CYP2E1-dependent benzene toxicity: the role of extrahepatic benzene metabolism

Benzene, a ubiquitous environmental pollutant, is haematotoxic and myelotoxic. As has been shown earlier, cytochrome P450 2E1 (CYP2E1)-dependent metabolism is a prerequisite for the cytotoxic and genotoxic effects of benzene, but which of the benzene metabolites produces toxicity is still unknown. The observed differences between the toxicity of benzene and that of phenol, a major metabolite of benzene, could be explained by alternative hypotheses. That is, whether (1) toxic benzene effects are caused by metabolites not derived from phenol (e.g. benzene epoxide, muconaldehyde). which are formed in the liver and are able to reach the target organ(s); or (2) benzene penetrates into the bone marrow, where local metabolism takes place, whereas phenol does not reach the target tissue because of its polarity. To further investigate hypothesis 2, we used various strains of mice (AKR, B6C3F1, CBA/Ca, CD-1 and C57B1/6), for which different toxic responses have been reported in the haematopoietic system after chronic benzene exposure. In these strains, CYP2E1 expression in bone marrow was investigated and compared with CYP2E1 expression in liver by means of two independent methods. Quantification of CYP2E1-dependent hydroxylation of chlorzoxazone (CLX) by high-performance liquid chromatography (HPLC; functional analysis) was used to characterize specific enzymatic activities. Protein identification was performed by Western blotting using CYP2E1-specific antibodies. In liver microsomes of all strains investigated, considerable amounts of CYP2E1-specific protein and correspondingly high CYP2E1 hydroxylase activities could be detected. No significant differences in CYP2E1-dependent enzyme activities were found between the five strains (range of medians, 4.6 12.0 nmol 6-OH-CLX/[mg protein x min]) in hepatic tissue. In the bone marrow, CYP2E1 could also be detected in all strains investigated. However, chlorzoxazone hydroxylase activities were considerably lower (range of medians, 0.2-0.8x10(-3) nmol 6-OH-CLX/[mg protein x min]) compared with those obtained from liver microsomes. No significant (P>0.05) interstrain differences in CYP2E1 expression in liver and/or bone marrow could be observed in the mouse strains investigated. The data obtained thus far from our investigations suggest that strain-specific differences in the tumour response of the haematopoietic system of mice chronically exposed to benzene cannot be explained by differences in either hepatic or in myeloid CYP2E1-dependent metabolism of benzene.

Influence of urine pH and urinary flow on the renal excretion of memantine

AIMS

The present study assessed the influence of urinary flow rate and urine pH on the renal excretion of the NMDA-receptor antagonist memantine.

METHODS

In a randomized, open, four-period cross-over trial, 12 healthy male volunteers received 10 mg memantine daily for 43 days. After reaching steady state conditions the volunteers were allocated to four different regimens to alter urine pH and urinary flow, which were each separated by a 1 week period while the study medication continued (A: acidification of urine pH, low urinary flow; B: acidification of urine pH, high urinary flow; C: alkalinization of urine pH, low urinary flow; D: alkalinization of urine pH, high urinary flow).

RESULTS

The renal clearance of memantine (CL(R)) in regimen A and B was 7-10 fold higher in comparison with regimen C and D (P<0.05). There were small but statistically significant differences of CL(R) between the two regimens with acidic urine pH (A: median: 210.2 ml min(-1) vs B: median: 218.7 ml min(-1)) and between the two regimens with alkaline urine pH (C: median: 19.4 ml min(-1) vs D: median: 30.5 ml min(-1)). The amount of memantine excreted into the urine within one regimen (Ae0-24h) was 5.7-7.4 fold higher in regimens A and B than C and D (P< 0.05). Differences of the AUC(0,24 h) and Cmax/AUC(0,24 h) were significant (P<0.05) between each of the regimens with acidic urine pH (A, B) and regimens (C, D) with alkaline urine pH (A vs C, A vs D, B vs C, B vs D) but not between regimens A vs B or C vs D.

CONCLUSIONS

The present study demonstrated a considerable effect of urine pH, whereas no clinically relevant change of the renal excretion of memantine with urinary flow could be detected. As the renal excretion of memantine may have an impact on therapeutic efficacy changes of dietary habits that may alter urine pH should be avoided during treatment with memantine.

Determination of 2-hydroxyphenylacetic acid (2HPAA) in urine after oral and parenteral administration of coumarin by gas-liquid chromatography with flame-ionization detection

The urinary excretion of 2-hydroxyphenylacetic acid (2HPAA) was studied in human volunteers after oral and parenteral doses of coumarin. The presence of 2HPAA in the urine was confirmed by gas chromatography mass spectroscopy (GC MS). Mass spectra of reference material and samples are presented. The determination of 2HPAA was carried out by GC with flame-ionization detection. Prior to analysis samples were extracted into ethyl ether and the analytes were derivatized with trimethlyphenylammonium hydroxide. A calibration range from 0.3 to 150 micrograms ml-1 was established using 3-hydroxyphenyl acetic acid (3HPAA) as an internal standard. On average less than 10% of the coumarin administered were excreted into the urine in the form of 2HPAA.

Pharmacokinetics and pharmacodynamics of candesartan after administration of its pro-drug candesartan cilexetil in patients with mild to moderate essential hypertension--a population analysis

OBJECTIVE

The pharmacokinetics and pharmacodynamics of the angiotensin (AT) II receptor, AT1-subtype, antagonist candesartan were investigated in a dose-finding study in 232 patients of either gender, aged 28-69 years and weighing 54-110 kg. The study was a double-blind, placebo-controlled trial in which oral doses of 2, 4, 8, 12 and 16 mg once daily were given as the pro-drug candesartan cilexetil from day 0 to day 28.

RESULTS

The population pharmacokinetics of candesartan could be best described by a two-compartment body model, parameterized in terms of clearance (14.1 1.h-1), central volume of distribution (118 1), peripheral volume (272 1) and intercompartmental clearance (15.4 1.h-1). From these model parameters, a cumulation half-life (t1/2, beta) of 29 h was derived. Age and weight were influencing factors for the distribution and elimination of the drug. Systolic and diastolic blood pressure were lowered by the treatment in a dose-dependent fashion. The maximum effect of each dose was reached after repeated administration. The link between plasma concentrations and effect could be described by a linear model when trough concentrations and blood pressure, measured at the same time, were modelled. In this model, the time dependence is implicitly handled as the trough concentrations increased during repeated administration. After treatment with the highest dose used in the trial (16 mg), the population estimate for the diastolic blood pressure was reduced from 103.2 mmHg (pre-dose day 0) to 93.3 mmHg (on day 29) and the systolic blood pressure from 154.6 mmHg (pre-dose day 0) to 137.9 mmHg (on day 29). None of the covariates (age, weight, gender) had an influence on the concentration-effect relationship.

Routine measurement of fluoxetine and norfluoxetine by high-performance liquid chromatography with ultraviolet detection in patients under concomitant treatment with tricyclic antidepressants

A robust and rapid high-performance liquid chromatography (HPLC) method is described for therapeutic drug monitoring of fluoxetine and norfluoxetine in the presence of six frequently-used tricyclic antidepressants and their respective metabolites. Liquid-liquid extraction into n-hexane/acetonitrile is used with reextraction into hydrochloric acid for clean-up. The chromatographic separation is carried out on a CN column. The minimum detectable amount is 3 ng injected on column. In addition to qualitative and quantitative validation data for the assay method, results from patient samples are presented. It is concluded that for patients treated with fluoxetine, therapeutic drug monitoring is valuable for optimizing the therapy.

Pharmacodynamic modelling of the analgesic effects of piritramide in postoperative patients

BACKGROUND

The concentration-effect relationship of piritramide, a synthetic opioid analgesic predominantly used for postoperative analgesia and analgosedation, has not been reported so far.

METHODS

Twenty-four patients of both genders aged 58.1 (11.7) yr (mean (SD)) received inhalational anaesthesia for abdominal surgery. Postoperative pain was assessed with a visual analogue scale (VAS). Analgesia was provided with piritramide, infused at a rate of 7 micrograms.kg-1.min-1 until analgesia was considered sufficient (VAS < 25) or up to a maximum dose of 0.2 mg/kg. The plasma concentrations of piritramide were determined by gas chromatography. An inhibitory fractional sigmoid Emax-model was used to describe the relation between effect site concentration and perceived pain.

RESULTS

The equilibration half-life between plasma and effect site concentrations (T1/2 (keo)) was 16.8 min (median; range: 4.4-41.6 min). The steady-state plasma concentration required to produce 50% of maximum analgesia (EC50) was 12.1 ng/ml (range: 2.9-29.8 ng/ml) and correlated with initial pain intensity. The slope factor gamma was 1.9 (range: 0.5-6.1) and increased with age. Clinically relevant respiratory depression did not occur. Due to the relatively large equilibration half-life of the effect compartment, the context-sensitive half-time of the effect site concentrations after short-time administration (< 2 h) clearly exceeded those of alfentanil, sufentanil, and fentanyl.

CONCLUSIONS

The analgesic effect of piritramide was adequately described by an inhibitory fractional Emax-model. In order to overcome the pronounced hysteresis, piritramide should initially be administered as an intravenous bolus of at least 5 mg.

Fenoterol but not dobutamine increases erythropoietin production in humans

OBJECTIVE

This study assessed the role of adrenergic signal transmission in the control of renal erythropoietin (EPO) production in humans.

METHODS

Forty-six healthy male volunteers underwent a hemorrhage of 750 ml. After phlebotomy, they received (intravenously for 6 hours in a parallel, randomized, placebo-controlled and single-blind design) either placebo (0.9% sodium chloride), or the beta 2-adrenergic receptor agonist fenoterol (1.5 microgram/min), or the beta 1-adrenergic receptor agonist dobutamine (5 micrograms/kg/min), or the nonselective beta-adrenergic receptor antagonist propranolol (loading dose of 0.14 mg/kg over 20 minutes, followed by 0.63 micrograms/kg/min).

RESULTS

The AUCEPO(0-48 hr)fenoterol was 37% higher (p < 0.03) than AUCEPO(0-48 hr)placebo, whereas AUCEPO(0-48 hr)dobutamine and AUCEPO(0-48 hr)propranolol were comparable with placebo. Creatinine clearance was significantly increased during dobutamine treatment. Urinary cyclic adenosine monophosphate excretion was increased only by fenoterol treatment, whereas serum potassium levels were decreased. Plasma renin activity was significantly increased during dobutamine and fenoterol infusion.

CONCLUSIONS

This study shows in a model of controlled, physiologic stimulation of renal erythropoietin production that the beta 2-adrenergic receptor agonist fenoterol but not the beta 1-adrenergic receptor agonist dobutamine is able to increase erythropoietin levels in humans. The result can be interpreted as a hint that signals for the control of erythropoietin production may be mediated by beta 2-adrenergic receptors rather than by beta 1-adrenergic receptors. It appears to be unlikely that an increase of renin concentrations or glomerular filtration rate is causally linked to the control of erythropoietin production in this experimental setting.

Modelling of non-linear pharmacokinetics in sheep after short-term infusion of cardiotoxic doses of imipramine

Imipramine was administered to sheep (n = 10) by intravenous infusion in high doses (450 mg-900 mg) to elicit cardiovascular shock. A cardiac assist device was then employed to manage the acute overdose situation. The concentration-time course of imipramine and its metabolite desmethylimipramine in plasma was measured by HPLC. As an indicator of imipramine's cardiotoxic effect, cardiac output was monitored. The aim of the study was to evaluate the pharmacokinetics under these conditions and to assess the efficiency of a cardiac assist device with (n = 5) and without (n = 5) an integrated haemoperfusion unit in removing drug from the circulation. The kinetics of imipramine could be described by a three compartment body model with concentration-dependent clearance resulting in non-linear kinetics. The changes in cardiac output with time could be linked to the pharmacokinetic model by a linear relationship. The cardiac assist device was found to contribute to the overall elimination of imipramine whereas the haemoperfusion unit had no clinically relevant impact.

Hypokalaemia in pregnant women treated with the beta 2-mimetic drug fenoterol--a concentration and time dependent effect

The effect of tocolytic treatment with fenoterol on plasma potassium concentrations was studied in 83 pregnant women on intravenous tocolytic therapy. Plasma concentrations of fenoterol and potassium were measured simultaneously, the time interval between initiation of therapy and taking the blood sample varying from 2 hours to 100 days. In a subset of 13 patients this blood sample was taken after two hours of therapy and pretreatment potassium concentrations were measured also. Pretreatment potassium concentrations were normal in these 13 patients and declined to 2.88 mmol/L (median) fenoterol concentrations being 320 ng/L through 1164 ng/L. Potassium concentrations measured later than 24 hours after initiation of therapy were all in the normal range corresponding fenoterol concentrations varying from 200 ng/L to 2504 ng/L. The multivariate statistical model for the description of all data showed that the duration of treatment was the only variable which explained the data to a significant extent. This might indicate that tolerance to the potassium lowering effect of fenoterol had developed within 24 hours after initiation of therapy. In the subset of 13 patients pretreatment potassium concentrations were found to be more important in explaining potassium concentrations than fenoterol concentrations at two hours. As we did not observe any adverse events in patients with low potassium concentrations and potassium concentrations were normal within 24 hours, we conclude that hypokalaemia due to fenoterol in the treatment of premature labor is not of clinical concern.

Erythropoietin production in healthy volunteers subjected to controlled haemorrhage: evidence against a major role for adenosine

1. This study was carried out to assess the role of adenosine in the regulation of human erythropoietin (EPO) production. To this end we investigated in healthy volunteers whether the nonspecific adenosine antagonist theophylline increases and the adenosine uptake inhibitor dipyridamole decreases EPO production in response to an haemorrhage of 750 ml. 2. Healthy male nonsmokers received i.v. in a parallel, randomized, single-blind trial theophylline (loading dose 5 mg kg-1 over 20 min, followed by 0.5 mg kg-1 min-1), dipyridamole (0.21 mg kg-1 h-1) or placebo (0.9% NaCl) for 6 h following the phlebotomy. EPO concentrations were followed up to 72 h after phlebotomy. 3. Following blood loss EPO concentrations increased during all treatments. The AUCEPO (0,72 h) were not statistically significantly different (theophylline: 398 +/- 30, dipyridamole: 301 +/- 15, placebo: 332 +/- 57 [mu ml-1 h]). Creatinine clearance and urinary cAMP excretion were unaltered by any treatment. Urinary excretion of adenosine was significantly increased during infusion of dipyridamole. Plasma renin activity was significantly increased during theophylline infusion. 4. In our model of controlled, physiological stimulation of EPO production by haemorrhage, adenosine appears unlikely to play a major role as a mediator of renal EPO production.

Concentration-effect relationship of the positive chronotropic and hypokalaemic effects of fenoterol in healthy women of childbearing age

OBJECTIVE

To analyse fenoterol-induced tachycardia and hypokalaemia, the most important and most frequent adverse effects of tocolytic therapy with beta 2-adrenoceptor agonists in females of childbearing age.

METHODS

The study was performed as a double blind, randomised, placebo controlled, cross over trial. Seven healthy women aged 22-38 y, received intravenous infusions of fenoterol at 3 different rates within the therapeutic range for tocolysis (0.5,1.0, and 2.0 micrograms.min-1) and placebo. The time courses of the plasma concentrations of fenoterol and potassium, and the heart rate were analysed with mixed effects pharmacokinetic-pharmacodynamic (PKPD) modeling using NONMEM.

RESULTS

The plasma concentration-time course followed a linear two compartment model. Fenoterol-induced tachycardia was described by a linear concentration-effect model with baseline. The estimated baseline and slope parameters were 78 beats.min-1 and 0.032 beats.min-1.microgram-1.1, respectively. Fenoterol-induced hypokalaemia could be described by a physiological indirect response model including feedback; the Estimated basal plasma potassium concentration was 3.93 mmol.1-1 and the slope factor for the fenoterol-induced relative increase in the efflux of potassium from the extracellular space was 6.22*10(-4) ng.1(-1).

CONCLUSION

The estimated population parameters permitted calculation of the expected time course of tachycardia and hypokalaemia in women after the initiation of tocolysis with fenoterol over the clinically relevant concentration range, and prediction of its variability. Based on simulation, our model predicted that a continuous infusion of 2.0 micrograms.min-1 (highest rate examined) would increase heart rate to 113 beats.min-1 at steady state and lower the plasma potassium concentration to 2.77 mmol.1(-1) 1.5 h after beginning the infusion. Thereafter, the plasma potassium concentration would slowly return to normal.

Pharmacokinetics of piritramide after an intravenous bolus in surgical patients

BACKGROUND

Piritramide is a synthetic opioid analgesic which is commonly used for postoperative analgesia. It is structurally related to meperidine, exhibiting full mu-receptor agonism. Pharmacokinetic data of the drug have not been reported so far.

METHODS

Plasma protein binding of piritramide was studied in vitro. The kinetics were examined after a single intravenous bolus (0.2 mg/kg) in 10 male patients aged 22-53 years undergoing elective minor surgery. Plasma and urine concentrations were determined by gas chromatography in samples drawn before and after the bolus. The concentration vs. time data were evaluated by nonlinear regression analysis, and the mean values and SD of the individual pharmacokinetic parameters were calculated. A three-compartment body model was fitted to the data.

RESULTS

The volume of distribution at steady state was 4.7 (0.7)l/kg, systemic plasma clearance was 7.8 (1.5) (mean (SD)) ml/kg/min. Renal clearance of unchanged piritramide was negligible (0.13 (0.09) ml/kg/min). The terminal elimination half-life was 8.0 (1.4) h. In vitro, the free fraction in plasma of piritramide did not change over the therapeutic concentration range (5.5 (1.3)% at a pH of 7.35) but decreased considerably with pH within the physiological range.

CONCLUSION

Since the elimination half-life of piritramide appears to exceed the duration of clinically effective analgesia observed during the treatment of acute pain, the dose of piritramide should be titrated carefully during long-term treatment to avoid accumulation that may lead to adverse effects.

Morphine-6-O-beta-D-glucuronide but not morphine-3-O-beta-D-glucuronide binds to mu-, delta- and kappa- specific opioid binding sites in cerebral membranes

We investigated the nature of interaction of morphine-3-O-beta-D-glucuronide (M3G) and morphine-6-O-beta-D-glucuronide (M6G) with opioid binding sites at the mu-, delta- and kappa-opioid receptors (mu-OR, delta-OR and kappa-OR) in cerebral membranes. Saturation binding experiments revealed a competitive interaction of M6G with all three opioid receptors. Inhibition binding experiments at the mu-OR employing combinations of morphine and M6G resulted in a rightward shift of the IC50 for morphine proportional to the M6G concentration, thus strengthening the finding of competitive interaction of M6G at the mu-opioid binding site. Data in absence and presence of M6G were included in a three-dimensional model. Compared to a model with one binding site a model with two binding sites significantly improved the fits. This might indicate that different mu-OR subtypes are involved. Hydrolysis of M6G to morphine was investigated and did not occur. Therefore the effects of M6G on binding to the mu-OR were due to M6G and not due to morphine. In contrast, M3G at the three opioid receptors was found to inhibit binding being about 300 times weaker than morphine. This effect was well explained by the amount of contaminating morphine (about 0.3%) identified by HPLC. We conclude that M6G binds to mu-, delta- and kappa-OR in a competitive manner. Some of our results on the mu-OR suggest two binding sites for agonists at the mu-OR and that M6G binds to both sites. Our results suggest that the high potency of M6G as an analgesic is mediated through opioid receptors. In contrast, M3G does not interact with the mu-, delta- or kappa-OR. We therefore doubt that any effect of M3G is mediated via opioid receptors.

Gender differences in pharmacokinetics

There is growing awareness that the underrepresentation of women in clinical trials and in particular in phase I studies may lead to incorrect handling of drugs. Despite the fact that investigations are not informed in a systematic way, there are a number of examples showing pharmacokinetic differences between gender. From the data actually presented, it can be concluded that the activity of CYP 3A4 activity as measured by elimination in vivo is higher in women compared to men. CYP isoenzymes other than CYP 3A4 seem to be more active in men than in woman, as are conjugation reactions, such as glucuronidation. The influence of changing hormonal levels during the lifetime of a woman has been looked at in some drugs but deserves further systematic investigation. The use of oral contraceptives can interfere with the metabolism of many drugs whereas, in pregnancy, the elimination of antiepileptics is increased which, without dose adjustment, leads to an increased number of seizures. The impacts of hormonal replacement therapy (HRT) on the pharmacokinetics of concomitantly given drugs is an important issue, as HRT is increasingly used, but more research is needed in this field.

Amiodarone in a newborn with ventricular tachycardia and an intracardiac tumor: adjusting the dose according to an individualized dosing regimen

We report the successful management of recurrent ventricular tachycardias in a newborn suffering from an intracardiac tumor. Amiodarone was the only agent able to control the tachycardias and did so as long as an individually titrated plasma concentration above 0.8 mu mol/L was maintained. Because no therapeutic plasma concentration has been defined in children and no kinetic studies are available in this population, we optimized the dosing regimen based on a computer simulation, taking into account the pharmacokinetic parameters of the patient and the individual concentration-effect relation.

[Age as a factor in dose-response relationship of drugs]

Drug therapy in the elderly requires careful individualization of the dosage. Whether dose adjustment is due to altered pharmacokinetic or due to altered pharmacodynamic is a matter of experimental evidence which can be found by performing studies with simultaneous measurements of concentration and effect over time. The kinetic of drugs in the elderly can be characterized by an altered volume of distribution, an altered protein binding, an impaired metabolism and renal excretion. There is a wide interindividual variation of the alterations which are further influenced by environmental factors such as smoking and nutrition. In generalization of the results it can be assumed that the concentration of drugs is elevated in the elderly and that the excretion will be prolonged. Hence, it is safe to reduce the dose in the elderly. The influence of age on factors which determine the effect of drugs is much less investigated than the factors influencing the pharmacokinetic. With respect to side-effects, it seems that the elderly population is a population at special risk. However, it is unclear whether this finding is explained on a pharmacodynamic basis (e.g., enhanced receptor sensitivity, impaired homeostatic mechanisms), as analyses are lacking in investigating the relationship between concentration and effect. As there is no evidence besides a special situation with betablockers that aged patients require higher doses than younger ones, it is wise to use doses at the lower range for the treatment of aged patients. In case of new symptom side-effects of drugs should be considered as the underlying cause.

Transpulmonary disposition of prilocaine, mepivacaine, and bupivacaine in humans in the course of epidural anaesthesia

The pulmonary first-pass kinetics of the amide-linked local anaesthetics prilocaine, mepivacaine and bupivacaine were studied in 33 patients after a single epidural injection. Drug concentrations were monitored before and after lung passage, i.e. in samples withdrawn simultaneously from mixed venous and arterial blood. In most cases, maximum plasma concentrations were observed 10 min after injection (range 2 to 30 min). Two min after injection the local anaesthetics were distinctly extracted by the lung (prilocaine 40%, mepivacaine 20%, and bupivacaine 12%). Prilocaine was retained by the lung more effectively than bupivacaine and mepivacaine. However, a transpulmonary concentration gradient could be observed only for a short time, i.e. maximum 15 min. Altogether, in the case of accidental fast absorption, e.g. inadvertent intravenous injection, arterial peak concentrations of these drugs will be attenuated by passage of the lung. However, the lung will not substantially lower the risk of toxicity by amide-linked local anaesthetics during normal conditions of regional anaesthesia where slow absorption occurs.

Biliary excretion of mezlocillin in patients with hepatic disease

In three patients with liver disease (2 patients with alcoholic liver cirrhosis and 1 patient with chronic cholangitis) total, renal, biliary and metabolic clearance of the acylureidopenicillin mezlocillin was examined under steady state conditions. Mezlocillin was infused for 6 hours at a constant infusion rate of 10 mg/min. Renal clearance was calculated based on urinary excretion rates. Duodenal perfusion and marker dilution technique was applied to determine biliary excretion rates of the drug. Clearances were estimated by dividing the excretion rate by the respective plasma concentration. Total clearance was calculated by dividing the infusion rate by the plasma concentration. Biliary clearance was markedly reduced in the patients compared to the data of 8 healthy controls (0.65 +/- 0.33 ml/min vs 98.6 +/- 42.5 ml/min). Total and renal clearance were diminished (total clearance: 121.4 +/- 21.6 ml/min vs 286.5 +/- 54.6 ml/min, renal clearance, 65.4 +/- 1.0 ml/min vs 137.6 +/- 32.6 ml/min). In contrast, metabolic clearance was not changed (53.3 23.1 ml/min vs 50.3 +/ 24.2 ml/min). As mezlocillin is well tolerated and has a wide margin of safety we do not recommend reduced dosage. On the contrary, it might even be necessary to increase the dose when treating biliary tract infections in patients with cholestasis in order to assure effective drug concentrations in the bile.

An inexpensive and sensitive method for the determination of quinidine in plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive, specific, and rapid high-performance liquid chromatographic method with ultraviolet detection for therapeutic drug monitoring of the cardioactive compound quinidine is described. The method uses only 50 microliters of serum, which is extracted into methyl-t-butylether at an alkaline pH and consequently reextracted into dilute hydrochloric acid. Quinidine is separated from quinine, the internal standard, and dihydroquinidine on a reversed phase C18 column. The minimum detectable amount is 1 ng injected on column. The method is both precise and accurate, as shown by the validation data presented, and can also be of use in pharmacokinetic investigations.