Intralipid emulsion treatment as an antidote in lipophilic drug intoxications.

Intravenous lipid emulsion (ILE) is a lifesaving treatment of lipophilic drug intoxications. Not only does ILE have demonstrable efficacy as an antidote to local anesthetic toxicity, it is also effective in lipophilic drug intoxications. Our case series involved 10 patients with ingestion of different types of lipophilic drugs. Intravenous lipid emulsion treatment improved Glasgow Coma Scale or blood pressure and pulse rate or both according to the drug type. Complications were observed in 2 patients (minimal change pancreatitis and probable ILE treatment-related fat infiltration in lungs). In our case series, ILE was used for different lipophilic drug intoxications to improve cardiovascular and neurologic symptoms. According to the results, it was found that ILE treatment is a lifesaving agent in lipophilic drug intoxications and it can be used in unconscious patients who have cardiac and/or neurologic symptoms but no history of a specific drug ingestion.

Influence of quinidine, cimetidine, and ketoconazole on the enantioselective pharmacokinetics and metabolism of metoprolol in rats.

Metoprolol is a beta-blocker and its racemic mixture is used for the treatment of hypertension. In the present study we investigated the influence of CYP2D and CYP3A on the stereoselective metabolism of metoprolol in rats. Male Wistar rats (n = 6 per group) received racemic metoprolol (15 mg/kg) orally, with or without pretreatment with the CYP inhibitor ketoconazole (50 mg/kg), cimetidine (150 mg/kg), or quinidine (80 mg/kg). Blood samples were collected up to 48 h after metoprolol administration. The plasma concentrations of the stereoisomers of metoprolol, O-demethylmetoprolol (ODM), alpha-hydroxymetoprolol (OHM) (Chiralpak AD column), and metoprolol acidic metabolite (AODM) (Chiralcel OD-R column) were determined by HPLC using fluorescence detection (lambda(exc) = 229 nm; lambda(em) = 298 nm). CYP3A inhibition by ketoconazole reduced the plasma concentrations of ODM and AODM and favored the formation of OHM. CYP2D and CYP3A inhibition by cimetidine reduced the plasma concentrations of OHM and AODM and favored the formation of ODM. The inhibition of CYP2D by quinidine reduced the plasma concentrations of OHM and favored the formation of ODM. In conclusion, the results suggest that CYP3A is involved in the formation of ODM and CYP2D is involved in the formation of AODM.

The calcium channel blocker felodipine attenuates the positive hemodynamic effects of the beta-blocker metoprolol in severe dilated cardiomyopathy--a prospective, randomized, double-blind and placebo-controlled study with invasive hemodynamic assessment.

BACKGROUND: In addition to standard therapy with ACE-inhibitors, digitalis and diuretics, beta-adrenergic receptor blockers have become a widely accepted strategy in the treatment of chronic heart failure. The role of calcium antagonists in CHF however remains controversial. To evaluate if a combination therapy of metoprolol and felodipine might improve hemodynamic parameters, a randomized and placebo-controlled study was designed. METHODS AND RESULTS: Sixty-three patients with DCMP, LVEF 3 months in NYHA II-III on standard medication were prospectively treated with either a) a combination of metoprolol+felodipine (MF group, n=20), b) metoprolol+felodipine-placebo (MP group, n=23), or c) metoprolol-placebo+felodipine-placebo (PP group, n=20). Compared to baseline, LVEF and LVEDD significantly improved after 6 months in the MP group (LVEF: 36+/-2% vs 29+/-2%, p<0.01; LVEDD: 68+/-3 mm vs 64+/-3 mm, p<0.05), whereas in the other treatment groups only minor changes were observed. A significant benefit in hemodynamic parameters as determined by right heart catheterization was noted also only in the MP group with a marked reduction in PAP mean (17 vs 24 mmHg, p<0.01), PCWP (10 vs 15 mmHg, p<0.001) resulting in a significant increase in cardiac and stroke volume index at rest with no marked changes in the MF and PP group. CONCLUSION: beta-blocker treatment in CHF patients improves left ventricular function and additionally invasive hemodynamic measurements both at rest and during exercise. In contrast, the combined therapy with the long-acting calcium antagonist felodipine neutralizes these beneficial effects of metoprolol therapy to almost placebo level, providing evidence based on hemodynamic measurements that this combination should be avoided in patients with CHF.

In vitro effects of racemates, separate enantiomers and major metabolites of mefloquine and halofantrine on metoprolol biotransformation by rat liver microsomes.

1. The effects of the anti-malarial drugs mefloquine and halofantrine and of their major metabolites on metoprolol metabolism by rat liver microsomes have been investigated. 2. The observed Km and Vmax, and the formation kinetics of alpha-hydroxymetoprolol and O-demethylmetoprolol, two major metoprolol metabolites, were in keeping with published data. 3. In vitro, mefloquine competitively inhibited metoprolol biotransformation, whereas halofantrine did so in a mixed fashion. The mefloquine Ki of metoprolol alpha-hydroxylation and O-demethylation were 3.4 and 5.8 microM respectively, whereas those of halofantrine were 0.15 and 0.32 microM respectively. 4. The main metabolites, N-debutylhalofantrine and carboxymefloquine, were 4-10-fold less inhibitory than the parent drugs. The difference in inhibitory potency of parent drugs and metabolites was higher for halofantrine than for mefloquine. The potency order for metoprolol metabolism inhibition was halofantrine >> mefloquine = N-debutylhalofantrine > carboxymefloquine. 5. A preliminary study with anti-malarial enantiomers showed a weak difference, in metoprolol metabolism inhibition between the enantiomers of halofantrine or mefloquine. 6. It is concluded that halofantrine is a potent inhibitor of metoprolol metabolism and that halofantrine metabolites or its enantiomers may have a different inhibitor potency than the parent drug: (1) the inhibition potency of these compounds should be studied in vitro and (2) their in vivo elimination half-life and plasma concentrations should be taken into be account to extrapolate this experimental results to in vivo.

The oxidative metabolism of metoprolol in human liver microsomes: inhibition by the selective serotonin reuptake inhibitors.

OBJECTIVE: Biotransformation of metoprolol to alpha-hydroxymetoprolol (HM) and O-demethylmetoprolol (ODM) is mediated by CYP2D6. The selective serotonin reuptake inhibitors (SSRIs) are known to inhibit CYP2D6. The aim was to study in vitro the potential inhibitory effect of SSRIs on metoprolol biotransformation. METHODS: Using microsomes from two human livers, biotransformation of metoprolol to alpha-hydroxymetoprolol (HM) and O-demethylmetoprolol (ODM) as a function of the concentrations of the SSRIs and of some of their metabolites was studied. RESULTS: The kinetics of the formation of both metabolites are best described by a biphasic enzyme model. The estimated values of Vmax and kM for the high affinity site are for the alpha-hydroxylation in human liver HL-1 32 pmol mg(-1) min(-1) and 75 micromol x l(-1) respectively, and in human liver HL-9 39 pmol mg(-1) x min(-1) and 70 micromol x l(-1) respectively; for the O-demethylation in HL-1 131 pmol mg(-1) min(-1) and 95 micromol x l(-1) respectively, and in HL-9 145 pmol mg(-1) min(-1) and 94 micromol x l(-1) respectively. Quinidine is for both pathways a potent inhibitor of the high-affinity site, with K(i) values ranging from 0.03 to 0.18 micromol x l(-1). Fluoxetine, norfluoxetine and paroxetine are likewise potent inhibitors, with Ki values ranging from 0.30 to 2.1 micromol x l(-1) fluvoxamine, sertraline, desmethylsertraline, citalopram and desmethylcitalopram are less potent inhibitors, with K(i) values above 10 micromol x l(-1). CONCLUSION: The rank order of the SSRIs for inhibition of metoprolol metabolism is comparable to that reported in the literature for other CYP2D6 substrates, with fluoxetine, norfluoxetine and paroxetine being the most potent. These findings need further investigation to determine their clinical relevance.

Influence of CYP2D6-dependent metabolism on the steady-state pharmacokinetics and pharmacodynamics of metoprolol and nicardipine, alone and in combination.

1 The metabolism of metoprolol depends in part on the genetically determined activity of the CYP2D6 isoenzyme. In vitro studies have shown that nicardipine is a potent inhibitor of CYP2D6 activity. Since the combination of metoprolol and nicardipine is likely to be used for the treatment of hypertension, we examined the interaction between these two drugs at steady-state. 2 Fourteen healthy volunteers, seven extensive and seven poor metabolisers of dextromethorphan were studied in a double-blind, randomised cross-over four-period protocol. Subjects received nicardipine 50 mg every 12 h, metoprolol 100 mg every 12 h, a combination of both drugs and placebo during 5.5 days. Steady-state pharmacokinetics of nicardipine and metoprolol were analyzed. Beta-adrenoceptor blockade was assessed as the reduction of exercise-induced tachycardia. 3 During treatment with metoprolol, alone or in combination with nicardipine, its steady-state plasma concentrations were higher in subjects of the poor metaboliser phenotype than in extensive metabolisers. Beta-adrenoceptor blockade was also more pronounced in poor metabolisers than in extensive metabolisers of dextromethorphan during treatment with metoprolol alone or in combination with nicardipine (24.0 +/- 2.4% vs 17.1 +/- 3.5% and 24.1 +/- 2.5% vs 15.4 +/- 2.7% reduction in exercise trachycardia, respectively, P < 0.01 in each case). 4 Nicardipine produced a small increase in plasma metoprolol concentration in extensive metabolisers from 35.9 +/- 16.6 to 45.8 +/- 15.4 ng ml(-1) (P < 0.02), but had no significant effect in poor metabolisers. However, nicardipine did not alter the R/S metoprolol ratio in plasma 3 h after dosing, the plasma concentration of S-(-)-metoprolol 3 h after dosing or the beta-adrenoceptor blockade produced by metoprolol in subjects of both phenotypes. The partial metabolic clearance of metoprolol to alpha-hydroxy-metoprolol was not altered significantly in extensive metabolisers. Plasma nicardipine concentration and beta-adrenoceptor blocking effects did not differ between the phenotypes and were not influenced by metoprolol. We conclude that beta-adrenoceptor blockade during repeated dosing with metoprolol is more pronounced in poor than in extensive metaboliser subjects, that nicardipine decreases a CYP2D6-independent route of metoprolol elimination but does not increase beta-adrenoceptor blockade during repeated dosing with metoprolol.

The interaction of alcohol and beta-blockers in arterial hypertension.

The acute effects of consuming alcohol after a single oral dose of 200 mg of metoprolol or placebo were examined in eight healthy men in a randomized, controlled study. Alcohol, in a dose of 0.75 g/kg body weight, did not abolish the antihypertensive effect of metoprolol upon supine systolic blood pressure. The interaction of alcohol with antihypertensive drugs requires further investigation as hypertensive patients who consume alcohol regularly are known to have less adequate blood pressure control.

Drug interaction between metoprolol and chlordiazepoxide.

We studied the effect of concomitant administration of chlordiazepoxide on the negative chronotropic effect of metoprolol in rabbits. Chlordiazepoxide administration for more than two weeks partly reversed the effect of metoprolol in three out of five rabbits, probably through hepatic enzyme induction.

Clinical experiences with prenalterol as an antidote to Beta-adrenoceptor blockade.

The cases presented in this paper suggest that prenalterol is useful in the treatment of myocardial depression due to beta-blockade. According to its pharmacological properties, prenalterol might even be the drug of choice in these situations. It is wellknown that massive beta-blocker overdosage may be difficult to manage and as the therapeutic guidelines in these cases have not yet been definitely stated, it is obvious that prenalterol in this context will be of utmost importance. What remains to be solved is the dosage level. So far, experience has shown that high doses, widely exceeding the recommended initial dose of 50-100 micrograms/kg, are necessary to restore normal circulation in massive beta-blocker overdosage.

The use of dobutamine in myocardial infarction for reversal of the cardiodepressive effect of metoprolol.

1 Ten patients with acute myocardial infarction were infused dobutamine in increasing doses up to 15 microgram kg--1 min--1. 2 Metoprolol (total dose 15 mg) was then given intravenously to nine of these patients and the beta-adrenoceptor against effects produced by dobutamine were effectively reversed. 3 Nine patients with acute myocardial infarction pretreated with metoprolol (15 mg) were infused dobutamine 15 microgram kg--1 min--1 for 10 min. This resulted in effective reversal of the beta-adrenoceptor antagonist effects induced by metoprolol, without the occurrence of serious arrhythmias or other unwanted effects. 4 Dobutamine may be valuable in counteracting any undesirable cardiodepressive effects of beta-adrenergic receptor blocking drugs (especially the cardioselective agents) in patients with acute myocardial infarction.