Table 4 Clinical efficacy studies: Chronic bronchitis and chronic respiratory conditions

Hayes (1956)

To determine the effectiveness of Robitussin® as an expectorant in productive cough due to chronic pulmonary disease

1–2 g Robitussin® (containing 100 mg guaifenesin and 1 mg desoxyephedrine HCl per 5 mL) vs placebo every 2–3 h, as required

Statistically significant changes compared to placebo:

• Reduction in chronic productive cough

• Decreased frequency of cough and sputum viscosity

Chodosh (1964)

To investigate the efficacy and mechanism of action of guaifenesin in bronchopulmonary diseases

Double-blind study:

100 mg guaifenesin tablet 4× daily vs placebo for 14 days (after placebo run-in)

Statistically significant changes compared to placebo:

• Increase in ease of expectoration

• Decrease in the measured sputum surface tension

Hirsch (1973)

To investigate the expectorant effect of guaifenesin in patients with chronic bronchitis

Single-blind crossover study:

800 mg or 1600 mg guaifenesin vs placebo alternating for 5 weeks

Double-blind crossover study:

1600 mg guaifenesin vs placebo daily for 5 days

No significant difference between guaifenesin and placebo in reducing sputum consistency, increasing sputum volume, improving ventilatory function or ease of expectoration

Wojcicki (1975)

To investigate the effect of guaifenesin on:

(i) Severity and frequency of cough, and

(ii) Tenaciousness of sputum

Double-blind crossover study:

120 mg guaifenesin vs 17 mg narcotine HCl, vs combination (120 mg guaifenesin +17 mg narcotine HCl), vs placebo, 3× daily for 7 days (per treatment)

Guaifenesin + narcotine HCl combination associated with statistically significant decreases in:

• Cough severity

• Cough frequency

Finiguerra (1982) (unpublished; data on file)

To determine the efficacy of guaifenesin for:

(i) Modifying the volume and viscosity of tracheobronchial secretions, and in

(ii) Providing symptomatic relief of difficult expectoration and cough in chronic bronchitis

Randomized double-blind parallel-group study:

190 mg guaifenesin vs placebo, 3× daily for 15 days

Statistically significant changes:

• Decrease in sputum volume and viscosity

• Decrease in cough severity

• Improvement in ease of expectoration

Parvez (1996)

To determine the usefulness of a multidimensional cough quantitation system for evaluating guaifenesin’s effects on cough and sputum

Randomized double-blind parallel-group study:

300 mg guaifenesin vs placebo, 4× daily for 14 days

Differences between guaifenesin and placebo groups:

• Guaifenesin significantly increased sputum volume; 37% difference on day 14 (p < 0.05)

• Significant reduction in fucose, a biomarker for sputum glycoprotein, in the guaifenesin group at day 14 (p < 0.01)

• Subjective measure of average intensity/cough at day 4 (p < 0.05)

• Trend for greater improvement in ease of expectoration at days 10 and 14 in the guaifenesin group but did not reach significance in the subgroup with productive cough (p < 0.01)