Factors affecting quinidine protein binding in humans

Plasma Protein Binding of Quinine: Binding to Human Serum Albumin, α1-Acid Glycoprotein and Plasma from Patients with Malaria

The binding of quinine to human serum albumin (HSA), α1-acid glycoprotein (AAG) and plasma obtained from healthy subjects (10 Caucasians and 15 Thais) and from Thai patients with falciparum malaria (n = 20) has been investigated. In healthy volunteers, plasma protein binding expressed as the percentage of unbound quinine was 7·9–31·0% (69–92·1% bound). The mean percentage of unbound quinine found with essentially fatty acid-free HSA (40 g L−1) was 65·4±1 −5% (mean±s.d.) and was comparable with the value (66·3 ± 3·8%, mean ± s.d.) for Fraction V HSA (40 g L−1)- This suggests that fatty acids do not influence the plasma protein binding of quinine. Binding of quinine to 0·7 g L−1 AAG was high (mean unbound 61·0 ± 5·0%), indicating that quinine is bound primarily to AAG and albumin, although other plasma proteins such as lipoproteins may be involved. The mean percentage of unbound quinine was slightly less in Caucasians (14·8 ± 6·7% unbound), compared with healthy Thai subjects (17·0 ± 6·7% unbound). The higher binding of quinine in Caucasian subjects was associated with a higher plasma AAG concentration observed in Caucasians. Mean percentage of unbound quinine was significantly lower in Thai patients with malaria (10·9 ± 4·0%) than in the healthy Thai subjects. The increase in the extent of quinine binding corresponded with the increase in the acute-phase reactant protein, AAG in the patients with malaria. Overall, when the data were combined there was a significant correlation (r = 0·846, P < 0·005) between the binding ratio (bound/unbound) of quinine and the plasma AAG concentration. This suggests that plasma AAG concentration may serve as a useful index to predict alterations in quinine binding. Although quinine is bound to albumin, it was not bound to either site I or site II on HSA as indicated from equilibrium dialysis and fluorescent probe displacement studies. Binding displacement studies revealed that there was no marked displacement of quinine by a variety of highly bound acidic and basic drugs, including other antimalarial drugs at their therapeutic concentrations.

Usefulness of monitoring free (unbound) concentrations of therapeutic drugs in patient management

Drugs are bound to various serum proteins in different degrees and only unbound or free drug is pharmacologically active. Although free drug concentration can be estimated from total concentration, for strongly bound drugs, prediction of free level is not always possible. Conditions like uremia, liver disease and hypoalbuminemia can lead to significant increases in free drug resulting in drug toxicity even if the concentration of total drug is within therapeutic range. Drug-drug interactions may also lead to a disproportionate increase in free drug concentrations. Elderly patients may have increased free drug concentrations due to hypoalbuminemia. Elevated free phenytoin concentrations have also been reported in patients with AIDS and pregnancy. Currently free drug concentrations of anticonvulsants such as phenytoin, carbamazepine and valproic acid are widely measured in clinical laboratories. Newer drugs such as mycophenolic acid mofetil and certain protease inhibitors are also considered as candidates for monitoring free drug concentration.

THEINTEGRATION OFPHARMACOKINETICS ANDPHARMACODYNAMICS: Understanding Dose-Response

Pharmacokinetic (PK) and pharmacodynamic (PD) studies have proven to be powerful and instructive tools, particularly in elucidating important aspects of human pharmacology. Nevertheless, they remain imperfect tools in that they only allow researchers to indirectly extrapolate, through computational modeling, the dynamic processes of drug action. Furthermore, neither tool alone provides a complete nor necessarily relevant picture of drug action. This review explores the utility and applications of PK and PD in the study of drugs, provides examples of lessons learned from their application to studies of human pharmacology, points out some of their limitations, and advances the thesis that these tools ideally should be employed together in an integrated approach. As we continue to apply these tools across the continuum of age and disease, they provide a powerful means to enhance our understanding of drug action, drug interactions, and intrinsic host factors that influence pharmacologic response.

Effect of alpha(1)-acid glycoprotein on the pharmacokinetics of tamsulosin in rats treated with turpentine oil

The pharmacokinetics of tamsulosin (TAM) was investigated using male Sprague-Dawley rats in which plasma alpha(1)-acid glycoprotein (alpha(1)-AGP) levels were elevated by the subcutaneous injection of 0.2 mL/kg of turpentine oil. alpha(1)-AGP levels increased about eight times after turpentine oil treatment, causing a threefold decrease in plasma unbound fraction (f(u)) of TAM. When 0.3 mg/kg of TAM was dosed intravenously, total and nonrenal clearances (CL(tot) and CL(nr)) in turpentine-treated rats were 47% and 44% lower than those in nontreated controls, respectively. The area under the concentration-time curve of plasma unbound TAM (AUC(inf,u)) was lower than that in the control. When 1 mg/kg of TAM was dosed orally, oral clearance (CL(oral)) in alpha1-AGP-induced rats was 65% lower than in the control. The AUC(inf,u) and unbound oral clearance (CL(oral,u)) were nearly equal in both groups. Moreover, a positive correlation was observed between fu and CL(oral) of TAM (r(2) = 0.603, P < 0.01), whereas no correlation was observed between f(u) and CL(oral,u). The absolute bioavailability (BA) increased from 19.2% to 46.9% by induction of alpha(1)-AGP. These results suggest that decreased f(u) caused by the elevation of plasma alpha(1)-AGP level affects the pharmacokinetics of TAM, but does not affect the CL(oral,u,) which represents the hepatic metabolism of TAM.

Standards of laboratory practice: cardiac drug monitoring

In this Standard of Laboratory Practice we recommend guidelines for therapeutic monitoring of cardiac drugs. Cardiac drugs are primarily used for treatment of angina, arrhythmias, and congestive heart failure. Digoxin, used in congestive heart failure, is widely prescribed and therapeutically monitored. Monitoring and use of antiarrhythmics such as disopyramide and lidocaine have been steadily declining. Immunoassay techniques are currently the most popular methods for measuring cardiac drugs. Several reasons make measurement of cardiac drugs in serum important: their narrow therapeutic index, similarity in clinical complications and presentation of under- and overmedicated patients, need for dosage adjustments, and confirmation of patient compliance. Monitoring may also be necessary in other circumstances, such as assessment of acetylator phenotypes. We present recommendations for measuring digoxin, quinidine, procainamide (and N-acetylprocainamide), lidocaine, and flecainide. We discuss guidelines for measuring unbound digoxin in the presence of an antidote (Fab fragments), for characterizing the impact of digoxin-like immunoreactive factor (DLIF) and other cross-reactants on immunoassays, and for monitoring the unbound (free fraction) of drugs that bind to α1-acid glycoprotein. We also discuss logistic, clinical, hospital, and laboratory practice guidelines needed for implementation of a successful therapeutic drug monitoring service for cardiac drugs.

Pharmacokinetics of tamsulosin hydrochloride in patients with renal impairment: effects of alpha 1-acid glycoprotein

The pharmacokinetics of tamsulosin hydrochloride in patients with renal impairment were compared with those in healthy volunteers, and the factors that influenced plasma levels of tamsulosin were elucidated. A single oral dose of 0.2 mg of tamsulosin was given and blood and urine samples were obtained for 36 hours after administration. Unbound plasma concentration of tamsulosin was measured by a combination of equilibrium dialysis and liquid chromatography tandem mass spectrometry methods to examine the effect of protein binding on the pharmacokinetics of tamsulosin. Mean values for maximum concentration (Cmax) and area under the concentration-time curve (AUC) of total drug (Cmax,t and AUC1) in patients with renal impairment were 73% and 211% greater, respectively, than those in healthy volunteers. Mean Cmax and AUC of unbound drug (Cmax,u and AUCu), however, were almost the same in the two groups. A high correlation was found between alpha 1-acid glycoprotein (alpha 1-AGP) concentration and AUCt, but no correlation was found between alpha 1-AGP concentration and AUCu,0-36) or between creatinine clearance (ClCR) and AUCu,0-36). These results show that in patients with renal impairment, the pharmacokinetics of tamsulosin are affected by the change in protein binding that is associated with alteration of plasma alpha 1-AGP concentration, but are not largely affected by the decrease in the renal excretion. Although total tamsulosin levels increased as plasma protein binding increased, unbound tamsulosin levels (which are directly associated with the pharmacologic effects) remained unchanged in these patients.

The safety and kinetics of intramuscular quinine in Malawian children with moderately severe falciparum malaria

The safety and kinetics of intramuscular quinine (10 mg salt/kg every 8 h for 3 doses) were assessed in Malawian children suffering from uncomplicated falciparum malaria, who were unable to take oral antimalarial drugs. Treatment was completed with oral pyrimethamine-sulfadoxine. The mean (+/- SD) peak plasma quinine concentration after the first injection was 9.0 (+/- 2.3) micrograms/ml, at 1.1 (+/- 0.7) h. Mean plasma concentrations increased further after the second and third doses to a maximum of 11.5 (+/- 2.6) micrograms/ml at 16.1 (+/- 3.2) h. No hypotension, hypoglycaemia or electrocardiographic abnormalities developed during quinine treatment. These results provide further evidence for the safety of intramuscular quinine in children with moderately severe malaria. Plasma concentrations of alpha 1-acid glycoprotein (AGP) were higher, and the degree of protein binding of quinine was greater, in acute malaria than in convalescence. There was a significant correlation between AGP concentration and the fraction of plasma quinine bound to plasma protein. These findings suggest a role for AGP in the binding of quinine in plasma in vivo and are of interest since unbound quinine is responsible for both the efficacy and toxicity of the drug.

Comparison of assay procedures used to measure total and unbound concentrations of quinidine

Individualized quinidine dosing through the assessment of serum concentrations is warranted because of the wide variability observed in its pharmacokinetic behavior and its reported narrow therapeutic index. The free fraction of quinidine also varies widely. Thus the development of procedures that could be widely used to determine quinidine free concentrations would be highly desirable. It was the purpose of this study to evaluate several procedures available to determine total serum quinidine concentrations (rate nephelometry [ICS], homogenous enzyme immunoassay [EMIT], and high-performance liquid chromatography [HPLC]). Furthermore, in samples from 46 patients, equilibrium dialysis and ultrafiltration procedures were compared for their ability to estimate quinidine free fraction. Finally, unbound concentrations of quinidine were compared using a modified EMIT procedure and a standard HPLC method to quantitate quinidine in ultrafiltrates from patient samples. For the measurement of total quinidine concentrations, reasonable agreement was seen when EMIT and ICS systems were compared with HPLC (ICS = 1.03.HPLC + 0.96, r = 0.93; EMIT = 1.08.HPLC + 0.38, r = 0.93) The mean errors, however, for these procedures were high (ICS +70 percent, range +7 to +233 percent; EMIT +35 percent, range 0 to 110 percent). Quinidine free fractions (QFF) determined by equilibrium dialysis (E) and ultrafiltration (U) showed good agreement (QFF(U) = 1.11.QFF(E) +0.0; r = 0.96). Unbound quinidine concentration determined by EMIT analysis of ultrafiltrate substantially overestimated the values obtained by HPLC analysis (mean error by EMIT 104 +/- 59 percent). It is concluded that HPLC is the method of choice for determining both total and unbound serum quinidine concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Lack of effect of treatment with human recombinant-tumour necrosis factor (HrTNF) on the binding of quinidine to alpha 1-acid glycoprotein (AGP)

Tumour necrosis factor (TNF) is known to be a key mediator in the acute phase response and its administration has been shown to cause a five fold increase in serum alpha 1-acid glycoprotein (AGP) concentration in the rat. Since, in man, plasma AGP level determines the protein binding of many important drugs (e.g. narcotic analgesics, phenothiazines, antiarrhythmics, calcium channel blockers) likely to be given to patients who will be treated with TNF, it is important to determine if TNF treatment of humans causes a similar increase in AGP concentration and drug binding. Therefore, the plasma protein binding of quinidine and the serum level of AGP were studied over a 4 day period in each of five cancer patients who were treated with human recombinant-tumour necrosis factor (HrTNF) using a dosage schedule of 6-8 x 10(+5) units/m2 daily for 5 days. It was observed that the quinidine binding ratio (the quotient of bound and free concentration in plasma) was highly correlated with the plasma concentration of AGP (r = 0.818) and that the mean pretreatment AGP concentration in the patients was about three times that found in normal subjects. However, no effects of the TNF treatment regime used in the present study could be demonstrated on either plasma AGP concentration or quinidine free fraction. These observations allow the tentative conclusion that HrTNF does not cause a significant increase in serum AGP level in cancer patients whose baseline AGP concentration is high. However, further study of the relationship between TNF treatment and serum AGP level is needed.

Dissociation of authentic and artifactual effect of circulating heparin on drug protein binding

The purpose of this study was to dissociate the authentic and artifactual effect of in vivo heparin on drug protein binding using protamine as an inhibitor of ex vivo lipolysis. A mixture of ethylenediamine tetra-acetic acid (EDTA, 5 mg ml-1) and protamine in the concentration range of 0 to 7.5 mg ml-1 was added to blood samples from 23 cardiac catheterized patients before (control) and 10 min after 3000 IU of intravenous heparin. In control samples, protamine does not interfere with the protein binding of lidocaine (L), quinidine (Q) or propranolol (P) when plasma pH is readjusted to 7.4. In the absence of protamine, heparin induced a significant increase in the free fraction by 40, 130, and 30 per cent for L, Q, and P, respectively (p less than 0.001), while free fatty acid (FFA) levels increased 2 to 6 fold. When protamine was present, the heparin-induced elevation in free fraction was significantly lower for L (16 per cent) and Q (77 per cent) but not for P; FFA levels were decreased at all protamine concentrations. Residual increases in free fraction and FFA levels compared to control values may represent the true in vivo effect of heparin at the peak activity of lipoprotein lipases. For L and Q, variations in free fraction were strongly associated with variations in FFA, but for P, no significant correlation was observed (r = 0.492). These results indicate that variations in free fraction of L and Q caused by heparin are, to a large extent, artifactual but may be prevented by use of protamine in collection tubes (5 to 7.5 mg ml-1). For P, the increase in free fraction was not mediated by variations of FFA indicating that another mechanism must be involved.

Role of plasma concentration monitoring in the evaluation of response to antiarrhythmic drugs

Plasma concentration monitoring of antiarrhythmic agents is valuable, but it is often misused or overemphasized in therapeutic decision-making. There are strict requirements for its appropriate use that are often not met--for both the newer and even the conventional antiarrhythmic drugs. For maximum value, there must be a reliable, accurate relation between the plasma drug concentration and drug action, a relation closer than that between dosage and drug action. The time of sample collection is important--most guidelines are based on "trough" plasma concentrations measured after steady-state equilibrium has been achieved. The use of an accurate, sensitive and specific assay is crucial to the value of plasma concentration monitoring guidelines. However, for agents having active metabolites, monitoring the concentration of only the parent drug can be misleading and limits (but does not necessarily eliminate) the value of plasma concentration monitoring guidelines for these agents. Plasma concentration monitoring of most antiarrhythmic agents is of value for certain specific purposes: to determine compliance to antiarrhythmic therapy, to detect and analyze possible drug interactions, to assess the benefit to risk ratio for increasing the dose of a particular antiarrhythmic agent, to maintain a stable drug effect in the presence of a patient's changing clinical condition and, to a limited extent, to assess the role of an agent in causing an adverse drug reaction. The importance of understanding the assay methods currently in use, as well as how plasma concentration monitoring of individual antiarrhythmic agents is affected by the presence of active metabolites, optical isomers differing in their activity and variations in protein binding, is essential in interpreting data obtained from plasma concentration monitoring.

The pharmacokinetics and pharmacodynamics of quinidine and 3-hydroxyquinidine

1. The pharmacokinetics and pharmacodynamics of quinidine and 3-hydroxyquinidine based upon measurements of total and unbound serum concentrations were determined after a single dose (400 mg) and at steady state (200 mg every 6 h). 2. The oral clearance (7.6 +/- 1.9 vs 4.8 +/- 2.0 ml min-1 kg-1; P less than 0.05) and renal clearance (1.2 +/- 0.3 vs 0.63 +/- 0.25 ml min-1 kg-1; P less than 0.005) or quinidine were lower during steady state than after the single dose. 3. The area under the serum concentration vs time curve (AUC) of 3-hydroxyquinidine was greater at steady state than after the single dose (2.0 +/- 0.7 vs 3.0 +/- 0.6 mg l-1 h; P less than 0.05) and its renal clearance was less (3.0 +/- 1.1 vs 1.54 +/- 0.38 ml min-1 kg-1; P less than 0.05). 4. The slope of the relationship between quinidine concentration and change in QTc interval was greater at steady state (40.1 +/- 21.7 vs 72.2 +/- 41.7 ms/(mg l-1); P less than 0.05).

Protein binding of cocaine in human serum

The protein binding characteristics of cocaine have not been extensively studied. Since cocaine is related to other local anesthetic compounds which are highly protein bound, we examined the binding of cocaine in human serum using an ultrafiltration method. The free fraction averaged 0.083 +/- 0.018 in the serum of 12 healthy volunteers. Binding was studied at concentrations ranging from 0.1 to 500 micrograms/ml and was concentration dependent, with increases being most pronounced at concentrations above 5 micrograms/ml. Two classes of binding sites were identified with affinity and capacity constants consistent with binding to alpha-1-acid glycoprotein (AAG) and albumin. The addition of AAG to serum resulted in a decrease in the free fraction from 0.079 to 0.041, while tris(butoxyethyl)phosphate increased the free fraction to 0.233. The binding ratio was found to be highly correlated with the AAG concentration (r = 0.89). In addition, the predicted free fraction in the absence of AAG (0.67) was in good agreement with the observed value of 0.647 in a solution of human serum albumin (4.5 g/dl). Of the metabolites of cocaine, only norcocaine displaced the parent drug from serum binding sites. These results indicate that cocaine is highly bound to serum proteins, primarily albumin and AAG. The significance of concentration-dependent binding to cocaine toxicity remains to be established.

Differences in the binding of quinine and quinidine to plasma proteins

1. Little is known about the comparative plasma protein binding of the antimalarial agents quinine (QN) and its isomer quinidine (QD). We have examined the in vitro binding of QN and QD to albumin, alpha 1-acid glycoprotein, normal human plasma, and maternal and foetal umbilical cord plasma. 2. QN was more avidly bound than QD, and binding of both drugs was substantially higher to alpha 1-acid glycoprotein than to albumin, indicating that alpha 1-acid glycoprotein is the more important binding protein. 3. Protein and drug concentration dependent binding was evident for both QN and QD. The unbound fraction of both drugs fell with increasing albumin (10 to 60 g l-1) and alpha 1-acid glycoprotein (0.5 to 2.0 g l-1) concentration, and there was a marked increase in unbound fraction of QN (6 to 19%) and QD (13 to 36%) in human plasma when drug concentrations were increased over the antimalarial therapeutic range (0.5 to 10 mg l-1). 4. In human volunteer plasma, the unbound fractions of QN and QD were 7.5 +/- 2.2% and 12.3 +/- 2.3% respectively, whilst the unbound fractions for both drugs were significantly higher in maternal plasma (QN = 13.0 +/- 5.4%, QD = 18.3 +/- 2.5%) and significantly higher still in foetal umbilical cord plasma (QN = 25.7 +/- 10%, QD = 35 +/- 5.3%).

Interaction of mixed micelles formed from glycocholic acid and lecithin with the protein binding of various drugs

Mixed micelles (MM) formed from glycocholic acid and lecithin are suited to solubilize lipophilic drugs for intravenous use. To test for possible drug-drug interactions, the protein binding of a series of agents known to bind to different sites on albumin (diazepam, warfarin, ketoprofen, frusemide, probenecid) and additionally (prazosin, quinidine, propranolol) or exclusively (disopyramide) to alpha 1-acid glycoprotein or to transcortin (prednisolone) was determined in the presence and absence of MM. Concentrations of MM, corresponding to the maximum possible plasma concentration achieved by injecting the highest clinical doses of MM into the systemic circulation, had little or no effect on the unbound fractions of drugs known to bind exclusively to albumin. Only at five times higher MM concentrations were the free fractions substantially increased (by up to 45%). Unbound fractions of drugs bound with high affinity but low capacity to alpha 1-acid glycoprotein were increased between 50-85% even at 'therapeutic' doses of MM. The present study suggests that drugs solubilized by MM should be given by slow injection or infusion to patients already receiving drugs which are highly bound to alpha 1-acid glycoprotein.

Total and unbound concentrations of quinidine and 3-hydroxyquinidine at steady state

Recent reports indicate that the metabolite of quinidine, 3-hydroxyquinidine, is pharmacologically active. It was the primary purpose of this study to determine total and unbound concentrations of quinidine and 3-hydroxyquinidine in 25 patients receiving quinidine for therapeutic purposes. At the peak, total quinidine and 3-hydroxyquinidine concentrations were 2.7 +/- 1.2 micrograms/ml and 0.57 +/- 0.33 micrograms/ml, respectively, and at the trough they averaged 2.0 +/- 0.91 micrograms/ml and 0.44 +/- 0.25 micrograms/ml. Interestingly, the unbound 3-hydroxyquinidine concentration frequently exceeded the unbound quinidine concentration, averaging 0.30 +/- 0.28 micrograms/ml at the peak and 0.22 +/- 0.14 micrograms/ml at the trough. Quinidine concentrations averaged 0.24 +/- 0.15 micrograms/ml and 0.18 +/- 0.12 micrograms/ml. The ratio of unbound 3-hydroxyquinidine: quinidine was significantly influenced by the unbound clearance of quinidine (r = 0.66). At low clearance values concentrations of both substances were elevated, with the quinidine concentration consistently exceeding that of 3-hydroxyquinidine. In contrast, at high clearance values 3-hydroxyquinidine concentrations were elevated and consistently exceeded the quinidine concentration. Thus, when quinidine concentrations are used to monitor the pharmacodynamic effect of quinidine, it is most appropriate to evaluate unbound concentrations of both quinidine and 3-hydroxyquinidine.

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.

Hepatic drug clearance following traumatic injury

Trauma is a complex disease state associated with physiologic changes that have the potential to alter hepatic drug clearance mechanisms. These responses include alterations in hepatic blood flow, reduction in hepatic microsomal activity, reduction in hepatic excretion processes, and changes in protein binding. Hepatic blood flow is influenced by sympathomimetic activity. Both animal and human studies demonstrate an initial reduction and subsequent increase in hepatic blood flow, which coincides with an observed increase and subsequent return to normal in serum catecholamine concentrations. Unfortunately, there are no human studies that address the importance these findings may have to the clearance processes of high intrinsic clearance compounds. Animal studies of trauma indicate that hepatic microsomal activity is depressed during the post-traumatic period. Reduction in the hepatic clearance of antipyrine, a model low intrinsic compound, has also been demonstrated in animal models of trauma. In addition to these effects, hepatic excretion of substances such as indocyanine green and bilirubin have been demonstrated to be impaired in both traumatized animals and humans. Finally, substantial increases in the serum concentration of the binding protein alpha 1-acid glycoprotein occur in trauma patients. This has been reported to be associated with subsequent decreases in the free fraction of lidocaine and quinidine. In addition to changing serum drug concentration/response relationships, the pharmacokinetic behavior of drugs bound to alpha 1-acid glycoprotein should also change. Preliminary observations in our laboratory in a dog model of surgically-induced trauma have shown a reduction in the total clearance of lidocaine and reduction in free lidocaine concentration.(ABSTRACT TRUNCATED AT 250 WORDS)