Bridging in vitro dissolution and in vivo exposure for acalabrutinib. Part II. A mechanistic PBPK model for IR formulation comparison, proton pump inhibitor drug interactions, and administration with acidic juices.

Acalabrutinib (Calquence®) 100 mg (bid) has received accelerated approval by FDA for the treatment of adult patients with mantle cell lymphoma (MCL) who have received at least one prior therapy. Acalabrutinib is a substrate of PgP and CYP3A4, with a significant fraction of drug metabolized by first pass gut extraction and 25% absolute bioavailability. The absorption of acalabrutinib is affected by stomach pH, with lower pharmacokinetic exposure observed following co-administration with proton pump inhibitors. During dissolution at pH values below its highest basic pKa, the two basic moieties of acalabrutinib react with protons from the aqueous solution, leading to a higher pH at the drug surface than in the bulk solution. A batch-specific product particle size distribution (P-PSD), was derived from dissolution data using a mechanistic model that was based on the understanding of surface pH and the contribution of micelles to the dissolution rate. P-PSD values obtained for various batches of acalabrutinib products in simple buffers, or in complex fluids such as fruit juices, were successfully integrated into a physiologically based pharmacokinetic (PBPK) model developed using GastroPlus v9.0™. The integrated model allowed the prediction of clinical pharmacokinetics under normal physiological stomach pH conditions as well as following treatment with proton pump inhibitors. The model also accounted for lower pharmacokinetic exposure that was observed when acalabrutinib was co-administered with the acidic beverages, grapefruit juice, (which contains CYP3A inhibitors), and orange drink (which does not contain CYP3A inhibitors), relative to administration with water. The integration of dissolution data in the PBPK model enables mechanistic understanding and the establishment of more robust in vitro-in vivo correlations (IVIVC) under a variety of conditions. The model can then distinguish the interplay between dissolution and first pass extraction and how in vivo stomach pH, saturation of gut PgP, and saturation or inhibition of gut CYP3A4, will impact the pharmacokinetics of acalabrutinib.

Population Pharmacokinetics of the BTK Inhibitor Acalabrutinib and its Active Metabolite in Healthy Volunteers and Patients with B-Cell Malignancies.

INTRODUCTION: Bruton tyrosine kinase (BTK) is a key component of B-cell receptor signalling, critical for cell proliferation. Acalabrutinib, a selective, covalent BTK inhibitor, recently received an accelerated approval in relapsed/refractory mantle cell lymphoma. This analysis characterized the population pharmacokinetics (PK) of acalabrutinib and its metabolite ACP-5862. METHODS: Data were obtained from six phase I/II trials in adult patients with B-cell malignancy and seven phase I trials in healthy volunteers. Pooled concentration-time data, at dose levels ranging from 15 to 400 mg, were analysed using non-linear mixed-effects modelling. Base model parameters were scaled with body weight and normalized to 70 kg (fixed exponents: 0.75 and 1 for clearance and volumes, respectively). A full covariate approach was used to evaluate any relevant effects of dose, health group/disease status, hepatic and renal impairment, use of acid-reducing agents, race and sex. RESULTS: A total of 11,196 acalabrutinib and 1068 ACP-5862 concentration-time samples were available. The PK of both analytes were well described using two-compartment disposition models. Acalabrutinib absorption was characterized using sequential zero- and first-order constants and a lag time. Apparent clearance (CL/F) of acalabrutinib was 169 L/h (95% CI 159-175). Relative to the 100 mg dose group, the 15 and 400 mg dose groups showed a 1.44-fold higher and 0.77-fold lower CL/F, respectively. The clearance for ACP-5862 was 21.9 L/h (95% CI 19.5-24.0). The fraction metabolized was fixed to 0.4. The central and peripheral volumes of distribution were 33.1 L (95% CI 24.4-41.0) and 226 L (95% CI 149-305) for acalabrutinib, and 38.5 L (95% CI 31.6-49.2) and 38.4 L (95% CI 32.3-47.9) for ACP-5862. None of the investigated covariates led to clinically meaningful changes in exposure. CONCLUSION: The PK of acalabrutinib and its metabolite ACP-5862 were adequately characterized. Acalabrutinib CL/F decreased with increasing dose, but the trend was small over the 75-250 mg range. No dose adjustment was necessary for intrinsic or extrinsic covariates.

Ketorolac tromethamine: stereo-specific pharmacokinetics and single-dose use in postoperative infants aged 2-6 months.

OBJECTIVE: We determined the postoperative pharmacokinetics (PK), safety, and analgesic effects of ketorolac in 14 infants (aged <6 months) receiving a single intravenous (IV) administration of racemic ketorolac or placebo. BACKGROUND: Information on the PK of ketorolac in infants is limited. Unblinded studies suggest ketorolac may be useful in infants. METHODS: This double-blinded, placebo-controlled study enrolled 14 infants (aged <6 months) postoperatively. At 6-18 h after surgery, infants were randomized to receive placebo, 0.5 mg·kg(-1), or 1 mg·kg(-1) ketorolac IV. All infants received morphine sulfate as needed for pain control. Blood was collected up to 12-h postdosing. Analysis used noncompartmental and compartmental population modeling methods. RESULTS: In addition to noncompartmental and empirical Bayes PK modeling, data were integrated with a previously studied data set comprising 25 infants and toddlers (aged 6-18 months). A two-compartmental model described the comprehensive data set. The population estimates of the R (+) isomer were (%CV): central volume of distribution 1130 (10%) ml, peripheral volume of distribution 626 (25%) ml, and clearance from the central compartment 7.40 (8%) ml·min(-1). Those of the S (-) isomer were 1930 (15%) ml, 319 (58%) ml, and 39.5 (13%) ml·min(-1). Typical elimination half-lives were 191 and 33 min, respectively. There was a trend for increased clearance and central volume with increasing age and weight. The base model suggested that clearance of the S (-) isomer was weakly related to age; however, when body size adjustment was added to the model, no covariates were significant. Safety assessment showed no changes in renal or hepatic function tests, surgical drain output, or continuous oximetry between groups. Cumulative morphine administration showed large inter-patient variability and was not different between groups. CONCLUSION: Stereo-isomer-specific clearance of ketorolac in infants (aged 2-6 months) shows rapid elimination of the analgesic S (-) isomer as reported in infants aged 6-18 months. No adverse effects were seen after a single IV ketorolac dose.