Improvement of drug release rate from carbopol 934P formulation.

Carbopol 934P (CP) is a mucoadhesive polymer which has been investigated as a useful adjuvant for bioadhesive drug delivery system. However, since the drug release rate from the solid formulation of CP is slow, it is difficult to take advantage of the polymer's mucoadhesive property in oral administration of fast-acting drugs. In this study, we prepared freeze-dried sodium salt of CP (FNaCP) in order to improve drug release from the formulation of CP. The drug release rate from the formulation of FNaCP was much faster than that of CP: the rate from the formulation of CP in JP XIII 1st fluid (pH 1.2) was faster than in JP XIII 2nd fluid (pH 6.8). To determine the cause of rapid drug release from FNaCP capsules, the change of CP gel properties with pH and ionic strength was investigated. Experimental results indicated that CP forms a swollen gel layer, a drug release barrier between the formulation of CP and the bulk release media. FNaCP was also thought to disperse rapidly in the 1st and 2nd fluids without formation of the swollen gel layer. In conclusion, since FNaCP improves the drug release rate from the solid CP formulation, it could be a useful adjuvant of an oral bioadhesive drug delivery system.

The enhancing mechanism of capric acid (C10) from a suppository on rectal drug absorption through a paracellular pathway.

Capric acid (C10) enhanced the absorption of cefoxitin sodium in a concentration-dependent manner following the rectal administration as a suppository in rats. The optimal concentration of C10 was 13%. C10 administered as a suppository also reduced rectal membrane resistance (Rm), showing that the above enhancing effect was induced by widening the paracellular pathway. Both the enhancing effect on the absorption and the reducing effect on Rm were inhibited by W7, an inhibitor of myosin light chain kinase. These results supported that, as shown in the in vitro Caco-2 cell system, the C10 effect on the paracellular pathway is due to activating the contraction of Ca(2+)-calmodulin-dependent actin filament.

Effect of phosphatidylcholine and cholesterol on pH-sensitive liposomes.

We previously reported that liposomes composed of phosphatidylethanolamine (PE) and fatty acid exhibited pH-dependent leakage, aggregation and fusion (N. Hazemoto, M. Harada, N. Komatubara, M. Haga and Y. Kato, Chem. Pharm. Bull., 38, 748 (1990)). In this study, we have examined the effects of phosphatidylcholine (PC) and cholesterol (Chol) on the pH-sensitivity of liposomes. Contents-leakage from liposomes was always accompanied by a change in light-scattering, suggesting that aggregation or fusion of liposomes causes the leakage. The pH-sensitivity was observed only when liposomes contained less than 32 mol% of PC. The leakage vs. pH curves shifted to the more acidic regions as the PC content of the liposomes increased, but the maximum leakage (%) did not change. The effect of cholesterol on the pH-sensitivity depended on the PC/PE ratio of the liposomes. Addition of cholesterol to PC/PE/oleic acid (OA) liposomes system induced two effects, that is, aggregation of liposomes via the reduction in PC content and the stabilization of the liposomal membrane. It was shown that pH-sensitivity can be controlled by addition of the appropriate amount of PC and/or Chol to liposomal lipids.

Enantiomeric difference in percutaneous penetration of propranolol through rat excised skin.

The percutaneous penetration of R-(+)- and S-(-)-propranolol (PL) through rat excised skin was investigated in vitro. The flux of S-(-)-PL after application to normal skin was high compared with that of R-(+)-PL. On the other hand, in damaged rat skin, the flux of R-(+)-PL was almost equivalent to that of S-(-)-PL. It is suggested that there is an enantiomeric difference between S-(-)- and R-(+)-PL in terms of penetration through rat stratum corneum.

[Percutaneous absorption of drug from alpha-olefin oligomer gel bases].

The percutaneous absorption of drug from the alpha-olefin oligomer (alpha-OL) gel base prepared by using palmitate of dextrin (Rheopearl KL) as a gelling agent was investigated by using the abdominal skin of rats in vivo. The 20, 30, 40 and 50 alpha-OLs with average molecular weights of 288, 380, 440 and 535, respectively were used in this study. The flurbiprofen (FP) was selected as a model drug. The percutaneous absorption of FP from the alpha-OL gel base was observed to be influenced by the molecular weight of alpha-OL. The percutaneous absorption profiles of FP from 40 and 50 alpha-OLs gel bases were almost the same. On the other hand, the absorption of FP from 30 alpha-OL gel base was significantly higher than those of 40 and 50 alpha-OLs gel bases. Furthermore, the percutaneous absorption of FP from 20 alpha-OL gel base was observed to be the highest in the test gel bases. In order to establish the reason for the differences in the percutaneous absorption of FP from 20, 30, 40 and 50 alpha-OLs gel bases, the apparent partition ratios of FP between water and four different alpha-OLs were determined as a parameter of the affinity of FP for the vehicle. Consequently, it has become apparent that the partition ratio exerts an influence on the percutaneous absorption of FP from the alpha-OL gel bases.

Enhancing effects of myristyl lactate and lauryl lactate on percutaneous absorption of indomethacin in rats.

The enhancing effects of myristyl lactate (ML) and lauryl lactate (LL) on the percutaneous absorption of indomethacin (ID) from test solutions in propylene glycol (PG) were investigated in rats. ID absorption was observed to be markedly enhanced by the addition of ML or LL to PG as compared with the control (PG alone). The marked enhancing effects were observed at concentrations greater than 3% ML and 3% LL in PG. In particular, the maximal enhancement of percutaneous absorption of ID was achieved at 5% ML and LL. To elucidate the mode of action of ML as an enhancer, the percutaneous absorption of ID through the skin pretreated with ML alone was investigated. It was suggested that ML acts on the stratum corneum to produce its effect.

Percutaneous absorption of indomethacin from mixtures of fatty alcohol and propylene glycol (FAPG bases) through rat skin: effects of oleic acid added to FAPG base.

The effects of oleic acid (OA) added to mixtures of fatty alcohol and propylene glycol (FAPG bases) on the percutaneous absorption of indomethacin (ID) were investigated by using the abdominal skin of rats in vivo. The percutaneous absorption of propylene glycol (PG) from FAPG base was simultaneously examined. The percutaneous absorption of ID from FAPG bases in the absence of OA was poor as compared with that from FAPG bases containing OA. It was observed that when OA was added to the vehicles in the range of 5 to 30%, the percutaneous absorption of ID from the vehicles was increased. In particular, the maximal enhancement of percutaneous absorption of ID was achieved at 5% OA. However, the enhancing effect of percutaneous absorption of ID diminished when the OA content in the vehicle exceeded 50%. PG was readily absorbed through the rat skin from FAPG bases and its percutaneous absorption profiles were similar to those of ID. It can be presumed that PG and ID penetrate together through the skin. In addition, it was confirmed that the percutaneous absorption of ID and PG from FAPG bases was not affected by the viscosity of the vehicle. If FAPG base is to be used as a vehicle for the purpose of percutaneous absorption of ID, OA is considered to be a useful additive.

Enhancing effect of cetyl lactate on the percutaneous absorption of indomethacin in rats.

The enhancing effect of cetyl lactate (CL) on the percutaneous absorption of indomethacin (ID) from test solutions in propylene glycol (PG) was investigated by using the abdominal skin of rats in vivo. The percutaneous absorption rate of ID from 1 or 3% CL-PG test solution through the intact skin of rats was observed to be faster than that from the control solution (without CL). The bioavailability of ID was about 0.04% for the control solution, 2.2% for 1% CL-PG and 6.8% for 3% CL-PG test solutions. These results suggest that CL functions as an enhancer for the percutaneous absorption of ID. Furthermore, marked enhancing effects on percutaneous absorption of ID were obtained at a concentration greater than 1% CL in PG. In order to elucidate the mode of action of CL as an absorption enhancer, the percutaneous absorption of ID from the control solution and 3% CL-PG test solution through damaged skin from which the stratum corneum had been stripped was additionally investigated. It was confirmed that CL acts on the stratum corneum to produce its effect.