The threat of allergies, which affect about one in five people in the US and Europe is emerging as a major public health challenge. The problem is also fast becoming severe in the developing world.
Very much an enigma
In spite of these trends, the World Allergy Organisation (WAO) notes that “services for patients with allergic diseases are fragmented and far from ideal,” and that this is true even in the developed world. The key reason is that allergies still remain little understood.
In Europe, for example, the EU Commission acknowledges that the epidemiology of allergies remains “very much an enigma.” In spite of “relatively homogeneous lifestyles” across the region, allergy rates vary from 3.7% among 13-14 year olds in Greece to 32.2% for the same age group in the United Kingdom.
Children hit hardest
As hinted by the EU Commission figures above, the impact of allergies is especially pronounced in a vulnerable demographic, namely children.
Indeed, the Florence, Italy-based European Academy of Allergy and Clinical Immunology (EAACI) reports that “the number of children with allergies has doubled in the last ten years, and visits to A&E have increased seven-fold.” The situation is no different in the US, where a recent study by the Centers for Disease Control and Prevention (CDC) finds allergy to be among the most common medical conditions affecting children aged below 17.
The allergy challenge has been confounded by the fact that its origins now include a bewildering (and growing) range of food products. In Europe, the InformAll Database (developed with funding from the European Union) currently contains information about the “more than 120 foods” reported to be associated with allergy.
The burden of this, once again, is disproportionately high on children. Globally, an estimated 220 to 250 million people could be suffering from food allergy, according to the WAO.
In Britain, the respected National Institute for Clinical Excellence (NICE) zeroes down on food allergy as being “among the most common of the allergic disorders” and “a major pediatric health problem” because of “the potential severity of reactions and a dramatic increase in prevalence over the past recent decades.”
Food allergies a specific challenge
Though the CDC study mentioned above found the biggest challenge for US children to be respiratory allergies, their share – at 17% – has remained constant since the late 1990s. The fastest growth, on the other hand, was shown with skin allergies, up from 7.4% in 1997–1999 to 12.5% in 2009–2011.
In contrast, the prevalence of food allergies in US children is not only smaller than either respiratory or skin allergies, but also showed a slower increase than the latter, from 3.4% to 5.1%.
However, the US figures conceal more than they reveal.
Firstly, managing (or even) identifying food allergies is not straightforward. Unlike respiratory allergies (which have a long-established intervention modus), or skin allergies (which are easier to pinpoint), the diagnosis of food allergies is far more problematic. This is because “nonallergic food reactions, such as food intolerance, are frequently confused” with food allergies.
The allergy continuum
Making things worse is the allergy continuum.
According to a review of two million patient visits in the US (the largest ever of its kind), food allergies in childhood are instrumental in the so-called ‘allergy march’, a medical condition by which there is an escalation in the risk “for the development of additional and more severe allergy-related conditions, including asthma, later in life.”
In other words, tackling food allergies effectively may hold the key to reducing the burden of other allergies in later life.
Profiling allergies: differences between children and adults
Food allergies in children are most commonly caused by eggs, milk, peanuts, tree nuts and wheat; in adults, milk and wheat are excluded as typical allergens, and instead replaced by fish and shellfish.
However, the EU Commission’s observation about the ‘enigma’ of allergies applies to food too. “In continental Europe, the most common food allergies are to fresh fruit and vegetables, whilst in Anglo-Saxon countries hazelnuts, peanuts and walnuts are the most problematic. Allergy to fish and shellfish prevails in Scandinavia and Northern Europe.”
Tracking the severity of allergies
An allergic reaction to food usually occurs quite quickly (in some cases, within minutes of eating a particular food, and in others, 2-3 hours afterwards). Typical symptoms include an abnormal swelling of the tongue, diarrhea, and hives.
In severe cases, the reaction (as with other allergies) is anaphylaxis, which can be life-threatening.
A study by Mayo Clinic covering a period of 10 years (1990 to 2000) found an age-specific rate for anaphylaxis highest in the under-19 year population (at 70 per 100,000 person-years, compared to an overall age- and sex-adjusted rate of just under 50). The Mayo clinic study also found that ingested foods accounted for one-third of all cases (33.2%), significantly ahead of the second- and third-ranked causes: insect stings with 18.5% and medication with 13.7%.
As troubling is the growth in the incidence of anaphylaxis, again in children. Hospital data from New York State shows that hospitalization for anaphylaxis among patients younger than 20 increased more than 4-fold between 1990 and 2006.
Growing costs
The economic impact of food allergy is significant. In the US, children’s food allergies are estimated to cost as much as $24.8 billion per year.
It is also growing. In the UK, hospitalization for food allergies has increased by as much as 500% since 1990.
Food allergies cannot be cured, but they can be managed by dietary control – in other words through avoidance of allergen-inducing foods. However, there is sometimes little room for a learning curve. In certain people, even tiny amounts of a food allergen (for example, 1/44,000 of a peanut kernel) can prompt an allergic reaction.
Currently, aside from avoidance, the standard of care for food allergies remains “ready access to self-injectable epinephrine.”
Both the US National Institutes of Health (NIH) and Britain’s NICE have drawn up recommendations for the diagnosis and management of food allergy. At the European level, the European Academy of Allergy and Clinical Immunology (EAACI) published its first guidelines on the subject in summer 2013.
An ‘allergy epidemic’: the institutional response
However, the challenge of food allergies is likely to continue.
One key gap is an institutional network of qualified specialists, which link in seamlessly into the wider public health system. In 2006, a subcommittee at Britain’s House of Lords concluded that allergy services were insufficient to deal with it and described the growing incidence of allergic conditions as an ‘allergy epidemic’. Their recommendations urged setting up “at least one allergy centre, led by a full time allergy specialist” in each Strategic Health Authority, supported by “a chest physician, dermatologist, ENT specialist, clinical immunologist, gastroenterologist, occupational health practitioner and pediatrician,” and assisted by “specialist nurses and dieticians trained in allergy.”
The House of Lords subcommittee also strongly called for “diagnostic facilities necessary to investigate complex allergies” staffed by personnel who have received “accredited allergy training.” In other words, such a system will only be meaningful if laboratories are harnessed to address the exploding allergy challenge, and provided with sufficient funds for equipment and staff. Until such time, the response will mean little more than using best practices guidelines (from bodies such as the NIH, NICE and the EAACI) to streamline what essentially remains an ad-hoc infrastructure.
The need for support by clinical labs is implicit in the NICE guidelines on food allergies, which stress that “skin prick tests and blood tests are equally cost-effective” and that “blood tests are cost-effective independent of number of individuals tested.” On the other hand, the guidelines also highlight the need for “valid test results” “to reduce incidence of adverse reactions and improve quality of life,” and prevent the (yet unquantified cost of) anxiety and worry, as well as the “avoidance of food that is actually safe to eat.”
The future: no cures in sight, yet
As of now, there is no cure for food allergies.
A seemingly-promising Phase II, randomized, double-blind study on the anti-asthmatic omalizumab against peanut allergy (one of the most dangerous food allergies) was stopped in 2011, with most subjects not reaching the endpoints. The investigators concluded that “no firm conclusions can be drawn” from their effort, but said it deserved “further investigation.”
The omalizumab research actually reached the same deadlock as another similar anti-IgE preparation, HU-9015, in 2003. This study was, ironically, stopped after its sponsors found the prospects for omalizumab to be more promising.
Nevertheless, researchers continue with their efforts, especially with regard to peanut allergy. As of this date, according to a communication from the National Institutes of Health, 14 studies and trials on peanut hypersensitivity alone are recruiting volunteers, one more than for asthma.
Methadone maintenance therapy is central to the treatment of opiate dependence. Assessment of adherence is essential to ensure success and to prevent misuse of prescribed medications. A variety of specimen types can be tested for methadone and its main metabolite using a number of different analytical methods. The benefits and limitation associated with each are discussed.
by Dr Elizabeth Fox and Dr Deepak Chandrajay
Introduction
Opiate dependence is an important problem worldwide. In the UK, individuals seeking help with their addiction are referred to substance misuse services where they are usually offered methadone or buprenorphine substitution therapy [1]. Methadone is a synthetic opioid with pharmacological actions similar to opiates mediated through the mu receptor. Treatment is initiated at a dose of 10–40 mg daily and gradually increased by 10–20 mg weekly. The usual maintenance dose is 60–120 mg daily, but some clients require a higher dose for symptomatic relief [2]. Its long half-life allows for a once-daily dosing schedule and the accumulation in the body means that steady-state plasma concentrations are easily achieved after repeated administration.
Methadone reduces or eliminates withdrawal symptoms and helps the subject reach a drug-free state in a controlled way. There is evidence of reduced illicit opiate misuse, criminal activity and mortality when patients are on maintenance therapy [2, 3]. Injecting behaviours and incidence of HIV infection are also reduced [4].
Methadone is a lipid soluble drug with an oral bioavailability of approximately 95%. It is metabolized by cytochrome P-450 (CYP) enzymes and demethylated to 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine (EDDP). Both parent drug and metabolite are excreted in the urine and can also be detected in blood, oral fluid, sweat and hair. Co-administration of CYP enzyme inducing drugs such as rifampicin, phenytoin, and zidovudine can precipitate opiate withdrawal symptoms. Fluoxetine and fluvoxamine can inhibit CYP enzymes and have an opposite effect on methadone metabolism [5].
In contrast to most other forms of therapeutic drug monitoring where blood concentration is maintained within a narrow therapeutic window, methadone is monitored almost exclusively to confirm adherence with the treatment regimen. The client may seek to falsify the drug test to feign adherence when the drug is actually being sold to others, or simply to mask illicit drug use. Such individuals will submit a specimen spiked with methadone mixture, therefore effective methods for methadone testing should use matrices which are resistant to tampering and/or include measures to detect falsified samples. Absence of EDDP from a methadone-positive urine sample strongly suggests that it has been spiked with medication. Measurement of urine creatinine will identify samples which have been diluted or substituted, for example with tea. Methadone mixture is green so a green tinge to urine should raise suspicions of sample spiking. The temperature and pH of fresh urine specimens can be recorded to assess reliability. Salivary IgG is useful to confirm integrity of oral fluid specimens.
Analytical methods used for methadone testing
The key analytical methods used to measure methadone and EDDP are immunoassay, liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and gas chromatography coupled to mass spectrometry (GC-MS). The benefits and limitations of each are summarized in Table 1. Immunoassay is rapid, high throughput when automated and low cost. Sensitivity is determined by the detection cut-off concentration of the test kit and specificity by the specific antibody used in the kit. Point-of-care test (POCT) kits are available for use with urine and oral fluid in the clinic and require little expertise or training. POCT offers the significant advantage of producing instant results that can be discussed during the consultation. Laboratory-based immunoassays can be run on multichannel clinical chemistry analysers and do not require additional staff training. All immunoassay-based techniques are prone to interference from unrelated compounds due to cross-reaction with the specific antibody. Cross reactivity data are available from the manufacturer and should be borne in mind when interpreting results. False-positive methadone results have been documented with diphenhydramine, doxylamine and phenothiazines [6]. Immunoassay-based tests, whether designed for POCT or laboratory use, are sold as screening tests. The manufacturers recommend the confirmation of positive results using an alternative methodology such as LC-MS/MS or GC-MS. That said, not all laboratories and substance misuse clinics routinely confirm methadone and EDDP positive results. UK Department of Health guidance on adherence testing recommends only that positive screen tests are confirmed ‘if appropriate’[1].
Mass spectrometric techniques offer the best possible sensitivity and specificity and are considered the ‘gold standard’. Test menus are user-defined which allows simultaneous detection of methadone and EDDP and any other drug as required. Disadvantages of these techniques are that they require expensive specialist instrumentation, labour intensive sample preparation, and complex data interpretation. Turnaround times can be lengthy and they are not amenable to POCT. LC-MS/MS methods require considerably less sample preparation than GC-MS and are now used in many clinical laboratories. A few labs including our own have adopted LC-MS/MS for first-line drug screening of urine and oral fluid specimens.
Specimen types for methadone testing
The main sample types are summarized in Table 2.
Urine
Regular urine testing is the most commonly used means of confirming adherence with methadone prescription. The advantages of urine are that both methadone and EDDP are readily detected and collection is easy and non-invasive. Presence of EDDP provides proof that methadone has been ingested and not spiked into the sample. A disadvantage of urine is that it is easy to manipulate. A sample of donor urine, if the donor is taking methadone, submitted in place of the patient’s own is difficult to recognize. Supervised collection is not always desirable as it is an invasion of privacy and subjects may suffer from ‘shy bladder’. The concentrations of methadone and EDDP do not correlate well with dose (because of the variability of untimed urine samples), so qualitative urine analysis is only suitable for confirming use.
Commercially available methadone and EDDP immunoassays typically have a fixed cut-off or detection threshold of between 100 and 300 µg/L. Multidrug panel tests usually include either methadone or EDDP. Choosing a test which specifically detects EDDP will minimize the chance that a spiked urine is passed off as positive. An estimated 4% of methadone-positive samples submitted to our laboratory lack detectable EDDP; a methadone-only assay would not identify these specimens (unpublished observation). Our approach to urine testing is to measure both methadone and EDDP by LC-MS/MS in all samples. The testing strategy in an increasing number of substance misuse clinics is to use POCT as a first-line test, then to refer suspicious or disputed samples to the lab for confirmation. A laboratory immunoassay would offer no further information for samples that have already been tested at the point of care and could theoretically suffer the same interference.
Oral fluid
An alternative matrix for methadone testing is oral fluid. The advantage of oral fluid is that collection is simple, easily observable and can be done in the consultation room. POCT devices are available for instant results or samples can be sent for laboratory analysis. Both immunoassay and mass spectrometric analytical methods are available. The amount of methadone and EDDP present in oral fluid is dependent upon salivary pH. Methadone is a basic drug and under acidic conditions it becomes ionized and ‘trapped’ in the saliva. Unstimulated saliva is more acidic than stimulated saliva so false negatives can be avoided by asking the subject to abstain from eating, drinking or chewing for 10 minutes prior to collection. A recent study involving subjects on daily methadone doses found that the concentration of methadone in saliva correlated poorly with dose and that EDDP was below detection in 12% of samples [7]. However, methadone was readily detectable in all samples suggesting that oral fluid is a useful specimen for confirming adherence. Oral fluid methadone does not reflect the plasma concentration so would not be useful for assessing dose adequacy. Contamination with methadone from the oral cavity is a problem and absence of EDDP, if measured, should be interpreted with caution as it does not necessarily equate to sample adulteration.
Blood
The main advantage of using blood to monitor methadone therapy is that it’s virtually impossible to falsify the sample. Plasma concentration correlates with methadone dose but the concentrations at which therapeutic effect is achieved have not been well defined. Several studies have suggested target concentrations; other studies have found no correlation between plasma concentration and either heroin use or opiate withdrawal symptoms [8]. A further study suggested that the pharmacodynamics of methadone can be altered by the presence of other drugs therefore altering the relationship between plasma methadone and effect [9]. There is debate in the literature as to whether plasma concentration is any more useful than daily dose for predicting response to treatment [10]. Given the polypharmacy present in the majority of subjects receiving methadone, routine use of plasma methadone to titrate dose is likely to need further evaluation. Intravenous drug users tend to have poor venous access so collecting samples may be challenging. Methods using dried blood-spot samples to circumvent this problem have been described but skin contamination with methadone is likely to be an issue [11]. Blood is not the ideal specimen to assess use of other substances because of the very short detection window, so additional testing may be required. In conclusion, blood testing is best reserved for difficult cases where knowledge of the plasma concentration may be helpful.
Other matrices
Monitoring of methadone therapy using sweat analysis has been evaluated. Patches are typically worn for up to 7 days then dispatched to the laboratory for analysis. They are tamper-evident and claim to be difficult to adulterate. Large inter- and intra-individual variations in sweat methadone concentration have been observed and there is only a weak correlation between patch concentration and dose. Sweat testing is, however, useful for detecting exposure to other substances so may be applicable to some cases. Hair analysis can be used to retrospectively confirm adherence with methadone treatment but is not useful for real-time assessment.
Concluding remarks
The current trend is for substance misuse services to perform methadone adherence testing in the clinic and refer samples to the laboratory for confirmation where necessary. Substance misuse clinic personnel are not laboratory scientists, therefore a key role of the laboratory that performs confirmatory testing is to develop a good working relationship and ensure all aspects of testing are fully understood.
References
1. Department of Health (England) and the devolved administrations. Drug Misuse and Dependence: UK Guidelines on Clinical Management. London: Department of Health (England), the Scottish Government, Welsh Assembly Government and Northern Ireland Executive. 2007; www.nta.nhs.uk/uploads/clinical_guidelines_2007.pdf.
2. National Institute for Health and Clinical Excellence. Methadone and buprenorphine for the management of opioid dependence. Technology appraisal guidance 114. NICE 2007; http://guidance.nice.org.uk/TA114.
3. Advisory Council on the Misuse of Drugs. Reducing drug-related deaths: a report by the Advisory Council on the Misuse of Drugs. ACMD, Home Office 2000; ISBN 0-11-341239-8.
4. NTORS, The National Treatment Outcome Research study. 2001; http://webarchive.nationalarchives.gov.uk/+/www.dh.gov.uk/en/publicationsandstatistics/publications/publicationspolicyandguidance/dh_4084908.
5. McCance-Katz EF, Sullivan L and Nallani S. Drug interactions of clinical importance among the opioids, methadone and buprenorphine and other frequently prescribed medications: a review. Am J Addict. 2010; 19(1): 4–16.
6. Lancelin F, Kraoul L, Flatischler N, Brovedani-Rousset S, Piketty ML. False-positive results in the detection of methadone in urines of patients treated with psychotropic substances. Clin Chem. 2005; 51(11): 2176–2177.
7. Gray TR, Dams R, Choo RE, Jones HE, Heustis MA. Methadone disposition in oral fluid during pharmacotherapy for opioid-dependence. Forensic Sci Int. 2011; 206 (1–3): 98–102.
8. Shiu JR, Ensom MHH. Dosing and monitoring of methadone in pregnancy: literature review. Can J Hosp Pharm. 2012; 65(5): 380–386.
9. Kharasch ED, Walker A, Whittington D, Hoffer C, Sheffels Beynek P. Methadone metabolism and clearance are induced by nelfinavir despite inhibition of cytochrome P4503A (CYP3A) activity. Drug Alcohol Depend. 2009; 101(3): 158–168.
10. Hallinan R, Ray J, Byrne A, Agho K, Attia J. Therapeutic thresholds in methadone maintenance treatment: a receiver operating characteristic analysis. Drug Alcohol Depend. 2006; 81(2): 129–136.
11. Saracino MA, Marcheselli C, Somaini L, Pieri MC, Gerra G, et al. A novel test using dried blood spots for the chromatographic assay of methadone. Anal Bioanal Chem. 2012; 404(2): 503–511.
The authors
Liz Fox* PhD, FRCPath and Deepak Chandrajay MBBS, MRCP
Specialist Laboratory Medicine, St James’s University Hospital, Leeds, UK
*Corresponding author
E-mail: Elizabeth.fox@leedsth.nhs.uk
November 2024
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