Physiologically Based Oral Absorption Modelling to Study Gut-Level Drug Interactions

Simultaneous Determination of Loratadine and Its Metabolite Desloratadine in Beagle Plasma by LC-MS/MS and Application for Pharmacokinetics Study of Loratadine Tablets and Omeprazole‑Induced Drug-Drug Interaction

Background

Loratadine (LTD) is a Biopharmaceutical Classification System II basic drug with pH-sensitive aqueous solubility and dissolution is a speed-limiting step of its absorption. The drug dissolution and the gastrointestinal tract pH conditions are likely to influence the in vivo pharmacokinetic behavior of LTD tablets.

Materials and Method

A rapid, sensitive, and reliable bioanalytical method for simultaneous quantitation of LTD and its active metabolite desloratadine (DL) in beagle plasma was developed and validated based on liquid chromatography tandem mass spectrometry (LC-MS/MS). Sample preparation in low plasma consumption was accomplished by liquid–liquid extraction. The chromatographic separation was achieved on a Phenomenex Kinetex C8 column using acetonitrile and 5 mM ammonium formate as the mobile phase. A comparative pharmacokinetics study of three LTD tablets with different dissolution rates was conducted in male beagles in fasting state and an omeprazole-induced drug–drug interaction (DDI) study was subsequently performed under pretreatment of omeprazole.

Results and Conclusion

The method showed a good linear correlation over the concentration ranges of 0.008–24 ng/mL for LTD and 0.8–800 ng/mL for DL, and was successfully applied to analyze the two compounds in beagle plasma. Pharmacokinetic results showed in the fasting state the three LTD tablets were equivalent in beagles in terms of effective components. DL of the three tablets were equivalent, indicating metabolite was less susceptible to pharmaceutic preparation factors for LTD tablets in beagles. Moreover, significant changes in LTD and DL pharmacokinetics parameters were observed under the effect of omeprazole-induced pH increase in gastrointestinal tract, suggesting that DDI effects are of concern for the curative effect of LTD when combined with omeprazole. The findings will contribute to the future pharmaceutical preparations research as well as the clinical application of LTD.

Application of Physiologically Based Pharmacokinetic Modeling to Evaluate the Drug-Drug and Drug-Disease Interactions of Apatinib

Aim: Apatinib is an orally administered vascular epidermal growth factor receptor (VEGFR)-tyrosine kinase inhibitors approved for the treatment of advanced gastric adenocarcinoma or gastric esophageal junction adenocarcinoma. Apatinib is predominantly metabolized by CYP3A4/5, followed by CYP2D6. The present study aimed to evaluate the potential drug–drug interaction (DDI) and drug–disease interaction (DDZI) risks of apatinib in Chinese volunteers.

Methods: Modeling and simulation were conducted using Simcyp Simulator. The input parameters required for modeling were obtained from literature research or experiments. Then, the developed physiologically based pharmacokinetic (PBPK) models were applied to evaluate single-dose DDI potential in Chinese healthy volunteers with weak and moderate CYP3A inhibitors, strong CYP2D6 inhibitors, as well as CYP3A4 inducers. The DDZI potential was also predicted in patients with hepatic or renal impairment.

Results: The developed PBPK models accurately assessed apatinib pharmacokinetics following single-dose administration in Chinese healthy volunteers and cancer patients. The DDI simulation showed 2–4-fold changes in apatinib exposures by moderate CYP3A4 inhibitors and CYP3A4 inducers. A moderate increase of apatinib exposure (1.25–2-fold) was found with strong CYP2D6 inhibitor. In the DDZI simulation with hepatic impairment, the AUC of apatinib was significantly increased by 2.25-fold and 3.04-fold for Child–Pugh B and Child–Pugh C, respectively, with slightly decreased C_max by 1.54 and 1.67-fold, respectively.

Conclusion: The PBPK models developed in the present study would be highly beneficial to quantitatively predict the pharmacokinetic changes of apatinib under different circumstances, which might be difficult to evaluate clinically, so as to avoid some risks in advance.

Square root law model for the delivery and intestinal absorption of drugs: a case of hydrophilic captopril

The in vivo release and absorption of drugs are dependent on the interplay between many factors related to compound, formulation, and physiological properties. The mathematical models of oral drug absorption attempt to strike a balance between a complete description that takes into consideration as many independent factors as possible, and simple models that operate with fewer parameters, based mainly on critical factors. The latter models are by far more robust and easier to apply to predict the extent and sometimes even the rate of absorption. The present paper attempted to develop a simple model to describe the time course of absorption of the hydrophilic drug captopril (CPT) at the early phases of absorption, with implications mainly in the induction and early stages of achieving its therapeutic effect. As a phenomenological model, the instantaneous release of CPT was considered in the gastrointestinal fluid, leading to a constant drug concentration for a prolonged time, followed by a ‘long path diffusion’ inside the intestinal wall and a very low concentration at the interface intestinal wall-blood. These conditions regarding CPT concentration were translated into initial and boundary mathematical conditions for the diffusion equation in the intestinal wall. The solution of the diffusion equation led in the end to a square root law describing the dependence between the fraction of the drug absorbed and time. The model was successfully applied to data obtained in five bioequivalence studies: three comparing plasma levels achieved after the administration of a single dose of CPT 50 mg, one evaluating CPT pharmacokinetics after a 100 mg dose, and a fifth comparing CPT pharmacokinetics of two fixed-dose combinations of CPT 50 mg and hydrochlorothiazide 25 mg.

Revising Pharmacokinetics of Oral Drug Absorption: I Models Based on Biopharmaceutical/Physiological and Finite Absorption Time Concepts

ABSRACT

PURPOSE: To demonstrate that oral drug absorption is terminated in finite time. To develop models based on biopharmaceutical/physiological and finite absorption time concepts.

METHODS

The models are based on i) the passive drug diffusion mechanism under the sink conditions principle ii) the rate limiting role of the drug's properties solubility and permeability and iii) the relevant restrictions associated with the gastrointestinal transit times of drug in the stomach, the small intestines and the colon. Two input functions of constant rate are considered for the absorption of drug from i) the stomach/small intestines with an upper limit of 5 h and ii) the colon with an upper limit of 30 h. Branched differential equations were written for the time course of drug in the body.

RESULTS

Simulations were performed using different scenarios, assuming a variety of drug properties and limited or non-existent absorption from the colon. Literature oral data of cephradine, ibuprofen, flurbiprofen and itraconazole were analyzed. For all drugs examined, nice fittings of the branched differential equations to the experimental data were observed.

CONCLUSIONS

For all drugs the absorption process was terminated in the small intestine. The meaning of partial AUCs, Cmax, tmax are questioned. Applications of these models to IVIVC are anticipated.

In Silico Prediction of the Absorption and Disposition of Cefadroxil in Humans using an Intestinal Permeability Method Scaled from Humanized PepT1 Mice

It is difficult to predict the pharmacokinetics and plasma concentration-time profiles of new chemical entities in humans based on animal data. Some pharmacokinetic parameters, such as clearance and volume of distribution, can be scaled allometrically from rodents, mammals, and nonhuman primates with good success. However, it is far more challenging to predict the oral pharmacokinetics of experimental drug candidates. In the present study, we used in situ estimates of intestinal permeability, obtained in silico and from rat, wild-type (WT), and humanized PepT1 (huPepT1) mice, to predict the systemic exposure of cefadroxil, an orally administered model compound, under a variety of conditions. Using the GastroPlus simulation software program (Simulations Plus, Lancaster, CA), we found that the C max and area under the plasma concentration-time curve from time zero to the last measurable concentration of cefadroxil were better predicted using intestinal permeability estimates (both segmental and jejunal) from huPepT1 than from WT mice, and that intestinal permeabilities based on in silico and rat estimates gave worse predictions. We also observed that accurate predictions were possible for cefadroxil during oral dose escalation (i.e., 5, 15, and 30 mg/kg cefadroxil), a drug-drug interaction study (i.e., 5 mg/kg oral cefadroxil plus 45 mg/kg oral cephalexin), and an oral multiple dose study [i.e., 500 mg (6.7 mg/kg) cefadroxil every 6 hours]. Finally, the greatest amount of cefadroxil was absorbed in duodenal and jejunal segments of the small intestine after a 5 mg/kg oral dose. Thus, by combining a humanized mouse model and in silico software, the present study offers a novel strategy for better translating preclinical pharmacokinetic data to oral drug exposure during first-in-human studies.