Additionally , while pharmaceutical companies try to ensure that each multi-dose bottle is accurately filled , small variations can occur , which could result in a positive discrepancy if a bottle is overfilled . A standard operating procedure ( SOP ) should be in place in all veterinary practices in the event of a discrepancy in the CDR , which should provide clarity and consistency for all staff handling CDs . The Veterinary Medicines Directorate ( VMD ) advises that discrepancies of up to 10 % should not cause concern . The VMD , along with Royal College of Veterinary Surgeons ( RCVS ) Practice Standards Inspectors , is aware that some wastage is unavoidable due to dead space ^{[ 8 ]} . The dead-space volume can be accounted for by recording an estimate of this volume under the ‘ amount discarded ’ column in the CDR ( Figure 2 ) alongside the volume dispensed . The exact dead-space volume will depend on the manufacturer and the sizes of the needle and syringe ^{[ 7 ]} .

Some veterinary practices use a standard discard volume within the CDR , regardless of the needle and syringe combination – a practice propagated by drug companies supplying CDRs with this standard volume pre-printed in the discard column ( Figure 3 ). These volumes range from 0.05 ml to 0.1 ml depending on individual practice protocol , with the RCVS recommending the former ^{[ 8 ]} .

Cambruzzi and Macfarlane ^{[ 9 ]} explored variations in syringe dead-space volumes compared with International Organization for Standardization ( ISO ) standards ( Table 1 ). Their study concluded that dead space across syringe sizes and brands varied and that not all were compliant with ISO standards . They found that 1 ml and 2.5 ml syringe dead space was 0.03 – 0.07 ml , and that needle dead space was 0.05 ml for 23G and 21G needles . From these results , Cambruzzi and Macfarlane ^{[ 9 ]} updated the discarded volume in their practice CDR to 0.10 ml . However , Cambruzzi and Macfarlane ' s study measured the dead-space volume for needles and syringes separately , not in combination , therefore this combined needle / syringe dead-space volume is only an estimate .

For each dose of drug prescribed ( e . g . 10 mg ( 1 ml ) administered to patient X ), record 1 ml as the amount given and 0.05 ml as the amount discarded . This is a good approximation of the dead space in each syringe and increases accuracy in record keeping .

Figure 3 . Example of guidance printed in one company ’ s controlled drug register for recording dead-space volumes .

Veterinary professionals have a duty to ensure that CD use is carefully monitored and recorded in compliance with the legislation , which includes maintaining accurate CDRs to ensure discrepancies can be rapidly identified and investigated .

With evidence to suggest that a standard discard volume of 0.05 – 0.10 ml will under-record the true volume lost to needle and syringe dead space ^{[ 9 ]} , this study aimed to explore the impact of needle and syringe size on dead-space volume to facilitate more accurate CD record keeping .

Table 1 . International Organization for Standardization ( ISO ) standard 7886-1 values for B Braun syringes ^{[ 9 ]} .

Size of syringe ( ml )

1 0.06

2.5 0.07

5 0.08

10 0.1

20 0.1

ISO 7886-1 reported dead-space value ( ml )

Name of Drug :...................................................................... Drug Strength :..................................... Drug Form :........................................................... Name and address of wholesaler *:.................................................................................................................................................................................

Received * Administered

Figure 2 . Example of a controlled drugs register .

24 Veterinary Nursing Journal