Evidence for Impaired Hepatic Vitamin K1 Metabolism in Patients Treated with N-Methyl-Thiotetrazole Cephalosporins

Use of Hypoprothrombinemia-Inducing Cephalosporins and the Risk of Hemorrhagic Events: A Nationwide Nested Case-Control Study

Objective

Existing data regarding the risk of hemorrhagic events associated with exposure to hypoprothrombinemia-inducing cephalosporins are limited by the small sample size. This population-based study aimed to examine the association between exposure to hypoprothrombinemia-inducing cephalosporins and hemorrhagic events using National Health Insurance Research Database in Taiwan.

Design

A nationwide nested case-control study.

Setting

National Health Insurance Research database.

Participants

We conducted a nested case-control study within a cohort of 6191 patients who received hypoprothrombinemia-inducing cephalosporins and other antibiotics for more than 48 hours. Multivariable conditional logistic regressions were used to calculate the adjusted odds ratio (aOR) and 95% confidence interval (CI) for hemorrhagic events associated with exposure to hypoprothrombinemia-inducing cephalosporins (overall, cumulative dose measured as defined daily dose (DDD), and individual cephalosporins).

Results

Within the cohort, we identified 704 patients with hemorrhagic events and 2816 matched controls. Use of hypoprothrombinemia-inducing cephalosporins was associated with increased risk of hemorrhagic events (aOR, 1.71; 95% CI, 1.42–2.06), which increased with higher cumulative doses (<3 DDDs, aOR 1.62; 3–5 DDDs, aOR 1.78; and >5 DDDs, aOR 1.89). The aOR for individual cephalosporin was 2.88 (95% CI, 2.08–4.00), 1.35 (1.09–1.67) and 4.57 (2.63–7.95) for cefmetazole, flomoxef, and cefoperazone, respectively. Other risk factors included use of anticoagulants (aOR 2.08 [95% CI, 1.64–2.63]), liver failure (aOR 1.69 [1.30–2.18]), poor nutritional status (aOR 1.41 [1.15–1.73]), and history of hemorrhagic events (aOR 2.57 [1.94–3.41]) 6 months prior to the index date.

Conclusions

Use of hypoprothrombinemia-inducing cephalosporins increases risk of hemorrhagic events. Close watch for hemorrhagic events is recommended when prescribing these cephalosporins, especially in patients who are at higher risk.

Oral anticoagulant therapy: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

The objective of this article is to summarize the published literature concerning the pharmacokinetics and pharmacodynamics of oral anticoagulant drugs that are currently available for clinical use and other aspects related to their management.

METHODS

We carried out a standard review of published articles focusing on the laboratory and clinical characteristics of the vitamin K antagonists; the direct thrombin inhibitor, dabigatran etexilate; and the direct factor Xa inhibitor, rivaroxaban

RESULTS

The antithrombotic effect of each oral anticoagulant drug, the interactions, and the monitoring of anticoagulation intensity are described in detail and discussed without providing specific recommendations. Moreover, we describe and discuss the clinical applications and optimal dosages of oral anticoagulant therapies, practical issues related to their initiation and monitoring, adverse events such as bleeding and other potential side effects, and available strategies for reversal.

CONCLUSIONS

There is a large amount of evidence on laboratory and clinical characteristics of vitamin K antagonists. A growing body of evidence is becoming available on the first new oral anticoagulant drugs available for clinical use, dabigatran and rivaroxaban.

Elevated international normalized ratio values associated with concomitant use of warfarin and ceftriaxone

PURPOSE

The case of a patient receiving long-term warfarin therapy who experienced elevated International Normalized Ratio (INR) values on two occasions after injections of ceftriaxone is reported.

SUMMARY

An elderly woman (age, 67 years) with multiple comorbidities who had been receiving warfarin therapy for about 8 years was given an intramuscular injection of ceftriaxone 1 g for the treatment of a urinary tract infection. Four days later, her INR (which had recently ranged from 1.9 to 3.0 at a weekly warfarin dosage of 52.5-54.5 mg) was 10.74. One scheduled warfarin dose was withheld and 5 mg of phytonadione administered; one day later, the INR was 3.4 (goal, 2.5-3.5). INR values remained stable for several weeks until the patient again received a 1-g ceftriaxone injection for an infection (she was also prescribed oral cefuroxime and phenazopyridine); four days later, the INR was 16.99. Again, the scheduled warfarin dose was withheld and 5 mg of phytonadione administered. One day later, the INR had declined to 4.6 but remained above the target range; therefore, warfarin was withheld for a second day, after which the patient received 7.5 mg of warfarin sodium daily for two days, resulting in an INR decrease to 2.1. The patient continued to receive 7.5 mg of warfarin sodium daily, and at one-week follow-up the INR value (2.5) was within the therapeutic range.

CONCLUSION

A 67-year-old American Indian woman with previously stable INR values during long-term warfarin therapy after mitral valve replacement surgery had INR elevations on two occasions after receiving ceftriaxone for urinary tract infections.

Diagnostic accuracy of α-fetoprotein and des-γ-carboxy prothrombin in screening for hepatocellular carcinoma in liver transplant candidates

AIM

  Although hepatocellular carcinoma (HCC)-specific serum tumor markers, α-fetoprotein (AFP) and des-γ-carboxy prothrombin (DCP), are used in the screening for HCC, their utility in pre-transplantation evaluation is not well established. This study aimed to evaluate the accuracy of AFP and DCP measurement for the diagnosis of HCC in liver transplant candidates.

METHODS

  A total of 315 consecutive adult patients (174 men and 141 women, mean age 52 years), who were to receive liver transplantation for end-stage liver diseases, were enrolled. The pre-transplant levels of AFP and DCP were compared with the histopathology of explanted liver.

RESULTS

  Hepatocellular carcinoma was present in the explanted liver of 106 recipients (median number of nodules 2, mean diameter 2.5 cm). The area under receiver operating characteristic curve for the diagnosis of HCC was 0.83 (95% confidence interval, 0.78-0.88) for AFP and 0.47 (0.41-0.54) for DCP. With the cut-off value of 100 mAU/mL, 20/106 (18.9%) patients with HCC and 54/194 (27.8%) patients without HCC were positive for DCP. DCP positivity was associated with vascular invasion, tumor differentiation and size among patients with HCC, which was associated with albumin level among patients without HCC. Vitamin K was administered prior to transplantation to 20 patients who were positive for DCP (two with and 18 without HCC), resulting in a decrease in DCP levels in 19 of them.

CONCLUSIONS

  Serum DCP levels may be raised in end-stage liver disease patients without HCC, and cannot be used as a reliable marker for HCC among liver transplant candidates.

Pharmacology and management of the vitamin K antagonists: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition)

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines (8th Edition). It describes the antithrombotic effect of the VKAs, the monitoring of anticoagulation intensity, and the clinical applications of VKA therapy and provides specific management recommendations. Grade 1 recommendations are strong and indicate that the benefits do or do not outweigh the risks, burdens, and costs. Grade 2 recommendations suggest that the individual patient's values may lead to different choices. (For a full understanding of the grading, see the "Grades of Recommendation" chapter by Guyatt et al, CHEST 2008; 133:123S-131S.) Among the key recommendations in this article are the following: for dosing of VKAs, we recommend the initiation of oral anticoagulation therapy, with doses between 5 mg and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 1B); we suggest against pharmacogenetic-based dosing until randomized data indicate that it is beneficial (Grade 2C); and in elderly and other patient subgroups who are debilitated or malnourished, we recommend a starting dose of < or = 5 mg (Grade 1C). The article also includes several specific recommendations for the management of patients with nontherapeutic INRs, with INRs above the therapeutic range, and with bleeding whether the INR is therapeutic or elevated. For the use of vitamin K to reverse a mildly elevated INR, we recommend oral rather than subcutaneous administration (Grade 1A). For patients with life-threatening bleeding or intracranial hemorrhage, we recommend the use of prothrombin complex concentrates or recombinant factor VIIa to immediately reverse the INR (Grade 1C). For most patients who have a lupus inhibitor, we recommend a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 1A]. We recommend that physicians who manage oral anticoagulation therapy do so in a systematic and coordinated fashion, incorporating patient education, systematic INR testing, tracking, follow-up, and good patient communication of results and dose adjustments [Grade 1B]. In patients who are suitably selected and trained, patient self-testing or patient self-management of dosing are effective alternative treatment models that result in improved quality of anticoagulation management, with greater time in the therapeutic range and fewer adverse events. Patient self-monitoring or self-management, however, is a choice made by patients and physicians that depends on many factors. We suggest that such therapeutic management be implemented where suitable (Grade 2B).

The pharmacology and management of the vitamin K antagonists: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy

This article concerning the pharmacokinetics and pharmacodynamics of vitamin K antagonists (VKAs) is part of the Seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The article describes the antithrombotic effect of VKAs, the monitoring of anticoagulation intensity, the clinical applications of VKA therapy, and the optimal therapeutic range of VKAs, and provides specific management recommendations. Grade 1 recommendations are strong, and indicate that the benefits do, or do not, outweigh the risks, burdens, and costs. Grade 2 suggests that individual patient's values may lead to different choices (for a full understanding of the grading see Guyatt et al, CHEST 2004; 126:179S-187S). Among the key recommendations in this article are the following: for dosing of VKAs, we suggest the initiation of oral anticoagulation therapy with doses between 5 and 10 mg for the first 1 or 2 days for most individuals, with subsequent dosing based on the international normalized ratio (INR) response (Grade 2B). In the elderly and in other patient subgroups with an elevated bleeding risk, we suggest a starting dose at < or = 5 mg (Grade 2C). We recommend basing subsequent doses after the initial two or three doses on the results of INR monitoring (Grade 1C). The article also includes several specific recommendations for the management of patients with INRs above the therapeutic range and for patients requiring invasive procedures. For example, in patients with mild to moderately elevated INRs without major bleeding, we suggest that when vitamin K is to be given it be administered orally rather than subcutaneously (Grade 1A). For the management of patients with a low risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before they undergo surgery (Grade 2C). For patients with a high risk of thromboembolism, we suggest stopping warfarin therapy approximately 4 days before surgery, to allow the INR to return to normal, and beginning therapy with full-dose unfractionated heparin or full-dose low-molecular-weight heparin as the INR falls (Grade 2C). In patients undergoing dental procedures, we suggest the use of tranexamic acid mouthwash (Grade 2B) or epsilon amino caproic acid mouthwash without interrupting anticoagulant therapy (Grade 2B) if there is a concern for local bleeding. For most patients who have a lupus inhibitor, we suggest a therapeutic target INR of 2.5 (range, 2.0 to 3.0) [Grade 2B]. In patients with recurrent thromboembolic events with a therapeutic INR or other additional risk factors, we suggest a target INR of 3.0 (range, 2.5 to 3.5) [Grade 2C]. As models of anticoagulation monitoring and management, we recommend that clinicians incorporate patient education, systematic INR testing, tracking, and follow-up, and good communication with patients concerning results and dosing decisions (Grade 1C+).

Vitamin K deficiency in severely disabled children

Vitamin K status was examined in 21 severely disabled children in our hospital from September 2001 to August 2002, and 9 children were found to have a vitamin K deficiency. The 21 patients were divided into two groups: group A, 9 patients with vitamin K deficiency, and group B, 12 patients without vitamin K deficiency. The laboratory data and background factors in the two groups were compared statistically. In group A, all patients received enteral nutrition and anticonvulsants. The protein induced by vitamin K absence-II values were elevated in eight patients. Seven exhibited a bleeding tendency. Six developed vitamin K deficiency in association with infection and four were treated with antibiotics. All showed a good response to the administration of vitamin K. The patients in group A had factors such as use of antibiotics, infection, and elemental nutrition at significantly higher rates than those in group B. Data indicating nutrition factors such as body weight, caloric intake, total protein level, and hemoglobin level were not significantly different between the two groups. Severely disabled children suffer from deficiencies of various nutritional elements. However, vitamin K deficiency in severely disabled children has not been fully investigated. Infection, use of antibiotics, and elemental nutrition are risk factors for vitamin K deficiency in severely disabled children. In severely disabled children, there might be marginal vitamin K intake via enteral nutrition, so more vitamin K supplementation is necessary, especially with infection and use of antibiotics.

Cefotetan-induced haemolytic anaemia. A review of 85 cases

OBJECTIVE

Reports of cefotetan-associated haemolytic anaemia have prompted a US Food and Drug Administration (FDA) review of the overall number, severity, and causality of such cases.

METHODS/RESULTS

A search of the FDA's Spontaneous Reporting System and the World Health Organization's database revealed 85 cases of haemolytic anaemia since the approval of cefotetan in 1985, 15 of them fatal. Moderate to severe haemolysis was reflected in a mean fall in haemoglobin levels by 6.65 mg/dl (n = 20) and a mean final haemoglobin concentration of 5.2 mg/dl (n = 52). Transfusion of packed red blood cells was required in 47 patients (55.3%). New onset renal dysfunction was noted in 7 patients (8.2%). The direct antiglobulin test was positive in 50 patients (59%), and serological studies revealed antibodies to cefotetan in 30 patients (35%).

CONCLUSION

These data suggest that treatment with cefotetan may induce severe autoimmune haemolytic anaemia.

[Coagulation abnormalities after total hip prosthesis (THP), a rare cause: antibiotic prophylaxis]

A 87-year-old patient developed coagulation abnormality following hip surgery related to the prophylactic use of cefamandole. Cefamandole as others cephalosporins with a methyl-tetrazol-thiol lateral chain interferes with the vitamin K regeneration cycle as do oral anticoagulants. Therefore, the use of others antibiotics or systematic vitamin K1 supplementation or single dose of cefamandole is recommended for patients with renal failure or with malnutrition. Vitamin K1 supplementation is a simple method resulting in complete resolution of the coagulation disorder.

Hypoprothrombinemia associated with cefmetazole

OBJECTIVE

To report a case of hypoprothrombinemia associated with the use of cefmetazole sodium, define patients at risk for this adverse effect, and identify options to prevent this problem.

CASE SUMMARY

A malnourished patient with endstage renal disease received cefmetazole following a below-the-knee amputation of the right leg. Three days later, a prothrombin time (PT) and an international normalized ratio (INR) were obtained and were markedly elevated from baseline; however, the patient had no clinical symptoms of bleeding. Cefmetazole was discontinued. Vitamin K and fresh frozen plasma were administered. The PT and INR normalized within 24 hours and remained normal throughout the remainder of hospitalization.

DISCUSSION

The incidence of hypoprothrombinemia associated with cefmetazole reported in the literature is conflicting and not consistent. There are three proposed mechanisms of cephalosporin-associated hypoprothrombinemia, two of which involve the N-methylthiotetrazole (NMTT) chain. The most plausible mechanism is NMTT inhibition of vitamin K epoxide reductase in the liver. Patients at an increased risk for this adverse event include those with low vitamin K stores, specifically patients who are malnourished, with low albumin concentrations and poor food intake. The elderly and patients with liver or renal dysfunction are examples of populations at risk.

CONCLUSIONS

Hypoprothrombinemia may occur with cephalosporins and is especially problematic with those containing an NMTT side chain. Clinicians need to identify patients at risk for developing antibiotic-associated hypoprothrombinemia, monitor them closely, and give vitamin K as prophylaxis accordingly.

Nutritional sources of vitamin K

OBJECTIVE

To review the function of vitamin K in clotting and methods of its analysis, to present results of previous studies on the role of dietary vitamin K in humans and animals, and to reanalyze these data in light of current methods.

DESIGN

A review of assumptions stated in the literature is presented, including the incorrect theory that a diet-induced deficiency of vitamin K is nonexistent and the unsubstantiated hypothesis that antibiotics can cause vitamin K deficiency by destroying intestinal bacteria.

CONCLUSION

The insistent belief that intestinal bacteria are an important source of vitamin K has led to erroneous conclusions about the sources of vitamin K for human nutrition. In the future, the importance of various sources of vitamin K, their pathways of absorption, and their susceptibility to administration of antibiotics should be evaluated without recourse to current assumptions.

Vitamin K--its essential role in craniofacial development. A review of the literature regarding vitamin K and craniofacial development

The normal vitamin K status of the human embryo appears to be close to deficiency. Maternal dietary deficiency or use of a number of therapeutic drugs during pregnancy, may result in frank vitamin K deficiency in the embryo. First trimester deficiency results in maxillonasal hypoplasia in the neonate with subsequent facial and orthodontic implications. A rat model of the vitamin K deficiency embryopathy shows that the facial dysmorphology is preceded by uncontrolled calcification in the normally uncalcified nasal septal cartilage, and decreased longitudinal growth of the cartilage, resulting in maxillonasal hypoplasia. The developing septal cartilage is normally rich in the vitamin K-dependent protein matrix gla protein (MGP). It is proposed that functional MGP is necessary to maintain growing cartilage in a non-calcified state. Developing teeth contain both MGP and a second vitamin K-dependent protein, bone gla protein (BGP). It has been postulated that these proteins have a functional role in tooth mineralization. As yet this function has not been established and abnormalities in tooth formation have not been observed under conditions where BGP and MGP should be formed in a non-functional form.

Retropharyngeal and bowel hematomas in an anticoagulated patient

As the indications for oral anticoagulation therapy increase, the number of patients being treated with anticoagulants and at risk for complications also will rise. Major bleeding episodes have been reported to occur in approximately 2-4% of patients being treated with oral anticoagulants. The case report of a patient with concurrent spontaneous retropharyngeal and small-bowel hematomas from overanticoagulation with warfarin is presented. The authors review the subtle presentation of retropharyngeal hematomas, common medications that may enhance warfarin anticoagulation, and therapy of potentially life-threatening hematomas. Airway management and possible surgical therapies to treat the complications of hematomas are discussed. Depending upon the indication for the initial anticoagulation, interim anticoagulation with heparin may be indicated.

Cephalosporin-Associated Hypoprothrombinemia: Case and Review of the Literature

Objective:

To present a case of cefotetan-associated hypoprothrombinemia and to review the literature concerning cephalosporin-associated hypoprothrombinemia.

Data Sources:

Information was collected by conducting a MEDLINE search for cases, clinical trials, reviews, and other articles pertaining to cephalosporin use and the development of hypoprothrombinemia.

Study Selection:

Studies, cases, and letters were selected if they addressed the development of hypoprothrombinemia in cephalosporin-treated patients.

Data Synthesis:

A case of hypoprothrombinemia is described in an 82-year-old woman who received cefotetan for the treatment of a urinary tract infection. A review of the literature revealed more than 50 reported cases and multiple clinical studies evaluating this adverse effect. The postulated mechanism behind this occurrence is the inhibition of the synthesis of vitamin K-dependent clotting factors by the N-methyl-thiotetrazole (NMTT) moiety found in certain cephalosporin side chains. Risk factors associated with the development of this adverse effect include advanced age, renal and hepatic impairment, recent surgical procedures, malnutrition, and the use of H2-antagonists.

Conclusions:

Cephalosporins containing the NMTT side chain are associated with the development of hypoprothrombinemia and possibly bleeding, especially in high-risk patients.

Vitamin K metabolism and nutriture

Vitamin K functions as a co-factor for the post-translational carboxylation of specific glutamate residues to gamma-carboxyglutamate (Gla) residues in several blood coagulation factors (II, VII, IX and X) and coagulation inhibitors (proteins C and S) in the liver; as well as a variety of extrahepatic proteins such as the bone protein osteocalcin. This review outlines some recent advances in our understanding of the metabolism of vitamin K and its role in human nutriture. The introduction of new methodologies to measure the low endogenous tissue concentrations of K vitamins and circulating plasma levels of des-gamma-carboxyprothrombin (PIVKA-II) have provided correspondingly more refined indices for the assessment of human vitamin K status. The assays for vitamin K have also been used to study the sources, intestinal absorption, plasma transport, storage and transplacental transfer of K vitamins and the importance of phylloquinone (vitamin K1) versus menaquinones (vitamins K2) to human needs. The ability to biochemically monitor subclinical vitamin K deficiency has reaffirmed the precarious vitamin K status of the newborn and led to an increased appreciation of the risk factors leading to haemorrhagic disease of the newborn and how this may be prevented. Biochemical studies are leading to an increased knowledge of the mode of action of traditional coumarin anticoagulants and how some unrelated compounds (e.g. antibiotics) may also antagonize vitamin K and cause bleeding. There is also an awareness of the possible deleterious effects of vitamin K antagonism or deficiency on non-hepatic Gla-proteins which may play some subtle role in calcium homeostasis.

Coagulation abnormalities and ivermectin

Prothrombin ratios were measured 13-16 days after treatment in 148 subjects from Sierra Leone taking part in a double-blind placebo-controlled trial of ivermectin. Prolonged prothrombin ratios were observed more frequently in the ivermectin group, although this difference was not significant and no patients suffered bleeding complications. Further investigation of these patients failed to reveal any abnormality of liver function, although factor VII and II levels were reduced in most affected individuals, suggesting interference with vitamin K metabolism. Ivermectin has a minimal effect on coagulation and concern about mass treatment for this reason appears to be unjustified.

Safety profile of cefodizime

The results of animal toxicology studies with cefodizime (CDZ) showed no reason for concern with respect to drug safety. Renal tolerance of CDZ proved to be better than that observed with other cephalosporins; furthermore, CDZ had no adverse effects on spermatogenesis, fertility or embryonic development. A total of 6,299 patients were treated with CDZ in clinical trials worldwide, while 1,225 patients received cefuroxime, cefotaxime, cefmenoxime or cefizoxime in comparative studies. The incidence of mortality in the repeated dose trials was 1.6% (CDZ) and 1.75% (comparators); the incidence of adverse drug reactions (ADRs) was 3.06% and 3.64%, respectively. ADRs were mostly of gastrointestinal or allergic nature. In no case was a causative relationship established between CDZ and the death of a patient. Any influence of CDZ on platelet count and function, plasma coagulation and vitamin K metabolism has been excluded. Cefodizime has a favorable risk/benefit ratio.

Effect of flomoxef on blood coagulation and alcohol metabolism

The effect of flomoxef, a newly developed oxacephem antibiotic with an N-hydroxyethyltetrazolethiol (HTT) side chain, on blood coagulation and alcohol metabolism was compared with that of a series of cephalosporin antibiotics with N-methyltetrazolethiol (NMTT), thiadiazolethiol (TDT) or methylthiadiazolethiol (MTDT) side chains in position 3' of the cephalosporin nucleus known to cause hypoprothrombinemia and bleeding in patients who are malnourished, debilitated and/or of high age. A disulfiram-like effect caused by inhibition of aldehyde dehydrogenase was observed for NMTT-containing antibiotics. Studies were carried out on healthy volunteers and on rats. Eight-day treatment with 2 g flomoxef i.v. once or twice daily in five and six healthy male volunteers, respectively, did not cause any significant changes in prothrombin time (PT), coagulation factors II, VII, IX or X, in hepaplastin values or fibrinogen levels, activated partial thromboplastin time (APTT), platelet counts, bleeding time, or collagen- and ADP-induced platelet aggregation. Inhibition of vitamin K epoxide reductase was observed in rats treated with flomoxef, yet to a much lesser extent than observed for cephalosporins with NMTT, TDT or MTDT side chains. This defect was quickly normalized by vitamin K injection. There were no differences between oxacephem (1-O) and cephem (1-S) compounds with respect to effects on blood clotting and platelet aggregation. Flomoxef and its side chain HTT showed no influence on alcohol metbolism.

Pharmacokinetics and hemostasis following administration of a new, injectable oxacephem (6315-S, flomoxef) in volunteers and in patients with renal insufficiency

Flomoxef is a new oxacephem of broad antibacterial activity. The compound is mainly excreted through the kidneys. Two dose finding studies in patients with various degrees of renal insufficiency revealed that the dosage of flomoxef has to be reduced exactly according to the renal function. Although the N-methylthiotetrazole group has been replaced by a hydroxyethyl group, an inhibitory effect of flomoxef on vitamin K metabolism persisted. This effect was, however, less pronounced than with latamoxef. Only patients with low vitamin K stores are endangered. For those in whom low vitamin K stores are suspected repeated controls of prothrombin time are advised during the treatment. In contrast to latamoxef the platelet system was not affected by flomoxef. With the exception of loose stools in some patients no other clinical side effects during treatment were observed.

Antibiotic treatment and associated prolonged prothrombin time

The incidence and type of pathology causing a prolonged prothrombin time and clinical bleeding episodes were assessed in a multicentre study of 1109 patients receiving cefotetan, a N-methyl-thiotetrazole (NMTT), or equivalent antibiotics. There was no significant difference in the incidence of a prolonged prothrombin time (9.9% with cefotetan, 8.0% with comparable antibiotics) of clinical bleeding episodes. However, prothrombin time increases of greater than 12 seconds were significantly (p = 0.002) greater with cefotetan (3.8%) than with comparators (0.8%). In both antibiotic groups increases in prothrombin time were more likely following surgery and in patients who were older, with a high platelet count, low albumin, or higher urea and creatinine concentrations. All antibiotic treatment can be associated with prolonged prothrombin times and new agents should always be assessed in a large multicentre study before the practical, clinical importance of haemostatic defects can be defined.

A fibroblast cell culture model to study vitamin K metabolism and the inhibition of vitamin K epoxide reductase by known and suspected antagonists

The metabolism and antagonism of vitamin K has been studied in cultured fibroblasts. Monolayers of 3T3 mouse fibroblasts (grown in the absence or presence of warfarin or other putative antagonists) were incubated for 24 h with [1',2'-3H2]phylloquinone (K1) or [1',2'-3H2]phylloquinone epoxide (K1O), the cells harvested and lipid extracts fractionated by high performance liquid chromatography. [3H]K1 was converted to [3H]K1O (about 20% of [3H] lipids) and to unidentified polar metabolites (30%). [3H]K1O was converted to [3H]K1 (3%) and to polar metabolites (50%). Cells grown with warfarin showed a marked increase in the [3H]K1O:K1 ratio and in the proportion of polar metabolites. The metabolic interconversion of K1 and K1O and inhibitory response to warfarin provide evidence for a fibroblast pathway analogous to the vitamin K-epoxide cycle in the liver. From the K1O:K1 ratios it was possible to grade the antagonism of vitamin K epoxide reductase activity by known and suspected inhibitors. Inhibitory ratios were seen for racemic warfarin down to 10(-8) M. S-warfarin was a more potent antagonist than the R-enantiomer. Consistently low K1O:K1 ratios were observed for N-methyl-thiotetrazole and antibiotics with (moxalactam) or without (cefotaxime) this side chain suggesting that none of these compounds are direct inhibitors of vitamin K epoxide reductase. Fibroblasts grown in cell culture provide a useful model to study the extrahepatic role of vitamin K and the mode of action of vitamin K antagonists.

Vitamin K (menaquinone-4) metabolism in liver disease

We measured menaquinone-4 (MK-4) and MK-4 epoxide concentrations in plasma and liver tissue after intravenous injection of 200 micrograms/kg MK-4 in 42 patients who underwent hepatectomy. They were classified into normal (N; n = 10), chronic hepatitis (CH; n = 12), and liver cirrhosis (LC; n = 20) groups, on the basis of the diagnosis given by the pathologist after examining resected liver specimens. The plasma MK-4 epoxide concentration reached maximum level (Cmax) 60 min after MK-4 injection. The Cmax in groups LC and CH were 85.9 and 126.3 nmol/l, respectively, which is significantly reduced compared with that of group N (184.4 nmol/l) (p less than 0.01 and p less than 0.05, respectively). The MK-4 concentrations in liver tissues of 24 patients 60 min after MK-4 injection were 2.77 in group N, 3.79 in group CH, and 3.83 nmol/g in group LC, and the MK-4 epoxide concentrations were 4.01, 3.09, and 2.62 nmol/g in the respective groups. Consequently, the ratio of MK-4 epoxide to total MK-4 (MK-4 + MK-4 epoxide) in groups CH and LC was significantly lower than in group N (p less than 0.01). It is concluded that the Cmax of MK-4 epoxide after MK-4 injection may serve as an indicator of liver function and that the low ratio of MK-4 epoxide to total MK-4 in the liver shows impairment in vitamin K metabolism.

Lack of effect of cefixime on the metabolism of vitamin K1

It seems that cephalosporins bearing a N-methyl-thio-tetrazole or a methyl-thiadiazole moiety in their molecule can cause hypoprothombinemia in patients via inhibition of the metabolism of vitamin K1 if they are in addition in a vitamin K1-deficient state. The authors therefore studied the effects of two different oral doses (200 and 400 mg) of the cephalosporin cefixime on the metabolism of vitamin K1 in healthy volunteers, because the accumulation of vitamin K1-2,3-epoxide in plasma is a sensitive marker of coumarin-like activity of drugs. The results indicate that the development of hypoprothrombinemia due to an impairment of the metabolism of vitamin K1 by cefixime seems unlikely because only trace amounts of vitamin K1-2,3-epoxide could be determined in the plasma of the subjects investigated.

Antimicrobial therapy for pediatric patients

New antimicrobial agents are being introduced for clinical use at an increasingly rapid rate. This has required physicians continually to review relevant data and determine unique properties that might guide selection among any new antibiotics as well as older ones. Efficacy, potential toxicity, and comparative cost (in that order) generally guide selection. The present comprehensive review examines currently available antibiotics along with some under investigation, emphasizing these three basic areas of consideration.