Information Resources

Title: DILUENT DIRECTORY

Version No: 1

Author: Paul Maltby

Date of Issue: 20/12/2012

Review Date: 18/12/2014

RADIOPHARMACEUTICAL DILUENT DIRECTORY

Introduction

The further dilution of from their original volume is undertaken either to ensure that the volume of the dose injected into the patient is practical, and/or to facilitate measurement of its radioactivity. However although the practice is commonplace, data to support it are scarce and are almost exclusively based on information obtained from manufacturers. This may be derived from either the Summary of Product Characteristics (SPC) and/or pack inserts or in the form of verbal advice from manufacturers following telephone inquiries.

Scale of Complexity

The act of dilution may vary from simply drawing the appropriate diluent up into the syringe which already contains the correct activity (but in a volume too small to handle) eg whilst administering a paediatric dose of a 99mTc radiopharmaceutical withdrawn from a high activity vial. At the other end of the scale it may be part of the manufacture of a batch of a longer lived radiopharmaceutical involving addition of several components; for example batch production of 125I Human Serum Albumin.

Dilution and the Medicines Act 1968

It has been stated [1,2] that where products are prepared or manufactured outwith the manufacturers’ instruction, the responsibility for the efficacy of the product lies with the unit preparing the product. This would clearly be the case for the second example described above where as a minimum, radiochemical purity (RCP), chemical purity and chemical identity of the new diluted product would need to be established throughout its assigned shelf life. Similarly, the preparation of a 99mTc kit to a volume greater than the maximum described in the SPC would need to have a radiochemical purity testing undertaken for its assigned shelf life.

At the other extreme, dilution of a dose in its final presentation form at the point of injection into the patient is clearly part of the process of administration and is not covered by the Medicines Act. The issue affecting radiopharmacies is that most dilution activities falls somewhere within these two extremes, with validated guidance from manufacturers or published data being minimal.

The aim of the following table is to provide information about the most appropriate diluent, the limitations of dilution, and reference source where known. The dilution of radiopharmaceuticals for long term storage as a manufacturing process is not within the scope of this table and radiopharmacy staff are advised to validate each circumstance where this may be attempted.

RADIOPHARMACEUTICAL DILUENT MAXIMUM REFERENCE VOLUME / COMMENT 99Tcm Kits1 sodium chloride see text - 0.9% 111In Octreoscan® sodium chloride 2 - 3ml Package 0.9% insert 111In Calcium DTPA sodium chloride not stated (Covidien) 0.9% (pyrogen free) 123I Sodium Iodide sodium chloride not stated SPC (Covidien) 0.9% 123I Sodium Iodide (GE Not company Healthcare) recommended information (pH critical) 123I Not SPC. Ethanol (DatScan®)(GE recommended based Healthcare) formulation of product 123I Iobenguane Sodium chloride (Adreview™) (GE 0.9% Healthcare) 123I Iobenguane (MIBG) water for injection not stated SPC (Covidien) or 5% in water 125I HSA (IBA/CISbio) sodium chloride Not stated Albumin 0.9% & benzyl advised to alcohol 0.9% or reduce albumin 15mg/ml “sticking” to soln. glassware 131I Sodium Iodide oral/IV Any suitable SPC. pH (all manufacturers) diluent. No should be incompatibilities kept to known neutral where possible 131I MIBG (diagnostic) (GE sodium chloride Healthcare) 0.9% 131I MIBG (therapeutic) (GE sodium chloride up to 50ml Company Healthcare) 0.9% information 90Y Yttrium Citrate Dilution not Company (IBA/CISbio) recommended: information pH critical 32P Sodium Phosphate Not Company (Polatom) recommended information 201Tl Thallous Chloride None stated: use (Covidien) sodium chloride 0.9%

1 99mTc Technetium based products obtained from commercial suppliers normally have a tightly defined volume range eg 1-10ml within which the product has been exhaustively tested for stability. All kits are prepared with sodium chloride 0.9% injection 67Ga Gallium Citrate None stated: use (Covidien) sodium chloride 0.9% 51Cr Edetate (EDTA) (GE sodium chloride Alternatively Healthcare) 0.9% and benzyl use sodium alcohol 1% chloride 0.9% for paediatrics due to benzyl alcohol toxicity 51Cr Sodium Chromate (GE sodium chloride up to 10ml Healthcare) 0.9% 18F sodium chloride 0.9% 153Sm Samarium EDTMP Not SPC Quadramet recommended 89Sr Strontium chloride Not SPC Metastron recommended

For 99mTc Technetium based products, in the authors’ experience, during administration, it is common practice for further dilution to take place with sodium chloride 0.9% injection to a volume at least twice that of the maximum described in the package insert.

However a further typical scenario where dilution is practiced would be one where a large (radio)activity in a relatively small volume is transferred from the kit vial to a sterile nitrogen filled vial and then diluted to a much larger volume to enable a standardised volume to be used for patient injection. In practice this could be a volume of 0.5ml (from a maximally diluted kit according to the manufacturers instructions) diluted to 2ml in the secondary container. This may then be used by the imaging department as a single (or multi-dose vial for several patients) over a period of a few hours. In this setting the diluted vial is now an unlicensed product and stability testing by RCP methods must have been undertaken to ensure it meets its specification throughout its assigned shelf life.

Conclusion

Dilution of radiopharmaceuticals as part of the process of their production or administration is not well documented, as is evident from the gaps in the above table. In addition, stability data are lacking when the product is stored in syringes, new containers (for example nitrogen filled vials) or in the original vial. Radiopharmaceutical manufacturers are reluctant to give approval to the practice of dilution on a large scale, thus the responsibility ultimately rests with the producing department or the ARSAC certificate holder authorising administration of the product to the patient.

Readers of this paper who are aware of alternative diluents or have further information concerning dilution in general are urged to contact [email protected].

References

1. Hesslewood SR, Palmer AM and Lazarus CR. Radiopharmaceutical "Kits": Use outside the manufacturers' instructions. The Hospital Pharmacist 1998;5:107-8 2. Ballinger J and Blower P. Radiochemical purity testing of 99mTc-labelled radiopharmaceuticals: how much is enough? Communications. 32(9):761-763, September 2011