BCH-2763, a novel potent parenteral thrombin inhibitor, is an effective antithrombotic agent in rodent models of arterial and venous thrombosis--comparisons with heparin, r-hirudin, hirulog, inogatran and argatroban

Current clinical use of heparin as an antithrombotic agent is limited by suboptimal efficacy and safety considerations. Thrombin's central role in thrombosis makes it an attractive target to develop more effective and safer antithrombotic agents. BCH-2763 is a novel, potent (Ki: 0.11 nM), low molecular weight (1.51 kDa), bivalent direct thrombin inhibitor. The antithrombotic efficacy of BCH-2763 in vivo following i.v. bolus plus infusion in rats was compared in arterial and venous thrombosis models with two other bivalent direct thrombin inhibitors, r-hirudin and hirulog, with two catalytic site-directed thrombin inhibitors, inogatran and argatroban, and with heparin. In vivo efficacy was related to inhibition in vitro of fibrin clot formation, thrombin-induced aggregation of rat or human washed platelets and activity of free and plasma clot-bound thrombin. All the direct thrombin inhibitors were effective on both arterial and venous thrombosis at markedly lower fold aPTT increases than heparin. The antithrombotic doses of all inhibitors against venous thrombosis were less than against arterial thrombosis. The rank order of potency based on doses (mg/kg/h) required for full efficacy against arterial thrombosis was BCH-2763 (1.2) > inogatran (1.5) > r-hirudin (1.8) > hirulog (3.3) > argatroban (> 3.0); heparin required a markedly higher dose (5.7). In venous thrombosis the doses required for full efficacy were substantially lower for the bivalent (BCH-2763: 0.12; r-hirudin: 0.12; hirulog: 0.18) than for the catalytic site-directed (inogatran: 0.48; argatroban: 0.90) thrombin inhibitors; the dose required for heparin was 0.19. All the direct thrombin inhibitors caused similar shifts in aPTT at doses required to inhibit arterial thrombosis, but BCH-2763 inhibited venous thrombosis at lower aPTT fold increases. In vivo antithrombotic efficacy of direct thrombin inhibitors correlated with their inhibitory activity in vitro against fibrin clot formation and platelet aggregation. In contrast to heparin, all the direct thrombin inhibitors inhibited plasma clot-bound thrombin, but the relative IC50s did not correlate with their antithrombotic efficacy. In summary, direct thrombin inhibitors are more effective than heparin in inhibiting arterial and venous thrombosis in rats with less aPTT increases. BCH-2763 is effective at lower doses than the other direct thrombin inhibitors and for venous thrombosis at a smaller aPTT increase. BCH-2763 may offer an improved therapeutic index in the treatment of thromboembolic complications over heparin and other direct thrombin inhibitors.

Binding characteristics of novel nonsteroidal antiestrogens to the rat uterine estrogen receptors

Tamoxifen (TAM), the only antiestrogen currently available for the endocrine therapy of breast cancer behaves as a mixed agonist/antagonist of estrogen action, thus limiting its therapeutic potential. We report the binding characteristics of a novel series of nonsteroidal antiestrogens to the rat uterine estrogen receptor. As measured by competition studies, the affinity of EM-652, the active metabolite of the prodrug EM-800, for the estrogen receptor is 7-11 times higher than that of 17beta-estradiol (E2), ICI 182780, and hydroxy-tamoxifen (OH-TAM), the active metabolite of Tamoxifen. EM-652 is 20x more potent than ICI 164384 and Droloxifene while it is 400 times more potent than Toremifene in displacing [3H]E2 from the rat uterine estrogen receptor. On the other hand, the prodrug EM-800 and Tamoxifen have respectively 150-fold and 410-fold less affinity for the estrogen receptor than the pure antiestrogen EM-652. No significant binding of EM-652, EM-800, TAM or OH-TAM was observed to the rat uterine progesterone receptor at concentrations up to 10,000 nM except for TAM that caused a 50% displacement of labeled R5020 at 4000 nM. No significant binding of EM-652 or EM-800 was observed on the rat ventral prostate androgen receptor or the rat uterine progesterone receptor. The present data demonstrate the high affinity and specificity of the new antiestrogen, EM-652, for the rat uterine estrogen receptor. The antiestrogen EM-652 thus becomes the compound having the highest known affinity for the estrogen receptor. Due to its unique potency and its pure antiestrogenic activity already demonstrated in many systems, this antiestrogen could well offer an important advance for the endocrine therapy of breast cancer, uterine cancer, and other estrogen-sensitive diseases in women.

Alcohol and other drugs of abuse in pregnancy

This paper presents an overview of the Mother-Baby Chemical Health Program (MBCHP), which was designed to decrease preterm births among pregnant women who use and abuse drugs. Three hundred and fifty-two patients enrolled in the program between January 1990 and December 1992 were followed. More than 90% of the women involved in the MBCHP did not use substances during their pregnancies. Approximately 93% of the participants delivered at 37 or more weeks gestation, and over 91% of the infants weighed 2500 grams or more.

Delay in hearing loss following drug administration. A consistent feature of amikacin ototoxicity

The time course of threshold increase in the VIII nerve compound action potential was studied in guinea pigs following amikacin administration at four different constant infusion rates. Despite the wide range of dosing durations required to achieve drug ototoxicity (2-24 days), the full development of both high and low frequency hearing loss was invariably found to be delayed with respect to the time of drug removal. The greatest degree of delayed hearing loss generally occurred within the first 7 days after drug removal, with smaller losses occurring during later time intervals. The delay showed a tendency to decrease as the ototoxic dose was increased. Using the data from the two highest dosing rates, it was estimated that a minimum of 4 days had to elapse before any hearing loss could be detected, once an ototoxic amount of drug had been administered. These data suggest that hearing loss is always substantially delayed with respect to the receipt of an ototoxic dose of amikacin, and that this must be taken into account when conducting animal experiments and when monitoring hearing in patients for the early detection of ototoxicity.

Drug abuse in pregnancy. Detection and intervention

Drug abuse in the obstetric population of a large urban HMO is discussed. Marijuana metabolites were detected in 9.1% of urines submitted for routine pregnancy testing, while cocaine use was detected in 1.3%. A separate group of urines submitted for urine culture at the time of the first obstetric visit were tested and showed levels of 5.0% and 0.2%, respectively. Cocaine use was associated in an estimated 1-2% of all live births. The unexpected magnitude of this problem led to the creation of an outreach clinic and a process of care. The preliminary experience of our program forms the basis of this report.

Incidence of amikacin ototoxicity: a sigmoid function of total drug exposure independent of plasma levels

A sigmoid curve was found to closely describe the relationship between the incidence of amikacin ototoxicity (greater than or equal to 15 dB hearing loss at a given frequency) and either (1) total dose, or (2) the area under the curve (AUC) describing plasma drug concentration v time over the total period of amikacin administration (total AUC) in continuously infused guinea pigs. Total dose or total AUC estimates of the drug exposure required to produce ototoxicity in 50% of the animals (ED50s) were not significantly different over an eight-fold range of dosing rates or plasma concentrations. A theoretical explanation for this result is that ototoxicity occurs only when a critical amount of drug is accumulated at the ototoxic site by an essentially unidirectional process with a rate that is slow and linearly related to the extracellular drug concentration. The sigmoid relationships for pooled data were parallel in slope for all hearing frequencies from 2 to 32 kHz, and the ED50s showed a strong negative linear relationship to the log of the hearing frequency over this range. The magnitude of ototoxicity expressed as the number of octaves (frequency ratios of 2) for which hearing loss damage was continuous from 32 kHz downward, was correlated to both total dose (r = .605) and total AUC (r = 0.703). No relationship between ototoxicity and plasma level or dosing rate was found. The extreme steepness of the dose-effect curve for the incidence of ototoxicity greatly amplified the variability between individuals and offers an explanation for the unpredictability of aminoglycoside ototoxicity in human patients. The results indicate that either total dose or total AUC (in cases of highly unpredictable blood levels), and not peak or trough serum levels, should be used as an index of ototoxic risk and that the safety limits of drug exposure should be set conservatively.