Plasma levels, protein binding, and elimination data of lidocaine and active metabolites in cardiac patients of various ages

A study on reducing the absorption of lidocaine from the airway in cats

Purpose:

To determine if the combination of lidocaine with epinephrine or gamma globulin would decrease the rate or reduce the amount of local absorption of lidocaine through the airway.

Methods:

Twenty adult male cats were randomly and evenly distributed into four groups: 1) Group LG: lidocaine administered with gamma globulin; 2) Group LS: lidocaine administered with physiological saline); 3) Group LE: lidocaine administered with epinephrine; 4) Group C: control group. Invasive blood pressure, heart rate, and concentration of lidocaine were recorded before and after administration.

Results:

The peak of plasma concentrations appeared difference (Group LG: 1.39 ± 0.23 mg/L; Group LS: 1.47 ± 0.29 mg/L and Group LE: 0.99 ± 0.08 mg/L). Compared to Group C, there were significant differences in the average heart rate of Groups LG, LS, and LE (P < 0.05). The average systolic blood pressures were significantly different when each group was compared to Group C (P < 0.05). The biological half-life, AUC0-120, peak time, and half-life of absorption among the three groups have not presented statistically significant differences (P > 0.05).

Conclusion:

Administering lidocaine in combination with gamma globulin through airway causes significant decrease the rate and reduce the amount of local absorption of lidocaine in cats.

Bioanalysis for plasma protein binding studies in drug discovery and drug development: views and recommendations of the European Bioanalysis Forum

Plasma protein binding (PPB) is an important parameter for a drug’s efficacy and safety that needs to be investigated during each drug-development program. Even though regulatory guidance exists to study the extent of PPB before initiating clinical studies, there are no detailed instructions on how to perform and validate such studies. To explore how PPB studies involving bioanalysis are currently executed in the industry, the European Bioanalysis Forum (EBF) has conducted three surveys among their member companies: PPB studies in drug discovery (Part I); in vitro PPB studies in drug development (Part II); and in vivo PPB studies in drug development. This paper reflects the outcome of the three surveys, which, together with the team discussions, formed the basis of the EBF recommendation. The EBF recommends a tiered approach to the design of PPB studies and the bioanalysis of PPB samples: ‘PPB screening’ experiments in (early) drug discovery versus qualified/validated procedures in drug development.

Pharmacologically active drug metabolites: impact on drug discovery and pharmacotherapy

Metabolism represents the most prevalent mechanism for drug clearance. Many drugs are converted to metabolites that can retain the intrinsic affinity of the parent drug for the pharmacological target. Drug metabolism redox reactions such as heteroatom dealkylations, hydroxylations, heteroatom oxygenations, reductions, and dehydrogenations can yield active metabolites, and in rare cases even conjugation reactions can yield an active metabolite. To understand the contribution of an active metabolite to efficacy relative to the contribution of the parent drug, the target affinity, functional activity, plasma protein binding, membrane permeability, and pharmacokinetics of the active metabolite and parent drug must be known. Underlying pharmacokinetic principles and clearance concepts are used to describe the dispositional behavior of metabolites in vivo. A method to rapidly identify active metabolites in drug research is described. Finally, over 100 examples of drugs with active metabolites are discussed with regard to the importance of the metabolite(s) in efficacy and safety.

Population pharmacokinetics of lidocaine administered during and after cardiac surgery

OBJECTIVE

The objective of this study was to determine the pharmacokinetics of lidocaine in a 48-hour infusion in patients undergoing cardiac surgery with cardiopulmonary bypass (CPB).

DESIGN

A retrospective substudy of a clinical trial assessing the efficacy of intravenous lidocaine for postoperative cognitive decline.

SETTING

A university hospital.

PARTICIPANTS

Ninety-nine patients undergoing cardiac surgery with CPB.

INTERVENTIONS

After the induction of anesthesia, lidocaine was administered as a bolus of 1 mg/kg and followed by a continuous infusion at 4 mg/min for the 1st hour, 2 mg/min for the 2nd hour, and 1 mg/min for the next 46 hours.

MEASUREMENTS AND MAIN RESULTS

Blood samples were taken at baseline, the end of CPB, and 24 and 48 hours after CPB for the measurement of the plasma concentration of lidocaine. Lidocaine levels increased significantly over time despite a constant rate of infusion (p < 0.05). The pharmacokinetics of lidocaine was best described by a 2-compartment model, and body weight was found to be a significant factor for the volume of the central compartment and clearance. The final pharmacokinetic parameters were V(1)(L) = 0.0619*weight, V(2)(L) = 187, CL(1) (L/min) = 0.00419*weight, and CL(2) (L/min) = 8.92.

CONCLUSIONS

A 2-compartment pharmacokinetic model best describes the plasma concentrations of a 48-hour lidocaine infusion in patients undergoing cardiac surgery with CPB. The inclusion of body weight as a covariate on clearance and central compartment improves the model. Lidocaine infusions should be dosed by body weight and decreased after 24 hours to avoid potential toxicity in long-term infusions.

Systemic administration of lidocaine reduces morphine requirements and postoperative pain of patients undergoing thoracic surgery after propofol-remifentanil-based anaesthesia

BACKGROUND AND OBJECTIVE

Remifentanil is being increasingly used as an analgesic in fast-track surgery, but severe postoperative pain may happen occasionally. In this study, we evaluated the effects of systemic administration of lidocaine on postoperative pain and morphine requirements after propofol-remifentanil-based anaesthesia.

METHODS

Forty patients undergoing thoracic surgery were randomly assigned to lidocaine (33.0 microg kg(-1) min(-1)) and physiological saline control groups in propofol-remifentanil-based anaesthesia. The setting of the plasma concentration (C(p)) of the target-controlled infusion of propofol was adjusted according to the bispectral index of the electroencephalogram and blood pressure. The C(p) and effect-site concentration (C(e)) of propofol were calculated by target-controlled infusion pump during the intraoperative period. Pain scoring includes a four-point verbal rating scale, Riker's sedation-agitation scale and a visual analogue scale; the morphine requirement in the postanaesthesia care unit and the morphine consumption via a patient-controlled analgesia device on the ward were recorded during the postoperative period.

RESULTS

Morphine requirements within 30, 30-60 and 0-120 min in the postanaesthesia care unit of the lidocaine group decreased significantly (P < 0.05, n = 20 per group) compared with that of the control group. The four-point verbal rating scale at 30 min in the postanaesthesia care unit, visual analogue scale at 6 h on coughing and patient-controlled analgesia morphine consumption during 2-6 h postoperative time were also significantly (P < 0.05, n = 20 per group) reduced in the lidocaine group. In addition, the intraoperative propofol C(e) in the lidocaine group during the periods of intubation, organ resection, closing of chest cavity and extubation was significantly lower (P < 0.05, n = 20 per group) than that in the control group under the same hypnotic depth.

CONCLUSION

Systemic administration of lidocaine could reduce morphine requirements, postoperative pain and intraoperative propofol C(e) of patients undergoing thoracic surgery after propofol-remifentanil-based anaesthesia.

Neuropsychiatric Side-Effects of Lidocaine: Examples from the Treatment of Headache and a Review

Lidocaine has been used in treatment of patients with refractory headache. Personal observations of neuropsychiatric toxicity in these patients led us to review our cases and the literature systematically for lidocaine side-effects, especially neuropsychiatric symptoms. In our series of 20 patients, side-effects were observed in all, the most frequent being neuropsychiatric (75%) and cardiological (50%). When reviewing published series on intravenous lidocaine use, reports of side-effects range from 0 to 100%, with neuropsychiatric symptoms being reported in 1.8–100%. Thirty-six case reports of lidocaine-induced psychiatric symptoms were also analysed. Psychiatric symptoms of toxicity were similar in most patients, despite their differing ages, pathologies, co-therapies and lidocaine dosages. In conclusion, lidocaine neuropsychiatric toxicity has a well-recognized stereotypical clinical presentation that is probably unrecognized in headache series. As lidocaine represents an emerging alternative therapy in headache, particularly in short-lasting unilateral neuralgiform headache attacks with conjunctival injection and tearing, clinicians and patients should be aware of the extent of this problem.

Randomized, double-blinded, placebo controlled study of neuroprotection with lidocaine in cardiac surgery

BACKGROUND AND PURPOSE

Cognitive decline after cardiac surgery remains common and diminishes patients' quality of life. Based on experimental and clinical evidence, this study assessed the potential of intravenously administered lidocaine to reduce postoperative cognitive dysfunction after cardiac surgery using cardiopulmonary bypass.

METHODS

After IRB approval, 277 patients undergoing cardiac surgery were enrolled into this prospective, randomized, double-blinded placebo controlled clinical trial. Subjects were randomized to receive: (1) Lidocaine as a 1 mg/kg bolus followed by a continuous infusion through 48 hours postoperatively, or (2) Placebo bolus and infusion. Cognitive function was assessed preoperatively and again at 6 weeks and 1 year postoperatively. The effect of lidocaine on postoperative cognition was tested using multivariable regression modeling; P<0.05 was considered significant.

RESULTS

Among the 241 allocated subjects (Lidocaine: n=114; Placebo: n=127), the incidence of cognitive deficit in the lidocaine group was 45.5% versus 45.7% in the placebo group (P=0.97). Multivariable analysis revealed a significant interaction between treatment group and diabetes, such that diabetic subjects receiving lidocaine were more likely to suffer cognitive decline (P=0.004). Secondary analysis identified total lidocaine dose (mg/kg) as a significant predictor of cognitive decline and also revealed a protective effect of lower dose lidocaine in nondiabetic subjects.

CONCLUSIONS

Lidocaine administered during and after cardiac surgery does not reduce the high rate of postoperative cognitive dysfunction. Higher doses of lidocaine and diabetic status were independent predictors of cognitive decline. Protective effects of lower dose lidocaine in nondiabetic subjects need to be further evaluated.

Simultaneous determination of nikethamide and lidocaine in human blood and cerebrospinal fluid by high performance liquid chromatography

Nikethamide and lidocaine are often requested to be quantified simultaneously in forensic toxicological analysis. A simple reversed-phase high performance liquid chromatography (RP-HPLC) method has been developed for their simultaneous determination in human blood and cerebrospinal fluid. The method involves simple protein precipitation sample treatment followed by quantification of analytes using HPLC at 263 nm. Analytes were separated on a 5 microm Zorbax Dikema C18 column (150 mm x 4.60 mm, i.d.) with a mobile phase of 22:78 (v/v) mixture of methanol and a diethylamine-acetic acid buffer, pH 4.0. The mean recoveries were between 69.8 and 94.4% for nikethamide and between 78.9 and 97.2% for lidocaine. Limits of detection (LODs) for nikethamide and lidocaine were 0.008 and 0.16 microg/ml in plasma and 0.007 and 0.14 microg/ml in cerebrospinal fluid, respectively. The mean intra-assay and inter-assay coefficients of variation (CVs) for both analytes were less than 9.2 and 10.8%, respectively. The developed method was applied to blood sample analyses in eight forensic cases, where blood concentrations of lidocaine ranged from 0.68 to 34.4 microg/ml and nikethamide ranged from 1.25 to 106.8 microg/ml. In six cases cerebrospinal fluid analysis was requested. The values ranged from 20.3 to 185.6 microg/ml of lidocaine and 8.0 to 72.4 microg/ml of nikethamide. The method is simple and sensitive enough to be used in toxicological analysis for simultaneous determination of nikethamide and lidocaine in blood and cerebrospinal fluid.

Effect of lidocaine on the minimum alveolar concentration of isoflurane in dogs

OBJECTIVE

To determine the influence of a low-dose constant rate infusion (LCRI; 50 microg kg(-1) minute(-1)) and high-dose CRI (HCRI; 200 microg kg(-1) minute(-1)) lidocaine infusion on the minimum alveolar concentration (MAC) of isoflurane (I) in dogs.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Ten mongrel dogs (four females, six males), weighing 20-26.3 kg.

METHODS

Dogs were anesthetized with I in oxygen and their lungs mechanically ventilated. Baseline MAC was determined using mechanical or electrical stimuli. Lidocaine (2 mg kg(-1) IV) was administered over 3 minutes, followed by the LCRI and MAC determination commenced 30 minutes later. Once MAC was determined following LCRI, the lidocaine infusion was stopped for 30 minutes. A second bolus of lidocaine (2 mg kg(-1), IV) was administered, followed by the HCRI and MAC re-determined. Concentrations of lidocaine and its metabolites were measured at end-tidal I concentrations immediately above and below MAC. Heart rates and blood pressures were measured.

RESULTS

Minimum alveolar concentration of I was 1.34 +/- 0.11 (%; mean +/- SD) for both types of stimulus. The LCRI significantly reduced MAC to 1.09 +/- 0.13 (18.7% reduction) and HCRI to 0.76 +/- 0.10 (43.3% reduction). Plasma concentrations (ng mL(-1), median; value below and above MAC, respectively) for LCRI were: lidocaine, 1465 and 1537; glycinexylidide (GX), 111 and 181; monoethylglycinexylidide (MEGX), 180 and 471 and for HCRI were: lidocaine, 4350 and 4691; GX, 784 and 862; MEGX, 714 and 710. Blood pressure was significantly increased at 30 minutes after high dose infusion.

CONCLUSION AND CLINICAL RELEVANCE

Lidocaine infusions reduced the MAC of I in a dose-dependent manner and did not induce clinically significant changes on heart rate or blood pressure.

Human variability in CYP3A4 metabolism and CYP3A4-related uncertainty factors for risk assessment

CYP3A4 constitutes the major liver cytochrome P450 isoenzyme and is responsible for the oxidation of more than 50% of all known drugs. Human variability in kinetics for this pathway has been quantified using a database of 15 compounds metabolised extensively (>60%) by this CYP isoform in order to develop CYP3A4-related uncertainty factors for the risk assessment of environmental contaminants handled via this route. Data were analysed from published pharmacokinetic studies (after oral and intravenous dosing) in healthy adults and other subgroups using parameters relating primarily to chronic exposure [metabolic and total clearances, area under the plasma concentration-time curve (AUC)] and acute exposure (Cmax). Interindividual variability in kinetics was greater for the oral route (46%, 12 compounds) than for the intravenous route (32%, 14 compounds). The physiological and molecular basis for the difference between these two routes of exposure is discussed. In relation to the uncertainty factors used for risk assessment, the default kinetic factor of 3.16 would be adequate for adults, whereas a CYP3A4-related factor of 12 would be required to cover up to 99% of neonates, which have lower CYP3A4 activity.

MEGX disposition in critically-ill trauma patients: subsequent assessments during the first week following trauma

The objective of this study was to evaluate MEGX disposition as a surrogate marker in assessing the influence that injury may exert on liver function during the first week after the traumatic event in young vs. elderly patients. The MEGX exposure over time was assessed at 0.25, 0.5, 1, 2, 4 and 6 h after the intravenous administration of a 1 mg/kg lidocaine test dose in 12 young and 7 elderly trauma patients on days 1, 4 and 7 after a severe injury (Apache II score > 10). MEGX plasma concentration-time profiles were consistently different on day 1 in the elderly vs. young, consistent with a statistically significant lower rate of both lidocaine clearance and MEGX formation, and with a considerably longer MEGX elimination in the elderly than in the young. This suggests an impairment of liver blood flow as a result of splanchnic vasoconstriction occurring mainly in elderly trauma patients. A significant improvement in MEGX disposition occurred on days 4 and 7 vs. the day of trauma in most elderly, whereas minor changes were observed in the young. Multiple factors may account for these major changes in the elderly: the more severe status, the major sensitivity to the pathophysiologic changes induced by trauma, and also at least partially the ageing processes. Although referring to a limited number of observations, our findings on MEGX disposition suggest that liver function may be affected by the severity of injury, even if the influence of age should not be underestimated in these patients.

Epinephrine does not reduce the plasma concentration of lidocaine during continuous epidural infusion in children

PURPOSE

During continuous epidural anesthesia with lidocaine, plasma monoethylglycinexylidide (MEGX), an active metabolite of lidocaine, increases continuously. We assessed the effect of epinephrine on the absorption of lidocaine and the accumulation of MEGX during continuous epidural anesthesia in children.

METHODS

Anesthesia was administered as an initial bolus of 5 mg x kg(-1) of 1% lidocaine solution followed by continuous infusion at 2.5 mg x kg(-1) x hr(-1). Patients in the control group (n = 8) received lidocaine alone, while patients in the epinephrine group (n = 8) received lidocaine + epinephrine (5 microg x mL(-1)). Concentrations of lidocaine and its active metabolite, MEGX, were measured in plasma samples obtained after 15 min, 30 min, and one, two, three, four, and five hours of infusion using high-performance liquid chromatography with ultraviolet detection.

RESULTS

Plasma lidocaine concentrations were higher in samples from the control group for the first hour; however, after two hours the levels were the same in all samples. Plasma MEGX levels increased continuously in both groups and were significantly higher in the control group samples. The sum of lidocaine + MEGX was higher in the control group for the first two hours but there was no significant difference between groups after three hours.

CONCLUSIONS

Reduction of the potential for systemic toxicity by the addition of epinephrine to lidocaine is limited, because the reduction of the sum of the plasma concentrations of lidocaine and its active metabolite MEGX is small and limited to the initial phase of infusion.

Endotoxic shock alters the pharmacokinetics of lidocaine and monoethylglycinexylidide

Significant hepatic dysfunction occurs following endotoxin administration. Although the metabolism of lidocaine to one of the primary metabolites of lidocaine, monoethylglycinexylidide (MEGX), has been used as a marker of hepatic function under various conditions, it remains unknown whether these compounds can be used in vivo to evaluate hepatic function in a rat model of endotoxic shock. To study this, cytochrome P450-3A4 (CYP3A4) was determined after harvesting hepatic microsomes, hepatic blood flow was determined using radioactive microspheres, and the pharmacokinetics of lidocaine and MEGX were evaluated. Adult male Sprague-Dawley rats were divided into endotoxin (45 mg/kg, intraperitoneally; n = 28) or control (n = 32) groups. The CYP3A4 was significantly reduced after endotoxic shock. Carboxylesterase (hydrolase S) content, which was used as a control for microsomal protein, was not significantly different between groups. Total hepatic blood flow was significantly decreased (36.2 +/- 8.4 mL/min/100 g tissue vs. 120.4 +/- 10.6 mL/min/100 g tissue), which was due to the decreased portal blood flow. For the lidocaine and MEGX experiment, lidocaine (2 mg/kg) was administered followed by serial blood samples collected up to 2 h for determination of serum lidocaine and MEGX concentrations. Mean arterial pressure (MAP) was recorded throughout the experiment. The MAP was significantly lower in the endotoxin treated rats vs. control 7.5 to 8 h following endotoxin administration. Serum concentrations of lidocaine were higher in endotoxic shock versus control animals at 2 h following lidocaine administration (1.5 +/- 0.13 mg/L vs. 0.11 +/- 0.03 mg/L). Similarly, MEGX concentrations were significantly higher in endotoxic shock versus control animals (0.55 +/- 0.04 mg/L vs. 0.16 +/- 0.02, respectively) under such conditions. These data demonstrate that the elimination of lidocaine and MEGX is impaired during endotoxic shock. The elevated lidocaine and MEGX concentrations are likely to be the result of primarily reduced hepatic blood flow and secondarily due to impaired CYP450, one of which was CYP3A4. The reduced elimination of MEGX concentrations is not due to decreased hepatic metabolism of the compound via carboxylesterase. The ratio of MEGX to lidocaine concentrations, which decreased significantly following endotoxic shock, appears to be a useful measure of hepatic function during endotoxic shock where profound reductions of hepatic blood flow are observed in addition to significant reductions in CYP450. The use of only MEGX concentrations in this endotoxic shock model is not useful in evaluating liver function.

CNS toxicity after topical application of EMLA cream on a toddler with molluscum contagiosum

EMLA (eutectic mixture of local anesthetics) cream is used topically to provide local anesthesia for a variety of painful superficial procedures. Although the side effects of EMLA are usually mild and transient local skin reactions, potential life threatening complications can be encountered. We report a case of central nervous toxicity after EMLA application for curettage of molluscum contagiosum lesions in a pediatric patient. This complication was the result of a therapeutic misadventure that led to an excessive application of EMLA cream over an extensive area causing an overdose of lidocaine and prilocaine with their subsequent systemic toxicities.

Value of the in vitro or in vivo monoethylglycinexylidide test for predicting liver graft function

BACKGROUND

An adequate function test for donor livers is still lacking. The monoethylglycinexylidide (MEGX) test, performed in vivo in the donor to measure the metabolic rate of lidocaine conversion to MEGX, has been proposed as a function test for donor livers to predict postoperative organ function.

METHODS

In the present study, we investigated whether the MEGX formation rate measured in needle biopsy specimens in vitro correlates with the rate of MEGX formation in vivo. The in vivo MEGX test was performed in the donors and in the recipients on days 1 and 2. The in vivo and in vitro MEGX tests were compared with posttransplant liver function in the recipients in order to investigate their possible relevance as predictors of graft function.

RESULTS

The MEGX formation rate in needle biopsy specimens in vitro showed a significant correlation with the MEGX serum concentration found in the donor. A low rate of MEGX formation in the biopsy specimens tended to predict initial poor function of the grafts. In the donor, the MEGX test did not correlate with general liver function after transplantation. Only the MEGX serum concentration in the recipients on day 2 gave an indication of graft function.

CONCLUSIONS

MEGX formation in liver biopsy specimens in vitro properly reflects metabolic function of the particular liver. Therefore, liver biopsies may be a valuable tool to help predict liver function in vivo. However, the MEGX test alone is not sufficient to provide the gold standard to determine liver function in donor and transplantation livers.

Effect of dehydration and hyperosmolal hydration on lignocaine and metabolites disposition in conscious rabbits

1. The present study aimed to investigate the effect of dehydration and hyperosmolal hydration on the disposition of lignocaine and two of its metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX). 2. Lignocaine was infused to three groups of conscious rabbits: controls, rabbits previously deprived of water for 48 h and rabbits receiving an infusion of 2.5% NaCl. 3. In dehydrated and hyperosmolal-hydrated rabbits, plasma osmolality was 321 +/- 1 and 313 +/- 1 mOsm kg-1, respectively (P < 0.01 compared to controls, 285 +/- 1 mOsm kg-1). In dehydrated animals, baseline values of plasma arginine vasopressin (AVP) concentrations and plasma renin activity (PRA) were higher than in controls, i.e. 12.4 +/- 1.4 pg ml-1 and 15.4 +/- 1.7 ng AI ml-1 h-1 vs. 3.4 +/- 0.2 pg ml-1 (P < 0.01), and 5.1 +/- 0.6 ng AI ml-1 h-1 (P < 0.01), respectively; atrial natriuretic peptide (ANP) decreased from 55 +/- 11 to 32 +/- 4 pg ml-1 (P < 0.05). Compared to controls, hyperosmolal hydration only increased AVP to 15.5 +/- 0.7 pg ml-1 (P < 0.01). 4. Under both experimental conditions, lignocaine plasma concentrations were almost double (P < 0.01) those in controls, due to a lower systemic clearance, e.g. 54 +/- 3 and 59 +/- 1 vs. 96 +/- 5 ml min-1 kg-1, respectively. Plasma levels of MEGX increased (P < 0.01) only in dehydrated animals, although GX plasma concentrations were augmented (P < 0.01) about three fold in both groups of animals. The changes in lignocaine plasma concentrations were correlated with AVP levels (R2 = 0.5168, P<0.001).5. To document the effect of AVP on hepatic plasma flow, another group of rabbits received on separate occasions two doses of AVP (17 and 84 ng kg-1) while receiving an infusion of in docyanine green. AVP reduced hepatic plasma flow from 38.9 +/-2.7 ml min-1 to 19.6 +/-2.5 ml min-1 (P<0.01).The predicted maximal AVP-induced decrease in hepatic plasma flow was 19.6 ml min-1 kg- 1(Emax), and AVP concentration eliciting 50% of Em.. (ED50) was 28.7 pg ml-1.6 It is concluded that both dehydration and hyperosmolal hydration alter the disposition of lignocaine and two of its metabolites.

Subcutaneous lidocaine for treatment of neuropathic cancer pain

Three patients with terminal malignancy reporting ineffective analgesia using systemic and subsequently spinal opiates were treated with subcutaneous infusion of 10% lidocaine hydrochloride. During the infusion, reasonably stable blood concentrations were achieved and maintained using a subcutaneous infusion at varying dose rates over days to months with improvement of the pain complaints which continued to be refractory to conventional analgesics. Blood lidocaine levels obtained at regular intervals revealed effective concentrations between 2 and 5 micrograms/ml for each patient.

Lidocaine absorption and metabolism after oropharyngeal application in young and young-elderly adults

The purpose of this study was to evaluate the effect of age on lidocaine absorption and metabolism after application to the oropharynx and vocal cords in a manner similar to preparation for flexible fiberoptic bronchoscopy. Five healthy volunteers were studied in each of two age groups: from 25 to 37 and 60 to 68 years of age. Each volunteer had a total of lidocaine 300 mg administered as a gargle, gel, or directly to the vocal cords. Blood samples and expectorant were collected to determine concentrations of lidocaine and its metabolites, monoethylglycinxylidide (MEGX) and glycinxylidide (GX). No differences in peak plasma lidocaine concentrations, 2.09 +/- 1.28 mumol/L (1 microgram/mL = 4.27 mumol/L) in young subjects, and 2.35 +/- 0.85 mumol/L in young-elderly subjects, or lidocaine AUC were seen between the two age groups. Lidocaine recovered in expectorant ranged from 96 to 168 mg. This study suggests that, over the age range studied, increased age does not impair lidocaine absorption from the oropharynx or lidocaine metabolism when topical lidocaine is used during flexible fiberoptic bronchoscopy.

Poisoning due to class 1B antiarrhythmic drugs. Lignocaine, mexiletine and tocainide

Since most of the toxicity associated with class 1B antiarrhythmic drugs is dose-related, this review examines adverse effects seen in both therapeutic practice and accidental or premeditated overdose. Toxicity is very common with these agents and can be life-threatening. A high percentage of patients must discontinue therapy because of adverse effects. Mexiletine and tocainide are structural analogues of lignocaine (lidocaine) and toxicity is similar with all 3 drugs. With gradual intoxication (the most common form) central nervous system effects such as lightheadedness, dizziness, drowsiness and confusion are seen first. Seizures and respiratory arrest can occur. Cardiovascular toxicity is manifested by progressive heart block, reduced cardiac contraction, hypotension and asystole. Both mexiletine and tocainide may have proarrhythmic effects. Gastrointestinal toxicity is also common. Shock, hypotension, cardiac failure and beta-blocker therapy reduce lignocaine clearance and enhance the risk of intoxication during routine therapy. Both lignocaine and mexiletine elimination is impaired in severe liver disease while tocainide clearance is reduced in renal failure. Management of toxicity is largely supportive and symptomatic. Lignocaine infusion must be discontinued and decontamination of the gut in the case of oral preparations is recommended. Serious intoxication requires intensive care unit admission. Haemodialysis or haemoperfusion may be helpful in serious lignocaine and tocainide poisoning. In institutions where extracorporeal circulatory assistance is available, massive lignocaine poisoning has been successfully treated with this intervention. In the therapeutic setting serious toxicity can be prevented by close clinical surveillance and appropriate dose reduction in patients with reduced drug clearance. Because of the large interindividual variation in lignocaine pharmacokinetic parameters, therapeutic drug monitoring is recommended if results can be reported quickly. Mexiletine and tocainide have stereoselective metabolism and assays do not distinguish the more active isomers. Therapeutic drug monitoring is less useful in this situation.

Therapeutic serum lidocaine and metabolite concentrations in patients undergoing electrophysiologic study after discontinuation of intravenous lidocaine infusion

Serum concentrations of lidocaine and its metabolites monoethylglycinexylidide (MEGX) and glycinexylidide (GX) were measured in seven patients after discontinuation of intravenous lidocaine necessary for control of spontaneous arrhythmias prior to electrophysiologic study. Standard loading doses of lidocaine were given intravenously followed by 2 mg/min infusions for 79.5 +/- 6.5 hours. Electrophysiologic studies all started more than 5 half-lives or 7.5 hours after discontinuation of intravenous lidocaine. Local anesthesia with subcutaneous lidocaine (mean 162 +/- 96 mg) was administered in six patients. Plasma concentrations of lidocaine and its metabolites were determined at the termination of the infusion, 2 and 4 hours afterwards, at the start of the electrophysiologic study prior to local anesthesia, and at the end of the study. Levels were also determined at 12 and 24 hours after discontinuation of the infusion. Mean plasma concentrations of lidocaine, MEGX, and GX at the start of the study were 1.02, 0.86, and 0.62 micrograms/ml, respectively. These had increased to 2.78, 0.92, and 0.68 by the end of the electrophysiologic study. One patient with coronary artery disease and prior out-of-hospital ventricular fibrillation had a therapeutic lidocaine level and no inducible arrhythmia at the time of the initial study. At a subsequent electrophysiologic study, no lidocaine or metabolites were detected in the serum and ventricular fibrillation was induced. Thus using the reported half-life of 90 minutes and discontinuing lidocaine 5 half-lives prior to electrophysiologic evaluation does not ensure lack of electrophysiologic effects of the parent compound or its metabolites. Lidocaine given for local anesthesia further increases lidocaine and metabolite levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Lidocaine treatment of neonatal convulsions, a therapeutic dilemma

Three infants with neonatal convulsions were given lidocaine infusions for three days, three weeks and three months, respectively, and the plasma concentrations of lidocaine and its metabolites were analyzed by HPLC. After a prolonged infusion there was considerable accumulation of the metabolites. This may account for the difficulty of stopping the infusion without relapse of the seizures.

Initial dosage selection of antiarrhythmic therapy

The success or failure of antiarrhythmic drug treatment depends, in part, on the selection of the initial dosage. Too low a dosage can lead to unnecessary (and frequently life-endangering) delays in achievement of arrhythmia suppression. Conversely, an excessively high dosage can lead to intolerable toxicity and cessation of treatment. The recommended approach to therapy is to begin with a relatively low dosage, i.e., the lowest dosage with a reasonable chance of producing a favorable response, and titrating the dose upward as needed. Dose titration should be guided by clinical response and, when appropriate, concentrations of the drug and any active metabolites in the plasma. In situations frequently encountered in practice, however, the initial dosage must be modified because of interindividual differences in drug disposition. These changes in drug pharmacokinetics can arise from a variety of factors, including disease processes (e.g., congestive heart failure, cirrhosis and renal failure), concomitant medications (e.g., hepatic enzyme inducers such as phenytoin and inhibitors such as amiodarone), drug formulation, protein binding and inherited drug metabolism capacity. Knowledge of these factors can help the clinician to avoid potential pitfalls in initial dosage selection and can enhance the changes of successful drug treatment of arrhythmias.

Increased efficacy and toxicity of lidocaine in patients on beta-blockers

The greatest differences in ventricular arrhythmias and adverse effects of lidocaine observed in this study were between patients on both lidocaine and a beta-adrenoceptor blocking agent and those on neither drug. Although free fractions of lidocaine and methylglycylxylidine tended to be higher in patients on beta-adrenoceptor blocking agents, this difference was not significant nor were any other differences in serum drug levels observed.

The pharmacokinetics of lignocaine and beta-adrenoceptor antagonists in patients with acute myocardial infarction

Lignocaine (lidocaine) and beta-adrenoceptor antagonists are widely used after acute myocardial infarction. The therapeutic value of these agents depends on the achievement and maintenance of safe and effective plasma concentrations. Lignocaine pharmacokinetics after acute myocardial infarction (MI) are controlled by a number of variables. The single most important is left ventricular function, which affects both volume of distribution and plasma clearance. Other major factors include bodyweight, age, hepatic function, the presence of obesity, and concomitant drug therapy. Lignocaine is extensively bound to alpha 1-acid glycoprotein, a plasma protein which is also an acute phase reactant. Increases in alpha 1-acid glycoprotein concentration occur after an acute MI, decreasing the free fraction of lignocaine in the plasma and consequently decreasing total plasma lignocaine clearance without altering the clearance of non-protein-bound lignocaine. Complex changes in lignocaine disposition occur with long term infusions, and therefore early discontinuation of lignocaine infusions (within 24 hours) should be undertaken whenever possible. Because the risk of ventricular tachyarrhythmia declines rapidly after the onset of an acute MI, lignocaine therapy can be rationally discontinued within 24 hours in most patients. Lignocaine has a narrow toxic/therapeutic index, so that pharmacokinetic factors are critical in dose selection. In contrast, beta-adrenoceptor antagonists' adverse effects are more related to the presence of predisposing conditions (such as asthma, heart failure, bradyarrhythmias, etc.) than to plasma concentration. The pharmacokinetics of beta-adrenoceptor antagonists are important to help assure therapeutic efficacy, to provide information about the anticipated time course of drug action, and to predict the possible role of ancillary drug effects (such as direct membrane action) and loss of cardioselectivity. Lipid solubility is the main determinant of the pharmacokinetic properties of a beta-adrenoceptor antagonist. Lipid-soluble agents like propranolol and metoprolol are well absorbed orally, and undergo rapid hepatic metabolism, with important presystemic clearance and a short plasma half-life. Water-soluble drugs like sotalol, atenolol, and nadolol are less well absorbed, and are eliminated more slowly by renal excretion. Clinical assessment of beta-adrenoceptor antagonism is more valuable than plasma concentration determinations in evaluating the adequacy of the dose of a particular beta-adrenoceptor antagonist.(ABSTRACT TRUNCATED AT 400 WORDS)

Free drug concentration monitoring in clinical practice. Rationale and current status

Recent advances in techniques to determine free drug concentrations have lead to a substantial increase in the monitoring of this parameter in clinical practice. The majority of drug binding to macromolecules in serum can be accounted for by association with albumin and alpha 1-acid glycoprotein. Albumin is the primary binding protein for acidic drugs, while binding to alpha 1-acid glycoprotein is more commonly observed with basic lipophilic agents. Alterations in the concentrations of either of these macromolecules can result in significant changes in free fraction. Diseases such as cirrhosis, nephrotic syndrome and malnourishment can result in hypoalbuminaemia. Burn injury, cancer, chronic pain syndrome, myocardial infarction, inflammatory diseases and trauma are all associated with elevations in the concentration of alpha 1-acid glycoprotein. Treatment with a number of drugs has also been shown to increase alpha 1-acid glycoprotein serum concentrations. A wide variety of biological fluids have been examined for their ability to provide an estimation of free drug concentration at receptor sites. The most useful fluid for estimating free drug concentrations appears to be plasma or serum, with subsequent treatment of the sample to separate free and bound drug by an appropriate technique. The two most widely used methods are equilibrium dialysis and ultrafiltration. Of these two, ultrafiltration has the greatest utility clinically because it is rapid and relatively simple. The major difficulty associated with this method involves the binding of drug to the ultrafilters, but significant progress has been made in solving this problem. Several authors have endorsed the routine use of free drug concentration monitoring. Data examining the clinical usefulness of free drug concentration monitoring for phenytoin, carbamazepine, valproic acid, disopyramide and lignocaine (lidocaine) are reviewed. While available evidence suggests that free concentrations may correlate with clinical effects better than total drug concentrations, there are insufficient data to justify the recommendation of the routine use of free drug concentration monitoring for any of these agents at present.

Protein binding and disposition of lignocaine in the elderly

Single dose studies were performed in six young and six elderly nonsmokers using lignocaine as a model drug with high intrinsic clearance. Subjects received lignocaine 250 mg orally and 50 mg intravenously in random order and drug concentrations in blood and plasma were measured for up to 8 h after dose. Protein binding was estimated at 37 degrees C by equilibrium dialysis. Indocyanine green kinetics were also calculated in each individual following 0.15 mg/kg intravenously. Bioavailability of lignocaine was greater in the elderly but there was no apparent difference in the rate of absorption. Intrinsic clearance of lignocaine was lower in the aged. Elimination half-life was longer in the elderly but there was no significant difference in apparent volume of distribution or systemic clearance of lignocaine. Plasma clearance of indocyanine green showed no correlation with systemic lignocaine clearance and was lower in the aged subjects. Blood/plasma lignocaine ratio was less than unity in both groups. Binding of lignocaine to plasma proteins showed concentration-dependence and was higher in the geriatric group. Maximum binding capacity of lignocaine was greater in the elderly but the binding affinity did not significantly change with age. Greater oral bioavailability of drugs like lignocaine may produce higher plasma concentrations in the elderly. Unlike indocyanine green, the systemic clearance of lignocaine was unaltered by age in this group of non-smokers. The protein-binding of lignocaine, like many other basic drugs, is increased in elderly subjects.

Metabolites of cardiac antiarrhythmic drugs: their clinical role

Most antiarrhythmic drugs are extensively metabolized, and the accumulation of the metabolites of several of these drugs has been documented. In some cases, the steady-state plasma concentrations of metabolites are considerably greater than is the concentration of the parent drug. Several of these metabolites have been evaluated in animal models for antiarrhythmic activity and their potencies have been defined relative to the activity of their parent compound. Evaluations of activity are generally conducted in animal arrhythmia models, and very few metabolites of antiarrhythmic drugs have been evaluated directly in patients. However, from knowledge of antiarrhythmic activity in animals and the degree to which a metabolite accumulates in the plasma of patients, one can make qualitative judgments about its therapeutic role. Such judgments, however, need to be recognized as tenuous. Quantitative judgments require further information regarding the relationship between the parent drug and metabolite when present simultaneously in the myocardium. One must consider whether the effects of the parent drug and metabolite are additive, synergistic, or even antagonistic. The latter case is most possible with drug-metabolite pairs where the metabolite accumulates substantially, but does not have significant antiarrhythmic potency. Other considerations include noncardiac effects of the metabolites. As in the case of the mono-desethyl metabolite of lidocaine, the significance of its accumulation relates more to central nervous system side effects than to direct cardiac actions. The role of active metabolites also much be considered in regard to differences in the disposition kinetics between the parent drug and metabolite. The most obvious situation where this is important is in designing clinical drug evaluation protocols. As illustrated by the metabolites of encainide and lorcainide, the time course of accumulation and disappearance of the metabolites may be much longer than that of the parent drug. Clinical evaluations at steady state must take into account the time required to achieve steady-state concentrations of the metabolites as well. Similarly, after discontinuation of drug administration, the time required before washout is complete may be totally dependent on the kinetics of the metabolite, and not the parent drug. Variability in metabolic activity also needs to be considered. It has been shown with procainamide and encainide that genetic factors can influence the rate of production of active metabolites and consequently influence the clinical efficacy of these drugs. Another consideration that deserves attention is the question of drug interactions.(ABSTRACT TRUNCATED AT 400 WORDS)