Agranulocytosis associated with aminoglutethimide: pharmacological and marrow studies

Aminoglutethimide-induced leucopenia in a mouse model: effects of metabolic and structural determinates

A model of human leucopenia has been developed further in the female mouse. Following daily administration to female mice of 50 mg/kg of the aromatase inhibitor aminoglutethimide, significant falls in platelet and white cell counts occurred after 2 and 3 weeks. At week 4, drug dosage was stopped and the cell counts recovered at the end of that week, although on rechallenge at the beginning of week 5, both platelet and white cell counts fell rapidly. Administration to the mice of structural analogues of aminoglutethimide, such as WSP-3, glutethimide and 4-nitroglutethimide, showed no reductions in platelet and white cell counts. The haemotoxicity of aminoglutethimide over 21 days was unaffected by the presence of either the P-450 inhibitor SKF-525A or the hepatic P-450 inducer phenobarbitone. However, the co-administration of cimetidine abolished the haemotoxicity of aminoglutethimide in terms of platelet and white cell levels. In in vitro studies, both aminoglutethimide and WSP-3 were oxidised to cytotoxic species, although aminoglutethimide was significantly more cytotoxic than WSP-3. The NADPH-dependent covalent binding of (14)C aminoglutethimide to mouse microsomes in vitro was significantly reduced by the presence of cimetidine. The activation of the compound to reactive species in vitro, the inhibitory effects of cimetidine in vivo and in vitro, as well as the rapid fall in the in vivo white cell count on rechallenge with aminoglutethimide suggest that this model illustrates a form of leucopenia which may be related to hapten formation and subsequent immune-mediated platelet and white cell lysis.

Phase II study of low dose aminoglutethimide 250 mg/day plus hydrocortisone in advanced postmenopausal breast cancer

Low dose aminoglutethimide 125 mg twice daily plus hydrocortisone 20 mg twice daily was shown to produce oestrogen and androgen suppression in postmenopausal women. A phase II study was carried out in 101 patients with advanced postmenopausal breast cancer. Objective response rates were 4% CR and 21% PR. Fourteen per cent had disease stabilization for more than 6 months (SD). Soft tissue sites showed the best response. Responses occurred in previous tamoxifen failures (28%) including SD. Toxicity was less than reported for higher dose regimens or low dose aminoglutethimide without hydrocortisone, particularly nausea and drowsiness. Survival from first relapse and start of therapy was not significantly different between PR and SD. This dosage regimen appears of comparable efficacy to previously reported higher dosage regimens with reduced toxicity compared to low dose regimens without hydrocortisone.

Interactions of aminoglutethimide with analgesics using antinociceptive tests in mice

The action of aminoglutethimide in alleviating bone pain in women with metastatic breast cancer may be due to either an inherent analgesic effect or an interaction with other analgesic drugs. These possibilities have been investigated in mice by conventional antinociceptive tests. In the abdominal constriction test, aminoglutethimide alone had a dose-related antinociceptive activity. A low dose (which had no pharmacological activity) when co-administered with an effective sub-maximal dose of the analgesic, potentiated the effects of the non-steroidal anti-inflammatory drugs (NSAIDs) tested. In the tail immersion test, aminoglutethimide was inactive and did not enhance the antinociceptive activity of the centrally acting analgesics. As cytochrome P450-dependent routes which are inhibited by aminoglutethimide are not involved in the metabolism of the NSAIDs studied, an interaction at the drug metabolism level cannot explain these results. The NSAID-like activity of aminoglutethimide provides some evidence that the drug's mode of action may involve more than the suppression of oestrogen biosynthesis.