[Principles of the pharmacology of local anesthetics]. / Grundlagen der Pharmakologie von Lokalanästhetika.

The development of local anesthetics revolutionized the performance of painful interventions. Local anesthetics have an effect on voltage-gated sodium channels in nerve fibers and modulate the conduction of impulses. With respect to the chemical structure, local anesthetics can be divided into amide and ester types. The structural differences of local anesthetics have an influence on the duration of action, the degradation pathways and specific side effects. Severe adverse events include cardiotoxicity and neurotoxicity. In addition to basic measures, such as the monitoring and securing of vital parameters, lipid infusion represents a treatment option in cases of intoxication. The recent developments of local anesthetics are particularly concerned with the reduction of toxicity and prolonging the duration of action.

Grouping of orally ingested silica nanomaterials via use of an integrated approach to testing and assessment to streamline risk assessment.

BACKGROUND: Nanomaterials can exist in different nanoforms (NFs). Their grouping may be supported by the formulation of hypotheses which can be interrogated via integrated approaches to testing and assessment (IATA). IATAs are decision trees that guide the user through tiered testing strategies (TTS) to collect the required evidence needed to accept or reject a grouping hypothesis. In the present paper, we investigated the applicability of IATAs for ingested NFs using a case study that includes different silicon dioxide, SiO2 NFs. Two oral grouping hypotheses addressing local and systemic toxicity were identified relevant for the grouping of these NFs and verified through the application of oral IATAs. Following different Tier 1 and/or Tier 2 in vitro methods of the TTS (i.e., in vitro dissolution, barrier integrity and inflammation assays), we generated the NF datasets. Furthermore, similarity algorithms (e.g., Bayesian method and Cluster analysis) were utilized to identify similarities among the NFs and establish a provisional group(s). The grouping based on Tier 1 and/or Tier 2 testing was analyzed in relation to available Tier 3 in vivo data in order to verify if the read-across was possible and therefore support a grouping decision. RESULTS: The measurement of the dissolution rate of the silica NFs in the oro-gastrointestinal tract and in the lysosome identified them as gradually dissolving and biopersistent NFs. For the local toxicity to intestinal epithelium (e.g. cytotoxicity, membrane integrity and inflammation), the biological results of the gastrointestinal tract models indicate that all of the silica NFs were similar with respect to the lack of local toxicity and, therefore, belong to the same group; in vivo data (although limited) confirmed the lack of local toxicity of NFs. For systemic toxicity, Tier 1 data did not identify similarity across the NFs, with results across different decision nodes being inconsistent in providing homogeneous group(s). Moreover, the available Tier 3 in vivo data were also insufficient to support decisions based upon the obtained in vitro results and relating to the toxicity of the tested NFs. CONCLUSIONS: The information generated by the tested oral IATAs can be effectively used for similarity assessment to support a grouping decision upon the application of a hypothesis related to toxicity in the gastrointestinal tract. The IATAs facilitated a structured data analysis and, by means of the expert's interpretation, supported read-across with the available in vivo data. The IATAs also supported the users in decision making, for example, reducing the testing when the grouping was well supported by the evidence and/or moving forward to advanced testing (e.g., the use of more suitable cellular models or chronic exposure) to improve the confidence level of the data and obtain more focused information.

Aerosolization Performance, Antitussive Effect and Local Toxicity of Naringenin-Hydroxypropyl-ß-Cyclodextrin Inhalation Solution for Pulmonary Delivery.

The aim of present study was to evaluate the feasibility of a naringenin-hydroxypropyl-ß-cyclodextrin (naringenin-HPßCD) inhalation solution for pulmonary delivery. Naringenin, a flavanone derived from citrus fruits, has been proven to exhibit excellent peripheral antitussive effect. To address the limitation of its poor oral bioavailability and low local concentration in the lung, a naringenin-HPßCD inhalation solution was prepared for pulmonary delivery. The aerosolization performance of formulation was evaluated by next generation impactor (NGI). Both dose-dependent and time-dependent antitussive effects of naringenin-HPßCD inhalation solution on acute cough induced by citric acid in guinea pigs were investigated. In vitro toxicity of naringenin-HPßCD inhalation solution in pulmonary Calu-3 cells was evaluated by MTS assay, and in vivo local toxicity investigation was achieved by assessing bronchoalveolar lavage (BALF) and lung histology after a 7-day inhalation treatment in guinea pigs. Fine particle fraction (FPF) of the formulation was determined as 53.09%. After inhalation treatment of 15 min, naringenin-HPßCD inhalation solution within the studied range of 0.2-3.6 mg/kg could dose-dependently reduce the cough frequency with the antitussive rate of 29.42-39.42%. Naringenin-HPßCD inhalation solution in concentration range of 100-400 µM did not decrease cell viability of Calu-3 cells, and the maximum effective dose (3.6 mg/kg) was non-toxic during the short-term inhalation treatment for guinea pigs. In conclusion, naringenin-HPßCD inhalation solution was capable for nebulization and could provide rapid response with reduced dose for the treatment of cough.

Toxicological testing of a photoactive phthalocyanine-based antimicrobial substance.

The aim of the study was toxicological testing of an innovative and efficient antimicrobial agent based on photoactive phthalocyanine (Pc) derivative. A promising Aluminium phthalocyanine (AlPc) with efficient and stable antimicrobial effects was subjected to a battery of toxicological tests to avoid local and systemic toxicity hazard. In compliance with the current European legislation restricting the use of experimental animals, the methods comprised exclusively in vitro procedures based on cellular and tissue models of human origin or mimicking human tissues. The battery of toxicological tests to identify local toxicity included skin corrosion/irritation, eye irritation, and phototoxicity. The basic systemic toxicity tests included acute toxicity, skin sensitization, genotoxicity, and endocrine disruption. The results showed that AlPc induced skin and eye irritation, exhibited borderline sensitization potential and mutagenic potential in one test strain of the Ames test, which was not confirmed in the chromosome aberration test. The AlPc was found to be phototoxic. The results from the cytotoxicity test designed for acute oral toxicity estimation were not conclusive, the acute toxicity potential has to be determined by conventional tests in vivo. Regarding endocrine disruption, no agonistic activity of the AlPc on human estrogen receptor α, nor human androgen receptor was observed. The skin penetration/absorption test revealed that the AlPc has not penetrated into the dermis and receptor fluid, confirming no risk of systemic exposure via the bloodstream.

Local Anesthetic Systemic Toxicity (LAST): Increasing Awareness Through Education.

PURPOSE: Local anesthetics are used for procedures in various settings. Although complications related to local anesthetic use is rare, adverse events do occur. A significant knowledge deficit was identified regarding local anesthetic systemic toxicity (LAST) signs, symptoms, and treatment. DESIGN: A learning needs assessment was performed at a local hospital to determine the nurses' baseline knowledge of LAST signs, symptoms, and treatment. METHODS: A self-paced web-based learning module was developed and completed by clinical nurses with an immediate post survey and 6-month follow-up survey. FINDINGS: The repeat learning needs assessment immediately after education resulted in more than 50% improvement in nurses' knowledge of LAST. A 6-month follow-up survey indicated that the gain in knowledge, signs, symptoms, and treatment of LAST was maintained. CONCLUSIONS: An educational gap was identified regarding clinical nurses' knowledge of LAST. An educational program was designed to improve baseline knowledge. The program goal was successfully met with more than half of nurses being able to identify signs, symptoms, and treatment of LAST.

LOCAL ANESTHETICS AND STEROIDS: CONTRAINDICATIONS AND COMPLICATIONS - CLINICAL UPDATE.

The objective of this clinical update, based on recently published literature, was to discuss incidence and characteristics of the most relevant clinical adverse effects associated with local anesthetic and steroid use in regional anesthesia and treatment of acute or chronic pain. A comprehensive review of the English-language medical literature search utilizing PubMed, Ovid Medline® and Google Scholar from 2015 to 2018 was performed. This narrative review provides anesthesia practitioners with updated evidences on complications and contraindications of local anesthetic and steroid use with emphasis on current points of view regarding prevention, early diagnosis and treatment of adverse events.

Toxicology Evaluation of Drugs Administered via Uncommon Routes: Intranasal, Intraocular, Intrathecal/Intraspinal, and Intra-Articular.

As the need for nasal, ocular, spinal, and articular therapeutic compounds increases, toxicology assessments of drugs administered via these routes play an important role in human safety. This symposium outlined the local and systemic evaluation to support safety during the development of these drugs in nonclinical models with some case studies. Discussions included selection of appropriate species for the intended route; conducting nonclinical studies that closely mimic the intended use with adequate duration; functional assessment, if deemed necessary; evaluation of local tissues with special histological staining procedure; and evaluations of safety margins based on local and systemic toxicity.

Myoglobin does not predict local toxicity in isolated limb perfusion.

INTRODUCTION: Isolated limb perfusion (ILP) is a treatment option for patients with in-transit metastases of malignant melanoma in the extremities, as well as locally advanced sarcoma. ILP allows for a delivery of high-dose chemotherapy to an isolated extremity with minimal systemic toxicity. However, local toxicity like oedema, blistering, nerve damage and compartment syndrome can occur. Myoglobin measurements have been used as a screening method to predict the most severe cases of local toxicity. The aim was to investigate if myoglobin is a predictive factor for local toxicity after ILP in patients with melanoma in-transit metastases. METHODS: One hundred and ninety-three patients were treated for the first time with ILP for in-transit metastases between 2001 and 2015. Myoglobin was measured once the first hours after the perfusion (POD0), and for the first five post-operative days (POD1-5). Local toxicity was graded according to Wieberdink, and grouped in mild (I and II), moderate (III), and severe (IV and V). Wieberdink-groups were compared with myoglobin measurements, and myoglobin measurements were compared between gender, perfusion time, perfusion temperature and cannulated vessels. RESULTS: There is no statistically significant difference in myoglobin serum levels during the first five days post perfusion between patients suffering from mild, moderate or severe local toxicity. There is no difference between toxicity groups when it comes to distribution of sex, tumour size, or tumour numbers. CONCLUSION: Levels of myoglobin do not predict local toxicity for patients with melanoma in-transit metastases treated with ILP when measured during the first five post-operative days.

Electrochemotherapy - Supplementary Treatment for Loco-regional Metastasized Breast Carcinoma Administered to Concomitant Systemic Therapy.

BACKGROUND: Electrochemotherapy (ECT) is an established procedure for treating breast cancer loco-regional recurrences following surgical intervention and/or radiotherapy. Limited information is available on ECT application as a concomitant procedure to systemic therapy in recurrent breast cancer. The primary objective of this study was to determine if the application of ECT in close temporal relation to systemic chemotherapy could lead to increased local and/or systemic side effects. For this purpose we evaluated the safety of ECT as a supplemental local therapy to systemic therapy. ECT local and systemic toxicity and side effects were recorded and whether the anticipated local therapeutic effect of ECT would be influenced by the concomitant use of systemic therapies was investigated. PATIENTS AND METHODS: This is an observational study. Thirty three patients with loco-regional metastasized breast carcinoma were treated and observed over a period of three years with 46 ECT applications for local tumour control in addition to established systemic therapy. A specific timeline for ECT administration was not fixed up, but was generally performed one week before the following chemotherapy administration with the aim to avoid the so called nadir, this means the peak period with risk of neutropenia. RESULTS: Data was collected over a period of three years on a population of 33 metastatic patients. Fifteen patients, received neo-adjuvant therapy as part of their primary treatment, but still had an advanced stage tumour. Some patients received repeated ECT applications. Objective tumour response was observed in 90% of the treated patients. Patients showed no increased local toxicity, especially no higher dermal toxicity, e.g. formation of local necrosis. CONCLUSIONS: ECT proved to be an effective supplement to a cytotoxic systemic therapy, especially for high-risk patients who did not respond well to systemic therapy of loco-regional metastases, without creating any greater systemic or loco-regional toxicities.

Lupeol derivative mitigates Echis carinatus venom-induced tissue destruction by neutralizing venom toxins and protecting collagen and angiogenic receptors on inflammatory cells.

BACKGROUND: Echis carinatus bite is a serious threat in South-Asian countries including India, as it causes highest number of deaths and terrifying long-term tissue destruction at the bitten site. Although venom metalloproteinases and hyaluronidases are the suggested key players, studies on the effect of venom on polymorphonuclear cells, peripheral blood mononuclear cells and platelets, and their role in long-term tissue destruction are still in infancy. While, the effect of venom on collagen receptors, integrin α2ß1/GP VI/DDR1 and CX3CR1 chemokine receptor present on these cells is an untouched area. METHODS: Lupeol, lupeol acetate, its synthetic derivatives 2-8 were screened for inhibition of E. carinatus venom induced-hemorrhage in mouse model where compound 8 was found to be the most potent. Further, compound 8 efficiently neutralized venom induced hemorrhage, edema, dermonecrosis, myonecrosis, myotoxicity, pro-coagulant, oxidative stress, inflammatory cytokines and cleavage of collagen and CX3CR1 receptors on inflammatory cells in in vivo, in silico, ex vivo and in vitro studies. CONCLUSIONS: This study for the first time demonstrated the cleavage of collagen receptors and the receptor for angiogenesis and wound healing by the venom and its inhibition by compound 8, as these are important for firm adhesion of inflammatory cells at the damaged site to resolve inflammation and promote tissue repair. GENERAL SIGNIFICANCE: This study provides a lead in venom pharmacology, wherein, compound 8 could be a therapeutic agent for the better management of viper venom-induced long-term tissue destruction.

[Principles of the pharmacology of local anesthetics]. / Grundlagen der Pharmakologie von Lokalanästhetika.

The development of local anesthetics revolutionized the performance of painful interventions. Local anesthetics have an effect on voltage-gated sodium channels in nerve fibers and modulate the conduction of impulses. With respect to the chemical structure, local anesthetics can be divided into amide and ester types. The structural differences of local anesthetics have an influence on the duration of action, the degradation pathways and specific side effects. Severe adverse events include cardiotoxicity and neurotoxicity. In addition to basic measures, such as the monitoring and securing of vital parameters, lipid infusion represents a treatment option in cases of intoxication. The recent developments of local anesthetics are particularly concerned with the reduction of toxicity and prolonging the duration of action.

Pharmacokinetics and Pharmacodynamics of Antibody-Drug Conjugates Administered via Subcutaneous and Intratumoral Routes.

We hypothesize that different routes of administration may lead to altered pharmacokinetics/pharmacodynamics (PK/PD) behavior of antibody-drug conjugates (ADCs) and may help to improve their therapeutic index. To evaluate this hypothesis, here we performed PK/PD evaluation for an ADC administered via subcutaneous (SC) and intratumoral (IT) routes. Trastuzumab-vc-MMAE was used as the model ADC, and NCI-N87 tumor-bearing xenografts were used as the animal model. The PK of multiple ADC analytes in plasma and tumors, and the in vivo efficacy of ADC, after IV, SC, and IT administration were evaluated. A semi-mechanistic PK/PD model was developed to characterize all the PK/PD data simultaneously. In addition, local toxicity of SC-administered ADC was investigated in immunocompetent and immunodeficient mice. Intratumoral administration was found to significantly increase tumor exposure and anti-tumor activity of ADC. The PK/PD model suggested that the IT route may provide the same efficacy as the IV route at an increased dosing interval and reduced dose level. SC administration of ADC led to local toxicity and reduced efficacy, suggesting difficulty in switching from IV to SC route for some ADCs. As such, this manuscript provides unprecedented insight into the PK/PD behavior of ADCs after IT and SC administration and paves the way for clinical evaluation of these routes.

Stereotactic partial breast irradiation in primary breast cancer: A comprehensive review of the current status and future directions.

In selected low-risk breast cancer patients, accelerated partial breast irradiation (APBI) may represent an alternative option to the whole breast irradiation to reduce the volume of irradiated breast and total treatment duration. In the last few years, preliminary data from clinical trials showed that stereotactic partial breast radiotherapy may have the advantage to be less invasive compared to other APBI techniques, with preliminary good results in terms of local toxicity and cosmesis: the use of magnetic resonance, fiducial markers in the tumor bed, and new breast devices support both a precise definition of the target and radiation planning. Systematic review registration: https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021257856, identifier CRD42021257856.

Spermine with Sodium Taurocholate Enhances Pulmonary Absorption of Macromolecules in Rats.

The improvement effect of the combined use of spermine (SPM), a polyamine, with sodium taurocholate (STC) on the pulmonary drug absorption was investigated utilizing poorly absorbable drugs with various molecular sizes in rats. The pulmonary absorption of rebamipide, a low molecular but poorly absorbable drug after oral administration, was significantly improved by the combined use of SPM with STC (SPM-STC formulation), while poly- L-lysine did not show a significant change in rebamipide absorption from the lungs. Furthermore, the safety of the SPM-STC formulation for the lungs was assessed in rats by the histopathological study and any local toxicity was not observed while poly-L-lysine, a typical chemical causing the toxicity for the epithelial cells, provided several histopathological changes. In addition, the SPM-STC formulation significantly improved the pulmonary absorption of fluorescein isothiocyanate dextran 4 (FD-4, Mw ca 4000) and interferon-α (IFN-α, Mw ca 25,000) as well. Our present results clearly indicated that the SPM-STC formulation significantly improved the pulmonary absorption of poorly absorbable small and large molecular drugs without any harmful effects on the lungs. Therefore, the SPM-STC formulation would be a useful one for the pulmonary absorption of drugs, specifically macromolecular ones, which are very difficult to be absorbed after oral administration.

Intra-articular use of analgesic/antinflammatory drugs in dogs and horses.

Joint pain is a major cause of lameness in animals such as horses and dogs, and it may affect their athletic performance and quality of life. The intra-articular administration of analgesic/antinflammatory drugs is a common practice in veterinary medicine, for both lameness diagnosis and joint pain management. It is used either perioperatively, such as in animals undergoing arthroscopy/arthrotomy, and in osteoarthritic animals. However, evidence regarding efficacy and safety of each drug is limited, and controversies persist in these areas. In particular, it is often uncertain whether a defined treatment is effective by simply relieving the symptomatic pain associated with the joint disease, or whether it has a positive effect on the joint environment. Moreover, there is still much hesitation about treatments for joint diseases, related to the time of their application for the best outcome, and to any possible deleterious side effects. This article includes a review of the literature concerning the main analgesic/antinflammatory drugs used intra-articularly for managing acute and chronic joint pain/inflammation in dogs and horses. Three main issues for each class of drugs are considered, including clinical efficacy, pharmacokinetics, and local cytotoxic effects.

A Fixed-Dose Combination, QXOH/Levobupivacaine, Produces Long-Acting Local Anesthesia in Rats Without Additional Toxicity.

QXOH, a QX314 derivative with longer duration and lesser local toxicity, is a novel local anesthetic in preclinical drug development. Previous studies demonstrated that bupivacaine can prolong the effects of QX314. So, we attempted to combine QXOH with levobupivacaine to shorten the onset time and lengthen the duration. In this study, we investigated the efficacy, local and systemic toxicity in rats. In subcutaneous infiltration anesthesia, the inhibition of cutaneous trunci muscle reflex for QXOH-LB was greater than QXOH and levobupivacaine in the first 8 h (QXOH-LB vs. QXOH, P = 0.004; QXOH-LB vs. LB, P = 0.004). The completely recovery time for QXOH-LB (17.5 ± 2.5 h) was significantly longer than levobupivacaine (9.0 ± 1.3 h, P = 0.034) and QXOH (9.8 ± 0.9 h, P = 0.049). In sciatic nerve block, QXOH-LB produced a rapid onset time, which was obviously shorter than QXOH. For sensory, the time to recovery for QXOH-LB was 17.3 ± 2.6 h, which was statistically longer than 6.0 ± 1.8 h for QXOH (P = 0.027), and 4 h for levobupivacaine (P = 0.001). Meanwhile, the time to motor recovery for QXOH-LB was 7.9 ± 2.8 h, significantly longer than 4 h for levobupivacaine (P = 0.003) but similar to 6.0 ± 1.7 h for QXOH (P = 0.061). In local toxicity, there was no significant difference of histological score regarding muscle and sciatic nerve in QXOH-LB, QXOH, levobupivacaine and saline (P < 0.01). In the combination, the interaction index of LD50 was 1.39, indicating antagonistic interaction between QXOH and levobupivacaine in terms of systemic toxicity. In this study, we demonstrated that QXOH-LB produced cutaneous anesthesia which was 2-fold greater than that produced by QXOH or LB alone, and elicited sciatic nerve block with a potency that was 5- and 3-fold that of LB and QXOH, respectively. Local tissue inflammation by QXOH-LB was mild, similar to that induced by LB. This fixed-dose combination led to an antagonistic interaction between QXOH and LB in terms of systemic toxicity. These results suggested that QXOH-LB induced a long-lasting local anesthesia, likely, avoiding clinically important local and systemic toxicities.

Arachidonic acid with taurine enhances pulmonary absorption of macromolecules without any serious histopathological damages.

Therapeutic peptides and protein are being used in several indications; however, their poor permeability still remains to be solved. This study focused on the pulmonary route of macromolecules. First, the effects of arachidonic acid (AA) as an absorption enhancer on drug serum concentration, after intratracheal administration, were investigated in rats. Second, the safety of AA was assessed in rats in an acute toxicity study for 7days. AA enhanced the exposure of both interferon-α (IFN-α) and fluorescein isothiocyanate 4000 (FD-4). In addition, the histopathological analysis indicated that AA caused alveolitis and bronchitis in rats. In combination with Taurine (Tau), these lung injuries were prevented through the histopathological analysis. The combined use of Tau with AA did not show any changes in the pharmacokinetics of FD-4. From these results, we suggest the combined use of AA with Tau as a novel formulation on the pulmonary route of macromolecule drugs. This formulation could improve the bioavailability of macromolecule drugs without any serious local damage to the lungs.

QX-OH, a QX-314 derivative agent, produces long-acting local anesthesia in rats.

QX-314 has been shown to produce long-acting local anesthesia in vivo in animals; however, translation to humans has been impeded by concerns about toxicity. We investigated whether the newly emerged QX-OH molecule could confer long-lasting anesthesia with a low local toxicity in rats. In rat sciatic nerve block model, QX-OH 25mM produced a longer sensory block than QX-314 25mM (median [25th, 75th percentiles], 5.5 [4.25, 6] h vs. 3 [3, 4] h; P=0.03). QX-OH 35mM produced a longer sensory block than QX-314 35mM (8 [6, 12] h vs. 6 [4, 6.5] h, P=0.038). QX-OH at 35 and 45mM generated longer motor blocks than QX-314, with tissue toxicity less than that of QX-314 at the same concentration. In contrast with bupivacaine, QX-OH was clearly superior in terms of sensory and motor blockade durations after a single bolus injection. There was no significant difference in tissue toxicity between QX-OH (25 and 35mM) and bupivacaine. In rat cutaneous trunci pinprick model, the QX-OH-induced pain threshold remained significantly different from baseline at 6h (25mM, P<0.0001), 10h (35mM, P<0.0001), and 12h (45mM, P<0.0001). The time required for full recovery from the subcutaneous anesthetic effect was significantly longer for QX-OH than for QX-314 and bupivacaine. So QX-OH produced concentration-dependent, reversible, and long-acting local anesthesia in animal models with a moderate local toxicity.

Dosis de prueba para anestesia regional / Test dose in regional anesthesia

Introducción: El uso de la dosis de prueba en anestesia regional no está estandarizado: no existe consenso sobre su dosis, el anestésico o el tipo de fármaco que se debe utilizar, y muchos anestesiólogos no la utilizan rutinariamente en su práctica. Objetivo: Hacer una revisión de la dosis de prueba para anestesia regional, sus indicaciones, su utilidad, los fármacos utilizados para ella y los signos considerados como positivos. Métodos: Se realizó una búsqueda no sistemática de publicaciones en bases de datos médicas que incluyeron MedLine, SciELO y Embase. Resultados:La aplicación de la dosis de prueba previa a la inyección total de anestésico local ayuda a detectar la colocación inadvertida de una aguja o catéter en el espacio intravascular o subaracnoideo. Conclusiones: La dosis de prueba debe utilizarse siempre que se utilicen dosis críticas de anestésico local o incluso dosis normales en pacientes con factores de riesgo. En analgesia para trabajo de parto la dosis de prueba no es necesaria.

Introduction: The use of the test dose in regional anesthesia is not standardized, and there is no consensus regarding what dose it should be or about the anesthetic or type of drug to be used. Moreover, many anesthesiologists do not use it routinely in their practice. Objective: To review the test dose for regional anesthesia, its indications and utility, the drugs used, and positive signs. Methods: A non-systematic search was conducted in medical database publications inclu-ding MedLine, SciELO and Embase. Results:The applicationofthe test dose beforegiving the fullinjectionofthe local anesthetic helps in detecting the inadvertent placement of the needle or catheter in the intravascular or the subarachnoid spaces. Conclusions: The test dose must be used every time critical doses of a local anesthetic are utilized or when normal doses are given to patients with risk factors. The test dose is not necessary in labor analgesia.