Higher concentration local anaesthetics causing prolonged anaesthesia. Do they? A literature review and case reports
Dr Angus Kingon
45 Grandview Street
Pymble NSW 2073
Higher concentration dental local anaesthetics (3% and 4%) have become more available in Australia in recent years. Benefits claimed include a faster onset of anaesthesia and improved success with injections compared to 2% solutions. Recent reports suggest that the higher concentration carries a greater risk of prolonged anaesthesia to the mandibular and particularly the lingual nerves. The literature was reviewed and those studies which demonstrated adverse effects of different concentrations of local anaesthetics were analysed. Recent cases are presented. There is an extensive international literature which confirms increased concentration of local anaesthetic does show an increased risk, by about ×6, of prolonged anaesthesia. Five case reports illustrate the impact of this complication on patients’ quality of life. Careful consideration needs to be given before using higher concentration local anaesthetic agents for mandibular and lingual blocks as lower concentration local anaesthetics are safer. If acceptable to individual patients, avoidance of block injections or any local anaesthetic for minor restorative tasks could be encouraged given the severity of the complication. It is safe to use the higher concentration agents for infiltrations away from major nerves.
The essence of sound therapeutics is for a drug to have maximum benefit with minimal risk. Dental local anaesthetics are a good example of a class of drugs with maximum benefit to the patient as they allow complex invasive procedures to be performed safely with minimum pain.1 However, there is a small but defined risk of adverse reactions, both locally and systemically, to local anaesthetic agents. These have recently been reported.2,3 In the development of these studies, it is evident that there is concern in the international literature of a risk of a relation between increased concentration and increased neurotoxicity.4–12 It has been claimed by clinical observation that 4% articaine has a faster onset of anaesthesia and fails to be effective less often; two features that practitioners consider important.13 The differing strengths of dental local anaesthetic agents available in the Australian market are summarized in Table 1.
Table 1. Concentration of local anaesthetic agent in dental anaesthetics in Australia
A review of the literature showed two large studies which systematically approached this issue. These were a 21-year longitudinal study in Ontario, Canada4 and a prospective national study in Denmark.6 In both studies, 4% local anaesthetic agents were introduced into the region mid-study and thus showed an increase in reporting of prolonged anaesthesia. Further studies have been reported from the San Francisco Bay area of California, USA.6,7 All of these studies carefully document their methodology, describing both their strengths and weaknesses.
Attempts at a comparable study in Australia were not possible as there is no mandatory central reporting mechanism, and the pharmaceutical companies and supply agents would not release data on the percentage sales of the different agents available in Australia.2
In this study, the international literature was reviewed in an attempt to determine the risk of increased concentration of local anaesthetic agents on the incidence of prolonged anaesthesia.
A comparison of the different international studies is presented in Table 2. These show an increased risk of approximately ×6 for higher concentration local anaesthetics.
Table 2. Ratio of reported prolonged anaesthesia from different concentrations of local anaesthetic agents
|Haas and Lennon4||1||6.76||5|
|Hillerup and Jensen6||1||1||14|
A small case series of prolonged anaesthesia from higher concentration local anaesthetic agents which have resulted in mandibular nerve problems is also presented. The lingual nerve was affected in four of the cases, and the mandibular nerve in one.
A medically fit 43-year-old male had a right mandibular block for cementation of a crown to the right mandibular first molar. One 2.2 ml cartridge of 4% local anaesthetic was administered by an experienced dentist. At the time of the injection he experienced an electric shock sensation at the site of the injection. Dysaesthesia, or painful numbness of the lingual nerve, continued but the mandibular nerve recovered.
The patient experienced difficulty in talking, eating and had altered taste. Soon after the injection he was accused of being under the influence of alcohol by a business associate as he couldn’t speak properly. Despite being given documentation of the nature of the problem, he has not received further earthmoving contract work from that associate. At 23 weeks following the injection he was examined by a neurologist who found a profound anaesthesia of all the right lingual nerve. There was a hyperaesthetic burning sensation on contact and loss of taste.
The patient was diagnosed as having a severe dysaesthetic injury but with some signs of recovery. On follow-up at 21 months there was no improvement.
A medically fit 61-year-old male had a right mandibular block for restoration of the right mandibular second premolar. One 2.2 ml cartridge of 4% local anaesthetic was administered by an experienced dentist. The injection was not painful but paraesthesia of the right lingual nerve persisted with the long buccal and mandibular nerves recovering sensation normally.
On review four weeks later, there had been a noticeable resolution of the paraesthesia reported by the patient. There was no interference with taste. On objective testing there was an equal response to sharp and blunt, two-point and directional sense between the right and left lingual nerves. The patient was diagnosed as having mild paraesthetic sensation which would resolve. On follow-up at four months, there was still a mild paraesthetic sensation.
A medically fit 66-year-old male had bilateral mandibular blocks for restoration of mandibular molars. One cartridge of 4% local anaesthetic was used for each side and this was administered by the same experienced dentist as Case 2. The left side mandibular nerve recovered normally but on the right side mental nerve anaesthesia persisted. He had normal right and left lingual nerve sensation and no taste deficit.
On review 10 days after the injection, the patient felt there had been a noticeable improvement in the last few days. On objective testing there was equal response to sharp and blunt, two-point and directional sense between the right and left mental nerves. The patient was diagnosed as having a mild paraesthetic sensation which would resolve. On follow-up at four months, there was still a mild paraesthetic sensation.
A medically fit 59-year-old male had a right mandibular block for filling his right mandibular second molar. One cartridge of 2.2 ml of 4% local anaesthetic was administered by an experienced general dentist. The patient experienced an electric shock sensation at the time of the injection. Dysaesthesia, or painful numbness of the right tongue, persisted but the mandibular nerve recovered.
The patient experienced difficulty in talking, eating and had altered taste. He is a health professional and had difficulty talking to patients. The area of numbness slowly decreased from posterior to anterior and by one year it was mainly a painful tongue tip. He was examined at 11 months and was found to have an equal right and left side sharp and blunt, two-point and directional sense. A 1 cm area on the right tongue tip was hypersensitive to contact. Taste was still altered. Nearly two years after the procedure, there has been no further improvement.
He was diagnosed as having a severe dysaesthetic injury of the right lingual nerve with evidence of slow recovery. He was placed on one vitamin B complex tablet per day. On follow-up at 12 months, he has ongoing problems.
A medically fit 55-year-old female had a right mandibular block for restoration of a right mandibular second molar. One cartridge of 2.2 ml of 3% local anaesthetic (mepivacaine HCl) was injected but failed to give adequate anaesthesia, so the experienced general dentist gave a further 2.2 ml. There was no pain at the injection site. The following day the patient rang to report ongoing numbness and tingling of the right lingual nerve. The right mandibular nerve had fully resolved.
The patient was examined at five weeks and found to have reduced sensation to objective sharp and blunt, two-point and directional sense. She had altered taste but normal olfaction. She was put on one tablet per day of vitamin B complex. She was advised to smell food first and place food on the left side of the tongue first to help improve her sense of taste.
She was diagnosed as having a severe right lingual nerve injury with probable slow recovery. She had loss of taste which was of particular concern to her as she was a keen amateur cook who liked cooking for her large extended family. There has been no resolution more than one year after the local anaesthetic was administered.
There are similarities in these case reports, all patients were fit and well, middle-aged Australians who had mandibular blocks for restorative purposes administered by experienced dentists. Two of the patients had electric shock sensations on injections but three did not. One had a repeat injection. Although it is commonly thought that electric shock pain on injection or repeat injections are associated with an increase in prolonged anaesthesia, this is not supported by the literature.2,6 They all suffered prolonged abnormal sensation in the mandibular or lingual nerves. None of these cases have yet to be fully resolved. The alteration in sensation appears to be different to surgically damaged nerves as there is a return of sensation as tested by objective tests, but the nerve area burns and is dysaesthetic. This gives the impression that the nerve is recovering but to date they have not recovered. Three of the patients had loss of taste.
This adverse complication to local anaesthesia resulted in considerable interference in the patients’ ability to generally enjoy life and work. Three patients presented with serious problems in talking, eating and taste.
These five cases support the argument that there is an increased risk of prolonged anaesthesia of the mandibular and, particularly, the lingual nerve from higher concentration local anaesthetic agents. The impact of this is illustrated as they were collected over a short period by the authors. Although it has been traditionally considered that direct needle trauma is the cause of paraesthesia, a recent review does not provide support for this mechanism.2 It must be appreciated that the incidence of these adverse responses is low when compared to the total number of block anaesthetics given. The international literature shows a risk of prolonged anaesthesia with an incidence ranging from 1 in 26 0007 to 1 in 750 0004 injections. The recent Australian study found an incidence of 1 in 27 415 although this figure has wide confidence limits.2
Prolonged anaesthesia may also occur when lower 2% local anaesthetic agents are used.2 The key issue is that the evidence indicates that there is a greater risk with a higher concentration of local anaesthetics. The increased risk is conservatively estimated at 5- to 7-fold.4–7 Other more anecdotal papers report an up to ×20 increase.11,12 Hence, clinicians need to first consider whether local anaesthesia is required at all for some restorative procedures. Up until the 1970s, local anaesthesia was largely reserved for extractions or very deep dentine or pulpal procedures. Now virtually every dental procedure is preceded by administration of local anaesthesia. Given the severity of the complications these five patients have had to endure, it raises the question of the need to administer local anaesthetic for every procedure; the wishes of each patient should be met but it is suggested that avoidance be considered if tolerated. Blocks are administered for most mandibular procedures but experienced clinicians have noted it is possible to effectively anaesthetize all of the teeth of the mandible, including the molars, by infiltration. Deposition of more local anaesthetic (than has been traditionally taught) on the lingual side allows this. Infiltration should be used for premolar and anterior teeth. Next to consider is the question of whether there is a benefit from using higher concentrations of a local anaesthetic agent as compared to a lower concentration. A randomized double-blind study showed no clinical differences between 4% and 2% articaine, both with 1 in 200 000 epinephrine infiltrations for tooth extractions.14 There was a lively correspondence in the Journal of the American Dental Association which compared 4% articaine with 2% lidocaine, and it was stated that it was difficult to demonstrate the superiority of articaine over lidocaine.15 The fact that higher concentrations of local anaesthetic agents are more neurotoxic than lower concentrations of the same agent has been conclusively shown in laboratory studies using lignocaine.16,17
If prolonged anaesthesia occurs following a local anaesthetic injection, the patient must be reviewed. They should not be dismissed or promised it will resolve. Referral to a specialist with an interest and experience in nerve injuries is strongly recommended. The indemnity insurer should be notified. The injury should be carefully documented and monitored until resolution or permanence. The use of a low daily dose of vitamin B complex to aid recovery has been recommended.2
There is a difficulty in determining the number and seriousness of prolonged anaesthesia to any concentration of local anaesthesia in Australia as there is no mandatory reporting requirement.2 One option is for dental practitioners to report current cases to the Australian Adverse Drug Reaction Committee of the Therapeutic Goods Administration. Reports should include the drug dose and type, the indication for the block, and the nature and duration of adverse reaction.18
The conclusion from this case series is that if sound therapeutic principles are to be followed, clinicians should use the minimum effective concentration of local anaesthetic agents for block anaesthetics. The higher concentrations can be more safely used for infiltrations, particularly in high pain situations such as acute irreversible pulpitis.