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The use of botulinum neurotoxin (BoNT) to produce temporary, localised muscle relaxation by partial chemical denervation has revolutionised the management of several neuromuscular conditions including cervical dystonia and focal spasticity
Donald Macarthur
BPharm MRPharmS
Independent Consultant
Produced through fermentation of Clostridium botulinum, a gram-positive, spore-forming, obligate anaerobe found naturally in soil, native BoNT is a high molecular weight complex. Two of the seven known toxin serotypes have been commercialised – BoNT/A and BoNT/B – and one or other is found in the five preparations marketed for therapeutic use in the UK and other parts of Europe (table 1).
Different strains of C. botulinum are used in manufacture, different methodologies are undertaken in purification, differing pHs, stabilisers and bulking agents are employed, and the injections are presented differently.
Clinically this means that the approved indications, diffusion characteristics, duration of action and adverse event profiles vary between the preparations. It is also well known that ‘units’ of biological activity used to quantify dosing of one brand cannot be compared or converted into ‘units’ of another brand due to bioassay specificity.
Human serum albumin is included in all five products to minimise adsorption of the toxin to the glass vial. Whilst there is a theoretical risk of albumin transmitting viruses and other pathogens, there are no reports of this when manufactured to Ph. Eur. specification.
Most products contain a number of haemagglutins and other non-toxic proteins that have no apparent therapeutic function. At physiological pH, following injection into the muscle, it is assumed these complexes disassociate, releasing active neurotoxin.
Repeated doses of foreign protein increase the risk of developing neutralising antibodies, and may lead to treatment failure and/or increasing dose requirements. The possibility of alternating serotypes in an attempt to overcome this problem has now been discounted. As many of the conditions for which BoNT is indicated require indefinite treatment, it has been recommended that the smallest protein load and longest dosing interval be employed.[1,2]
Pure toxin is one of the most dangerous substances known. Though the days are long gone when hospital staff had to go to extreme safety measures to dilute it to safe concentrations, care with handling and disposal of the commercial preparations are still necessary. Shaking or other violent action when reconstituting the powder risks denaturing the toxin. Vacuum dried forms are useful as the vacuum will pull the solvent slowly into the vial itself, with the presence of a vacuum offering reassurance the seal is intact. Injections should be prepared over plastic-lined paper towels to catch any spillage, which can be inactivated by autoclaving or by use of dilute (0.5%) hypochlorite solution. Used vials and syringes should not be emptied but placed with other contaminated material into containers and disposed of as medical biohazardous waste.
Storage conditions
One of the most striking differences between the products, of great relevance to hospital pharmacists, is the recommendation for their storage (table 2).
Unopened vials of only one of the five brands – which also has the longest shelf life – may be stored at room temperature (below 25oC), the other four requiring handling and storage at 2–8oC to avoid losing their biological effectiveness.
The recommended diluent for each of the BoNT brands is sterile preservative-free normal saline, though addition of a bacteriostat (benzyl alcohol) has been reported to reduce pain on injection.[3] From a microbiological point of view, the resultant solution should be used immediately and only once, unless reconstitution is carried out strictly under aseptic conditions.[4,5]
Though dosage varies widely depending on the injection site, most lesions require only part use of a vial. To save costs, interest has been expressed in how long potency and/or speed of onset of action are retained after reconstitution to allow serial re-extraction. Several studies have looked at the stability post-reconstitution of refrigerated BoTN,[6–8] or to the effects of freezing/thawing,[9–12] and arrived at conflicting results. On balance, the evidence seems to suggest diluted toxin, at least with the brands studied, can continue to be used for longer periods than recommended. However this will be outside the terms of the marketing authorisation and hence at the responsibility of the individual physician.
[[HPE51.50]]
Problems with the cold chain
Cold chain is a temperature-controlled supply chain entailing an uninterrupted series of storage, transportation and handling activities which maintain a defined temperature range of 2–8oC. Neither the European Medicines Agency nor the European Commission gives specific guidance and EU legislation only deals with the matter in general terms. Detail is left to individual member states, In the UK, for example, the Medicines and Healthcare products Regulatory Agency has issued an Information Letter,[13] with the British Association of Pharmaceutical Wholesalers[14] producing a protocol for its members.
Maintenance of the cold chain up to the time of product handover to a hospital/clinic/pharmacy is often entrusted to a specialist carrier, and in all cases subject to vigorous and robust validation and monitoring procedures. There is total journey control, with the carrier able to track delivery conditions every step of the way from the manufacturer. In the unlikely event of temperature excursion – when temperature loggers or probes show the required temperature zone has been exceeded – affected items can be immediately identified and quarantined, with well-rehearsed recall procedures quickly instigated. However, as a temperature-sensitive product moves from its distributor to the market there are many more possibilities for things to go wrong.
Purpose-built pharmaceutical refrigerators are recommended for storage of cold chain lines. There is automatic defrost and air is circulated by a fan, which provides temperature uniformity and rapid temperature recovery after the door has been opened, as long as the refrigerator is not overstocked and its contents are evenly distributed. Temperature monitoring is usually via an externally visible digital maximum/minimum thermometer, backed-up with an audio-visual alarm.
As well as temperature excursion, standard domestic refrigerators carry the risk of products freezing if they come in contact with the chiller plate or coil. The same risk applies to contact with ice packs in isotherm boxes during transit. Some product types are as much at risk from freezing as from elevated temperatures. Freezing can cause irreversible damage and some suspensions may not completely redisperse. It can also allow contamination via hairline cracks or free glass spicules, causing serious local adverse reactions.
Pharmacists are generally alert to the demands of cold chain transport/storage and the products affected, so the benefits of using non-refrigerated lines, when there is a choice, are best seen at ward or clinic level. Specific issues here are the very limited refrigerator space available, poorer temperature monitoring than in the hospital pharmacy, and the need to allow vials to warm up before their contents are injected. Cold chain excellence, however, depends on much more than infrastructure. Staff have to have the knowledge and training, and institutions must have the correct processes in place.
[[HPE51.51]]
People make mistakes
That mistakes can be made was well illustrated recently with vaccines, the most common type of cold chain product used by GP practices and NHS trusts in England and Wales. Prompted by a recall of 560 patients from two practices for repeat vaccination following incorrect storage, a 2009 audit revealing 40% of vaccines in one region were stored incorrectly, and 260 separate reports of related incidents over a four-year period (table 3), the NHS’ National Patient Safety Agency issued a rapid response alert on the issue in January this year.[15] Similar concerns with vaccine storage have been reported in Ireland[16] and Canada,[17] suggesting the problem is widespread.
It is not difficult to imagine similar occurrences with other refrigerator lines, in fact these might be more common as users will be less familiar with their storage demands.
Maintaining the cold chain is expensive. Wholesalers estimate the costs of shipping at an assured 2–8oC range is approximately double that for products able to withstand ambient conditions. This additional cost is effectively passed on to the health service, as discounts on cold chain purchases are not offered to community pharmacy customers and as a result the products are included on ‘the list of drugs for which discount is not deducted’ (Part II of the English Drug Tariff) so the ‘clawback’ does not apply.
Cold chain failures are even more expensive. As a minimum, a quality check has to be undertaken. Stock might need to be destroyed and treatment may need to be repeated. Providers rarely take out insurance to cover this risk. Most users are likely to err on the side of caution in all but the most minor breach of the cold chain, assuming this breach is recognised and acted upon in the first place. The problem is likely to get worse. Based on projected market growth rates, seven of the top-10 global medicines in 2014 are expected to require cold-chain handling.[18]
This independently written article was financially supported by Merz Pharmaceuticals with an unrestricted grant
References
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13. MAIL No 99, January/February 1997; www.mhra.gov.uk.
14. www.bapw.org.uk.
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18. Cold Chain Biopharma Logistics Sourcebook 2010, Pharmaceutical Commerce.
