthy adult volunteers donated blood. Each sample was divided equally among three test tubes. Tube 1 served as a negative control. Sodium nitrite .18 mol/L with dextrose .23 mol/L was added to tube 2 and to tube 3. Next, phosphate-buffered saline solution (PBS) was added to tube 2 and NAC (200 mg/mL) to tube 3. Serial methemoglobin levels were measured over 5.5 hours.

RESULTS

Maximum methemoglobin levels were observed at 1.5 hours for both the NAC-nitrite and the PBS-nitrite sample (62.7% +/- 8.1% and 65.1% +/- 7.0%, respectively; data expressed as mean +/- SD). The mean difference in methemoglobin between NAC-nitrite and PBS-nitrite was significant at 4.5 hours (29.3% +/- 23.0%, P = .046). The mean rate of methemoglobin decline in NAC-nitrite samples was also different from that of PBS-nitrite samples (10.7% +/- 1.0% versus 2.9% +/- 2.3%, P = .002). The rate of decline was linea (zero order) in the NAC nitrite samples and represented by the equation: % change methemoglobin = .18 x time in minutes. Area under the concentration-time curve was also different among groups (P < .05).

CONCLUSION

In this in vitro model, NAC reduced chemically induced methemoglobin.

Role of antimalarials in rheumatoid arthritis – the British experience

Antimalarials have been used to treat rheumatoid arthritis (RA) for over 40 years, the first report of suggestive efficacy being published in 1951. Over the years they have become part of the established treatment of RA being one of a category of drugs referred to as disease modifying anti-rheumatic drugs (DMARDs). The onset of action with antimalarials is slow. Most patients use these drugs in combination with non-steroidal anti-inflammatory drugs (NSAIDs) and analgesics. This article reviews the evidence for the efficacy of antimalarials, their place in comparison to other DMARDs and comments on the current use in RA as perceived in British rheumatology.

Role of antimalarials in rheumatoid arthritis--the British experience

Antimalarials have been used to treat rheumatoid arthritis (RA) for over 40 years, the first report of suggestive efficacy being published in 1951. Over the years they have become part of the established treatment of RA being one of a category of drugs referred to as disease modifying anti-rheumatic drugs (DMARDs). The onset of action with antimalarials is slow. Most patients use these drugs in combination with non-steroidal anti-inflammatory drugs (NSAIDs) and analgesics. This article reviews the evidence for the efficacy of antimalarials, their place in comparison to other DMARDs and comments on the current use in RA as perceived in British rheumatology.

Bone mass measurement and bone metabolism in rheumatoid arthritis: a review

The involvement of bone in rheumatoid arthritis (RA) is well recognized, and hand bone densitometry appears to be a promising new technique to monitor disease progression by assessing serial changes in hand bone mass in patients with RA. New biochemical markers of bone formation (i.e. osteocalcin) show contradictory results in different studies, although markers of bone resorption (i.e. urinary collagen cross-links) have shown significant increase in patients with RA. Bone histomorphometric studies suggest that the periarticular osteopenia in RA could be related to increased bone turnover locally, whereas generalized osteoporosis could be due to a global negative remodelling balance. The important factors implicated in the pathogenesis of the bone loss are circulating cytokines [e.g. tumour necrosis factor alpha (TNF alpha), interleukin (IL) 1 and IL6] produced by the inflammatory process, use of oral corticosteroids (in the dose of > or = 5 mg) and reduced mobility due to functional impairment. Apart from this underlying osteoporosis, patients with RA have an increased risk of falls secondary to functional impairment and there is an increased risk of fractures in patients with RA. Very few studies are presently available looking at the therapeutic measures to prevent osteoporosis in RA. Future drug trials on the treatment of RA should include bone mass measurement, especially of the hand, as one of the outcome measures.