Herbicide formulations

BACKGROUND

Herbicides comprise nearly half of the 5 billion pounds of pesticide active ingredients used worldwide annually. The active ingredient must be formulated with other ingredients to allow mixing, dilution, application, and stability. Liquid commercial formulations for spray foliar application include water-soluble liquids, emulsifiable concentrates, suspension concentrates or "flowables," and gels. Dry formulations that are mixed with water for spray application include wettable powders and water-dispersible granules. Granules are broadcast directly out of the bag. The carrier in liquid formulations is either water or an organic solvent or oil. The general chemical class of the carrier may be deduced based on the solubility characteristics of the active ingredient. Cosolvents may be necessary to optimize solubility and stability. Surfactants are nearly universally present in herbicide formulations or added prior to application. They aid uniform spreading of the spray droplet on the leaf and penetration of its waxy cuticle by the active ingredient. In solvent-based formulations, surfactants permit a stable oil-in-water emulsion to form when diluted with water for actual use. New surfactant systems are currently of intense competitive importance. Other formulation ingredients include pH adjusters, buffers, milling aids, antifoaming agents, acid scavengers, dyes, suspending agents, preservatives, dispersants, emulsifiers, densifiers, antifreeze, and crystal promoters. In highly regulated environments, the other formulation components in pesticides are receiving scrutiny. In the US, the EPA's strategy has been to categorize currently used formulation ingredients into 4 lists based on their toxicology profiles. The ultimate outcome is to have all inert ingredients on List 4, Minimal Risk. List 4 ingredients are generally regarded as safe or have current use patterns that do not pose an unreasonable risk of adverse effect to public health or the environment.

Malposition of pediatric gastric lavage tubes demonstrated radiographically

Gastric lavage may be indicated in the initial treatment of toxic substance ingestion. We retrospectively surveyed the charts of 36 pediatric patients who underwent gastric lavage to evaluate the clinical and radiographic evidence indicating proper tube placement. Only 14 patients had a radiograph prior to lavage, and 50% of these documented malposition. The most common was excess tube insertion, stretching the stomach inferiorly towards the pelvis. The traditionally acceptable clinical test by auscultation of insufflated air was favorable in 100% of patients, thus failing to detect all of the malpositionings documented radiographically. We suggest that initial insertion of tube length be based on the patient's height or length using an adaptation of Strobel's previously published formula for esophageal pH probe placement: Tube Insertion Depth (TID), orogastric = 9.7 cm + (0.226 x length of patient in cm) and TID, nasogastric = 8 cm + (0.252 x length of patient in cm). These formulae have been displayed in graphic form for easy use. Diagnostic imaging remains the only certain means to document tube placement. Prospective studies to validate the formulae in clinical use are ongoing.

Taiwan National Poison Center survey of glyphosate--surfactant herbicide ingestions

Between January, 1986 and September, 1988, the Taiwan National Poison Center recorded 97 telephone consultations (49 male, 48 female) on cases of ingestion of glyphosate-surfactant herbicide concentrate containing the isopropylamine salt of glyphosate (N-phosphonomethyl glycine, CAS 1071-83-6) and a non-ionic tallow amine surfactant. Eleven of the cases resulted in fatalities, all among those attempting suicide. The average amount ingested by survivors was 120 +/- 112 mL and by nonsurvivors was 263 +/- 100 mL (p less than or equal to 0.0001). The average age of survivors was 35 +/- 15 years compared to 54 +/- 11 years for fatalities (p less than or equal to 0.0002). Irritation of the oral mucous membrane and gastrointestinal tract was the most frequently reported effect. Other effects recorded were pulmonary dysfunction, oliguria, metabolic acidosis, hypotension, leukocytosis and fever. Fourteen patients received either atropine or pralidoxime plus atropine despite the fact that glyphosate does not inhibit acetylcholinesterase. Thirteen percent of patients received a urine test for paraquat or treatment customarily used for paraquat ingestion, possibly reflecting similar initial presentations following ingestion of these two herbicides. Laboratory differentiation is essential if any doubt exists about which herbicide was ingested. Patients ingesting large volumes of concentrated glyphosate-surfactant herbicide formulations require close observation and supportive treatment.

Hypertension as an unusual feature in an outbreak of tetrodotoxin poisoning

We report an outbreak of tetrodotoxin poisoning resulting from consumption of ovaries of an unidentified species of fish. Thirty victims manifested the typical neurologic symptoms of tetrodotoxin poisoning. Although hypotension is the classically described blood pressure reaction, eight individuals developed hypertension (average blood pressure 192/110 mm Hg); one died of acute pulmonary edema. Semi-quantitative tetrodotoxin bioassay of two uneaten ovaries revealed tetrodotoxin concentrations of 54 Mouse Units/gm and 287 Mouse Units/gm, respectively. To gain insight into the unusual phenomenon of hypertension observed in our outbreak, we interviewed the victims, performed a funduscopic exam for hypertensive retinopathy and checked their blood pressure periodically in the ensuing year. Mild hypertension evidenced by retinopathy and elevated blood pressure was found in all seven who manifested hypertension during the acute event and survived. We postulate that individuals with pre-existing hypertension responded to the relatively small doses of tetrodotoxin with a dramatic rise in blood pressure. This resulted in the fatal outcome for one individual with severe coronary artery disease. Hypertension should be recognized as a possible feature of tetrodotoxin poisoning, especially in predisposed individuals.

Multiple-dose pharmacokinetics of rimantadine in elderly adults

To assess the possible effect of aging on rimantadine hydrochloride pharmacokinetics, single- and multiple-dose kinetics were determined in 18 healthy adults with ages between 51 and 79 years. Subjects ingested single 100-mg oral doses of rimantadine after an overnight fast, followed after 5 days by a dosage of 100 mg twice a day for 9.5 days. No differences were observed among the age-stratified groups in measured or derived pharmacokinetic parameters. Peak concentrations in plasma (mean +/- standard deviation) following the single- and multiple-dose regimens, respectively, were 89 +/- 25 and 417 +/- 129 ng/ml for subjects who were 50 to 60 years of age (group 1), 92 +/- 24 and 401 +/- 84 ng/ml for those 61 to 70 years of age (group 2), and 100 +/- 14 and 538 +/- 51 for those 71 to 79 years of age (group 3). The elimination half-life in plasma following multiple doses averaged 33.5 h for group 1, 32.5 h for group 2, and 38.6 h for group 3. Steady-state concentrations in nasal mucus developed by day 5 of dosing (1.5-fold higher than concentrations in plasma), and rimantadine remained detectable in secretions for 5 days after the last dose in 65% of subjects. Stepwise regression analysis suggested that changes in maximum concentration in plasma and area under the concentration-time curve at steady state may be related to creatinine clearance. The results indicate that no important differences in rimantadine multiple-dose pharmacokinetics exist among healthy elderly adults with ages between 51 and 79 years.

Rimantadine hydrochloride and amantadine hydrochloride use in influenza A virus infections

Amantadine and rimantadine are oral antiviral drugs useful in the prophylaxis and treatment of influenza A virus infections. This article reviews the pharmacology, antiviral activity and mechanism of action, pharmacokinetics, toxicities, efficacy, and clinical applications of these agents. When administered in equivalent dosages (200 mg per day), rimantadine has prophylactic efficacy comparable to amantadine but lower potential for causing adverse effects. Despite structural similarities, these drugs differ significantly in their pharmacokinetics, and these differences may account for rimantadine's more favorable toxicity profile. Both drugs provide therapeutic benefit if administered early in uncomplicated influenza, and studies are currently in progress to determine the effectiveness of oral rimantadine in preventing or treating the serious complications of influenza A virus infections.

Capsicum and capsaicin--a review: case report of the use of hot peppers in child abuse

Capsaicin, the active principle of hot peppers of the genus Capsicum, exhibits broad bioactivity. It targets neuronal structures which contain substance P, clinically seen as gastrointestinal and dermatologic irritation, bronchospasm and fibrinolysis. As a research tool, capsaicin profoundly alters neurologic anatomy and function. We review the toxicity of capsaicin and comment briefly on the use of hot peppers in child abuse.