Effect of drug lipophilicity on in vitro release rate from oil vehicles using nicotinic acid esters as model prodrug derivatives

The rate constants for transfer of a homologous series of nicotinic acid esters from oil vehicles to aqueous buffer phases were determined using a rotating dialysis cell. The chemical stability of butyl nicotinate has been investigated at 60 degrees C over pH range 0.5--10. Maximum stability occurs at pH 4--5 and an inflection point was seen around the pK(a). For the nicotinic acid esters, a linear correlation was established between the first-order rate constant related to attainment of equilibrium, k(obs) and the apparent partition coefficient, P(app): log k(obs)=-0.83log P(app)+0.26 (k(obs) in h(-1), n=9). For hexyl nicotinate with a true partition coefficient of 4 it was possible to determine k(obs) by decreasing pH in the aqueous release medium to 2.05. Thus, under the latter experimental conditions estimation of the relative release rates for the esters were performed. The ratio between the specific rate constant k(ow), related to the transport from oil vehicle to aqueous phase, for ethyl and hexyl nicotinate was 139. The hydrophobic substituent constant for a methylene group, pi(CH(2)), was determined for nicotinic acid esters in different oil/buffer partitioning systems to 0.54--0.58. Addition of hydroxypropyl-beta-cyclodextrin to the aqueous release medium did not enhance the transport rate of the esters from the oil phase.

Cell mixing between the embryonic midbrain and hindbrain

Segmentation is a mechanism that controls spatial organization along the anteroposterior axis of the neural tube and is particularly well characterized for the hindbrain region [1]. The generation of distinct and regionally specific structures from each rhombomere is achieved with the almost complete absence of cell mixing between neighboring rhombomeres [2, 3]. Here, we have examined cell mingling at the isthmus, where Otx2-expressing midbrain cells abut Gbx2-expressing hindbrain cells [4]. The sharp line of demarcation between the two expression domains suggests that this interface would be a compartment boundary, with no intermixing of cells, but this has not been directly tested. We have used short-term reaggregation assays to compare the adhesive properties of cells derived from midbrain and anterior hindbrain and cell labeling in vivo directly to monitor cell behavior at the midbrain/hindbrain boundary. Interestingly, our data demonstrate that, in contrast to the rhombomeres, differential adhesion does not seem to operate between the midbrain and anterior hindbrain and that cells move between the two territories. We conclude that these two subdivisions are not maintained by cell lineage restriction but by cells maintaining labile fates.

High-throughput screening applied to drug synthesis process development

Combinatorial chemistry and high-throughput screening have greatly increased the rate of lead drug molecule discovery. The increase in the number of compounds in the early phase of the drug development pipeline has, however, created a bottleneck in the development of cost-effective, scalable chemical processes for the manufacture of these drug candidates. Thus, pharmaceutical chemical development groups and their suppliers are implementing their own forms of high-throughput screening to improve their productivity to solve this bottleneck. Developments for implementing high-throughput screening for chemical process development are reviewed.

Pregnancies before and after HIV diagnosis in a european cohort of HIV-infected women. European Study on the Natural History of HIV Infection in Women

OBJECTIVES

Because most HIV-infected women are of reproductive age, we investigated whether their reproduction planning was affected by their HIV diagnosis.

DESIGN

The European women study is a prospective, multicentre cohort of 485 HIV-infected women with a known interval of seroconversion.

METHODS

The incidence of pregnancy was measured with person-time methods. Generalized estimating equation analysis was used to determine risk factors for pregnancy and pregnancy outcomes.

RESULTS

In 449 women, the age-adjusted incidence of pregnancies decreased from 8.6 before HIV diagnosis to 8.2 and 6.0 per 100 person-years in 0-4 and over 4 years after HIV diagnosis, respectively (P = 0.14). The proportion of induced abortions increased from 42% before to 53% after HIV diagnosis (P < 0.05). The risk of spontaneous abortion did not increase as a result of HIV infection. Since 1995, the proportion of births increased (P = 0.009), whereas that of induced abortions decreased (P = 0.01) compared with earlier years. An increased risk of pregnancy after HIV diagnosis was found in northern and central European women compared with southern European women; there was a lower risk in single women than in women with a steady partner. Of all pregnant women, single women, women between 15 and 25 years of age, and women with multiple partners were at increased risk for induced abortion both before and after HIV diagnosis.

CONCLUSION

The incidence of pregnancy decreased with HIV disease progression. Pregnancies after HIV diagnosis appear to be related largely to social and cultural attitudes. The number of induced abortions was high before HIV diagnosis and it significantly increases thereafter.

Assessment of rate of drug release from oil vehicle using a rotating dialysis cell

The rate constants for transfer of model compounds (naproxen and lidocaine) from oily vehicle (Viscoleo) to aqueous buffer phases were determined by use of the rotating dialysis cell. Release studies were done for the partly ionized compounds at several pH values. A correlation between the overall first-order rate constant related to attainment of equilibrium, k(obs), and the pH-dependent distribution coefficient, D, determined between oil vehicle and aqueous buffer was established according to the equation: logk(obs)=-0.71 logD-0.22 (k(obs) in h(-1)). Based on this correlation it was suggested that the rate constant of a weak electrolyte at a specified D value could be considered equal to the k(obs) value for a non-electrolyte possessing a partition coefficient, P(app), the magnitude of which was equal to D. Specific rate constants k(ow) and k(wo) were calculated from the overall rate constant and the pH-dependent distribution coefficient. The rate constant representing the transport from oily vehicle to aqueous phase, k(ow), was found to be significantly influenced by the magnitude of the partition coefficient P(app) according to: logk(ow)=-0.71 logP(app)-log(P(app)+1)-0.22 (k(ow) in h(-1)).

Modification of in vitro drug release rate from oily parenteral depots using a formulation approach

Rate constants for transfer of naproxen and lidocaine from different oils and oil mixtures to aqueous buffer, pH 6.00, were determined using the rotating dialysis cell. Significantly different first-order rate constants related to attainment of equilibrium, k(obs), were derived depending on the type of oil/oil mixtures used in the release experiments. For the drugs a linear correlation was found between logk(obs) and the logarithm of the partition coefficient P(app): logk(obs)=-0.68 logP(app)-0.25 (k(obs) in h(-1), n=26). A linear relationship was observed between the calculated and experimentally determined P(app) values for the oil mixtures investigated. The specific rate constants, k(ow) and k(wo), related to the partition process were derived from the determined k(obs) and P(app) values. The rate constant k(ow) representing the rate of transfer of the solute from the oil phase to the aqueous buffer was shown to be strongly dependent on the partition coefficient according to the relationship: logk(ow)=-0.68 logP(app)-log(P(app)+1)-0.25 (k(ow) in h(-1), n=26). In particular, diminished release rates were seen for oil mixtures containing castor oil most likely afforded by hydrogen bonding between the solute and the hydroxy groups of the latter vegetable oil. In this study it has been possible to alter P(app) for a specific compound up to a factor of 10 by variation of the composition of the oil vehicle. Such a span of P(app) values results in in vitro release rates differing a factor of 37. Thus, by proper design of the oil vehicle composition it should be possible to modify the release rate for a specific compound within certain limits.

Cervical squamous intraepithelial lesions in HIV-infected women: prevalence, incidence and regression. European Study Group on Natural History of HIV Infection in Women

OBJECTIVES

To assess the impact of HIV-related immunodeficiency and antiretroviral treatment on the occurrence and evolution of abnormal Papanicolaou tests.

STUDY DESIGN

Cohort of 485 HIV-infected women with a known date of infection, enrolled during May 1993-April 1998 in 23 centres (gynaecology, infectious disease or STD clinics, or drug treatment centres) in 12 European countries; in 21 centres, follow-up was performed every 6 months (median follow-up: 2 years).

METHODS

Human papillomavirus (HPV) was detected at inclusion by Southern blot and PCR. The prevalence of squamous intraepithelial lesions (SIL), the incidence of SIL and regression from low-grade SIL were studied according to CD4 count after controlling for HPV detection results.

RESULTS

Compared with women with CD4 cell counts > 500 x 10(6)/l, women with CD4 cell counts < 200 x 10(6)/l had a twofold increase in both prevalence and incidence of SIL and in non-regression from untreated low-grade SIL; in addition, these women had a lower response rate to treatment of high-grade cervical intraepithelial neoplasia. The increase in SIL incidence associated with a low CD4 cell count was significant in women not receiving antiretroviral treatment (relative risk, CD4 cell count 200-499 x 10(6)/l, 1.9; CD4 cell count < 200 x 10(6)/l, 2.9; CD4 cell count > 500 x 10(6)/l, reference), whereas it was less marked and not statistically significant in treated women.

CONCLUSIONS

Severe HIV-related immunodeficiency strongly increases the risk of occurrence of SIL; antiretroviral treatment may reduce this risk, probably by restoring or at least preserving immune function.

Sexually transmitted infections in European HIV-infected women: incidence in relation to time from infection. European Study on the Natural History of HIV Infection in Women

OBJECTIVES

To investigate the prevalence and incidence of sexually transmitted infections (STI) in HIV-infected women in relation to time from infection and sexual behaviour.

DESIGN

The European study on the natural history of HIV infection in women is a prospective cohort study of 487 HIV-infected women with a known interval of seroconversion from 12 European countries.

METHODS

Incidence was measured with person-time methods. Generalized estimating equations analysis was used to determine risk factors for STI.

RESULTS

At entry, 15% of the women were diagnosed with at least one acute STI (chlamydial infection, trichomoniasis or gonorrhoea), 10% with at least one other STI (genital warts or genital ulcerations) and 13% with vaginal candidiasis. Although frequently diagnosed during follow-up, the occurrence of acute STI and vaginal candidiasis decreased, whereas the occurrence of other STI increased with ongoing time from HIV infection. Furthermore, women with a history of prostitution [relative risk (RR), 2.00; 95% confidence interval (95% CI), 1.20-3.33] and women with irregular condom use (RR, 7.74; 95% CI, 3.52-17.0) were at higher risk for an acute STI.

CONCLUSIONS

Although STI diagnoses were frequent, the occurrence of acute STI declined with time from infection which might be explained by changed sexual behaviour over time. The occurrence of other STI increased with time from HIV infection, presumably due to reactivation as a result of immunosuppression.

Metabolism and excretion of citalopram in man: identification of O-acyl- and N-glucuronides

The antidepressant citalopram (CT), a selective serotonin uptake inhibitor, was given in its labelled form, [14C]-CT, as a single oral dose in 50 ml aqueous solution (0.1 mmol/30 microCi/1.1 MBq) to four healthy male volunteers. Concentrations of radioactivity in whole blood and plasma were similar. The respective pharmacokinetic parameters were: Cmax = 214+/-41 and 246+/-69 nmol eq./litre, Tmax = 3 and 2 h, AUC = 18289+/-2959 and 14537+/-2883 nmol eq. h/litre, and t1/2 = 90.2+/-22.5 and 79.5 +/- 14.9 h respectively. A mean of 85.2 +/- 10.4% of the radioactive dose was recovered after 17 days of collection of excreta. The majority of radioactivity was excreted in urine (74.7+/-8.9%) and the remaining part in faeces (10.5+/-2.3%). The HPLC profile of urinary components showed that besides the known metabolites of citalopram, three glucuronides were present. The relative amounts of CT and its metabolites in urine collected for 7 days were: CT (26 %), N-demethyl-CT (DCT, 19%), N,N-didemethyl-CT (DDCT,9%), the N-oxide (7%), the quaternary ammonium glucuronide of CT (CT-GLN, 14%), the N-glucuronide of DDCT (DDCT-GLN, 6%), and the glucuronide of the acid metabolite (CT-acid-GLN, 12%) formed by N,N-dimethyl deamination of CT. CT-GLN was isolated using preparative chromatography and identified by LC-MS-MS and NMR. DDCT-GLN and CT-acid-GLN were identified by LC-MS. This study shows that protracted renal excretion represents the major route of elimination, with a small fraction voided with faeces. A considerable portion of the urinary excreted dose consists of N-glucuronides of CT and DDCT together with the O-acyl glucuronide of CT-acid.

Nitric oxide concentrations and cerebrospinal fluid parameters in an experimental animal model of Streptococcus pneumoniae meningitis

Streptococcus pneumoniae is a common cause of meningitis. Nitric oxide (NO) has been implicated in causing cerebral edema. Modulating NO production in cerebrospinal fluid (CSF) may have a role in the treatment of bacterial meningitis. Experimental S. pneumoniae meningitis was induced in a rabbit model to determine CSF parameters and NO concentrations. An electrochemical probe in the CSF throughout the 7-hour experiment monitored NO concentrations. The animals had S. pneumoniae (10(5)) injected intracisternally and incubated for 1 hour. Cerebrospinal fluid 200-300 microl was obtained by intracisternal puncture at zero, 2, 4, and 7 hours after drug administration to measure glucose, protein, and lactic acid by standard chemical methods. White blood cell count was measured by hemocytometry. Three groups of five animals were used-control (C), ceftriaxone (CTX), and ceftriaxone plus dexamethasone (CTX+D). Ceftriaxone concentrations in CSF were obtained by microdialysis and analyzed by high-performance liquid chromatography. Mean (+/- SEM) CSF white blood cell count was significantly higher at 2 hours in the C group than in the other two groups (C 7307 +/- 1302, CTX 605 +/- 345, CTX+D 730 +/- 43/mm3, p<0.002). Ceftriaxone induced a significant rise in protein at 4 hours compared with the other groups (C 364 +/- 107, CTX 1158 +/- 797, CTX+D 365 +/- 100 mg/dl, p<0.02). Cerebrospinal fluid lactic acid was significantly different at 4 and 7 hours between C and CTX+D groups (4-hr C 8.0 +/- 2.2, CTX+D 2.0 +/- 0.4 mmol/L, p<0.05; 7-hr C 10.2 +/- 2.4, CTX+D 2.8 +/- 0.8 mmol/L, p<0.01). Median NO concentrations were significantly elevated in the control group compared with the other two groups (C 11.7, CTX 6.8, CTX+D 6.5 micro, p<0.02 C vs CTX, p<0.01 C vs CTX+D). Average (+/- SEM) NO concentrations were significantly higher in the C group at 4 hours (18.1 +/- 0.4, CTX 5.8 +/- 1.8 microM, p<0.05; CTX+D 11.5 +/- 4.0 microM, p>0.05), whereas they did not rise significantly until 7 hours in the CTX group (CTX 18.7 +/- 0.7, C 8.9 +/- 0.4 microM, p=0.055; CTX+D 8.1 +/- 2.2 microM, p<0.05). These results indicate that ceftriaxone with or without dexamethasone significantly decreases lactic acid concentrations and white cell penetration into the CSF in an experimental model of S. pneumoniae meningitis. In addition, ceftriaxone induced a significant elevation in CSF protein. Median NO production in the CSF was significantly attenuated by ceftriaxone.

Comparison of the disposition of hepatically-generated morphine-3-glucuronide and morphine-6-glucuronide in isolated perfused liver from the guinea pig

PURPOSE

Humans and guinea pigs metabolise morphine extensively, forming the isomers morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in relatively similar ratios. Both metabolites are formed in the liver, and their greater polarity relative to the parent aglycone may limit their permeability across hepatic membranes. This study compared the disposition of hepatically-generated M3G and M6G in perfused livers isolated from guinea pigs.

METHODS

Livers were perfused at 30 ml/min in a non-recirculating manner with Krebs bicarbonate buffer containing morphine (6 to 7 microM). Perfusing medium, venous perfusate and bile were collected at regular intervals and concentrations of morphine, M3G and M6G determined by reversed-phase HPLC.

RESULTS

Concentrations of morphine, M3G and M6G in perfusate and the rates of biliary excretion of M3G and M6G were consistent between 20 and 50 min of perfusion. The mean (+/-s.d.) ratio for the rate of formation of M3G relative to M6G was 3.7 +/- 1.5. A mean 33 +/- 3% of morphine extracted by the liver was recovered as summed M3G and M6G. Of the M3G and M6G formed during a single passage, 19 +/- 11% and 9 +/- 9%, respectively, was excreted into bile; the values were significantly different (P = 0.002).

CONCLUSIONS

A greater fraction of hepatically-generated M3G excreted into bile compared to that for M6G reflects differences in their relative transport across sinusoidal and canalicular membranes of hepatocytes, possibly via carrier-mediated systems.

Setting the stage for health impact assessment

Defining health impact assessment as any combination of procedures or methods by which a proposed policy or program may be judged as to the effect(s) it may have on the health of a population, we make recommendations about how to evaluate the health impact of all government-initiated policies. Such health impact cannot be assessed in the absence of a conceptual or organizing framework that provides the requisite guideposts--population health goals and targets. Health impact assessment offers an approach to ensuring that governments' program and policy initiatives align, or are congruent with, the agreed-upon health goals. It suggests that proposed national policies should be supported or resisted on the basis of their probable influence on the health of populations. In the current Canadian national policy framework, however, there are no underpinnings on which to situate such a process. The specification of consensus goals and objectives with measurable targets can provide the requisite guideposts and benchmarks for health impact assessment. Such an undertaking can set the stage and provide the necessary foundation for an effective health impact assessment process.

Reductant-independent ATP hydrolysis catalyzed by homologous nitrogenase proteins from Azotobacter vinelandii and heterologous crosses with Clostridium pasteuranium

Reductant-independent ATPase activity was initiated and studied for Azotobacter vinelandii and Clostridium pasteuranium nitrogenase proteins (Av1, Cp1 and Av2, Cp2, 1 designating the iron molybdenum protein and 2 the iron protein) and their heterologous crosses by two methods: (1) allowing dithionite to be depleted from a normal assay in the presence of substrate levels of MgATP and (2) using reduced but reductant-free nitrogenase proteins in the presence of substrate levels of MgATP. In both cases, at a 1:1 protein ratio, MgATP is converted initially to MgADP with a specific activity of 400-500 nmol MgATP hydrolyzed/min.mg Av1, but in slower steps the MgADP is converted to AMP and, after 12 h, AMP is ultimately converted to adenosine. This reactivity requires the presence of both proteins, increases with increasing Av2/Av1 ratio, and is not a result of unique redox states of either protein. For Av1-Av2, ATP hydrolysis in the absence of Mg2+ occurred at nearly the same rate as reductant-dependent MgATP hydrolysis. Reductant-independent ATPase activity also occurred for the Av1-Cp2 and Cp1-Av2 heterologous crosses and was 2-fold and 18-fold slower than the Av1-Av2 or Cp1-Cp2 combinations. In both cases further hydrolysis of MgADP to AMP and AMP to adenosine occurred. A unique nucleotide hydrolysis system is apparently operating in the complex formed between the two nitrogenase proteins in the absence of reductant. The relationship between the reductant-independent and reductant-dependent activities of nitrogenase catalysis is explored.

Metal ion binding to apo, holo, and reconstituted horse spleen ferritin

The binding of Cd2+, Zn2+, Cu2+, Ni2+, Co2+, Mn2+, and Mg2+ to apo, holo, reconstituted horse spleen ferritin (HoSF), and native holo HoSF with phosphate removed was measured by gel-exclusion chromatography. Three classes of strong binding interactions (Kd < 10(-7) M) with apo HoSF at pH 7.5 were found for the various M2+ studied: high stoichiometric binding (30-54 M2+/HoSF) for Cd2+, Zn2+, Cu2+, with two protons released per metal bound; intermediate binding (16 M2+/HoSF) for Ni2+ and Co2+, with one proton released per metal bound; and low levels of binding (2-12 M2+/HoSF) for Mn2+, Mg2+, and Fe2+, with < 0.5 protons released per metal bound. M2+ binding to apo HoSF was nearly abolished at pH 5.5, except for Fe2+ and Cu2+, which remained unaffected by pH alteration. Holo HoSF bound much higher levels of M2+, a result directly attributable to the presence of phosphate binding sites. This conclusion was confirmed by decreased binding of M2+ to HoSF reconstituted in the absence of phosphate and by native holo HoSF with phosphate chemically removed. The binding of Cd2+ to apo HoSF was 54 per HoSF, but in the presence of developing core, the amount bound decreased to about 30 Cd2+/HoSF. This result indicated that Cd2+ and developing core were competing for the same sites on the HoSF interior, suggesting that 24 of the Cd2+ were bound to the inside surface. No other M2+ studied bound to the interior of HoSF by this criterion. Several of the M2+ appeared to bind strongly to the phosphate-free mineral core surface in reconstituted HoSF.

Intraoperative ultrasonography in detection of hepatic metastases from colorectal cancer

PURPOSE

This study was designed to compare diagnostic accuracies of measuring liver enzymes, preoperative ultrasonography, surgical examination, and intraoperative ultrasonography for detection of liver metastases from colorectal cancer.

METHODS

Blind, prospective comparisons of diagnostic examinations mentioned above were performed in 295 consecutive patients with colorectal cancer. An experienced ultrasonologist performed the preoperative examinations, and results were unknown to the other experienced ultrasonologist who performed the intraoperative examinations. The latter, also was unaware of the findings by the surgeon. The presence of metastases was further assessed by ultrasonography three months postoperatively, as well as additional surgery and liver biopsy in some of the patients.

RESULTS

The sensitivity of intraoperative ultrasonography (62/64) was significantly superior to that of surgical exploration (54/64) and that of preoperative ultrasonography (45/64). The lowest sensitivity was presented by liver enzymes. Bilobar metastases were detected in 42 of 46 patients by intraoperative ultrasonography but in only 33 patients by the surgeon. Intraoperative ultrasonography demonstrated the highest specificity of all examinations.

CONCLUSIONS

Intraoperative ultrasonography reduces the number of patients with liver metastases from being subjected to superfluous or even harmful liver surgery, and it may increase the number in whom liver surgery will prolong life.

Use of iotrolan versus ethiodized poppy-seed oil in hysterosalpingography

PURPOSE

To compare use of the water-soluble, nonionic isosmolar dimer iotrolan with that of ethiodized poppy-seed oil in hysterosalpingography with regard to side effects, diagnostic quality, and postexamination conception rates.

MATERIALS AND METHODS

A prospective randomized design was used in a study of 245 patients. Questionnaires and patient records were used to acquire information. All examinations and ratings of diagnostic quality were performed by the same three investigators. Statistical calculations were performed with the chi 2 test, including the Mantel-Haenszel variant, and the Kruskal-Wallis test.

RESULTS

No substantial differences between the contrast media could be detected concerning pain during the procedure, delayed pain, or postexamination bleeding. Visualization of the uterine cavity and ampullary rugae was markedly better with use of iotrolan. The postexamination conception rate was higher with use of ethiodized poppy-seed oil (24.0%) but was not significantly different statistically (P = .44) from that seen after use of iotrolan (19.8%).

CONCLUSION

The authors believe the use of iotrolan is preferable to that of ethiodized poppy-seed oil.