CYP3A inductive potential of the rifamycins, rifabutin and rifampin, in the rabbit

The Effect of Carbamazepine on Performance, Carcass Value, Hematological and Biochemical Blood Parameters, and Detection of Carbamazepine and Its Metabolites in Tissues, Internal Organs, and Body Fluids in Growing Rabbits

Antiepileptic drugs (e.g., carbamazepine; CBZ) are widely prescribed for various conditions beyond epilepsy, including neurologic and psychiatric disorders. These medications can have both favorable and unfavorable impacts on mood, anxiety, depression, and psychosis. CBZ has been found at low concentrations (in the unit of nanograms per liter) in rivers, surface water, and even drinking water. As a result, when reclaimed wastewater is used for irrigation in agricultural ecosystems, CBZ can be reintroduced into the environment. That is why we tested different doses of CBZ in rabbits' feed as the meat is consumed in every community, has no religious barriers, and the potential risk of consuming meat which has been exposed to CBZ treatment is not known. Also, the evidence of the effect of CBZ on rabbits is missing. Mainly, the CBZ doses affected the count of leukocytes and other blood traits, meaning the higher the dose, the higher the reduction. Moreover, there were only low amounts of CBZ in rabbits' meat or tissues when they were exposed to the treatment.

Addressing the Challenges of Tuberculosis: A Brief Historical Account

Tuberculosis (TB) is a highly contagious disease that still poses a threat to human health. Mycobacterium tuberculosis (MTB), the pathogen responsible for TB, uses diverse ways in order to survive in a variety of host lesions and to subsequently evade immune surveillance; as a result, fighting TB and its associated multidrug resistance has been an ongoing challenge. The aim of this review article is to summarize the historical sequence of drug development and use in the fight against TB, with a particular emphasis on the decades between World War II and the dawn of the twenty first century (2000).

Pharmacokinetic drug-drug interaction between erlotinib and paracetamol: A potential risk for clinical practice

BACKGROUND

Erlotinib is a tyrosine kinase inhibitor available for the treatment of non-small cell lung cancer. Paracetamol is an analgesic agent, commonly used in cancer patients. Because these drugs are often co-administered, there is an increasing issue of interaction between them.

OBJECTIVE

The aim of the study was to investigate the effect of paracetamol on the pharmacokinetic parameters of erlotinib, as well as the influence of erlotinib on the pharmacokinetics of paracetamol.

METHODS

The rabbits were divided into three groups: the rabbits receiving erlotinib (I_ER), the group receiving paracetamol (II_PR), and the rabbits receiving erlotinib+paracetamol (III_ER+PR). A single dose of erlotinib was administered orally (25mg) and was administered intravenously (35mg/kg). Plasma concentrations of erlotinib, its metabolite (OSI420), paracetamol and its metabolites - glucuronide and sulphate were measured with the validated method.

RESULTS

During paracetamol co-administration we observed increased erlotinib maximum concentration (C_max) and area under the plasma concentration-time curve from time zero to infinity (AUC_0-∞) by 87.7% and 31.1%, respectively. In turn, erlotinib lead to decreased paracetamol AUC_0-∞ by 35.5% and C_max by 18.9%. The mean values of paracetamol glucuronide/paracetamol ratios for C_max were 32.2% higher, whereas paracetamol sulphate/paracetamol ratios for C_max and AUC_0-∞ were 37.1% and 57.1% lower in the II_PR group, when compared to the III_ER+PR group.

CONCLUSIONS

Paracetamol had significant effect on the enhanced plasma exposure of erlotinib. Additionally, erlotinib contributed to the lower concentrations of paracetamol. Decreased glucuronidation and increased sulphation of paracetamol after co-administration of erlotinib were also observed.

Rifampicin and rifapentine significantly reduce concentrations of bedaquiline, a new anti-TB drug

Objectives

Bedaquiline is the first drug of a new class approved for the treatment of TB in decades. Bedaquiline is metabolized by cytochrome P450 (CYP) 3A4 to a less-active M2 metabolite. Its terminal half-life is extremely long (5–6 months), complicating evaluations of drug–drug interactions. Rifampicin and rifapentine, two anti-TB drugs now being optimized to shorten TB treatment duration, are potent inducers of CYP3A4. This analysis aimed to predict the effect of repeated doses of rifampicin or rifapentine on the steady-state pharmacokinetics of bedaquiline and its M2 metabolite from single-dose data using a model-based approach.

Methods

Pharmacokinetic data for bedaquiline and M2 were obtained from a Phase I study involving 32 individuals each receiving two doses of bedaquiline, alone or together with multiple-dose rifampicin or rifapentine. Sampling was performed over 14 days following each bedaquiline dose. Pharmacokinetic analyses were performed using non-linear mixed-effects modelling. Models were used to simulate potential dose adjustments.

Results

Rifamycin co-administration increased bedaquiline clearance substantially: 4.78-fold [relative standard error (RSE) 9.10%] with rifampicin and 3.96-fold (RSE 5.00%) with rifapentine. Induction of M2 clearance was equally strong. Average steady-state concentrations of bedaquiline and M2 are predicted to decrease by 79% and 75% when given with rifampicin or rifapentine, respectively. Simulations indicated that increasing the bedaquiline dosage to mitigate the interaction would yield elevated M2 concentrations during the first treatment weeks.

Conclusions

Rifamycin antibiotics reduce bedaquiline concentrations substantially. In line with current treatment guidelines for drug-susceptible TB, concomitant use is not recommended, even with dose adjustment.

The influence of the time of day on midazolam pharmacokinetics and pharmacodynamics in rabbits

BACKGROUND

This study evaluates the time-of-day effect on midazolam and 1-OH midazolam pharmacokinetics, and on the sedative pharmacodynamic response in rabbits. Also, circadian fluctuations in rabbits' vital signs, such as the blood pressure, heart rate and body temperature were examined. The water intake was measured in order to confirm the presence of the animals' diurnal activity. The secondary aim involved the comparison of two methods of data analysis: a noncompartmental and a population modeling approach.

METHODS

Twelve rabbits were sedated with intravenous midazolam 0.35 mg/kg at four local times: 09.00, 14.00, 18.00 and 22.00 h. Each rabbit served as its own control by being given a single infusion at the four different times of the day on four separate occasions. The values of the monitored physiological parameters were recorded during the experiment and arterial blood samples were collected for midazolam assay. The pedal withdrawal reflex was used as the measurement of the sedation response. Two and one compartmental models were successfully used to describe midazolam and 1-OH midazolam pharmacokinetics. The categorical pharmacodynamic data were described with a logistic model.

RESULTS AND CONCLUSIONS

We did not find any time-of-day effects for the pharmacokinetic and pharmacodynamics parameters of midazolam. For 1-OH midazolam, statistically significant time-of-day differences in the apparent volume of distribution and clearance were noticed. They corresponded well with the rabbits' water intake. The noncompartmental and model-based parameters were essentially similar. However, more information can be obtained from the population model and this method should be preferred in chronopharmacokinetic and chronopharmacodynamic studies.

Rifamycins--obstacles and opportunities

With nearly one-third of the global population infected by Mycobacterium tuberculosis, TB remains a major cause of death (1.7 million in 2006). TB is particularly severe in parts of Asia and Africa where it is often present in AIDS patients. Difficulties in treatment are exacerbated by the 6-9 month treatment times and numerous side effects. There is significant concern about the multi-drug-resistant (MDR) strains of TB (0.5 million MDR-TB cases worldwide in 2006). The rifamycins, long considered a mainstay of TB treatment, were a tremendous breakthrough when they were developed in the 1960's. While the rifamycins display many admirable qualities, they still have a number of shortfalls including: rapid selection of resistant mutants, hepatotoxicity, a flu-like syndrome (especially at higher doses), potent induction of cytochromes P450 (CYP) and inhibition of hepatic transporters. This review of the state-of-the-art regarding rifamycins suggests that it is quite possible to devise improved rifamycin analogs. Studies showing the potential of shortening the duration of treatment if higher doses could be tolerated, also suggest that more potent (or less toxic) rifamycin analogs might accomplish the same end. The improved activity against rifampin-resistant strains by some analogs promises that further work in this area, especially if the information from co-crystal structures with RNA polymerase is applied, should lead to even better analogs. The extensive drug-drug interactions seen with rifampin have already been somewhat ameliorated with rifabutin and rifalazil, and the use of a CYP-induction screening assay should serve to efficiently identify even better analogs. The toxicity due to the flu-like syndrome is an issue that needs effective resolution, particularly for analogs in the rifalazil class. It would be of interest to profile rifalazil and analogs in relation to rifampin, rifapentine, and rifabutin in a variety of screens, particularly those that might relate to hypersensitivity or immunomodulatory processes.

Effect of simvastatin on steroid-induced osteonecrosis evidenced by the serum lipid level and hepatic cytochrome P4503A in a rabbit model

OBJECTIVE

This study was designed to investigate the efficacy of lipid-lowering agents in preventing steroid-induced osteonecrosis and the mechanism by which they do so in a rabbit model.

METHODS

Female Japanese white rabbits were randomly allocated to receive probucol (group P), pravastatin (group PS), simvastatin (group SS), or saline (group C) for 6 weeks (n = 15 in groups P, PS, and SS; n = 30 in group C). Methylprednisolone (20 mg/kg) was injected at 3 weeks after starting treatment, and the femurs were histologically examined bilaterally 3 weeks after methylprednisolone injection. Midazolam clearance was measured before treatment and before methylprednisolone injection to determine hepatic cytochrome P4503A (CYP3A) levels.

RESULTS

The incidence of osteonecrosis in the proximal metaphysis of the femurs in groups PS and SS was significantly lower than in group C (P < 0.05 and P < 0.0001, respectively), whereas it did not differ between groups P and C. It was significantly lower in group SS than in group PS (P < 0.05). Plasma concentrations of lipids (low-density lipoprotein, triglyceride, free fatty acid, and total cholesterol) in groups P, PS, and SS were significantly lower than in group C; and hepatic CYP3A levels were significantly higher in group SS than in groups P or PS after treatment (P < 0.005 for both).

CONCLUSIONS

Simvastatin and pravastatin significantly reduced the incidence of steroid-induced osteonecrosis in rabbits. Simvastatin was more effective in reducing the incidence of the disease, and increased CYP3A activity is a possible mechanism for this effect.

Treatment Options for HIV-Associated Tuberculosis

The vicious interaction between the human immunodeficiency virus (HIV) infection and tuberculosis (TB) pandemics poses special challenges to national control programs and individual physicians. Although recommendations for the treatment of TB in HIV-infected patients do not significantly differ from those for HIV-uninfected patients, the appropriate management of HIV-associated TB is complicated by health system issues, diagnostic difficulties, adherence concerns, overlapping adverse-effect profiles and drug interactions, and the occurrence of paradoxical reactions after the initiation of effective antiretroviral therapy. In this article, recommended treatment strategies and novel approaches to the management of HIV-associated TB are reviewed, including adjuvant treatment and options for treatment simplification. A focused research agenda is proposed in the context of the limitations of the current knowledge framework.

DIFFERENTIATION OF GUT AND HEPATIC FIRST-PASS LOSS OF VERAPAMIL IN INTESTINAL AND VASCULAR ACCESS-PORTED (IVAP) RABBITS

Low and varied oral bioavailability (BA) of some drugs has been attributed to extraction by the intestine and liver. However, the role of the intestine is difficult to directly assess. We recently developed an in vivo intestinal and vascular access-ported (IVAP) rabbit model that allows for a direct assessment of the contributions of the gut and the liver to the first-pass loss of drugs. The current studies validate the utility of the IVAP rabbit model using verapamil (VL). VL pharmacokinetics (PK) were determined after intravenous (i.v.), portal venous (PV), and upper small intestinal (USI) administration. In the i.v. dose range studied, VL exhibited linear PK. The PV concentration of VL was significantly lower than systemic concentrations after i.v. administration, suggesting significant intestinal second-pass extraction. The intestinal and hepatic extraction of VL, calculated directly from area under the curve measurements, were 79% and 92%, respectively, and are in contrast to our previous dog results that showed VL intestinal extraction to be negligible. Assessing the role of intestinal extraction using an "indirect" method was not predictive, further showing the utility of this direct measurement model. The BA of VL after USI administration was 1.65%, much lower than that reported for rats, dogs, or humans. However, humans and rabbits behave similarly in that the contribution of intestinal extraction for VL is high. In conclusion, the current results demonstrate the utility of the rabbit IVAP model in studying the first- and second-pass intestinal and hepatic loss of drugs and other xenobiotics.