Role of hydrogen sulfide in the pain processing of non-diabetic and diabetic rats.

Hydrogen sulfide (H2S) is a gasotransmitter endogenously generated from the metabolism of L-cysteine by action of two main enzymes called cystathionine ß-synthase (CBS) and cystathionine γ-lyase (CSE). This gas has been involved in the pain processing and insulin resistance produced during diabetes development. However, there is no evidence about its participation in the peripheral neuropathy induced by this metabolic disorder. Experimental diabetes was induced by streptozotocin (50mg/kg, i.p.) in female Wistar rats. Streptozotocin injection increased formalin-evoked flinching in diabetic rats as compared to non-diabetic rats after 2 weeks. Peripheral administration of NaHS (an exogenous donor of H2S) and L-cysteine (an endogenous donor of H2S) dose-dependently increased flinching behavior in diabetic and non-diabetic rats. Contrariwise, hydroxylamine (HA, a CBS inhibitor) and DL-propargylglycine (PPG, a CSE inhibitor) decreased formalin-induced nociceptive behavior in both experimental groups. In addition, an ineffective dose of HA and PPG partially prevented the L-cysteine-induced hyperalgesia in diabetic and non-diabetic rats. Interestingly, HA and PPG were three order of magnitude more potent in diabetic rats respect to non-diabetic rats, whereas NaHS was ten times more potent in the streptozotocin-diabetic group. Nine to 11 weeks after diabetes induction, tactile allodynia was observed in the streptozotocin-injected rats. On this condition, subcutaneous administration of PPG or HA reduced tactile allodynia in diabetic rats. Paradoxically, H2S levels were decreased in nerve sciatic, dorsal root ganglion and spinal cord, but not paw nor blood plasma, during diabetes-associated peripheral neuropathy development. Collectively, results suggest that H2S synthesized by CBS and CSE participate in formalin-induced nociception in diabetic and non-diabetic rats, as well as; in tactile allodynia in streptozotocin-injected rats. In addition, data seems to indicate that diabetic rats are more sensible to H2S-induced hyperalgesia than normoglycemic rats.

B-vitamin mixture improves the analgesic effect of diclofenac in patients with osteoarthritis: a double blind study.

According to the high consumption of the mixture of B vitamins and diclofenac in several countries, this combination has constituted a frequently used option in pain therapy from inflammatory origin. Although the evidence obtained from inflammatory pain animal models has shown the existence of analgesic synergy between diclofenac and the B vitamins mixture, the corresponding clinical evidence is scarce. A double-blind, randomized clinical trial study was designed to characterize the analgesic effect and safety of diclofenac and B vitamins against diclofenac alone in patients with severe osteoarthritis. Forty eight patients programmed to total knee arthroplasty with a pain level ≥7 in a 1-10 cm visual analogue scale were allocated to receive a single intramuscular injection of sodium diclofenac (75 mg) alone or combined with thiamine (100 mg), pyridoxine (100 mg) and cyanocobalamin (5 mg), and the pain level was evaluated during 12 h post-injection. Diclofenac+B vitamins mixture showed a superior analgesic effect during the assessed period and also a better assessment of the pain relief perception by patients than diclofenac alone. This study constitutes a clinical support on the improvement of the analgesic effect of diclofenac by B vitamins in patients with osteoarthritis programmed to total knee arthroplasty, as a clinical model of inflammatory pain.

Ketorolac tromethamine improves the analgesic effect of hyoscine butylbromide in patients with intense cramping pain from gastrointestinal or genitourinary origin.

The symptomatic treatment of pain associated with spasm of gastrointestinal or genitourinary origin can include the use of spasmolytic agents and/or non-steroidal anti-inflammatory drugs. However, the evidence of a superior effectiveness of combination in comparison with individual drugs is scarce and controversial. A double-blind, randomised, clinical trial study was designed to characterize the analgesic effect and safety of ketorolac and hyoscine butylbromide against hyoscine butylbromide alone in patients with ambulatory acute cramping pain of gastrointestinal and genitourinary origin. 160 patients with a pain level ≥4 in a 1-10 cm visual analogue scale were allocated to receive a fixed dose of ketorolac/hyoscine butylbromide (10 mg/20 mg) or hyoscine butylbromide (20 mg) alone at 6 h intervals, during a 48 h period. Both treatments were similarly effective when compared as a whole or when groups were classified by pain origin. Conversely, when treatments were grouped by pain intensity, ketorolac/hyoscine butylbromide combination showed a significant better pain relief profile than hyoscine butylbromide alone in pain intensity ≥7, but not <7. Data indicate that the oral ketorolac/hyoscine butylbromide mixture could be a better option than hyoscine butylbromide alone in the treatment of some acute intense cramping painful conditions.

Pharmacokinetics of lidocaine and its metabolite as a hepatic function marker in dogs.

Measuring hepatic metabolic function is critical for detection and treatment of liver failure. Several tests have been widely used to characterize the integrity of liver; however, they do not evaluate the metabolic function of the organ, most requiring multiple blood draws. The purpose of this study was to establish if the ratio of the lidocaine metabolite monoethylglycinexylidide (MEGX) divided by lidocaine concentration at 30 min post intravenous lidocaine administration is a good marker of metabolic activity of the liver. Nine healthy and two partially hepatectomized and auto-transplanted dogs were included in the study. A single 1.5 mg/kg intravenous dose of lidocaine and serum samples were obtained at selected times for 150 minutes. Serum concentrations of lidocaine and MEGX were determined by a validated high-performance liquid chromatographic method. Pharmacokinetic parameters were obtained by non-compartmental methods and ratio of AUC of MEGX divided by AUC of lidocaine was determined for each dog. This ratio was correlated with the ratio of the concentration of the compounds obtained 30 minutes after drug administration. A good concordance was obtained, suggesting that ratio obtained with a single sample may be useful to predict the hepatic metabolism function. To validate the test, dogs hepatectomized and auto-transplanted were plotted and the results obtained were within the values obtained in healthy dogs. These results suggest that ratio of MEGX/lidocaine obtained 30 min after administration could be a good marker of hepatic metabolic function.

The role of peripheral 5-HT1A, 5-HT1B, 5-HT1D, 5-HT1E and 5-HT1F serotonergic receptors in the reduction of nociception in rats.

This study assessed the possible antinociceptive role of peripheral 5-HT(1) receptor subtypes in the rat formalin test. Rats were injected into the dorsum of the hind paw with 50 microl of diluted formalin (1%). Nociceptive behavior was quantified as the number of flinches of the injected paw. Reduction of flinching was considered as antinociception. Ipsilateral, but not contralateral, peripheral administration of the 5-HT(1) receptor agonists R(+)-UH-301 (5-HT(1A); 0.1-3 microg/paw), CGS-12066A (5-HT(1B); 0.01-0.3 microg/paw), GR46611 (5-HT(1B/1D); 0.3-10 microg/paw), BRL54443 (5-HT(1E/1F); 3-300 microg/paw) or LY344864 (5-HT(1F); 3-300 microg/paw) significantly reduced formalin-induced flinching. The corresponding vehicle was devoid of any effect by itself. The local antinociceptive effect of R(+)-UH-301 (0.3 microg/paw) was significantly reduced by WAY-100635 (30-100 microg/paw; a 5-HT(1A) receptor antagonist). Moreover, the antagonists GR55562 (30-100 microg/paw; 5-HT(1B/D)) or SB224289 (30-100 microg/paw; 5-HT(1B)) dose-dependently reduced the antinociceptive effect of CGS-12066A (0.3 microg/paw) whereas GR55562 (30-100 microg/paw) or BRL15572 (30-100 microg/paw, 5-HT(1D)) reduced the antinociceptive effect of GR46611 (0.3 microg/paw). Interestingly, the effects of BRL54443 and LY344864 (300 microg/paw each) were partially reduced by methiothepin, but not by the highest doses of WAY-100635, SB224289 or BRL15572. The above antagonists did not produce any effect by themselves. These results suggest that peripheral activation of the 5-HT(1A,) 5-HT(1B), 5-HT(1D), 5-HT(1F) and, probably, 5-HT(1E) receptor subtypes leads to antinociception in the rat formalin test. Thus, the use of selective 5-HT(1) receptor agonists could be a therapeutic strategy to reduce inflammatory pain.

Comparative bioavailability of two oral formulations of levofloxacin in healthy Mexican volunteers.

OBJECTIVE: To assess the bioequivalence of two levofloxacin 500 mg tablets marketed in Mexico. MATERIAL AND METHODS: The clinical investigation was designed as a randomized, open-labeled, two-part, two-treatment, two-period crossover study, in 27 healthy male volunteers. 1 tablet of each formulation was administered with 200 ml of water after 10 h overnight fast. After dosing, serial blood samples were collected for a period of 24 h. Plasma concentrations were determined by a validated high-performance liquid chromatographic method and pharmacokinetic parameters were obtained by non-compartmental approach. Analysis of variance (ANOVA) was carried out using log-transformed AUClast, AUC yen and Cmax and untransformed tmax, and 90% confidence intervals for AUClast, AUC yen and Cmax were calculated. If the 90% confidence intervals (CI) for AUClast, AUC yen and Cmax fell fully within the interval 80 - 125%, the bioequivalence of the two formulations was established. RESULTS: The means (test and reference) for AUClast were 58.869 and 56.297 microg x h/ml, for AUC yen were 63.456 and 60.748 microg x h/ml and for Cmax were 8.691 and 8.445 microg/ml. The geometric mean ratios of the test formulation to reference formulation for AUClast, AUC yen and Cmax (CI) were 104.53% (102.73 - 106.36%), 104.37% (102.04 - 106.75%) and 103.45% (95.57 - 111.97%), respectively. All 90% CI for AUClast, AUC yen and Cmax fell within the Mexican Federal Commission for Prevention of Sanitary Risks (COFEPRIS) accepted bioequivalence range of 80 - 125%. CONCLUSIONS: Based on the results, the formulations tested are bioequivalent.

Oral pharmacokinetics of meloxicam in the rat using a high-performance liquid chromatography method in micro-whole-blood samples.

The pharmacokinetics of meloxicam, a potent analgesic and antiinflammatory drug used in several rheumatic diseases, has been studied in rats that received oral doses of 3.2, 5.6 or 10 mg/kg of meloxicam. Blood samples were obtained at selected times during 24 h after administration, and meloxicam concentrations were determined by a validated high-performance liquid chromatography (HPLC) method, using micro-whole-blood samples, developed in our laboratory. After administration of meloxicam, blood concentrations increased reaching a dose-dependent maximal concentration in about 2 h. Then, concentrations decayed with a half-life of 9 h. An increase in C(max) and AUC as a function of the dose was observed, and no statistically significant difference was observed in AUC/dose or C(max)/dose between doses. However, linearity could not be concluded because of the wide variability observed.

Analgesic efficacy and bioavailability of ketorolac in postoperative pain: a probability analysis.

BACKGROUND: The analgesic efficacy and bioavailability of 30 mg intramuscular ketorolac was studied in 24 patients with severe or very severe postoperative pain. METHODS: Pain and pain relief were determined by a five-point verbal rating scale and data were submitted to a probability analysis. Ketorolac plasma levels were determined by high-performance liquid chromatography. RESULTS: Two patients chose not to finish the study; 22 patients completed the study achieving at least good pain relief. Of these 22 patients, 13 reached complete pain relief. Ketorolac was rapidly absorbed. Notwithstanding, pain relief increased gradually, showing considerable delay with regard to plasma concentrations. Analysis of the probability-time curves revealed that 25% of the patients obtained moderate pain relief at 7 min after ketorolac administration, 50% at 11 min, 75% at 29 min, and 95% at 60 min. Good pain relief was achieved in 25, 50, and 75% of the patients at 1.1, 1.8, and 2.7 h, respectively. Complete pain relief was achieved in 25% and 50% of the patients at 2.6 h and 3.7 h, respectively. The probability of exhibiting an acceptable pain relief in responsive patients for more than 5 h was 0.97. No serious side effects were detected. CONCLUSIONS: Results show that 30 mg intramuscular ketorolac is an adequate treatment for postoperative pain in the Mexican population. Therefore, the use of higher doses is not justified. Due to gradual installation of analgesia, administration of additional analgesic medication before 1 h is not recommended.

Pharmacokinetic-pharmacodynamic modeling: why?

At present, pharmacokinetic-pharmacodynamic (PK-PD) modeling has emerged as a major tool in clinical pharmacology to optimize drug use by designing rational dosage forms and dosage regimes. Quantitative representation of the dose-concentration-response relationship should provide information for prediction of the level of response to a certain level of drug dose. Several mathematical approaches can be used to describe such relationships, depending on the single dose or the steady-state measurements carried out. With concentration and response data on-phase, basic models such as fixed-effect, linear, log-linear, E(MAX), and sigmoid E(MAX) can be sufficient. However, time-variant pharmacodynamic models (effect compartment, acute tolerance, sensitization, and indirect responses) can be required when kinetics and response are out-of-phase. To date, methodologies available for PK-PD analysis barely suppose the use of powerful computing resources. Some of these algorithms are able to generate individual estimates of parameters based on population analysis and Bayesian forecasting. Notwithstanding, attention must be paid to avoid overinterpreted data from mathematical models, so that reliability and clinical significance of estimated parameters will be valuable when underlying physiologic processes (disease, age, gender, etc.) are considered.

Comparative bioavailability evaluation of two cyclosporine oral formulations in healthy Mexican volunteers.

BACKGROUND: The use of conventional cyclosporine (Sandimmune) requires great care, as this drug exhibits a narrow therapeutic index and wide interindividual variability in its pharmacokinetics. Recently, a new microemulsion formulation (Neoral) was developed. With this formulation, cyclosporine is absorbed at the small intestine without the presence of bile. Therefore, the objective of this study was to compare the bioavailability of cyclosporine after the administration of conventional and microemulsion formulations in healthy Mexican volunteers in order to approach the optimal dosage regimen of microemulsion in the Mexican population. METHODS: The trial was conducted using 23 healthy volunteers according to a randomized crossover design. Volunteers received one 7.5-mg/kg dose as each formulation, with a 1-week washout period between treatments. Blood samples of 0.5 mL were obtained according to the following schedule: 0, 0.5, 1, 2, 3, 4, 5, 6, 8, 12, and 24 h after medication. RESULTS: These indicated that Cmax and AUC0-24 values were higher with the microemulsion than with the conventional formulation. CONCLUSIONS: The microemulsion had a better absorption profile than the conventional formulation, because plasma levels with the conventional formulation demonstrated oscillations rather than reflecting an erratic absorption. Lower doses of the microemulsion are required to obtain Cmax values similar to those obtained with conventional cyclosporine.

Influence of sex on the pharmacokinetics of tolmetin in the rat.

The purpose of this study was to investigate sex-related differences in the pharmacokinetics of tolmetin, a potent nonsteroidal anti-inflammatory drug, in the rat. Male and female Wistar rats received oral tolmetin at two dose levels, 3.2 and 10 mg/kg. Blood samples were drawn at selected times after drug administration, and tolmetin concentration in whole blood was determined. Tolmetin was rapidly absorbed in all cases. C(max) increased with the dose, but was similar in both sexes. Notwithstanding, tolmetin half-life was significantly prolonged in females compared with males. As a result of the prolonged half-life, area under the curve values were significantly higher in females than in males. Tolmetin clearance was significantly reduced in females. The present results strongly suggest sex-related differences in the pharmacokinetics of tolmetin in the rat. Tolmetin elimination appears to be impaired in females, compared with males. The existence of sex-related differences in tolmetin pharmacokinetics in other species, including humans, requires further investigation.

Pharmacokinetic-pharmacodynamic modeling of tolmetin antinociceptive effect in the rat using an indirect response model: a population approach.

The relationship between the pharmacokinetics and the antinociceptive effect of tolmetin was characterized by an indirect model using a population approach. Animals received an intra-articular injection of uric acid in the right hindlimb to induce its dysfunction. Once dysfunction was complete, rats received an oral tolmetin dose of 1, 3.2, 10, 31.6, 56.2 or 100 mg/kg and antinociceptive effect and blood tolmetin concentration were simultaneously evaluated. Tolmetin produced a dose-dependent recovery of functionality, which was not directly related to blood concentration. An inhibitory indirect response model was used based on these response patterns and the fact that tolmetin reduced nociception by inhibiting prostaglandin synthesis. Pharmacokinetic (PK) and pharmacodynamic (PD) data were simultaneously fitted using nonlinear mixed effects modeling (NONMEM) to the one-compartment model and indirect response model. The individual time courses of the response were described using Bayesian analysis with population parameters as a priori estimates. There was good agreement between the predicted and observed data. Population analysis yielded a maximal inhibition of the nociceptive response of 76% and an IC50 of 9.22 micrograms/ml. This IC50 is similar to that for tolmetin-induced prostaglandin synthesis inhibition in vitro (3.0 micrograms/ml). The present results demonstrate that mechanism-based PK-PD analysis using a population approach is useful for quantitating individual responses as well as reflecting the actual mechanism of action of a given drug in vivo.

Determination of diclofenac in micro-whole blood samples by high-performance liquid chromatography with electrochemical detection. Application in a pharmacokinetic study.

A rapid and sensitive method for the determination of diclofenac (CAS 15307-86-5) in whole blood samples by high-performance liquid chromatography with amperometric detection has been developed. This method was then used to study the pharmacokinetics of oral diclofenac sodium in the rat. The method includes a single extraction of acidified whole blood with ethyl acetate. Extracts were analyzed on a reversed-phase column eluted with a mixture of acetonitrile and 0.075 mol/l sodium acetate solution (pH 3.3) and detected amperometrically at + 1.1 V against Ag/AgCl. Retention times for diclofenac and the internal standard (naproxen) were 3.5 and 6 min, respectively. The method was linear in the range of 25 to 2000 ng/ml and the detection limit of the method was 10 ng/ml, using 100 microliters of whole blood sample. Employing this method, the oral pharmacokinetics of diclofenac in the rat was studied. Wistar male rats received an oral dose of 1, 3.2 or 10 mg/kg of diclofenac and blood samples were drawn at selected times during 12 h. After administration of diclofenac, a rapid increase of circulating concentrations was observed reaching a maximum in about 10 min. Then concentration decayed with a half-life of about 15 h. It is concluded that the method here reported is adequate for realization of pharmacokinetic studies of diclofenac in small species.

Pharmacokinetic-pharmacodynamic modeling of the antinociceptive effect of diclofenac in the rat.

The relationship between the pharmacokinetics and the antinociceptive effect of diclofenac was evaluated using the pain-induced functional impairment model in the rat. Male Wistar rats were injected with uric acid in the knee joint of the right hind limb, which induced its dysfunction. Once the dysfunction was complete, animals received a p.o. dose of 0.56, 1, 1.8, 3.2, 5.6 or 10 mg/kg of sodium diclofenac, and the antinociceptive effect and drug blood concentration were simultaneously evaluated at selected times for a period of 6 h. Diclofenac produced a dose-dependent antinociceptive effect, measured as a recovery of the functionality of the injured limb. However, the onset of the antinociceptive effect was delayed with respect to blood concentrations. Moreover, the effect lasted longer than expected from pharmacokinetic data. Therefore, when functionality index was plotted against diclofenac blood concentration, an anticlockwise hysteresis loop was observed for all doses. Hysteresis collapse was achieved using the effect-compartment model, and the plot of functionality index against diclofenac concentration in the effect-compartment data was well fitted by the sigmoidal Emax model. Our data suggest slow equilibrium kinetics between diclofenac concentration in blood and at its site of action, which leads to a delayed onset of the antinociceptive effect as well as a longer duration of the response resulting from drug accumulation in synovial fluid.

Bioavailability of oral cyclosporine in healthy Mexican volunteers: evidence for interethnic variability.

The existence of population variations in cyclosporine pharmacokinetics could be expected, as this drug, similar to nifedipine, is biotransformed by cytochrome P-450 subfamily 3A4, and the existence of interethnic variability in nifedipine disposition has been demonstrated previously. The bioavailability of oral cyclosporine was studied in 23 healthy Mexican volunteers receiving 7.5-mg/kg doses of cyclosporine. Blood samples were drawn over 24 hours, and concentration of cyclosporine in whole blood was determined by a radioimmunoassay using monoclonal antibodies specific for the unchanged drug. The bioavailability of cyclosporine exhibited wide interindividual variability. Maximum concentration (Cmax) ranged from 528 ng/mL to 2,689 ng/mL, area under the concentration-time curve (AUC) ranged from 6,550 ng.hr/mL to 18,562 ng.hr/mL, and time to reach Cmax (tmax) ranged from 1 to 8 hours. Half-life (t1/2) exhibited less important variations, ranging from 4.4 to 9.1 hours. The bioavailability of oral cyclosporine in Mexicans was higher than that reported for white populations under similar conditions. The present results suggest the existence of interethnic variability in the pharmacokinetics of cyclosporine, as is the case with nifedipine.