Pharmacokinetic and pharmacodynamic considerations in drug therapy of cardiac emergencies

Impact of lipopolysaccharide-induced inflammation on the disposition of the aminocephalosporin cefadroxil

The purpose of this study was to determine if the disposition of cefadroxil, an α-amino-containing β-lactam antibiotic, changes during lipopolysaccharide (LPS)-induced acute inflammation. Six hours after LPS or saline treatment, mice received 1 nmol/g cefadroxil intravenously along with inulin for glomerular filtration rate (GFR) determination. Serial blood samples, along with tissue and urine samples, were collected at predetermined time points. In order to determine inflammation-induced changes in GFR, renal tubular secretion, and reabsorption, it was necessary to coadminister 70 mg/kg probenecid. Changes in the expression of the mRNA of transporters involved in cefadroxil disposition in the kidneys and choroid plexus were also investigated 6 h after LPS treatment. The results demonstrated marked increases in blood, cerebrospinal fluid, and tissue cefadroxil concentrations with LPS treatment. Tissue-to-blood concentration ratios were decreased by 4.6-fold in the choroid plexus and by 2.5-fold in the kidneys during LPS-induced inflammation. Renal, but not choroid plexus, mRNA expression of peptide transporter 2, organic-anion transporter 1 (OAT1), OAT3, and multidrug resistance-associated protein 4 was mildly reduced in LPS-treated mice. The renal clearance of cefadroxil was substantially decreased by LPS treatment (3-fold). GFR was also reduced by 3-fold in LPS-treated mice, but no significant differences in the fractional reabsorption of cefadroxil and renal secretion once normalized by GFR were observed. These findings demonstrated that LPS-induced inflammation has a dramatic effect on the renal excretion of cefadroxil. It appears that changes in transporter expression played a minor role during LPS treatment but that renal dysfunction, associated with GFR reduction, was responsible for the substantial increase in plasma cefadroxil concentration-time profiles.

Pharmacokinetics in special populations

Pharmacokinetics are typically dependent on a variety of physiological variables (e.g., age, ethnicity, or pregnancy) or pathological conditions (e.g., renal and hepatic insufficiency, cardiac dysfunction, obesity, etc.). The influence of some of these conditions has not always been thoroughly assessed in the clinical studies of antiallergic drugs. However, the knowledge of the physiological grounds of the pharmacokinetics can provide some insight for predicting the potential alterations and guiding the initial prescription strategies. It is important to recognize that both pharmacokinetic and pharmacodynamic differences between populations should be considered. The available information on drugs used for the therapy of allergic diseases is reviewed in this chapter.

Vasopressors for cardiopulmonary resuscitation. Does pharmacological evidence support clinical practice?

Adrenaline (epinephrine) has been used for cardiopulmonary resuscitation (CPR) since 1896. The rationale behind its use is thought to be its alpha-adrenoceptor-mediated peripheral vasoconstriction, causing residual blood flow to be diverted to coronary and cerebral circulations. This protects these tissues from ischaemic damage and increases the likelihood of restoration of spontaneous circulation. Clinical trials have not demonstrated any benefit of adrenaline over placebo as an agent for resuscitation. Adrenaline has deleterious effects in the setting of resuscitation, predictable from its promiscuous pharmacological profile. This article discusses the relevant pharmacology of adrenaline in the context of CPR. Experimental and clinical evidences for the use of adrenaline and alternative vasopressor agents in resuscitation are given, and the properties of an ideal vasopressor are discussed.

Pharmacokinetic and pharmacodynamic considerations when treating patients with sepsis and septic shock

Sepsis and septic shock are accompanied by profound changes in the organism that may alter both the pharmacokinetics and the pharmacodynamics of drugs. This review elaborates on the mechanisms by which sepsis-induced pathophysiological changes may influence pharmacological processes. Drug absorption following intramuscular, subcutaneous, transdermal and oral administration may be reduced due to a decreased perfusion of muscles, skin and splanchnic organs. Compromised tissue perfusion may also affect drug distribution, resulting in a decrease of distribution volume. On the other hand, the increase in capillary permeability and interstitial oedema during sepsis and septic shock may enhance drug distribution. Changes in plasma protein binding, body water, tissue mass and pH may also affect drug distribution. For basic drugs that are bound to the acute phase reactant alpha(1)-acid glycoprotein, the increase in plasma concentration of this protein will result in a decreased distribution volume. The opposite may be observed for drugs that are extensively bound to albumin, as the latter protein decreases during septic conditions. For many drugs, the liver is the main organ for metabolism. The determinants of hepatic clearance of drugs are liver blood flow, drug binding in plasma and the activity of the metabolic enzymes; each of these may be influenced by sepsis and septic shock. For high extraction drugs, clearance is mainly flow-dependent, and sepsis-induced liver hypoperfusion may result in a decreased clearance. For low extraction drugs, clearance is determined by the degree of plasma binding and the activity of the metabolic enzymes. Oxidative metabolism via the cytochrome P450 enzyme system is an important clearance mechanism for many drugs, and has been shown to be markedly affected in septic conditions, resulting in decreased drug clearance. The kidneys are an important excretion pathway for many drugs. Renal failure, which often accompanies sepsis and septic shock, will result in accumulation of both parent drug and its metabolites. Changes in drug effect during septic conditions may theoretically result from changes in pharmacodynamics due to changes in the affinity of the receptor for the drug or alterations in the intrinsic activity at the receptor. The lack of valid pharmacological studies in patients with sepsis and septic shock makes drug administration in these patients a difficult challenge. The patient's underlying pathophysiological condition may guide individual dosage selection, which may be guided by measuring plasma concentration or drug effect.

Pharmacokinetic considerations

Limited studies of the pharmacokinetics of pain medication suggest altered serum elimination when the liver is hypoperfused or affected by severe cirrhosis. Drugs that are eliminated by Phase I oxidation reactions are sensitive to changes in hepatic blood flow, while drugs eliminated by Phase II glucuronidation are more affected by diseased hepatocytes. Additionally, alterations in renal function decrease elimination of both parent drugs and metabolites, resulting in toxicity for selected opioids such as meperidine and morphine. Caution is suggested in drawing general conclusions from pharmacokinetic patterns of opioid elimination discussed in this review. Practitioners should be aware that drugs with short duration of action may have long half-lives and accumulate in end-stage liver and renal disease. While pharmacokinetic differences have been described in various populations, the clinical effects and adverse outcomes are greatly influenced by numerous independent physiologic alterations seen in critical care patients. Patients with severe alterations in liver and renal function should be administered pain medications judiciously because these patients are predisposed to metabolic disarrays. These patients should not be denied pain care, but they may benefit from smaller, less frequently administered doses, rather than continuous infusion of opioid drugs. Titration of doses to clinical effects with careful patient assessment for adverse effects is crucial for achieving desired therapeutic outcomes with analgesic agents in the ICU.

Controversies in cardiopulmonary resuscitation: pediatric considerations

This article addresses some therapeutic controversies concerning medications that may be needed during advanced pediatric life support (APLS) and the routes of administration that may be selected. The controversies that are discussed include the appropriateness and selection of various routes for drug administration during APLS; the determination of whether epinephrine hydrochloride is the adrenergic agent of choice for APLS and its appropriate dose; treatment of acidosis associated with a cardiopulmonary arrest; recommendations for atropine sulfate doses; and the role, if any, of calcium in APLS. Background information differentiating pediatric from adult cardiopulmonary arrest is presented to enable the reader to have a better understanding of the specific needs of children during this life-threatening emergency. The article also presents an overview of various drugs used for APLS and a table of their typically recommended doses and routes of administration.

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.

Plasma concentrations and haemodynamic effects of nimodipine in patients resuscitated after cardiac arrest

As the pharmacokinetics of a drug may be altered in haemodynamically compromised patients, the plasma concentrations and haemodynamic effects of the calcium entry blocker nimodipine have been examined in patients resuscitated after out-of-hospital cardiac arrest. In 7 patients nimodipine was infused at increasing rates up to 30 micrograms.kg-1.h-1. The plasma concentrations increased with increasing dose; at the highest dose a mean steady-state plasma concentration of 22.1 ng.ml-1 was obtained, and the mean plasma clearance was 1.41.kg-1.h-1. There were no marked changes in mean arterial blood pressure or heart rate. In 9 other patients nimodipine was given as a bolus infusion of 10 micrograms.kg-1 over 3 min, followed by a continuous infusion of 30 micrograms.kg-1.h-1. A mean steady-state plasma concentration of 17.6 ng.ml-1 was obtained and the mean plasma clearance was 1.91.kg-1.h-1. Heart rate did not change significantly, but the mean arterial blood pressure fell. The data indicate that in patients resuscitated after cardiac arrest, the pharmacokinetics of nimodipine are not markedly different from patients with other conditions, e.g. subarachnoid haemorrhage. However, if a loading dose is given to obtain a steady-state concentration sooner, there will be a fall in arterial blood pressure.

Clinical pharmacological and therapeutic considerations in general intensive care. A review

The application of clinical pharmacological concepts and therapeutic standards in intensive care settings presents particularly difficult problems due to the lack of adequately controlled background information and the highly variable and rapidly evolving clinical conditions where drugs must be administered and their impact evaluated. In this review, an attempt has been made to discuss the available knowledge within the framework of a problem-oriented approach, which appears to provide a more clinically useful insight than a drug-centred review. Following a brief discussion of the scanty data and the most interesting models to which reference can be made from a pharmacokinetic point of view (the burn patient being taken as an example), the review concentrates on the main general intervention strategies in intensive care patients. These are based mainly on non-pharmacological measures (correction of fluid and electrolyte balance, total parenteral nutrition, enteral nutrition, oxygenation and ventilatory management) and are discussed with respect to the specific challenge they present in various clinical conditions and organ failure situations. In addition, 4 major selected clinical conditions where general management criteria and careful use of prophylactic and therapeutic drug treatments must interact to cope with the variety of presentations and problems are reviewed. These include: acute cerebral damage; anti-infective prophylaxis and therapy; cardiovascular emergencies; and problems of haemostasis. Each problem is analysed in such a way as to frame the pharmacological intervention in its broader context of the underlying (established or hypothesised) pathophysiology, with special attention being paid to those methodological issues which allow an appreciation of the degree of reliability of the data and the recommendations which appear to be practiced (often haphazardly) in intensive care units. The thorough review of the published literature provided (up to mid-1986) clearly shows that in this field the quality of randomised controlled and epidemiological studies is rather unsatisfactory. It would be highly beneficial to research and to clinical care if larger multicentric protocols and prospective epidemiological comparative investigations could be carried out to investigate more timely and adequately the variables which determine drug action, and the final outcome in the many subgroups of patients which must be considered in a proper stratification of intensive care unit populations.

Influence of cardiopulmonary resuscitation on plasma concentrations of nimodipine in the dog

The influence of cardiopulmonary resuscitation on the plasma concentrations of nimodipine in the anaesthetized dog has been examined. Nimodipine was given as a bolus injection followed by a maintenance infusion. When, during the maintenance infusion, the dogs were subjected to cardiac arrest followed by external cardiac massage combined with artificial ventilation (basic life support), a fast and almost threefold increase in the steady-state plasma concentrations of nimodipine was observed. When the maintenance infusion of nimodipine was stopped immediately before cardiac arrest and basic life support, the nimodipine concentrations decreased. These results indicate that during basic life support, there is a decreased transfer of infused nimodipine from plasma to the tissues. This is also supported by the fact that for antipyrine, a drug with a smaller volume of distribution than nimodipine, the increase in plasma concentrations when infused during cardiac arrest and basic life support, was much smaller. When nimodipine was started after restoration of the spontaneous circulation (advanced life support) in dogs that had been subjected to cardiac arrest and basic life support, the plasma concentrations were not significantly higher than in control dogs. It can be concluded that the fate of nimodipine is markedly altered during basic life support but not in the period following restoration of spontaneous circulation.

Effect of mechanical ventilation on hepatic drug pharmacokinetics

Mechanical ventilation was able to induce a decrease in cardiac output and regional blood flow, especially hepatic flow. Thus, hepatic elimination of drugs with a high hepatic-extraction ratio, which was linked to alteration in hepatic blood flow, could be reduced during mechanical ventilation. The aim of this work was to determine the effect of mechanical ventilation on pharmacokinetic parameters of lidocaine, which is a well-known nonrestrictive elimination drug at the hepatic level. Five patients (mean age, 58 years) with normal hepatic function and quite similar gasometric parameters before and after weaning from mechanical ventilation were studied. With a washout period of 48 hours between mechanical ventilation and spontaneous ventilation, each patient was submitted to the following protocol: lidocaine in a bolus (1.5 mg/kg intravenously), followed by infusion (1.0 to 1.7 mg/min for 120 minutes). The results were that the peak plasma concentration after the bolus during mechanical ventilation was 3.22 +/- 0.37 mg/L (mean +/- SE) vs 2.40 +/- 0.35 mg/L during spontaneous ventilation (p less than 0.02). Steady-state plasma concentration during mechanical ventilation was 2.10 +/- 0.20 mg/L vs 1.64 +/- 0.16 mg/L during spontaneous ventilation (p less than 0.01). Total clearance was 604.2 +/- 87.0 ml/min during mechanical ventilation vs 775.0 +/- 112.1 ml/min during spontaneous ventilation (p less than 0.01). Elimination half-life was 245.2 +/- 50.6 minutes during mechanical ventilation vs 160.0 +/- 40.6 minutes during spontaneous ventilation (p less than 0.05). Distribution volume was 188.6 +/- 50.2 L during mechanical ventilation and 183.0 +/- 50.8 L during spontaneous ventilation (not significant). These preliminary data clearly demonstrated a decrease in lidocaine elimination in patients submitted to mechanical ventilation, but the magnitude of dosage adjustment of such a highly hepatic-extracted drug in patients submitted to mechanical ventilation remains to be investigated.

Pharmacokinetic differences between peripheral and central drug administration during cardiopulmonary resuscitation

Advanced resuscitation techniques are dependent on drug therapy to increase survival. Because drugs must reach their site of action instantaneously, the choice of appropriate route of administration may be critical. To study the pharmacokinetics of drug administration by peripheral and central venous routes during resuscitation, nine mongrel dogs were studied. Arterial blood pressure and electrocardiograms were monitored continuously. Cardiac output was evaluated before resuscitation to determine control levels. After thoracotomy and fibrillation of the heart, cardiac massage was started with a frequency of compression maintained at 60/min. Bolus injections of two different radioisotopes were given simultaneously through a peripheral and a central vein. Isotope activity was sampled through a catheter in the right femoral artery at 5 second intervals for 90 seconds and at 30 second intervals for 210 seconds. The major differences between the two routes of administration were that central injection produced a 270% higher peak concentration (p less than 0.001) and significantly shorter lag times to the first appearance of tracer (16 +/- 7 versus 38 +/- 13 seconds, p less than 0.05) and times to peak concentration (13 +/- 5 versus 27 +/- 12 seconds, p less than 0.01). In contrast, there were no significant differences in area under the time-counts curve, mean residence time, total body clearance and steady state volume of distribution. The central compartment volume of distribution was significantly smaller after central than after peripheral injection (26.1 +/- 56 versus 76.3 +/- 16.5 ml, p less than 0.01). The therapeutic implications of these findings must be investigated for individual drugs used during cardiorespiratory resuscitation to determine the most appropriate route and dosage for each agent.