Comparative antiandrogenic potency of spironolactone and cimetidine: assessment by the chicken cockscomb topical bioassay

Follicular (pilosebaceous unit) deposition and pharmacological behavior of cimetidine as a function of formulation

The effect of formulation on cimetidine delivery to the pilosebaceous unit and other skin phases was studied. In vitro and in vivo deposition determinations as well as a pharmacodynamic antiandrogenic sebaceous gland bioassays were made. A complex variety of factors influence how the formulation affects both the degree of drug deposition and its pharmacological activity in the pilosebaceous unit. When cimetidine was applied in formulations at pH values where it was predominately unionized, the thermodynamic driving force proved the dominant factor in influencing the extent of drug deposition into the pilosebaceous unit. Although more cimetidine was deposited into the pilosebaceous unit in vivo from the phospholipid-based liposomal formulation when cimetidine was ionized, this formulation was also the only one devoid of significant antiandrogenic action. Of great importance, it is clear from the studies that deposition from complex formulations, such as liposomes, where bilayer/drug interactions can persist in the skin, may give a false impression of the activity of a drug within a tissue. Moreover, data for cimetidine in 50% alcohol solution show that one can maintain local effects while reducing systemic activity by simply manipulating drug concentration in the application.

Effect of cimetidine on eggshell quality and plasma 25-hydroxycholecalciferol in laying hens

Experiments were conducted to investigate the effect of feeding cimetidine (CIMET), ranging from 0 to 750 mg/kg, on vitamin D3 metabolism and eggshell calcification in laying hens fed two levels of vitamin D3 (500 and 2,000 ICU/kg). Final BW and feed intake were not significantly affected by either CIMET or vitamin D3 level. Feeding 500 and 750 mg of CIMET significantly decreased total egg production in hens fed either level of vitamin D3, but no differences were observed at lower CIMET levels. Tibia ash decreased significantly in hens fed 150 to 750 mg of CIMET, regardless of the vitamin D3 level. Plasma Ca and inorganic P concentrations were decreased in hens fed high CIMET levels (500 and 750 mg/kg) at Week 2, but no differences were observed at Week 4. Feeding CIMET (500 and 750 mg/kg) significantly decreased plasma 25-hydroxycholecalciferol (25-OHD3) levels at Week 2 in hens fed both vitamin D3 diets but not at Week 4. Eggshell breaking force, shell thickness, and percentage shell weight were decreased significantly by CIMET in all experiments; however, in one experiment, shell quality recovered by Week 8. These results suggest that the CIMET-induced reduction in bone mineralization, eggshell quality, and plasma 25-OHD3 levels could be due to interference of CIMET with vitamin D3 metabolism in vitamin D3-replete laying hens. Shell quality decreased in CIMET-treated hens fed the higher vitamin D diet even though 250-HD3 plasma levels were three times higher than in hens fed the lower vitamin D diet, suggesting that CIMET affected shell quality through some mechanism other than inhibition of 250-HD3 synthesis.