Analytical techniques developed to provide risk management of cytotoxic preparative activities
BSc MSc MRSC CChem
Head of Research and
D C Rigge
Chemotherapy remains the best systemic treatment for cancer but the effects of cytotoxic agents on normal healthy cells presents occupational risks to pharmacy and clinical staff. Discussion about safe handling of cytotoxic drugs in UK’s NHS pharmacy preparation facilities has been ongoing for many years.[1-3] As recently as 20 years ago cytotoxic preparation operated in clean room facilities equipped only with Class II microbiological safety cabinets. Since that time there was a steady move towards barrier technology, such as that provided by negative pressure isolators, which remain the recommended devices for operator and product protection. This development has greatly improved safety levels and reduced risks for NHS pharmacy staff who handle these products. There is still concern, however, for those people who may be exposed to very low levels on a regular basis.
Experts continue to debate safe exposure levels for workers handling chemotherapy agents. Controlled epidemiological surveys suggest that cytotoxic drugs are associated with reproduction toxicology, embryo toxicity and teratogenicity, as well as an increased risk of malignant tumours. In the US the National Institute for Occupational Safety and Health (NIOSH) published a health alert  highlighting the awareness among health workers and their employers to health risks posed by working with hazardous drugs. Although there are no occupational exposure limits established for any cytotoxic drug, NIOSH concluded that the problem associated with continued exposure is very real and emphasised the need for control measures to be adopted.
Studies investigating the workplace monitoring of cyclophosphamide in healthcare premises in Alberta, Canada reported low or undetectable levels on work surfaces. They did however report high levels on the surfaces of manufacturers’ vials, an area of contamination control requiring further investigation.
For the development of a cytotoxic residue monitoring facility several factors needed to be considered.
Methodology-Conventional High Performance Liquid Chromatography/Ultra Violet (HPLC/UV) detection methods, the type abundant in QC laboratories are unlikely to provide the required sensitivity. Investment in high specificity, high
sensitivity detection equipment such as mass spectrometry is required.
- Monitoring – The method needed to be able to detect and quantify a range of drugs and be effective in monitoring the most abundant and highest risk agent.
- Staff sensitivities- The provision of data to raise awareness may create anxiety within the pharmacy workforce. Communication of results requires support from the laboratory and other NHS pharmacy resources.
- Value-Pharmacy teams need to understand the benefits of residue monitoring in their drive to create cleaner, safer and risk reduced activities.
Such a service will need to provide education and guidance when results are provided. It also needs to assist units in resolving contamination problems by providing advice on clean down methods and, where necessary, provide further testing to confirm successful decontamination.
Survey of Drugs in Use
Quality Control North West (QCNW) performed a comprehensive survey of pharmacy units in the North West region of England to establish the range and fre-quencies of use of individual agents. Units were asked to report compounds manipulated in their units with an indication of frequency (Table 1). The most frequently used agent is cyclophosphamide with 70% of units using it at least once per day and 96% using it least once per week. Other drugs handled on a regular basis are doxorubicin, methotrexate, mitomycin and the vinca alkaloids.
Those conducting the study developed analytical methods to target the drugs used most often. Adopting the general principle that if hospitals maintain good contamination control of their most frequently used drugs, then there is a high level of confidence that all cytotoxic drug residues are controlled.
The researchers at QCNW developed analytical methods for testing residues using Liquid Chromatography/ Mass Spectrometry (LC/MS). This technique is highly selective and extremely sensitive. Of the top 13 drugs used in the North West of England, they developed methods for nine using one of three specific LC/MS methods. They developed sampling protocols using readily available consumables in hospital pharmacies. The issue of discrete kits with detailed sampling instructions controlled sampling and sample handling processes. As samples needed to be protected from temperature excursions and the rigours of transportation, test kits were assembled and supplied in sturdy insulated boxes. Ice packs were included in the kit and frozen by the client to when sending off the samples.
To ensure standardisation of the sampling technique, the laboratory used one of their analysts to train each client during their initial monitoring exercise. The sampling method involved the application of a sterile wipe moistened with 0.5 ml of a methanol/water mixture. Those collecting the sampled carefully drew the wipe across an area of the working surface (about 10 x 10 cm) using vertical and horizontal strokes. They then placed the wipe in a polypropylene container (20 ml BD syringes have been successfully use) and returned to the laboratory within 24 hours. Laboratory extracted the swab with a defined volume of a methanol/water mixture and tested volumes of the extract solvent using one of the specific LC/MS methods.
Liquid Chromatography/Mass Spectrometry (LC/MS)
This technique incorporates conventional High Pressure Liquid Chromatography (HPLC) with a highly sensitive detector which is capable of identifying and quantifying compounds according to their mass to charge ratio (m/z). The HPLC separates and introduces the compounds into the electro-spray ionisation chamber on the Mass Spectrometer (MS), here the sample is ionised and desolvated before being drawn into the mass analyser under high vacuum and voltage potentials. The sample passes through a quadrupole which separates ions allowing only ions of specific mass to enter the ion trap. The ion trap has the capability to isolate and fragment different compounds through the optimisation of the oscillating electric fields (RF voltages). The combination of isolating and fragmenting a compound makes the MS more specific and sensitive.
Validation of methods
The laboratory used a standard approach to the validation of methods for each drug.
- Chromatographic within day repeatability-Performed on an analytical standard solution and indicating the variation in response from repeated injections.
- Linearity-Determined by calculation of a least squares regression coefficient for solutions applied to the LC/MS over a defined range.
- Drug recovery from the swab material –Determined in triplicate by application of a known quantity of target drug applied to a wipe, the wipe then extracted and extracts tested according to the test protocol.
- Drug recovery from an impervious surface (glass plate) – Determined in triplicate by application of a quantity of the target drug onto the surface of a glass tile. The solvent was allowed to evaporate to dryness in a current of air. The glass tile was then wiped and the wipe processed according to the test method.
- Stability of extracts – The stability of drugs following their uptake onto the swab was determined by spiking a series of wipes with the target drug and extracting at differing times up to seven days after being stored refrigerated.
- Limits of detection (LOD) and limits of quantification (LOQ) – Established using the signal to noise ratio (x 3 for LOD and x 10 for LOQ).
Since commencing the testing 30 aseptic units in the North West of England have performed a residues survey at least once in the course of about one year. The data from three of the most abundantly found drug residues are presented in Figures 1 to 3. In most cases, residues were found to be below the LOD of the analytical method. Occasionally samples have been tested showing residues several hundred times higher than the LOQ. So far there is no correlation between the incidence of high residue level to sampling position in the isolator or the room.
The laboratory has started to gather considerable amounts of data from its client base. In this survey, aseptic units were given the opportunity to decide the numbers and locations of their samples and were only trained in the technique for sampling. The next phase is to introduce greater standardisation of sample locations with the units directed to monitor in specific areas. This will extend to include surfaces of incoming drug containers and areas where pharmacist-releasing activities take place.
With cyclophosphamide being our most extensively handled drug, it is the most useful monitor of cleanliness and environmental control. Through simple statistical analysis, the declaration of a provisional ALARA (as low as is reasonably achievable)7 level for North West units. The level has been set at 700 pg/cm2. Twelve out of 120 individual samples in the survey exceeded this level (Table 3).
The ALARA is used to trigger a phone call to the lead pharmacist to discuss the data and to initiate a specific clean down. Extensive research has been performed on the merits of detergent and chemical clean-down of cytotoxic residues. However QCNW has issued the following advise on cleaning when a high residue is reported:
- Clean areas thoroughly using a sterile detergent solution.
- Rinse with sterile distilled water.
- Clean using sterile 70% IPA/IMS
- Re-sample and submit to QCNW.
Application of this simple process has resulted in considerable reductions in residue levels from resubmitted samples. Aseptic units finding high levels of cytotoxic residues are also advised to re-evaluate their routine clean down procedures and aseptic practices.
Environmental control and therefore occupational health and safety is likely to be best serviced by controlling the high-risk drugs in terms of their usage and their physical/chemical properties. In the North West of England the highest risk drug has been identified as cyclophosphamide. Laboratory experience suggests cyclophosphamide is one of the more difficult drugs to remove by none destructive cleaning. It has also been reported to be susceptible to sublimation, presenting even greater challenges in its environmental control.
Our cytotoxic monitoring service provides analysis of a wide range of drugs and new methods are being developed. The sensitivity of LC/MS provides the unique opportunity to monitor these compounds at ever decreasing levels thus keeping pace with improving ALARA levels.
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