NUTRITION RESEARCH, Vol. 9, pp. 1101-1108, 1989 0271-5317/89 $3.00 + .00 Printed in the USA. Copyright (c) 1989 Pergamon Press plc. All rights reserved.

EFFECT OF NUTRITIONAL STATUS ON CHLORAMPHENICOL PHARMACOKINETICS (CAP)

Maria E. Bravo (Chemist) I, Maria Gladys Barrera, RN I, AquilesArancibia (Chemist) 2 and Ricardo Uauy, M.D., Ph.D. ''3

i Inst i tuto de Nutrici6n y Tecnologia de los Alimentos (INTA), Universidad de Chile.

~Departamento de Ciencias Farmacologicas, Facultad de Ciencias BAsicas y Farmace~ticas, Universidad de Chile.

3Department of Pediatrics and Center for Human Nutrition, University of Texas Southwestern Medical Center at Dallas.

ABSTRACT

Fourteen healthy males 19-40 years old were selected according to nutrit ional status using weight/height (W/H) as % of ideal and body fat derived from fat fold measurements. The "underweight group" had W/H ranging from 80-100 ((mean+SD 91.7+6.4 and 18.2+2.6% body fat, the control group had W/H I00-120 (mean-+ SD 108.8 • and (24.4 + 3% fat). Both groups received 25 mg/kg-body weight CAP as succinate by intravenous bolus. Blood samples were obtained at O, 30, 60, 90, 120, 240 and 360 min. Free plasma CAP levels were measured by a radioenzymatic method. Pharmacokinetics parameters were obtained from the linear regression of log e plasma concentration versus time: slope (K), half l i f e (t I/2), distribution volume (Vd), I/kg BW; Vd I/kg fat. No significant differences were found between the two groups for the classic pharmacokinetics parameters, but Vd I/kg fat was signif icantly different between the groups 6.52 + 2.51 for the underweight versus 4.1 + 0.44 for control (p<O.02). We conclude that CAP distribution volume is modified by nutrit ional status; this should be considered in evaluating drug kinetics for therapy.

KEY WORDS: nutrit ional status, pharmacokinetics, body fat, chloramphenicol, underweight.

Address all correspondence to: Ricardo Uauy, M.D., Ph.D., The University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75235-9063

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1102 M.E. BRAVO et al.

INTRODUCTION

A number of physiological and pathological conditions may alter the pharmacokinetics of drugs in man. Among these, renal fai lure produces the most severe changes, specially for those drugs that are eliminated by the kidney (I- 2). Kinetics characteristics become important in order to establish appropriate dosage regimens for drugs. In addition, knowing the effects of various disease states on drug pharmacokinetics may be useful to optimize therapy in patients with altered physiological or disease conditions.

The importance of performing pharmacokinetic studies in subjects with different nutrit ional conditions has also been recognized (3). In our laboratory we have become interested in this problem and have recently studied the pharmacokinetics of gentamicin (4) and sulfamethoxazole in marasmic children (5).

Chloramphenicol (CAP) is an antimicrobial agent widely employed in the treatment of typhoid fever which is a highly prevalent disease in underdeveloped countries. The high l iposolubi l i ty of CAP determines a greater distr ibution in the adipose tissue relative to other organs. A volume of distr ibution of 1.4 I kg -I has been reported (6). Other pharmokinetic studies indicate a large var iab i l i ty in elimination constants specially for children (7). In this study we evaluated the effect of nutrit ional status on the pharmacokinetics properties of CAP.

PATIENTS AND METHODS

Fourteen healthy non-smoking male volunteers aged between 19-40 years who had fasted overnight participated in this study. No alcohol or drug other than the test compounds were permitted during the study. A complete physical examination and routine laboratory analysis were performed to discard any underlying disease. The subjects were distributed in two groups according to their nutrit ional status defined by weight for height (W/H) cr i ter ia. The underweight group (n=7) less than 100% of ideal W/H relative to the WHO standards (8) and the control group (n=7) presented W/H greater than 100% but did not exceed 120% of the standard. Height and weight were measured on two opportunities. Percentage of body fat was calculated from measurement of four skinfolds as suggested by Durnin et al (9).

Chloramphenicol succinate (CAP-S) was prepared in a steri le isotonic glucose solution (glucose 5%) and injected using a constant intravenous infusion over 10 minutes at a dose of 25 mg/kg/body weight. Dosage was verified measuring the CAP concentration of the pharmaceutical product according to USP XXI Convention (]0). No food was permitted in the four hours following drug infusion. The subjects were kept fasting for a period of 3 hrs prior to drug administration.

Venous blood samples were drawn from the contralateral arm and at O, 0.5, I, 1.5, 2, 4 and 6 hrs. after dosing, collected in centrifuge tubes containing oxalate as anticoagulant. Plasma obtained by centrifugation was frozen (-4~ unti l the day of analyses and free chloramphenicol was measured by the radioenzymatic method of Lietmann (11).

NUTRITION AND CAP KINETICS 1103

The purpose of this study was explained to all subjects and their written consent obtained. The study protocol was approved by the Institutional Ethics Committee at INTA which regulates the use of humans as experimentaT subjects.

PHARMACOKINETIC ANALYSIS

CAP plasma concentrations declined according to a single exponential decay. Classic pharmacokinetics techniques (12) were employed to treat the plasma data to calculate the elimination half- l i fe, t i/2, and the elimination rate constant K. Since total CAP and not CAP succinate was measured, 70% bioavailability was considered (30% excretion of intact chloramphenicol succinate) to obtain an estimation of the volume of distribution, total body clearance, metabolic and renal clearances.

Two sample two tailed student's "t" test at a 0.05 significance level was used to assess differences between the two groups.

RESULTS

Table i shows the (mean • SD) anthropometric characteristics of subjects: age, weight, height, percentage of ideal weight for height in reference to WHO standard, surface area, lean body weight (LBW), fat weight (FW). The sum of skinfolds served to calculate body density and body fat. Highly significant differences are noted for all indices except height and age.

TABLE I

Characteristics of Subjects Studied

Underweight (n=7) Control (n=7)

Age (yr) 26.6 • 7.7 32.3 • 7.0 Height (cm) 163.6 • 5.4 165.5 • 8.1 Weight (kg) 57.2 • 3.5 t 69.5 • 7.0 W/H* (%) 91.1 • 6.7 t 110.9 • 4.7 Surface area (m2) 1.61 • 0.1 1.77 • 0.1 Skinfolds (mm) 41.2 • 5.6 t 65.8 r 7.8 % Body fat (kg) 18.2 • 2.6 # 24.4 • 3.1 Fat Weight (kg) 10.5 • 1.2 t 17.0 r 2.9 Lean Weight (kg) 47.3 • 2.6 w 52.4 • 5.3

Values represent mean • standard deviation (n) = Number of subjects

of ideal W/H of the WHO Standard t p<O.O01; #p<O.O05; w p<O.05 difference between control and underweight

Table 2 summarizes the routine laboratory analysis for each group, values are expressed as mean • SD. The groups exhibit similar results for all tests.

1104 M.E. BRAVO et al.

TABLE 2

Laboratory Finding of the Subjects

Underweight (n = 7 ) Control (n = 7)

Hematocrit % 43.2 • 2.4 41.5 • 2.6 Plasma Protein g/dl 7.4 • 0.57 7.3 • 0.45

Albumin g/dl 4.5 • 0.74 4.9 • 0.45 Transaminases

GOT* 32.3 • 10.3 32.0 r 7.8 GPT* 24.1 • 3.9 21.6 • 4.7

Bilirubin Direct mg/dl 0.15 • 0.0 0.14 • 0.05 Total mg/dl 0.69 • 0.30 0.56 • 0.25

Urea N mg/dl 11.8 • 3.1 13.6 • 2.4 Creatinine

Plasma mg/dl 0.84 • 0.09 0.83 • 0.08 Urine mg/dl 75.8 • 30.9 70.5 • 18.1 Clearance ml/min 99.6 • 19.6 93.9 • 27.1

Values represent mean • standard deviation * Karmen Units/dl

Pharmacokinetic parameters are listed in Table 3. These include volume of distribution and clearance corrected for fat weight. No significant differences were found for classical pharmacokinetics parameters. However when Vd is expressed in I/kg FW there is a highly significant difference (p<.02). The "underweight" showed a significantly greater value.

TABLE 3

Pharmacokinetics Parameters in Subjects After the Intravenous Administration of 25 mg/kg Body Weight of CAP Hemisuccinate

Underweight (n=7) Control (n=7)

Elimination half l i fe (h) Elimination constant (h-l) Absolute volume of distribution(1) Distribution volume per kg total (I/kg) Distribution volume per kg IBW (I/kg) Distribution volume per kg fat (I/kg fat) Total metabolic clearance (ml/min) Total metabolic clearance (ml/min/kg) Total metabolic clearance (ml/min/kg fat) Renal clearance (ml/min/1.73 m2) Area under curve (mg/h/l)

2.9 (1.6 - 4.0) 0.25(0.17-0.45) 68.0(41.7-106.2) 1.2 (0.9 - 1.8) 1.1 (0 .8 - 1.7) 6.5 (4.1 - 11.6) * 293 (165 - 605) 5.2 (3 .0 - 11.2) 24.4 (15 .5 -41 .1 ) 29.0 (4.6 - 70.9) 66.9 (24.9-105.8)

2.6 (0.9 - 3.5) 0.33(0.20-0.70) 70.2(52.0-93.0) 1.0 (0.9 - 1.2) 1.1 (o.8- 1.3) 4.1 (3.6 - 4.40) 387 (228 - 889) 5.5 (3.5 - 13.2) 23.0 (12.8-58.9) 33.2 (15.1-60.3) 63.9 (21.5-86.1)

Mean (Range) values *p<O.02 underweight versus control group

IBW = Ideal Body Weight

NUTRITION AND CAP KINETICS II05

Disposition curves of chloramphenicol from plasma after intravenous bolus infusion for both groups are shown in Figure i. The control group at 30 minutes after the injection reached higher CAP concentrations than the underweight group; however this difference was not statist ically significant. After one hour the plasma concentration declined in a similar fashion for both group.

2 0

A

o

~ o (.,)

(/)

/ n

n 5

o

o - - -.o UNDERWEIGHT

= : C O N T R O L

\ \ \

I I I I I I t 2 3 4 5 6

T I M E ( h o u r s )

FIG. 1: Plasma chloramphenicol concentration following an intravenous administration of 25 mg/kg body weight of chloramphenicol equivalent. Values represent mean • SEM (for drawing purposes values are slightly shifted to the lef t) .

1106 M.E. BRAVO et al.

DISCUSSION

The influence of body composition on disposition of drug has not been fu l ly settled. Chloramphenicol is a drug with a narrow therapeutic index (13), used very frequently to treat typhoid fever. The selection of the correct basis to calculate the most appropriate dosing for patients of different weight and body composition is highly relevant. The goal of this study was to determine the effect of differences in body fat within a range commonly observed in patients on chloramphenicol kinetics.

Our results in "healthy" subjects with different amount of body fat indicate that there are no significant differences in the kinetics of CAP when the general pharmacokinetics parameters are compared. Elimination ha l f - l i fe showed great var iab i l i ty (0.90-3.95 hrs) in accordance with the data of Friedman et al (14), this great var iabi l i ty apparently is due to differences in hepatic metabolism.

CAP is inactivated primarily in l iver by glucoronyl transferase and converted to CAP glucuronide which is excreted through the b i l iary tract (15). CAP and i ts metabolites are rapidly excreted in the urine, over a 24 hr period 75-90% of an orally administered dose is so excreted, about 5-10% is in the biologically active form. The unaltered antibiotic is eliminated mainly by glomerular f i l t ra t ion ; the inactive degradation products are eliminated primarily by tubular secretion.

CAP is one of many drugs which gain access to all tissues penetrating cells due to i ts solubi l i ty in the l ip id layer of cell membranes. In cells and in the plasma CAP binds reversibly to "si lent receptors" such as albumin according to i ts concentration and i ts a f f in i ty for binding sites on proteins. Drug metabolizing enzymes in l iver cells act as non-specific receptor sites and bind l ipophi l ic drugs. Because of their ab i l i ty to conjugate CAP, they reduce i ts active concentration. Glazko et al (16) has studied CAP distr ibution in rats, dogs and guinea-pig proving that is not uniformly distributed. The highest concentrations are found in l iver and kidney and the lowest in brain, to date no studies have evaluated the differences in body fat on CAP kinetics.

To further analyze the effect our results we have f i t ted Vd/kg fat weight versus kg of fat to a logarithmic curve (Fig. 2) and have found a significant correlation. This finding indicates that the volume of distr ibution of CAP per unit of fat weight increases as body fat decreases suggesting that probably a different a f f in i ty exists between the antibiotic and different types of organ fat, therefore distribution volume per unit of fat weight wi l l decrease as adipose tissue increases.

NUTRITION AND CAP KINETICS 1107

15

'~ I0 4 - -

3

�9 UNDERWEIGHT x CONTROL

p < O.OI �9 Y = 1 8 . 0 9 - 4 . 9 6 In X

' / I I I 5 I 0 15 2 0

Kg f a t w e i g h t

FIG. 2: Distribution volume per kg of body fat Vd (I/kg) fat weight as a function of absolute body fat weight.

Studies performed by Abernethy (17) concerned with both hydrophilic and lipophilic drugs have pointed that in obese subjects, there are alterations in drug distribution. Adipose tissue distribution for a specific drug,appears to depend largely upon its intrinsic characteristics of l ipophil icity.

Our study is concerned with populations with small differences in fat content additional studies including subjects over 120% W/H and under 80% W/H are needed before this information can be used across the full range of body weights.

Based on these preliminary results we conclude that body fat affects mainly the distribution volume of chloramphenicol but does not alter other pharmacokinetic parameters. The difference in distribution volume is apparent only when expressed per unit of body fat weight. As body fat decreases there may be an increased aff inity for chloramphenicol suggesting a differential uptake of visceral relative to peripheral adipose tissue.

ACKNOWLEDGEMENTS

This work was supported by a Grant No. 678-8355 del Servicio de Desarrollo Cientifico, Artistico y de Cooperacion Internacional, Universidad de Chile.

1108 M.E. BRAVO et al.

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Accepted for publication May 12, 1989.