Drug-drug interactions of new active substances: mibefradil example

INTRODUCTION

Mibefradil was approved as a novel calcium antagonist in Switzerland in 1996. Following its launch as an antihypertensive and anti-anginal agent, there were reports about serious pharmacokinetic and pharmacodynamic interactions occurring with other drugs frequently administered to patients with cardiovascular diseases. Despite appropriate modifications of the prescribing information, such interactions continued to occur. The drug was finally withdrawn after a study in patients with congestive heart failure showed a trend to higher mortality with mibefradil. This increase in mortality could again be due to multiple interactions between mibefradil and other drugs. In retrospect, it can be concluded that several of the interactions, including the theoretical risk of severe toxicity in some patients, could have been and in fact were predicted on the basis of the data available before introduction to the market. Depending on the benefits, these problems would however not necessarily represent an unacceptable risk for a new active compound.

RESULTS AND CONCLUSION

The most important points revealed by this analysis were: (1) when interpreting the results of interaction studies, it is important to consider not only the mean of the interaction effect but also the observed and the theoretically conceivable extreme effects in individual subjects and (2) a drug with a high interaction potential may represent a high risk even if an adequate warning is included in the product information. The need for specific pharmacokinetic and pharmacodynamic interaction studies with new drugs and the limitations of the pivotal clinical efficacy and safety studies during phase III in order to reveal such interactions are discussed.

[Retrospective study of drug-induced agranulocytosis in hospitalized patients in Geneva and comparison with cases reported to IOCM]

In a retrospective study, 19 cases classified as idiosyncratic drug-induced agranulocytosis were found among 162 files of patients hospitalized in internal medicine clinics of the university hospital where this diagnosis had been coded. This would give an estimated incidence of 2.6 cases per million inhabitants per year for the Geneva area. In most cases several drugs were implicated in causation of the episodes. Suspected drugs were those commonly reported in the literature, but also some drugs which might already have been taken to treat infectious complications of agranulocytosis. A comparison of the Geneva cases with those notified to the Swiss Intercantonal Office for the Control of Medicines reveals a similar profile of involved drugs.

Renal biopsy findings and followup of renal function in rheumatoid arthritis patients treated with cyclosporin A. An update from the International Kidney Biopsy Registry

OBJECTIVE

To review data from the International Kidney Biopsy Registry, which describes the occurrence of cyclosporin A (CSA)-induced nephropathy, and to discuss the potential risk factors for its development.

METHODS

The report examines data on a total of 60 first and 14 second renal biopsies performed in rheumatoid arthritis (RA) patients treated with CSA for up to 87 months.

RESULTS

Five of the 60 patients with RA included in the Biopsy Registry had findings consistent with CSA-induced nephropathy at first biopsy. One further patient had such findings at second biopsy. Of the 22 patients who started CSA at dosages < 4 mg/kg/day and subsequently received dosages no higher than 5 mg/kg/ day, none developed CSA-induced nephropathy. Continuous assessment of renal function did not show any evidence of deterioration over time in patients maintained on low-dose CSA.

CONCLUSION

The data indicate that in RA patients being treated according to current dosing recommendations, the risk of developing CSA-induced nephropathy is low.

[Large-cell eosinophilic tumors of the thyroid gland]

Problems surrounding malignancy of large-cell oxyphilic thyroid tumors, frequently but not quite correctly designated as Hürthle-cell tumors, are still under discussion. Whether a reliable histopathological diagnosis of malignancy can already be made on the primary lesion was tested in a series of 55 large-cell oxyphilic tumors of the thyroid seen at the Department of Pathology of the University of Zurich between 1962 and 1973, hence with a follow-up period of at least 10 years. One case was excluded due to insufficient histological slides. 34 of the remaining 54 neoplasms were reclassified histopathologically as carcinomas, 15 as adenomas and 5 as borderline tumors with doubtful malignancy. In 16 of the 35 carcinoma patients the clinical course or later pathological findings were in accordance with the histopathological diagnosis of malignancy. 6 patients had local recurrences and in 7 cases the clinical data were insufficient. Only 5 of the 34 cancer cases definitely showed no further signs of malignancy. On the other hand, only one of the 7 adenoma patients developed lung metastases, 15 years after thyroidectomy, though in this case only one histological slide could be re-examined, which is obviously an insufficient number to exclude malignancy. 3 of the 5 patients with borderline lesions followed up over a period of at least 10 years developed no signs of malignancy. In the light of these results, some 2/3 of large-cell oxyphilic thyroid tumors must be classified as carcinomas (mainly follicular) provided that only isolated tumors and not large-cell oxyphilic nodules of adenomatous goiters are considered. Benign large-cell oxyphilic tumors of the thyroid do, however, exist. Histopathologically it is quite possible to diagnose a primary lesion accurately as malignant or benign, if it is screened very carefully for capsular perforation and vascular invasion, the most reliable signs of malignancy in such tumors apart from metastases.