Pharmacokinetics of isradipine in patients with chronic liver disease

Extracorporeal treatment for calcium channel blocker poisoning: systematic review and recommendations from the EXTRIP workgroup

BACKGROUND

Calcium channel blockers (CCBs) are commonly used to treat conditions such as arterial hypertension and supraventricular dysrhythmias. Poisoning from these drugs can lead to severe morbidity and mortality. We aimed to determine the utility of extracorporeal treatments (ECTRs) in the management of CCB poisoning.

METHODS

We conducted systematic reviews of the literature, screened studies, extracted data, summarized findings, and formulated recommendations following published EXTRIP methods.

RESULTS

A total of 83 publications (6 in vitro and 1 animal experiments, 55 case reports or case series, 19 pharmacokinetic studies, 1 cohort study and 1 systematic review) met inclusion criteria regarding the effect of ECTR. Toxicokinetic or pharmacokinetic data were available on 210 patients (including 32 for amlodipine, 20 for diltiazem, and 52 for verapamil). Regardless of the ECTR used, amlodipine, bepridil, diltiazem, felodipine, isradipine, mibefradil, nifedipine, nisoldipine, and verapamil were considered not dialyzable, with variable levels of evidence, while no dialyzability grading was possible for nicardipine and nitrendipine. Data were available for clinical analysis on 78 CCB poisoned patients (including 32 patients for amlodipine, 16 for diltiazem, and 23 for verapamil). Standard care (including high dose insulin euglycemic therapy) was not systematically administered. Clinical data did not suggest an improvement in outcomes with ECTR. Consequently, the EXTRIP workgroup recommends against using ECTR in addition to standard care for patients severely poisoned with either amlodipine, diltiazem or verapamil (strong recommendations, very low quality of the evidence (1D)). There were insufficient clinical data to draft recommendation for other CCBs, although the workgroup acknowledged the low dialyzability from, and lack of biological plausibility for, ECTR.

CONCLUSIONS

Both dialyzability and clinical data do not support a clinical benefit from ECTRs for CCB poisoning. The EXTRIP workgroup recommends against using extracorporeal methods to enhance the elimination of amlodipine, diltiazem, and verapamil in patients with severe poisoning.

Phenytoin Toxicity After Transjugular Intrahepatic Portosystemic Shunt (TIPS)

BACKGROUND

Transjugular intrahepatic portosystemic shunt (TIPS) alters portal blood flow and may impact drug metabolism and bioavailability. However, little evidence has been published to provide guidance on medication alterations after TIPS procedures.

CASE REPORT

We report a patient who developed phenytoin toxicity requiring a prolonged readmission after a TIPS procedure. It is likely that the TIPS procedure altered phenytoin metabolism and led to toxicity in this patient. Phenytoin is an antiepileptic drug that is primarily eliminated by hepatic metabolism. It is possible that phenytoin toxicity may occur after TIPS, and that decreased dose requirements may be a durable effect of the procedure. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: TIPS is now the most common portal hypertension decompressive procedure performed by interventional radiologists and has become the primary portosystemic shunt (surgical or percutaneous) performed in the United States. Patients with a history of TIPS procedures commonly present to tertiary- and quaternary-care emergency departments with complex clinical presentations. Greater familiarity with the potential effects of TIPS on drug metabolism may help emergency physicians prevent adverse drug effects and optimize clinical outcomes.

Reduced duodenal cytochrome P450 3A protein expression and catalytic activity in patients with cirrhosis

The small intestine and liver express high levels of cytochrome P450 3A (CYP3A), an enzyme subfamily that contributes significantly to drug metabolism. In patients with cirrhosis, reduced metabolism of drugs is typically attributed to decreased liver function, but it is unclear whether drug metabolism in the intestine is also compromised. In this study, we compared CYP3A protein expression and in vitro midazolam hydroxylation in duodenal mucosal biopsies from subjects with normal liver function (controls; n = 20) and subjects with various levels of severity of cirrhosis (n = 23). In samples from subjects with cirrhosis, duodenal CYP3A expression and total midazolam hydroxylation were lower by 47 and 34%, respectively, as compared with samples from controls. Greater decreases in CYP3A expression were seen in subjects with more severe cirrhosis. Therefore, patients with advanced cirrhosis may have greater drug exposure following oral dosing as a result of both impaired liver function and decreased intestinal CYP3A expression and activity.

Metabolism of aminopyrine and derivatives in man: in vivo study of monomorphic and polymorphic metabolic pathways

1. The main metabolic pathways involved in the biodisposition of aminopyrine have been monitored in vivo in 60 healthy volunteers by measuring the amount of parent drug and metabolites recovered in the urine 24 h after oral administration of 250 mg aminopyrine. 2. The amount of metabolites in the 24-h urine was (mean +/- SD of 60 individuals): unchanged aminopyrine, 0.2 +/- 0.2 mg; methyl aminoantipyrine, 4.5 +/- 2.8 mg; formyl aminoantipyrine, 18.5 +/- 10.1 mg; aminoantipyrine, 9.2 +/- 6.6 mg; and acetyl aminoantipyrine, 31.8 +/- 21.1 mg. 3. Large interindividual differences (12-200-fold changes) are present in all the metabolic steps involved in aminopyrine biotransformation. These differences are not related to gender, intake of caffeine or alcohol, or known drug-metabolizing polymorphisms such as those involved in debrisoquine or mephenytoin metabolism. In contrast, smoking resulted in a decrease in the N(4)-demethylation ratio (p = 0.011). 4. The interindividual differences followed an apparently normal distribution in the N(4)- and N(2)-dimethylation and formylation pathways (p > 0.1). In contrast, acetylation follows a polymorphic distribution (p < 0.03), with an apparent antimode ratio close to 4. With the exception of the acetylation pathway, all of the metabolic ratios correlated between themselves (p < 0.001).