The effect of liver cirrhosis on the pharmacokinetics of phenprocoumon

HIV/HCV-coinfection: which role can new antiretrovirals such as integrase inhibitors play?

End-stage liver disease has become one of the most frequent causes of death in HIV/HCV-coinfected patients. The role of new antiretrovirals in the progression of liver fibrosis has yet to be defined. However with significant toxicities and drug-to-drug interactions of nucleoside reverse transcriptase inhibitors in combination with ribavirin, with drug to drug interaction of HIV protease inhibitors with HCV protease inhibitors and calcineurin-inhibitors, new antiretrovirals lacking these interactions represent attractive alternatives in the setting of anti-HCV therapy or post liver transplantation. In the following review we want to focus on the new class of HIV integrase inhibitors and discuss present data with regard to special issues of HIV and HCV co-infection.

Lack of effect of certain histamine H2-receptor blockers on the glucuronidation of 7-hydroxy-4-methylcoumarin by human liver microsomes

Contrary to the general belief that cimetidine and ranitidine spare glucuronidation of drugs, some authors have indicated that both cimetidine and ranitidine could inhibit the glucuronidation of paracetamol (acetaminophen) by cultured rat hepatocytes. Thus, we tested the effect of three histamine H2-receptor blockers (cimetidine, ranitidine and famotidine) on the glucuronidation of 7-hydroxy-4-methylcoumarin (7-OH-4-MC) by human liver microsomes. None of the drugs studied produced significant inhibition of the glucuronidation of 7-OH-4-MC when used at concentrations up to 1.5 mM. Thus, even the new H2-receptor blocker, famotidine, spares glucuronidation. These findings further support the previous reports which suggest that glucuronide conjugation in humans is spared by H2-receptor blockers.

Glucuronidation of 7-hydroxy-4-methylcoumarin by microsomes from normal and diseased human livers

Glucuronidation of 7-hydroxy-4-methylcoumarin (7-H-4-MC) by microsomal UDP-glucuronosyltransferases from 12 human liver biopsy samples was studied. Glucuronidation rates were highest for livers with mild cholestasis while those for livers with mild fatty changes were similar to normal livers. The lowest rates were exhibited by livers showing primary or metastatic carcinoma on histological examination. Thus, glucuronidation of not only bile acids but also of other substrates such as 7-H-4-MC may be elevated in cholestasis. These results are also consistent with other studies stating that glucuronidation might be spared in certain mild hepatic diseases.

The effects of frusemide and probenecid on the pharmacokinetics of phenprocoumon

We have studied the pharmacokinetics of phenprocoumon with and without co-administration of frusemide and probenecid in two groups of 17 healthy volunteers. Frusemide 40 mg b.i.d. for 7 days did not interact with phenprocoumon to a significant extent. Probenecid 500 mg q.i.d. for 7 days significantly accelerated the overall elimination of phenprocoumon, as indicated by a decrease in AUC from 295 to 157 micrograms.h.ml-1, and a reduction in the fraction of the dose excreted by the kidneys. The data are consistent with inhibition of the glucuronidation of phenprocoumon by probenecid. Its accelerated elimination may be a consequence of the increased formation of hydroxylated metabolites.

Effect of oral contraceptive steroids on the pharmacokinetics of phenprocoumon

1. The effect of chronic administration of oral contraceptive steroids (OCS) on the pharmacokinetics of the oral anticoagulant phenprocoumon was investigated in seven healthy females. 2. Plasma concentrations of phenprocoumon and the urinary recovery of unchanged as well as conjugated drug were measured following a single oral dose of 0.22 mg kg-1. A group of seven non-smoking, drug-free women matched for age and body weight served as controls. 3. Administration of OCS was associated with a significant increase in the clearance of phenprocoumon from 1.6 +/- 0.7 to 2.0 +/- 0.7 ml min-1 kg-1 (P less than 0.05). The urinary recovery of phenprocoumon glucuronide was significantly higher in OCS users (21.0 +/- 16 vs 14.0 +/- 10 (% of dose); P less than 0.05). No difference in plasma protein binding of phenprocoumon was observed, being 99.2 +/- 0.07 in both groups. 4. The accelerated glucuronidation of phenprocoumon in OCS users suggests the need for careful monitoring of the anticoagulatory response in these subjects, especially when the OCS are withdrawn.

Plasma levels and urinary excretion of lormetazepam in patients with liver cirrhosis and in healthy volunteers

Plasma levels and urinary excretion of lormetazepam (Noctamid-ampoules; 2 mg/10 ml) were studied after i.v. (0.015 mg/kg b.w.) and after p.o (0.03 mg/kg b.w.) administration of the drug to five patients with cirrhosis of the liver (C) and to five young male volunteers (N). The cirrhotic patients exhibited higher drug plasma levels (Cmax p.o.: 11-43 ng/ml [C] vs. 11-16 ng/ml [N]) and higher AUC0-24 values of the unchanged drug (i.v.: 66-102 ng.h/ml [C] vs. 54-72 ng.h/ml [N]; p.o.: 83-188 ng.h/ml [C] vs. 74-113 ng.h/ml [N]). The absolute bioavailability was increased in the C-group with 57-134% vs. 52-84% [N]. The total plasma clearance of lormetazepam was 3 ml/min/kg in the C-group and 4 ml/min/kg in the N-group and thus within the range known for elderly and young male subjects. Conversely to the parent compound, the AUC-figures of its 3-OH-glucuronide were higher in the N-group (346-434 ng.h/ml) than in the C-group (149-371 ng.h/ml). In 24 h pooled urine samples of both groups, the glucuronide of lorazepam, the N-demethylated metabolite, accounted for approximately 5-14% of the dose fraction excreted as lormetazepam glucuronide. Apart from increased levels of the unchanged drug due to porto-systemic shunt and/or disease-dependent lower glucuronidation rate, the pharmacokinetics of lormetazepam were not altered in cirrhotic patients. It can therefore be concluded that for this group of patients the drug can be administered according to the same dose regimen as that used for normal subjects.

The effect of wheat bran on the pharmacokinetics of phenprocoumon in normal volunteers

Observations of a variable anticoagulatory response in patients being treated by phenprocoumon and wheat bran resulted in a study of seven healthy volunteers. Up to 168 h after the administration of phenprocoumon, both in the fasting state and following the ingestion of 35 g wheat bran in a crossover design, blood samples were taken and urine was collected. The usual pharmacokinetic parameters were calculated from the concentrations measured. Following the ingestion of wheat bran, a decreased absorption rate for phenprocoumon but no decrease in overall bioavailability was observed. In addition, a decrease in total body clearance of phenprocoumon and an increase in the free plasma fraction of phenprocoumon, resulting in decreased free drug clearance, was seen after wheat bran administration. No differences were observed in the urinary excretion of either phenprocoumon or its metabolite. These findings cannot be completely explained by our present knowledge and need further investigation.