Consensus Statements on the Use of Novel Formulations of Isotretinoin: A Modified Delphi Process.

Oral isotretinoin remains a mainstay of treatment for severe, recalcitrant nodular acne. Novel formulations of isotretinoin have been developed over the past decade, including lidose isotretinoin and micronized isotretinoin. It is important to understand the differences between isotretinoin formulations to help guide clinical decision-making and selection of isotretinoin therapy. This study aims to provide evidence-based consensus statements regarding the use of novel formulations of isotretinoin for the treatment of moderate-to-severe acne. The Expert Consensus Group consisted of dermatologists with expertise in the treatment of acne. Voting members met in person to conduct a modified Delphi process; a maximum of 2 rounds of voting were conducted for each consensus statement. A total of 5 statements were generated regarding the use of novel formulations of isotretinoin, addressing the efficacy, tolerability, and side effects of novel isotretinoin formulations. All 5 statements achieved agreement with high consensus. The Expert Consensus Group agrees that individualized selection of isotretinoin therapy is important to maximize efficacy and minimize side effects. Compared to generic isotretinoin, micronized isotretinoin may require lower doses to achieve sufficient plasma concentrations. With the increased bioavailability of micronized formulation, there is no need to calculate cumulative dose; instead, the general recommendation with micronized isotretinoin is to treat for at least 5 months, or longer if needed to achieve clearance. Micronized isotretinoin can be taken in the fed or fasted state and has an acceptable safety profile. J Drugs Dermatol. 2024;23(6):429-432.     doi:10.36849/JDD.7971.

Enhancing Bioavailability: Advances in Oral Isotretinoin Formulations.

Oral isotretinoin continues to be unsurpassed in efficacy for acne. However, it is associated with potential adverse events including risk of fetal defects, necessitating appropriate mitigation strategies. Furthermore, the variance in bioavailability of the original formulation when ingested in fed versus fasted conditions can lead to differences in daily dosing and duration of exposure. Advances in formulation, with lidose encapsulation and subsequently with micronization, have led to iterative improvements in reducing bioavailability variation between fed and fasted conditions. Differences in bioavailability during fasting were 60% less for originator oral isotretinoin, 33% less for lidose-encapsulated form, and 20% less for micronized-isotretinoin formulation. The latter also demonstrated overall greater bioavailability such that a 20% dose reduction was required compared to the originator and lidose-encapsulated formulations. By reducing the effect of high-fat/high calorie food co-ingestion, this micronized formulation may facilitate clarity in determining appropriate oral isotretinoin dose requirements in achieving optimal patient outcomes.

ARTICLE: Advances in Oral Isotretinoin Therapy.

Since its approval in 1982, oral isotretinoin has revolutionized acne therapy. However, oral isotretinoin use has long been associated with challenges of variable bioavailability and food dependence. It is recommended to ingest oral isotretinoin with a high-fat meal in order to maximize absorption, but many patients fail to adhere to this recommendation. This may lead to inadequate isotretinoin absorption levels. Patients who fail to achieve isotretinoin target cumulative dose are more likely to experience symptom relapse. To address the challenge of traditional isotretinoin variable bioavailability, subsequent isotretinoin formulations have attempted to improve its absorption abilities. In 2014, an isotretinoin formulation utilizing Lidose technology, known as Absorica, showed significant improvements in absorption levels compared to traditional oral isotretinoin in the fasted state. In 2019, isotretinoin absorption levels were further advanced in a new formulation approved by the FDA known as Absorica LD. Utilizing advanced micronization technology that physically reduces the size of the drug molecule, Absorica LD exhibits twice the absorption levels of Absorica under fasting conditions. In the fed state, Absorica LD achieves similar plasma levels to Absorica with a 20 percent lower dose. Absorica LD also produces consistent serum isotretinoin levels irrespective of gastrointestinal contents. By eliminating the “food effect” seen in traditional oral isotretinoin, Absorica LD has the potential to improve patient adherence and long-term patient outcomes. J Drugs Dermatol. 20:5(Suppl):s5-11.

Comparative Pharmacokinetic Profiles of a Novel Low-dose Micronized-isotretinoin 32 mg Formulation and Lidose-isotretinoin 40 mg in Fed and Fasted Conditions: Two Open-label, Randomized, Crossover Studies in Healthy Adult Participants.

Two open-label, crossover studies compared the bioavailability of Micronized-isotretinoin 32 mg and Lidose-isotretinoin 40 mg in healthy adults. In the fed bioequivalence/food-effect study, participants (n = 71) received single doses of fed-state Micronized-isotretinoin 32 mg, fed-state Lidose-isotretinoin 40 mg and fasted-state Micronized-isotretinoin 32 mg. In the fasting study, participants (n = 18) received single doses of fasted-state Micronized-isotretinoin 32 mg and fasted-state Lidose-isotretinoin 40 mg. Bioavailability was assessed by isotretinoin LnAUC0­t, LnAUC0­∞ and LnCmax in blood samples taken pre-dosing and over 96 h post-dosing. The 90% confidence intervals for baseline-adjusted least squares geometric mean ratios for LnAUC0­t, LnAUC0­∞ and LnCmax fell within the 80­125% range for bioequivalence for fed-state Micronized-isotretinoin 32 mg vs. fed-state Lidose-isotretinoin 40 mg. Fasted-state Micronized-isotretinoin 32 mg had ~2 times higher bioavailability than fasted-state Lidose-isotretinoin 40 mg. Food had no effect on the rate and a marginal effect on the extent of absorption of Micronized-isotretinoin 32 mg.

Stem cell membrane-coated isotretinoin for acne treatment.

BACKGROUND: Topical isotretinoin is commonly used to treat acne. However, topical isotretinoin has side effects and can hardly permeate through the stratum corneum, the most important skin barrier. Therefore, this study aimed to demonstrate the efficacy of nanoparticles as stable carriers with great curative effects, low side effects, and strong transdermal ability. RESULTS: In a rabbit model of hyperkeratinization, STCM-ATRA-NPs showed significant therapeutic efficacy. By contrast, negative therapeutic efficacy was observed in a golden hamster model of hyper sebum production. Scanning electron microscopy and Fourier transform infrared spectral analyses showed that nanoparticles could penetrate the stratum corneum. Western blotting demonstrated that the nanoparticles could enhance the transdermal efficacy of isotretinoin by reducing the effect of keratin and tight junction proteins. Further, nanoparticles enhanced endocytosis, thereby promoting drug penetration and absorption into the skin. CONCLUSION: STCM-ATRA-NPs were demonstrated to control isotretinoin release, reducing its side effects, and efficiently permeating through the skin by reducing the effect of keratin and tight junction proteins and enhancing endocytosis.

Isotretinoin conundrum: a randomized, openlabel, crossover study in Mexico to evaluate the bioavailability and bioequivalence of three pharmaceutical preparations of isotretinoin in healthy participants.

OBJECTIVE: The oral retinoid agent isotretinoin (13-cis-retinoic acid) is approved for the treatment of severe recalcitrant cystic acne. For registrational renewal of Oratane® in Mexico (isotretinoin; Laboratorios Dermatologicos Darier S.A. de C.V., Mexico), it was necessary to establish bioequivalence to the reference product Roaccutan® (Isotretinoin; Roche, Mannheim, Germany). Three prior studies failed to establish the bioequivalence of Oratane to Mexican-sourced Roaccutan. However, 13 studies demonstrated the bioequivalence of Oratane to Roaccutane® from multiple sources. This study compared the bioavailability of Oratane with that of Mexicansourced Roaccutan and Australian-sourced Roaccutane. METHODS: Study participants received each of the three agents in a randomized, open-label, 6-sequence, 3-way crossover study with a 2-week washout period between treatments. RESULTS: Pharmacokinetic analysis revealed that peak plasma concentration (Cmax) and area under the plasma concentration-time curve from time 0 (dosing) to infinite time (AUC0-∞) were lower for Roaccutan than for Roaccutane and Oratane (Cmax: 1,023.35, 1,223.08, and 1,224.25 ng/mL, respectively; AUC0-∞: 13,653.65, 15,681.35 and 15,733.55 ng/mL x h, respectively). The 90% CIs (test/reference) for the ratios of the geometric means indicated that Oratane was bioequivalent to Roaccutane but not to Roaccutan. In addition, Roaccutane (R2) was not bioequivalent to Roaccutan (R1; R1/R2 90% CIs: Cmax, 76.12 - 91.04; AUC0-t, 82.19 - 91.13; AUC0-∞, 82.94 - 91.57). CONCLUSION: Oratane and Australian-sourced Roaccutane could be considered bioequivalent, but neither formulation was found to be bioequivalent to Mexican-sourced Roaccutan.

Nanocolloidal carriers of isotretinoin: antimicrobial activity against Propionibacterium acnes and dermatokinetic modeling.

Acne, a common skin disease in teenagers, is caused by Propionibacterium acnes (P. acnes). Isotretinoin (ITR) is though reported to have immense antiacne potential, yet there are hardly any reports vouching its antimicrobial activity. The present study, therefore, was undertaken to study the antimicrobial activity of ITR and evaluate the effect of its encasement in nanocarriers on its minimum inhibitory concentration (MIC). The nanocarriers were also evaluated for the skin transport characteristics. MICs of pure drug and entrapped drug in nanolipid carriers (ITR-NLCs) and in solid lipid nanoparticles (ITR-SLNs) were determined by broth dilution method against clindamycin phosphate as the reference antibiotic. It was observed that ITR possessed marked antimicrobial activity against anaerobic pathogen, P. acnes. Nanocarriers loaded with ITR, that is, SLNs and NLCs, enhanced the antimicrobial activity even at lower concentrations vis-à-vis the drug alone and improved drug transport potential vis-à-vis the commercial gel. The unique findings could be the result of effective adhesion of ITR-loaded nanocarriers to the bacterial membranes and release of drug directly to the target. Besides establishing ITR as an antimicrobial agent against acne-causing bacteria, the current work ratifies immense potential of nanocolloidal carriers like SLNs and NLCs to treat acne in a more efficient manner.

Comparative pharmacokinetic profiles of a novel isotretinoin formulation (isotretinoin-Lidose) and the innovator isotretinoin formulation: a randomized, 4-treatment, crossover study.

BACKGROUND: A high-fat meal is needed for optimal absorption of isotretinoin. A new formulation of isotretinoin, which enhances absorption of isotretinoin in the absence of dietary fat, has recently been approved by the Food and Drug Administration (FDA). OBJECTIVE: We sought to compare the pharmacokinetic profiles of a new formulation of isotretinoin (isotretinoin-Lidose) with the innovator isotretinoin formulation. METHODS: This study was an open-label, single-dose, randomized, 4-treatment, crossover comparative trial between a new and innovator formulation of isotretinoin in the fasting and fed states. RESULTS: Both formulations were bioequivalent under fed conditions. As expected in a fasting state, absorption of both formulations was reduced. A considerable difference between the 2 drugs occurred under fasted conditions-there was a marked improvement in overall bioavailability of the isotretinoin-Lidose formulation. Mean plasma levels of the isotretinoin-Lidose formulation during fasting reached 66.8% of that observed with a fatty meal, and those of the isotretinoin formulation only reached 39.6% of that observed with a fatty meal. LIMITATIONS: Only the FDA-stipulated standard high-fat, high-calorie meal of 50-g fat was studied in the fed state. CONCLUSION: Isotretinoin-Lidose formulation is bioequivalent to the innovator formulation under fed conditions with regard to its pharmacokinetic profile but delivers twice as much isotretinoin and 4-oxo-isotretinoin when administered after an overnight fast.

Improving bioavailability with a novel isotretinoin formulation (isotretinoin-Lidose).

Current practice guidelines recommend administration of oral isotretinoin with high-fat meals, which may pose issues with patient compliance. Isotretinoin-Lidose (Epuris™), approved by Health Canada in November 2012 and scheduled for commercial release June 2013, is based on novel lipid encapsulation technology (Lidose®) to enclose isotretinoin, thereby increasing drug absorption during fasted states. An open label, single dose randomized crossover study demonstrated pharmacokinetic bioequivalence of isotretinoin-Lidose to standard isotretinoin formulations during fed states, with significantly greater absorption during fasting. Isotretinoin-Lidose, may lead to more consistent plasma levels of isotretinoin during variable dietary conditions, providing the potential for enhanced patient outcomes.

The relevance of nanotechnology, hepato-protective agents in reducing the toxicity and augmenting the bioavailability of isotretinoin.

Acne Vulgaris is one of the most common chronic inflammatory skin disorders that affect majority of teen-agers worldwide. Isotretinoin (ITT) is the drug of choice in the management of acne, but, it suffers from serious side-effects including hepatotoxicity, and some psychological disturbances following its oral intake. The objective of this study was to develop and optimize ITT loaded nanoemulsions (ITT-SNEDDS) and to incorporate resveratrol (RSV)in optimum formulation to decrease ITT side effects The ITT solubility was first tested in various essential oils, surfactants, and co-surfactants to select the essential nanoemulsion ingredients. Mixture design was applied to study the effect of independent variables and their interactions on the selected dependent responses. The developed ITT-SNEDDS were characterized for their globule size and ex vivo permeation. The optimized batch was further loaded with RSV and evaluated for in vitro and ex vivo permeation and for in vivo hepatotoxicity. The developed ITT-SNEDDS exhibited globule size below 300 nm, up to 272.27 ± 7.12 mcg/cm2.h and 61.27 ± 2.83% of steady-state flux (JSS) and permeability % respectively. Optimum formulation consisted of 0.15 g oil mixture, 0.6 g of surfactant (Labrasol), and 0.250 g co-surfactant (Transcutol). Permeability studies confirmed the enhanced permeation percentage of ITT (40.77 ± 1.18%), and RSV (29.94 ± 2.02%) from optimized formulation, with enhanced steady-state flux (JSS). In vivo studies demonstrated the superior hepatoprotective activity of optimized formulation compared to a different drug formulations and marketed product. Therefore, RVS loaded ITT-SNEDDS might be a successful strategy for acne management with improved action, and minimum side effects.

Role of UDP-glucuronosyltransferase isoforms in 13-cis retinoic acid metabolism in humans.

13-cis Retinoic acid (13cisRA, isotretinoin) is an important drug in both dermatology, and the treatment of high-risk neuroblastoma. 13cisRA is known to undergo cytochrome P450-mediated oxidation, mainly by CYP2C8, but phase II metabolic pathways have not been characterized. In the present study, the glucuronidation activities of human liver (HLM) and intestinal microsomes (HIM), as well as a panel of human UDP-glucuronosyltransferases (UGTs) toward both 13cisRA and the 4-oxo metabolite, 4-oxo 13cisRA, were compared using high-performance liquid chromatography. Both HLM and, to a greater extent, HIM catalyzed the glucuronidation of 13cisRA and 4-oxo 13cisRA. Based on the structures of 13cisRA and 4-oxo 13cisRA, the glucuronides formed are conjugated at the terminal carboxylic acid. Further analysis revealed that UGT1A1, UGT1A3, UGT1A7, UGT1A8, and UGT1A9 were the major isoforms responsible for the glucuronidation of both substrates. For 13cisRA, a pronounced substrate inhibition was observed with individual UGTs and with HIM. UGT1A3 exhibited the highest rate of activity toward both substrates, and a high rate of activity toward 13cisRA glucuronidation was also observed with UGT1A7. However, for both substrates, K(m) values were above concentrations reported in clinical studies. Therefore, UGT1A9 is likely to be the most important enzyme in the glucuronidation of both substrates as this enzyme had the lowest K(m) and is expressed in both the intestine and at high levels in the liver.

The metabolism and pharmacokinetics of isotretinoin in patients with acne and rosacea are not influenced by ethanol.

BACKGROUND: Isotretinoin is effective in the treatment of severe acne and rosacea. Both parent drug and its main metabolite 4-oxo-isotretinoin are potentially teratogenic compounds and contain a carboxylic acid moiety. In the presence of ethanol, naturally occurring as well as synthetic retinoids also containing a carboxylic acid moiety are capable of undergoing an ethyl esterification with the metabolic formation of more lipophilic compounds with a much longer terminal half-life. OBJECTIVES: To determine if isotretinoin (13-cis-RA), its main metabolite 4-oxo-isotretinoin (4-oxo-13-cis-RA), and other possible metabolites in the presence or absence of ethanol are converted to their corresponding ethyl derivatives in patients with severe acne or rosacea after multiple isotretinoin dosing. In addition, pharmacokinetic parameters of the parent drug and its 4-oxo metabolite were determined. PATIENTS/METHODS: Eleven patients with severe acne or rosacea were treated with isotretinoin daily for 3 months and investigated pharmacokinetically during 24 h after 1 month of treatment and for up to 28 days after discontinuation of therapy. A possible influence of ethanol was evaluated using a simple self-administered questionnaire and by measuring serum ethanol levels during treatment. The concentrations of isotretinoin, 4-oxo-isotretinoin and possible ethylated and nonethylated metabolites were measured by reverse-phase high-performance liquid chromatography. RESULTS: Although seven of 11 patients had a considerable weekly alcohol intake, no endogenous synthesis of ethyl derivatives of isotretinoin, the main 4-oxo metabolite or the all-trans compounds was chromatographically detectable in any of the patients' plasma samples during the treatment period. Multiple dose pharmacokinetic data for the parent drug and its main metabolite were comparable to previous studies. CONCLUSIONS: The metabolism and pharmacokinetics of isotretinoin and its main metabolites are not influenced by ethanol during long-term isotretinoin treatment. After ceasing long-term isotretinoin therapy the recommended period of 1 month for using anticonceptive measures in fertile women seems adequate.

Phase I trial of belinostat in combination with 13-cis-retinoic acid in advanced solid tumor malignancies: a California Cancer Consortium NCI/CTEP sponsored trial.

PURPOSE: The reported maximum tolerated dose (MTD) of single-agent belinostat is 1000 mg/m2 given days 1-5, every 21 days. Pre-clinical evidence suggests histone deacetylase inhibitors enhance retinoic acid signaling in a variety of solid tumors. We conducted a phase I study of belinostat combined with 50-100 mg/m2/day 13-cis-retinoic acid (13-cRA) in patients with advanced solid tumors. METHODS: Belinostat was administered days 1-5 and 13-cRA days 1-14, every 21 days. Dose-limiting toxicity (DLT) was defined as cycle 1 hematologic toxicity grade ≥ 3 not resolving to grade ≤ 1 within 1 week or non-hematologic toxicity grade ≥ 3 (except controlled nausea and vomiting and transient liver function abnormalities) attributable to belinostat. RESULTS: Among 51 patients, two DLTs were observed: grade 3 hypersensitivity with dizziness and hypoxia at 1700 mg/m2/day belinostat with 100 mg/m2/day 13-cRA, and grade 3 allergic reaction at 2000 mg/m2/day belinostat with 100 mg/m2/day 13-cRA. The MTD was not reached. Pharmacokinetics of belinostat may be non-linear at high doses. Ten patients had stable disease, including one with neuroendocrine pancreatic cancer for 56 cycles, one with breast cancer for 12 cycles, and one with lung cancer for 8 cycles. Partial responses included a patient with keratinizing squamous cell carcinoma of the tonsils, and a patient with lung cancer. CONCLUSIONS: The combination of belinostat 2000 mg/m2 days 1-5 and 13-cRA 100 mg/m2 days 1-14, every 21 days, was well-tolerated and an MTD was not reached despite doubling the established single-agent MTD of belinostat.

Pharmacokinetics and metabolism of all-trans- and 13-cis-retinoic acid in pulmonary emphysema patients.

Retinoids promote lung alveolarization in animal models and were administered to patients as part of the Feasibility of Retinoid Therapy for Emphysema (FORTE) study. This FORTE substudy investigated the pharmacokinetic profiles of 2 retinoic acid isomers-all-trans-retinoic acid (ATRA) and 13-cis-retinoic acid (13-cRA)-in subjects with emphysema, evaluated strategies to overcome self-induced ATRA catabolism, and identified pharmacodynamic relationships. Comprehensive and limited pharmacokinetics were obtained at multiple visits in emphysema subjects treated with placebo (n = 30), intermittent dosing (4 days/week) with low-dose ATRA (1 mg/kg/day, n = 21), or high-dose ATRA (2 mg/kg/day, n = 25) or daily administration of 13-cRA (1 mg/kg/day, n = 40). High-dose ATRA produced the highest peak plasma ATRA Cmax. However, at follow-up, plasma ATRA C(max) was significantly decreased from baseline in subjects whose day 1 levels exceeded 100 ng/mL (P < .0001). In contrast, administration of 13-cRA produced lower plasma ATRA C(max) (<100 ng/mL), but the levels were significantly higher at follow-up than those on day 1 (P < .001). Plasma ATRA levels as determined on day 1 correlated with changes in pulmonary diffusing capacity at 6 months, consistent with concentration-dependent biologic effects (r2 = -0.25). The authors conclude that intermittent therapy with high-dose ATRA produced the greatest ATRA exposure, but alternative approaches for limiting self-induced ATRA catabolism should be sought.

Biopharmaceutics of 13-cis-retinoic acid (isotretinoin) formulated with modified beta-cyclodextrins.

13-cis-Retinoic acid (13-cis-RA), also known as isotretinoin, is commonly used in the management of severe acne. Its clinical efficacy in oncology has also been documented. As a vitamin A derivative, it is not soluble in water. This solubility barrier not only affects its oral absorption but also makes parenteral delivery difficult. Recently, water-soluble formulations of 13-cis-RA have been attempted with 2-hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and randomly methylated-beta-cyclodextrin (RM-beta-CD). In this study, the pharmacokinetic profiles of these two formulations were assessed in Sprague-Dawley rats after single intravenous or oral administration. We found that 13-cis-RA was eliminated from the body through a dose-independent process after intravenous injection of either sodium salt or the HP-beta-CD formulation within the tested dosage range (2.0-7.5mg/kg). Furthermore, HP-beta-CD did not alter the kinetic profile of 13-cis-RA after intravenous administration in comparison with 13-cis-RA sodium salt. We also found that RM-beta-CD dramatically enhanced the oral absorption of 13-cis-RA. At 10.0mg/kg, the bioavailability of 13-cis-RA formulated with RM-beta-CD was about three-fold higher than that of the control (13-cis-RA suspended in 0.5% carboxymethylcellulose (CMC)). Similarly, the oral absorption of 13-cis-RA was not saturated within our tested range (2.5-10.0mg/kg) and the bioavailability remained unchanged. These results demonstrated that HP-beta-CD and RM-beta-CD were suitable excipients for the delivery of 13-cis-RA.

Pharmacokinetics and pharmacogenetics of 13-cis-retinoic acid in the treatment of neuroblastoma.

There are a number of factors relating to the clinical pharmacology of 13-cis-Retinoic Acid (13-cisRA) which, taken together, provide a strong case for the potential benefit of a therapeutic monitoring approach to ensure that uniform plasma concentrations of 13-cisRA are achieved in all patients. Firstly, low dose, continuous use of 13-cisRA has been shown to provide limited or no clinical benefit in neuroblastoma patients, whereas a high-dose, intermittent regimen resulted in a significant improvement in event-free survival. This suggests that dose levels and therefore plasma concentrations of drug are important determinants of 13-cisRA efficacy. Secondly, the currently used 13-cisRA dosing regimen of 160 mg/m(2)/day results in a >10-fold variation in plasma concentrations, with plasma concentrations observed in a significant percentage of patients below those required for activity in neuroblastoma cells in vitro. Importantly, there would appear to be limited intra-patient variation in 13-cisRA plasma concentrations, i.e. those patients with lower 13-cisRA plasma concentrations following a single dose of 13-cisRA are likely to have similarly low concentrations following all doses of 13-cisRA on subsequent courses. As 13-cisRA is given as chronic treatment, those patients experiencing lower plasma concentrations on the current dosing regimen will potentially be exposed to sub-therapeutic concentrations of drug for the entire 6 month treatment period. While this type of pharmacokinetic monitoring approach may prove to be beneficial in the short term, an increased knowledge of pharmacogenetic factors influencing to the metabolism of 13-cisRA may ultimately allow us to identify patients who may be less likely to benefit from treatment due to an increased rate of parent drug metabolism. In this respect, pharmacogenetic studies assessing the relative expression levels or mutations in enzymes such as cytochrome P450 (CYP) and particularly CYP26 are needed to assess any potential association with rate of metabolism in vivo.

Steady state pharmacokinetics of oral treatment with 13-cis-retinoic acid or all-trans-retinoic acid in male and female adult rats.

Male and female Sprague-Dawley rats were orally gavaged with 13-cis-retinoic acid (7.5 or 15 mg/kg) or all-trans-retinoic acid (10 or 15 mg/kg) for 7 consecutive days. Blood was collected out to 8 hr after the last gavage on day 7. HPLC serum concentrations of 13-cis-retinoic acid, all-trans-retinoic acid, and 13-cis-4-oxo-retinoic acid were subjected to model independent pharmacokinetic analyses. Peak serum levels of 563 to 1640 ng/ml were observed for rats treated with 13-cis-retinoic acid at 1.5-2 hr after gavage. Peak serum levels of 183 to 267 ng/ml at 1.5 hr after gavage were observed for all-trans-retinoic acids. The elimination half-life of 13-cis-retinoic acid was about 1.5 hr while the elimination half-life of all-trans-retinoic acid was slightly longer. There were no sex differences for any parameter. Serum levels resulting from the 7.5 mg/kg 13-cis-retinoic acid were similar to those of human Accutane users.

Pharmacokinetics and pharmacodynamics of ch14.18/CHO in relapsed/refractory high-risk neuroblastoma patients treated by long-term infusion in combination with IL-2.

Ch14.18 manufactured in Chinese hamster ovary (CHO) cells is currently being evaluated in clinical trials. Short-term infusion (STI) (8-20 h/day; 4-5 days) of 100 mg/m2 ch14.18/CHO (dinutiximab ß) per cycle in combination with cytokines is standard treatment of neuroblastoma (NB) patients. As pain is a limiting factor, we investigated a novel delivery method by continuous long-term infusion (LTI) of 100 mg/m2 over 10 days. 53 NB patients were treated with 5-6 cycles of 6 × 106 IU/m2 subcutaneous interleukin-2 (d 1-5, 8-12), LTI of 100 mg/m2 ch14.18/CHO (d 8-18) and 160 mg/m2 oral 13-cis-retinoic acid (d 22-35). Human anti-chimeric antibody (HACA), antibody-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity were determined. With LTI, we observed a maximum concentration of ch14.18/CHO (Cmax) of 12.56 ± 0.68 µg/ml and a terminal half-life time (t1/2 ß) of 32.7 ± 16.2 d. The clearance values for LTI and STI of 0.54 ± 0.13 and 0.41 ± 0.29 L/d m2 and area under the serum concentration-time curve (AUC) values of 189.6 ± 41.4 and 284.8 ± 156.8 µg×d/ml, respectively, were not significantly different. Importantly, we detected ch14.18/CHO trough concentration of ≥ 1 µg/ml at time points preceding subsequent antibody infusions after cycle 1, allowing a persistent activation of antibody effector mechanisms over the entire treatment period of 6 months. HACA responses were observed in 10/53 (19%) patients, similar to STI (21%), indicating LTI had no effect on the immunogenicity of ch14.18/CHO. In conclusion, LTI of ch14.18/CHO induced effector mechanisms over the entire treatment period, and may therefore emerge as the preferred delivery method of anti-GD2 immunotherapy to NB patients.