Current concepts of the actions of paracetamol (acetaminophen) and NSAIDs.

There is much uncertainty about the mechanism of action of paracetamol (acetaminophen). It is commonly stated that, unlike the non-steroidal anti-inflammatory drugs (NSAIDs), it is a weak inhibitor of the synthesis of prostaglandins. This conclusion is made largely from studies in which the synthesis of prostaglandins was measured in homogenized tissues. However, in several cellular systems, paracetamol is an inhibitor of the synthesis of prostaglandins with IC(50) values ranging from approximately 4 microM to 200 microM. Paracetamol is not bound significantly to plasma proteins and therefore the concentrations in plasma can be equated directly with those used in in vitro experiments. After oral doses of 1 g, the peak plasma concentrations of paracetamol are approximately 100 microM and the plasma concentrations are therefore in the range where marked inhibition of the synthesis of prostaglandins should occur in some cells. Paracetamol is metabolized by the peroxidase component of prostaglandin H synthase but the relationship of this to inhibition of the cyclooxygenase or peroxidase activities of the enzyme is unclear. Paracetamol is also metabolized by several other peroxidases, including myeloperoxidase, the enzyme in neutrophils which is responsible for the production of hypochlorous acid (HOCl). The metabolism of paracetamol by myeloperoxidase leads to the decreased total production of HOC1 by both intact neutrophils and isolated myeloperoxidase, even though the initial rate of production of HOC1 is increased. The IC(50) value, derived from inhibition of the total production of HOC1 by isolated myeloperoxidase, is 81 microM. Several NSAIDs inhibit functions of neutrophils in media containing low concentrations of protein but their effects, in contrast to that of paracetamol, are generally produced only at concentrations greater than those of the unbound drug in plasma during treatment with the NSAIDs. However, neutrophils isolated during treatment with NSAIDs, such as piroxicam, ibuprofen and indomethacin show decreased function. Paracetamol has little or no anti-inflammatory activity by itself but may potentiate the clinical activity of NSAIDs in the treatment of rheumatoid arthritis.

A 20-year population-based study of postdiarrheal hemolytic uremic syndrome in Utah.

OBJECTIVE: To determine epidemiologic features, trends in frequency, and predictors of clinical outcome of postdiarrheal hemolytic uremic syndrome (HUS) in Utah. DESIGN: A 20-year population-based study of HUS with a review of the HUS registry, hospital records, transplant registry, and a survey of pediatricians and pediatric nephrologists to ensure completeness of ascertainment. POPULATION: All Utah residents under 18 years of age with HUS occurring after a diarrheal prodrome between 1971 and 1990. OUTCOME MEASURES: Incidence of HUS, severity, complications, and long-term sequelae. RESULTS: There were 157 cases during 20 years; 140 (89%) occurred after a diarrheal prodrome. The mean annual incidence was 1.42/100,000 children (range 0.2 to 3.4/100,000 children/year). Periods of high incidence occurred; however, there was no overall sustained increase in incidence. Escherichia coli O157:H7 was isolated from the stool of 62% of children who had specimens submitted. There were no differences between the first and second decade in the proportion with diarrheal prodrome, bloody diarrhea, most abnormal laboratory values, hospital course, or outcome. However, admission laboratory abnormalities were more severe during the first decade suggesting a delay in diagnosis. Age < 2 years, anuria before admission, and higher white blood cell counts on admission predicted severe disease. Bad outcome (death, end-stage renal disease, or stroke) occurred in 11%; 5% died. Chronic renal sequelae, usually mild, were found on follow-up (median 6.5 years) in 51% of survivors. CONCLUSIONS: HUS has been an important clinical and public health problem in Utah for 20 years. The consistency of the clinical and epidemiologic features over 2 decades suggests that a common etiologic agent has accounted for most cases of HUS in this region since 1971.

Long-term outcome and prognostic indicators in the hemolytic-uremic syndrome.

We examined 61 patients an average of 9.6 years (range 5 to 18 years) after an episode of childhood hemolytic-uremic syndrome. Twenty-four (39%) had one or more abnormalities. Seven (11%) had proteinuria and six (10%) had low creatinine clearance as solitary abnormalities. Eight (13%) had both proteinuria and reduced creatinine clearance; three (5%) had a combination of hypertension, proteinuria, and low creatinine clearance. Abnormalities sometimes appeared after an interval of apparent recovery. Logistic regression analysis showed that duration of anuria was the best predictor of disease at follow-up. No patients who had anuria lasting longer than 8 days or oliguria exceeding 15 days escaped chronic disease. However, 45% of those with disease had no anuria, and a third had no oliguria. Physicians should therefore be cautious in assuming recovery from HUS on the basis of a single evaluation and should periodically evaluate patients for an extended period.