Analgesics and asthma

Adverse drug reactions and drug-drug interactions with over-the-counter NSAIDs

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen have a long history of safe and effective use as both prescription and over-the-counter (OTC) analgesics/antipyretics. The mechanism of action of all NSAIDs is through reversible inhibition of cyclooxygenase enzymes. Adverse drug reactions (ADRs) including gastrointestinal bleeding as well as cardiovascular and renal effects have been reported with NSAID use. In many cases, ADRs may occur because of drug-drug interactions (DDIs) between the NSAID and a concomitant medication. For example, DDIs have been reported when NSAIDs are coadministered with aspirin, alcohol, some antihypertensives, antidepressants, and other commonly used medications. Because of the pharmacologic nature of these interactions, there is a continuum of risk in that the potential for an ADR is dependent on total drug exposure. Therefore, consideration of dose and duration of NSAID use, as well as the type or class of comedication administered, is important when assessing potential risk for ADRs. Safety findings from clinical studies evaluating prescription-strength NSAIDs may not be directly applicable to OTC dosing. Health care providers can be instrumental in educating patients that using OTC NSAIDs at the lowest effective dose for the shortest required duration is vital to balancing efficacy and safety. This review discusses some of the most clinically relevant DDIs reported with NSAIDs based on major sites of ADRs and classes of medication, with a focus on OTC ibuprofen, for which the most data are available.

The modern pharmacology of paracetamol: therapeutic actions, mechanism of action, metabolism, toxicity and recent pharmacological findings

Paracetamol is used worldwide for its analgesic and antipyretic actions. It has a spectrum of action similar to that of NSAIDs and resembles particularly the COX-2 selective inhibitors. Paracetamol is, on average, a weaker analgesic than NSAIDs or COX-2 selective inhibitors but is often preferred because of its better tolerance. Despite the similarities to NSAIDs, the mode of action of paracetamol has been uncertain, but it is now generally accepted that it inhibits COX-1 and COX-2 through metabolism by the peroxidase function of these isoenzymes. This results in inhibition of phenoxyl radical formation from a critical tyrosine residue essential for the cyclooxygenase activity of COX-1 and COX-2 and prostaglandin (PG) synthesis. Paracetamol shows selectivity for inhibition of the synthesis of PGs and related factors when low levels of arachidonic acid and peroxides are available but conversely, it has little activity at substantial levels of arachidonic acid and peroxides. The result is that paracetamol does not suppress the severe inflammation of rheumatoid arthritis and acute gout but does inhibit the lesser inflammation resulting from extraction of teeth and is also active in a variety of inflammatory tests in experimental animals. Paracetamol often appears to have COX-2 selectivity. The apparent COX-2 selectivity of action of paracetamol is shown by its poor anti-platelet activity and good gastrointestinal tolerance. Unlike both non-selective NSAIDs and selective COX-2 inhibitors, paracetamol inhibits other peroxidase enzymes including myeloperoxidase. Inhibition of myeloperoxidase involves paracetamol oxidation and concomitant decreased formation of halogenating oxidants (e.g. hypochlorous acid, hypobromous acid) that may be associated with multiple inflammatory pathologies including atherosclerosis and rheumatic diseases. Paracetamol may, therefore, slow the development of these diseases. Paracetamol, NSAIDs and selective COX-2 inhibitors all have central and peripheral effects. As is the case with the NSAIDs, including the selective COX-2 inhibitors, the analgesic effects of paracetamol are reduced by inhibitors of many endogenous neurotransmitter systems including serotonergic, opioid and cannabinoid systems. There is considerable debate about the hepatotoxicity of therapeutic doses of paracetamol. Much of the toxicity may result from overuse of combinations of paracetamol with opioids which are widely used, particularly in USA.

Safety of etoricoxib, a specific cyclooxygenase-2 inhibitor, in asthmatic patients with aspirin-exacerbated respiratory disease

BACKGROUND

Treatment of rheumatic conditions is limited in patients with asthma owing to concerns of nonsteroidal anti-inflammatory drugs potentially provoking asthma. Cross-sensitivity to all anti-inflammatory drugs that inhibit cyclooxygenase enzymes occurs in these individuals.

OBJECTIVES

To study the safety of etoricoxib, a specific cyclooxygenase-2 inhibitor, and to determine whether it cross-reacts with asthma in patients with aspirin-exacerbated respiratory disease (AERD).

METHODS

This study included 77 patients who had experienced asthma induced by aspirin and at least 1 other nonsteroidal anti-inflammatory drug. Baseline evaluation included blood pressure measurement, nasal examination, spirometry, and peak expiratory flow rate measurement. Patients were given placebo the first day and then were challenged with once-daily etoricoxib in 3 different doses: 60 mg on day 2, 90 mg on day 3, and 120 mg on day 4. If no evidence of intolerance was seen, each patient was rechallenged with 60 or 90 mg of etoricoxib once daily (according to the rheumatic condition) 7 days later. Reassessment of the baseline measurements was performed daily from day 1 to day 4 after the initial challenge, on day 7 after rechallenge, and after 1 month of drug intake. If the patient developed any mucosal or skin reaction, hypotension, upper or lower airway obstruction, conjunctival reaction, or laryngeal edema during the challenge test, it was considered a positive response.

RESULTS

Etoricoxib was well tolerated, without any signs of immediate or delayed hypersensitivity in aspirin- and nonsteroidal anti-inflammatory drug-induced asthmatic patients. None of 77 study patients experienced any symptoms or developed dyspnea, change in nasal examination, significant variation in peak expiratory flow rate greater than 20%, or decline in forced expiratory volume in 1 second greater than 15% during etoricoxib challenge. The exact 1-sided confidence interval for the probability of etoricoxib inducing cross-reactions in patients with AERD was 0% to 2%.

CONCLUSIONS

These results confirm the lack of cross-reactivity between specific cyclooxygenase-2 inhibitors and aspirin in AERD. Etoricoxib was safe for treating inflammation in patients with AERD.

Aspirin-induced asthma: clinical aspects, pathogenesis and management

Aspirin (acetylsalicylic acid)-induced asthma (AIA) consists of the clinical triad of asthma, chronic rhinosinusitis with nasal polyps, and precipitation of asthma and rhinitis attacks in response to aspirin and other NSAIDs. The prevalence of the syndrome in the adult asthmatic populations is approximately 4-10%. Respiratory disease in these patients may be aggressive and refractory to treatment. The aetiology of AIA is complex and not fully understood, but most evidence points towards an abnormality of arachidonic acid (AA) metabolism. Cyclo-oxygenase (COX), the rate-limiting enzyme in AA metabolism, exists as two main isoforms. COX-1 is the constitutive enzyme responsible for synthesis of protective prostanoids, whereas COX-2 is induced under inflammatory conditions. A number of theories regarding its pathogenesis have been proposed. The shunting hypothesis proposes that inhibition of COX-1 shunts AA metabolism away from production of protective prostanoids and towards cysteinyl leukotriene (cys-LT) biosynthesis, resulting in bronchoconstriction and increased mucus production. The COX-2 hypothesis proposes that aspirin causes a structural change in COX-2 that results in the generation of products of the lipoxygenase pathway. It is speculated that this may result in the formation of mediators that cause respiratory reactions in AIA. Related studies provide evidence for abnormal regulation of the lipoxygenase pathway, demonstrating elevated levels of cys-LTs in urine, sputum and peripheral blood, before and following aspirin challenge in AIA patients. These studies suggest that cys-LTs are continually and aggressively synthesised before exposure to aspirin and, during aspirin-induced reactions, acceleration of synthesis occurs. A genetic polymorphism of the LTC4S gene has been identified consisting of an A to C transversion 444 nucleotides upstream of the first codon, conferring a relative risk of AIA of 3.89. Furthermore, carriers of the C444 allele demonstrate a dramatic rise in urinary LTE(4) following aspirin provocation, and respond better to the cys-LT antagonist pranlukast than A444 homozygotes.AIA patients have an aggressive form of disease, and treatment should include combination therapy with inhaled corticosteroids, beta(2)-adrenoceptor agonists and LT modifiers. Furthermore, recently developed inhibitors of COX-2 may be safer in patients with AIA.

Safety of COX-2 inhibitors in asthma patients with aspirin hypersensitivity

OBJECTIVE

To review the safety of cyclooxygenase-2 (COX-2) inhibitors in asthma patients with aspirin hypersensitivity.

DATA SOURCES

Clinical studies were identified using MEDLINE (1966-September 2002). Key search terms included cyclooxygenase inhibitors, aspirin, asthma, and hypersensitivity. English-language articles were identified and included. References from the identified articles were also reviewed.

DATA SYNTHESIS

The literature provides information regarding the safety of COX-2 inhibitors in asthma patients with aspirin-exacerbated respiratory disease (AERD). The mechanism of AERD involves inhibition of cyclooxygenase, particularly COX-1. Inhibition of COX-1 causes an increased production of certain inflammatory mediators, which results in the reactions seen with AERD. Considering this mechanism, COX-2 inhibitors may be an alternative to aspirin or nonsteroidal antiinflammatory drugs (NSAIDs) in a patient with AERD. This article analyzes 4 studies to evaluate the safety of COX-2 inhibitors in this population.

RESULTS

The 4 studies evaluated included a total of 172 patients with AERD. All patients included demonstrated intolerance to aspirin or NSAIDs and tolerated the selective COX-2 inhibitor administered.

CONCLUSIONS

COX-2 inhibitors provide a potentially safe alternative for treatment of inflammatory conditions in patients with AERD.

Paracetamol and asthma

Paracetamol (acetaminophen) is one of the over-the-counter analgesics that is used frequently for the self-management of some of the common disorders. There seems to be two types of relations between paracetamol and asthma - paracetamol intolerance leading to bronchospasm in analgesic-induced asthmatics; and the relation between asthma and the amount and frequency of consumption of paracetamol. Paracetamol is generally recommended as one of the safer analgesics in both analgesic tolerant and intolerant asthmatics, without the fear of severe bronchospasm that aspirin and other non-steroidal anti-inflammatory drugs can induce in these patients. However, Paracetamol is reported to cross-react with aspirin at a rate of approximately 20-30% in a dose-dependent way. Therefore, it should not be recommended to analgesic intolerant asthmatics, without performing oral provocation tests to prove its safety. The possible association between the amount and frequency of paracetamol consumption and the prevalence and degree of asthma as suggested by some of the recent surveys, needs to be investigated further.