Conservative management of infected necrosis complicating severe acute pancreatitis

OBJECTIVES

Patients with severe necrotizing pancreatitis are at risk for infection, a major cause of morbidity and mortality. Most patients with infected pancreatic tissue require surgical intervention (necrosectomy), which is associated with high morbidity and mortality. A subset of these patients can be managed successfully with conservative management combined with prolonged courses of antibiotics.

METHODS

Three cases of severe acute pancreatitis seen at our institution are described, in which the patients developed aspirate-proven pancreatic infections. The patients were nonetheless stable from a clinical standpoint and were treated with long courses of antibiotics known to penetrate the pancreas; emergent surgery was deferred.

RESULTS

In two patients, surgery was completely avoided, with good clinical outcome. In the third patient, elective surgery was undertaken 12 wk after the episode of acute pancreatitis, to perform necrosectomy on organized pancreatic necrosis and to evaluate the patient's biliary tree. There were no postoperative complications.

CONCLUSIONS

A subset of patients with severe acute pancreatitis complicated by infection can be successfully managed with long term antibiotics and other supportive measures. High risk necrosectomy can, in some instances, be delayed or avoided entirely.

Type I collagen-phosphophoryn interactions: specificity of the monomer-monomer binding

It has been postulated that phosphophoryn (PP) molecules bind specifically to type I collagen fibrils as the key event in inducing matrix mineralization in dentin. The nature and specificity of the collagen molecule-PP interaction has been examined by rotary shadowing-electron microscopy of mixtures of native, monomeric lathyritic rat skin collagen and purified rat incisor PP. An antibody to the amino-telopeptide of the collagen alpha1(I)-chain was used to determine the N-terminal end of the collagen molecules. Solutions of collagen and PP in 0.01 M ammonium formate (+/- antibody) were mixed and spread in 70% glycerol-30% 0.01 M ammonium formate on freshly cleaved mica surfaces using the sandwich technique. After rotary shadowing with Pt and backcoating with a carbon film, the spreads were viewed in a JEOL 1200EX TEM. The PP appeared as 15-nm diameter globules, the collagen as semi-flexible 270 nm filaments. At neutral pH and low PP/collagen mixing ratios, a single interaction site was evident, centered at approximately 210 nm from the N-terminus. The binding interaction induced a local conformational change in the collagen, bending the molecule and reducing its effective length. The sequence within the collagen-PP-binding domain has a net-positive charge but contains both positively and negatively charged groups.

X-ray absorption microtomography (microCT) and small beam diffraction mapping of sea urchin teeth

Two noninvasive X-ray techniques, laboratory X-ray absorption microtomography (microCT) and X-ray diffraction mapping, were used to study teeth of the sea urchin Lytechinus variegatus. MicroCT revealed low attenuation regions at near the tooth's stone part and along the carinar process-central prism boundary; this latter observation appears to be novel. The expected variation of Mg fraction x in the mineral phase (calcite, Ca(1-x)Mg(x)CO(3)) cannot account for all of the linear attenuation coefficient decrease in the two zones: this suggested that soft tissue is localized there. Transmission diffraction mapping (synchrotron X-radiation, 80.8 keV, 0.1 x 0.1mm(2) beam area, 0.1mm translation grid, image plate area detector) simultaneously probed variations in 3-D and showed that the crystal elements of the "T"-shaped tooth were very highly aligned. Diffraction patterns from the keel (adaxial web) and from the abaxial flange (containing primary plates and the stone part) differed markedly. The flange contained two populations of identically oriented crystal elements with lattice parameters corresponding to x=0.13 and x=0.32. The keel produced one set of diffraction spots corresponding to the lower x. The compositions were more or less equivalent to those determined by others for camarodont teeth, and the high Mg phase is expected to be disks of secondary mineral epitaxially related to the underlying primary mineral element. Lattice parameter gradients were not noted in the keel or flange. Taken together, the microCT and diffraction results indicated that there was a band of relatively high protein content, of up to approximately 0.25 volume fraction, in the central part of the flange and paralleling its adaxial and abaxial faces. X-ray microCT and microdiffraction data used in conjunction with protein distribution data will be crucial for understanding the properties of various biocomposites and their mechanical functions.

X-ray microCT study of pyramids of the sea urchin Lytechinus variegatus

This paper reports results of a novel approach, X-ray microCT, for quantifying stereom structures applied to ossicles of the sea urchin Lytechinus variegatus. MicroCT, a high resolution variant of medical CT (computed tomography), allows noninvasive mapping of microstructure in 3-D with spatial resolution approaching that of optical microscopy. An intact pyramid (two demipyramids, tooth epiphyses, and one tooth) was reconstructed with 17 microm isotropic voxels (volume elements); two individual demipyramids and a pair of epiphyses were studied with 9-13 microm isotropic voxels. The cross-sectional maps of a linear attenuation coefficient produced by the reconstruction algorithm showed that the structure of the ossicles was quite heterogeneous on the scale of tens to hundreds of micrometers. Variations in magnesium content and in minor elemental constitutents could not account for the observed heterogeneities. Spatial resolution was insufficient to resolve the individual elements of the stereom, but the observed values of the linear attenuation coefficient (for the 26 keV effective X-ray energy, a maximum of 7.4 cm(-1) and a minimum of approximately 2 cm(-1) away from obvious voids) could be interpreted in terms of fractions of voxels occupied by mineral (high magnesium calcite). The average volume fraction of mineral determined for a transverse slice of the demipyramid near where it joins an epiphysis was 0.46; for a slice 3.3 mm adoral it was 0.70. Local volume fractions of mineral approached 1, and, away from resolvable voids, considerable portions of the demipyramids had volume fractions of calcite at or below approximately 0.33. MicroCT imaging of a demipyramid before and after infiltration with a high absorptivity fluid (sodium polytungstate) confirmed the determination of the volume fractions of minerals.

Three-dimensional microarchitecture of the plates (primary, secondary, and carinar process) in the developing tooth of Lytechinus variegatus revealed by synchrotron X-ray absorption microtomography (microCT)

This paper reports the first noninvasive, volumetric study of entire cross-sections of a sea urchin tooth in which the individual calcite structural elements could be resolved. Two cross-sectionally intact fragments of a Lytechinus variegatus tooth were studied with synchrotron microCT (microcomputed tomography) with 1.66 microm voxels (volume elements). These fragments were from the plumula, that is the tooth zone with rapidly increasing levels of mineral; one fragment was from a position aboral of where the keel developed and the second was from the zone where the keel was developing. The primary plates, secondary plates, carinar process plates, prisms, and elements of the lamellar-needle complex were resolved. Comparison of the microCT data with optical micrographs of stained thin sections confirmed the identifications and measured dimensions of the characteristic microarchitectural features. The interplay of reinforcing structures (plates and prisms) was more clearly revealed in the volumetric numerical data sets than in single or sequential slices. While it is well known that the primary plates and prisms in camarodont teeth are situated to improve resistance to bending (which can be termed primary bending), the data presented provide a new understanding of the mechanical role of the carinar process plates, that is, a geometry consistent with that required in the keel to resist lateral or transverse bending of the tooth about a second axis. The increase in robustness of teeth incorporating lateral keel reinforcement suggests that the relative development of carinar processes (toward a geometry similar to that of L. variegatus) is a character which can be used to infer which sea urchins among the stirodonts are most primitive and among the camarodonts which are more primitive.

Lipoprotein(a), other lipoproteins and hemostatic profiles in patients with ischemic stroke: the relation to cardiogenic embolism

Lipoprotein and hemostatic profiles including coagulation inhibitors were determined in 136 patients with acute ischemic stroke. Based on clinical examination, cerebral computed tomography, Doppler ultrasonography of precerebral arteries and transthoracic echocardiography, the strokes were classified as cardioembolic (n = 38), non-cardioembolic (n = 92), and mixed cardioembolic/hypertensive (n = 6). Patients with cardioembolic stroke were older than patients with non-cardioembolic stroke. Lipoprotein(a) was higher in the cardioembolic than in the non-cardioembolic group. Lipoprotein(a) was not significantly correlated to the other lipid levels and may represent an independent lipid risk factor. The non-cardioembolic group had higher levels of total cholesterol, triglycerides, total cholesterol/high-density lipoprotein cholesterol ratio, low-density lipoprotein cholesterol, apolipoprotein A1, and apolipoprotein B. The cardioembolic group had higher concentrations of fibrinogen and D-dimer, and lower levels of antithrombin, protein C, protein S and heparin cofactor 2 than the non-cardioembolic group. The differences in the hemostatic profile are consistent with thrombosis due to activated coagulation being more involved in the pathogenesis of cardioembolic than of non-cardioembolic stroke. Lipoprotein(a) seems to be more associated with coagulation markers of thrombosis than with atherosclerosis, whereas the other lipids mainly seem to be risk factors for atherosclerosis.

Liver Transplant After Normothermic Regional Perfusion From Controlled Donors After Circulatory Death: The Norwegian Experience

BACKGROUND

In order to meet the increasing demand for donor organs, the concept of donation after circulatory death (DCD) was reintroduced in Norway, first as a pilot study, followed by the use of DCD as institutional practice. We report the current Norwegian experience with liver transplant after DCD.

METHODS

After acceptance from next of kin, life support was withdrawn from patients with devastating brain injury and cardiac arrest observed. After a 5-minute "no-touch" period, extracorporeal membrane oxygenation for post mortem normothermic regional perfusion (NRP) by extracorporeal membrane oxygenator circuit was established. Data from all liver transplant recipients receiving controlled DCD (cDCD) livers in Oslo were analyzed.

RESULTS

From 2015 to 2017, a total of 8 patients underwent liver transplant with cDCD and NRP liver grafts in Norway. Median Model for End-Stage Liver Disease score was 26 (range, 6-40). There were no cases of delayed graft function or graft loss. Seven patients have reached 1 year of follow-up, and 1 patient has reached 6 months. Two patients have recurrence of primary disease (primary sclerosing cholangitis and steatohepatitis). All patients had normalized liver function at last follow-up. Two patients underwent procedures for biliary complications. In 1 patient, leakage from the cystic duct was successfully handled endoscopically by stenting. In the other patient, a suspected stricture on magnetic resonance imaging led to an endoscopic retrograde cholangiopancreatography, which did not confirm signs of biliary stenosis. There was 1 instance of hepatic artery stenosis, which was managed with endovascular technique.

CONCLUSION

The results after liver transplant using cDCD with NRP are good. The rate of complications seems to be within the same range as when using conventional donation after brain death grafts.

Open Abdomen Treated with Negative Pressure Wound Therapy: Indications, Management and Survival

BACKGROUND

Open abdomen treatment (OAT) is a significant burden for patients and is associated with considerable mortality. The primary aim of this study was to report survival and cause of mortality after OAT. Secondary aims were to evaluate length of stay (LOS) in intensive care unit (ICU) and in hospital, time to abdominal closure and major complications.

METHODS

Retrospective review of prospectively registered patients undergoing OAT between October 2006 and June 2014 at Trondheim University Hospital, Norway.

RESULTS

The 118 patients with OAT had a median age of 63 (20-88) years. OAT indications were abdominal compartment syndrome (ACS) (n = 53), prophylactic (n = 29), abdominal contamination/second look laparotomy (n = 22), necrotizing fasciitis (n = 7), hemorrhage packing (n = 4) and full-thickness wound dehiscence (n = 3). Eight percent were trauma patients. Vacuum-assisted wound closure (VAWC) with mesh-mediated traction (VAWCM) was used in 92 (78 %) patients, the remaining 26 (22 %) had VAWC only. Per-protocol primary fascial closure rate was 84 %. Median time to abdominal closure was 12 days (1-143). LOS in the ICU was 15 (1-89), and in hospital 29 (1-246) days. Eighty-one (68 %) patients survived the hospital stay. Renal failure requiring renal replacement therapy (RRT) (OR 3.9, 95 % CI 1.37-11.11), ACS (OR 3.1, 95 % CI 1.19-8.29) and advanced age (OR 1.045, 95 % CI 1.004-1.088) were independent predictors of mortality in multivariate analysis. The nine patients with an entero-atmospheric fistula (EAF) survived.

CONCLUSION

Two-thirds of the patients treated with OAT survived. Renal failure with RRT, ACS and advanced age were predictors of mortality, whereas EAF was not associated with increased mortality.

Pharmacokinetic evaluation of haemoperfusion in phenobarbital poisoning

Charcoal haemoperfusion was performed for 5-12 h in three patients with maximal plasma phenobarbital concentrations of 600, 946 and 1044 mumol/l (138, 217 and 240 micrograms/ml). During haemoperfusion with constant blood flow phenobarbital elimination followed first order kinetics with half-lives of 11.1, 10.0 and 7.2 h, respectively. After termination of the haemoperfusion there was no rebound effect in plasma phenobarbital concentration and the elimination was first order with half-lives of 51, 82 and 48 h, respectively. Thus, the plasma phenobarbital half-life was reduced by 78-88% during haemoperfusion. In the same period 76-86% of the total body clearance of phenobarbital was due to the haemoperfusion column at a calculated volume of distribution of phenobarbital of 1.1-1.21/kg. This is clear evidence for recommending haemoperfusion in cases of serious poisoning with phenobarbital.

Synchrotron X-ray studies of the keel of the short-spined sea urchin Lytechinus variegatus: absorption microtomography (microCT) and small beam diffraction mapping

In sea urchin teeth, the keel plays an important structural role, and this paper reports results of microstructural characterization of the keel of Lytechinus variegatus using two noninvasive synchrotron x-ray techniques: x-ray absorption microtomography (microCT) and x-ray diffraction mapping. MicroCT with 14 keV x-rays mapped the spatial distribution of mineral at the 1.3 microm level in a millimeter-sized fragment of a mature portion of the keel. Two rows of low absorption channels (i.e., primary channels) slightly less than 10 microm in diameter were found running linearly from the flange to the base of the keel and parallel to its sides. The primary channels paralleled the oral edge of the keel, and the microCT slices revealed a planar secondary channel leading from each primary channel to the side of the keel. The primary and secondary channels were more or less coplanar and may correspond to the soft tissue between plates of the carinar process. Transmission x-ray diffraction with 80.8 keV x-rays and a 0.1 mm beam mapped the distribution of calcite crystal orientations and the composition Ca(1-x)Mg(x)CO(3) of the calcite. Unlike the variable Mg concentration and highly curved prisms found in the keel of Paracentrotus lividus, a constant Mg content (x = 0.13) and relatively little prism curvature was found in the keel of Lytechinus variegatus.

Improved high-performance liquid chromatographic method for analysis of L-carnitine in pharmaceutical formulations

A reversed-phase high performance liquid chromatographic method for analysis of L-carnitine is described. The improved method is able to provide a high resolution between L-carnitine and crotonoylbetaine, a major impurity and degradation product, and suitable for quantitative analysis of L-carnitine in pharmaceutical formulations, such as solution, tablets, and capsules. The resolution, linearity, accuracy and reproducibility of the method are discussed.

Data Quality of Surgery for Carotid Artery Stenosis. Are the National Vascular Registries Reliable?

OBJECTIVES

To study completeness of reporting carotid endarterectomies, including peri-operative stroke and mortality rate, in a national vascular registry, NorKar, and a national administrative registry, The Norwegian Patient Register (NPR).

DESIGN

Comparative registry-based national study.

MATERIALS

Member hospitals of NorKar, including 89% of carotid endarterectomies in Norway, were compared with relevant data in NPR for the years 2000-2002.

METHODS

We compared procedure-codes, diagnosis-codes, in-hospital death and the occurrence of peri-operative stroke after treatment for carotid artery stenosis in the two registries to evaluate completeness.

RESULTS

Compared with the NPR numbers, 16% of carotid endarterectomies were missing in the reports from member hospitals of NorKar. Further, during this three-year period, there was an under-reporting of seven strokes and two deaths. The discrepancy was most pronounced in 2001.

CONCLUSIONS

There is an under-reporting of patients operated on for carotid artery stenosis in NorKar according to NPR numbers as well as an under-reporting of early deaths and strokes. There is a need for better quality data in the NorKar Registry. Registry quality would be likely to improve if patient identifiable data were available in both registries.

Sialography and CT-sialography in the diagnosis of parotid masses

Parotid masses were evaluated by sialography and CT-sialography in 22 patients. Nineteen were benign tumors and one a metastasis. All were identified by CT. Two patients with sialoadenitis were misinterpreted at CT. All benign tumors appeared as lobulated, sharply marginated masses, embedded in displaced glandular parenchyma. The metastasis was lobulated, irregular and located within the gland. With sialography, 17 tumors were identified and 3 small superficial tumors overlooked. Both patients with sialoadenitis were diagnosed by sialography. CT-sialography is recommended in patients with suggested parotid masses, and sialography in suggested inflammatory disease.

Effects of various granulating systems on the bioavailability of naproxen sodium from polymeric matrix tablets

Naproxen sodium and a cellulose ether derivative were granulated with either water or a poly(meth)acrylic acid ester copolymer aqueous dispersion to make three controlled-release matrix dosage forms. The different polymeric matrix systems contained hydroxypropyl methylcellulose (formulation A), hydroxypropyl cellulose:poly(meth)acrylic acid ester copolymer (formulation B), and hydroxypropyl methylcellulose:poly(meth)acrylic acid ester copolymer (formulation C). All three hydrophilic matrix tablets demonstrated identical in vitro dissolution rates. The three controlled-release formulations were compared with a marketed immediate-release naproxen sodium dosage form (formulation D) in a single-dose crossover study in six healthy volunteers. The AUC values for controlled-release dosage forms A and C were larger than those for formulations B and D. However, the reasons why the AUC for formulations A and C is larger than that for formulations B versus D can be explained differently. Formulations A and C more effectively maintain naproxen plasma levels than formulation D by reducing the amount of naproxen unbound to plasma proteins, therefore reducing naproxen available for urinary excretion. Naproxen sodium delivered from formulations A and C is also probably much better absorbed than from that from formulation B, possibly due to less drug entrapment. More importantly, although all three CR formulations had identical in vitro dissolution profiles, naproxen sodium plasma levels were better maintained (based on AUC) in subjects taking formulations A and C, which contained a lower polymer content and did not use hydroxypropyl cellulose. The tmax values were larger for the three controlled-release dosage forms. Also, the Cmax value for the conventional dosage form was nearly twofold higher than that observed for the controlled-release dosage forms.

Long-term anticoagulant therapy in cerebrovascular disease: does bleeding outweigh the benefit?

OBJECTIVE

The aim of the present study was to determine the risk of major haemorrhagic complications, stroke and other cardiovascular events, and mortality during long-term anticoagulant therapy (ACT) in patients with cerebrovascular disease not included in any prospective trials.

DESIGN

The data were collected retrospectively.

SETTING

All patients with symptomatic cerebrovascular disease discharged from the Stroke Unit, Aker University Hospital, Oslo, with ACT (warfarin) during 1983 through to 1986 were included.

SUBJECTS

The material consists of 161 patients with a mean age of 67.8 (range 40-90) years. The reason for initiating ACT was frequent transient ischaemic attacks (TIAs) in 52 patients, stroke in progression (SIP) in 33 patients, and probable embolic stroke in 76 patients. International normalized ratio (INR) of 4.2-2.8 was aimed at.

MAIN OUTCOME MEASURES

Major haemorrhagic complications, recurrent stroke and survival was determined for the total material, and in the subgroups non-valvular atrial fibrillation (NVAF, n = 49), TIAs, and SIP.

RESULTS

The mean duration of ACT was 21.1 (range 0.5-60.2) months with a total of 282.9 patient-years. The rate of major (including fatal) haemorrhagic complications was 4.6% per year, and the rate of fatal haemorrhagic complications was 1.4% per year. The complication rates in the subgroups of patients did not differ significantly from that in the total material. Only two out of the 13 major haemorrhagic complications occurred during the initial 6 months of ACT. No strokes occurred in the TIA subgroup. The rate of recurrent stroke (excluding intracranial haemorrhage) was 3.9% per year for all patients, 4.7% per year for the patients with NVAF, and 4.2% per year for the patients with SIP.

CONCLUSIONS

The total results suggest a positive net effect of ACT in patients with NVAF and TIAs. Without comparable data, no definite conclusions concerning the effect of ACT on patients with SIP can be drawn. The rate of bleeding complications was similar to that in other studied materials and is not negligible. In patients with SIP and TIAs, ACT beyond 6 months should probably only be continued if aspirin is not tolerated or has proven ineffective in the particular patient.

Fatal stroke in migraine: a case report with autopsy findings

A 50-year-old woman with migraine was admitted to hospital shortly after having abruptly developed hemiparesis. CT scan revealed infarction in the territory of the right middle cerebral artery. Death ensued after three days due to cerebral edema with herniation. Autopsy revealed no pathologic findings in the heart or in the extra- or intracranial arteries. It is suggested that the fatal stroke may have resulted from arterial spasm caused by ergotamine overdosage and possibly complicated by thrombosis.

Effects of lower body pressure changes on pulmonary function

PURPOSE

During and following exercise there are a number of changes in pulmonary function, among which is a decrease in forced vital capacity (FVC). Several potential mechanisms may explain this decreased FVC, including an exercise-induced increase in thoracic blood volume.

METHODS

We tested the hypothesis that altered thoracic blood volume alone, as produced by the application of 30 mm Hg lower body negative (LBNP) or positive pressure (LBPP) for 5 min, would change FVC and forced expiratory volume in 1 s (FEV1.0). Further, we tested whether the changes in pulmonary function were related to initial lung volume and whether the lower body pressure changes led to an altered lung compliance as measured by static pressure-volume curves.

RESULTS

Results indicated that with LBNP, FVC, and FEV1.0 were significantly increased by approximately 0.15 L and 0.18 L, respectively. When LBPP was applied, FVC and FEV1.0 were decreased by approximately 0.18 and 0.14 L, respectively. The increase in FVC with LBNP was significantly related to the original FVC (r = 0.66, P < 0.05). There was no significant correlation between the increase in FEV1.0 and the original FEV1.0 (r = 0.48, P > 0.05). Pulmonary compliance was not changed significantly by the application of LBPP.

CONCLUSIONS

These results suggest that part of the change in pulmonary function following heavy exercise is related to an increased thoracic blood volume. The lack of change in lung compliance suggests that the effect of altered thoracic blood volume is to displace air and not to change the mechanical properties of the lungs.

Multiple microscopy modalities applied to a sea urchin tooth fragment

Two synchrotron X-ray microscopy methods, phase-contrast microradiography (the propagation method) and absorption microCT (high-resolution computed tomography or microtomography), and laser-scanning confocal microscopy (visible wavelength) were used to study a fragment of the keel of a tooth of the sea urchin Lytechinus variegatus. Stripes observed in the phase-contrast images of the fragment were also seen in confocal micrographs. MicroCT showed that the stripes were due to two parallel planar arrays of low-absorption channels within the bulk of the keel. In the phase microradiographs, maximum contrast stripes appear when a channel image from one row coincides with a channel image from the second row; otherwise, contrast is minimal. Long channels do not appear to have been observed previously in keels of sea urchin teeth.

Rapid intraoperative construction of autologous small caliber blood vessels

Autologous pericardium, briefly tanned in glutaraldehyde, is an excellent biomaterial when used in various cardiac procedures, including repair and replacement of heart valves. A generalized lack of calcification and an absence of inflammatory response in these combined experiences has led the authors to consider the use of treated autologous pericardium for the construction of substitute small caliber blood vessels. Rapid, intraoperative construction of a vascular graft from autologous pericardium, briefly treated in 0.62% glutaraldehyde, is accomplished through the use of two concentric, mating helical stents that support a rectangular pattern of tissue into a cylindrical, nonkinking, compliant conduit. A disposable automated assembly tool provides for precise assembly of the tissue and stents. The tools and methods for construction of vascular grafts from nonvascular tissue are known as the Rapidgraft (Ramus Medical Technologies, Santa Barbara, CA). The technique can be used with any suitable tissue. Accelerated fatigue test studies have confirmed that stent supported pericardial grafts are capable of withstanding physiologic pressures and flows beyond 7 equivalent years. Six autologous pericardial grafts measuring 5 mm in diameter by 5.5 cm in length showed 100% patency beyond 5 months in a growing calf carotid artery model. Pathological examination of explanted grafts confirm the presence of a continuous endothelial lined surface, infiltration of the tissue by fibrous connective tissue such that the individual layers of the pericardial vessel wall could not be identified, and there was no inflammatory response. Based on the encouraging results in animal studies, a small multicenter clinical trial has been initiated to evaluate the performance of the Rapidgraft as a replacement conduit for the radial artery in cases in which the radial artery has been harvested as a coronary artery bypass conduit. Results from the radial artery trial will be used as an indication to evaluate the Rapidgraft as a coronary artery substitute. We conclude that the material properties, including the biological origin of a vessel wall, may be significant determinants of graft patency, and that the Rapidgraft may be an answer to the need for small caliber arterial graft with the potential for long-term patency and durability.

Kinetic studies of the degradation of oxycarbonyloxymethyl prodrug of Adefovir and Tenofovir in solution

The decomposition kinetics of bis-POC PMEA and bis-POC PMPA followed pseudo-first order kinetics with the corresponding mono-POC ester detected as the only observable degradation product for all the pH values studied. The rates of hydrolysis of bis-POC PMEA over the pH range studied was described by [formula: see text] The 18O incorporation studies revealed that hydrolysis of bis-POC PMEA at pH 7.0 primarily proceeds via P-O cleavage with an additional minor pathway involving C-O bond cleavage. Hydrolysis of bis-POC PMPA was found to be about 2 fold slower than bis-POC PMEA at pH values above 6.0.