Relationship between nonphenacetin combined analgesics and nephropathy: a review. Ad Hoc Committee of the International Study Group on Analgesics and Nephropathy

Long-term adverse effects of paracetamol - a review

Paracetamol (acetaminophen) is the most commonly used drug in the world, with a long record of use in acute and chronic pain. In recent years, the benefits of paracetamol use in chronic conditions has been questioned, notably in the areas of osteoarthritis and lower back pain. Over the same period, concerns over the long-term adverse effects of paracetamol use have increased, initially in the field of hypertension, but more recently in other areas as well. The evidence base for the adverse effects of chronic paracetamol use consists of many cohort and observational studies, with few randomized controlled trials, many of which contradict each other, so these studies must be interpreted with caution. Nevertheless, there are some areas where the evidence for harm is more robust, and if a clinician is starting paracetamol with the expectation of chronic use it might be advisable to discuss these side effects with patients beforehand. In particular, an increased risk of gastrointestinal bleeding and a small (~4 mmHg) increase in systolic blood pressure are adverse effects for which the evidence is particularly strong, and which show a degree of dose dependence. As our estimation of the benefits decreases, an accurate assessment of the harms is ever more important. The present review summarizes the current evidence on the harms associated with chronic paracetamol use, focusing on cardiovascular disease, asthma and renal injury, and the effects of in utero exposure.

Caffeine in the management of patients with headache

Caffeinated headache medications, either alone or in combination with other treatments, are widely used by patients with headache. Clinicians should be familiar with their use as well as the chemistry, pharmacology, dietary and medical sources, clinical benefits, and potential safety issues of caffeine. In this review, we consider the role of caffeine in the over-the-counter treatment of headache. The MEDLINE and Cochrane databases were searched by combining “caffeine” with the terms “headache,” “migraine,” and “tension-type.” Studies that were not placebo-controlled or that involved medications available only with a prescription, as well as those not assessing patients with migraine and/or tension-type headache (TTH), were excluded. Compared with analgesic medication alone, combinations of caffeine with analgesic medications, including acetaminophen, acetylsalicylic acid, and ibuprofen, showed significantly improved efficacy in the treatment of patients with TTH or migraine, with favorable tolerability in the vast majority of patients. The most common adverse events were nervousness (6.5%), nausea (4.3%), abdominal pain/discomfort (4.1%), and dizziness (3.2%). This review provides evidence for the role of caffeine as an analgesic adjuvant in the acute treatment of primary headache with over-the-counter drugs, caffeine doses of 130 mg enhance the efficacy of analgesics in TTH and doses of ≥100 mg enhance benefits in migraine. Additional studies are needed to assess the relationship between caffeine dosing and clinical benefits in patients with TTH and migraine.

Common Analgesic Agents and Their Roles in Analgesic Nephropathy: A Commentary on the Evidence

An association between non-opioid analgesic agents and chronic kidney disease has long been suspected. The presumed development of chronic renal impairment following protracted and excessive use of non-opioid analgesia is known as analgesic nephropathy. Many clinicians accept analgesic nephropathy as a real entity despite the paucity of scientific evidence. This narrative review aims to summarize the literature in the field. The weight of available observational literature suggests that long-term ingestion of paracetamol and combination mixtures of aspirin and paracetamol are likely to contribute to chronic renal impairment. However, there is no convincing data to implicate non-steroidal anti-inflammatory drugs or aspirin monotherapy in the development of analgesic nephropathy. In the absence of high-level evidence, while controversy persists, it may be prudent for physicians to consider all non-narcotic analgesics to be nephrotoxic with long-term use.

Non-steroidal anti-inflammatories and the development of analgesic nephropathy: a systematic review

BACKGROUND

Analgesic nephropathy (AN) is chronic renal impairment as a direct consequence of chronic heavy analgesia ingestion. An association between non-steroidal anti-inflammatory agents and chronic kidney disease (CKD) has long been suspected. Despite ample observational data obtained in recent decades the relationship remains uncertain. This systematic review intends to summarize the available literature and to define the role of non-steroidal anti-inflammatories in the natural history of AN.

METHODS

We conducted a systematic literature search for articles describing the association between non-steroidal anti-inflammatory abuse and renal insufficiency. No restriction was placed on publication date, but papers were limited to English language, observational design, and human studies.

RESULTS

Nine articles met our inclusion criteria and were discussed in this review. This includes 5 cohort studies and 4 case-control trials, with a combined population of 12,418 study subjects and 23,877 controls. Eight of the nine reports failed to identify any increased risk of chronic renal impairment with heavy non-steroidal anti-inflammatory consumption. Study methods were heterogeneous and the overall quality of data was relatively poor.

CONCLUSION

A relationship between non-steroidal anti-inflammatory medicines and the development of CKD has never been proven. Based on the available scientific evidence non-steroidal anti-inflammatory agents do not appear to be implicated in the pathogenesis of AN.

Validation of potential candidate biomarkers of drug-induced nephrotoxicity and allodynia in medication-overuse headache

Background

Medication-overuse headache (MOH) is a chronic disorder that results from the overuse of analgesics drugs, triptans or other acute headache compounds. Although the exact mechanisms underlying MOH remain still unknown, several studies suggest that it may be associated with development of “central sensitization”, which may cause cutaneous allodynia (CA). Furthermore, the epidemiology of drug-induced disorders suggests that medication overuse could lead to nephrotoxicity. The aim of this work was to confirm and validate the results obtained from previous proteomics studies, in which we analyzed the urinary proteome of MOH patients in comparison with healthy non-abusers individuals.

Methods

MOH patients were divided into groups on the basis of the drug abused: triptans, non-steroidal anti-inflammatory drugs (NSAIDs) and mixtures, (mainly containing indomethacin, paracetamol and, in some cases, caffeine). Healthy subjects, with a history of normal renal function, were used as controls. In this study, four proteins that were found differentially expressed in urine, and, on the basis of the literature review, resulted related to kidney diseases, were verified by Western Blot and Enzyme-linked Immunosorbent Assay (ELISA); Prostaglandin-H2 D-synthase (PTGDS), uromodulin (UROM), alpha-1-microglobulin (AMBP) and cystatin-C (CYSC).

Results

Western blot analysis allowed to validate our previous proteomics data, confirming that all MOH patients groups show a significant over-excretion of urinary PTGDS, UROM, AMBP and CYSC (excluding triptans group for this latter), in comparison with controls. Moreover, the expression of PTGDS was further evaluated by ELISA. Also by this assay, a significant increase of PTGDS was observed in all MOH abusers, according to 2-DE and Western blot results.

Conclusions

In this study, we confirmed previous findings concerning urinary proteins alterations in MOH patients, identified and demonstrated the over-expression of PTGDS, UROM, AMBP, and CYSC, particularly in NSAIDs and mixtures abusers. Over-expression of these proteins have been related to renal dysfunction and probably, PTGDS, to the development of CA. The detection and confirmation of this proteins pattern represent a promising tool for a better understanding of potential nephrotoxicity induced by drugs overuse and may enhance awareness related to the MOH-associated risks, even in absence of clinical symptoms.

Paracetamol and analgesic nephropathy: Are you kidneying me?

INTRODUCTION

Analgesic nephropathy is a disease resulting from the frequent use of combinations of analgesic medications over many years, leading to significant impairment of renal function. The observation of a large number of cases of renal failure in patients abusing analgesic mixtures containing phenacetin led to the initial recognition of the nephrotoxicity from the use of analgesics. Phenacetin was subsequently exclusively blamed for this disease. However, the role of a single analgesic as a sole cause of analgesic nephropathy was challenged, and a number of researchers have since attempted to determine the extent of involvement of other analgesics including nonsteroidal anti-inflammatory drugs (NSAIDs), aspirin, and paracetamol.

CASE PRESENTATION

We present the case of an 83-year-old woman with a history of NSAID-induced nephropathy with poor pain control and reluctance to use paracetamol. We attempt to briefly review the evidence of paracetamol being implicated in the development of analgesic-induced nephropathy.

CONCLUSION

There is a lack of concrete data regarding causative analgesics, including paracetamol. Patients should therefore not be withheld paracetamol, an effective and commonly recommended agent, for fear of worsening renal function.

A group-randomized trial of shared decision making for non-steroidal anti-inflammatory drug risk awareness: primary results and lessons learned

RATIONALE, AIMS AND OBJECTIVES

Frequent use and serious adverse effects related to non-steroidal anti-inflammatory drugs (NSAIDs) underscore the need to raise patient awareness about potential risks. Partial success of patient- or provider-based interventions has recently led to interest in combined approaches focusing on both patient and physician. This research tested a shared decision-making intervention for increasing patient-reported awareness of NSAID risk.

METHODS

A group randomized trial was performed in Alabama from 2005 to 2007. Intervention group doctor practices received continuing medical education (CME) about NSAIDs and patient activation tools promoting risk assessment and communication during visits. Comparison group doctor practices received only CME. Cross-sectional data were collected before and after the intervention. Generalized linear latent and mixed models with logistic link tested relationships among the intervention, study phase, intervention by study phase interaction and patient-reported awareness of risks with either prescription or over-the-counter (OTC) NSAIDs.

RESULTS

Three hundred and forty-seven patients at baseline and 355 patients at follow-up participated in this study. The intervention [adjusted odds ratio (AOR)=0.74, P=0.248], follow-up study phase (AOR=1.31, P=0.300) and intervention by study phase interaction (AOR=0.98, P=0.942) were not significantly associated with patient-reported awareness of any prescription NSAID risk. Follow-up study phase was associated with increased odds of reporting any OTC NSAID risk awareness (AOR=2.99, P<0.001), but the patient activation intervention and intervention by study phase interaction were not significantly associated with patient-reported awareness of any OTC NSAID risk (AOR=0.98, P=0.929; AOR=0.87, P=0.693, respectively).

CONCLUSIONS

Our point-of-care intervention encouraging shared decision making did not increase NSAID risk awareness.

Combined analgesics in (headache) pain therapy: shotgun approach or precise multi-target therapeutics?

BACKGROUND

Pain in general and headache in particular are characterized by a change in activity in brain areas involved in pain processing. The therapeutic challenge is to identify drugs with molecular targets that restore the healthy state, resulting in meaningful pain relief or even freedom from pain. Different aspects of pain perception, i.e. sensory and affective components, also explain why there is not just one single target structure for therapeutic approaches to pain. A network of brain areas ("pain matrix") are involved in pain perception and pain control. This diversification of the pain system explains why a wide range of molecularly different substances can be used in the treatment of different pain states and why in recent years more and more studies have described a superior efficacy of a precise multi-target combination therapy compared to therapy with monotherapeutics.

DISCUSSION

In this article, we discuss the available literature on the effects of several fixed-dose combinations in the treatment of headaches and discuss the evidence in support of the role of combination therapy in the pharmacotherapy of pain, particularly of headaches. The scientific rationale behind multi-target combinations is the therapeutic benefit that could not be achieved by the individual constituents and that the single substances of the combinations act together additively or even multiplicatively and cooperate to achieve a completeness of the desired therapeutic effect.As an example the fixed-dose combination of acetylsalicylic acid (ASA), paracetamol (acetaminophen) and caffeine is reviewed in detail. The major advantage of using such a fixed combination is that the active ingredients act on different but distinct molecular targets and thus are able to act on more signalling cascades involved in pain than most single analgesics without adding more side effects to the therapy.

SUMMARY

Multitarget therapeutics like combined analgesics broaden the array of therapeutic options, enable the completeness of the therapeutic effect, and allow doctors (and, in self-medication with OTC medications, the patients themselves) to customize treatment to the patient's specific needs. There is substantial clinical evidence that such a multi-component therapy is more effective than mono-component therapies.

A risk-benefit assessment of paracetamol (acetaminophen) combined with caffeine

OBJECTIVE

To determine the risk: benefit of paracetamol combined with caffeine in the short-term management of acute pain conditions.

DESIGN

Database searches were conducted to identify double-blind trials comparing paracetamol/caffeine with paracetamol alone (benefit analysis) and any data pertaining to hepatotoxicity of paracetamol when combined with caffeine (risk analysis).

INTERVENTIONS

Paracetamol/caffeine (1,000 mg/130 mg) vs paracetamol (1,000 mg) alone.

OUTCOME MEASURES

Assessment of benefit has been derived by meta-analysis. Information on the pain condition and number of patients studied, dosing regimen, study design and analgesic outcome measures (total pain relief scores) was extracted and dichotomous outcomes were obtained by calculating the number of patients in each treatment group who achieved at least 50% of the maximum total pain relief score. Assessment of risk has been made by appraisal of the literature.

RESULTS

Eight studies from four papers provided sufficient quantitative data for satisfactory meta-analysis. The relative benefit (of achieving at least 50% pain relief) of paracetamol/caffeine vs paracetamol alone was 1.12 (95% Confidence Interval 1.05-1.19) across a number of acute pain states (dysmenorrhoea, headache, post-partum pain, and dental pain). Review of the effects of the combination of paracetamol and caffeine on the liver revealed no compelling data to suggest a clinically meaningful increase in hepatotoxicity with use of paracetamol/caffeine combinations.

CONCLUSIONS

Paracetamol/caffeine (1,000 mg/130 mg) is effective and safe for use in acute management of pain. The hepatotoxicity of overdoses of paracetamol results from its oxidative metabolism, caffeine does not produce any increase in oxidative metabolism of therapeutic concentrations of paracetamol.

Chronic headaches and medication overuse

Chronic headaches represent a significant burden for the affected individuals and for the society, and a major challenge for successful care. Among the various types of chronic headaches, those that are associated with medication overuse (medication-overuse headache, MOH) are of particular importance because of the large proportion of patients who complain of this condition and their poor outcome. Most patients with MOH had migraine as primary headache. Practically, almost all drugs used for the symptomatic relief of migraine, including triptans and analgesics can cause MOH. Although the pathophysiology of MOH is unknown, recent studies hypothesize that plastic changes in specific pain areas of the central nervous system are main contributors to establishing MOH. Not infrequently, drug overuse is associated with habituation and failure of previously effective medications. Finally, treatment of MOH is poorly evidence based and mostly relies on clinical experience and belief.

Chronic kidney disease and cancer: a troubling connection

Chronic kidney disease (CKD) and cancer are connected in a number of ways in both directions: cancer can cause CKD either directly or indirectly through the adverse effects of therapies; CKD may, conversely, be a risk factor for cancer; and both may be associated because they share common risk factors, often toxins. In this review, we briefly address the issue of paraneoplastic nephropathies as well as that of toxin-related cancers and CKD, including analgesic and aristolochic acid nephropathies. We then focus on the links between the various stages of CKD and cancer incidence, and critically examine major epidemiologic surveys in the field. Compared with the general population, kidney transplant recipients have a threefold to fourfold increase in overall cancer risk, and relative risks higher than 3 for about 20 specific tumors, most, but not all, of which are known or suspected to be caused by viral agents. After dialysis, cancer risk increases 10% to 80% according to studies, with relative risks significantly higher than in the general population, for about 10 cancer sites. There is emerging evidence for an excess risk of cancer in patients in early CKD stages.

Non-phenacetin analgesics and analgesic nephropathy: clinical assessment of high users from a case-control study

BACKGROUND

A recent large-scale case-control study on analgesic nephropathy (SAN) [1] found no increased risk of end-stage renal disease (ESRD) in users of combined or single formulations of phenacetin-free analgesics. In a subgroup of 22 high users, however, a dose-dependent increased risk was found, which raised the question if these patients presented or not with analgesic nephropathy (AN).

METHODS

The individual questionnaires of this subgroup of high users were reviewed, and the total lifetime intake of different types of analgesics was calculated. For evidence of AN, the following data were considered: (1) the amount and type of analgesics consumed, (2) the cause of ESRD, as diagnosed by the nephrologist in charge of the patient and (3) renal imaging and other relevant laboratory data.

RESULTS

This group of ESRD patients consumed on average 7.8 kg of antipyretic analgesics (range 30.8-2.7 kg) over an average of 21.5 years (range 35-6 years). Single analgesics were exclusively used by 12 patients (54.5%) and combined analgesics by 5 patients (22.7%), while 5 patients used both. None of the patients was diagnosed as having AN, and a review of the questionnaires did not disclose evidence suggestive of AN. The possibility that, irrespective of AN, the analgesic (ab)use contributed to the progression of existing renal diseases cannot be answered in the absence of well-defined criteria. The data supporting the existence of such an analgesic-associated nephropathy (AAN) are, however, not consistent and most likely due to confounding by indication.

CONCLUSION

In a group of ESRD patients with high use of non-phenacetin analgesics, no evidence of AN was found. There is no evidence that (ab)use of analgesics or NSAIDs other than phenacetin leads to a pathologically or clinically defined renal disease that could be named AN or AAN.

Analgesic nephropathy and renal replacement therapy in Australia: trends, comorbidities and outcomes

BACKGROUND AND OBJECTIVES

This study examined age-specific incidence and prevalence of renal replacement therapy attributed to analgesic nephropathy from 1971 through 2005 and adjusted comorbidity prevalence and survival of patients who had analgesic nephropathy and were on renal replacement therapy (compared with control subjects without diabetes).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective cohort study, using data from the Australia and New Zealand Dialysis and Transplant registry, included all patients who were aged 35 to 84 yr and started long-term renal replacement therapy in Australia from 1971 through 2006.

RESULTS

Of 31,654 incident renal replacement therapy patients, 10.2% had analgesic nephropathy. Incidence and prevalence of renal replacement therapy attributed to analgesic nephropathy decreased earlier and faster among younger (age <55 yr) patients. Prevalence of analgesic nephropathy among 75- to 84-yr-old renal replacement therapy patients is still increasing. Compared with control subjects without diabetes, comorbidities (coronary artery, cerebrovascular, peripheral vascular, and chronic lung diseases) were more prevalent among patients with analgesic nephropathy at renal replacement therapy start. All-cause, cardiovascular, infection, and cancer mortality were higher among patients who had analgesic nephropathy and were on renal replacement therapy. For both comorbidities and mortality, the associations were stronger in younger patients.

CONCLUSIONS

Trends in renal replacement therapy attributed to analgesic nephropathy differed by age. Patients with analgesic nephropathy have more comorbidities and poorer survival on renal replacement therapy, especially among younger patients.

Analgesics use and ESRD in younger age: a case-control study

BACKGROUND

An ad hoc peer-review committee was jointly appointed by Drug Authorities and Industry in Germany, Austria and Switzerland in 1999/2000 to review the evidence for a causal relation between phenacetin-free analgesics and nephropathy. The committee found the evidence as inconclusive and requested a new case-control study of adequate design.

METHODS

We performed a population-based case-control study with incident cases of end-stage renal disease (ESRD) under the age of 50 years and four age and sex-matched neighborhood controls in 170 dialysis centers (153 in Germany, and 17 in Austria) from January 1, 2001 to December 31, 2004. Data on lifetime medical history, risk factors, treatment, job exposure and intake of analgesics were obtained in a standardized face-to-face interview using memory aids to enhance accuracy. Study design, study performance, analysis plan, and study report were approved by an independent international advisory committee and by the Drug Authorities involved. Unconditional logistic regression analyses were performed.

RESULTS

The analysis included 907 cases and 3,622 controls who had never used phenacetin-containing analgesics in their lifetime. The use of high cumulative lifetime dose (3rd tertile) of analgesics in the period up to five years before dialysis was not associated with later ESRD. Adjusted odds ratios with 95% confidence intervals were 0.8 (0.7 - 1.0) and 1.0 (0.8 - 1.3) for ever- compared with no or low use and high use compared with low use, respectively. The same results were found for all analgesics and for mono-, and combination preparations with and without caffeine. No increased risk was shown in analyses stratifying for dose and duration. Dose-response analyses showed that analgesic use was not associated with an increased risk for ESRD up to 3.5 kg cumulative lifetime dose (98 % of the cases with ESRD). While the large subgroup of users with a lifetime dose up to 0.5 kg (278 cases and 1365 controls) showed a significantly decreased risk, a tiny subgroup of extreme users with over 3.5 kg lifetime use (19 cases and 11 controls) showed a significant risk increase. The detailed evaluation of 22 cases and 19 controls with over 2.5 kg lifetime use recommended by the regulatory advisors showed an impressive excess of other conditions than analgesics triggering the evolution of ESRD in cases compared with controls.

CONCLUSION

We found no clinically meaningful evidence for an increased risk of ESRD associated with use of phenacetin-free analgesics in single or combined formulation. The apparent risk increase shown in a small subgroup with extreme lifetime dose of analgesics is most likely an indirect, non-causal association. This hypothesis, however, cannot be confirmed or refuted within our case-control study. Overall, our results lend support to the mounting evidence that phenacetin-free analgesics do not induce ESRD and that the notion of "analgesic nephropathy" needs to be re-evaluated.

Case-control study on analgesics and nephropathy (SAN): protocol

Background

The association between intake of non-phenacetin-containing analgesics and the occurrence of chronic renal failure is still controversially discussed. A new epidemiologic study was planned and conducted in Germany and Austria.

Methods/design

The objective of the international, multicenter case-control study was to evaluate the association between end-stage renal disease (ESRD) and use of non-phenacetin-containing analgesics with particular emphasis on combined formulations. A targeted sample of 1000 new (incident) dialysis patients, aged less than 50 years, was planned to recruit between January 1, 2001 and December 31, 2004. The age limit was chosen to avoid contamination of the study population with phenacetin-containing analgesics to the extent possible. Four control subjects per ESRD case, matched by age, sex, and region were selected from the population living in the region the case came from.

Lifetime exposure to analgesics and potential renal risk factors were recorded in a single face-to-face interview. A set of aids was introduced to reinforce the memory of study participants.

A standardized, pre-tested interview questionnaire (participants), a medical documentation sheet (physicians in dialysis centres), a logbook for all activities (dialysis centres) were used to collect the necessary data.

Quality management consisted of the standardized procedures, (re-) training and supervision of interviewers, regular checks of all incoming data for completeness and plausibility.

The study is scientifically independent and governed by a international Scientific Advisory Committee that bridged the gap between the sponsoring companies and the investigators. Also other advisory groups assisted the managing committee of the study. All relevant German and Austrian nephrological associations supported the study, and the study design was carefully reviewed and approved by the Kidney Foundation of Germany.

Discussion

The study is expected to answer the main research question by end 2005. There is however a high potential for various biases that we tried to address with adequate measure. One limitation however cannot be overcome: The methodologically needed age-limitation of the study will make it not easy to generalize the results to age groups over 50 years. It might be suggested to repeat the study for persons over 50 years in 10 years when contamination with phenacetin use early in life is likely to be outgrown.

Analgesic nephropathy in Hungary: the HANS study

BACKGROUND

The diagnosis of analgesic nephropathy has improved significantly with modern imaging techniques. We reviewed a large portion of the Hungarian dialysis population to obtain additional insight into the problem.

METHODS

Twenty-two participating dialysis units enrolled 1400 patients on renal replacement therapy between 1 January 1995 and 1 January 1998. Patients with no known aetiology (n = 284) were interviewed and studied with renal imaging. We assessed the presence of decreased renal mass combined with either bumpy contours, papillary calcification, or both. The subjects studied were interrogated extensively.

RESULTS

Our survey suggested analgesic nephropathy in 47 of 1400 patients (3.3%), 3-fold higher than the EDTA database estimate for Hungary. The analgesics most commonly abused were phenacetin-containing mixtures. The driving symptoms were mainly headache and joint pain. Cardiovascular complications were more common than in the rest of the dialysis population, independent of smoking and lipid values (P<0.01).

CONCLUSIONS

Phenacetin should be banned. Our study results support the need for longitudinal cohort and case-control studies in Hungary.

Caffeine as a promoter of analgesic-associated nephropathy--where is the evidence?

Individual groups of nephrologists - in their responsibility for their patients - initiated a most controversial discussion whether or not caffeine - coformulated to analgesics - might initiate or sustain analgesic overdosing. The original sources (data) of such suspicion have got lost during the debate of the last two decades. Therefore, it seemed to be appropriate to investigate the original data background and the reasons why nephrologists started to suspect caffeine as a stimulant of analgesic overdosing by employing a systematic and exhaustive review of primary nephrological publications. Their selection followed a precise selection plan, including all epidemiological studies on analgesic-associated nephropathy, the original papers of all groups having been involved in those studies, further originals from the mainly involved countries (academically, politically), and any literature thereof cited as a proof. The following results emerged from the investigation: (i) The epidemiological studies warranted no conclusion about a role of caffeine in prompting excessive analgesic use. (ii) The identified groups of nephrologists provided not substantial data to advocate the said suspicion, except for the observation of a preferential choice of phenacetin-containing combinations, especially powder preparations. (iii) Only two cited original data sources revealed drug-seeking behaviour with phenacetin-containing preparations which subsided, after phenacetin was banned from the respective markets. Conclusively, it appears that there is no substantial data to support a pivotal role of caffeine in initiating or sustaining analgesic overdosing. However, there is strong data that phenacetin, by its psychotropic properties, may have caused drug-seeking behaviour and thus led to analgesic overdosing. This conclusion is convincingly supported by thorough pharmacokinetic investigations. Note: All caffeine-related statements within the reviewed literature have been collected in tables (referred to as Table SX) which are provided in full text for check on the following website: http://www.blackwellpublishing.com/products/journals/suppmat/FCP/FCP174/FCP174sm.htm

Confounding by indication in epidemiologic studies of commonly used analgesics

Confounding by indication is a bias frequently encountered in observational epidemiologic studies of drug effects. Because the allocation of treatment in observational studies is not randomized and the indication for treatment may be related to the risk of future health outcomes, the resulting imbalance in the underlying risk profile between treated and comparison groups can generate biased results. Confounding by indication is often present in studies of drugs that are not widely prescribed, because the indications for their use are narrow and not likely to be present in comparison groups; however, this bias is also observed in the study of widely used over-the-counter and prescription drugs, are exemplified by studies of analgesics. In this article we review examples from the published literature to demonstrate how confounding by indication can affect the findings of pharmacoepidemiologic studies relating analgesic use to various health outcomes.

Recent developments in toxic nephropathy

Toxic nephropathy is an important cause of reversible renal injury if detected early. Renal damage can be due to several different mechanisms affecting different segments of the nephron, renal microvasculature or interstitium. Clinical signs may not be apparent in the early stages and assessment of renal function should include thorough evaluation of glomerular filtration rate, proximal and distal tubular function. A kidney biopsy may be indicated to establish the cause and effect relationship. The presence of comorbid conditions such as older age, diabetes mellitus, hypertension and congestive heart failure have a significant influence on the patient's ability to recover from the toxic effects. A significant degree of drug-induced renal toxicity is only acceptable if the causative agent is used for the curative treatment of an underlying disease but not if the aim is the palliative or supportive therapy. The decision to reduce the dose or to stop the toxic agent must be based on the ultimate goal of therapy and the patient's baseline health status.

Acetaminophen, aspirin, and chronic renal failure

BACKGROUND

Several epidemiologic studies have demonstrated an association between heavy consumption of nonnarcotic analgesics and the occurrence of chronic renal failure, but it is unclear which is the cause and which is the effect

METHODS

In a nationwide, population-based, case-control study of early-stage chronic renal failure in Sweden, face-to-face interviews were conducted with 926 patients with newly diagnosed renal failure and 998 control subjects, of whom 918 and 980, respectively, had complete data. We used logistic-regression models to estimate the relative risks of disease-specific types of chronic renal failure associated with the use of various analgesics

RESULTS

Aspirin and acetaminophen were used regularly by 37 percent and 25 percent, respectively, of the patients with renal failure and by 19 percent and 12 percent, respectively, of the controls. Regular use of either drug in the absence of the other was associated with an increase by a factor of 2.5 in the risk of chronic renal failure from any cause. The relative risks rose with increasing cumulative lifetime doses, rose more consistently with acetaminophen use than with aspirin use, and were increased for most disease-specific types of chronic renal failure. When we disregarded the recent use of analgesics, which could have occurred in response to antecedents of renal disease, the associations were only slightly attenuated

CONCLUSIONS

Our results are consistent with the existence of exacerbating effects of acetaminophen and aspirin on chronic renal failure. However, we cannot rule out the possibility of bias due to the triggering of analgesic consumption by predisposing conditions.

Direct toxicity of nonsteroidal antiinflammatory drugs for renal medullary cells

Antipyretic analgesics, taken in large doses over a prolonged period, cause a specific form of kidney disease, characterized by papillary necrosis and interstitial scarring. Epidemiological evidence incriminated mixtures of drugs including aspirin (ASA), phenacetin, and caffeine. The mechanism of toxicity is unclear. We tested the effects of ASA, acetaminophen (APAF, the active metabolite of phenacetin), caffeine, and other related drugs individually and in combination on mouse inner medullary collecting duct cells (mIMCD3). The number of rapidly proliferating cells was reduced by approximately 50% by 0.5 mM ASA, salicylic acid, or APAF. The drugs had less effect on confluent cells, which proliferate slowly. Thus, the slow in vivo turnover of IMCD cells could explain why clinical toxicity requires very high doses of these drugs over a very long period. Caffeine greatly potentiated the effect of acetaminophen, pointing to a potential danger of the mixture. Cyclooxygenase (COX) inhibitors, indomethacin and NS-398, did not reduce cell number except at concentrations greatly in excess of those that inhibit COX. Therefore, COX inhibition alone is not toxic. APAF arrests most cells in late G(1) and S and produces a mixed form of cell death with both oncosis (swollen cells and nuclei) and apoptosis. APAF is known to inhibit the synthesis of DNA and cause chromosomal aberrations due to inhibition of ribonucleotide reductase. Such effects of APAF might account for renal medullary cell death in vivo and development of uroepithelial tumors from surviving cells that have chromosomal aberrations.