Incidence, predictability, and pathogenesis of amiodarone-induced thyrotoxicosis and hypothyroidism.

PURPOSE: To determine the incidence and predictability and to elucidate the pathogenesis of amiodarone-induced thyrotoxicosis (AIT) and hypothyroidism (AIH). PATIENTS AND METHODS: A prospective study was performed in 58 consecutive euthyroid patients living in an area with moderately sufficient iodine intake, who had never been treated for thyroid disease and who started amiodarone therapy for the first time. MAIN OUTCOME MEASURES: Development of thyrotoxicosis or hypothyroidism. RESULTS: The follow-up period was 6 to 54 months (mean, 21 months). The incidence of AIT was 12.1%. A steady occurrence of new cases was observed. The development of AIT was unpredictable and of unexplained sudden onset. The incidence of AIH was 6.9%. All AIH cases occurred early in the course of amiodarone therapy. The development of AIH was related to pre-existent thyroid disease: the relative risk for women with microsomal and/or thyroglobulin autoantibodies prior to treatment was 13.5 (95% confidence interval 3.2 to 57.4). The development of AIT or AIH was not related to the extent of iodine overload or to the occurrence of de novo thyroid autoantibodies. When a decreased thyrotropin (TSH) response to thyrotropin-releasing hormone occurred (in the absence of AIT), continuation of amiodarone medication was associated with a normalization of the TSH response in eight of 11 cases (73%); in contrast, an increased TSH response (in the absence of AIH) returned to normal in one of four cases (25%). CONCLUSION: In euthyroid subjects living in an area with a moderately sufficient intake of iodine, there is a higher incidence of AIT than of AIH. AIH is an early event, occurring especially in women with thyroid autoantibodies prior to treatment. Cases of AIT continue to occur during amiodarone therapy; its development is unpredictable and of unexplained sudden onset. The value of regular thyroid function testing is therefore limited during amiodarone administration.

Treatment of recurrent chronic bacterial prostatitis by local injection of thiamphenicol into prostate.

Twenty-nine patients were treated for recurrent chronic bacterial prostatitis by an injection of 2 Gm. thiamphenicol glycinate via the perineal route directly into the prostate. Escherichia coli was identified as the pathogen responsible for this infection in 83 per cent of the cases. Using this medication locally, cure was obtained in 66 per cent of the patients. Thiamphenicol levels in prostatic fluid varied between 1 and 4,000 micrograms./ml. and were unrelated to the time after intraprostatic administration. However, in most cases they were high enough to inhibit most strains of gram-negative bacilli responsible for prostatitis. Serum levels were correlated with the time after injection and decreased over twenty-four-hour observation from 25 to 0.3 micrograms./ml. The pH of the prostatic fluid measured in 24 patients varied from 7.1 to 8.7 with a mean value of 7.9 and was markedly higher than the pH value of 6.5 reported for men without inflammatory prostatic disease. The elevated pH of prostatic fluid could explain the failure of short-term trimethoprim/sulfamethoxazole (Co-trimoxazole) treatment in our patients. The cure rate of the localized thiamphenicol treatment was higher than was reported with short- and long-term trimethoprim/sulfamethoxazole therapy. We concluded that direct injection into the prostate offers a good alternative for treatment of more resistant chronic infections of the prostate.

A comparative study of the homogeneous enzyme immunoassay (EMIT) and two radioimmunoassays (RIA's) for digoxin.

Our experience with the determination of digoxin in plasma or serum using a homogeneous enzyme immunoassay technique (EMIT) is reported. The day-to-day precision of the EMIT digoxin assay was investigated with different series of calibrators. Coefficients of variation varied from 10 to 25 percent in the range of 0.65--7.0 ng digoxin/ml. The accuracy was established by determining the mean recovery (96 percen) of spiked serum samples (0.0--6.0 ng digoxin/ml). The cross reactivity of structure related compounds: digitoxin, spironolactone (Aldactone) and prednisone were investigated. Amniotic fluid, umbilical cord serum and serum of pregnant patients were examined for false positive reaction. Serum samples of 111 patients from two hospitals, who were treated with digoxin, were analysed by EMIT and 3H-radioimmunoassay (RIA); 38 of these samples were also determined by 125I-RIA. A good correlation was found between EMIT assay and these techniques (r =0.90 and 0.91, respectively).

Amiodarone and desethylamiodarone concentrations in plasma and tissues of surgically treated patients on long-term oral amiodarone treatment.

The tissue disposition of amiodarone and its metabolite desethylamiodarone was studied in 12 surgical patients with various types of arrhythmias after chronic oral treatment with amiodarone. Amiodarone and desethylamiodarone concentrations in plasma and tissues were determined using a simple and sensitive high performance liquid chromatographic method. The mean plasma level of amiodarone and desethylamiodarone was found to increase from 0.55 microgram/ml to 1.40 microgram/ml and 0.68 microgram/ml to 1.80 microgram/ml for the respective components following the increase of the daily oral dose from 200 mg to 600 mg of amiodarone and indicates a linear relationship between plasma concentrations and dose. The mean levels of both drugs in different parts of the heart varied for amiodarone from 15 to 48 micrograms/g and for desethylamiodarone from 48 to 71 micrograms/g, with the highest values present in the epicardially resected ventricular myocardium. The mean cardiac tissue/plasma ratios ranged for amiodarone from 12 to 35 and for desethylamiodarone from 35 to 61 and show an extensive tissue uptake in the different parts of the heart for both drugs, with the metabolite accumulation 2 to 5 times higher than the parent compound. Relatively low levels, ranging for amiodarone from 2 to 15 micrograms/g and for desethylamiodarone from 5 to 25 micrograms/g, were observed in skeletal muscle, epidermis, skin and femoral artery. By far the largest content of the drugs was found in adipose tissue with mean concentrations of 207 +/- 98 micrograms/g and 82 +/- 43 g/g respectively for the parent compound and its metabolite, which suggests that fat constitutes the main depot of the drugs.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacokinetics and body distribution of amiodarone and desethylamiodarone in rats after oral administration.

The pharmacokinetics and body distribution of amiodarone and desethylamiodarone were studied in rats after single oral administration of 100 mg/kg and 200 mg/kg of amiodarone. The time-course of the concentrations of the drug and its main metabolite was determined by high performance liquid chromatography in serum and tissues up to 24 h. The mean absorption half-life of amiodarone was 1.83 h for both dosages and the mean elimination half-life was 15 h after the 100 mg/kg dosage and 105 h after the 200 mg/kg dosage. The mean bioavailability of oral amiodarone ranged from 17% to 60% with an average of 39%. Desethylamiodarone, the major metabolite of amiodarone, was present over the 24 h period of observation in relatively low levels of 30 to 60 ng/ml after the 100 mg/kg dose and 50 to 110 ng/ml after the 200 mg/kg dose respectively, which is circa 4% and 7% of the corresponding parent drug level. Amiodarone is preferentially distributed in decreasing order in lung, liver, thyroid gland, kidney, heart, adipose tissue, muscle tissue and brain. The metabolite desethylamiodarone exhibited a distribution pattern comparable to the parent drug. However, its maximum concentrations in serum and tissues were consistently lower than the corresponding amiodarone concentrations and varied from 18 to 55% (mean 27%), depending on the acute oral dose applied and on the kind of tissue. The amiodarone tissue/serum concentration ratios were high in lung tissue (60-100) and moderate to high in the other tissues except brain (3-60), and indicate an extensive distribution of the drug with the lung as an organ with specific binding sites or uptake mechanisms and adipose tissue as a reservoir with a large storage capacity. The metabolite tissue/serum concentration ratios were very high in lung tissue (500-800), high in renal, thyroid, liver and adipose tissue (80-200) and moderate in the other tissues except for brain (20-60); they indicate a very extensive distribution of desethylamiodarone with, primarily, lung and to some lesser extent kidney, liver and thyroid gland as organs with sites of metabolism and/or specific binding sites or uptake mechanisms and fat as a reservoir for the drug. A marked increase in the accumulation of amiodarone and desethylamiodarone was observed in adipose tissue after chronic oral administration, whereas the rise in kidney and brain was less pronounced and in the remaining tissues it was insignificant. Our data suggest that the rat is a good model for describing the single oral dose pharmacokinetics and body distribution of amiodarone and desethylamiodarone in man.

Pharmacokinetics and body distribution of amiodarone and desethylamiodarone in rats after intravenous administration.

The pharmacokinetics and body distribution of amiodarone and desethylamiodarone were investigated in rats following a single intravenous dose of 100 mg/kg and 150 mg/kg of amiodarone. The decline in serum and tissue concentrations of amiodarone and desethylamiodarone are described by biexponential functions. All aspects of the typical kinetic profile of the drug and its major metabolite, desethylamiodarone, are discussed. Amiodarone is preferentially distributed in decreasing order in thyroid gland, lung, kidney, liver, heart, adipose tissue, skeletal muscle and brain. The metabolite desethylamiodarone showed a distribution pattern which is similar to that observed for the parent drug. Our study indicates an extensive distribution of amiodarone, with the thyroid gland and lung as organs with specific binding sites or uptake mechanisms and adipose tissue as a depot with a large storage capacity. We also found a very extensive distribution of the metabolite desethylamiodarone with mainly lung and thyroid gland and to some lesser extent kidney, liver and heart as organs with sites of metabolism and/or specific binding sites or uptake mechanisms and fat as a reservoir for the drug. Our data demonstrate the advantages of intravenous loading dosages of amiodarone over oral doses, since considerably higher and longer lasting effective serum and tissue concentrations of amiodarone are reached while lower quantities of the less cardio-active metabolite are formed.

Placental transfer of thiamphenicol in term pregnancy.

The placental transfer of thiamphenicol was studied in 21 subjects at term after an intravenous bolus injection of 1000 mg of the drug. Detectable antibiotic levels were present in umbilical blood and amniotic fluid within 15 min of maternal administration. With the dosage applied, minimum concentrations required for the inhibition of many Gram-positive and Gram-negative organisms causing intrauterine infections were attained in maternal plasma, cord plasma and amniotic fluid. The value of thiamphenicol for the treatment of intrauterine infections is discussed.

Use of amiodarone during pregnancy.

UNLABELLED: Five cases are studied in which amiodarone (AM) was given during pregnancy, in two of them also during the breast feeding period, to estimate the risks for adverse effects. We measured the concentrations of AM and its major metabolite desethylamiodarone (DEA) in maternal plasma, cord plasma, infant plasma, placental tissue and breast milk and the thyroid hormones were measured in maternal and neonatal serum. Also, the neonates were examined for AM-associated adverse effects over a period varying from 8 months up to 5 years. We observed a limited maternal-fetal transfer of AM and DEA, while the concentration of DEA in placental tissue is relatively high. Considerable amounts of AM and DEA were present in breast milk. One infant appeared to be hypothyroid, detected by the neonatal thyroid screening. He was treated with triiodothyronine for weeks, until it was clear that the thyroid dysfunction was resolved. The other infants had normal screening results. No effect of the AM medication was observed on growth, liver function or cornea and skin. IN CONCLUSION: although pregnancy and lactation are no absolute contraindications for use of AM, special precautions are necessary. It is unavoidable that in some cases the pregnant mother, and especially her infant, becomes hypothyroid. AM has to be administered in the lowest possible dose, and the maternal and neonatal thyroid function must be controlled as long as the exposure to AM lasts.

Measurement of flecainide plasma concentrations by high performance liquid chromatography with fluorescence detection.

A simple, rapid, selective, and sensitive high performance liquid chromatographic method for the assay of flecainide in plasma has been developed. The method includes extraction of plasma samples via activated BondElut C8 disposable columns with methanol at pH 9.0 after addition of internal standard, and initially on column washings of samples at pH 9.0 with water and acetonitrile. The obtained methanolic extract is directly injected into the liquid chromatograph. Separation is performed using a Radial-Pak C18 5-micron column operating in combination with a radial compression separation unit and a methanol:25% ammonia (99.9:0.1, v/v) mobile phase. The eluent is monitored with a fluorescence detector operating at an excitation wavelength of 293 nm and an emission filter of 340 nm. Endogenous substances or a variety of drugs concomitantly used in flecainide therapy do not interfere with the assay. The plasma calibration curve of flecainide is linear in the concentration range of 25 to 1000 ng/mL. The mean recovery of flecainide from plasma with concentrations varying from 50 to 1000 ng/mL is 100 +/- 3%. The limit of sensitivity of the assay is 10 ng/mL. The intra- and inter-day coefficient of variation for replicate analysis of spiked plasma samples is less than 5 and 10% respectively. The mean plasma flecainide level in 48 patients, using a mean oral daily maintenance dose of 283 +/- 72 mg for at least one week was 557 +/- 250 ng/mL. The relationship between the steady state flecainide plasma concentration and daily flecainide maintenance dose in mg in 48 patients was investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

LC/MS determination of bromazepam, clopenthixol, and reserpine in serum of a non-fatal case of intoxication.

Combined liquid chromatography and mass spectrometry (LC/MS) with a moving belt interface can be used as a rapid method for the determination of bromazepam, clopenthixol, and reserpine in serum samples obtained from cases of acute overdoses with combinations of these drugs. Low resolution detection limits are about 100 pg for the three drugs, while in high resolution mode the detection limit for bromazepam is shown to be at least 35 pg. Accurate masses were obtained in a serum sample within 5 ppm using high voltage scanning over a narrow mass range for about 10 ng of bromazepam and clopenthixol, respectively. Chemical deactivation of the belt was shown to effectively reduce memory effects and to improve the desorption characteristics of the belt leading to higher yields of evaporated intact molecules.

Column liquid chromatography of tricyclic antidepressants.

A column liquid chromatographic system for the analysis of tricyclic antidepressants in serum is described. A high separation efficiency can be obtained with a mixture of ethyl acetate, n-hexane and methylamine as eluent on a silica gel column. The retention is easily regulated by varying the concentration of n-hexane, the modifier methylamine and the water content of the ethyl acetate. Examples are given of separation of test mixtures of tricyclic antidepressants and of some of these drugs in serum. UV detection permits determinations down to the 10-ng level in serum.

High-performance liquid chromatographic method for the simultaneous determination of pentisomide and its major metabolite N-desisopropylpentisomide in plasma, urine and tissues using solid-phase extraction.

A rapid, sensitive and selective high-performance liquid chromatographic method for the simultaneous determination of pentisomide and its major metabolite desisopropylpentisomide in plasma, urine and tissues has been developed. The method for plasma samples, urine samples and tissue samples, after homogenizing with 50% ethanol, involves extraction of samples via activated Bond-Elut C8 disposable columns with methanol at pH 10 after addition of internal standard, and initially on column washing of samples at pH 10 with water and acetonitrile. The obtained methanolic extract is evaporated to dryness under nitrogen at 25 degrees C; the sample residue is then reconstituted in mobile phase and an aliquot of this solution is injected into the liquid chromatograph. Separation is performed using a Nova-Pak C18 4 microns particle size column operating in combination with radial compression separation unit and a methanol-water-di-sec.-butylamine-phosphoric acid (40:60:0.5:0.2, v/v) pH 3.5 mobile phase with ultraviolet detection at 258 nm. Endogenous substances or a variety of drugs concomitantly used in pentisomide therapy, with the exception of disopyramide, do not interfere with the assay. The mean recovery of pentisomide and desisopropylpentisomide from plasma and urine and from tissues is more than 91 and 86%, respectively. The limit of detection of the assay is 10 ng/ml for both drugs. The intra- and inter-day coefficient of variation for replicate analyses of spiked plasma samples is less than 7 and 8%, respectively. Mean steady-state plasma levels of pentisomide and desisopropylpentisomide in patients on chronic oral therapy are reported.

Concentration of thiamphenicol in the human prostate and testis.

The concentration of thiamphenicol in prostatic tissue, testicular tissue and serum after a single intravenous injection of 1 g thiamphenicol glycinate ester was investigated. The prostatic and testicular specimens were obtained by prostatectomy and plastic orchidectomy, respectively, from patients with adenomas and carcinomas of the prostate. 2 h after dosing, the prostatic tissue concentration ranged from 2.1 to 15.1 microgram/g (mean value 5.7 microgram/g) and the testicular tissue from 3.4 to 8.4 microgram/g (mean value 6.1 microgram/g). At the same time the thiamphenicol serum levels varied in the patients with prostate adenomas from 4.6 to 14.5 microgram/ml (mean 8.9 microgram/ml) and in the prostate carcinoma patients from 5.2 to 10.4 microgram/ml (mean 8.5 microgram/ml). Several factors influencing the diffusion of thiamphenicol into the prostate and testis are discussed. The levels of thiamphenicol in the prostate and testis suggest that the antibiotic may be valuable for the treatment of infections of the prostate and testis caused by gram-positive and gram-negative cocci, but is of questionable value for the treatment of infections caused by gram-negative bacilli.

A rapid gas chromatographic determination of thiamphenicol in plasma and amniotic fluid.

A rapid gas chromatographic method for the determination of thiamphenicol in plasma and amniotic fluid is described. The antibiotic is extracted from biological fluids with ethyl acetate and, after concentration of the extract, the trimethylsilyl derivative of the drug is determined by electron-capture gas chromatography using a 63Ni detector. After the intravenous administration of a single dose of 500 mg of thiamphenicol during the first stage of spontaneous labour to clinically normal gravidae at term, transmission of the drug across the placenta was demonstrated by a combination of gas chromatography and mass spectrometry.

EMIT-st drug detection system for screening of barbiturates and benzodiazepines in serum.

The determination of barbiturates and benzodiazepines in serum using the EMIT-st drug detection system is reported. The within-day and the day-to-day precision of this assay was investigated by replicate analysis (n = 20) of the serum negative (no drug) and serum positive control of secobarbital (8.0 micrograms/mL) and diazepam (1.0 microgram/mL), respectively. In all cases the coefficients of variation for intra- and interday analysis for both drugs were between 9 and 15%. No temperature influence on the benzodiazepine assay could be observed by running the tests at temperatures ranging from 20 to 25 degrees C as well as at a temperature of 23 degrees C. The specificity and sensitivity of the EMIT-st assay was investigated by measuring various serum concentrations of 14 different barbiturates and 15 different benzodiazepines. A definitive positive response was obtained at a level of 10 micrograms/mL for 5 out of the 14 barbiturates. A positive result at a concentration of 1 microgram/mL was obtained for 10 of the 15 benzodiazepines. A good correlation in response was found for the barbiturates and benzodiazepines compared to the HPLC and GC procedures at concentrations above the detection limit of the assay. In our opinion the EMIT-st tests are useful to clinical toxicological practice. However, the applicability of the screenings test for barbiturates is limited since only a number of these compounds can be detected.

Penetration into human urogenital tissues, muscle tissues, rib and cerebrospinal fluid of thiamphenicol.

The penetration of D(+)-threo-2-dichloroacetamido-1-(p-methylsulfonylphenyl)-1,3-propanediol (thiamphenicol, TAP, Urfamycine) into human renal, ureter, prostatic, testicular and muscle tissue, perirenal fat, rib as well as cerebrospinal fluid (CSF) after a single i.v. injection of 1.0 g of thiamphenicol glycinate ester was investigated. 2 h after TAP administration to 17 patients with severely diseased kidneys, the antibiotic concentration in renal tissue ranged from 9.8 to 138.7 microgram/g (mean value 40.4 +/- 29.9 microgram/g), in ureter tissue from 6.3 to 62.0 microgram/g (mean value 20.8 +/- 17.0 microgram/g), in muscle tissue from 1.7 to 13.7 microgram/g (mean value 8.2 +/- 3.6 microgram/g), in rib from 0.8 to 3.4 microgram/g (mean value 2.4 +/- 1.5 microgram/g) and in perirenal fat from 0.6 to 5.7 microgram/g (mean value 2.1 +/- 1.5 microgram/g). At the same time the TAP serum level varied from 4.6 to 15.2 microgram/ml (mean value 9.4 +/- 3.1 microgram/ml). Prostatic tissue concentration, measured in 16 patients with prostate adenomas, varied at 2 h after dosing, from 2.1 to 15.1 microgram/g (mean value 5.7 +/- 3.8 microgram/g). The simultaneous serum level was between 4.6 and 14.5 microgram/ml (mean value 8.9 +/- 3.4 microgram/ml). In 6 of these patients additionally CSF level was measured at 1.5 h post inj. and ranged from 0.11 to 0.65 microgram/ml (mean value 0.32 +/- 0.19 microgram/ml). Testicular tissue concentration assessed in 7 patients with prostate carcinomas varied at 2 h after i.v. injection from 3.4 to 8.4 microgram/g (mean value 6.1 +/- 1.9 microgram/g). The respective serum level in these patients was between 5.2 and 10.4 microgram/ml (mean value 8.5 +/- 1.7 microgram/ml). Several factors affecting the diffusion of TAP into the reported tissues and CSF are discussed. TAP should be regarded as an antibiotic with good penetration into urogenital tissues.

The concentration of thiamphenicol in severely diseased human kidneys.

The concentration of thiamphenicol in serum and renal tissue was determined in 17 patients with severly diseased kidneys after an intravenous injection of 1000 mg of the drug. Two hours after the administration the renal tissue concentrations ranged in patients with hydronephrotic kidneys from 38.0-63.5 microgram/g, in patients with cirrhotic kidneys from 17.9-42.7 microgram/g, in patients with pyonephrosis from 9.8-17.6 microgram/g and in patients with renal carcinoma from 37.7-64.2 microgram/g. The patient with the renal sarcoma had a level of 138.7 microgram/g. At the same time the serum concentration ranged from 4.6-15.2 microgram/ml. The highest renal tissue/serum concentration ratios of thiamphenicol were observed in patients with hydronephrotic kidneys and renal tumours, the lowest in cases of pyonephrosis. The influence of severe renal disease on the renal tissue/serum concentration ratios of thiamphenicol is discussed. The high renal tissue levels of thiamphenicol in patients with severely diseased kidneys fulfill an important condition for the antibacterial chemotherapy of kidney infections.

Amiodarone reduces the effect of T3 on beta adrenergic receptor density in rat heart.

The effect of injection of 1 mg/kg triiodothyronine on cardiac beta-adrenoceptor state was investigated in hypothyroid rats and compared to the effect in hypothyroid rats pretreated with amiodarone (200 mg/kg/day for 8 days). The Kd values of iodocyanopindolol binding to the beta-receptors were not influenced by either T3 injection or by amiodarone treatment. In the absence of amiodarone, injection of triiodothyronine resulted in a small decrease in receptor density at 6 hr, followed by an increase at 24 hr. Rats treated with amiodarone showed a similar response pattern to hormone injection (i. e. a small decrease in receptor density at 6 hr, followed by an increase at 24 hr), but the amplitude of the response was significantly reduced. Moreover, in vehicle injected rats amiodarone treatment resulted in a decrease in receptor density when rats were mildly hypothyroid, but not when rats were severely hypothyroid. It is concluded that amiodarone interferes (directly or indirectly) with thyroid hormone action in the heart.

Tissue distribution of amiodarone and desethylamiodarone in rats after multiple intraperitoneal administration of various amiodarone dosages.

Tissue distribution of amiodarone (Cordarone) and desethylamiodarone in the rat was studied after repeated intraperitoneal administration of the drug. Tissue and serum concentrations of amiodarone and desethylamiodarone were determined by high-performance liquid chromatography. The levels of amiodarone and desethylamiodarone in serum and tissues obtained after repeated intraperitoneal application of doses varying from 25 mg to 200 mg/kg show that the accumulation of amiodarone and desethylamiodarone in the rat is dose-dependent and both drugs are preferentially distributed in decreasing order in adipose tissue, lung, liver, kidney and thyroid gland. The penetration of the drug and its metabolite into brain was poor and with all the applied dosages brain levels were considerably lower than the corresponding serum levels. Desethylamiodarone serum and tissue concentrations were substantially lower than the corresponding amiodarone concentrations and varied from 1 to 48% (mean 15%) depending on the dosage used and the kind of tissue. The amiodarone tissue/serum concentration ratios were exceptionally high in adipose tissue (1,000-4,000) and moderate to high in the other tissues except brain (5-90), and indicate an extensive distribution of the drug with fat as a reservoir with a large storage capacity. The levels of amiodarone and desethylamiodarone, obtained with 50 mg/kg and 100 mg/kg dosages, showed in function of time clearly an increase in serum and tissues. The observed amiodarone tissue/serum ratios in function of time revealed no further significant increase (p less than or equal to 0.05) after 3 injections over a 6-day period, indicating the attainment of "steady-state".(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue distribution of amiodarone and desethylamiodarone in rats after repeated oral administration of various amiodarone dosages.

Tissue distribution of amiodarone (Cordarone) and desethylamiodarone in the rat was investigated after repeated oral application of various dosages of the drug. Serum and tissue concentrations ofBamiodarone and desethylamiodarone were assessed by high-performance liquid chromatography. The amiodarone and desethylamiodarBne serum and tissue levels obtained after repeated oral application of doses ranging from 25 to 100 mg/kg reveal that the accumulation of amiodarone and desethylamiodarone in the rat is dose-dependent. Amiodarone is preferentially distributed in decreasing order in adipose tissue, lung, thyroid gland, kidney and liver whereas its metabolite shows the highest affinity for lung then followed by kidney, thyroid gland, adipose tissue and liver. The penetration of amiodarone and desethylamiodarone into brain was poor and with all the applied dosages brain levels were in the same range as the corresponding serum levels. Desethylamiodarone serum and tissue concentrations were consistently lower than the corresponding amiodarone concentrations and varied from 5 to 78% (mean 45%) depending on the dose administered and the kind of tissue. The amiodarone tissue/serum concentration ratios were very high in adipose tissue (220-340) and moderate to high in the other tissues except brain (3-100) and indicate an extensive distribution of the drug with fat as a depot with a large storage capacity. The desethylamiodarone tissue/serum concentration ratios were very high in lung tissue (50-620), high in renal, thyroid and adipose tissue (20-390) and moderate in the other tissues except brain (3-90), respectively, and indicate an extensive distribution of the metabolite with fat as a reservoir and lung, kidney and thyroid gland, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)