Plasma disposition of vitamin K1 in relation to anticoagulant poisoning

Short-term treatment with cholestyramine increases long-acting anticoagulant rodenticide clearance from rabbits without affecting plasma vitamin K1 levels nor blood coagulation

Administration of high dose vitamin K1 (VK1) overcomes coagulopathy and bleeding elicited by acute poisoning with long-acting anti-coagulant rodenticides (LAARs). However, long-term (months) treatment is required due to long LAAR biological half-lives that may lead to poor compliance and recurrent coagulopathy. The half-lives of LAARs are extended by slow metabolism, and similar to warfarin, are thought to undergo enterohepatic recirculation. We now show that treatment with the bile acid sequestrant cholestyramine (CSA) administered concomitantly with VK1 decreases plasma LAAR levels and increases LAAR fecal excretion. Daily CSA treatment for 14 days did not reduce plasma VK1 levels, nor increase prothrombin time. Collectively, these data show that CSA accelerates LAAR clearance from rabbits without adverse effects on VK1 anti-coagulation, and could provide an additional therapeutic option for treatment of LAAR poisoning.

Warfarin Overdose in an Adolescent Not Dependent on Anticoagulation: Reversal Strategy and Kinetics

INTRODUCTION

Warfarin induces coagulopathy. Guidelines protocolize reversal of supratherapeutic international normalized ratio (INR) in patients dependent on anticoagulation, but practices vary for reversing warfarin-induced coagulopathy after overdose in non-warfarin-dependent patients.

CASE REPORT

This is the report of a 15-year-old female who ingested her father's warfarin (100-200 mg) in a self-harm attempt. At hour 24 post-ingestion, her INR was 2.00 and she was admitted for monitoring. Reversal of coagulopathy was initially deferred pending the INR trend. The INR was 5.10 at hour 60 and 2.5 mg oral vitamin K1 (VK1) was given. At hour 85, the INR peaked at 6.67 and she received a second oral dose of 2.5 mg VK1. On day 8, she was medically cleared with an INR of 1.31. On day 11, she developed lower abdominal pain and diarrhea. Imaging revealed a duodenal hematoma, and symptoms improved spontaneously. She was again medically cleared 13 days post-ingestion. Her serum warfarin concentration peaked at 19 mcg/mL at hour 46. Serial warfarin concentrations were obtained, demonstrating first-order elimination kinetics and a 30-hour half-life.

CONCLUSION

A restrictive approach to coagulopathy reversal in non-warfarin-dependent patients with intentional warfarin overdose may result in worsening coagulopathy, bleeding, and lengthy hospital stay. Given the risk for significant, prolonged coagulopathy, these patients should be treated early with VK1, with subsequent serial INR monitoring and probable additional VK1 dosing. Delayed peak warfarin concentrations support consideration of gastrointestinal decontamination in late presenters.

Unintentional ingestion of a high dose of acenocoumarol in a young child

Acute intoxication with a vitamin K antagonist may cause serious coagulopathy. We report the accidental ingestion of a high dose of acenocoumarol in a young child. Two intravenous administrations of 5 mg of vitamin K, in combination with fast and repeated administration of activated charcoal and sodium sulfate, were sufficient to prevent coagulopathy and related symptoms, despite a confirmed elevated blood acenocoumarol concentration (260 µg/L).

Toxic time bombs: Frequent detection of anticoagulant rodenticides in urban reptiles at multiple trophic levels

Anticoagulant rodenticides (ARs) are regularly used around the world to control pest mammals. Second-generation anticoagulant rodenticides (SGARs) are highly persistent in biological tissue and have a high potential for bioaccumulation and biomagnification. Consequently, exposure and poisoning of non-target organisms has been frequently documented, especially in countries with unregulated AR sales and usage. Most of this research has focussed on rodent-predators, usually raptors and predatory mammals, although exposure has also been documented in invertebrates and insectivorous fauna. Few studies have explored non-target exposure in reptiles, despite species sharing similar trophic positions and dietary preferences to other exposed fauna. We tested three abundant urban reptile species in Perth, Western Australia that differ in diet and trophic tiers for multiple AR exposure, the dugite Pseudonaja affinis (rodent-predator), the bobtail Tiliqua rugosa (omnivore) and the tiger snake Notechis scutatus occidentalis (frog-predator). We found frequent exposure in all three species (91% in dugites, 60% in bobtails and 45% in tiger snakes). Mean combined liver concentrations of ARs of exposed individuals were 0.178 mg/kg in dugites, 0.040 mg/kg in bobtails and 0.009 mg/kg in tiger snakes. High exposure frequency and liver concentration was expected for the dugite. Exposure in the other species is more surprising and implies widespread AR contamination of the food web. We discuss the likelihood of global AR exposure of urban reptiles, highlight the potential for reptiles to be important vectors of ARs in the food web and highlight implications for humans consuming wild reptiles.

Anticoagulant rodenticide exposure in an Australian predatory bird increases with proximity to developed habitat

Anticoagulant rodenticides (ARs) are commonly used worldwide to control commensal rodents. Second generation anticoagulant rodenticides (SGARs) are highly persistent and have the potential to cause secondary poisoning in wildlife. To date no comprehensive assessment has been conducted on AR residues in Australian wildlife. My aim was to measure AR exposure in a common widespread owl species, the Southern Boobook (Ninox boobook) using boobooks found dead or moribund in order to assess the spatial distribution of this potential threat. A high percentage of boobooks were exposed (72.6%) and many showed potentially dangerous levels of AR residue (>0.1 mg/kg) in liver tissue (50.7%). Multiple rodenticides were detected in the livers of 38.4% of boobooks tested. Total liver concentration of ARs correlated positively with the proportions of developed areas around points where dead boobooks were recovered and negatively with proportions of agricultural and native land covers. Total AR concentration in livers correlated more closely with land use type at the spatial scale of a boobook's home range than at smaller or larger spatial scales. Two rodenticides not used by the public (difethialone and flocoumafen) were detected in boobooks indicating that professional use of ARs contributed to secondary exposure. Multiple ARs were also detected in recent fledglings, indicating probable exposure prior to fledging. Taken together, these results suggest that AR exposure poses a serious threat to native predators in Australia, particularly in species using urban and peri-urban areas and species with large home ranges.

Anticoagulant rodenticide use, non-target impacts and regulation: A case study from Australia

The impacts of anticoagulant rodenticides (ARs) on non-target wildlife have been well documented in Europe and North America. While these studies are informative, patterns of non-target poisoning of wildlife elsewhere in the world may differ substantially from patterns occurring in Australia and other countries outside of cool temperate regions due to differences in the types of ARs used, patterns of use, legislation governing sales, and potential pathways of secondary exposure. Most of these differences suggest that the extent and severity of AR poisoning in wildlife may be greater in Australia than elsewhere in the world. While many anecdotal accounts of rodenticide toxicity were found - especially in conjunction with government control efforts and island eradications - no published studies have directly tested rodenticide exposure in non-target Australian wildlife in a comprehensive manner. The effects of private and agricultural use of rodenticides on wildlife have not been adequately assessed. Synthesis of reviewed literature suggests that anticoagulant rodenticides may pose previously unrecognised threats to wildlife and indigenous people in Australia and other nations with diverse and abundant reptile faunas relative to countries with cooler climates where most rodenticide ecotoxicology studies have been conducted. To address the identified knowledge gaps we suggest additional research into the role of reptiles as potential AR vectors, potential novel routes of human exposure, and comprehensive monitoring of rodenticide exposure in Australian wildlife, especially threatened and endangered omnivores and carnivores. Additionally, we recommend regulatory action to harmonise Australian management of ARs with existing and developing global norms.

Self-Nanoemulsifying Lyophilized Tablets for Flash Oral Transmucosal Delivery of Vitamin K: Development and Clinical Evaluation

Owing to limited solubility, vitamin K undergoes low bioavailability with large inter-individual variability after oral administration. This article aimed to prepare self-nanoemulsifying lyophilized tablets (SNELTs) for the flash oral transmucosal delivery of vitamin K. Twenty-one formulae of vitamin K self-nanoemulsifying drug delivery systems (SNEDDS) were prepared using different concentrations of vitamin K, Labrasol, and Transcutol according to mixture design. The SNEDDS was loaded on porous carriers and formulated as lyophilized tablets. The release profile and the pharmacokinetic parameters of vitamin K SNELTs were evaluated in comparison with commercial tablets and ampoules on human volunteers. Results revealed that the optimized SNEDDS showed the smallest and most stable nanoemulsion globules. SNELTs were prepared successfully and showed substantial superiority drug release compared with the commercial tablets. Interestingly, SNELTs enhanced both rate and extent of vitamin K absorption as well as relative bioavailability (169.67%) in healthy subjects compared with the commercial tablets. SNELTs revealed promising no significant difference in the area under the curve compared with the commercial intramuscular injection. SNELTs enhanced dissolution and bioavailability that expected to have the strong impact on the efficiency of vitamin K in the prophylaxis and treatment of bleeding disorders in patients with hepatic dysfunction.

Antidote Use in the Critically Ill Poisoned Patient

The proper use of antidotes in the intensive care setting when combined with appropriate general supportive care may reduce the morbidity and mortality associated with severe poisonings. The more commonly used antidotes that may be encountered in the intensive care unit ( N-acetylcysteine, ethanol, fomepizole, physostigmine, naloxone, flumazenil, sodium bicarbonate, octreotide, pyridoxine, cyanide antidote kit, pralidoxime, atropine, digoxin immune Fab, glucagon, calcium gluconate and chloride, deferoxamine, phytonadione, botulism antitoxin, methylene blue, and Crotaline snake antivenom) are reviewed. Proper indications for their use and knowledge of the possible adverse effects accompanying antidotal therapy will allow the physician to appropriately manage the severely poisoned patient.

How I treat poisoning with vitamin K antagonists

Severe deficiency of vitamin K-dependent proteins in patients not maintained on vitamin K antagonists is most commonly associated with poisoning by or surreptitious ingestion of warfarin, warfarin-like anticoagulants, or potent rodenticides ("superwarfarins"), such as brodifacoum. Serious bleeding manifestations are common. Superwarfarins are 2 orders of magnitude more potent than warfarin and have a half-life measured in weeks. These rodenticides are readily available household environmental hazards and are sometimes consumed accidentally or as manifestations of psychiatric disease. Immediate diagnosis and proper therapy is critically important to minimize morbidity and mortality because this condition, affecting thousands of patients annually, is reversible. Treatment with large doses of oral vitamin K1, often over months to years, to maintain a near-normal prothrombin time can reverse the coagulopathy associated with superwarfarins. Although these patients initially present to various medical specialties, the hematologist is often consulted to offer the definitive diagnosis and proper therapy.

Effects of vitamin K3 and K5 on proliferation, cytokine production, and regulatory T cell-frequency in human peripheral-blood mononuclear cells

AIMS

The effects of vitamin K (VK) derivatives VK3 and VK5 on human immune cells have not been extensively investigated. We examined the effects of VK3 and VK5 on proliferation, apoptosis, cytokine production, and CD4+CD25+Foxp3+ regulatory T (Treg) cell-frequency in human peripheral blood mononuclear cells (PBMCs) activated by T cell mitogen in vitro.

MAIN METHODS

Anti-proliferative effects of VK3 and VK5 on T-cell mitogen activated PBMCs were assessed by WST assay procedures. Apoptotic cells were determined as Annexin V positive/propidium iodide (PI) negative cells. Cytokine concentrations in the supernatant of the culture medium were measured with bead-array procedures followed by analysis with flow cytometry. The CD4+CD25+Foxp3+Treg cells in mitogen-activated PBMCs were stained with fluorescence-labeled specific antibodies followed by flow cytometry.

KEY FINDINGS

VK3 and VK5 suppressed the mitogen-activated proliferation of PBMCs significantly at 10-100μM (p<0.05). The data also suggest that VK3 and VK5 promote apoptosis in the mitogen-activated T cells. VK3 and VK5 significantly inhibited the production of tumor necrosis factor (TNF) α, interleukin (IL)-4, -6, and -10 from the activated PBMCs at 10-100μM (p<0.05). In contrast, VK3 and VK5 significantly increased Treg cell-frequency in the activated PBMCs at concentrations more than 10μM (p<0.001).

SIGNIFICANCE

Our data suggest that VK3 and VK5 attenuate T cell mediated immunity by inhibiting the proliferative response and inducing apoptosis in activated T cells.

Antiproliferative and apoptosis-inducing effects of lipophilic vitamins on human melanoma A375 cells in vitro

The effects of six lipophilic vitamins: tretinoin (ATRA), vitamin D(3) (VD(3)), VE, VK(1), VK(3), and VK(5) on cell proliferation and apoptosis in human A375 melanoma cells were investigated. VD(3), VK(3), and VK(5) were found to inhibit cell proliferation significantly at concentration ranges of 10-100 μmol/L (p<0.01), while the other vitamins did not show inhibitory effects at 100 μmol/L. VK(3) and VK(5) showed the strongest effects with IC(50) values of less than 10 μmol/L. Dacarbazine slightly inhibited the proliferation of A375 cells at a concentration range of 25-100 μmol/L, but the effects were not statistically significant. VK(3) and VK(5) increased annexin-V positive apoptotic cells, as well as activating caspase-3, in A375 cells. Our findings showed that VD(3), VK(3,) and VK(5) inhibited the growth of dacarbazine resistant human melanoma cells, while ATRA, VE, and VK(1) had little effect on the cell growth. The effects of VK(3) and VK(5) were observed at concentrations lower than 10 μmol/L, which are suggested to have resulted from apoptosis-induction in the melanoma cells.

A hetero-dimer model for concerted action of vitamin K carboxylase and vitamin K reductase in vitamin K cycle

Vitamin K carboxylase (VKC) is believed to convert vitamin K, in the vitamin K cycle, to an alkoxide-epoxide form which then reacts with CO(2) and glutamate to generate γ-carboxyglutamic acid (Gla). Subsequently, vitamin K epoxide reductase (VKOR) is thought to convert the alkoxide-epoxide to a hydroquinone form. By recycling vitamin K, the two integral-membrane proteins, VKC and VKOR, maintain vitamin K levels and sustain the blood coagulation cascade. Unfortunately, NMR or X-ray crystal structures of the two proteins have not been characterized. Thus, our understanding of the vitamin K cycle is only partial at the molecular level. In this study, based on prior biochemical experiments on VKC and VKOR, we propose a hetero-dimeric form of VKC and VKOR that may explain the efficient oxidation and reduction of vitamin K during the vitamin K cycle.

Korean patients with superwarfarin intoxication and their outcome

This observational study aimed at evaluating recent superwarfarin intoxication of Korean patients. Ten patients were diagnosed as or highly suspicious for superwarfarin intoxication. Case report forms described by attending hematologists of the patients were collected and analyzed. Bleeding symptoms were varied among the patients. Patients uniformly showed prolonged prothrombin time (PT) and activated thromboplastin time (aPTT) with decreased activity of vitamin K dependent coagulation factors. Positive serum brodifacoum test results in 4 of 5 requested patients contributed to confirmatory diagnosis. Psychiatric interview revealed an attempted ingestion in one patient. High dose vitamin K1 therapy promptly corrected prolonged PT and aPTT, but hasty discontinuation caused repeated bleeding diathesis in 6 patients. Route of intoxication was unknown or not definite among 8 of 10 patients. Three patients had a possibility of environmental exposure considering their occupations: there might be intoxication by transdermal absorption or inhalation. Therefore, high dose and prolonged use of vitamin K1 therapy is necessary for effective detoxification. Further detailed investigation on environmental exposure and efforts to improve availability of the blood level test in clinic are requested.

Bromadiolone toxicokinetics: diagnosis and treatment implications

INTRODUCTION

Ingestion of bromadiolone can lead to prolonged and life-threatening coagulopathy. Traditional treatment of bromadiolone intoxication relies on the coagulation profile. Currently, there is scanty information on bromadiolone elimination kinetics and half-life.

CASE REPORT

We report a case of bromadiolone poisoning in a 40-year old female who, by history, ingested four 42.5-gram bags of rat poison (0.005% bromadiolone), equivalent to 8.5 mg bromadiolone (0.17 mg/kg body weight), four days prior to admission. On admission, her prothrombin time was 92.0 seconds, international normalized ratio was 5.7, and activated partial thromboplastin time was 50.2 seconds with no bleeding on clinical examination. The first plasma bromadiolone level (5 days post-ingestion) was 92 ng/mL. Serial measurement of plasma bromadiolone levels confirmed the diagnosis and demonstrated that bromadiolone obeys the elimination kinetic of a two-compartment model with a rapid, fairly steep decline phase (half-life 3.5 days) followed by a slower termination phase (half-life 24 days). Plasma bromadiolone level of less than 10 ng/mL in our patient was associated with a consistently normal coagulation profile without vitamin K1 therapy.

CONCLUSIONS

There is a lack of information on the toxicodynamics and toxicokinetics of bromadiolone in humans; further studies are needed before the plasma bromadiolone level can serve as one of the logical and safe therapeutic endpoints for vitamin K1 therapy.

Appraisal of current vitamin K dosing algorithms for the reversal of over-anticoagulation with warfarin: the need for a more tailored dosing regimen

Warfarin is the most commonly prescribed oral anticoagulant in the UK for the treatment and prevention of thromboembolic disorders. Vitamin K administration is an effective way of reversing excessive anticoagulation. Over-anticoagulated patients present with a wide range of international normalized ratio (INR) values and may respond differently to a fixed dose of vitamin K. Current dosing algorithms for vitamin K administration in the non-urgent treatment of over-anticoagulation do not take this variability in response into account. Consequently, over a third of over-anticoagulated patients still remain outside their target INR 24 h after treatment. Such patients are therefore prone to either haemorrhage (if the patient is still over-anticoagulated) or thromboembolism (if the INR reversal is over-corrected). A number of factors such as patient age, body weight, co-morbidity, frailty, warfarin daily dose and CYP2C9 and VKORC1 polymorphism could affect response to vitamin K and thus the rate and extent of INR reversal. There is a need for a more individualized approach to the reversal of over-anticoagulation in asymptomatic or mildly haemorrhagic patients in order to improve the safety of warfarin therapy.

Successful reversal of anticoagulant effect of superwarfarin poisoning with recombinant activated factor VII

The use of second-generation anticoagulants termed "superwarfarins" as rodenticides, although widespread, is poorly controlled. Products containing superwarfarin have been marketed in over-the-counter rodenticides and can be easily purchased. Poor control potentiates the risk of accidental or intentional poisoning, but clinicians may underestimate the incidence of superwarfarin toxicity. Therefore, when cases of unexplained acquired coagulopathy and selective deficiency of vitamin K-dependent clotting factors occur in patients in the absence of liver disease or inhibitors, physicians should consider the possibility of superwarfarin poisoning as a cause. According to our own experience, recombinant activated factor VII (NovoSeven; Novo Nordisk, Bagsvaerd, Denmark) appears to be a safe and effective therapy for acute bleeding caused by superwarfarin poisoning. Due to the extended half-life of the second-generation rodenticides, follow-up therapy with oral vitamin K1 should be of long-term duration.

Anticoagulant Rodenticides

Anticoagulant pesticides are used widely in agricultural and urban rodent control. The emergence of warfarin-resistant strains of rats led to the introduction of a new group of anticoagulant rodenticides variously referred to as 'superwarfarins', 'single dose' or 'long-acting'. This group includes the second generation 4-hydroxycoumarins brodifacoum, bromadiolone, difenacoum, flocoumafen and the indanedione derivatives chlorophacinone and diphacinone. Most cases of anticoagulant rodenticide exposure involve young children and, as a consequence, the amounts ingested are almost invariably small. In contrast, intentional ingestion of large quantities of long-acting anticoagulant rodenticides may cause anticoagulation for several weeks or months. Occupational exposure has also been reported. Anticoagulant rodenticides inhibit vitamin K(1)-2,3 epoxide reductase and thus the synthesis of vitamin K and subsequently clotting factors II, VII, IX and X. The greater potency and duration of action of long-acting anticoagulant rodenticides is attributed to their: (i) greater affinity for vitamin K(1)-2,3-epoxide reductase; (ii) ability to disrupt the vitamin K(1)-epoxide cycle at more than one point; (iii) hepatic accumulation; and (iv) unusually long biological half-lives due to high lipid solubility and enterohepatic circulation. Substantial ingestion produces epistaxis, gingival bleeding, widespread bruising, haematomas, haematuria with flank pain, menorrhagia, gastrointestinal bleeding, rectal bleeding and haemorrhage into any internal organ; anaemia may result. Spontaneous haemoperitoneum has been described. Severe blood loss may result in hypovolaemic shock, coma and death. The first clinical signs of bleeding may be delayed and patients may remain anticoagulated for several days (warfarin) or days, weeks or months (long-acting anticoagulants) after ingestion of large amounts. There are now sufficient data in young children exposed to anticoagulant rodenticides to conclude that routine measurement of the international normalised ratio (INR) is unnecessary. In all other cases, the INR should be measured 36-48 hours post exposure. If the INR is normal at this time, even in the case of long-acting formulations, no further action is required. If active bleeding occurs, prothrombin complex concentrate (which contains factors II, VII, IX and X) 50 units/kg, or recombinant activated factor VII 1.2-4.8 mg or fresh frozen plasma 15 mL/kg (if no concentrate is available) and phytomenadione 10mg intravenously (100 microg/kg bodyweight for a child) should be given. If there is no active bleeding and the INR is < or =4.0, no treatment is required; if the INR is > or =4.0 phytomenadione 10mg should be administered intravenously.

Intentional Warfarin Overdose

Warfarin toxicity is common and usually results from dose changes or drug interactions. There are few reported cases of intentional overdose. The management of warfarin overdose is usually complicated by the patient using warfarin therapeutically, often for a mechanical heart valve or pulmonary embolus prophylaxis. Untreated patients have a significant bleeding risk, but treatment carries a significant risk of complete reversal of anticoagulation and consequent risk of thrombosis. The objective of this study was to describe warfarin overdoses and complications of treatment and develop a safe approach to management. Three patients are described. Two patients received a single 10-mg dose of vitamin K. Both required anticoagulation, and in one, warfarin resistance persisted for 2 weeks. In a third patient serial INR, factor levels and warfarin concentrations were measured, and incremental doses of vitamin K (up to 7.5 mg) were given based on INR. This patient did not require anticoagulation, and regular warfarin therapy was recommenced after 4 days. Patients intentionally overdosing on warfarin can be classified into three groups based on preexisting indications for warfarin: nontherapeutic, moderate risk, and major risk for thromboembolic complications. All patients should have regular INR measurements (6-hourly) to catch rapid rises. Patients not on warfarin therapeutically can be given 10 mg of vitamin K1 and repeat INRs as an outpatient. Titrating intravenous vitamin K with doses of 0.5 to 2.0 mg when INR > 5 is appropriate to reduce INR without causing warfarin resistance. The high-risk group must be kept anticoagulated, and warfarin resistance avoided.

Delivery systems for antioxidant nutrients

The novel role of oxidants and antioxidants as part of cell signaling cascades has opened new areas of research in several disease states and their therapeutic strategies. For successful therapeutic manipulation of reactive oxygen species (ROS)-mediated cellular signaling pathways, it would necessitate control of the critical balance of oxidants/antioxidants in the target site by the antioxidant. Another way of controlling the critical balance is to avoid excessive generation of ROS from nutrients and/or drugs. From the viewpoint of controlling the balance between the oxidant and antioxidant status, this review focuses on the prodrug approach for delivery systems of vitamin E, a major antioxidant nutrient in the membrane, and on the reductive activation-independent delivery system of vitamin K hydroquinone by a prodrug approach, which can avoid excessive generation of ROS synchronized with the activation process of vitamin K.

Efficacy and safety of intravenous phytonadione (vitamin K1) in patients on long-term oral anticoagulant therapy

OBJECTIVES

To determine the safety and efficacy of intravenously administered phytonadione (vitamin K1) in patients on routine oral warfarin anticoagulation.

PATIENTS AND METHODS

This retrospective cohort study comprised adults who were taking warfarin, were not bleeding, and received intravenous phytonadione anticoagulation therapy before a diagnostic or therapeutic procedure between September 1, 1994, and March 31, 1996. The main outcome measures were adverse reactions to intravenously administered phytonadione, prothrombin-international normalized ratio time values, the incidence of bleeding and thrombosis after the procedure, and the time between the procedure and return to anticoagulation after resumption of warfarin treatment.

RESULTS

Two (1.9%) of the 105 patients studied had suspected adverse reactions to intravenous phytonadione (dyspnea and chest tightness during infusion in both). For the 82 patients who underwent a procedure, the median time from phytonadione to procedure onset was 27 hours (range, 0.7-147 hours), which was significantly less for patients receiving an initial phytonadione dose of more than 1 mg (P=.009). None had thromboembolism after surgery, although 2 (2.4%) of the 82 patients had procedure-associated major bleeding. For the 60 patients resuming warfarin therapy after a procedure, the median time to return to therapeutic anticoagulation was 4.1 days (range, 0.8-31.7 days) and was unaffected by the phytonadione dosage.

CONCLUSIONS

Intravenous phytonadione appears to be safe and is effective for semiurgent correction of long-term oral anticoagulation therapy before surgery. In small doses, it does not prolong the patient's time to return to therapeutic anticoagulation.

Phytonadione therapy in a multiple-drug overdose involving warfarin

We cared for a patient who ingested an unknown amount of acetaminophen with zopiclone and warfarin. The only liver function test that was abnormal was an increased international normalized ratio (INR), which remained elevated despite treatment with subcutaneous phytonadione and a prolonged infusion of N-acetylcysteine. An interaction between acetaminophen and warfarin may have decreased the hepatic metabolism of warfarin. The patient received numerous antibiotics that may have contributed to the increased INR. The prolonged elevation of INR also may have been due to infrequent administration of phytonadione.

Long-acting anticoagulant overdose: brodifacoum kinetics and optimal vitamin K dosing

Ingestion of long-acting anticoagulant rodenticides such as brodifacoum can lead to prolonged and life-threatening coagulopathy. A paucity of conflicting information is available on brodifacoum's half-life and elimination pharmacokinetics. In addition, the optimal dose, duration, and route of administration of vitamin K(1) therapy are unknown. We report the case of a 52-year-old man who ingested eight 43-g boxes of a rodenticide (d-Con Mouse-Prufe II; 0.005% brodifacoum; Reckitt & Colman, Wayne, NJ). This case demonstrates that after stabilization with fresh frozen plasma, high-dose oral vitamin K(1) therapy ( congruent with 7 mg/kg per 24 hours divided every 6 hours) was effective in treating brodifacoum-induced coagulopathy. The concentration of vitamin K(1) required for normal coagulation in this case was less than the accepted value of 1 microg/mL, which is derived from a rabbit model. In this case, brodifacoum appears to follow zero-order elimination pharmacokinetics. In future cases of patients with ingestions of long-acting anticoagulants who present with coagulopathy, it may be useful to obtain serial brodifacoum concentrations to determine elimination curves to help predict the duration of oral vitamin K(1) therapy.

Plasma concentrations after intravenous administration of phylloquinone (vitamin K(1)) in preterm and sick neonates

Vitamin K prophylaxis usually is administered orally or intramuscularly, but in neonatal intensive care oral administration might not be feasible and intramuscular administration is not general practice in very small infants. No data are available about plasma levels after intravenous administration of vitamin K to neonates. Therefore, we investigated plasma levels in 18 infants: 14 preterms with a birthweight of 1785+/-648 g and 4 sick newborns with a birth-weight of 3167+/-510 g after administration of a single dose of 0.3+/-0.1 mg/kg phylloquinone (vitamin K(1)) (Konakion MM((R)), Roche) intravenously after birth. Blood was collected 22.9+/-18.4 hours after intravenous administration of vitamin K(1). In 10 neonates a second sample was obtained 111.8+/-49.1 hours after the first vitamin K(1) administration. Gas chromatography-mass spectrometry (GC-MS) was used as the method for determination of vitamin K(1). The measured plasma concentration after intravenous administration of vitamin K(1) was 191.3+/-102.6 ng vitamin K in the first sample /mL in the first sample and 98.7+/-75.2 ng vitamin K(1)/mL in the second samples. These results are similar to those described in newborns after oral administration of 3 mg vitamin K(1) and after intramuscular administration of 1.5 mg vitamin K(1). In conclusion, the recommendation of the producer to give 0.4 mg/kg of vitamin K intravenously to neonates, in whom oral or intramuscular administration is not feasible, seems to be rational.

A prospective randomized study to determine the optimal dose of intravenous vitamin K in reversal of over-warfarinization

The optimal management of asymptomatic overanticoagulated patients remains unknown. We measured international normalized ratio (INR), activated partial thromboplastin time (APTT) and prothrombin fragment 1 + 2 (F1 + 2) over 7 d in 24 asymptomatic or mildly haemorrhagic patients on warfarin with prolonged INR of > 7.0 who were randomized to receive 0.5 mg, 1 mg or 2 mg intravenous vitamin K. Of six severely overanticoagulated patients (INR > 9.5 with APTT ratio > 2), five failed to achieve an INR < or = 4.0 on day 1, irrespective of vitamin K dose given. In the remaining 18 cases, an optimal response (INR 2-4 at day 1) was observed in 67% of those receiving 0.5 mg vitamin K, but only in 33% of those receiving 1 or 2 mg, the majority of whom developed an INR < 2.0. Our results support an optimal dose of 0.5 mg i.v. vitamin K for most overanticoagulated patients, with possibly a repeat dose in the small group of severely overanticoagulated patients.

Vitamin K status of lactating mothers and their infants

Vitamin K deficiency remains a world-wide problem in the newborn. Vitamin K traverses the placenta from mother to infant very poorly and is present only in very low concentrations in human milk. Thus, it is not surprising that the newborn infant has undetectable vitamin K serum levels with abnormal amounts of the coagulation proteins and undercarboxylated prothrombin. Hemorrhagic disease of the newborn, secondary to vitamin K deficiency, remains largely a disease of breastfed infants. Lactating mothers easily achieve the recommended dietary allowance for vitamin K (1 microg kg(-1) d(-1)) and the breast milk concentration is readily increased by increasing maternal vitamin K intake. Breastfed infants do not receive the recommended vitamin K intake via human milk. To prevent vitamin K deficiency in the newborn, intramuscular or oral vitamin K prophylaxis is necessary.

Course of the international Normalized Ratio in response to oral vitamin K1 in patients overanticoagulated with phenprocoumon

Oral vitamin K1 is used for the treatment of excessive anticoagulation. Detailed information on changes in the International Normalized Ratio (INR) in response to vitamin K1 is not available. We therefore measured the INR for the first 7 d following the oral intake of 1-5 mg of vitamin K1 in 24 patients routinely treated with phenprocoumon who had an INR > or =6.0 at presentation. On the first 2 d after administration of vitamin K1, the mean INR decreased by 40% and 23% respectively. After day 2, the day-to-day proportional change in the mean INR depended on the dose of vitamin K1 and varied from a decrease of 12% to an increase of 21%. On day 7 the mean INR was higher than on day 2 in three out of five treatment groups. Between day 2 and day 7, in general, 32% of the patients had an INR value within the target zone, 25% had an INR value > or =6.0 and 8% had an INR value <2.0. These findings suggest that our routine treatment of overanticoagulation in patients on phenprocoumon should be intensified to improve its efficacy.

Management of oral anticoagulant-induced intracranial haemorrhage

Intracranial haemorrhage is an infrequent but often fatal complication of oral anticoagulant therapy which will become more common as anticoagulant use increases. The risk of anticoagulant-induced intracranial haemorrhage may be reduced by judicious prescribing, identification of patients at high risk of bleeding, and close monitoring by experienced staff. The presenting features of intracranial haemorrhage are often vague and physicians should be aware of the need for urgent investigation of all anticoagulated patients with neurological symptoms. Current guidelines for immediate reversal of anticoagulation recommend administration of vitamin K1 and factor replacement with either factor concentrates or fresh frozen plasma. In this review we discuss recent evidence suggesting prothrombin complex concentrates lead to faster, and more complete, correction of coagulation and, in the context of intracranial bleeding, may be associated with improved neurological status. Evidence for the risks of short-term cessation of anticoagulants, in the immediate period following an intracranial haemorrhage, and their subsequent reintroduction is also discussed.

Covert poisoning with difenacoum: clinical and toxicological observations

1. The coumarin anticoagulant difenacoum was detected by high performance liquid chromatography (HPLC) with multi-wavelength UV detection in plasma from a 41 years old man who presented with a severe deficiency of vitamin K-dependent clotting factors of unknown aetiology. A longitudinal toxicological study of the consequent coagulopathy is described. 2. Plasma concentrations of difenacoum declined from 0.97 to 0.11 mgl-1 in 47 days with a terminal half life of 11.7 days. Rifampacin (300 mg bd) had no apparent effect on the terminal half life of the drug. Subsequently plasma concentrations of difenacoum and descarboxyprothrombin (DCP) unexpectedly increased. 3. Seven months after exposure clotting times were prolonged. The patient continued to have episodes of epistaxis, haematoma, purpurae and bruising and he required frequent treatment with Fresh Frozen Plasma in additional to oral phylloquinone (200 mg day-1). 4. Intermittent and unexpected increases in plasma concentrations of difenacoum and descarboxypro-thrombin suggested that covert, repeated ingestion of the anticoagulant was the most likely cause of the poisoning. The measurement of low concentrations of plasma phylloquinone except following supervised ingestion of the vitamin indicated that as an outpatient, the subject was not compliant with treatment despite his protestations to the contrary. He continued to deny this even when confronted by laboratory findings and at no time did he ever admit to self-poisoning.

Plasma vitamin K1 and PIVKA-II after oral administration of mixed-micellar or cremophor EL-solubilized preparations of vitamin K1 to normal breast-fed newborns

BACKGROUND

Vitamin K1 prophylaxis in neonates is required for prevention of vitamin K1 deficiency bleeding. Although intramuscular administration of vitamin K1 is safe, this invasive method is not generally accepted. We therefore examined the pharmacokinetics of two orally administered vitamin K1 preparations in normal, fully breast-fed newborns.

METHODS

Within 1 hour of birth, each baby was randomized to a 2 mg dose of either a conventional Cremophor EL-solubilized preparation of vitamin K1 (Konakion drops, F. Hoffmann-La Roche, n = 16), or a new mixed-micellar preparation of vitamin K1 (Konakion MM, F. Hoffmann-La Roche, n = 14). The concentrations of vitamin K1, des-gamma-carboxyprothrombin (PIVKA-II), and total bound bilirubin were measured in plasma samples taken at 24 hours, 4 days, and 24 days after birth.

RESULTS

The median concentration of plasma vitamin K1 was higher at all three time points in the group that received the mixed-micellar preparation, but the difference was only significant (p < 0.05) at 4 days. At 24 hours and 4 days, PIVKA-II was detectable in a significantly lower proportions of infants receiving the new mixed-micellar preparation than those receiving the Cremophor EL preparation (21% vs. 75% at 24 hours, p < 0.05 and 14% vs. 50% at 4 days, p < 0.05). None of the infants in the study had detectable PIVKA-II levels 24 days after birth.

CONCLUSIONS

Our results suggest that when given orally, the mixed-micellar preparation is superior to the conventional formulation because it increases plasma vitamin K1 concentrations to higher levels, suggesting superior bioavailability, and decreases PIVKA-II concentrations more efficiently, suggesting a faster pharmacodynamic response.

Intravenous vitamin K1 prior to orthotopic heart transplantation: effects in vivo and in vitro

BACKGROUND

Vitamin K1 is used to reverse warfarin's anticoagulant action. It is unclear whether intravenous vitamin K1 is safe or efficacious prior to urgent cardiac surgery.

METHODS

We retrospectively and prospectively examined the effects of preoperative intravenous vitamin K1 in vivo (administered for warfarin reversal immediately before heart transplantation) on intraoperative blood product utilization, hemodynamics and coagulation parameters. We also determined the direct effects of vitamin K1 in vitro on rings of human saphenous vein and internal mammary artery.

RESULTS

In the retrospective limb, 29 of 67 patients were administered vitamin K1 preoperatively via slow intravenous infusion. Vitamin K1 administration produced no adverse outcome but did not affect subsequent perioperative use of blood products. In the prospective limb (n = 10), vitamin K1 significantly (P < or = 0.01, Student t-test) altered mean arterial pressure (from 85 +/- 15 to 76 +/- 16 mmHg), systemic vascular resistance (from 1364 +/- 308 to 1078 +/- 252 dyn.s.cm-5), and cardiac index (from 2.3 +/- 0.3 to 2.7 +/- 0.3 L/min/m2) (mean +/- SD). Significant decreases in prothrombin time (19.8 +/- 2.7 to 17.7 +/- 1.8 s) and activated clotting time (164 +/- 26 to 137 +/- 24 s) were observed at 60 min. In vitro vitamin K1 (10(-7) to 10(-4) M) had no effect on the tone of noradrenaline-constricted rings.

CONCLUSIONS

Vitamin K1, administered by intravenous infusion prior to heart transplantation, did not alter subsequent perioperative blood product administration. Vitamin K1 rapidly reversed the anticoagulant effect of warfarin and produced modest hemodynamic changes. The decrease in systemic vascular resistance is probably not due to a direct effect of vitamin K1 on vascular smooth muscle.

'Superwarfarin' poisoning leading to prolonged coagulopathy

An elderly Chinese was admitted for haemetemesis. Investigations revealed markedly prolonged clotting times that recurred every few days despite administration of fresh frozen plasma and vitamin K. The derangement in coagulation lasted more than 3 months. In view of the absence of liver disease or malabsorption syndromes, long-acting anticoagulant ('superwarfarin') ingestion was suspected. The diagnosis of rodenticide poisoning was hampered by the lack of available assays. Diagnosis of brodifacoum intoxication using HPLC was confirmed only months after prolonged treatment with high dose vitamin K1. Superwarfarin poisoning should be suspected in cases of deranged coagulation refractory to treatment since these over-the-counter rodenticides are easily available.

Vitamin K prodrugs: 2. water-soluble prodrugs of menahydroquinone-4 for systemic site-specific delivery

PURPOSE

The hydrochloride salts of the N,N-dimethylglycine esters of menahydroquinone-4 (1-mono, 1; 4-mono, 2; and 1,4-bis, 3) were assessed in vivo as prodrug for the systemic site-specific delivery system of menahydroquinone-4 (MKH), the active form of menaquinone-4 (MK-4, vitamin K2(20)).

METHODS

The disposition of MK-4 and menaquinone-4 epoxide (MKO) following the intravenous administration of the prodrugs and MK-4 preparation solubilized with surfactant (H-MK-4) were studied in vitamin K cycle inhibited rats. The relative bioavailability of MKH after the administration of the prodrugs was assessed from the area under the plasma concentration of MKO vs. time curve (AUCMKO). The specific delivery of MKH to its active site (liver) and coagulation activity after the administration of selected prodrug 1 were then compared with those of H-MK-4 in warfarin poisoned rats.

RESULTS

All compounds showed linear pharmacokinetics, and significant bioavailability of MKH was also observed following the administration of 1 (188%), 2 (87%) and 3 (135%). Prodrug 1 caused the following increases; AUCliver of MKO from 70.7 +/- 5.77 (H-MK-4) to 167 +/- 7.89 nmol.h/g, MRTliver of MKO, from 3.87 +/- 0.307 to 8.57 +/- 0.432 h. The liver accumulation of intrinsic 1 reached a maximum (88% of dose) by 0.25 h. The rapid and liver-selective uptake and liver esterase mediated MKH regeneration characteristics of 1 enhanced the delivery of MKH to its active site and the selective advantage was increased 5.7 fold. The coagulation activity was extended 1.9 fold by 1 administration.

CONCLUSIONS

The results indicated that these highly water-soluble and liver-esterase hydrolyzable ester derivatives of MKH are potential candidates for parenteral prodrugs which can thus achieve the systemic site-specific delivery of MKH. Such effective and selective delivery of MKH to its active site can therefore lead to enhanced pharmacological efficacy and can also avoid the toxicity induced by the solubilizing agent used in the H-MK-4 preparation.

Vitamin K prodrugs: 1. Synthesis of amino acid esters of menahydroquinone-4 and enzymatic reconversion to an active form

The efficacy and toxicity of vitamin K depends on the pathway and the extent of enzymatic reductive activation to vitamin K hydroquinone, which is an essential cofactor for the synthesis of clotting factors. Parenteral use of vitamin K is impaired by its water insolubility. With the aim to improve delivery problems associated with menahydroquinone-4 (MKH, 2), an active form of menaquinone-4, N,N-dimethylglycine esters of 2 (1-mono, 4-mono, and 1,4-bis) were synthesized and assessed as potential water-soluble prodrugs for parenteral use. The esters can deliver the hydroquinone to its active site without a quinone reductive activation step. The hydrochloride salts of the esters were found to be quite soluble in water. The hydrolysis of the esters in 20% rat liver homogenate 9000 x g supernatant, rat plasma and phosphate buffer, pH 7.4, at 37 degrees C was kinetically studied in the presence and absence of an esterase inhibitor. The hydrolysis was catalyzed by esterases located in the rat liver and rat plasma and quantitatively yielded 2. These results suggest that esterification of 2 with N,N-dimethylglycine is a promising way for obtaining water-soluble prodrug forms of 2. Based on the high susceptibility to liver esterase, the esters are potential prodrugs for achieving the site-specific delivery of 2.

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.

Fatal rodenticide poisoning with brodifacoum

The increased prevalence of rodents resistant to warfarin led to the development of the hydroxycoumarin anticoagulant brodifacoum. A 25-year-old man attempted suicide by consuming four boxes of d-CON Mouse-Prufe II; each box contains 42 g of bait that is 0.005% brodifacoum. He presented to a hospital nine days later with syncope, hematochezia, gross hematuria, epistaxis, anemia, and a severe coagulopathy. Radiographic studies were consistent with pleural, pericardial, and mediastinal hemorrhages. Vitamin K and fresh frozen plasma were given, and he was later discharged on oral phytonadione (vitamin K1). The patient's coagulopathy recurred, necessitating multiple plasma transfusions and prolonged treatment with oral phytonadione. Fifteen weeks after hospital discharge, he presented again with a history of additional brodifacoum ingestion. Neurologic status was initially normal, but in the emergency department he suddenly became comatose soon after emesis was induced with syrup of ipecac. Computed tomography of the brain revealed a subarachnoid hemorrhage that led to brain death less than 24 hours later. This case demonstrates the severe and prolonged coagulopathy that can result from ingestion of brodifacoum, a compound that has a toxic potency about 200-fold that of warfarin and a half-life as much as 60 times longer.

The bioavailability of a mixed micellar preparation of vitamin K1, and its procoagulant effect in anticoagulated rabbits

We have investigated the pharmacokinetics and procoagulant activity of a new, mixed-micellar preparation of vitamin K1 (MM-K) in male New Zealand White rabbits. Oral administration of MM-K alone caused a significant (P less than 0.01) increase in the plasma concentrations of vitamin K1 as measured by normal-phase high-performance liquid chromatography (HPLC). Maximum plasma concentrations of vitamin K1 (450 ng mL-1, range 133-824 ng mL-1) were recorded at 3.3 h (range 3-5 h), and were significantly (P less than 0.05) greater than those seen after administration of an existing polyethoxylated castor oil preparation (PE-K; Konakion), which were 260 ng mL-1, range 198-390 ng mL-1 (tmax 0.8 h, range 0.4-1.2 h). AUC after MM-K (4.6 micrograms mL-1 h-1, range 2.1-6.3 micrograms ML-1 h-1) was also significantly (P less than 0.05) greater than after PE-K (1.6 micrograms mL-1 h-1, range 1.0-2.1 micrograms ML-1 h-1). However, the bioavailability of vitamin K1 after administration of MM-K was poor (9.4%), and there was considerable intra-individual variability between the concentrations of vitamin K1 recorded in the plasma samples. Both preparations of vitamin K1 stimulated clotting factor synthesis in rabbits anticoagulated with the potent and long-acting coumarin, brodifacoum. Maximum stimulation of clotting factor synthesis by vitamin K1 after MM-K was 87%, range 44-124% (%PCA). The maximum was seen later (tmax 12 h) than after PE-K (PCA 82%, range 47-125%; tmax 5 h). However, there was considerable intra-individual variability in response to both MM-K and PE-K.(ABSTRACT TRUNCATED AT 250 WORDS)

Extreme warfarin intoxication secondary to possible covert drug ingestion

A young adult male patient presented with an excessively prolonged prothrombin time (greater than 90 sec) following approximately two weeks of therapy with oral warfarin sodium, in doses between 2.5 and 5 mg/d. Repeated administration of vitamin K and fresh frozen plasma was required to reverse the anticoagulation and maintain a normalized prothrombin time. Serial warfarin plasma concentration measurements were used to interpret the apparently unusual prothrombin time response profile and to detect the possibility of covert drug ingestion.

Evaluation of coagulation factor abnormalities in long-acting anticoagulant overdose

Newer Rodenticides of the long-acting anticoagulant or "superwarfarin" class are gaining popularity. Since few cases of severe, prolonged anticoagulation after ingestion have been reported, the course of toxicity is not precisely understood. In this case of an intentional ingestion of brodifacoum, a longitudinal analysis of specific coagulation factor derangements was carried out in an attempt to guide a future treatment strategy for this type of toxicity. Results of this analysis demonstrated a profound decrease in levels of factors II, VII, IX, and X, lasting at least 43 days post ingestion. Treatment with subcutaneous vitamin K1 in doses up to 100 milligrams per day was without complication and was effective in reversing the coagulopathy produced by brodifacoum.

The relationship between inhibition of vitamin K1 2,3-epoxide reductase and reduction of clotting factor activity with warfarin

1 The effect of low dose steady state warfarin (0.2 mg and 1 mg daily) on clotting factor activity and vitamin K1 metabolism was studied in seven healthy volunteers. 2 Steady state plasma warfarin concentrations were 41-99 ng ml-1 for the 0.2 mg dose and 157-292 ng ml-1 for the 1 mg dose. 3 There was a significant prolongation of the mean prothrombin time (0.9 s) after 1 mg warfarin daily, but no significant change in prothrombin time after 0.2 mg warfarin daily. There was no significant change in individual clotting factor activity (II, VII, IX or X) with either dose of warfarin. 4 Following the administration of a pharmacological dose of vitamin K1 (10 mg), all seven volunteers had detectable levels of vitamin K1 2,3-epoxide with both doses of warfarin (Cpmax 31-409 ng ml-1). 5 Both the Cpmax and the AUC for vitamin K1 2,3-epoxide were significantly greater on 1 mg of warfarin daily than 0.2 mg daily (P less than 0.01). 6 The apparent dissociation between inhibition of vitamin K1 2,3-epoxide reductase and reduction of clotting factor activity, produced by warfarin, may reflect the insensitivity of functional clotting factor assays to a small reduction in clotting factor concentration.

Warfarin poisoning and vitamin K antagonism in rat and human liver. Design of a system in vitro that mimics the situation in vivo

The present paper describes a system in vitro that has been developed to mimic vitamin K metabolism and vitamin K function in liver. In this system the two pathways that are known to participate in vitamin K reduction are active and the vitamin K-dependent carboxylase accepts a synthetic pentapeptide as substrate. With this system in vitro the effect of warfarin on both pathways was examined under conditions which simulated a warfarin-poisoned liver. Identical experiments were completed with rat and human liver. All activities currently associated with vitamin K metabolism and vitamin K function were similar in the rat and human systems. Warfarin neutralized the ability of pathway I (the vitamin K epoxide reductase pathway) to produce reduced and active vitamin K cofactor for the carboxylase. In both the rat and the human system, however, when warfarin was present, reduced vitamin K cofactor was produced by pathway II (the dehydrogenase pathway). The data are consistent with observations in vivo on the effect of vitamin K1 when used as an antidote. This suggests that the system in vitro reflects the mechanism in vivo by which vitamin K1 overcomes warfarin poisoning.