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

Pharmacokinetic determinants for the right dose of antiarrhythmic drugs

INTRODUCTION

Antiarrhythmic drugs (AADs) show a narrow therapeutic range and marked intersubject variability in pharmacokinetics (PK), which may lead to inappropriate dosing and drug toxicity.

AREAS COVERED

The aim of the present review is to describe PK properties of AADs, discussing the main changes in different clinical scenarios, such as the elderly and patients with obese, chronic kidney, liver, and cardiac disease, in order to guide their right prescription in clinical practice.

EXPERT OPINION

There are few data about PK properties of AADs in a special population or challenging clinical setting. The use and dose of AADs is commonly based on physicians' clinical experience observing the clinical effects rather than being personalized on the individual patients PK profiles. More and updated studies are needed to validate a patient centered approach in the pharmacological treatment of arrhythmias based on patients' clinical features, including pharmacogenomics, and AAD pharmacokinetics.

Brain targeting by intranasal drug delivery (INDD): a combined effect of trans-neural and para-neuronal pathway

The effectiveness of intranasal drug delivery for brain targeting has emerged as a hope of remedy for various CNS disorders. The nose to brain absorption of therapeutic molecules claims two effective pathways, which include trans-neuronal for immediate action and para-neuronal for delayed action. To evaluate the contribution of both the pathways in absorption of therapeutic molecules and nanocarriers, lidocaine, a nerve-blocking agent, was used to impair the action potential of olfactory nerve. An anti-Parkinson drug ropinirole was covalently complexes with (99m)Tc in presence of SnCl2 using in-house developed reduction technology. The radiolabeled formulations were administered intranasally in lidocaine challenged rabbit and rat. The qualitative and quantitative outcomes of neural and non-neural pathways were estimated using gamma scintigraphy and UHPLC-MS/MS, respectively. The results showed a significant (p ≤ 0.005) increase in radioactivity counts and drug concentration in the brain of rabbit and rat compared to the animal groups challenged with lidocaine. This concludes the significant contribution (p ≤ 0.005) of trans-neuronal and para-neuronal pathway in nose to brain drug delivery. Therefore, results proved that it is an art of a formulator scientist to make the drug carriers to exploit the choice of absorption pathway for their instant and extent of action.

Comparative study between the protective effects of Saudi and Egyptian antivenoms, alone or in combination with ion channel modulators, against deleterious actions of Leiurus quinquestriatus scorpion venom

This study compared efficacy of two polyvalent antivenoms (Saudi Arabian and Egyptian), against lethality and pathophysiological changes of Leiurus quinquestriatus quinquestriatus (LQQ) scorpion venom in mice. Additionally, the study examined whether treatment with selected ion channel modulators, lidocaine, nimodipine or amiodarone would be effective, alone or combined with the antivenoms. The protein concentration of the Saudi antivenom was 1/3 of Egyptian, indicating lesser immunogenicity, while both preservative contents were within limits. In immunodiffusion experiments, both exhibited prominent precipitin bands indicating high concentrations of specific antibodies. Neutralizing capacities (60-70 LD(50)) stated on labels were confirmed. Both antivenoms significantly (P < 0.001) prolonged survival time (from 26.9 +/- 1.18 min, 100% dead with venom to 224-300 min, 0-30% dead) of envenomed mice, whether injected iv before or 5 min after venom. Injection of either antivenom plus ion channel modulators, gave comparable results to that observed in mice treated with antivenoms alone. The Na(+) channel blocker lidocaine and the Ca(2+) channel blocker nimodipine on their own significantly protected the animals (P < 0.05), but to a lesser extent. The two antivenoms, significantly ameliorated the venom-evoked changes in serum LDH (P < 0.001) and CKMB (P < 0.01) plus cardiac TNFalpha and nitrate/nitrite levels (P < 0.001). When combined with lidocaine or nimodipine, the effects were not greater than antivenom alone. Moreover, the antivenoms ameliorated characteristic venom-evoked changes in the isolated perfused Langendorff hearts. Lidocaine and amiodarone were more effective than nimodipine. In Conclusion both Saudi and Egyptian antivenoms protected mice from the pathological and lethal effects of LQQ scorpion. Sodium and calcium channel blockers, lidocaine and nimodipine, may be useful when antivenoms are not available.

Pharmacokinetics of lidocaine and its metabolite in peridural anesthesia administered to pregnant women with gestational diabetes mellitus

BACKGROUND

Peridural blockade with lidocaine, bupivacaine, and fentanyl is an anesthetic procedure extensively used in obstetrics, justifying the pharmacokinetic study of these drugs during labor.

OBJECTIVE

To investigate the influence of the physiopathological changes of gestational diabetes mellitus (GDM) on the pharmacokinetics of lidocaine and its metabolite monoethylglycinexylidide (MEGX) in pregnant women subjected to peridural anesthesia.

PATIENTS AND METHODS

Ten normal pregnant women (group 1) and six pregnant women with GDM (group 2) were studied, all of them at term. The patients received 200 mg 2% lidocaine hydrochloride without a vasoconstrictor by the peridural locoregional route. Maternal blood samples were collected at predetermined times for the analysis of lidocaine and MEGX by chromatography and pharmacokinetic analysis.

RESULTS

The median pharmacokinetic parameters of lidocaine for groups 1 and 2 (P </= 0.05), respectively, were as follows: for Cmax 879.11 and 1,145.58 ng/ml, AUC(0-infinity) 256.01 and 455.95 mug min(-1) ml(-1), Cl/f/kg 10.61 and 5.64 ml min(-1) kg(-1), and Vd/f/kg 3.26 and 2.19 L/kg. The median pharmacokinetic parameters of MEGX for groups 1 and 2 (P </= 0.05), respectively, were as follows: for Cmax 82.71 and 141.38 ng/ml, Tmax 44.71 and 193.14 min, t(1/2)alpha 7.64 and 59.77 min, alpha 0.097 and 0.012/min, and AUC(0-infinity) 29.91 and 108.23 mug min(-1) ml(-1).

CONCLUSION

The present data permit us to conclude that the apparent clearance of lidocaine and MEGX was reduced in diabetic patients compared to normal women, suggesting that GDM inhibits the CYP1A2/CYP3A4 isoforms responsible for the metabolism of this drug and its metabolite.

Validation of a semi-automated human hepatocyte assay for the determination and prediction of intrinsic clearance in discovery

An automated high throughput human hepatocyte assay has been established with a 96-well format using a Tecan Genesistrade mark Workstation. Validation of this assay was performed with nine commercially available compounds and an additional 10 Pfizer compounds with varying hepatic extraction ratios (E(H)) ranging from 0.02 to approximately 1. The incubation conditions in the automated assay are readily and precisely controlled and cell viability of over 80% was achieved in the automated assay further confirming its utility for absorption, distribution, metabolism, and excretion (toxicity) (ADME (T)) screening. The results of the nine commercial compounds correlate with both manually executed (R(2)=0.97) and literature reported experimental results (R(2)=0.93). Overall, measured E(H)s were within two-fold of the literature values for approximately 90% of the 19 compounds tested. Additionally, good inter- and intra-day reproducibility was observed for all the 19 compounds. In conclusion, an automated and robust assay suitable for simultaneously testing up to 48 compounds with multiple time points has been validated. Throughput of 192 compounds per run can be achieved using 384-well plates to meet increasing needs in drug discovery. Currently, this automated assay is used to support early discovery profiling towards lead optimization of various discovery targets/programs.

Pharmacokinetics and transplacental transfer of lidocaine and its metabolite for perineal analgesic assistance to pregnant women

BACKGROUND

Obstetrical analgesia continues to be challenging to science in the search for safe and effective methods that will permit the use of these procedures allied to improved obstetrical and perinatal results.

OBJECTIVE

The objective of the present study was to investigate the pharmacokinetics and the placental transfer of lidocaine and its metabolite in parturients whose pregnancies were resolved by the vaginal route under perineal analgesia.

PATIENTS AND METHODS

The study was conducted on 23 pregnant women who received perineal analgesia with 20 ml 2% lidocaine (400 mg) during the expulsive period of labor. Maternal venous blood samples were obtained from 0 min to 360 min after drug administration, and umbilical venous blood was obtained at delivery. Lidocaine and monoethylglycinexylidide (MEGX) were determined using high-performance liquid chromatography. The fetal/maternal ratios of the drugs were determined on the basis of maternal and fetal concentrations at delivery.

RESULTS

Maximum lidocaine concentrations at the median times of 15 min were 3.22 microg/ml. The pharmacokinetic parameters were: half-life t1/2alpha 24.0 min, area under the curve (AUC)0-infinity 460.2 microg/min per ml, t1/2beta 180.0 min, clearance 12.2 ml/min per kg and volume distribution 3.1 l/kg. The fetal/maternal ratio for lidocaine at delivery was 0.46, with the latency time between drug administration and delivery being 11.0 min. Maximum MEGX concentrations at the median time of 90 min were 229.0 ng/ml. The t1/2 for MEGX was 240 min, and AUC0-infinity was 82.4 microg min/ml.

CONCLUSION

Lidocaine administered by the perineal route presented a tmax of 15 min, significantly lower than when the drug was administered peridurally, revealing that the time between administration and the occurrence of the analgesic effect was shorter. The study demonstrated placental transfer of lidocaine at ratios of about 50% for lidocaine at the time of delivery. The MEGX placental transfer demonstrated fetal concentration higher than the maternal at the time of delivery.

Quantitative structure-pharmacokinetic relationship modelling: apparent volume of distribution

The purpose of this study was to develop a quantitative structure-activity relationship (QSAR) for the prediction of the apparent volume of distribution (Vd) in man for a heterogeneous series of drugs. The relationship of many computed, and some experimental, structural descriptors with Vd, and the Vd corrected for protein binding (unbound Vd), was investigated. Models were constructed using stepwise regression analysis for all the 70 drugs in the dataset, as well as for acidic drugs and basic drugs separately. The predictive power of the models was assessed using half the chemicals as a test set, and revealed that the models for Vd yielded lower prediction errors than those constructed for the unbound Vd (mean fold error of 2.01 for Vd compared with 2.28 for unbound Vd). Moreover, the separation of the compounds into acids and bases did not reduce the prediction error significantly.

Development and validation of a 96-well equilibrium dialysis apparatus for measuring plasma protein binding

A 96-well equilibrium dialysis block was designed and constructed that is compatible with most standard 96-well format laboratory supplies and instruments. The unique design of the dialysis apparatus allows one to dispense and aspirate from either or both the sample and dialysate sides from the top of the apparatus, which is not possible with systems currently on the market. This feature permits the investigator to analyze a large number of samples, time points, or replicates in the same experiment. The novel alignment of the dialysis membrane vertically in the well maximizes the surface-to-volume ratio, eliminates problems associated with trapped air pockets, and allows one to add or remove samples independently or all at once. Furthermore, the design of the apparatus allows both the sample and dialysate sides of the dialysis well to be accessible by robotic systems, so assays can be readily automated. Teflon construction is used to minimize nonspecific binding of test samples to the apparatus. The device is reusable, easily assembled, and can be shaken in controlled temperature environments to decrease the time required to reach equilibrium as well as facilitate dissolution of test compounds. Plasma protein binding values obtained for 10 diverse compounds using standard dialysis equipment and the 96-well dialysis block validates this method.

Intraosseous lidocaine provides effective analgesia for percutaneous vertebroplasty of osteoporotic fractures

PURPOSE

To assess the safety and efficacy of intraosseous lidocaine (IL), in comparison with iv nalbuphine and propacetamol (NP) for analgesia during percutaneous vertebroplasty (PV) in order to avoid general anesthesia in elderly patients.

METHODS

Patients (age 68 +/- 13 yr, weight 66 +/- 6 kg) undergoing PV for osteoporotic fractures were randomized prospectively into two groups: NP (n=50) and IL (n=50). All patients were premedicated (oral hydroxyzine 1 mg.kg(-1)) and had skin infiltration with 5 mL of 1% lidocaine prior to vertebral puncture. Thirty minutes before the procedure, Group NP received, in a blinded manner, 50 mL of iv nalbuphine (0.3 mg.kg(-1)) and propacetamol (30 mg.kg(-1)) while Group IL received 50 mL of iv saline. During vertebral puncture, Groups NP and IL received, in a blinded manner, 1 mL.10 kg(-1) of intraosseous saline and 1% lidocaine respectively. Pain was assessed during vertebral puncture and cement injection with a four-point verbal rating scale. Additionally, lidocaine plasma kinetics were obtained in 11 IL patients.

RESULTS

Analgesic efficacy was similar in the IL and NP groups (85 vs 84%). Group NP had more side effects. Lidocaine peak recorded concentration was 2.6 +/- 0.1 microg.mL(-1) i.e., about three times less than the reported toxic limits.

CONCLUSION

IL is as effective as the association of iv NP for analgesia in PV. However, considering that both protocols were insufficient in about 15% of cases, other modalities are needed to further improve analgesia and avoid general anesthesia during vertebroplasty.

Protein binding predictions in infants

Plasma binding protein levels are lower in the newborn than in the adult and gradually increase with age. At birth, human serum albumin (HSA) concentrations are close to adult levels (75%-80%), while alpha 1-acid glycoprotein (AAG) is initially half the adult concentration. As a result, the extent of drug binding to HSA is closer to that of the adult than are those drugs bound largely to AAG. A model that incorporates the fraction unbound in adults and the ratio of the binding protein concentration between infants and adults successfully predicted the fraction unbound in infants and children.

Lidocaine and surgical modification reduces mortality in a rat model of cardiac failure induced by coronary artery ligation

Coronary artery ligation in the rat provides a useful experimental model of cardiac failure; however, this procedure carries with it a high mortality rate (50%). In this study, we used lidocaine (10 mg/kg, i.m.) before coronary artery ligation and 2 h after surgery to minimise the incidence of ventricular fibrillation (VF) that leads to sudden death in this model. We found that coronary artery ligation, using lidocaine in conjunction with a modified surgical procedure, had a mortality rate of 15%, much lower than reported in previous studies using this model. These modifications allow for the production of larger infarcts with 29% of animals having an infarct size > 50% of the epicardial surface. Infarct size in our myocardial infarction (MI) group varied between 5% and 75% of the left ventricular (LV) surface area resulting in a mean infarct size of 41.3 +/- 1.3% for the epicardial surface and 40.0 +/- 1.3% for the endocardial surface.

Pharmacology of pediatric resuscitation

The resuscitation of children from cardiac arrest and shock remains a challenging goal. The pharmacologic principles underlying current recommendations for intervention in pediatric cardiac arrest have been reviewed. Current research efforts, points of controversy, and accepted practices that may not be most efficacious have been described. Epinephrine remains the most effective resuscitation adjunct. High-dose epinephrine is tolerated better in children than in adults, but its efficacy has not received full analysis. The preponderance of data continues to point toward the ineffectiveness and possible deleterious effects of overzealous sodium bicarbonate use. Calcium chloride is useful in the treatment of ionized hypocalcemia but may harm cells that have experienced asphyxial damage. Atropine is an effective agent for alleviating bradycardia induced by increased vagal tone, but because most bradycardia in children is caused by hypoxia, improved oxygenation is the intervention of choice. Adenosine is an effective and generally well-tolerated agent for the treatment of supraventricular tachycardia. Lidocaine is the drug of choice for ventricular dysrhythmias, and bretylium, still relatively unexplored, is in reserve. Many pediatricians use dopamine for shock in the postresuscitative period, but epinephrine is superior. Most animal research on cardiac arrest is based on models with ventricular fibrillation that probably are not reflective of cardiac arrest situations most often seen in pediatrics.

Lidocaine prophylaxis for fatal ventricular arrhythmias after acute myocardial infarction

OBJECTIVE

To compare the efficacy and safety of a 40-hour lidocaine infusion after completion of a 8-hour open-label infusion for prophylaxis of primary ventricular fibrillation in patients with uncomplicated acute myocardial infarction.

METHODS

This was a double-blind, randomized placebo-controlled trial held in the coronary care unit of a large nonprofit hospital. We studied 200 patients with uncomplicated acute myocardial infarction in Killip class I or II who came to the hospital within 6 hours of onset of symptoms and 22 patients who had ventricular fibrillation before the start of the study. Intervention consisted of an 8-hour lidocaine infusion followed by placebo or lidocaine for an additional 40 hours. The infusion rate was adjusted in patients > or = 70 years old and in those < 50 kg or > or = 90 kg. Measurements recorded were baseline demographic characteristics, incidence of ventricular arrhythmias, adverse reactions, and death.

RESULTS

New congestive heart failure developed during the randomized phase in 9% of patients receiving lidocaine and in 2% of patients receiving placebo (p = 0.03). Ventricular fibrillation did not occur during the treatment period, and sustained ventricular tachycardia developed in one patient receiving placebo. The in-hospital mortality rate was comparable in both groups (4% versus 2%; p = 0.68) but was much higher (13.6%) in patients with initial ventricular fibrillation not included in the randomized study.

CONCLUSIONS

A 40-hour age- and weight-adjusted lidocaine infusion administered after an initial 8-hour infusion provoked more congestive heart failure than placebo. In view of the absence of ventricular fibrillation episodes with both infusions, caution should be used when lidocaine is administered for longer than 8 hours in patients with uncomplicated myocardial infarction.

Microassay of propranolol enantiomers and conjugates in human plasma and urine by high-performance liquid chromatography after chiral derivatization for pharmacokinetic study

A microdetermination of propranolol enantiomers and of their glucuronide and sulphate conjugates in human plasma and urine by reversed-phase HPLC after chiral derivatization is described. After extraction from 100 microliters of plasma or urine with racemic 4-methylpropranolol as internal standard (I.S.), the enantiomers are derivatized with R(+)-phenylethylisocyanate as chiral derivatization reagent. Chromatography is performed on Novapak C18 column with fluorescence detection. Glucuronide and sulphate conjugates are cleaved prior to extraction by incubating, respectively, the samples with glucuronidase-arylsulphatase and saccharic acid 1-4 lactone as specific glucuronidase inhibitor. The retention times of propranolol and I.S. enantiomer derivatives are short (tR = 5.5-6.2 min and 8.8-10.1 min, respectively). The diastereomeric derivatives are very stable and show good peak symmetry and resolutions (RS = 2 and 2.2). The use of 4-methylpropranolol as I.S. improves significantly relative standard deviations (RSD: 1.7-5.1). Sensitivity is about 1 ng ml-1 per enantiomer. The method is applied to pharmacokinetic studies of racemic propranolol in human plasma and urine. S-propranolol and its conjugates show higher concentrations than R-propranolol and its conjugates in plasma and urine.

Treatment of the cutaneous pain of acute herpes zoster with 9% lidocaine (base) in petrolatum/paraffin ointment

BACKGROUND

Treatment of the pain of acute herpes zoster by local anesthetic injections has drawbacks. Topical percutaneous local anesthesia (TPLA) may offer another strategy of providing regional analgesia in affected patients.

OBJECTIVE

We evaluate the analgesic efficacy and safety of 9% (wt/vol) lidocaine (base) in petrolatum/paraffin ointment in patients with acute herpes zoster.

METHODS

Ointment was applied to the affected skin of 22 patients. Pain, tenderness, sensitivity to pinprick and cold, and blood lidocaine concentration were measured repeatedly during a 20-hour interval and intermittently thereafter.

RESULTS

Mean pain, tenderness, and cutaneous sensation scores were reduced at measurements taken from 4 to 20 hours after ointment application (p < 0.05), but not every patient obtained relief. No patient had local skin irritation or systemic toxic effects related to the local anesthetic.

CONCLUSIONS

TPLA is a promising therapy for control of cutaneous pain of acute herpes zoster. Controlled studies should be performed to prove efficacy, determine optimal TPLA formulation, and define dosage limits.

Pharmacokinetics and pharmacodynamics in the critically ill patient

1. Until recently, when drugs were used in critically ill patients they were expected to behave in the same way as in less seriously ill patients. Now the unpredictability of even the most reliable drugs has been recognized. With this there is an awareness of the adverse effects drugs may have on organs other than the ones the drug was intended to act on. In patients with multiorgan dysfunction, poly-pharmacy is usually needed. The drugs may not only interfere with the action of each other at the receptor and enzyme level, but may also change protein binding and elimination. All these effects may be unimportant in less seriously ill patients, but may affect outcome in the critically ill. A high degree of awareness and suspicion of unknown drug-induced adverse reaction is needed by clinicians and pharmacologists alike.

Intravenous benztropine and propranolol challenges in tardive akathisia

We challenged five patients suffering from tardive akathisia (TA) with intravenous benztropine (2 mg), propranolol (1 mg) and placebo (saline) using a random, double-blind cross-over design to examine the effects of the drugs on the subjective, objective and global manifestations of neuroleptic-induced akathisia. Benztropine produced a marginally significant, and propranolol a significant improvement in the overall manifestations of the disorder. The patients demonstrated a considerable placebo effect and marked variation in their responses to the drugs. The implications of these findings for the pathophysiology of TA in relation to acute akathisia and tardive dyskinesia are discussed.

A new ECG measure (RSh) for detecting possible sodium channel blockade in vivo in rats

A new electrocardiographic (ECG) measure for detecting possible sodium channel blocking actions of drugs in anaesthetized rats is described. The conventional measures for sodium channel blockers are increased QRS width and/or P-R prolongation, however, these are limited in their sensitivity. This new measure, RSh, is the height from the peak of the R wave to the bottom of the S wave; it is more sensitive to known sodium channel blocking agents than conventional measures. This was shown by comparing the ECG effects of sodium channel blocking class I antiarrhythmic drugs from the three subclasses lidocaine (Ia), quinidine (Ib), and flecainide (Ic). In each case, RSh increased before changes could be detected in QRS or P-R. With tetrodotoxin and quinacainol, a new class I agent, changes in RSh correlated directly with previously reported changes in dV/dtmax of intracellular potentials recorded in vivo from epicardial cells. Representatives from antiarrhythmic classes II, III, and IV were also tested and only changed RSh when they had known sodium channel blocking properties at high doses. Other physiological maneuvers for altering heart rate, such as changing vagal activity, administration of catecholamines, or direct right atrial pacing, did not alter RSh. Thus RSh is a useful in vivo measure for the detection of possible class I antiarrhythmic actions. It has the advantages of being sensitive, selective, easy to measure, and involving minimal preparation.

Role of lidocaine (lignocaine) in managing status epilepticus

Lidocaine (lignocaine) was given in 42 episodes of status epilepticus (SE) in 36 patients either because of limited pulmonary reserve (22 patients) or because of lack of response to diazepam (14 patients). Lidocaine (1.5-2 mg/kg) was given intravenously in two minutes. A further identical bolus was infused if no response had occurred or if seizures recurred. With the first bolus 11 episodes of SE did not stop, but 31 responded, always in less than one minute. In 19 episodes, however, this response lasted less than 30 minutes. Twelve episodes did not recur, but 30 needed a second bolus because of recurrence. Of these, 19 episodes responded at once but SE reappeared in seven. In these seven episodes the mean control time with the second dose was 102 minutes. Five of these subsequently responded to a continuous infusion of lidocaine. Eleven patients, who had not responded to the first bolus, had no response to the second. Lidocaine is a drug that may be epileptogenic at high doses. At the doses used here, however, lidocaine seems to be a rapid acting anticonvulsant, useful in the short term management of SE and may be indicated in patients in whom respiratory or consciousness depression is undesirable and in those with no response to diazepam. The absence of response to lidocaine indicates SE resistant to treatment and poor prognosis. These data show that prompt lidocaine administration may be worthwhile when management of respiratory depression is not possible.

Determinants and significance of diltiazem plasma concentrations after acute myocardial infarction. The Multicenter Diltiazem Postinfarction Trial Research Group

A total of 1,975 plasma diltiazem concentrations were obtained from 1,067 patients enrolled in a multicenter secondary intervention study of diltiazem after acute myocardial infarction. To evaluate the determinants and significance of diltiazem concentrations in this patient population, we related drug concentrations to a variety of clinical variables recorded on the case history forms. Multiple linear regression analysis showed that (1) time from the last drug dose, (2) drug dose taken, (3) patient height (an index of lean body weight), and (4) patient age were important determinants of plasma concentration. For an equivalent dose, plasma diltiazem concentrations in a 75-year-old patient were about double those of a 25-year-old patient. Total weight and drug dose prescribed did not significantly affect plasma concentrations. Whereas drug concentrations were higher (p = 0.01) among patients with left-sided heart failure, they were not altered by renal dysfunction, hepatic disease or beta blockers. Diltiazem concentrations were a significant determinant of diastolic arterial pressure (p less than 10(-9), but neither systolic pressure nor heart rate were significantly related to diltiazem concentration. The overall incidence of adverse experiences was not related to drug concentrations, but the occurrence of second- and third-degree atrioventricular block in the coronary care unit and the need for a temporary pacemaker were substantially higher among patients with a drug concentration greater than 150 ng/ml (7.4 and 1.9%, respectively) than among patients with lower concentrations (2.6% for atrioventricular block, 0.3% for pacemaker; p = 0.02 for each). The risk of atrioventricular block was particularly increased by high diltiazem concentrations in the face of acute inferior infarction. These results suggest that diltiazem's pharmacologic and clinical effects in a large population are concentration-related, and that the consideration of patient size, age, and left ventricular function in selecting a diltiazem dose may allow for effective drug therapy with a reduced likelihood of adverse effects.

Pharmacokinetics in acute illness

Severe illness at any age is accompanied by organ dysfunction, the administration of numerous drugs and complex changes in drug absorption, disposition and action. The clinician faced with a seriously ill patient should be aware of the important principles of drug treatment in critical illness. With acute illness of all types, the premature infant and the octogenarian lie at opposite ends of an age spectrum which encompasses the gamut of human disease and changeable organ pathophysiology. The common requirement of this host of variables is a flexible management plan, and careful observation of the patient's response to a therapeutic regimen which has been based on a sound knowledge of drug pharmacokinetics.

Decreased absorption as a possible cause for the lower bioavailability of a sustained-release propranolol

The influence of sustained absorption on the oral availability of propranolol (P) and the metabolic disposition of P were investigated by obtaining the partial metabolic clearances (CLm) following long-acting P (LA) dosing in comparison with the conventional propranolol tablet (CP). Ten healthy volunteers were given a single oral dose of an LA capsule (60 mg) and CP (20 mg x 3) using a crossover design. Blood and urine samples were collected over 24- and 48-h postdose periods, respectively. Concentrations of P, propranolol glucuronide (PG), 4-hydroxypropranolol (4P), 4-hydroxypropranolol glucuronide (4PG), 4-hydroxypropranolol sulfate (4PS), and naphthoxylactic acid (NLA) were determined by HPLC with fluorescence and UV detection. Significant differences were observed between LA and CP in the area under the plasma concentration-time curves (AUCs) for P, PG, and NLA and in the amounts excreted into urine (Ae) for all measured metabolites (i.e., PG, 4P, 4PG, 4PS, and NLA). The parallel decrease of the AUC for P and the excreted amounts of all measured metabolites following LA dosing resulted in partial metabolic clearances (CLm) and renal clearances (CL) for P and its metabolites that were similar to those observed for CP. Therefore, the hepatic metabolism of P would not be affected by the slower absorption at a single oral dose of 60 mg. These results indicate that the poor absorption of P from the gastrointestinal tract might be one of the factors causing the low bioavailability of P observed after administration of the sustained-release formulation.

Effects of cardiovascular disease on pharmacokinetics

The pathophysiologic changes occurring in cardiovascular disease can affect the kinetics of drugs in several different ways. The present review examines these modifications and the underlying mechanisms. The kinetics of specific agents, such as antiarrhythmic, antihypertensive, cardiotonic, and other drugs are considered, and the clinical implications are outlined. The clinician should be aware of these modifications, because they require an adjustment of the dosage regimen. A rational basis for a correct therapeutic choice can be provided by adequate knowledge of these modifications.