Relationship Between Paracetamol Plasma Levels and its Analgesic Effect in the Rat

The relationship between plasma levels of paracetamol and its analgesic effect was studied in the rat using a model of pain-induced functional impairment (PIFI). Female Wistar rats received an intraarticular injection of 30% uric acid in the knee of the right hind limb, inducing its dysfunction. Animals then received oral paracetamol at doses of 178, 316 or 562 mg kg−1and the recovery of functionality over time was considered as an expression of analgesia. Paracetamol plasma levels were determined by HPLC. Results showed that there is a direct relationship between paracetamol plasma levels and its analgesic effect that follows a sigmoidal model according to the Hill equation. The PIFI model appears to be a useful tool to establish pharmacokinetic/pharmacodynamic relationships for non-narcotic analgesics.

Impact of serum acetaminophen concentration on changes in serum potassium, creatinine and urea concentrations among patients with acetaminophen overdose

BACKGROUND

Acetaminophen overdose may be accompanied by electrolyte disturbances. The basis for electrolyte change appears to be due to increased fractional urinary electrolyte excretion.

PURPOSE

This study investigated the impact of serum acetaminophen concentration on changes in serum potassium, creatinine and urea concentrations in patients with acetaminophen overdose.

METHODS

This was a retrospective cohort study which included patients admitted to the emergency department and hospital within 24 h of acetaminophen ingestion. The study was conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Data are presented as mean ± SD and as medians (interquartile range) and groups were compared using independent two-tailed Student t-test. Statistical Package for Social Sciences (SPSS) 15 was used for data analysis.

RESULTS

Two hundred and eighty-three patients were studied (44 males and 239 females), mean age 23 ± 7.5 years. Patients who had a serum acetaminophen concentration above a 'possible toxicity' treatment line were associated with an elevation in serum creatinine concentration (p=0.044) and a reduction in the serum potassium concentration (p<0.001) but were not associated with a reduction in serum urea concentration (p>0.99). During the study period, 63.3% (179 patients) had serum potassium concentrations less than the normal concentration (3.5 mmol/l) and 31.4% (89 patients) had serum urea concentrations less than the normal concentration (2.5 mmol/l). The serum creatinine concentration in all patients was within the normal range.

CONCLUSIONS

Acetaminophen appears to cause a concentration-dependent reduction of potassium concentrations and an elevation of creatinine concentrations of short duration (<24 h) after overdose.

[Comparative pharmacokinetics of antigrippin-maximum administered in capsules and powder for preparing solutions]

Comparative pharmacokinetics of anti-influenza drug composition Antigrippin-maximum administered in capsules and a powder for preparing solutions has been studied after single administraton in a group of 18 healthy volunteers. Both preparations [manufactured by the Antiviral Research and Production Corporation (St Petersbutg) contain 6 active components, including paracetamol, rimantadine, loratadine, ascorbic acid, calcium gluconate, and rutoside in equal amounts. The concentrations of unchanged paracetamol, rimantadine, and loratadine in the blood plasma were degtermined by HPLC with mass-spectrometric and UV detection. The pharmacokinetic parameters of allindicated active components exhibited no detectable distinctions, except for the time to attaining maximum concentration ofparacetamol and the value of the maximum concentration of loratadine.

Development and validation of stability-indicating HPLC method for the simultaneous determination of paracetamol, tizanidine, and diclofenac in pharmaceuticals and human serum

A method is described for the simultaneous determination of paracetamol, tizanidine, and diclofenac in mixtures. The method was based on HPLC separation of the three drugs followed by UV detection at 254 nm. The separation was carried out on a Hypersil ODS, C18 (250 x 4.6 mm id, 10 microm particle size) column using the mobile phase aqueous 0.2% ammonium carbonate-methanol (60 + 40, v/v) at a flow rate of 1 mL/min. The linear regression analysis data were used for the regression curve in the range of 170-10 000 ng/mL for paracetamol, 120-10 000 ng/mL for tizanidine, and 20-10 000 ng/mL for diclofenac. No chromatographic interference from tablet excipients was found. In order to check the selectivity of the proposed method, degradation studies were carried out using hydrolysis (acid, basic, and neutral), thermolysis, and oxidation. The developed method, after being validated in terms of precision, robustness, recovery, LOD, and LOQ, was successively applied to the analysis of pharmaceutical formulations and human serum.

Assessing the impact of vomiting episodes on outcome after acetaminophen poisoning

Identifying indices of poor prognosis at first presentation after acetaminophen poisoning is the key to both improving clinical care and determining targets for intervention. This study intended to document the prevalence, clinical characteristics and predictors of vomiting and to investigate the relationship between episodes of vomiting at first hospital presentation and outcome in acetaminophen poisoning. This retrospective cohort study included patients who attended the emergency department and were admitted within 24 hr of acetaminophen ingestion. The study was conducted over a period of 5 years from 1 January 2004 to 31 December 2008. Parametric and non-parametric tests were used to test differences between groups depending on the normality of the data. SPSS 15 was used for data analysis. Data from 291 patients were included. Vomiting was present in 65.3% of patients with acetaminophen poisoning at the time of first presentation. Multiple logistic regression showed that significant risk factors for vomiting were present among patients who reported an ingested dose of acetaminophen ≥10 g (p < 0.001) and a latency time of more than 8 hr (p = 0.030). Overall, an increasing trend in prothrombin time (p = 0.03), serum bilirubin (p < 0.001), serum creatinine (p = 0.005), serum potassium (p < 0.001), length of hospital stay (p < 0.001) and the prevalence of patients who had a serum acetaminophen level above a 'possible toxicity' treatment line (p = 0.001) were associated with an increased number of episodes of vomiting. In conclusion, vomiting was common among patients with acetaminophen poisoning. This study suggests that an increase in episodes of vomiting at first presentation appears to be an important risk marker of subsequent nephrotoxicity and hepatotoxicity.

Effect of activated charcoal in reducing paracetamol absorption at a supra-therapeutic dose

BACKGROUND

Activated charcoal (AC) is recommended for treatment of acute poisoning, thereby decreasing gastrointestinal tract absorption. AC from different sources may have different adsorptive capacity. The AC that is available in Thailand has not been proven yet for its efficacy The authors simulated paracetamol overdose model for the present study.

OBJECTIVE

To assess the efficacy of AC that is available in Thailand in decreasing absorption of paracetamol at supratherapeutic dose.

MATERIAL AND METHOD

This was a two-arm, prospective, crossover study. Washout period was 1 week Twelve healthy male volunteers participated. All volunteers were randomly assigned to either sequence of control-experiment (CE) or EC. The participants ingested 60 mg/Kg of paracetamol at Time=0. At Time = 0.25 hour, they ingested 50 g of AC as slurry with 250 ml of water when they were assigned as E, but drank 250 mL of water when were assigned as C. Blood samples were serially collected for determination of paracetamol concentration and calculating pharmacokinetic parameters, area under the time-concentration curve (AUC (0, infinity)).

RESULTS

Means of the AUC (0, infinity) were 313.7 +/- 29.8 and 184.8 +/- 91.6 mg-h/ L in the control and experimental arm, respectively It was statistically different (p = 0.01).

CONCLUSION

The tested AC was found to be able to reduce the absorption of the supratherapeutic dose of paracetamol.

Relationship between serum acetaminophen concentration and N-acetylcysteine-induced adverse drug reactions

Intravenous N-acetylcysteine is usually regarded as a safe antidote. However, during the infusion of the loading dose, different types of adverse drug reactions (ADR) may occur. The objective of this study was to investigate the relation between the incidence of different types of ADR and serum acetaminophen concentration in patients presenting to the hospital with acetaminophen overdose. This is a retrospective study of patients admitted to the hospital for acute acetaminophen overdose over a period of 5 years (1 January 2004 to 31 December 2008). Parametric and non-parametric tests were used to test differences between groups depending on the normality of the data. SPSS 15 was used for data analysis. Of 305 patients with acetaminophen overdose, 146 (47.9%) were treated with intravenous N-acetylcysteine and 139 (45.6%) were included in this study. Different types of ADR were observed in 94 (67.6%) patients. Low serum acetaminophen concentrations were significantly associated with cutaneous anaphylactoid reactions but not other types of ADR. Low serum acetaminophen concentration was significantly associated with flushing (p < 0.001), rash (p < 0.001) and pruritus (p < 0.001). However, there were no significant differences in serum acetaminophen concentrations between patients with and without the following ADR: gastrointestinal reactions (p = 0.77), respiratory reactions (p = 0.96), central nervous reactions (p = 0.82) and cardiovascular reactions (p = 0.37). In conclusion, low serum acetaminophen concentrations were associated with higher cutaneous anaphylactoid reactions. Such high serum acetaminophen concentrations may be protective against N-acetylcysteine-induced cutaneous ADR.

Acetaminophen elimination half-life in humans is unaffected by short-term consumption of sulfur amino acid-free diet

Sulfation and glutathione (GSH) conjugation are important pathways for elimination of acetaminophen (APAP). Previous studies in rodents show that limitation of dietary sulfur amino acids (SAAs) reduces biosynthesis of 3'-phosphoadenosine-5'-phosphosulfate, the precursor for sulfation, and GSH, the precursor for the mercapturatic acid pathway. The amount of SAA needed for the metabolism of two doses of APAP is equivalent to 62% of the recommended dietary allowance (RDA) for SAA in humans. A decrease in the activity of these metabolic pathways could lead to decreased elimination of the reactive metabolite of APAP and possibly affect risk of APAP use. To determine whether intake of a SAA-deficient diet alters APAP metabolism, a pilot clinical study with a double-blind, cross-over design was performed. Subjects received the RDA for SAA for 3 days for equilibration. After admission to the clinical research unit, subjects were given a chemically defined diet with 100 or 0% of the RDA for SAA for 2 days. On day 3, two doses of APAP (15 mg/kg) or placebo were given successively within a 6-h interval. Plasma samples were collected at baseline and hourly for 12 h, and two 6-h urine aliquots were collected during this time course. The data show that SAA limitation 1) did not change the pattern of APAP metabolites in plasma or urine and 2) did not alter APAP pharmacokinetics. Thus, the results show that 2 days of diet completely devoid of SAA have no effect on APAP metabolism or disposition in healthy humans.

[Intravenous or oral N acetylcysteine therapy in paracetamol poisoned patients. Should treatment guidelines be reviewed?]

Danish paracetamol (PCM) poisoned patients are treated with N-acetylcysteine (NAC) intravenously for 36 hours. This probably leads to overtreatment. Today, patients with poor prognoses can be identified and, in addition, NAC may have serious side effects. We reviewed the literature (route of administration, duration and timing of treatment) and found that intravenous NAC often leads to side effects (some serious), primarily when serum paracetamol is low. These patients are often only mildly poisoned and they may therefore benefit from a shorter, orally administered regimen (equally efficient and with fewer side effects than intravenously administered NAC).

A modified low-cost colorimetric method for paracetamol (acetaminophen) measurement in plasma

BACKGROUND

Despite a significant increase in the number of patients with paracetamol poisoning in the developing world, plasma paracetamol assays are not widely available. The purpose of this study was to assess a low-cost modified colorimetric paracetamol assay that has the potential to be performed in small laboratories with restricted resources.

METHODS

The paracetamol assay used in this study was based on the Glynn and Kendal colorimetric method with a few modifications to decrease the production of nitrous gas and thereby reduce infrastructure costs. Preliminary validation studies were performed using spiked aqueous samples with known concentrations of paracetamol. Subsequently, the results from the colorimetric method for 114 stored clinical samples from patients with paracetamol poisoning were compared with those from the current gold-standard high-performance liquid chromatography method. A prospective survey, assessing the clinical use of the paracetamol assay, was performed on all patients with paracetamol poisoning attending the Peradeniya General Hospital, Sri Lanka, over a 10-month period.

RESULTS

The recovery study showed an excellent correlation (r(2) > 0.998) for paracetamol concentrations from 25 to 400 mg/L. The final yellow color was stable for at least 10 min at room temperature. There was also excellent correlation with the high-performance liquid chromatography method (r(2) = 0.9758). In the clinical cohort study, use of the antidote N-acetylcysteine was avoided in over a third of patients who had the plasma paracetamol concentration measured. The cost of consumables used per assay was $0.50 (US).

CONCLUSIONS

This colorimetric paracetamol assay is reliable and accurate and can be performed rapidly, easily, and economically. Use of this assay in resource-poor clinical settings has the potential to have a significant clinical and economic impact on the management of paracetamol poisoning.

Paracetamol (acetaminophen) clearance in patients with cirrhosis of the liver

The pharmacokinetics of paracetamol were studied in 11 patients with cirrhosis of the liver and 12 controls. The average biological half-life after oral administration of 1 g paracetamol was significantly prolonged in patients with hepatic cirrhosis compared to the controls (3.7 hr vs.2.1 hr) and, correspondingly, the average plasma clearance was significantly reduced from 337 ml x min-1 in the controls to 162 ml x min-1 in the patients with cirrhosis of the liver. After subchronic dosing of paracetamol with 1 g paracetamol t. i. d. the plasma half-lives of paracetamol remained unchanged. Steady-state levels of paracetamol were significantly increased in the patients with cirrhosis of the liver. A significant correlation between the values of plasma clearance of paracetamol and prothrombin time (r = +0.88), galactose elimination capacity (r = +0.66), plasma albumin (r = +0.85) was found. No clinical or biochemical signs of hepatotoxicity were observed during the study.

Hepatotoxicity despite early administration of intravenous N-acetylcysteine for acute acetaminophen overdose

OBJECTIVES

The objective was to evaluate the effectiveness of intravenous N-acetylcysteine (IV NAC; 300 mg/kg over 21 hours) in early acute acetaminophen (APAP) overdose patients.

METHODS

This observational case series included patients hospitalized between 2004 and 2007 for acute APAP overdoses and who were reported to a regional poison center. Inclusion criteria were plasma APAP concentrations on or above the treatment line on the Rumack-Matthew nomogram, administration of IV NAC within 8 hours of ingestion, and follow-up to known outcome. The hospital chart of each patient who received IV NAC for longer than the standard 21 hours was reviewed. Hepatotoxicity was defined as hepatic aminotransferase levels greater than 1,000 IU/L.

RESULTS

Seventy-seven patients met inclusion criteria and received at least 21 hours of IV NAC for an acute APAP overdose. Seven patients received antidotal therapy for greater than 21 hours. These patients tended to have ingested combination preparations, have very high initial plasma APAP concentrations, and had persistently elevated plasma concentrations during their hospital stay. Hepatotoxicity occurred in 4 patients (5.2%, 95% confidence interval [CI] = 0.2% to 10.1%), including 1 death and 1 liver transplantation.

CONCLUSIONS

Hepatotoxicity developed in 5.2% of cases, suggesting that the 21-hour IV NAC regimen is suboptimal in some patients. In addition to high initial plasma APAP concentrations, APAP product formulation and persistently elevated plasma APAP concentrations were identified as factors possibly associated with developing hepatotoxicity. The authors propose a tailored approach to the discontinuation of IV NAC and point out the need for reevaluation of optimal doses and duration of therapy.

Pre-operative carbohydrate loading may be used in type 2 diabetes patients

BACKGROUND

Post-operative insulin resistance and hyperglycaemia are associated with an impaired outcome after surgery. Pre-operative oral carbohydrate loading (CHO) reduces post-operative insulin resistance with a reduced risk of hyperglycaemia during post-operative nutrition. Insulin-resistant diabetic patients have not been given CHO because the effects on pre-operative glycaemia and gastric emptying are unknown.

METHODS

Twenty-five patients (45-73 years) with type 2 diabetes [glycated haemoglobin (HbA1c) 6.2 +/- 0.2%, mean +/- SEM] and 10 healthy control subjects (45-72 years) were studied. A carbohydrate-rich drink (400 ml, 12.5%) was given with paracetamol 1.5 g for determination of gastric emptying.

RESULTS

Peak glucose was higher in diabetic patients than in healthy subjects (13.4 +/- 0.5 vs. 7.6 +/- 0.5 mM; P<0.01) and occurred later after intake (60 vs. 30 min; P<0.01). Glucose concentrations were back to baseline at 180 vs. 120 min in diabetic patients and healthy subjects, respectively (P<0.01). At 120 min, 10.9 +/- 0.7% and 13.3 +/- 1.2% of paracetamol remained in the stomach in diabetic patients and healthy, subjects respectively. Gastric half-emptying time (T50) occurred at 49.8 +/- 2.2 min in diabetics and at 58.6 +/- 3.7 min in healthy subjects (P<0.05). Neither peak glucose, glucose at 180 min, gastric T50, nor retention at 120 min differed between insulin (HbA1c 6.8 +/- 0.7%)- and non-insulin-treated (HbA1c 5.6 +/- 0.4%) patients.

CONCLUSIONS

Type 2 diabetic patients showed no signs of delayed gastric emptying, suggesting that a carbohydrate-rich drink may be safely administrated 180 min before anaesthesia without risk of hyperglycaemia or aspiration pre-operatively.

Evaluation of a urine screen for acetaminophen

BACKGROUND

Acetaminophen (APAP) is a leading cause of fatal overdose. This study examined the performance characteristics of the Biosite Triage TOX Drug Screen qualitative APAP urine test (urine screen) in a clinical setting.

METHODS

Paired urine and serum waste samples (collected within 2 hours of one another) were quantitatively analyzed for APAP concentration and compared to the urine screen results.

RESULTS

A total of 191 paired samples met inclusion criteria. The urine screen did not report a negative result for the 21 samples with a serum APAP concentration of > or =10microg/mL and had a sensitivity of 100% (95% confidence interval [CI], 85-100%). The urine screen had a sensitivity of 96% (95% CI, 91-99%) and a specificity of 90% (95% CI, 82-95%) for detecting urine APAP concentrations > 5microg/mL by gas chromatograph mass spectroscopy (GCMS) methods, and a sensitivity of 81% (95% CI, 73-87%) and a specificity of 95% (95% CI, 85-98%) by high-pressure liquid chromatography (HPLC) methods.

CONCLUSIONS

The urine screen detected urine APAP concentrations with good accuracy and may be an effective screen to rule out acute APAP overdose in some circumstances. Its clinical utility is discussed.

Mechanism of action of exenatide to reduce postprandial hyperglycemia in type 2 diabetes

We examined the contributions of insulin secretion, glucagon suppression, splanchnic and peripheral glucose metabolism, and delayed gastric emptying to the attenuation of postprandial hyperglycemia during intravenous exenatide administration. Twelve subjects with type 2 diabetes (3 F/9 M, 44 +/- 2 yr, BMI 34 +/- 4 kg/m2, Hb A(1c) 7.5 +/- 1.5%) participated in three meal-tolerance tests performed with double tracer technique (iv [3-3H]glucose and oral [1-14C]glucose): 1) iv saline (CON), 2) iv exenatide (EXE), and 3) iv exenatide plus glucagon (E+G). Acetaminophen was given with the mixed meal (75 g glucose, 25 g fat, 20 g protein) to monitor gastric emptying. Plasma glucose, insulin, glucagon, acetaminophen concentrations and glucose specific activities were measured for 6 h post meal. Post-meal hyperglycemia was markedly reduced (P < 0.01) in EXE (138 +/- 16 mg/dl) and in E+G (165 +/- 12) compared with CON (206 +/- 15). Baseline plasma glucagon ( approximately 90 pg/ml) decreased by approximately 20% to 73 +/- 4 pg/ml in EXE (P < 0.01) and was not different from CON in E+G (81 +/- 2). EGP was suppressed by exenatide [231 +/- 9 to 108 +/- 8 mg/min (54%) vs. 254 +/- 29 to189 +/- 27 mg/min (26%, P < 0.001, EXE vs. CON] and partially reversed by glucagon replacement [247 +/- 15 to 173 +/- 18 mg/min (31%)]. Oral glucose appearance was 39 +/- 4 g in CON vs. 23 +/- 6 g in EXE (P < 0.001) and 15 +/- 5 g in E+G, (P < 0.01 vs. CON). The glucose retained within the splanchnic bed increased from approximately 36g in CON to approximately 52g in EXE and to approximately 60g in E+G (P < 0.001 vs. CON). Acetaminophen((AUC)) was reduced by approximately 80% in EXE vs. CON (P < 0.01). We conclude that exenatide infusion attenuates postprandial hyperglycemia by decreasing EGP (by approximately 50%) and by slowing gastric emptying.

[Analytic role in clinical toxicology--impact on the diagnosis and treatment of a poisoned patient]

The measurement of plasma or urine levels of drugs or toxins at an appropriate time after ingestion and assessment of the clinical status can have a significant impact in the clinical management of a poisoned patient. Qualitative screening of blood and urine is helpful in identifying ingested toxins, whereas quantitative analyses are useful in determining appropriate therapy with selected toxins (e.g., salicylate, paraquat, and acetaminophen). The common analgesic acetaminophen, which is available without prescription, is a potential hepatotoxin on overdose. The most widely accepted approach to determine the risk of hepatotoxicity following acute, single ingestion is to plot the plasma acetaminophen concentration on the Rumack-Matthew nomogram. This nomogram is based on a series of patients with and without hepatotoxicity and their corresponding blood levels. Antidotal treatment should be administered to any patient with a plasma level in the potentially toxic range. As an aid in the diagnosis and treatment of toxic incidents, as well as in monitoring the effectiveness of treatment regimens, an analytical approach is useful to clearly identify the nature of the toxic exposure and measure the amount of the toxic substance which has been absorbed. A cardinal rule in the treatment of poisoning cases is to remove any unabsorbed material, limit the absorption of additional poison, and hasten its elimination. The laboratory serves an additional purpose in the treatment phase by monitoring the amount of toxic agent remaining in circulation or measuring that excreted.