Guaifenesin
Guaifenesin
Generic Name
Guaifenesin
Brand Names
Mucinex®, Robitussin® Expectorant, Tussin® Expectorant) is a widely used expectorant that facilitates clearance of mucus from the respiratory tract.
Mechanism
- Osmotic mucolytic: Increases the water content of sputum, reducing viscosity and allowing easier expectoration.
- Surfactant activity: Stimulates secretion of lung surfactant, further loosening mucus.
- Cough‑relief synergy: Works best when combined with cough suppressants or decongestants, but does not suppress the cough reflex itself.
> *Key point*: Guaifenesin does not act as a bronchodilator; it merely makes mucus less tenacious so that the body can cough it up.
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Pharmacokinetics
| Parameter | Details |
| Absorption | Rapid oral absorption; peak plasma concentration 0.5–1 hr after dosing. |
| Bioavailability | ~24–31 % (poorly absorbed but therapeutic effect achieved at lower doses). |
| Distribution | Widely distributed; negligible protein binding (<4 %). |
| Metabolism | Minimal hepatic metabolism; primarily unchanged. |
| Elimination | Renal clearance dominates; mean plasma half‑life ≈ 4–5 h. |
| Special Populations | No dose adjustment needed in mild–moderate renal impairment; caution in severe CKD. |
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Indications
- Productive cough associated with *acute bronchitis*, *chronic bronchitis*, *COPD*, or *post‑viral* respiratory infections.
- Excess mucus production in upper respiratory tract infections (e.g., sinusitis, pharyngitis) where clearance is desired.
- Adjunct therapy in cough‑disease management regimens (often combined with decongestants or antihistamines).
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Contraindications
- Hypersensitivity to guaifenesin or any excipient.
- Children <4 months: Not recommended.
- Avoid in patients with contraindicated comedications that may cause edema or hypotension (e.g., potassium‑sparing diuretics, NSAIDs).
- Pregnancy & Lactation: Category C; use only if benefit outweighs risk.
- Renal Impairment: Use with caution; monitor for accumulation.
- Alcohol: No significant interaction, but GC‑affecting medications should be used cautiously.
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Dosing
| Population | Dose | Frequency | Notes |
| Adults & Adolescents (≥12 yrs) | 200–400 mg PO q6 h OR 600 mg PO q12 h | Flex dosing; adjust to 1–2 g per day | Prefer split dosing; may increase with dehydration risk. |
| Children (6–11 yrs) | 5 mg/kg PO q8 h (max 400 mg) | Frequency based on weight | Verify weight‑specific kits. |
| Children (2–5 yrs) | 4 mg/kg PO q12 h (max 400 mg) | Frequency based on weight | Pediatric syrups recommended. |
| Infants <2 yrs | Not recommended | — | Safety data lacking. |
Administration Tips:
• Keep patient well‑hydrated; suggests water or soft drinks.
• Take 30 min before meals for optimal absorption.
• For nocturnal cough, a single bedtime dose (200‑400 mg) may suffice.
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Adverse Effects
| Category | Examples | Incidence | Remarks |
| GI | Nausea, abdominal discomfort | ≤10 % | Increased with high doses; ensure hydration. |
| Central | Dizziness, headache | ≤5 % | Rare; usually mild. |
| Dermatologic | Rash, pruritus | ≤3 % | Can indicate hypersensitivity – discontinue. |
| Respiratory | Coryza, mild wheeze | ≤2 % | Not a typical effect; monitor in asthmatics. |
| Serious | Anaphylaxis, angioedema, severe edema | <0.1 % | Immediate cessation and emergency care. |
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Monitoring
- Renal function: Check BUN/creatinine in patients with CKD or on diuretics.
- Hydration status: Patients with excess fluid loss (fever, vomiting) should be encouraged to remain well‑hydrated.
- Symptom progression: Short‑term, expect increased sputum production; lack of improvement may signal alternative pathology.
- Allergic reactions: Watch for rash or respiratory distress particularly within 24 h of starting therapy.
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Clinical Pearls
1. Synergy with decongestants – Pairing guaifenesin with pseudoephedrine or phenylephrine yields better mucus clearance than either alone.
2. Avoid routine use in dry cough – It offers minimal benefit for non‑productive coughs; consider a suppressant instead.
3. Dose titration can reduce GI upset – Start at 200 mg q6 h; if tolerated, increase to 400 mg, but avoid doses >4 g/day to limit nausea.
4. Empirical evidence is limited – Randomized trials show modest benefit; patient education about realistic outcomes is key.
5. Use caution in asthma – Though it does not worsen bronchospasm, the viscous sputum reduction may worsen hyperinflation in severe, uncontrolled asthma; monitor closely.
6. Children ≤4 yrs – Expectorant use is largely unsupported; symptomatic relief via steam or saline nebulization is preferred.
7. Drug interaction alert – Guaifenesin may increase the serum concentration of newer antacids (e.g., calcium carbonate) by altering gastric pH; switch to non‑acidic formulations if needed.
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• *This drug card is for educational purposes and reflects current pharmacological knowledge as of 2026. Always consult up‑to‑date prescribing information before clinical use.*