The effects of storage upon in vitro and in vivo characteristics of soft gelatin capsules containing digoxin

Abstract

The effects of both the (+)-and ( -)-enantiomen of VII were reversed by P2S in both tests in the same manner as the effects of any of the ethyl S-alkylmethylphosphonothioates. It is noteworthy that although the (+)-and (-)-isomers of VII inhibit acetylcholinesterase at different rates and substantially faster than the (+)-and (-)-isomers of the S-alkyl methylphosphonothioates (e.g. I( +) and I( -)), the reactivation profiles of all four compounds were indistinguishable.The results of the in vivo experiments showed marked differences from those obtained in vitro. The rank order of the LD50 values did not correspond with the rank order of potency of the compounds in the in vitro tests ( Table 2). Moreover there was sometimes no significant difference between the LD50 values of an enantiomeric pair even though the (-)-isomer was in vitro clearly a more potent anti-acetylcholinesterase than the (+)isomer. In the case of one compound, ethyl S-propyl methylphosphonothioate (I), the (+)-isomer was significantly more toxic than the (-)-isomer in contrast to the results of the in vitro results.In the gastrocnemius muscle, as is shown in Fig. 2, the administration of P2S at a dose of 130pmol kg-l, during poisoning by the (-)-enantiomer of I, reestablished neuromuscular function whereas similar P2S treatment of poisoning by the (+)-enantiomer and the racemate failed to restore neuromuscular function. Compounds I1 and 111 showed similar behaviour. In marked contrast, the effects of both the (+)-and (-)-muscle enantiomers of VII on the gastrocnemius preparation were reversed by administration of p2sThe difference in response to P2S of the (+)-( -)-enantiomen of the ethyl-methylphosphonothioates I, I1 and 111 was consistent with the prelimi observation that rats poisoned by (+)ethyl-smethylphosphonothioate (I+) failed to respond to P2S-atropine treatment. Thus whereas for I(, (Green, Muir & others, 1977) gave a Protection ratio of d 8.5 (protection ratio = LDSO of Sarin in trak e animals/LDSO of Sarin in untreated animals) th protection ratios of I(+) and I(&) were 2.2 and respectively. In marked contrast, but in agreement With the results on the gastrocnemius preparation, p2s, atropine treatment of poisoning by VII( i), VII(+) and VII(-) gave protection ratios Of 24, 70 and 55 respectively. To our knowledge there is no recorded precedent for the difference of the (+)-and (-1-enantiorners of the ethyl-methylphosphonothioates observed in viva. previous comparisons (Fukuto, 1971) of the enanti,,. mers of alkylphosphonothioate anticholinesterases have been concerned mainly with the insecticidal activity and stereoselectivity of cholinesterases from different SO^^^ and so no indications of possible mechanistic in viva differences in animals were obtained. That metabolic activation of the (+)-isomers occurs, is an attractive proposition.

Dissolution of Gelatin Capsules: Evidence and Confirmation of Cross-Linking

“…Studies were conducted to determine the effect of prolonged storage conditions on the bioavailability and clinical efficacy of drugs in gelatin capsules. Cases were also reported in which the bioavailability of the drug from the stressed capsules did not significantly alter in vivo performance when compared to freshly prepared capsules (10,(20)(21)(22)(23). A comparison of the in vitro dissolution rate of drug release from stressed gelatin capsules with their in vivo performance has been reported (5).…”

Crosslinking Studies in Gelatin Capsules Treated with Formaldehyde and in Capsules Exposed to Elevated Temperature and Humidity

“…Incomplete in vitro capsule shell dissolution and subsequent drug release problems have recently received attention. This problem was first reported in 1974 for a hard gelatin capsule (HGC) product containing chloramphenicol1 and in 1977 for a soft gelatin capsule (SGC) product containing digoxin 2. These and later cases were associated with adverse storage conditions of elevated temperature, humidity, or prolonged storage.…”