Even levobupivacaine and ropivacaine (single-enantiomer derivatives), developed to ameliorate cardiovascular side effects, still harbor the potential to disrupt cardiac function. Toxicity from anesthetic combinations is additive. Endocrine
Endocrine and metabolic systems only have slightly adverse effects with most cases being without clinical repercussions. Immunologic allergy
Adverse reactions to local anesthetics (especially the esters) are not uncommon, but legitimate allergies are very rare. Allergic reactions to the esters is usually due to a sensitivity to their metabolite, para-aminobenzoic acid, and does not result in cross-allergy to amides. Therefore, amides can be used as alternatives in those patients. Nonallergic reactions may resemble allergy in their manifestations. In some cases, skin tests and provocative challenge may be necessary to establish a diagnosis of allergy. Also cases of allergy to paraben derivatives occur, which are often added as preservatives to local anesthetic solutions. Methemoglobinemia
Methemoglobinemia is a process where iron in hemoglobin is altered, reducing its oxygen-carrying capability, which produces cyanosis and symptoms of hypoxia. Exposure to aniline group chemicals such as   benzocaine, lidocaine, and prilocaine can produce this effect, especially benzocaine. The systemic toxicity of prilocaine is comparatively low, but its metabolite, o-toluidine, is known to cause methemoglobinemia. Second-generation effects
Application of local anesthetics during oocyte removal during in vitro fertilisation has been up to debate. Pharmacological concentrations of anesthetic agents have been found in follicular fluid. Clinical trials have not concluded any effects on pregnant women.
There is greatest chance of this occurring in a posterior superior alveolar nerve block or in a pterygomandibular block.Giving local anaesthesia to patients with liver disease can have significant consequences. Thorough evaluation of the disease should be carried out to assess potential risk to the patient as in significant liver dysfunction, the half-life of amide local anaesthetic agents may be drastically increased thus increasing the risk of overdose. Local anaesthetics and vasoconstrictors may be administered to pregnant patients however it is very important to be extra cautious when giving a pregnant patient any type of drug. Lidocaine can be safely used but bupivacaine and mepivacaine should be avoided. Consultation with the obstetrician is vital before administrating any type of local anaesthetic to a pregnant patient. Recovery
Permanent nerve damage after a peripheral nerve block is rare. Symptoms are likely to resolve within a few weeks. The vast majority of those affected (92%–97%) recover within four to six weeks; 99% of these people have recovered within a year. An estimated one in 5,000 to 30,000 nerve blocks results in some degree of permanent persistent nerve damage.Symptoms may continue to improve for up to 18 months following injury. Potential side effects
General systemic adverse effects are due to the pharmacological effects of the anesthetic agents used. The conduction of electric impulses follows a similar mechanism in peripheral nerves, the central nervous system, and the heart. The effects of local anesthetics are, therefore, not specific for the signal conduction in peripheral nerves.