Martin J. Smilkstein

Efficacy of Oral N-Acetylcysteine in the Treatment of Acetaminophen Overdose

During the investigational use of oral N-acetylcysteine as an antidote for poisoning with acetaminophen, 11,195 cases of suspected acetaminophen overdose were reported. We describe the outcomes of 2540 patients with acetaminophen ingestions treated with a loading dose of 140 mg of oral N-acetylcysteine per kilogram of body weight, followed four hours later by 70 mg per kilogram given every four hours for an additional 17 doses. Patients were categorized for analysis on the basis of initial plasma acetaminophen concentrations and the interval between ingestion and treatment. Hepatotoxicity developed in 6.1 percent of patients at probable risk when N-acetylcysteine was started within 10 hours of acetaminophen ingestion and in 26.4 percent of such patients when therapy was begun 10 to 24 hours after ingestion. Among patients at high risk who were treated 16 to 24 hours after an acetaminophen overdose, hepatotoxicity developed in 41 percent--a rate lower than that among historical controls. When given within eight hours of acetaminophen ingestion, N-acetylcysteine was protective regardless of the initial plasma acetaminophen concentration. There was no difference in outcome whether N-acetylcysteine was started zero to four or four to eight hours after ingestion, but efficacy decreased with further delay. There were 11 deaths among the 2540 patients (0.43 percent); in the nine fatal cases in which aminotransferase was measured before treatment, values were elevated before N-acetylcysteine was started. No deaths were clearly caused by acetaminophen among patients in whom N-acetylcysteine therapy was begun within 16 hours. We conclude that N-acetylcysteine treatment should be started within eight hours of an acetaminophen overdose, but that treatment is still indicated at least as late as 24 hours after ingestion. On the basis of available data, the 72-hour regimen of oral N-acetylcysteine is as effective as the 20-hour intravenous regimen described previously, and it may be superior when treatment is delayed.

Simple and Inexpensive Fluorescence-Based Technique for High-Throughput Antimalarial Drug Screening

ABSTRACT Radioisotopic assays involve expense, multistep protocols, equipment, and radioactivity safety requirements which are problematic in high-throughput drug testing. This study reports an alternative, simple, robust, inexpensive, one-step fluorescence assay for use in antimalarial drug screening. Parasite growth is determined by using SYBR Green I, a dye with marked fluorescence enhancement upon contact with Plasmodium DNA. A side-by-side comparison of this fluorescence assay and a standard radioisotopic method was performed by testing known antimalarial agents against Plasmodium falciparum strain D6. Both assay methods were used to determine the effective concentration of drug that resulted in a 50% reduction in the observed counts (EC50) after 48 h of parasite growth in the presence of each drug. The EC50s of chloroquine, quinine, mefloquine, artemisinin, and 3,6-bis-ε-(N,N-diethylamino)-amyloxyxanthone were similar or identical by both techniques. The results obtained with this new fluorescence assay suggest that it may be an ideal method for high-throughput antimalarial drug screening.

1996 Annual report of the American association of poison control centers toxic exposure surveillance system

Toxic Exposure Surveillance System (TESS) data are compiled by the American Association of Poison Control Centers (AAPCC) on behalf of US poison centers. These data are used to identify hazards early, focus prevention education, guide clinical research, and direct training. TESS data have prompted product reformulations, repackaging, recalls, and bans; are used to support regulatory actions; and form the basis of postmarketing surveillance of newly released drugs and products. From its inception in 1983, TESS has grown dramatically, with increases in the number of participating poison centers, population served by those centers, and reported human exposures (Table 1A).1-19 The cumulative AAPCC database now contains 33.8 million human poison exposure cases. This report includes 2,380,028 human exposure cases reported by 64 participating poison centers during 2002, an increase of 4.9% compared to 2001 poisoning reports.

Discovery of dual function acridones as a new antimalarial chemotype

Preventing and delaying the emergence of drug resistance is an essential goal of antimalarial drug development. Monotherapy and highly mutable drug targets have each facilitated resistance, and both are undesirable in effective long-term strategies against multi-drug-resistant malaria. Haem remains an immutable and vulnerable target, because it is not parasite-encoded and its detoxification during haemoglobin degradation, critical to parasite survival, can be subverted by drug–haem interaction as in the case of quinolines and many other drugs. Here we describe a new antimalarial chemotype that combines the haem-targeting character of acridones, together with a chemosensitizing component that counteracts resistance to quinoline antimalarial drugs. Beyond the essential intrinsic characteristics common to deserving candidate antimalarials (high potency in vitro against pan-sensitive and multi-drug-resistant Plasmodium falciparum, efficacy and safety in vivo after oral administration, inexpensive synthesis and favourable physicochemical properties), our initial lead, T3.5 (3-chloro-6-(2-diethylamino-ethoxy)-10-(2-diethylamino-ethyl)-acridone), demonstrates unique synergistic properties. In addition to ‘verapamil-like’ chemosensitization to chloroquine and amodiaquine against quinoline-resistant parasites, T3.5 also results in an apparently mechanistically distinct synergism with quinine and with piperaquine. This synergy, evident in both quinoline-sensitive and quinoline-resistant parasites, has been demonstrated both in vitro and in vivo. In summary, this innovative acridone design merges intrinsic potency and resistance-counteracting functions in one molecule, and represents a new strategy to expand, enhance and sustain effective antimalarial drug combinations.

Antimalarial Activity of Natural and Synthetic Prodiginines

Prodiginines are a family of linear and cyclic oligopyrrole red-pigmented compounds. Herein we describe the in vitro antimalarial activity of four natural (IC(50) = 1.7-8.0 nM) and three sets of synthetic prodiginines against Plasmodium falciparum. Set 1 compounds replaced the terminal nonalkylated pyrrole ring of natural prodiginines and had diminished activity (IC(50) > 2920 nM). Set 2 and set 3 prodiginines were monosubstituted or disubstituted at either the 3 or 5 position of the right-hand terminal pyrrole, respectively. Potent in vitro activity (IC(50) = 0.9-16.0 nM) was observed using alkyl or aryl substituents. Metacycloprodiginine and more potent synthetic analogues were evaluated in a P. yoelii murine patent infection using oral administration. Each analogue reduced parasitemia by more than 90% after 25 (mg/kg)/day dosing and in some cases provided a cure. The most favorable profile was 92% parasite reduction at 5 (mg/kg)/day, and 100% reduction at 25 (mg/kg)/day without any evident weight loses or clinical overt toxicity.

Optimization of endochin-like quinolones for antimalarial activity

Our prior work on tricyclic acridones combined with a desire to minimize the tricyclic system led to an interest in antimalarial quinolones and a reexamination of endochin, an experimental antimalarial from the 1940s. In the present article, we show that endochin is unstable in the presence of murine, rat, and human microsomes which may explain its relatively poor antimalarial activity in mammalian systems. We also profile the structure-activity relationships of ≈ 30 endochin-like quinolone (ELQ) analogs and highlight features that are associated with enhanced metabolic stability, potent antiplasmodial activity against multidrug resistant strains of Plasmodium falciparum, and equal activity against an atovaquone-resistant clinical isolate. Our work also features an ELQ construct containing a polyethylene glycol carbonate pro-moiety that is highly efficacious by oral administration in a murine malaria model. These findings provide compelling evidence that development of ELQ therapeutics is feasible.

Design, Synthesis, and Evaluation of 10-N-Substituted Acridones as Novel Chemosensitizers in Plasmodium falciparum

ABSTRACT A series of novel 10-N-substituted acridones, bearing alkyl side chains with tertiary amine groups at the terminal position, were designed, synthesized, and evaluated for the ability to enhance the potency of quinoline drugs against multidrug-resistant (MDR) Plasmodium falciparum malaria parasites. A number of acridone derivatives, with side chains bridged three or more carbon atoms apart between the ring nitrogen and terminal nitrogen, demonstrated chloroquine (CQ)-chemosensitizing activity against the MDR strain of P. falciparum (Dd2). Isobologram analysis revealed that selected candidates demonstrated significant synergy with CQ in the CQ-resistant (CQR) parasite Dd2 but only additive (or indifferent) interaction in the CQ-sensitive (CQS) D6. These acridone derivatives also enhanced the sensitivity of other quinoline antimalarials, such as desethylchloroquine (DCQ) and quinine (QN), in Dd2. The patterns of chemosensitizing effects of selected acridones on CQ and QN were similar to those of verapamil against various parasite lines with mutations encoding amino acid 76 of the P. falciparum CQ resistance transporter (PfCRT). Unlike other known chemosensitizers with recognized psychotropic effects (e.g., desipramine, imipramine, and chlorpheniramine), these novel acridone derivatives exhibited no demonstrable effect on the uptake or binding of important biogenic amine neurotransmitters. The combined results indicate that 10-N-substituted acridones present novel pharmacophores for the development of chemosensitizers against P. falciparum.

Magnesium levels after magnesium-containing cathartics

To determine the effect on serum Mg++ levels of oral Magnesium-containing cathartics (MgCC) used in the treatment of suspected drug overdose, a prospective, non-randomized study of 24 cases of suspected drug overdose was conducted. Ten cases admitted to the observation unit were assigned to the single dose MgCC group. Fourteen cases admitted to either the ICU or the observation unit were assigned to the multiple dose MgCC group. Single dose cases received 30 gm of magnesium sulfate (MgSO4) at 0 hours. Multiple dose cases received 3 30 gm doses of MgSO4 at 0, 4, and 8 hours. Mg++ levels were measured prior to each MgSO4 dose and 1 and 4 hours after the final dose in both groups. In the single dose group, there was no difference between baseline Mg++ levels and post MgSO4 levels, and only 2/10 developed slightly elevated levels (2.2, 2.3 mEq/L). In the multiple dose group, levels increased and remained significantly higher than baseline after the second MgSO4 dose, and 9/14 developed elevated levels (2.2 to 5.0 mEq/L). All patients who developed elevated Mg++ levels had normal BUN and creatinine values. When the single and multiple dose groups were compared, baseline Mg++ levels were no different (1.68 +/- 0.21 vs 1.69 +/- 0.24, p = 0.952), but peak Mg++ levels were significantly higher in the multiple dose group (1.80 +/- 0.31 vs 2.61 +/- 0.86, p = 0.004). Cases that developed hypermagnesemia had slightly higher baseline Mg++ levels (1.78 +/- 0.22 vs 1.60 +/- 0.19 mEq/L, p = 0.041). In the multiple dose group, higher peak Mg++ levels were noted in cases involving ingestions of anticholinergic or opioid drugs (2.83 vs 1.98, p = 0.025). Hypermagnesemia developed in some cases with normal renal function, blood pressure, and urine output. We conclude that significant hypermagnesemia can occur rapidly after use of multiple dose Mg++ cathartics in standard doses in patients with normal renal function.

A drug-selected Plasmodium falciparum lacking the need for conventional electron transport

Mitochondrial electron transport is essential for survival in Plasmodium falciparum, making the cytochrome (cyt) bc(1) complex an attractive target for antimalarial drug development. Here we report that P. falciparum cultivated in the presence of a novel cyt bc(1) inhibitor underwent a fundamental transformation in biochemistry to a phenotype lacking a requirement for electron transport through the cyt bc(1) complex. Growth of the drug-selected parasite clone (SB1-A6) is robust in the presence of diverse cyt bc(1) inhibitors, although electron transport is fully inhibited by these same agents. This transformation defies expected molecular-based concepts of drug resistance, has important implications for the study of cyt bc(1) as an antimalarial drug target, and may offer a glimpse into the evolutionary future of Plasmodium.

Delayed cardiotoxicity following quinine overdose: a case report

Quinine poisoning typically results in a constellation of non-life threatening symptoms which include tinnitus, deafness, nausea, vomiting, vision changes, headache, and hypotension. Cardiac conduction defects, dysrhythmias, and cardiovascular collapse have all been reported after overdose and generally occur within 8 hours of ingestion. We report a unique case of delayed cardiotoxicity following quinine ingestion. Toxicity included marked ventricular conduction abnormalities for which serum alkalinization appeared to be therapeutically beneficial, and torsades de pointes requiring overdrive pacing for termination.