Chloramphenicol stearate

Physical interactions between drug and excipient also can compromise quality. Adsorption of drug by microcrystalline cellulose resulted in drug dissolution being less than complete. Interaction between chloramphenicol stearate and colloidal silica during grinding led to polymorphic transformation. 

Chloramphenicol stearate Milling in a Pulverisette 5 grinder (Fritsch) (agate mortar and balls) with colloidal silica or microcrystalline cellulose [102,103]... 

Surfactants. The use of surfactants is greatly restricted in formulating ophthalmic solutions. The order of surfactant toxicity is anionic > cationic >> nonionic. Several nonionic surfactants are used in relatively low concentrations to aid in dispersing steroids in suspensions and to achieve or to improve solution clarity. Those principally used are the sorbitan ether esters of oleic acid (Polysorbate or Tween 20 and 80), polymers of oxyethylated octyl phenol (Tyloxapol), and polyoxyl 40 stearate. The lowest concentration possible is used to perform the desired function. Their effect on preservative efficacy and their possible binding by macromolecules must be taken into account, as well as their effect on ocular irritation. The use of surfactants as cosolvents for an ophthalmic solution of chloramphenicol has been described [271]. This com-... 

Polyoxyethylene stearates are unstable in hot alkaline solutions owing to hydrolysis, and will also saponify with strong acids or bases. Discoloration or precipitation can occur with salicylates, phenolic substances, iodine salts, and salts of bismuth, silver, and tannins.Complex formation with preservatives may also occur. The antimicrobial activity of some materials such as bacitracin, chloramphenicol, phenoxymethylpenicillin, sodium penicillin, and tetracycline may be reduced in the presence of polyoxyethylene stearate concentrations greater than 5% w/w. ... 

Dilatometric analysis is a less widely used technique for characterising polymorphs, but has, for example, been applied to the study of polymorphic transformations occurring in theobroma oil, methyl stearate and chloramphenicol [25]. Substances which contract as they transform from a metastable (less dense) polymorph to a stable (more dense) polymorph can be studied by measuring their specific volume as a function of temperature. A recent study involved the combined use of dilatometry and neutron scattering to characterise the orthorhombic and monoclinic polymorphs of ra-nitrophenol [ 130]. Crystals of both polymorphs showed significant anisotropy of expansion and it was possible to reconcile the direction of lowest expansion with that of the hydrogen bonding interactions. Attempts to correlate these results with those obtained from IR and Raman spectra were subsequently reported [131]. 

Esters of the 3-carboxylic acid group of ampicillin (Section 13.1) are used as pro-drugs, e.g. bacampicillin, talampicillin, and pivampicillin. Their more lipophilic properties ensure better oral absorption. The active drug is liberated by the non-specific esterases of the bloodstream. Esters of erythromycin 4.47)., such as the stearate or ethyl succinate, survive the stomach s acidity, which erythromycin does not, but are hydrolysed back to the true drug in the duodenum. Children, who intensely dislike the bitter taste of chloramphenicol, are given the succinate ester. In both cases, hydrolysis liberates the true drug. 

Separations of chloramphenicol and its palmitate and stearate (see Table 26) were done on silica gel HPTLC plates (Merck) (61) with the following solvents ... 

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