Inhibition of desipramine 2-hydroxylation by quinidine and quinine.

Urinary excretion of desipramine (DMI) and 2-hydroxydesipramine (2-OH-DMI) after single oral doses of 25 mg DMI was investigated in seven rapid and three slow debrisoquin hydroxylators, before and after pretreatment with either quinidine or its diastereoisomer quinine. After treatment with 800 mg quinidine daily for 2 days, excretion of 2-OH-DMI decreased by 96% in rapid hydroxylators and 68% in slow hydroxylators. After treatment with 750 mg quinine/day for 2 days, excretion of 2-OH-DMI in rapid hydroxylators was 54% lower than during the control experiment, whereas in slow hydroxylators no significant changes in the excretion pattern were observed. Unchanged DMI constituted only a minor fraction of recovered drug and no significant changes in its recovery were observed in either phenotypic group after pretreatment with quinidine or quinine. Thus both quinidine and quinine decreased the excretion of 2-OH-DMI. At similar does the effect of quinidine was much stronger than that of quinine, virtually transforming rapid hydroxylators into slow hydroxylators. The mechanism probably involves a stereoselective inhibition of DMI 2-hydroxylation.

Effect of cigarette smoking on fluvoxamine pharmacokinetics in humans.

OBJECTIVES: Although fluvoxamine inhibits the biotransformation of drugs known to be metabolized by CYP1A2, there are no data available with regard to the importance of CYP1A2 for the metabolism of fluvoxamine itself. Because smoking induces the metabolism of drugs catalyzed by CYP1A2, this study investigated the pharmacokinetics of fluvoxamine in smokers and nonsmokers. METHODS: The serum concentration of fluvoxamine was determined by high-performance liquid chromatography for 48 hours after oral administration of a single dose of 50 mg fluvoxamine to 12 smokers (> or = 10 cigarettes per day) and 12 nonsmokers. RESULTS: The smokers had significantly lower areas under the serum concentration-time curve and significantly lower maximal serum concentrations than the nonsmokers (mean +/- SD, 771 +/- 346 versus 1110 +/- 511 nmol.hr.L-1 [p = 0.012] and 39.1 +/- 17.3 versus 57.7 +/- 21.5 nmol.L-1 [p = 0.012], respectively). The terminal elimination half-life did not differ significantly between smokers and nonsmokers (10.1 +/- 1.9 and 10.7 +/- 2.3 hours, respectively). The oral clearance was high among both smokers (4.1 +/- 1.9 L.min-1) and nonsmokers (3.3 +/- 2.7 L.min-1; difference not significant). CONCLUSION: Smokers had lower serum concentrations of fluvoxamine than nonsmokers after a single oral dose of fluvoxamine. This finding is consistent with a possible role of CYP1A2 in fluvoxamine metabolism.

Interactions in the renal and biliary elimination of digoxin: stereoselective difference between quinine and quinidine.

The interactions between digoxin and quinine and quinidine that affect the renal and biliary clearances of digoxin were investigated in eight healthy subjects. Digoxin (0.5 to 0.75 mg/day) was given alone and with concomitant administration of quinine (750 mg/day) to reach a steady-state level. In four of the subjects, the study was repeated by administration of equimolar doses of the diastereoisomer quinidine together with digoxin, enabling a within-subject comparison of the effects of the two isomers on digoxin clearance. The biliary excretion of digoxin was studied by use of a modified duodenal marker perfusion technique. A marked reduction was found in the steady-state biliary clearance of digoxin from control value 134 +/- 57 ml/min (mean +/- SD) to 87 +/- 39 ml/min during treatment with quinine (p less than 0.05) and from 95 +/- 24 to 55 +/- 27 ml/min during treatment with quinidine (p less than 0.01; n = 4). Quinidine reduced the renal clearance of digoxin (155 +/- 26 versus 110 +/- 21 ml/min) (p less than 0.05; n = 4), whereas quinine had no such effect (177 +/- 40 versus 185 +/- 53 ml/min; not significant). These findings explain the difference in magnitude between quinidine and quinine in regard to the interaction with digoxin and imply a different degree of stereoselectivity for these isomers in the renal and biliary secretory systems of digoxin.

Theophylline metabolism in relation to antipyrine, debrisoquine, and sparteine metabolism.

Theophylline plasma clearance (Clp) and clearance to its metabolites ( Clm ), as well as antipyrine saliva clearance ( Clsal ) and its Clm were compared in a crossover study in 25 healthy subjects. They were selected with regard to smoking status (nine smokers, 16 nonsmokers) and oxidation phenotype of debrisoquine and sparteine (six poor metabolizers [PMs] and 19 extensive metabolizers [EMs]). Clm of theophylline (1,3-dimethyluric acid, 1-methyluric acid, and 3-methylxanthine) correlated (r greater than or equal to 0.92) to each other and to total theophylline Clp (r greater than or equal to 0.97). Smokers had higher Clm to all metabolites, particularly by the N-demethylation pathways. After correction for the effect of smoking, there was no difference between EMs and PMs with regard to theophylline Clp or Clm . Antipyrine clearances by EMs and PMs ( Clsal and Clm of 4-OH-antipyrine, 3-OH- methylantipyrine , or norantipyrine) also did not differ. Antipyrine Clsal and Clm correlated to theophylline Clp (r between 0.50 and 0.69). It is concluded that theophylline metabolism (N-demethylations and C-oxidation) is not under the same genetic control as sparteine and debrisoquine oxidations, and that there may be a partial overlap in factors that regulate the metabolism of theophylline and antipyrine.

Kinetics and dynamics of disopyramide and its dealkylated metabolite in healthy subjects.

The kinetics and dynamics of total and free (unbound) disopyramide (D) after dosing with D, 1.5 and 2 mg/kg iv, were compared with those of the dealkylated metabolite (MND) after dosing with MND, 0.5 and 1.5 mg/kg iv, in six healthy subjects. Dynamic parameters included ECG with measurement of the QT interval corrected for heart rate (QTc), systolic time intervals, vitamin C-stimulated saliva secretion, pupil size, and maximum accommodation capacity. Mean values of total clearance, apparent volume of distribution, and elimination t1/2 of MND were 5.9, 2.3, and 0.4 times those of total D, respectively. D significantly prolonged the QTc and systolic time intervals and induced transient inhibition of stimulated saliva secretion. In contrast, MND induced no substantial change in either the QTc or systolic time intervals, but did induce more persistent inhibition of salivary secretion. If anticholinergic potency is determined as the degree of inhibition of stimulated saliva flow per plasma concentration unit, MND was three times as potent as its parent when measured at maximum inhibition. There were no consistent drug effects on the ocular parameters. The effect of D on QTc correlated with both total and free plasma concentrations. Furthermore, its transient salivary inhibitory effect paralleled its initial rapid decline in plasma concentration. There was no relationship between the MND plasma concentration and its salivary inhibitory effect. We conclude that disopyramide significantly affected the QTc and systolic time intervals in healthy subjects, while MND in a similar dose had no such effects. MND more strongly inhibited stimulated saliva flow, indicating a more potent anticholinergic effect than D.

Digoxin-verapamil interaction: reduction of biliary but not renal digoxin clearance in humans.

The interaction between digoxin and verapamil was studied in six patients (mean age +/- SD, 61 +/- 5 years) with chronic atrial fibrillation. The effects of adding verapamil (240 mg/day) on steady-state plasma concentrations and renal and biliary clearances of digoxin were studied in a crossover manner. The biliary clearance of digoxin was determined by a duodenal perfusion technique. Verapamil induced a 44% increase in steady-state plasma concentrations of digoxin, from 0.80 +/- 0.24 to 1.15 +/- 0.40 nmol/L (p less than 0.01). The biliary clearance of digoxin decreased by 43%, from 187 +/- 89 to 101 +/- 55 ml/min (p less than 0.05), in the presence of verapamil, whereas the renal clearance was unaffected (153 +/- 31 versus 173 +/- 51 ml/min; difference not significant). Our results indicate that the main inhibitory effect of verapamil on digoxin elimination is on the biliary route.

Cardiac effects of treatment with quinidine and digoxin, alone and in combination.

Systolic time intervals (QS2-I and LVET-I) and echocardiographically determined ejection fraction and velocity of circumferential fiber shortening were recorded in 10 healthy volunteers as measures of inotropic effect during maintenance treatment with 4 consecutive drug regimens: (1) quinidine, 1,200 mg/day; (2) digoxin, average dose 0.31 mg/day; (3) the combination of (1) and (2); and (4) digoxin alone (average dose 0.65 mg/day) to provide the same steady-state serum concentration of digoxin as during the period with combination of digoxin and quinidine. The steady-state serum concentration of digoxin during the low-dose regimen increased from 0.72 +/- 0.15 (mean +/- standard deviation [SD]) to 1.63 +/- 0.28 nmol/liter when quinidine was added. With the high dose of digoxin alone, the serum digoxin level reached 1.68 +/- 0.50 nmol/liter. Skeletal muscle digoxin concentrations during these periods were 27.7 +/- 8.3, 48.7 +/- 16.2, and 51.6 +/- 23.6 nmol/kg of dry weight, respectively. The skeletal muscle to serum concentration ratio of digoxin decreased significantly during quinidine treatment. Systolic time intervals were significantly prolonged by quinidine alone and shortened by digoxin alone, the latter effect being dose-dependent. Subtracting the effect of quinidine itself, the induced increase in digoxin level caused a significant increase in inotropic effect. When these corrected values were compared with those attained during the period with the same steady-state digoxin concentration but in the absence of quinidine, no significant differences were found. Echocardiographically measured ejection fraction and velocity of circumferential fiber shortening showed trends for similar drug effects, as did the systolic time intervals. This study, performed under steady-state conditions, demonstrates that the quinidine-induced increase in steady-state serum digoxin concentration will, with due consideration to quinidine's own pharmacodynamic properties, be accompanied by increased cardiac effects. This indicates that quinidine is not interfering with active receptor sites in the heart for digoxin.

Prevalence of diabetes and impaired glucose tolerance in patients treated with clozapine compared with patients treated with conventional depot neuroleptic medications.

BACKGROUND: Recent case reports suggest the association of the emergence of diabetes mellitus with clozapine treatment, although conventional neuroleptics have also been implicated. This study was conducted to determine if there is an increased risk of diabetes mellitus and/or impaired glucose tolerance (IGT) during clozapine treatment compared with treatment with conventional depot neuroleptics. METHOD: In a district hospital in northern Sweden, blood glucose tests and, if necessary an oral glucose tolerance test were used to assess the prevalence of diabetes mellitus or IGT in 63 patients treated with clozapine compared with 67 patients treated with conventional depot neuroleptics (haloperidol, zuclopenthixol, fluphenazine, perphenazine, or flupenthixol). Diabetes mellitus and impaired glucose tolerance were classified according to World Health Organization criteria. RESULTS: There were 3 dropouts in the clozapine group and 4 in the control group. Of subjects treated with clozapine, 12% (7/60) had type 2 diabetes mellitus, and 10% (6/60) had IGT. Of subjects treated with depot injections of neuroleptics, 6% (4/63) had type 2 diabetes mellitus and 3% (2/63) had IGT. None in either group had type 1 diabetes mellitus. Subjects in the clozapine group were significantly (p < .001) younger than subjects in the control group, whereas the 2 groups did not differ with respect to body weight, body mass index, or prevalence of diabetes mellitus in first-degree relatives. CONCLUSION: Subjects treated with clozapine were more often classified as having type 2 diabetes mellitus or IGT compared with subjects in the control group. This difference did not, however, achieve statistical significance (p=.06).

HMG-CoA reductase inhibitors and myotoxicity.

The 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors specifically inhibit HMG-CoA reductase in the liver, thereby inhibiting the biosynthesis of cholesterol. These drugs significantly reduce plasma cholesterol level and long term treatment reduces morbidity and mortality associated with coronary heart disease. The tolerability of these drugs during long term administration is an important issue. Adverse reactions involving skeletal muscle are not uncommon, and sometimes serious adverse reactions involving skeletal muscle such as myopathy and rhabdomyolysis may occur, requiring discontinuation of the drug. Occasionally, arthralgia, alone or in association with myalgia, has been reported. In this article we review scientific data provided via Medline, adverse drug reaction case reports from the Swedish Drug Information System (SWEDIS) and the World Health Organization's International Drug Information System (INTDIS) database, focusing on HMG-CoA reductase inhibitor-related musculoskeletal system events. Cytochrome P450 (CYP) 3A4 is the main isoenzyme involved in the metabolic transformation of HMG-CoA reductase inhibitors. Individuals with both low hepatic and low gastrointestinal tract levels of CYP3A4 expression may be at in increased risk of myotoxicity due to potentially higher HMG-CoA reductase inhibitor plasma concentrations. The reported incidence of myotoxic reactions in patients treated with this drug class varies from 1 to 7% and varies between different agents. The risk of these serious adverse reactions is dose-dependent and may increase when HMG-CoA reductase inhibitors are prescribed concomitantly with drugs that inhibit their metabolism, such as itraconazole, cyclosporin, erythromycin and nefazodone. Electrolyte disturbances, infections, major trauma, hypoxia as well as drugs of abuse may increase the risk of myotoxicity. It is important that the potentially serious adverse reactions are recognised and correctly diagnosed so that the HMG-CoA reductase inhibitor may at once be withdrawn to prevent further muscular damage.

DMSA administration to patients with alleged mercury poisoning from dental amalgams: a placebo-controlled study.

The present investigation was performed to determine the effect of 14-day oral administration of meso-2.3-dimercaptosuccinic acid (DMSA) on the urinary mercury excretion and the potential reduction of blood and plasma mercury concentrations, and also to relate these effects to possible decrease of symptoms, allegedly associated with amalgam fillings. Twenty subjects, relating their symptoms to mercury from amalgam fillings, received 20 mg/kg DMSA or placebo for 14 days. Their symptoms and mood states were recorded during the study and at a check-up 3 months later. Interpretation was based on intra-individual differences. DMSA-treatment resulted in an average increase in urinary mercury excretion by 65% and a decrease in blood mercury levels of 0.04 microgram/L/day. At the check-up after 3 months, urinary mercury excretion had returned to the pre-treatment level. No treatment effect of DMSA was apparent on subjective symptoms and mood state. One statistically significant treatment effect was noted-a decrease in fatigue-inertia in the DMSA-group-but there was no demonstrable correlation with increased urinary excretion or decreased blood concentration of mercury. Three subjects showed hypersensitive reactions, probably DMSA-specific, at the end of the treatment period. This placebo-controlled study provides no scientific support for diagnostic or therapeutic administration of DMSA for symptoms allegedly associated with chronic mercury exposition from dental amalgam fillings.

Pharmacokinetic properties of a new sustained-release theophylline preparation.

A newly developed compressed theophylline tablet with slow in vitro dissolution rate was investigated in six healthy volunteers. The mean bioavailability of theophylline during a single oral dose was 97%, which did not significantly differ from the i.v. reference. The bioavailability of Teovent-SR measured during a dosing interval at steady state was on the average 110%, significantly (p less than 0.05) higher than the i.v. standard. This points to the possibility of a lower total clearance under conditions of multiple dosing of theophylline. Thus a single i.v. dose may not be the proper reference for evaluating bioavailability of theophylline during steady state. During maintenance administration of the tablet every 12 h the maximum plasma level of theophylline was reached after 4 h. The maximum concentration during a dosage interval at steady state was on the average 22% (range 14-32) higher than the mean concentration, whereas the trough level was on the average 28% (range 20-43) below the mean. During 8.5 h, i.e., 70% of the 12 h dosing interval, at least 75% of the maximum concentration was maintained. This theophylline formulation has a complete bioavailability and slow-release characteristics that produce reasonably stable plasma concentrations over a dosing interval of 8-12 h.

The effect of food and bile acid administration on the relative bioavailability of cyclosporin.

1. The relative bioavailability of cyclosporin was studied in 11 healthy volunteers after single oral capsule doses of cyclosporin on three separate occasions; fasting, with breakfast and with breakfast together with bile acid tablets (400 mg of cholic acid and 100 mg of dehydrocholic acid). 2. There was a significant increase in the area under the blood concentration vs time curve (AUC) of cyclosporin when the drug was taken together with breakfast and bile acid tablets (9078 ng ml-1 h) as compared with breakfast alone (7453 ng ml-1 h, P less than 0.05) or fasting conditions (7283 ng ml-1 h, P less than 0.01). 3. A blood drug concentration vs time curve displaying two peaks was present in 9/11 subjects when cyclosporin was taken with breakfast or with breakfast and bile acid tablets, but only one peak was present when cyclosporin was taken during fasting, suggesting an enterohepatic circulation of cyclosporin or a second absorption phase after the meal. 4. In a separate study, 12 h trough blood cyclosporin concentrations were measured before and after 1 week of bile acid treatment in 19 clinically stable, out-patient transplant recipients who were treated with oral cyclosporin solution (mean dose 2.0 mg kg-1 twice daily). The administration of cyclosporin was not standardized with regard to food intake. There was no significant difference in the blood concentrations of cyclosporin before and after bile acid treatment (114 +/- 38 ng ml-1 vs 121 +/- 38 ng ml-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Felodipine reduces the absorption of theophylline in man.

Ten healthy male volunteers (mean age 26 years) received 200 mg theophylline aminopropanol orally 8-hourly for 4 days, followed by 5 mg felodipine 8-hourly for 6 days, and then the combination of oral felodipine and theophylline for a further 4 days. Plasma concentrations of theophylline and felodipine were determined, and theophylline and its metabolites in urine were also measured. Felodipine led to a reduction in the plasma AUC of theophylline of 18.3%. The metabolic and renal clearances of theophylline remained unchanged, but the total recovery of theophylline-derived products was significantly reduced during felodipine treatment. No change in felodipine pharmacokinetics was observed during simultaneous treatment with theophylline. Compared to theophylline treatment alone, the diastolic blood pressure was significantly reduced during felodipine treatment alone and in combination with theophylline. It is concluded that felodipine slightly but significantly lowered the plasma theophylline concentration by interfering with its absorption. The interaction in most instances would probably be of minor clinical consequence.

Effect of salbutamol on digoxin pharmacokinetics.

A single dose of the beta 2-adrenoceptor agonist salbutamol has previously been shown to decrease serum digoxin concentration in healthy volunteers. A possible explanation of the phenomenon is a beta 2-adrenoceptor-mediated increase in the specific binding of digoxin to skeletal muscle. The present study was undertaken to further elucidate the effect of salbutamol on the pharmacokinetics of digoxin in man. Nine volunteers were studied on two occasions during salbutamol or placebo treatment. On test days salbutamol, 4 micrograms.kg-1.h-1 or saline was infused for 10 h, preceded and followed by four and three days, respectively, of oral administration. A single i.v. injection of digoxin 15 micrograms.kg-1, was given 20 min after starting the infusion. At the end of the infusion a muscle biopsy was taken from the vastus lateralis. Blood samples for the analysis of serum digoxin and potassium were repeatedly taken over 72 h. Urine was collected over a period of 24 h for determination of the renal excretion of digoxin and potassium. The serum digoxin concentration, expressed as the AUC 0-6 h was 15% lower during salbutamol infusion than during saline infusion. Salbutamol caused significantly faster elimination of digoxin from the central volume of distribution to deeper compartments. Salbutamol had no effect on the renal clearance of digoxin. The skeletal muscle digoxin concentration tended to be higher (48%) during salbutamol compared to placebo treatment. The serum potassium concentration was significantly lower after salbutamol compared to placebo, as was the rate of renal excretion of potassium.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of gender and oral contraceptives on CYP2D6 and CYP2C19 activity in healthy volunteers.

AIMS: The study was carried out in order to assess the effects of gender and the use of oral contraceptives (OCs) on CYP2D6 and CYP2C19 activities in healthy volunteers. METHODS: Six hundred and eleven Caucasian volunteers (330 males and 281 females; age range 18-49 years) were phenotyped with respect to CYP2D6 and CYP2C19 by means of the probe drugs dextromethorphan and mephenytoin, respectively. Extensive metabolisers were selected for this study. RESULTS: The median dextromethorphan/dextrorphan metabolic ratio in non-OC using females was significantly lower than in males (0.067 vs 0.080; P = 0.033) (mean difference in ln dextromethorphan/dextrorphan metabolic ratio 0.023, 95% CI 0.03-0.43). For the mephenytoin S/R ratio, no such difference was observed. However, OC using females had a significantly higher median mephenytoin S/R ratio than non-OC using females (0.230 vs 0.090; P < 0.001) (mean difference in ln mephenytoin S/R ratio 0.082, 95% CI 0.60-1.04). Moreover, females using combined OCs had a significantly higher median ratio than females using OCs with progestins only (median 0.258 vs 0.135; P = 0.008) (mean difference in ln mephenytoin S/R ratio 0.82, 95% CI 0.21-1.34). CONCLUSIONS: Given certain assumptions, the study indicates that females in the fertile age have a slightly higher CYP2D6 activity compared with males. There was no evidence of a gender difference in CYP2C19 activity. The use of combined OCs reduces the activity of CYP2C19, an effect that seems to be related to the ethinyloestradiol component.

Spontaneous reporting of adverse drug reactions by nurses.

BACKGROUND: Spontaneous reporting of adverse drug reactions (ADRs) remains one of the most effective methods to detect new and serious drug reactions. However, it is well known that there is a high degree of under-reporting. OBJECTIVE: This study was carried out as an attempt to improve and increase the reporting of ADRs by investigating the utility of nurses reporting in addition to physicians, as usual. METHODS: During a 12-month study period, nurses working at two departments of geriatric medicine in northern Sweden received special instruction regarding drugs and ADRs, ADR reporting and special aspects of ADRs in elderly people. The reports from the nurses were scrutinized concerning the seriousness of the reaction, reported drugs and type of reaction (type A or B). All nurses working at the two departments (117) were eligible to report but in practice only those attending the teaching sessions did so. A comparison with historical reporting and with reporting from other geriatric departments in Sweden was also carried out. At the end of the study all participating nurses received a questionnaire aimed at investigating their attitudes towards ADR reporting. RESULTS: After the 12-month study period 18 ADR reports involving 22 reactions had been received. Seven of these were assessed as serious reactions. All of the reactions were of type A. In comparison, during the corresponding time period from the study clinics during the preceding year, only two reports were registered. During the study period only 15 reports were registered from the other 50 geriatric departments in Sweden. CONCLUSION: Even though the total number of ADR reports was small, our data indicate a substantial increase in the reporting rate. This indicates that instructed and interested nurses could play an important role in detecting and reporting suspected ADRs.