Paul Catz

Transdermal delivery of levonorgestrel I: Alkanols as permeation enhancers in vitro

The effect of alcoholic penetration enhancers on the transdermal delivery of levonorgestrel (LN) was investigated. A series of albanais was tested in vitro it for their ability to enhance the delivery of LN through excised rat skins. The steady-state flux of LN was measured using donor phase compositions of water fethanol mixtures, and the neat straight chain alkanols ethanol, propanol, butanol, pentanol, hexanol, and octanol. The steady-state flux of LN was found to increase as the alkyl chain length increased from C2 to C4. This was followed by a decrease in the steady-state flux as the alkyi chain length increased above 1 -butanol. Three secondary alkanols, 2-propanol, 2-butanol, and 2-pentanol were also tested as penetration enhancers. The same trend was evident: steady-state flux was highest for 2-butanol with 2-propanol and 2-pentanol giving lower steady-state fluxes. The flux of LN was lower for secondary alkanols relative to the corresponding primary alkanol. Propylene glycol was also tested as an enhancer. Overall, the steady-state flux using this penetration enhancer was about that of water, which was low relative to all the alkanols. Flux of LN through human cadaver skin from pure ethanol was about four times lower than through rat skin. A mechanism for permeability enhancement based on the alkanol structure and water-solubility is presented as well as a discussion of the data as it relates to development of a transdermal delivery system for LN.

Transdermal delivery of levonorgestrel. VIII. Effect of enhancers on rat skin, hairless mouse skin, hairless guinea pig skin, and human skin

Abstract The penetration enhancing effect of ethyl acetate, with or without ethanol as a cosolvent, was evaluated in vitro on rat skin, hairless mouse skin, hairless guinea pig skin, and human cadaver skin using the contraceptive drug levonorgestrel. Under the influence of the enhancers, the relative skin permeability of levonorgestrel through the four skin types showed a clear trend: hairless mouse skin >hairless guinea pig skin ∼ rat skin > human skin. These results show that rodent skins are poor models for human skin under the conditions used. The steady-state flux of levonorgestrel through human skin was increased about 7-fold 0.03 μg/cm 2 h vs 0.2 μg/cm 2 h when neat ethyl acetate was used in place of ethanol as the donor vehicle. Adding polyethylene glycol 400 (PEG 400; 40% v/v in saline) to the receptor solution increased the steady-state flux of levonorgestrel through human skin only slightly relative to saline as a receptor solution. The lag time of levonorgestrel through human skin was longer relative to that for the rodent skins tested. The flux of ethyl acetate and ethanol through all the skins was also measured. The rodent skins were all much more permeable towards both solvents than was human skin. For each skin type tested, there appeared to be a direct correlation between the cumulative amount of solvent permeating through the skin and the cumulative amount of drug permeating through the skin.

Simple alkyl esters as skin permeation enhancers

Abstract The use of simple alkyl esters, in particular ethyl acetate, as skin permeation enhancers for drugs is presented. Ethyl acetate was found to increase the transdermal flux of levonorgestrel, estradiol, hydrocortisone, 5-fluorouracil, and nifedipine through rat skin in vitro relative to that when ethanol or water were used as reference solvents. Relative to water, the flux of levonorgestrel was increased 80 fold using pure ethyl acetate. Relative to pure ethanol as a reference permeation enhancer, the flux of levonorgestrel was increased 12 to 15 fold using either pure ethyl acetate or volume fractions of ethyl acetate in ethanol down to 0.18 as permeation enhancers. Butyl acetate was also tested with levonorgestrel and was found to increase the flux about 7 fold relative to pure ethanol. The fluxes of estradiol, hydrocortisone, 5-fluorouracil, and nifedipine were increased from 75 to 650 fold, depending on the drug, when ethyl acetate was used as a permeation enhancer relative to that when water was used as an enhancer, and from 9 to 34 fold relative to that when ethanol was used as an enhancer. Also discussed are the possible mechanisms of action by which ethyl acetate increases the percutaneous absorption of drugs and use of ethyl acetate in transdermal drug delivery systems.

Development of a new generation of 4-aminoquinoline antimalarial compounds using predictive pharmacokinetic and toxicology models.

Among the known antimalarial drugs, chloroquine (CQ) and other 4-aminoquinolines have shown high potency and good bioavailability. Yet complications associated with drug resistance necessitate the discovery of effective new antimalarial agents. ADMET prediction studies were employed to evaluate a library of new molecules based on the 4-aminoquinolone-related structure of CQ. Extensive in vitro screening and in vivo pharmacokinetic studies in mice helped to identify two lead molecules, 18 and 4, with promising in vitro therapeutic efficacy, improved ADMET properties, low risk for drug-drug interactions, and desirable pharmacokinetic profiles. Both 18 and 4 are highly potent antimalarial compounds, with IC(50) values of 5.6 and 17.3 nM, respectively, against the W2 (CQ-resistant) strain of Plasmodium falciparum (for CQ, IC(50) = 382 nM). When tested in mice, these compounds were found to have biological half-lives and plasma exposure values similar to or higher than those of CQ; they are therefore desirable candidates to pursue in future clinical trials.

Percutaneous penetration of methyl phosphonate antisense oligonucleotides

Abstract A series of antisense methyl phosphonate oligonucleotides (MPOs) were evaluated in vitro for skin penetration and retention using either hairless mouse or human cadaver skin. Several skin penetration enhancers were used to promote uptake of MPOs ranging in molecular weight from 1834 to 5500. In general, as the molecular weight of the MPOs increased, the penetration rate decreased. Tape stripping experiments with both hairless mouse skin and human cadaver skin indicated that the stratum corneum is the primary barrier to penetration. Comparison of a 14-mer MPO and the same MPO modified by the introduction of one negative charge (phosphate linkage) per molecule reduced the skin permeability by about 10-fold. The amount of MPO retained in the dermis at the end of the 24 h permeation experiments indicated that most of the compounds were able to reach a nominal target concentration of 1.0 μM. The largest MPO tested (18-mer, Mol. Wt 5500) gave the least amount of material penetrating through human cadaver skin, but depending on the vehicle, was retained in nearly sufficient amounts in the target tissues (dermis). Thus, the 18-mer represents a logical candidate for further evaluation due to the potential for delivery into the target tissue with limited systemic exposure.

Alkyl esters as skin permeation enhancers for indomethacin

Abstract The use of simple alkyl esters as skin permeation enhancers for indomethacin is described. The esters investigated were methyl acetate, ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and methyl valerate. Other solvents tested as enhancers were water, ethanol, diethyl succinate, ethyl acetoacetate, dimethyl sulfoxide, and Azone. The steady-state flux of indomethacin as measured in vitro through excised rat skin was enhanced about 1500-fold by ethyl acetate, methyl acetate, and methyl propionate relative to that from water. Relative to pure ethanol as permeation enhancing solvent, flux was enhanced over 20-fold using these three solvents. The other alkyl esters were about as effective as ethanol at increasing transdermal flux of indomethacin. Azone (5% in propylene glycol) increased the flux of indomethacin about 1100-fold relative to water and about 14-fold relative to ethanol. Dimethyl sulfoxide (30% in propylene glycol) and ethyl acetate (30% in propylene glycol) were relatively ineffective at increasing the flux of indomethacin. The use of ethyl acetate as a skin permeation enhancer in transdermal drug delivery is discussed.

Transdermal delivery of levonorgestel II: Effect of prodrug structure on skin permeability in vitro

The effect of prodrug structure on the permeability of levonorgestrel (LN) through rat skin in vitro was investigated. Two types of prodrugs were synthesized and tested. One type of prodrug was more hydrophilic relative to LN; the second type of prodrug prepared were simple alkyl esters with lower melting points relative to LN. The hydrophilic derivatives were designed to partition into the viable epidermis to a greater extent than LN; the low melting point derivatives were also designed to have increased flux due to greater solubility in the skin. The hydrophilic prodrugs prepared were LN-glycidol and LN-hexanediol; the ester prodrugs were LN-hexanoate and LN-pentanoate. The transdermi steady-state flux through rat skin in vitro of LN using LN-glycidol was 1.95 μg/(cm2 h) using ethanol as the donor phase solvent; steady-state LN flux was 0.95 μg/(cm2 h) using LN-hexanediol. These fluxes are approximately 20 to 40 times higher than free LN. Unfortunately, both LN-glycidol and LN-hexanediol were hydrolytically unstable in neutral to basic solutions. The ester prodrugs were more hydrolytically stable but the fluxes were lower. The steady-state flux of LN using LN-hexanoate was 0.18 μg/(cm2 h); the flux, which had not yet reached steady-state after 66 h, of LN using LN-pentanoate was 0.08 μg/(cm2 h). No ester prodrug was detected in the receptor phase at any time indicating complete hydrolysis by the presence of esterase in the skin. No hydrolysis was measured in the donor phase over the course of the experiment. These results indicate that the structure of LN can be modified by the prodrug approach to increase the flux of LN through rat skin in vitro.

Effect of resveratrol on 17β-estradiol sulfation by human hepatic and jejunal S9 and recombinant sulfotransferase 1E1

The purpose of this study was to investigate the sulfation of resveratrol (3,5,4′-trihydroxystilbene) and its potential to exhibit drug-drug interactions via sulfation. The possible interaction of resveratrol with 17β-estradiol (E2), a major estrogen hormone and prototypic substrate for sulfate conjugation, was studied. Resveratrol and E2 are both known to undergo sulfate conjugation catalyzed by human sulfotransferases (SULTs). Resveratrol is a phytoestrogen with mixed estrogen agonist/antagonist properties that is being developed as a chemopreventive agent. The sulfate conjugation of E2 and resveratrol were studied individually using S9 fractions from human liver and jejunum as well as recombinant human SULT isoforms. The sulfation of E2 (3–20 nM) was then investigated in the presence of various concentrations (0, 0.5, 1, and 2 μM) of resveratrol using the two S9 preparations as well as recombinant SULT1E1, the major isoform responsible for E2 sulfation. Resveratrol inhibited E2 sulfation with estimated Ki values of 1.1 μM (liver), 0.6 μM (jejunum), and 2.3 μM (SULT1E1), concentrations that could be pharmacologically relevant. The results suggest that these phytoestrogens can potentially alter the homeostasis of estrogen levels. These findings also imply that resveratrol may inhibit the metabolism of other estrogen analogs or therapeutic agents such as ethinylestradiol or dietary components that are also substrates for SULT1E1.

Pharmacokinetics of the Antimalarial Drug, AQ-13, in Rats and Cynomolgus Macaques

The purpose of this study was to evaluate the bioavailability and pharmacokinetics of a new antimalarial drug, AQ-13, a structural analog of chloroquine (CQ) that is active against CQ-resistant Plasmodium species, in rats and cynomolgus macaques. Sprague-Dawley rats (n = 4/sex) were administered a single dose of AQ-13 intravenously (i.v.) (10 mg/kg) or orally (20 or 102 mg/kg). Blood and plasma samples were collected at several timepoints. AQ-13 achieved C max after oral administration at approximately 3 to 4 h and could be detected in blood for 2 to 5 days after oral administration. The ratio of area under the curve (AUC) values at the high and low dose for AQ-13 deviated from an expected ratio of 5.0, indicating nonlinear kinetics. A metabolite peak was noted in the chromatograms that was identified as monodesethyl AQ-13. Oral bioavailability of AQ-13 was good, approximately 70%. The pharmacokinetics of AQ-13 was also determined in cynomolgus macaques after single (i.v., 10 mg/kg; oral, 20 or 100 mg/kg) and multiple doses (oral loading dose of 50, 100, or 200 mg/kg on first day followed by oral maintenance dose of 25, 50, or 100 mg/kg, respectively, for 6 days). The AUC and C max values following single oral dose administration were not dose proportional; the C max value for AQ-13 was 15-fold higher following an oral dose of 100 mg/kg compared to 20 mg/kg. MonodesethylAQ-13 was a significant metabolite formed by cynomolgus macaques and the corresponding C max values for this metabolite increased only 3.8-fold over the dose range, suggesting that the formation of monodesethyl AQ-13 is saturable in this species. The bioavailability of AQ-13 in cynomolgus macaques following oral administration was 23.8% for the 20-mg/kg group and 47.6% for the 100-mg/kg group. Following repeat dose administration, high concentrations of monodesethyl AQ-13 were observed in the blood by day 4, exceeding the AQ-13 blood concentrations through day 22. Saturation of metabolic pathways and reduced metabolite elimination after higher doses are suggested to play a key role in AQ-13 pharmacokinetics in macaques. In summary, the pharmacokinetic profile and metabolism ofAQ-13 are very similar to that reported in the literature for chloroquine, suggesting that this new agent is a promising candidate for further development for the treatment of chloroquine-resistant malaria.

Effect of cosolvents on ethyl acetate enhanced percutaneous absorption of levonorgestrel

Abstract The effect of various cosolvents on ethyl acetate (EtAc) enhanced percutaneous absorption of levonorgestrel (LN) was studied using excised hairless mouse skin. The steady-state flux of LN through hairless mouse skin was increased when mixtures of EtAc and ethanol (EtOH) were used as donor phase solvents relative to that when neat EtAc was used. For example, the flux of LN was increased about 2 fold (4.5 to 10 μg/cm2 h) when EtOH was added to EtAc at a volume fraction of 0.5 relative to neat EtAc. In contrast, the flux of LN from water was measured at 0.02 μg/cm2 h. Adding oleic acid or isopropyi myristate at a volume fraction of 0.5 in EtAc lowered the flux to approximately 1.0 μg/cm2 h. In contrast, when oleic acid was added to EtAc/EtOH (1:1) or EtOH, both at a volume fraction of 0.05, the transdermal flux of LN was found to be 9 and 7 μg/cm2 h, respectively. Apparent diffusion coefficients and partition coefficients were calculated and it was found that EtAc and EtOH increased the diffusivity of LN relative to water while skin/vehicle partition coefficients correlated roughly with the observed flux of LN from the saturated solutions, with the exception of the water vehicle.