Pharmacokinetics of zidovudine and acetaminophen in a patient on chronic acetaminophen therapy

Acetaminophen safety and hepatotoxicity--where do we go from here?

Acetaminophen has been widely used for > 50 years in the treatment of pain and fever and provides for the safe and effective relief of these symptoms. In a small minority of patients, however, acetaminophen is responsible for life-threatening liver injury and accounts for up to 50% of all adult cases of acute liver failure in the US. Although approximately two-thirds of adult overdoses are associated with suicide attempts, many are inadvertent, often due to the use of multiple acetaminophen formulations over many days. Additionally, some individuals appear to experience acetaminophen toxicity at 'therapeutic' doses of < 4 g/day, for reasons unknown. In pediatric populations, the overwhelming majority of acetaminophen overdoses are due to unintentional overdoses, except for the predominance of suicidal ingestions in the teenage population. This article seeks to review the mechanism and metabolism of acetaminophen and the features of toxicity in adults, pediatric and special populations. Additionally, expert opinion is presented herein to aid in reducing the frequency and severity of liver injury from acetaminophen.

Paracetamol: new vistas of an old drug

Paracetamol (acetaminophen) is one of the most popular and widely used drugs for the treatment of pain and fever. It occupies a unique position among analgesic drugs. Unlike NSAIDs it is almost unanimously considered to have no antiinflammatory activity and does not produce gastrointestinal damage or untoward cardiorenal effects. Unlike opiates it is almost ineffective in intense pain and has no depressant effect on respiration. Although paracetamol has been used clinically for more than a century, its mode of action has been a mystery until about one year ago, when two independent groups (Zygmunt and colleagues and Bertolini and colleagues) produced experimental data unequivocally demonstrating that the analgesic effect of paracetamol is due to the indirect activation of cannabinoid CB(1) receptors. In brain and spinal cord, paracetamol, following deacetylation to its primary amine (p-aminophenol), is conjugated with arachidonic acid to form N-arachidonoylphenolamine, a compound already known (AM404) as an endogenous cannabinoid. The involved enzyme is fatty acid amide hydrolase. N-arachidonoylphenolamine is an agonist at TRPV1 receptors and an inhibitor of cellular anandamide uptake, which leads to increased levels of endogenous cannabinoids; moreover, it inhibits cyclooxygenases in the brain, albeit at concentrations that are probably not attainable with analgesic doses of paracetamol. CB(1) receptor antagonist, at a dose level that completely prevents the analgesic activity of a selective CB(1) receptor agonist, completely prevents the analgesic activity of paracetamol. Thus, paracetamol acts as a pro-drug, the active one being a cannabinoid. These findings finally explain the mechanism of action of paracetamol and the peculiarity of its effects, including the behavioral ones. Curiously, just when the first CB(1) agonists are being introduced for pain treatment, it comes out that an indirect cannabino-mimetic had been extensively used (and sometimes overused) for more than a century.

[Clinical evaluation of the efficacy of the paracetamol and caffeine combination in the treatment of tension headache]

Tension type headache in both its forms, episodic and chronic, is the most common type of headache experienced by the population. The headache attack or the prevention of new crises may be treated with pharmacological as well as non-pharmacological measures. This study included 5,490 patients from out-patient clinics and medical offices covering various regions of Brazil. Approximately 95% of the subjects had episodic tension type headache, while 5% had chronic tension type headache. The majority of the patients presented with crisis of moderate intensity (62.19%). In 5,419 patients a tension type headache crisis was treated with acetaminophen 1000 mg and caffeine 130 mg. In 93.98%, onset of relief occurred within 2 hours of taking the medication. In 77.61%, complete reversion of the crisis occurred within 2 hours. Good/excellent efficacy ratings were achieved in 61.93%/37.80% of the cases according to the physician's assessment and in 48.51%/40.29% according to the patients' assessment. Adverse events, commonly gastrointestinal manifestations, were reported by 5.57% of the patients. This is a Brazilian study of the efficacy and safety of the combined use of acetaminophen-caffeine for the treatment of tension type headache.

Adverse effects and drug interactions of medications commonly used in the treatment of adult HIV positive patients

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