Population pharmacokinetics and exposure-response of trilaciclib in extensive-stage small cell lung cancer and triple-negative breast cancer

AIMS

Trilaciclib is a first-in-class, intravenous cyclin-dependent kinase 4/6 inhibitor that provides multilineage protection from chemotherapy-induced myelosuppression. This analysis aimed to characterize the population pharmacokinetics (PK) of trilaciclib, identify potential covariates influencing trilaciclib PK, and evaluate exposure-response relationships in extensive-stage small cell lung cancer (ES-SCLC) and triple-negative breast cancer (TNBC) trials.

METHODS

Population PK analysis was performed using data from healthy volunteers (n = 72), patients with ES-SCLC (n = 111) and patients with TNBC (n = 14). Exposure-response analyses were conducted to investigate the impact of trilaciclib exposure (AUC) on myeloprotective efficacy, antitumour efficacy and safety. Logistic regression and Cox regression models were used for binary and time-to-event endpoints, respectively.

RESULTS

Trilaciclib PK was described by a three-compartment model. Sex, body surface area, baseline albumin concentration and age were identified as significant covariates on trilaciclib PK but did not have clinically relevant impact on exposure. Based on exposure-response analyses, lower and higher exposures of trilaciclib at clinical doses (200-280 mg/m² ) were associated with similar myeloprotective effects. Trilaciclib exposure did not impact the antitumour effects of chemotherapy. Higher exposure to trilaciclib was associated with higher probabilities of headache, phlebitis/thrombophlebitis and injection site reactions.

CONCLUSION

No dose adjustments are required based on the covariates tested. Trilaciclib resulted in optimal myeloprotective effects with no impact on antitumour effects of chemotherapy. However, higher exposure increased the probabilities of adverse events. The data further support selection of the recommended phase 2 dose (trilaciclib 240 mg/m² ).

Population pharmacokinetics and exposure-response analyses of teduglutide in adult and pediatric patients with short bowel syndrome

Teduglutide is a recombinant analog of human glucagon‐like peptide‐2 that regulates the functional and structural integrity of the cells lining the gastrointestinal tract. Teduglutide is approved for the treatment of patients with short bowel syndrome (SBS) who are dependent on parenteral support (PS). Population pharmacokinetic (PK) and exposure‐response analyses were performed to support teduglutide dosing in patients with SBS. The analysis included 219 patients with SBS (aged <1 year, 5 patients; 1–11 years, 86 patients; 12–17 years, 8 patients; 18–79 years, 120 patients), and 259 non‐SBS subjects (including healthy volunteers and subjects with renal or liver impairment). A one‐compartment model with first‐order absorption and linear elimination adequately characterized the PKs of teduglutide. In patients with SBS, the apparent clearance (CL/F), volume of distribution (V/F), and elimination half‐life of teduglutide were 16.0 L/h, 33.9 L, and 1.47 h, respectively. CL/F depended on body weight and renal function, and V/F depended on body weight and age. Maximum concentration (C_max) of teduglutide was similar in adult and pediatric patients, and in Japanese and non‐Japanese patients. A time‐ and exposure‐response model dependent on the C_max of teduglutide adequately characterized the reduction in PS over more than 2 years of treatment. Daily dosing of 0.05 mg/kg teduglutide resulted in a maximum reduction in PS of 5.76 L/week. Higher C_max values were associated with a more important reduction in PS over time. Adult and pediatric patients with SBS presented similar PKs and response to teduglutide.

Population Pharmacokinetics and Exposure-Response Analyses to Guide Dosing of Icatibant in Pediatric Patients With Hereditary Angioedema

Elevated bradykinin levels are responsible for the development of clinical symptoms in patients with hereditary angioedema (HAE). Icatibant is a bradykinin type 2 receptor antagonist indicated for the acute treatment of HAE attacks. A population modeling and simulation approach was used to examine sources of variability impacting icatibant pharmacokinetics (PK) and provide guidance on icatibant dosing in pediatric patients with HAE. An exposure‐response analysis was performed for the time to onset of symptom relief (TOSR). Data from 141 adults (133 healthy, 8 with HAE) who received subcutaneous icatibant 30 mg and 31 pediatric patients with HAE who received 0.4 mg/kg (capped at 30 mg) were included in the analysis. Icatibant PK was described by a 2‐compartment model with linear elimination. Complete absorption of icatibant was expected within 1 hour of dosing. The apparent clearance and central volume of distribution were 15.4 L/h and 20.4 L, respectively. Icatibant PK was mainly dependent on body weight. The mean TOSR was very short (1.38 hours). A flat exposure‐response was observed, confirming that the relationship plateaued at the level of exposure observed in pediatric patients. Simulations confirmed that weight band–based dosing regimens (10 mg [12‐25 kg], 15 mg [26‐40 kg], 20 mg [41‐50 kg], 25 mg [51‐65 kg], and 30 mg [>65 kg]) resulted in exposure similar to the 0.4‐mg/kg dose. This analysis showed that icatibant undergoes rapid absorption, reaches levels required for therapeutic response, and promptly relieves HAE symptoms. A weight band–based dosing regimen is appropriate in pediatric patients with HAE.

Pharmacokinetics, Pharmacodynamics, and Exposure-Response of Lanadelumab for Hereditary Angioedema

Hereditary angioedema (HAE) with C1 inhibitor deficiency is a rare disorder characterized by unpredictable, potentially life‐threatening recurrent angioedema attacks. Lanadelumab is a fully human monoclonal antibody with selective binding to active plasma kallikrein, and prevents the formation of cleaved high molecular weight kininogen (cHMWK) and bradykinin, thereby preventing HAE attacks. The clinical pharmacology of lanadelumab was characterized following subcutaneous administration in 257 subjects (24 healthy subjects and 233 patients with HAE). The pharmacokinetics of lanadelumab were described using a one‐compartment model with first‐order rate of absorption and linear clearance, showing slow absorption and a long half‐life (14.8 days). A covariate analysis retained body weight and health status on apparent clearance (CL/F) and body weight on volume of distribution (V/F). Population estimates of CL/F and V/F were 0.0249 L/hour (0.586 L/day) and 12.8 L, respectively. An indirect‐response Imax model showed 53.7% maximum suppression in cHMWK formation with a low potential for interactions with concomitant medications (analgesic, anti‐inflammatory, and antirheumatic medications). A 300 mg dose administered Q2W was associated with a mean steady‐state minimum concentration (C_min,ss; 25.4 μg/mL) that was ~ 4.5‐fold higher than the half‐maximal inhibitory concentration for cHMWK reduction (5.71 μg/mL). Exposure‐response analyses suggest that 300 mg Q2W dosing was associated with a significantly reduced HAE attack rate, prolonged time to first attack after treatment initiation, and lower need for concomitant medications. The response was comparable across patient body weight groups. Findings from this analysis support the dosing rationale for lanadelumab to prevent attacks in patients with HAE.

A randomized, double-blind, placebo-controlled, pharmacokinetic and pharmacodynamic study of a fixed-dose combination of phentermine/topiramate in adolescents with obesity

AIMS

To assess the pharmacokinetic (PK) and pharmacodynamic characteristics of VI-0521, a fixed-dose combination of immediate-release phentermine (PHEN) and extended-release topiramate (TPM) in adolescents aged 12 to 17 years with obesity, and to report weight loss and adverse events using this drug combination.

MATERIALS AND METHODS

This was a multicentre, randomized, double-blind, parallel-design, placebo-controlled study in adolescents with obesity. A total of 42 adolescents were randomly assigned in a 1:1:1 ratio to placebo, or to a mid-dose (PHEN/TPM 7.5 mg/46 mg), or a top-dose (PHEN/TPM 15 mg/92 mg) of VI-0521. A total of 26 adolescents were included in the PK analysis (14 from the mid-dose group and 12 from the top-dose group).

RESULTS

On day 56, arithmetic means of terminal elimination half-life, apparent clearance (CL/F) and apparent central volume of distribution (Vc/F) were consistent across dose levels for both PHEN and TPM. Arithmetic means of CL/F and Vc/F for PHEN and TPM administered as a combination in adolescents with obesity were within 10% to 30% of those previously assessed in adults with obesity enrolled in phase II and III studies. A higher proportion of adolescents in both the mid- and top-dose groups (13.3% and 50.0%, respectively) compared with placebo (0.0%) reached ≥5% weight loss at day 56. The least squares (LS) mean change in systolic blood pressure from baseline to day 56 was -5.2 mmHg for the placebo group, -2.5 mmHg for the mid-dose group, and - 5.5 mmHg for the top-dose group. The LS mean change in diastolic blood pressure from baseline to day 56 was -2.4 mmHg for the placebo group, +3.8 mmHg for the mid-dose group, and + 2.0 mmHg for the top-dose group. Participants in the top-dose group had increases in heart rate from baseline of 4.1 bpm, while participants in the mid-dose group experienced a mean decrease in heart rate of 4.5 bpm at day 56. Both PHEN/TPM dose combinations were safe and well tolerated.

CONCLUSIONS

Treatment of adolescents with obesity using a fixed-dose combination of PHEN/TPM for 8 weeks resulted in exposure to PHEN and TPM that was comparable to that observed in adults, statistically significant weight loss, and a tolerable safety profile. These data indicate that both mid- and top-dose levels are appropriate for longer-term safety and efficacy studies in adolescents.

Population Pharmacokinetic-Pharmacodynamic Model of Serum Transthyretin Following Patisiran Administration

Hereditary transthyretin-mediated amyloidosis is an inherited, rapidly progressive, life-threatening disease caused by mutated transthyretin (TTR) protein. Patisiran is a small interfering RNA (siRNA) formulated in a lipid nanoparticle that inhibits hepatic TTR protein synthesis by RNA interference. We have developed an indirect-response pharmacokinetic-pharmacodynamic model relating plasma siRNA (ALN-18328) levels to serum TTR reduction across five clinical studies. A sigmoidal function described this relationship, with estimated Hill coefficient of 0.548, and half maximal inhibitory concentration (IC₅₀), IC₈₀, and IC₉₀ values of 9.45, 118.5, and 520.5 ng/mL, respectively. Following patisiran 0.3 mg/kg every 3 weeks (q3w), steady-state plasma ALN-18328 exposures were between IC₈₀ and IC₉₀, yielding average serum TTR reductions of 80%-90% from baseline. Covariate analysis indicated similar TTR reduction across evaluated intrinsic and extrinsic factors, obviating the need for dose adjustment. Modeling results support the recommended patisiran dosing schedule of 0.3 mg/kg q3w, with a maximum dose of 30 mg for patients weighing ≥100 kg.

Population Pharmacokinetics and Exposure-Response Analyses for CPX-351 in Patients With Hematologic Malignancies

CPX-351, a dual-drug liposomal encapsulation of cytarabine and daunorubicin at a synergistic ratio, is approved in the United States for adults with newly diagnosed therapy-related acute myeloid leukemia or acute myeloid leukemia with myelodysplasia-related changes. Population pharmacokinetics analyses were performed using nonlinear mixed-effect modeling on pooled data from 3 clinical studies, and the impact of CPX-351 exposures on efficacy and safety was assessed. The pharmacokinetics of cytarabine and daunorubicin were described using 2-compartment models with linear elimination. None of the evaluated covariates had a clinically significant impact on plasma exposure to total cytarabine or daunorubicin, while bilirubin and formulation showed statistically significant effects on pharmacokinetic parameters of cytarabine and daunorubicin, respectively. In patients with mild/moderate renal impairment or serum bilirubin ≤3 mg/dL, plasma exposures to cytarabine and daunorubicin following CPX-351 were within the variability range for patients with normal kidney function or serum bilirubin levels. Exposure-response analysis demonstrated that better efficacy outcomes were associated with higher CPX-351 exposure quartiles. Early mortality rates in all CPX-351 exposure quartiles were lower vs the 7 + 3 control group, and lower mortality rates were associated with higher exposure quartiles. A trend toward greater frequency of grade 3 treatment-emergent adverse events (but not grade 4/5 events) was observed at higher CPX-351 exposure quartiles. Overall, the population pharmacokinetic analyses indicate no adjustments to the recommended dose and schedule of CPX-351 are warranted for patients with mild/moderate renal impairment or serum bilirubin ≤3 mg/dL. Results from the exposure-response analyses suggest the current CPX-351 regimen provides a favorable risk-benefit profile.

A Randomized, First-in-Human, Healthy Volunteer Trial of sutimlimab, a Humanized Antibody for the Specific Inhibition of the Classical Complement Pathway

Aberrant activation of the classical complement pathway is the common underlying pathophysiology of orphan diseases such as bullous pemphigoid, antibody‐mediated rejection of organ transplants, cold agglutinin disease, and warm autoimmune hemolytic anemia. Therapeutic options for these complement‐mediated disorders are limited and sutimlimab, a humanized monoclonal antibody directed against complement factor C1s, may be potentially useful for inhibition of the classical complement pathway. A phase I, first‐in‐human, double‐blind, randomized, placebo‐controlled, dose‐escalation trial of single and multiple doses of sutimlimab or placebo was conducted in 64 volunteers to evaluate safety, tolerability, pharmacokinetic, and pharmacodynamic profiles. Single and multiple infusions of sutimlimab were well tolerated without any safety concerns. sutimlimab exhibited a steep concentration–effect relationship with a Hill coefficient of 2.4, and an IC₉₀ of 15.5 μg/mL. This study establishes the foundation for using sutimlimab as a highly selective inhibitor of the classical complement pathway in different diseases.

A randomized, open-label, multicenter, phase II study evaluating the efficacy and safety of BTH1677 (1,3-1,6 beta glucan; Imprime PGG) in combination with cetuximab and chemotherapy in patients with advanced non-small cell lung cancer

Introduction BTH1677, a 1,3–1,6 beta-glucan immunomodulator, stimulates a coordinated anti-cancer immune response in combination with anti-tumor antibody therapies. This phase II study explored the efficacy, pharmacokinetics (PK), and safety of BTH1677 combined with cetuximab/carboplatin/paclitaxel in untreated stage IIIB/IV non-small cell lung cancer (NSCLC) patients. Methods Patients were randomized 2:1 to the BTH1677 arm (N=60; BTH1677, 4 mg/kg, weekly; cetuximab, initial dose 400 mg/m² and subsequent doses 250 mg/m², weekly; carboplatin, 6 mg/mL/min AUC (area-under-the-curve) by Calvert formula, once each 3-week cycle [Q3W]); and paclitaxel, 200 mg/m², Q3W) or Control arm (N=30; cetuximab/carboplatin/paclitaxel as above). Carboplatin/paclitaxel was discontinued after 4–6 cycles; patients who responded or remained stable received maintenance therapy with BTH1677/cetuximab (BTH1677 arm) or cetuximab (Control arm). Investigator and blinded central radiology reviews were conducted. Efficacy assessments included objective response rate (ORR; primary endpoint), disease control rate, duration of objective response, time-to-progression and overall survival (OS); safety was assessed by adverse events (AEs). Potential biomarker analysis for BTH1677 response was also conducted. Results Compared to control treatment, the addition of BTH1677 numerically increased ORR by both investigator (47.8% vs 23.1%; p=0.0468) and central (36.6% vs 23.1%; p=0.2895) reviews. No other endpoints differed between arms. PK was consistent with previous studies. BTH1677 was well tolerated, with AEs expected of the backbone therapy predominating. Biomarker-positive patients displayed better ORR and OS than negative patients. Conclusions BTH1677 combined with cetuximab/carboplatin/paclitaxel was well tolerated and improved ORR as first-line treatment in patients with advanced NSCLC. Future patient selection by biomarker status may further improve efficacy

ClinicalTrials.gov Identifier: NCT00874848

BTH1677 in combination with cetuximab with and without irinotecan in patients with advanced metastatic colorectal cancer

Aim: Investigate the safety, pharmacokinetics (PK) and efficacy of BTH1677/cetuximab, with and without irinotecan, in patients with metastatic colorectal cancer (mCRC). Patients & methods: Patients with recurrent or progressive mCRC were assigned to BTH1677/cetuximab/irinotecan (group 1; n = 10) or BTH1677/cetuximab (group 2; n = 22). Adverse events, PK parameters and tumor response were assessed. Results & conclusion: Adverse events were consistent with those expected of the backbone therapy of cetuximab/irinotecan (group 1) or cetuximab alone (group 2). The BTH1677 PK profiles were similar in the two groups. The overall response rates were 30.0% (group 1) and 22.7% (group 2); in KRAS wild-type subset analysis, rates were 42.9% and 45.5%, respectively. BTH1677 therapy was tolerable and warrants further evaluation for treatment of mCRC.

Modeling and Experimental Studies of Obeticholic Acid Exposure and the Impact of Cirrhosis Stage

Obeticholic acid (OCA), a semisynthetic bile acid, is a selective and potent farnesoid X receptor (FXR) agonist in development for the treatment of chronic nonviral liver diseases. Physiologic pharmacokinetic models have been previously used to describe the absorption, distribution, metabolism, and excretion (ADME) of bile acids. OCA plasma levels were measured in healthy volunteers and cirrhotic subjects. A physiologic pharmacokinetic model was developed to quantitatively describe the ADME of OCA in patients with and without hepatic impairment. There was good agreement between predicted and observed increases in systemic OCA exposure in subjects with mild, moderate, and severe hepatic impairment, which were 1.4‐, 8‐, and 13‐fold relative to healthy volunteers. Predicted liver exposure for subjects with mild, moderate, and severe hepatic impairment were increased only 1.1‐, 1.5‐, and 1.7‐fold. In subjects with cirrhosis, OCA exposure in the liver, the primary site of pharmacological activity along with the intestine, is increased marginally (∼2‐fold).

Pharmacokinetic profile of defibrotide in patients with renal impairment

Hepatic veno-occlusive disease, also called sinusoidal obstruction syndrome (VOD/SOS), is an unpredictable, potentially life-threatening complication of hematopoietic stem cell transplant conditioning. Severe VOD/SOS, generally associated with multiorgan dysfunction (pulmonary or renal dysfunction), may be associated with >80% mortality. Defibrotide, recently approved in the US, has demonstrated efficacy treating hepatic VOD/SOS with multiorgan dysfunction. Because renal impairment is prevalent in patients with VOD/SOS, this Phase I, open-label, two-part study in adults examined the effects of hemodialysis and severe or end-stage renal disease (ESRD) on defibrotide pharmacokinetics (PK). Part 1 compared defibrotide PK during single 6.25 mg/kg doses infused with and without dialysis. Part 2 assessed defibrotide plasma PK after multiple 6.25 mg/kg doses in nondialysis-dependent subjects with severe/ESRD versus healthy matching subjects. Among six subjects enrolled in Part 1, percent ratios of least-squares mean and 90% confidence intervals (CIs) on dialysis and nondialysis days were 109.71 (CI: 97.23, 123.78) for maximum observed plasma concentration (C_max); 108.39 (CI: 97.85, 120.07) for area under the concentration–time curve to the time of the last quantifiable plasma concentration (AUC_0–t); and 109.98 (CI: 99.39, 121.70) for AUC extrapolated to infinity (AUC_0–∞). These ranges were within 80%–125%, indicating no significant effect of dialysis on defibrotide exposure/clearance. In Part 2, defibrotide exposure parameters in six subjects with severe/ESRD after multiple doses (AUC_0–t, 113 µg·h/mL; AUC over dosing interval, 113 µg·h/mL; C_max, 53.8 µg/mL) were within 5%–8% of parameters after the first dose (AUC_0–t, 117 µg·h/mL; AUC_0–∞, 118 µg·h/mL; C_max, 54.9 µg/mL), indicating no accumulation. Defibrotide peak and extent of exposures in those with severe/ESRD were ~35%–37% and 50%–60% higher, respectively, versus controls, following single and multiple doses. One adverse event (vomiting, possibly drug-related) was reported. These findings support defibrotide prescribing guidance stating no dose adjustment is necessary for hemodialysis or severe/ESRD.

The effect of plasmapheresis on blood pressure in voluntary plasma donors

BACKGROUND AND OBJECTIVES

Donor plasmapheresis involves the removal of a weight-adjusted volume of plasma and the return of cellular components to the donor. Although plasma volume generally returns to normal, some residual effect on vital signs may be possible. This analysis was performed to determine the possible effects of plasmapheresis on blood pressure.

MATERIALS AND METHODS

A 16-week study was conducted to evaluate the effects of plasma donations on cholesterol levels in healthy donors. From this study, the vital signs obtained prior to donation were analysed using statistical and dynamic analytical predictive models.

RESULTS

Preliminary analyses revealed a change in systolic and diastolic blood pressure from the corresponding baseline values (Pearson Coefficient -0.44 and -0.47, respectively). Statistical models predicted a marked decrease in systolic and diastolic blood pressure following multiple donations in donors with baseline pressure in the Stage 2 hypertension range with less pronounced decreases predicted in Stage 1 donors. Little or no change in blood pressure was predicted in donors with baseline normal blood pressure or prehypertension. Dynamic models including time between donations supported these results and predicted a recovery period of about 14 days without donation in donors with Stage 2 baseline levels.

CONCLUSIONS

Results suggest that systolic and diastolic blood pressure may be decreased following plasmapheresis used for plasma donations at intervals of <14 days in donors with high baseline blood pressure levels.

Population pharmacokinetic analysis of thrombomodulin alfa to support dosing rationale in patients with renal impairment

Thrombomodulin alfa is a soluble recombinant human thrombomodulin that was reported to enhance the reversal of disseminated intravascular coagulation (DIC) in subjects with sepsis or hematologic malignancy and reduce mortality in subjects with sepsis and DIC. Population pharmacokinetic (PK) analysis of thrombomodulin alfa was performed based on rich samples collected in 24 healthy subjects (0.02 and 0.06 mg/kg) and sparse samples collected in 368 subjects with sepsis and DIC (0.06 mg/kg). Sources of variability (baseline characteristics, markers of renal/liver function, hematocrit, and disease severity) were explored using non-linear mixed effect modeling to support dosing rationale in patients with sepsis and DIC. Plasma concentrations of thrombomodulin alfa were best fitted with a one-compartment model. Body weight and creatinine clearance were important covariates describing the PK of thrombomodulin alfa. Typical CL values in patients with normal renal function, or mild, moderate and severe renal impairment were 0.158, 0.145, 0.128, and 0.105 L/h, respectively. Based on simulations, a 0.06 mg/kg dosing of thrombomodulin alfa is expected to result in drug exposure within the therapeutic range of the product (300-5,400 ng/mL), with minimum risks of bleeding in patient with normal and impaired renal functions.

Pharmacokinetics of oral treprostinil sustained release tablets during chronic administration to patients with pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a progressive vascular disease that ultimately leads to right ventricular failure and death. Treprostinil diolamine is an oral prostacyclin analogue; sustained release tablets of oral treprostinil are currently being evaluated for efficacy and safety as a potential therapy in patients with PAH. Previous attempts at developing an oral prostanoid have been limited by rapid absorption and short plasma half-life; thus, the aim of this study was to characterize the pharmacokinetic profile of treprostinil diolamine in PAH patients after chronic dosing. The study enrolled 74 PAH patients who had been taking treprostinil diolamine for a minimum of 4 weeks (range: 0.5-16 mg). We collected plasma samples over 12 hours and estimated pharmacokinetic parameters using noncompartmental methods. Seventy patients had complete data. After chronic twice-daily oral dosing of treprostinil diolamine, mean area under the curve (AUC0-12) of treprostinil increased from 5244 to 20,4086 pg·hr-·mL- and mean maximum observed plasma concentration (Cmax) increased from 1383 to 33588 pg/mL. The apparent clearance (CL/F) was similar across all doses, indicating a linear dose-exposure relationship after twice-daily dosing. We conclude that twice-daily oral treprostinil provides sustained and proportional treprostinil concentrations over a wide range of doses during chronic administration to PAH patients.

Pharmacokinetics, Tolerability, and Performance of a Novel Matrix Transdermal Delivery System of Fentanyl Relative to the Commercially Available Reservoir Formulation in Healthy Subjects

A novel transdermal formulation of fentanyl-containing dipropylene glycol droplets dispersed in a silicone matrix with a rate-controlling membrane was developed. Healthy male subjects (n = 24) received repeated 72-hour applications of fentanyl (50 mug/h) as the novel matrix and the conventional reservoir formulations in a randomized, 2-way crossover study. Blood samples were collected, and serum concentrations of fentanyl were assayed using liquid chromatography with mass spectrometry detection. The mean area under the curve (AUCtau) and peak concentrations (C(max)) of the matrix formulation were 84 838 pg.h/mL and 1680 pg/mL, respectively. Ratio and 90% confidence intervals of AUCtau and C(max) between the 2 formulations were within 80% to 125%. Adherence of the matrix formulation was higher than the reservoir formulation (62.5 vs 56.2%, P < .0001), without affecting skin irritation. Vital signs and adverse events of the 2 formulations were similar in nature and frequency. The novel matrix formulation displayed enhanced adherence and resulted in similar pharmacokinetics and tolerability as the reservoir formulation.

Ammonia control in children with urea cycle disorders (UCDs); phase 2 comparison of sodium phenylbutyrate and glycerol phenylbutyrate

Twenty four hour ammonia profiles and correlates of drug effect were examined in a phase 2 comparison of sodium phenylbutyrate (NaPBA) and glycerol phenylbutyrate (GPB or HPN-100), an investigational drug being developed for urea cycle disorders (UCDs).

STUDY DESIGN

Protocol HPN-100-005 involved open label fixed-sequence switch-over from the prescribed NaPBA dose to a PBA-equimolar GPB dose with controlled diet. After 7 days on NaPBA or GPB, subjects underwent 24-hour blood sampling for ammonia and drug metabolite levels as well as measurement of 24-hour urinary phenyacetylglutamine (PAGN). Adverse events (AEs), safety labs and triplicate ECGs were monitored.

RESULTS

Eleven subjects (9 OTC, 1 ASS, 1 ASL) enrolled and completed the switch-over from NaPBA (mean dose=12.4 g/d or 322 mg/kg/d; range=198-476 mg/kg/d) to GPB (mean dose=10.8 mL or 0.284 mL/kg/d or 313 mg/kg/d; range=192-449 mg/kg/d). Possibly-related AEs were reported in 2 subjects on NaPBA and 4 subjects on GPB. All were mild, except for one moderate AE of vomiting on GPB related to an intercurrent illness. No clinically significant laboratory or ECG changes were observed. Ammonia was lowest after overnight fast, peaked postprandially in the afternoon to early evening and varied widely over 24h with occasional values >100 μmol/L without symptoms. Ammonia values were ~25% lower on GPB vs. NaPBA (p≥0.1 for ITT and p<0.05 for per protocol population). The upper 95% confidence interval for the difference between ammonia on GPB vs. NaPBA in the ITT population (95% CI 0.575, 1.061; p=0.102) was less than the predefined non-inferiority margin of 1.25 and less than 1.0 in the pre-defined per-protocol population (95% CI 0.516, 0.958; p<0.05). No statistically significant differences were observed in plasma phenylacetic acid and PAGN exposure during dosing with GPB vs. NaPBA, and the percentage of orally administered PBA excreted as PAGN (66% for GPB vs. 69% for NaPBA) was very similar. GPB and NaPBA dose correlated best with urinary-PAGN.

CONCLUSIONS

These findings suggest that GPB is at least equivalent to NaPBA in terms of ammonia control, has potential utility in pediatric UCD patients and that U-PAGN is a clinically useful biomarker for dose selection and monitoring.

Phase 2 comparison of a novel ammonia scavenging agent with sodium phenylbutyrate in patients with urea cycle disorders: safety, pharmacokinetics and ammonia control

Glycerol phenylbutyrate (glyceryl tri (4-phenylbutyrate)) (GPB) is being studied as an alternative to sodium phenylbutyrate (NaPBA) for the treatment of urea cycle disorders (UCDs). This phase 2 study explored the hypothesis that GPB offers similar safety and ammonia control as NaPBA, which is currently approved as adjunctive therapy in the chronic management of UCDs, and examined correlates of 24-h blood ammonia.

METHODS

An open-label, fixed sequence switch-over study was conducted in adult UCD patients taking maintenance NaPBA. Blood ammonia and blood and urine metabolites were compared after 7 days (steady state) of TID dosing on either drug, both dosed to deliver the same amount of phenylbutyric acid (PBA).

RESULTS

Ten subjects completed the study. Adverse events were comparable for the two drugs; 2 subjects experienced hyperammonemic events on NaPBA while none occurred on GPB. Ammonia values on GPB were approximately 30% lower than on NaPBA (time-normalized AUC=26.2 vs. 38.4 micromol/L; Cmax=56.3 vs. 79.1 micromol/L; not statistically significant), and GPB achieved non-inferiority to NaPBA with respect to ammonia (time-normalized AUC) by post hoc analysis. Systemic exposure (AUC(0-24)) to PBA on GPB was 27% lower than on NaPBA (540 vs. 739 microgh/mL), whereas exposure to phenylacetic acid (PAA) (575 vs. 596 microg h/mL) and phenylacetylglutamine (PAGN) (1098 vs. 1133 microg h/mL) were similar. Urinary PAGN excretion accounted for approximately 54% of PBA administered for both NaPBA and GPB; other metabolites accounted for <1%. Intact GPB was generally undetectable in blood and urine. Blood ammonia correlated strongly and inversely with urinary PAGN (r=-0.82; p<0.0001) but weakly or not at all with blood metabolite levels.

CONCLUSIONS

Safety and ammonia control with GPB appear at least equal to NaPBA. Urinary PAGN, which is stoichiometrically related to nitrogen scavenging, may be a useful biomarker for both dose selection and adjustment for optimal control of venous ammonia.

Pharmacokinetics, safety, and tolerability of teduglutide, a glucagon-like peptide-2 (GLP-2) analog, following multiple ascending subcutaneous administrations in healthy subjects

Teduglutide, a glucagon-like peptide-2 (GLP-2) analog, is currently being evaluated for the treatment of short-bowel syndrome, Crohn's disease, and other gastrointestinal disorders. The pharmacokinetics, safety, and tolerability of teduglutide in healthy subjects (N = 64) were assessed following daily subcutaneous administrations for 8 days in a double-blinded, randomized, placebo-controlled, ascending-dose study. Teduglutide treatments were administered as a 50-mg/mL (10, 15, 20, 25, 30, 50, and 80 mg) or 20-mg/mL (20 mg) formulation. Blood samples were collected on days 1 and 8, and plasma concentrations of teduglutide were measured using a liquid chromatography/tandem mass spectrometry method. Mean systemic exposures to teduglutide were very similar on days 1 and 8, suggesting minimal, if any, accumulation following once-daily repeated administrations. The apparent clearance of teduglutide following administration of the 50-mg/mL formulation was constant over the dose range, with mean values in male and female subjects of 0.155 and 0.159 L/h/kg, respectively. Peak plasma concentrations and total exposure of teduglutide after subcutaneous injection of a 20-mg/mL formulation (1.0 mL) were approximately 15% and 78% higher than those observed with the 50-mg/mL formulation (0.4 mL), respectively. Teduglutide treatments were safe and well tolerated. All but 1 adverse event was assessed as mild or moderate in severity. No relationship between teduglutide treatments and frequency of adverse events was observed, with the exception of injection site pain, which increased as a function of dose and injected volume. Results from the current study will assist in the dose selection in future efficacy studies.

Pharmacokinetics of lamivudine, zidovudine, and nevirapine administered as a fixed-dose combination formulation versus coadministration of the individual products

The pharmacokinetics of 150 mg lamivudine, 300 mg zidovudine, and 200 mg nevirapine were assessed following single oral administration of a fixed-dose combination tablet and coadministration of the separate innovator products in healthy male subjects (n = 64) under fasting conditions in an open-label, randomized, 2-way crossover study. Multiple blood samples were collected up to 72 hours and plasma concentrations of antiretrovirals were assayed using liquid chromatography/tandem mass spectrometry methods. Pharmacokinetic parameters were calculated using noncompartmental methods, and bioequivalence was assessed using an analysis of variance model. The ratio of the least squares mean (fixed-dose combination to individual products) and 90% confidence intervals of AUC(0-t), AUC(0-infinity), and C(max) for lamivudine, zidovudine, and nevirapine were all within 80.0% to 125.0%, suggesting a similar rate and extent of antiretroviral exposure in the bloodstream. Mean oral clearance (CL/F) values of lamivudine, zidovudine, and nevirapine for the fixed-dose combination were 23.7, 127, and 1.65 L/h, respectively. The fixed-dose combination and individual products were equally safe and well tolerated, with only a few subjects experiencing drug-related adverse events. The current fixed-dose combination of lamivudine, zidovudine, and nevirapine is expected to provide a similar efficacy/safety profile as coadministration of the individual products, a better adherence to treatment, and considerable cost savings in the treatment of HIV.

Pharmacokinetics of eugenol and its effects on thermal hypersensitivity in rats

Neuropathic pain is a type of chronic pain following central or peripheral nervous system lesions that cause allodynia (pain initiated by a non-painful stimulus) and hyperalgesia (increased pain sensation following a painful stimulus). The first objective of the study was to evaluate the pharmacokinetics of eugenol, the principle chemical constituent of clove oil, following a gavage administration (40 mg/kg) in male Sprague-Dawley rats. The second objective was to evaluate the effect of repeated oral administrations of eugenol on hyperalgesia and allodynia using an experimental model of neuropathic pain in rats. Thermal and mechanical sensitivity (Hargreave's test and von Frey filaments) were determined in sciatic nerve cuff-implanted rats. Sensitivities were assessed following repeated oral administrations of 40 mg/kg of eugenol or saline for 5 days (n=6 per group). Pharmacokinetic parameters were calculated using noncompartmental methods. Serial blood samples were collected over 24 h. Concentrations of eugenol in blood and plasma peaked rapidly following oral administration. Mean T(1/2) values of eugenol in plasma and blood were long (14.0 and 18.3 h, respectively), suggesting a potential accumulation of the drug following repeated administrations. Reaction time to thermal stimuli appeared to increase constantly following repeated administrations of eugenol. On the last day of treatment, eugenol treatments resulted in a statistically significant prolongation of the reaction time to thermal stimuli in rats compared to the saline group (Mean+/-S.E.M.: 11.4+/-1.23 vs. 6.1+/-0.53 s, P<0.01). These results support the hypothesis that eugenol may alleviate neuropathic pain and that the cumulative effect of the drug may be in part responsible for this effect following repeated daily administrations.

Two open-label, randomized, crossover studies assessing the bioequivalence of ofloxacin administered as immediateand extended-release formulations in healthy subjects

BACKGROUND

Ofloxacin is a fluoroquinolone agent available as an immediate-release (IR) tablet formulation administered twice daily. An extended-release (ER) formulation of ofloxacin has been developed for oncedaily administration.

OBJECTIVES

The present studies compared the pharmacokinetic (PK) and safety profiles of the ER and IR formulations of ofloxacin.

METHODS

Based on specific inclusion and exclusion criteria, healthy adult male and female volunteers were selected to receive single and multiple oral doses of ofloxacin ER 400 mg QD and ofloxacin IR 200 mg BID in 2 separate open-label, randomized, crossover studies. Multiple blood samples were collected, and plasma concentrations of ofloxacin were analyzed using a high-throughput liquid chromatography system. PK parameters were calculated using noncompartmental methods. Safety was assessed in the clinical pharmacology unit based on vital signs, electrocardiograms (ECGs), and reported adverse events. The relationship of an adverse event to study drugs (definitely, probably, possibly, remotely, or unrelated) was assessed by the principal investigator.

RESULTS

Forty healthy subjects were included in each study. Thirty-seven subjects (28 men, 9 women; mean age, 37 years; mean weight, 71.2 kg) completed the single-dose study, and 38 subjects (33 men, 5 women; mean age, 36 years; mean weight, 72.2 kg) completed the multiple-dose study. With the exception of 3 black subjects in each study of African-American origin, all subjects in both studies were white. The mean AUC(0-24) values for the ER formulation in the single-and multiple-dose studies (18.6 and 21.4 mg . h/L, respectively) were similar to those for the IR formulation (17.7 and 22.8 mg x h/L), with the 90% CIs falling between 80.0 and 125.0. Mean C(max) values for the ER formulation in the single- and multiple-dose studies (2.02 and 2.12 mg/L) were also similar to those for the IR formulation (1.74 and 1.85 mg/L). Under steady-state conditions, median T(max) values for the ER formulation were significantly longer than those for the IR formulation (5.00 vs 2.00 hours, respectively; P < 0.05). All vital signs and ECGs were within normal ranges during the single- and multipledose studies. Adverse events probably related to study drugs (eg, nausea, loose stools, emesis) were similar in nature and frequency between the 2 formulations. No serious adverse events were reported during either study.

CONCLUSION

In these 2 trials in a selected group of healthy adult male and female volunteers, the ER and IR formulations of ofloxacin displayed a similar rate and extent of bioavailability and comparable safety profiles.

Comparative bioequivalence study between a novel matrix transdermal delivery system of fentanyl and a commercially available reservoir formulation

AIM

To determine the pharmacokinetics, safety and performance of a novel matrix formulation of fentanyl.

METHODS

Transdermal fentanyl was administered as the novel matrix and the Durogesic reservoir formulations (24 subjects, 100 microg h(-1)) in a randomized, fully replicate, four-way crossover study. Serum concentrations of fentanyl were assayed by LC/MS/MS. Pharmacokinetic parameters of fentanyl and performance (adherence and skin irritability) were evaluated.

RESULTS

Test/reference ratio (90% confidence intervals) for AUC(0-t), AUC(inf) and C(max) were 105.5% (99.4, 112.0), 105.3% (99.3, 111.6) and 111.4% (100.4, 123.6), respectively. Adherence and skin irritability results of the two formulations were similar.

CONCLUSION

The two formulations are expected to result in similar efficacy for the management of severe pain.

Pharmacokinetics and anesthetic activity of eugenol in male Sprague-Dawley rats

Eugenol, the principle chemical constituent of clove oil, has recently been evaluated for its anesthetic and analgesic properties in fish and amphibians. The objective of this study was to determine the pharmacokinetic (PK) and anesthetic activity of eugenol in rats. Male Sprague-Dawley rats received single i.v. doses of eugenol (0, 5, 10, 20, 40 and 60 mg/kg) and anesthetic level was evaluated with the withdrawal reflex. For the 20 mg/kg dose level, blood and urinary samples were collected over 1 h for the PK assessment. Plasma and blood concentrations of eugenol, as well as metabolite identification in urine, were determined using a novel dansyl chloride derivatization method with liquid chromatography mass spectrometry (LC/MS/MS). PK parameters were calculated using noncompartmental methods. Eugenol-induced loss of consciousness in a dose-dependent manner, with mean (+/-SEM) recovery in reflex time of 167 +/- 42 sec observed at the highest dose level. Mean systemic clearance (Cl) in plasma and blood were 157 and 204 mL/min/kg, respectively. Glucuronide and sulfate conjugates were identified in urine. Overall, eugenol produced a reversible, dose-dependent anesthesia in male Sprague-Dawley rats.

The effect of AST-120 on the single-dose pharmacokinetics of losartan and losartan acid (E-3174) in healthy subjects

AST-120 is an orally administered adsorbent used to slow the progression of chronic kidney disease (CKD). This was a randomized, open-label, 5-way crossover study to assess the effect of AST-120 on the pharmacokinetics of losartan and its active metabolite (E-3174) in healthy subjects. Losartan (100 mg) was administered alone under fasting (A) and fed (B) conditions, and results were compared when AST-120 (3 g thrice daily for 2 days) was administered 60 minutes after (C), 30 minutes prior to (D), and 30 minutes after (E) losartan. Plasma concentrations of losartan and E-3174 were assayed by high-performance liquid chromatography with mass spectrometry detection. Under fed conditions, treatment C had no significant effect on the AUC(0-t) and Cmax of losartan and E-3174. Treatments D and E resulted in a marked decrease in Cmax of losartan and E-3174. Therefore, administration of AST-120 60 minutes after losartan under fed conditions may be preferred over other dosing regimens for CKD patients.

Bioequivalence of abacavir generic and innovator formulations under fasting and fed conditions

OBJECTIVE

Abacavir sulfate is a synthetic carbocyclic nucleoside analogue indicated for the treatment of HIV-1 infection in combination with other antiretroviral agents. The objective of the current study was to determine the bioequivalence between a generic formulation of abacavir and the innovator product.

MATERIAL AND METHODS

A total of 80 subjects were randomly assigned to receive a single 300 mg oral dose of abacavir sulfate as the generic (Ranbaxy-Abacavir, Ranbaxy Laboratories Ltd., equivalent to 300 mg of abacavir) and innovator (Ziagen, GlaxoSmithKline) tablet formulations in 2-way crossover studies performed under fasting (n=40) and fed (n=40) conditions. Multiple blood samples were collected over 14 hours and plasma concentrations of abacavir were assayed using an LC/MS/MS method with a limit of quantitation of 25.0 ng/ml. Pharmacokinetic (PK) parameters were calculated using noncompartmental methods.

RESULTS

Under fasting conditions, geometric mean area under the curve from time 0 to the last measurable concentration (AUC(0-t)), area under the curve extrapolated to infinity (AUC(0-infinity) and maximum plasma concentrations (Cmax) of abacavir for the generic (5565 ng x h/ml, 5668 ng x h/ml and 2526 ng/ml, respectively) and innovator (5675 ng x h/ml, 5770 ng x h/ml and 2528 ng/ml, respectively) products were very similar. Under fed conditions, mean values of AUC(0-t) AUC(0-infinity) and Cmax for the generic (4487 ng x h/ml, 4571 ng x h/ml and 1841 ng/ml, respectively) and innovator (4574 ng x h/ml, 4654 ng x h/ml and 1781 ng/ml, respectively) formulations were also very similar. Ratios of LSM and 90% confidence intervals of PK parameters between the 2 formulations were within 80.0 - 125.0% under fasting and fed conditions, suggesting that the 2 tablet formulations resulted in similar rate and extent of bioavailability. Adverse events for the generic and innovator products were similar in nature and frequency in the fasting and fed studies. CONCLUSIONS Based on the above results, the generic tablet formulation of abacavir developed by Ranbaxy should be equally effective as the innovator product.

Comparative bioavailability study of zidovudine administered as two different tablet formulations in healthy adult subjects

AIM

Zidovudine is a synthetic nucleoside analogue of thymidine with activity against the human immunodeficiency virus type 1 (HIV-1). In patients with HIV infections or the acquired immunodeficiency syndrome (AIDS), zidovudine is a first-line therapy that was shown to reduce morbidity, mortality, and hospitalization. A generic formulation of zidovudine offers the possibility of considerable savings to HIV/AIDS patients in developed and Third World countries. The objective of the current study was to characterize the pharmacokinetic and safety profiles of zidovudine administered as a generic tablet formulation relative to the innovator product.

VOLUNTEERS AND METHODS

A total of 68 healthy adult volunteers received a 300 mg oral dose of zidovudine as the generic formulation (AVIRO-Z 300 mg tablet, Ranbaxy Laboratories Limited) and as the innovator product (Retrovir tablet, GlaxoSmithKline) in a randomized, 2-way crossover study. Multiple blood samples were collected over 12 hours and plasma concentrations of zidovudine were assayed using an LC/MS/MS method with an analytical range of 5.00 to 2,000 ng/ml. Pharmacokinetic parameters were calculated using non-compartmental methods.

RESULTS

Mean plasma concentrations of zidovudine declined in a mono-exponential manner, with mean concentration values falling below the limit of quantitation 12 hours after administration of both formulations. Mean area under the curve from time 0 to the last measurable concentration (AUC(0-t)), mean area under the curve from time 0 to infinity (AUC(0-infinity)) and peak plasma concentrations (C(max)) of zidovudine for the generic tablet formulation (2,220.6 ng x h/ml, 2,236.0 ng x h/ml and 1,087.9 ng/ml, respectively) were very similar to those observed for the innovator product (2,139.7 ng x h/ml, 2,158.6 ng x h/ml and 1,066.5 ng/ml, respectively). Ratios of least-squares means and 90% confidence intervals of AUC(0-t) AUC(0-infinity) and C(max) between the 2 formulations were within 80-125%, suggesting that the two tablet formulations displayed similar rate and extent of bioavailability. The oral clearance (CL/F) of zidovudine for the generic and innovator formulations were 2.11 1/h/kg and 2.16 1/h/kg, respectively. For the two formulations, adverse events were similar in nature and frequency.

CONCLUSION

Since the two formulations displayed similar in vivo delivery rate of zidovudine in the bloodstream, the generic tablet formulation of zidovudine developed by Ranbaxy should be equally effective as the innovator product and is expected to produce considerable cost-savings in AIDS patients worldwide.

Comparative bioavailability of a generic capsule formulation of the reverse transcriptase inhibitor efavirenz and the innovator product

OBJECTIVE

Efavirenz is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that has been used successfully for more than a decade to treat human immunodeficiency virus (HIV) infection. The objective of the current study was to determine the bioequivalence between a generic capsule formulation of efavirenz and the innovator product.

MATERIAL AND METHODS

A total of 41 healthy subjects (34 males and 8 females) received a single 200 mg oral dose of efavirenz as the generic (Ranbaxy-Efavirenz, Ranbaxy Laboratories Ltd.) and innovator (Sustiva, Bristol-Myers Squibb) capsule formulations under fasting conditions in a randomized, 2-way crossover study. Multiple blood samples were collected over 72 hours and plasma concentrations of efavirenz were assayed using an LC/MS/MS method. Pharmacokinetic (PK) parameters were calculated using non-compartmental methods.

RESULTS

Plasma concentrations of efavirenz peaked within 2.5 hours and then declined in a multi-exponential manner for both formulations. At 72 hours post dose, all plasma concentrations of efavirenz were above the LOQ of the assay (10 ng/ml). Mean area under the curve from 0 - 72 hours (AUC0-72) and maximum plasma concentrations (Cmax) of efavirenz for the generic capsule formulation were 22,840 ng x h/ml and 1,199 ng/ml, respectively. Ratios and 90% confidence intervals of PK parameters between the two formulations were within 80.0 - 125.0%, suggesting that the two capsule formulations resulted in similar rate and extent of bioavailability under fasting conditions. Adverse events were similar in nature and frequency for the two formulations.

CONCLUSIONS

Based on the above results, the generic capsule formulation of efavirenz developed by Ranbaxy should be as effective as the innovator product.

Effect of repeated oral administrations of the oral adsorbent AST-120 on serum creatinine and other markers of renal function. A randomized controlled study in patients with chronic kidney disease

BACKGROUND

AST-120 is an orally administered adsorbent used in Japan for prolonging time to initiation of hemodialysis and improving uremic symptoms in patients with chronic kidney disease (CKD). As AST-120 is suspected to reduce the progression of CKD by adsorbing renal toxins in the gastrointestinal tract, the objective of the current study was to determine whether binding of AST-120 to creatinine in the intestines could acutely alter creatinine balance, thereby limiting the utility of serum creatinine (sCr) as a measure of progression of renal function. Such information may be critical for the design of future studies to assess the efficacy of AST-120 in CKD patients.

METHODS

Patients with CKD (n = 20) received oral doses of AST-120(3 g t.i.d.) and placebo in a two-way crossover study. Blood and urine were collected for determination of sCr, 24-hour urinary creatinine (UcrV), creatinine clearance (Ccr), and urea nitrogen clearance (URCL). Differences between treatments were assessed using an ANCOVA model.

RESULTS

Following AST-120 and placebo treatments, mean sCr (1.73 and 1.79 mg/dl, respectively) and UcrV (1,264.73 and 1,286.05 mg) values were not significantly different. No significant differences were observed for Ccr and URCL.

CONCLUSION

These results indicate that AST-120 has no acute impact on creatinine balance in patients with CKD. Consequently, sCr and other markers of renal function are acceptable measures for assessing changes in renal function following AST-120 treatment.

Development of a rapid and sensitive LC–ESI/MS/MS assay for the quantification of propofol using a simple off-line dansyl chloride derivatization reaction to enhance signal intensity

A rapid, selective and sensitive method was developed for the determination of propofol concentration using an off-line dansyl chloride derivatization step to enhance signal intensity. The method consisted of a protein precipitation extraction followed by derivatization with dansyl chloride and analysis by liquid chromatography ionspray tandem mass spectrometry (LC-ESI/MS/MS). The separation was achieved using a 100 mm x 2 mm C8 analytical column combined with an isocratic mobile phase composed of 80:20 acetonitrile: 0.5% formic acid in water. Signal intensity of the propofol-dansyl chloride derivative was increased up to 200-fold as compared to the underivatized propofol in positive electrospray mode. An analytical range of 20-20,000 ng/mL was used in the calibration curve of plasma and blood samples. The novel method met all requirements of specificity, sensitivity, linearity, precision, accuracy and stability. A pharmacokinetic study was performed in rats and the novel analytical method was used as a routine analysis to provide enhanced measurements of plasma and blood concentrations of propofol. Blood and plasma pharmacokinetic results show that a very important fraction of propofol distributes into red blood cells. In conclusion, a rapid and sensitive LC-ESI/MS/MS method using a derivatization agent was developed to enhance signal intensity of propofol. Routine analysis with the novel method provided accurate results and enhanced the detection levels of plasma and blood concentrations of propofol to better characterize the in vivo biodisposition of propofol.

A novel, lipid-free nanodispersion formulation of propofol and its characterization

PURPOSE

Propofol is a widely used anesthetic agent with highly desirable fast "on" and "off" effects. It is currently formulated as lipid emulsions, which are known to support microbial growth. In this study, a novel, lipid-free nanodispersion formulation of propofol was characterized.

METHODS

The formulation was evaluated for its physical and chemical stability, in vitro compatibility with red blood cells, and its antimicrobial effectiveness. In vivo pharmacokinetic and pharmacodynamic properties of the formulation were evaluated in rats.

RESULTS

Our data suggest that this lipid-free formulation is physically and chemically stable. Compared to the commercial emulsion formulation Diprivan, it causes less hemolysis with red blood cells and has improved antimicrobial activity. In addition, the lipid-free formulation demonstrates similar pharmacological effects to Diprivan in rats.

CONCLUSIONS

This novel, lipid-free formulation exhibits improved in vitro properties without compromising in vivo effects, therefore representing a promising new alternative for propofol.

Enhancing the uptake of dextromethorphan in the CNS of rats by concomitant administration of the P-gp inhibitor verapamil

Clinical trials evaluating high doses of dextromethorphan hydrobromide (DM) for the treatment of neurological disorders have resulted in numerous adverse events due to the presence of its active metabolite dextrorphan (DX). Since the uptake of drugs in the CNS can be modulated by P-glycoprotein (P-gp) inhibition at the blood-brain barrier (BBB), we propose to determine whether the P-gp inhibitor verapamil can enhance the uptake of DM in the CNS. Rats (n=42) received an oral dose of DM (20 mg/kg) alone or 15 min after an intravenous dose of verapamil (1 mg/kg). Rats were euthanized at different time points over 12 h, and concentrations of DM and DX (conjugated and unconjugated) were assessed in plasma, brain and spinal cord using a LC-ESI/MS/MS method. Pharmacokinetic parameters were calculated using noncompartmental methods. Verapamil treatments did not affect the biodisposition of DM in plasma. On the other hand, verapamil treatments increased the area under curve of DM in the brain (from 1221 to 2393 ng h/g) and spinal cord (from 1753 to 3221 ng h/g) by approximately 2-fold. The uptake of DX in brain and spinal cord were markedly lower than those of DM and increased by only 15% and 22% following verapamil treatments, respectively. These results suggest that the P-gp inhibitor verapamil can enhance the uptake of DM in the CNS without affecting that of DX. This change is most likely related to an inhibition of P-gp or other transporters located in the BBB since the biodisposition of DM in plasma remained unaffected by verapamil treatments.

Production of ex vivo lipopolysaccharide-induced tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 is suppressed by trans-resveratrol in a concentration-dependent manner

Trans-resveratrol is a biologically active compound present in certain foods that has anti-inflammatory and anticancer properties. These beneficial effects are derived from both the immune system and cytokines. The purpose of this study was to determine the immunomodulatory effect of trans-resveratrol on the ex vivo production of inflammatory and anti-inflammatory cytokines stimulated by lipopolysaccharides (LPS). Trans-resveratrol (0, 0.01, 0.1, 1, and 10 microM) was added to blood samples from male Sprague-Dawley rats (n = 6) along with 100 U of LPS (Escherichia coli serotype, 055B5). The samples were then incubated for 4 h at 37 degrees C and centrifuged. Finally, concentrations of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and IL-6 in the plasma were analyzed using an enzyme-linked immunosorbent assay (ELISA). The production of inflammatory (TNF-alpha and IL-1beta) and anti-inflammatory (IL-6) cytokines was suppressed by trans-resveratrol in a concentration-dependent manner. These results support the hypothesis that the immunomodulatory effect of trans-resveratrol plays an important role in disease conditions that involve an overproduction of inflammatory cytokines.

Synovial fluid levels and serum pharmacokinetics in a large animal model following treatment with oral glucosamine at clinically relevant doses

OBJECTIVE

To examine the concentration of glucosamine in the synovial fluid and its pharmacokinetics in serum in a large animal model following dosing with glucosamine HCl at clinically relevant levels.

METHODS

Eight adult female horses were studied. After an overnight fast, glucosamine HCl (20 mg/kg of body weight) was administered by either nasogastric (NG) intubation or intravenous (IV) injection. Blood samples were collected before dosing and at 5, 15, 30, 60, 120, 180, 240, 360, 480, and 720 minutes after dosing. Synovial fluid samples were collected from the radiocarpal joints 48 hours before dosing and at 1 and 12 hours after dosing. Glucosamine was assayed by fluorophore-assisted carbohydrate electrophoresis.

RESULTS

The maximum concentration of glucosamine in serum reached approximately 300 muM ( approximately 50 microg/ml) following IV dosing and approximately 6 microM (approximately 1 microg/ml) following NG dosing. Synovial fluid concentrations reached 9-15 microM with IV dosing and 0.3-0.7 microM with NG dosing, and remained elevated (range 0.1-0.7 microM) in most animals even at 12 hours after dosing. Following NG dosing, the median serum maximal concentration of 6.1 microM (range 4.38-7.58) was attained between 30 minutes and 4 hours postdose. The mean apparent volume of distribution was 15.4 liters/kg, the mean bioavailability was 5.9%, and the mean elimination half-life was 2.82 hours.

CONCLUSION

Clinically relevant dosing of glucosamine HCl in this large monogastric animal model results in serum and synovial fluid concentrations that are at least 500-fold lower than those reported to modify chondrocyte anabolic and catabolic activities in tissue and cell culture experiments. We conclude that the apparent therapeutic benefit of dietary glucosamine on pain and joint space width in humans and animals may be secondary to its effects on nonarticular tissues, such as the intestinal lining, liver, or kidney, since these may be exposed to much high levels of glucosamine following ingestion.

Pharmacokinetics of omeprazole in healthy adults and in children with gastroesophageal reflux disease

Studies of the pharmacokinetics of omeprazole in children with gastroesophageal reflux disease (GERD) remain scarce despite the vast number of reports on its efficacy. The objectives of this study were to assess the pharmacokinetics of omeprazole in healthy adults and in children with GERD. Omeprazole (Losec, delayed-release capsules) was administered orally to 18 healthy adults (mean age 36.8 years) and 12 children with GERD (mean age 6.1 years). Blood samples were collected over 5 hours, and plasma concentrations were assessed using liquid chromatography. Population pharmacokinetic parameters were calculated using NONMEM. A 1-compartment model with zero-order absorption and a lag time was used. The population approach was well suited to the limited number of samples available, and residual variability was low. Oral clearance (CL/F) and apparent volume of distribution (V(ss)/F) in healthy adults (Mean +/- SD: 0.62 +/- 0.27 L/h/kg and 0.76 +/- 0.26 L/kg, respectively) were not significantly different than those in children with GERD (0.51 +/- 0.34 L/h/kg and 0.66 +/- 0.25 L/kg, respectively). Healthy adults displayed a statistically significantly longer delay in drug absorption (Lag time: 0.62 +/- 0.15 hours) as compared with that observed in children with GERD (0.12 +/- 0.03 hours, P < 0.05). On the basis of these findings, omeprazole dosings on a milligram-per-kilogram basis are recommended with no further adjustments for the treatment of GERD in children.

Influence of concomitant quinidine administration on dextromethorphan disposition in rats

High doses of dextromethorphan (DM) have been clinically investigated for the treatment of multiple neuronal disorders including neuropathic pain. Several authors have suggested the concomitant administration of DM and a CYP2D6 reversible inhibitor in order to enhance the exposure of DM and limit the exposure to total dextrorphan (DX). The present study proposes to determine whether or not a single dose of quinidine is sufficient to enhance the plasma concentrations of DM in rats and keep those of DX at a minimal level. Oral doses of DM (50 mg/kg) were administered with increasing dose levels of quinidine (0, 2, 20, and 50 mg/kg) to male Sprague-Dawley rats and blood samples were collected over 24 h. Plasma concentrations of DM and total DX were determined using ESI-LC/MS/MS. Quinidine coadministration resulted in a more than twofold increase in the area under the curve of DM with an ED(50) of approximately 2 mg/kg whereas those of total DX were only increased by 21%. These results support the working hypothesis that a single dose of quinidine may enhance the plasma concentrations of DM relative to those of total DX and may therefore improve the treatment of neuropathic pain.

Liposomal tobramycin against pulmonary infections of Pseudomonas aeruginosa: a pharmacokinetic and efficacy study following single and multiple intratracheal administrations in rats

OBJECTIVE

To determine the pharmacokinetics and efficacy of tobramycin against pulmonary infections of Pseudomonas aeruginosa in rats after intratracheal administration of conventional and liposomal formulations.

METHODS

Male Sprague-Dawley rats were inoculated with 10(6) cfu of a mucoid variant of P. aeruginosa (MIC of tobramycin for PA 508 = 1 mg/l) and tobramycin (conventional or liposomal formulations) was administered in single (490 microg) and multiple dose (490 microg during 4 days) experiments. Rats were killed at multiple time points to determine the residual cfu of P. aeruginosa and tobramycin amounts in lungs. Pharmacokinetic parameters were calculated using a two-compartment model with NONMEM.

RESULTS

Mean (+/-S.D.) elimination half-life (t(1/2beta)) and pulmonary exposure (AUC) of the conventional formulation were 14.0 +/-4.0 h and 663 +/-89 microg x h/lungs, respectively. The pharmacokinetic profile of liposomal tobramycin was markedly different, with a longer t(1/2beta) (34.4 +/-5 h, P < 0.05), resulting in an increased AUC (3890 +/-560 microg x h/lungs, P < 0.05). chi(2) analyses were carried out on cfu data distributed in the following categories: below 10(3), 10(3)-10(5), and above 10(5) cfu. In the single dose experiments, approximately 90% of the observations were above 10(5) cfu for both formulations. Significant differences in cfu distribution were observed after multiple treatments, with approximately 10% of the observations falling below 10(3) cfu of P. aeruginosa for the conventional formulation versus 30% for the liposomal formulation.

CONCLUSION

The liposomal formulation of tobramycin promoted drug retention in lungs and improved its efficacy after multiple treatments.

Pharmacokinetics and efficacies of liposomal and conventional formulations of tobramycin after intratracheal administration in rats with pulmonary Burkholderia cepacia infection

The objective of the present study was to determine the pharmacokinetics and efficacies of liposomal and conventional formulations of tobramycin against Burkholderia cepacia in a model of chronic lung infection. Male Sprague-Dawley rats were inoculated intratracheally with 10(6) CFU of a very resistant strain of B. cepacia (strain BC 1368; MIC, 128 micro g/ml) to establish lung infection. A 1,200- micro g dose of tobramycin was administered intratracheally as a liposomal formulation and as a conventional formulation. Rats were anesthetized and exsanguinated by cardiac puncture at different times over 24 h to assess pulmonary tobramycin concentrations and the number of residual CFU. Pharmacokinetic parameters were calculated by using a two-compartment model with NONMEM. The mean half-life at the beta phase (t(1/2beta)) and the pulmonary exposure (the area under the concentration-time curve [AUC]) of liposomal tobramycin were 19.7 h (coefficient of variation [CV], 24.2%) and 6,811 micro g. h/lungs (CV, 19.7%), respectively. The pharmacokinetics of conventional tobramycin were statistically different, with a t(1/2beta) and AUC of 12.9 h (CV, 31.4%) and 821 micro g. h/lungs (CV, 15.0%), respectively. Pearson chi-square analyses were performed on residual CFU data distributed in the following categories: <10(3), 10(3) to 10(5), and >10(5). Differences in CFU data between formulations showed a statistical trend (P < 0.10) when data from all time points were used, and statistically significant differences were found after 12 h (P < 0.05), with greater eradication achieved with the liposomal formulation. In conclusion, intratracheal administration of tobramycin in liposomes was associated with marked changes in the pharmacokinetics of the drug in the lung and an apparent trend for a prolonged efficacy against B. cepacia. These results support the hypothesis that inhalation of liposomal tobramycin may improve the management of chronic pulmonary infections caused by resistant bacteria in patients with cystic fibrosis.

Cyclosporin A in blood and brain tissue following intra-carotid injections in normal and stroke-induced rats

Administration of Cyclosporin A (CsA) to rats undergoing reversible global or focal ischemia has been demonstrated to be variably neuroprotective. As CsA does not readily cross the blood-brain barrier, the variability may be due to differences in bioavailability of CsA to the ischemic brain. We have, therefore, quantitated CsA levels in blood and brain following intra-carotid injection in rats undergoing permanent right middle cerebral artery (MCA) occlusion using a three-vessel model of focal cerebral ischemia. After 30 min of three-vessel occlusion, CsA (10 mg/kg) was injected into the left external carotid artery followed by reversal of the left common carotid artery occlusion. At various times post-injection, blood samples were collected from the vena cava and samples of ischemic or sham-operated cortex were obtained for CsA quantitation by tandem mass spectrometry. Pharmacokinetic parameters were determined using non-linear mixed-effects modeling. CsA areas under the curve between normal and stroke-induced rats were not significantly different in blood (18355 vs. 19405 ng x h/ml, NS) or in brain tissue (15664 vs. 14931 ng x h/g, NS). These results demonstrate that intra-carotid injection of CsA results in high levels in brain (brain-blood ratio from 0.5 to 1). No significant differences in blood and brain exposure were observed between normal and stroke-induced rats. Therefore, reduced cerebral blood flow in the ischemic territory did not limit CsA availability to the cortex. In addition, CsA intra-carotid administration was neuroprotective following 24 h recovery as there was a significant decrease in the infarct area of the affected hemisphere compared to saline injected rats as estimated by TTC staining of viable tissue.

Metabolism and disposition of resveratrol in rats: extent of absorption, glucuronidation, and enterohepatic recirculation evidenced by a linked-rat model

Pharmacokinetics of trans-resveratrol in its aglycone (RES(AGL)) and glucuronide (RES(GLU)) forms were studied following intravenous (15 mg/kg i.v.) and oral (50 mg/kg p.o.) administration of trans-resveratrol in a solution of beta-cyclodextrin to intact rats. In addition, the enterohepatic recirculation of RES(AGL) and RES(GLU) was assessed in a linked-rat model. Multiple plasma and urine samples were collected and concentrations of RES(AGL) and RES(GLU) were determined using an electrospray ionization-liquid chromatography/tandem mass spectrometry method. After i.v. administration, plasma concentrations of RES(AGL) declined with a rapid elimination half-life (T(1/2), 0.13 h), followed by sudden increases in plasma concentrations 4 to 8 h after drug administration. These plasma concentrations resulted in a significant prolongation of the terminal elimination half-life of RES(AGL) (T(1/2TER), 1.31 h). RES(AGL) and RES(GLU) also displayed sudden increases in plasma concentrations 4 to 8 h after oral administration, with T(1/2TER) of 1.48 and 1.58 h, respectively. RES(AGL) bioavailability was 38% and its exposure was approximately 46-fold lower than that of RES(GLU) (AUC(inf), 7.1 versus 324.7 micromol.h/l). Enterohepatic recirculation was confirmed in the linked-rat model since significant plasma concentrations of RES(AGL) and RES(GLU) were observed in bile-recipient rats at 4 to 8 h. The percentages of the exposures of RES(AGL) and RES(GLU) that were due to enterohepatic recirculation were 24.7 and 24.0%, respectively. The fraction of drug excreted in the urine over a period of 12 h was negligible. These results confirm that RES(AGL) is bioavailable and undergoes extensive first-pass glucuronidation, and that enterohepatic recirculation contributes significantly to the exposure of RES(AGL) and RES(GLU) in rats.

A pharmacokinetic study of amoxycillin in febrile beagle dogs following repeated administrations of endotoxin

The pharmacokinetics of amoxycillin was studied in nine male beagle dogs under healthy and febrile conditions. In Period 1, dogs received 20 mg/kg of an oral suspension of amoxycillin. Intravenous doses of saline, 2 and 20 microg/kg of endotoxin (LPS from Escherichia coli serotype) were administered to dogs (three per group) prior to administration of 20 mg/kg of amoxycillin in Period 2. Rectal temperature and behavioral changes were recorded and blood samples were collected over 12 h for pharmacokinetic analysis. Amoxycillin was assessed in plasma using liquid chromatography coupled with mass spectrometry. Plasma concentrations were analysed using a one-compartment model with lag-time for absorption using an iterative two-stage method. As compared with control groups, amoxycillin clearance decreased significantly with preliminary treatments of 2 microg/kg endotoxin (0.209 vs. 0.140 L/h kg, P < 0.05) and 20 microg/kg endotoxin (0.214 vs. 0.075 L/h kg, P < 0.05). As a result of this, the area under curve for the 2 and 20 microg/kg endotoxin groups increased significantly 100.4 vs. 149.4 microg h/mL (P < 0.05) and 99.2 vs. 277.7 microg h/mL (P < 0.05), respectively. Other drugs currently used for the treatment of fever and septic shock should be re-evaluated using a febrile animal model to avoid improper dose administration.

Stereoselective disposition of propranolol in rabbits. Role of presystemic organs and dose

The kinetics of propranolol enantiomers are stereoselective when high doses of the racemic drug are given po. To document whether the dose and/or the route of administration determines the stereoselective kinetics of propranolol enantiomers, conscious rabbits received 40, 80, or 120 mg/kg po or 0.5 or 10 mg/kg iv doses of racemic propranolol, and serial blood samples were obtained to assay propranolol enantiomers. At low po and iv doses, the kinetics of the propranolol enantiomers were identical. After the 120 mg/kg po dose, the kinetics of the enantiomers were stereoselective, i.e. the AUC0-->infinity for (S)-(-)-propranolol was greater than the AUC0-->infinity for (R)-(+)-propranolol (p < 0.05). The iv injection of 10 mg/kg generated zero-order kinetics, and (S)-(-)-propranolol was eliminated faster than the antipode. Propranolol enantiomer plasma protein binding was not stereoselective. In vitro, after the incubation of 5.8 or 58 microM (RS)-propranolol with cells of the intestinal mucosa or the liver, (R)-(+)-propranolol was more rapidly metabolized than (S)-(-)-propranolol at both concentrations in the intestine and at the higher concentration in the liver. Incubation of the individual enantiomers (2.9 and 29 microM) showed that in the intestine the intrinsic clearance of (R)-(+)-propranolol was greater than that of (S)-(-)-propranolol but in the liver there was preferential saturation of (S)-(-)-propranolol clearance. In conclusion, at low po or iv doses the kinetics of (RS)-propranolol are not stereoselective because the liver overshadows the effect of the intestine, and at high po doses the kinetics of propranolol enantiomers are stereoselective because of hepatic saturation of (S)-(-)-propranolol clearance.