Pharmacokinetics of bupivacaine in cats

One of the common questions that we receive is regarding doses of local anaesthetics in cats when multiple nerve blocks are required.

In this recent paper entitled "Pharmacokinetics of bupivacaine after bilateral maxillary and caudal inferior alveolar nerve blocks using two injection volumes in cats," the authors set out to investigate the effect of multiple bupivacaine nerve blocks. The nerve blocks used were bilateral maxillary and bilateral caudal inferior alveolar nerve blocks, which are the four sites which you would block if you were to perform work on all four dental arcades in a cat. Ten cats were included in the study. The cats were anaesthetised with acepromazine, methadone, propofol, and isoflurane.They were randomised to receive either 0.2 ml (BUPI2) or 0.3 ml(BUPI3) of 0.5% bupivacaine per site. This equated to 4 mg and 6 mg of bupivacaine per cat. So, there were five cats in each group.Blood was collected at time zero and then at the following times after the dental blocks: 2, 7, 20, 30, 60, 120, 240, 360, 480, and 600 minutes. Plasma concentrations of bupivacaine were assessed, and pharmacokinetics were described using non-compartmental analysis. The pharmacokinetics are described below.

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Mean doses of bupivacaine were significantly different (BUPI2: 0.88 ± 0.14 mg/kg; BUPI3: 1.22 ± 0.21 mg/kg). For BUPI2 and BUPI3, mean maximum bupivacaine plasma concentrations (Cmax) were 825 ± 299 and 926 ± 197 ng/ml at 5.0 ± 2.7 and 9.6 ± 5.8 mins (time to peak concentration); mean area under the curve to the last measured concentration was 142 ± 36 and 180 ± 60 min*µg/ml; mean clearance was 5.4 ± 0.8 and 7 ± 5.7 ml/min/kg; mean elimination half-life was 245 ± 54 and 278 ± 90 mins; and mean residence time to the last measured concentration was 185 ± 13 and 182 ± 33 mins, respectively. Concentrations of bupivacaine were detected up to 600 mins (72 ± 22 ng/ml in BUPI2 and 104 ± 55 ng/ml in BUPI3)

The analysis documents that concentrations of bupivacaine were detected up to 600 minutes after the nerve blocks were performed. This was a pharmacokinetic study, so it doesn't examine the pharmacodynamics, i.e. how effective the nerve blocks were and how long the nerve blocks lasted for. What this information does tell us is that bupivacaine is rapidly absorbed into the plasma after peripheral nerve blocks – hence the importance of staying within our safe dose limits.

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The doses chosen, the volumes chosen are of interest because they reflect what we would commonly see used in clinical practice, i.e. between 0.2 and 0.3 ml per block. These are the volumes that keep us within our safety dose limit of up to 2 mg per kg in cats.

Let’s just run the maths so we are clear on our safe doses. We’ve used bupivacaine 0.5% for this – we know that the higher the concentration, the more effective the block so I always prefer 0.5% over 0.25%. We’ve assumed all 4 sites to block.

	Max dose 2mg/kg	Total mls of 0.5%	Volume per block
3kg cat	6mg	1.2ml	0.3ml
5kg cat	10mg	2.0ml	0.5ml

The above calculation shows the limit in volume for a given weight. For these blocks we know 0.2-0.3ml is effective – but that you have a degree of flexibility to go up to 0.5ml. A situation where this is relevant is where you block 4 quadrants, but one block is not effective. In a 5kg cat I would use 0.3ml/site so a total of 1.2ml out of my safe limit of 2.0ml. If I find that one block hasn’t worked, then I know I have the option of repeating that block with another 0.3ml and will still remain in my safe dose limit. For more information on which nerve blocks are suitable for cats undergoing dental work, you can watch our webinar on local anaesthetic techniques for dental.

Read our Reflect article on dental pain in cats

Reference

Steagall PV, Monteiro BP, Garbin M, Benito J, Ruel HL, Cagnardi P. Pharmacokinetics of bupivacaine after bilateral maxillary and caudal inferior alveolar nerve blocks using two injection volumes in adult cats. J Feline Med Surg. 2026 Jan;28(1):1098612X251407158. doi: 10.1177/1098612X251407158.

This post was written by Matt Gurney.

Matt & Carl established Zero Pain Philosophy to provide educational resources & telemedicine to veterinary professionals globally, enabling optimal management of pain.

Matt sees referrals in the pain clinic at Eastcott Referrals. You can also receive telemedicine advice from us here if you have a pain case where you need a helping hand.

Matt Gurney is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and works at Anderson Moores Veterinary Specialists. Matt is Past President of the European College of Veterinary Anaesthesia & Analgesia and works at Eastcott Referrals in the UK.

Carl Bradbrook is an RCVS & European Specialist in Veterinary Anaesthesia & Analgesia and is Past President of the Association of Veterinary Anaesthetists. Carl works at Anderson Moores Veterinary Specialists in the UK.

The intended audience for this pain update is veterinary professionals. This pain update is based on clinical experience and independent opinion.