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Biomedical subjects

J P Shaw

Publications and source records attributed to J P Shaw.

At least 19 recordsLinked to original sources

Pharmacokinetics, serum inhibitory and bactericidal activity, and safety of telavancin in healthy subjects.

The pharmacokinetics, tolerability, and serum inhibitory and bactericidal titers of telavancin, a new rapidly bactericidal lipoglycopeptide with multiple mechanisms of action against gram-positive pathogens, were assessed in a two-part, randomized, double-blind, placebo-controlled, ascending-dose study with 54 healthy men. In part 1, single ascending intravenous doses of 0.25 to 15 mg/kg of body weight were studied. In part 2, multiple ascending doses (30-min infusions of 7.5 to 15 mg/kg/day) were studied over 7 days. Following the administration of multiple doses, steady state was achieved by days 3 to 4. At day 7 after the administration of telavancin at 7.5, 12.5, and 15 mg/kg/day, peak concentrations in plasma were 96.7, 151.3, and 202.5 microg/ml, respectively, and steady-state area-under-the-curve values were 700, 1,033, and 1,165 microg x h/ml, respectively. The elimination half-life ranged from 6.9 to 9.1 h following the administration of doses > or =5 mg/kg. Most adverse events were mild in severity. At 24 h postinfusion, serum from subjects given telavancin demonstrated potent bactericidal activity against methicillin-resistant Staphylococcus aureus and penicillin-resistant Streptococcus pneumoniae strains. The results suggest that telavancin may be an effective once-daily therapy for serious bacterial infections caused by these pathogens.

Adolescent↗

Seasonal variation in cytochrome P450 immunopositive protein levels, lipid peroxidation and genetic toxicity in digestive gland of the mussel Mytilus edulis.

The relationship between cytochrome P450 1A- and 2E-immunopositive proteins, lipid peroxidation and DNA strand breaks (SBs) was studied in Mytilus edulis digestive gland at different seasons and at different sites around the UK coast. Cytochrome P4501A (CYP1A)-immunopositive protein and DNA strand breaks were generally lowest in December but there was no correlation between PAH exposure (indicated by chemical measurement and CYP1A-immunopositive protein expression) and DNA strand breaks which was highest at the relatively non-polluted site (Port Quin). As with CYP1A, CYP2E1-immunopositive protein was maximal at most sites in May. Lipid peroxidation, in contrast, did not alter markedly throughout the year. In conclusion, DNA strand breakage was not correlated with any of the above parameters although it did correlate with "scope for growth" as did the inverse of PAH levels. The study highlights the need to establish the relative contribution of DNA damage and DNA repair processes to the production of DNA strand breaks and emphasises the need to consider seasonal variation in interpretation of biomarkers.

Animals↗

Laparoscopic appendectomy for Crohn's disease of the appendix presenting as acute appendicitis.

BACKGROUND: Crohn's disease confined to the appendix is rare but has been well described in the literature. It can mimic acute appendicitis clinically. After surgical treatment, recurrences of Crohn's disease are rare. We report the first case of treatment by laparoscopic appendectomy of Crohn's disease confined to the appendix. METHODS: A healthy 32-year old man presented with a week-long history of vague lower abdominal pain. Diagnostic work-up, which included CT, enteroclysis, and routine blood work, revealed a patent appendiceal lumen with an inflammatory mass in the right lower quadrant. RESULTS: Diagnostic laparoscopy revealed an inflamed appendix, and a laparoscopic appendectomy was performed, with frozen-section examination revealing Crohn's disease of the appendix. Two years after surgery, the patient has not had a recurrence of symptoms. CONCLUSIONS: Crohn's disease of the appendix can mimic acute appendicitis, although often with a more indolent course. The disease may be treated successfully by laparoscopic appendectomy, with good long-term results.

Acute Disease↗

Three cases of small bowel intussusception in relation to a rare lesion: inflammatory fibrous polyps.

BACKGROUND/AIMS: Inflammatory fibrous polyps (IFPs), also known as inflammatory pseudotumors, occur rarely in the gastrointestinal tract. IFPs have variable presentations, often presenting as small bowel obstruction due to intussusception or, less commonly, as an incidental finding on radiological examinations or screening colonoscopies. The diagnosis and management of IFPs will be discussed through a review of the literature and a series of cases from our own institution. METHODS: A retrospective analysis of the diagnosis, management and complications of IFPs was performed by a literature review. This was accompanied by a series of 3 cases of IFPs, 2 of which causing intussusception, diagnosed and treated in our own institution. CONCLUSIONS: IFP is a rare disease and has a variable presentation, from asymptomatic to small bowel obstruction due to intussusception. IFPs cannot be differentiated from malignancy without histological examination. Therefore, whether diagnosed incidentally or in the setting of intussusception, the treatment of IFPs is surgical resection of the involved bowel.

Adult↗

The BBXB motif of RANTES is the principal site for heparin binding and controls receptor selectivity.

The chemokine RANTES (regulated on activation normal T cell expressed and secreted; CCL5) binds selectively to glycosaminoglycans (GAGs) such as heparin, chondroitin sulfate, and dermatan sulfate. The primary sequence of RANTES contains two clusters of basic residues, (44)RKNR(47) and (55)KKWVR(59). The first is a BBXB motif common in heparin-binding proteins, and the second is located in the loop directly preceding the C-terminal helix. We have mutated these residues to alanine, both as point mutations as well as triple mutations of the 40s and 50s clusters. Using a binding assay to heparin beads with radiolabeled proteins, the (44)AANA(47) mutant demonstrated an 80% reduction in its capacity to bind heparin, whereas the (55)AAWVA(59) mutant retained full binding capacity. Mutation of the (44)RKNR(47) site reduced the selectivity of RANTES binding to different GAGs. The mutants were tested for their integrity by receptor binding assays on CCR1 and CCR5 as well as their ability to induce chemotaxis in vitro. In all assays the single point mutations and the triple 50s cluster mutation caused no significant difference in activity compared with the wild type sequence. However, the triple 40s mutant showed a 80-fold reduction in affinity for CCR1, despite normal binding to CCR5. It was only able to induce monocyte chemotaxis at micromolar concentrations. The triple 40s mutant was also able to inhibit HIV-1 infectivity, but consistent with its abrogated GAG binding capacity, it no longer induced enhanced infectivity at high concentrations.

Animals↗

Substrate recognition domains within extracellular signal-regulated kinase mediate binding and catalytic activation of mitogen-activated protein kinase phosphatase-3.

Mitogen-activated protein (MAP) kinase phosphatase-3 (MKP-3) is a dual specificity phosphatase that inactivates extracellular signal-regulated kinase (ERK) MAP kinases. This reflects tight and specific binding between ERK and the MKP-3 amino terminus with consequent phosphatase activation and dephosphorylation of the bound MAP kinase. We have used a series of p38/ERK chimeric molecules to identify domains within ERK necessary for binding and catalytic activation of MKP-3. These studies demonstrate that ERK kinase subdomains V-XI are necessary and sufficient for binding and catalytic activation of MKP-3. These domains constitute the major COOH-terminal structural lobe of ERK. p38/ERK chimeras possessing these regions display increased sensitivity to inactivation by MKP-3. These data also reveal an overlap between ERK domains interacting with MKP-3 and those known to confer substrate specificity on the ERK MAP kinase. Consistent with this, we show that peptides representing docking sites within the target substrates Elk-1 and p90(rsk) inhibit ERK-dependent activation of MKP-3. In addition, abolition of ERK-dependent phosphatase activation following mutation of a putative kinase interaction motif (KIM) within the MKP-3 NH(2) terminus suggests that key sites of contact for the ERK COOH-terminal structural lobe include residues localized between the Cdc25 homology domains (CH2) found conserved between members of the DSP gene family.

Amino Acid Sequence↗

Stereoselective glucuronidation of formoterol by human liver microsomes.

AIMS: Formoterol is a beta2-adrenoceptor agonist marketed as a racemic mixture of the active (R; R)- and inactive (S; S)-enantiomers (rac-formoterol). The drug produces prolonged bronchodilation by inhalation but there is significant interpatient variability in duration of effect. Previous work has shown that in humans formoterol is metabolized by conjugation with glucuronic acid but little is known about the stereoselectivity of this reaction. The aim of the present study was to investigate the glucuronidation of formoterol enantiomers in vitro by human liver microsomes. METHODS: The kinetics of formation of formoterol glucuronides during incubation of racemate and of single formoterol enantiomers with human liver microsomes (n=9) was characterized by chiral h.p.l.c. assay. RESULTS: The kinetics of glucuronidation of the two formoterol enantiomers obeyed the Michaelis-Menten equation. Glucuronidation of formoterol was stereoselective and occurred more than two times faster for (S; S)-formoterol than for (R; R)-formoterol. In incubations with single formoterol enantiomers, the median (n=9) Km values for (R; R)-glucuronide and (S; S)-glucuronide were 827.6 and 840.4 microm, respectively, and the median V max values were 2625 and 4304 pmol min-1 mg-1, respectively. Corresponding values determined in incubations with rac-formoterol were 357.2 and 312.1 microm and 1435 and 2086 pmol min-1 mg-1 for (R; R)- and (S; S)-glucuronide, respectively. Interindividual variation was large with the ratio of V max/Km (S; S/R; R) ranging from 0.57 to 6.90 for incubations with rac-formoterol. CONCLUSIONS: Our study demonstrates that glucuronidation of formoterol by human liver microsomes is stereoselective and subject to high interindividual variability. These findings suggest that clearance of formoterol in humans is subject to variable stereoselectivity which could explain the variation in duration of bronchodilation produced by inhaled formoterol in patients with asthma.

Aged↗

Jejunal diverticulosis: a rare entity with multiple presentations, a series of cases.

BACKGROUND/AIMS: Jejunal diverticulosis (JD) is a rare disease that has a variable presentation. The signs, symptoms, diagnosis, complications and treatment of JD will be discussed through a review of the literature and a series of cases from our own institution. METHODS: A retrospective analysis of the diagnosis, treatment and complications of JD was performed by a literature review. This was accompanied by a series of four cases of JD diagnosed and treated in our own institution. CONCLUSIONS: JD is a rare disease in which most patients are asymptomatic. However, JD's different complications are serious and can be fatal. The treatment is mainly surgical; however, there have been cases where nonsurgical management was successful.

Aged↗

Rapid chiral high-performance liquid chromatographic assay for salmeterol and alpha-hydroxysalmeterol. Application to in vitro metabolism studies.

A rapid and sensitive chiral high-performance liquid chromatographic (HPLC) assay for the simultaneous determination of salmeterol and its principal human metabolite alpha-hydroxysalmeterol is described. The two pairs of enantiomers were resolved on a chiral-cellobiohydrolase column and detected by electrochemical detection at +700 mV. Standard curves were linear over the concentration range 0.1 to 4.0 microM for alpha-hydroxysalmeterol enantiomers and 2.5 to 40.0 microM for salmeterol enantiomers. Intra- and inter-day coefficients of variation were < 10%. The method was applied to a study of human hepatic metabolism in vitro which showed that microsomal metabolism of salmeterol to alpha-hydroxysalmeterol is not stereoselective.

Albuterol↗

Administration of 9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) to gravid and infant rhesus macaques (Macaca mulatta): safety and efficacy studies.

9-[2-(R)-(phosphonomethoxy)propyl]adenine (PMPA) significantly inhibits viral reverse transcription and has been reported to sustain low virus load in SIV-infected rhesus monkeys. Based on these findings, studies were conducted to assess the safety, efficacy, and placental transfer of PMPA when administered once daily subcutaneously to gravid rhesus monkeys during the second and third trimesters and their offspring (30 mg/kg/day). Fetuses (SIV-infected, N = 6; noninfected, N = 6) were monitored sonographically, and maternal/fetal blood samples were collected at select time points for hematologic, clinical chemical, virologic, immunologic, and pharmacologic assessments. Newborns were delivered by cesarean section at term and nursery reared for postnatal studies. Infants were administered PMPA once daily beginning on day 2 of life until 9 months postnatal age. Results of these studies have shown significant placental transport of PMPA, with peak fetal levels at 1 to 3 hours post-maternal administration; a significant and sustained reduction in viral load in SIV-infected fetuses and infants; and marked improvements in outcome (e.g., survival, growth, health) in SIV-infected offspring. However, decreased infant body weights and alterations of select serum biochemical parameters (e.g., decreased phosphorus levels, elevated alkaline phosphatase) have been shown to occur in approximately 67% of PMPA-treated infants, with severe growth restriction and bone-related toxicity in approximately 25% of animals studied. These data suggest that although PMPA holds great promise for HIV-infected patients, there is the potential for bone-related toxicity at chronic, high dosages, particularly in infants.

Adenine↗

Reuse of catheters for percutaneous transluminal coronary angioplasty: effects on procedure time and clinical outcomes.

In July 1996, because of concern regarding the possible transmission of Creutzfeldt-Jakob disease, the province of Quebec stopped the reuse of percutaneous transluminal coronary angioplasty (PTCA) catheters. Prior to this time, PTCA balloon catheters were used a maximum of four times and guide catheters a maximum of two times in the cardiac catheterization laboratory at our institution. After this time, only new catheters were used. In order to examine the effects of catheter reuse on duration of PTCA procedures and clinical outcomes, we compared 53 consecutive patients undergoing PTCA prior to 21 July 1996 with 54 consecutive patients undergoing PTCA after that time. A total of 81 men and 26 women underwent PTCA (average age, 64 +/- 12 years). There were no significant differences between the single-use and reuse groups with respect to baseline characteristics. There were also no significant differences in the numbers of PTCA catheters used (97 vs. 103, P = NS) or angiographic success rates (88% vs. 83%, P = NS). There was a trend for total procedure time and fluoroscopy time to be slightly longer for single-use compared with reuse cases (49.2 vs. 45.7 min and 19.7 vs. 16.8 min, respectively; P = NS for both comparisons). However, after controlling for case severity and the use of stents, there were no significant differences in total procedure time or fluoroscopy time between the two groups. We found little evidence to suggest that the reuse of PTCA catheters is associated with longer total procedure time or fluoroscopy time. We conclude that if catheter reuse is not found to be associated with infectious disease transmission, its widespread use should be considered. Cathet. Cardiovasc. Intervent. 48:54-60, 1999.

Aged↗

Aryl ester prodrugs of cyclic HPMPC. I: Physicochemical characterization and in vitro biological stability.

PURPOSE: The chemical, enzymatic, and biological stabilities and physical properties of a series of salicylate and aryl ester prodrugs of the antiviral agent, cyclic HPMPC, were evaluated to support the selection of a lead compound for clinical development. METHODS: Chemical stabilities of the prodrugs in buffered solutions at 37 degrees C were determined. Stability was also studied in the presence of porcine liver carboxyesterases (PLCE) at pH 7.4 and 25 degrees C. Tissue stabilities were examined in both human and dog intestinal homogenates, plasmas and liver homogenates. Prodrug and product concentrations were determined by reverse phase HPLC. RESULTS: Chemical degradation of the prodrugs resulted in the formation of both cyclic HPMPC and the corresponding HPMPC monoester. Chemical stability was dependent on the orientation of the exo-cyclic ligand; the equatorial isomers were 5.4- to 9.4-fold more reactive than the axial isomers. In the presence of PLCE, the salicylate prodrugs cleaved exclusively to give cyclic HPMPC and not the HPMPC monoester. In plasma, but not intestinal or liver homogenates, the salicylate esters of cyclic HPMPC cleaved readily with a rate dependent on the chain length of the alkyl ester substituent. CONCLUSIONS: The carboxylate function on the salicylate prodrugs of cyclic HPMPC provides an additional handle to chemically modify the lipophilicity, solubility and the biological reactivity of the prodrug. In tissue and enzymatic studies, the major degradation product is cyclic HPMPC. The salicylate ester prodrugs are attractive drug candidates for further in vivo evaluation.

Animals↗

Changing patterns in the use of slow acting antirheumatic drugs for the treatment of rheumatoid arthritis.

AIM: To report on the changing use of slow acting antirheumatic drugs in the treatment of rheumatoid arthritis by contrasting prescribing patterns in 1990 and 1995. METHOD: Data were extracted from the case notes of 103 outpatients with rheumatoid arthritis. Results were compared with those obtained in 1990 in a survey of 81 patients using identical methods. RESULTS: There was a significant increase in the use of methotrexate between 1990 and 1995, and a marked decrease in the use of auranofin. A new feature was the use of drugs in combination. Methotrexate was the most effective agent and auranofin least effective (p = 0.02). The agent with the highest average toxicity score was D-penicillamine. The long term tolerability of methotrexate was superior, with a median time for remaining on therapy 6.4 times longer than that of the other slow acting antirheumatic drugs (p = 0.01). CONCLUSIONS: Our results suggest that identified trends in the altered use of slow acting antirheumatic drugs for treatment of rheumatoid arthritis are rationally based on the increased use of the most effective agents and decreased use of those with greater toxicity and lesser efficacy.

Adult↗

Seroprevalence of Helicobacter pylori in a longitudinal study of New Zealanders at ages 11 and 21.

BACKGROUND: Helicobacter pylori seroprevalence increases with age in adult life but spontaneous reversion may occur in childhood and adolescence. AIMS: To determine the seroprevalence of H. pylori in a longitudinal study of New Zealanders at ages 11 and 21. METHODS: Serum from members of the Dunedin Multidisciplinary Health and Development Study (DMHDS) at age 11 (n = 561; 303 males, 258 females) and 21 (n = 785; 413 males, 372 females) was tested for H. pylori antibodies. A large proportion of those tested at age 11 was retested at age 21 (n = 465; 262 males, 203 females). Serological status was examined in terms of gender, socioeconomic status (SES) and self-reported use of antibiotics. RESULTS: The seroprevalence of H. pylori decreased by 38% from 6.6% (37/561) at age 11 to 4.1% (32/785) at age 21. Seroprevalence at age 11 was not associated with gender or SES. For those tested at both ages, the drop in seroprevalence from 6.7% to 4.1% was statistically significant (t = 2.57, p < 0.01, paired t-test) and was much greater in females (71%) than males (12%). Of the 31 seropositive individuals at age 11, 17 (six males, 11 females) seroreverted and self-reported antibiotic use in the year preceeding age 21 was more common in females (eight/11) than males (zero/six). Of the 434 seronegative individuals at age 11, only five (four males, one female) had seroconverted at age 21. CONCLUSIONS: Seroprevalence in the DMHDS declined from age 11 to 21 predominantly in females. The decline involved a greater rate of seroreversion and lower rate of seroconversion in females than males.

Adolescent↗

Pharmacokinetics and bioavailability of the anti-human immunodeficiency virus nucleotide analog 9-[(R)-2-(phosphonomethoxy)propyl]adenine (PMPA) in dogs.

The pharmacokinetics, bioavailability, and metabolism of the anti-human immunodeficiency virus nucleotide analog 9[(R)-2-(phosphonomethoxy)propyl]adenine (PMPA) were determined in beagle dogs following intravenous, intraperitoneal, and oral administration. Fasted male beagle dogs (n = 5) were pretreated with pentagastrin and received PMPA (10 mg/kg of body weight) by the intravenous and oral routes with a washout period of 1 week between doses. A further group of male dogs received PMPA as a single dose via the intravenous (1 mg/kg; n = 5) and the intraperitoneal (10 mg/kg; n = 3) routes, with 1-week washout period between doses. The concentrations of PMPA in plasma and urine were determined over 48 h postdosing by fluorescence derivatization and high-performance liquid chromatography (HPLC). The potential for metabolism or biliary excretion of PMPA was evaluated in a dog with a chronic indwelling bile cannula. Urine, feces, and bile were collected at intervals over 48 h following the intravenous administration of [14C]PMPA (10 mg/kg; 55 microCi/kg). The concentrations of PMPA in plasma after intravenous injection were best described by an open two-compartment model with a terminal half-life of approximately 10 h. PMPA was excreted unchanged in urine (70%); recovery in feces (0.42%) or bile (0.26%) was negligible. The plasma clearance of PMPA (0.28+/-0.05 liter/h/kg) was substantially greater than the glomerular filtration rate in this species, suggesting active tubular secretion of PMPA. No metabolites of [14C]PMPA were observed in urine, feces, or bile on the basis of HPLC with radioactive flow detection. The remainder of the dose was probably excreted unchanged in urine beyond 48 h postdosing. The mean+/-standard deviation observed bioavailabilities of PMPA following oral and intraperitoneal administration at 10 mg/kg were 17.1%+/-1.88% and 73.5%+/-10.5%, respectively.

Adenine↗

Usage patterns of transdermal nicotine when purchased as a non-prescription medicine from pharmacies.

OBJECTIVE: To assess nicotine patch use in smokers who purchased the product as a non-prescription medicine from pharmacies. DESIGN: A questionnaire administered at the time of purchase. SETTING: Community pharmacies throughout New Zealand. SUBJECTS: A total of 805 male and female purchasers of nicotine patches aged 18 through 87 years. MAIN OUTCOME MEASURES: Patterns of usage including self-reported smoking history, previous quit-smoking attempts, previous and current use of transdermal nicotine and other products, side effects, and concomitant smoking. RESULTS: Most respondents (74%) had attempted to quit smoking previously, many of whom (53%) had used a non-prescription nicotine replacement product. Approximately 60% of purchasers were first-time users. For those continuing a course of treatment, there was no evidence of use for longer than the manufacturer's recommendation (12 weeks). Twenty-eight per cent of respondents reported continuing smoking while using transdermal nicotine, although the number of cigarettes smoked was much less than in the reported smoking history. Side effects were reported by 24% of patch users in the current course, but there was no evidence of significant safety problems. CONCLUSIONS: This survey provides preliminary data on the non-prescription usage of transdermal nicotine when purchased through pharmacies.

Administration, Cutaneous↗

Determination of the structure of alanine racemase from Bacillus stearothermophilus at 1.9-A resolution.

The molecular structure of alanine racemase from Bacillus stearothermophilus was determined by X-ray crystallography to a resolution of 1.9 A. The alanine racemase monomer is composed of two domains, an eight-stranded alpha/beta barrel at the N-terminus, which includes residues 1-240, and a C-terminal domain essentially composed of beta-strand (residues 241-388). In the structure of the dimer the mouth of the alpha/beta barrel of one monomer faces the second domain of the other monomer. The pyridoxal 5'-phosphate (PLP) cofactor lies in and above the mouth of the alpha/beta barrel and is covalently linked via an aldimine linkage to Lys39, which is at the C-terminus of the first beta-strand of the alpha/beta barrel. This is the first example of a PLP cofactor binding in the active site of a alpha/beta barrel. A number of other residues are involved in maintaining the position of the PLP in the protein. Of these, Arg219 is the most interesting, as it forms a hydrogen bond with the pyridine nitrogen of the cofactor. This is the first known occurrence of such an interaction with PLP and is expected to influence the electron delocalization in the PLP-alanine intermediates. A second arginine residue, Arg136, donates a hydrogen bond to the phenolic oxygen of PLP and may be involved in the binding of substrate as well as stabilization of intermediates. Finally, Tyr265', from the second monomer, is postulated to be 2 proton donor to the carbanion intermediate.

Alanine Racemase↗

Oral formulations of adefovir dipivoxil: in vitro dissolution and in vivo bioavailability in dogs.

The effect of formulation on oral bioavailability of the antiviral nucleotide analogue adefovir from the prodrug adefovir dipivoxil was examined in beagle dogs. A suspension formulation of adefovir dipivoxil granules was administered to five fasted male beagle dogs (250 mg prodrug per dog; 135.7 mg-equiv of adefovir per dog). Tablets prepared from the same granulation (batch B94) were administered at 2 x 125 mg prodrug per dog. In addition, the same tablets were administered to dogs in the fed state or following pentagastrin pretreatment. Two further tablet batches (H94 and D501) with slight formulation changes were also evaluated in pentagastrin pretreated dogs (n = 5). Concentrations of adefovir in plasma were determined by HPLC following fluorescence derivatization. Tablet dissolution was examined at pH 2.0. One batch of adefovir dipivoxil tablets showed a 5-fold slower dissolution rate in vitro (B94 = H94 >> D501). Adefovir dipivoxil was completely converted to adefovir following oral absorption in dogs. The oral bioavailability of adefovir from the suspension was 35.0 +/- 8.9%. The oral bioavailability of adefovir from the tablet formulation was 34.7 +/- 10.3%, 37.2 +/- 4.5%, and 44.9 +/- 5.9% in fasted dogs, fed dogs and fasted dogs pretreated with pentagastrin, respectively. All three tablet batches had equivalent bioavailability in dogs. Oral bioavailability of adefovir from the prodrug in dogs (35-46%) was unaffected by formulation, food, or the acidic pH of the gastrointestinal tract. In vitro dissolution of adefovir dipivoxil tablets did not correlate with oral bioavailability. Oral bioavailability of adefovir dipivoxil appears to be limited by low permeability and biological conversion of the prodrug to adefovir.

Adenine↗