Acute respiratory infections are highly prevalent in the population, with the common cold, flu-like syndromes, tracheobronchitis, sinusitis, laryngitis and pneumonias being particularly important. When the aetiology is presumably bacterial, treatment is based on the use of antibiotics and medication for symptomatic relief. However, the most common clinical entities, the common cold and the flu-like syndrome, have a viral aetiology, for which symptomatic treatment remains, in most cases, the standard recommendation.
The common cold is the most frequently encountered disease in medical practice . It affects most adults, on average two to four times a year, and accounts for up to 40% of work absences among the economically active population in the United States .
This syndrome affects the upper airways, sometimes in association with low-grade fever and systemic symptoms, and usually presents with at least two of the following symptoms: cough, dysphonia, throat discomfort, sore throat, nasal congestion, rhinorrhoea, sneezing, headaches, myalgia and fever . Symptoms usually peak at 2 to 3 days and have a mean duration of 7 to 10 days . This definition has been prospectively validated in other studies and is that most frequently used in clinical studies of patients with the common cold . Although most cases are caused by the rhinovirus, other agents may be involved, such as the respiratory syncytial virus, adenovirus, coronavirus, and influenza and parainfluenza viruses .
Flu-like syndrome is characterized by sudden onset of fever, headache, cough, sore throat, myalgia, nasal congestion, weakness and loss of appetite . Complications, such as pneumonia, otitis and sinusitis, may occur .
Some of the medications studied for the treatment of the common cold are antihistamines, anticholinergics, alpha-adrenergic agonists, membrane stabilizers, nonsteroidal anti-inflammatory drugs, vitamin C, glucocorticoids, zinc, herbal medications and alpha-interferon. Clinical trials of high-dose vitamin C have not found any benefits in the treatment of the common cold . Recent studies of Echinacea purpurea, a herbal medicine, did not find any clinical benefits for patients with the common cold [9–12]. The results of meta-analyses about the efficacy of zinc are contradictory, and there is weak evidence of its benefit in well-designed studies [13–15].
The symptomatic treatment of the common cold has been evaluated in Cochrane meta-analyses. The first included 32 studies with a total of 8930 patients and investigated the administration of antihistamines in the common cold. Results showed that monotherapy did not improve symptoms in either children or adults . The combined use of antihistamines and decongestants may alleviate symptoms in adults, but results are heterogeneous [15, 17]. Another meta-analysis investigated the use of nasal decongestants in the common cold in 286 adults, and found no benefit for the relief of nasal congestion [15, 18]. Another recent meta-analysis  suggests that a triple combination of antihistamine, decongestant and analgesic provided some general benefit in adults and older children.
Most cases of influenza require the use of drugs for symptomatic relief [1, 20]. In clinical practice, treatment directed to the aetiological agent is not routine, but became considerably more frequent after the H1N1 pandemic in 2009 .
Therefore, patients continue to use medications that produce symptomatic relief because of the epidemiological relevance and the intensity of symptoms of flu-like syndromes and the common cold.
This study evaluated the efficacy and safety of a fixed-dose combination of paracetamol, chlorphenamine and phenylephrine in the symptomatic treatment of the common cold and flu-like syndromes by analysing symptom score reductions during and after treatment, duration of symptoms, return to usual activities and adverse events in both groups.
No other randomized clinical trial (RCT) evaluated the safety and efficacy of this specific fixed-dose combination for the common cold in adults. This was the first RCT conducted in Brazil designed to also assess adverse cardiovascular effects of phenylephrine.