Understanding Chloramphenicol and Its Primary Use
Chloramphenicol is a potent, broad-spectrum antibiotic that functions by inhibiting bacterial protein synthesis [1.7.6]. It is primarily bacteriostatic, meaning it stops bacteria from multiplying [1.3.2]. In its ophthalmic form (eye drops or ointment), it is prescribed for serious surface-level bacterial infections of the eye, such as bacterial conjunctivitis, when other, less potentially hazardous antibiotics are ineffective or contraindicated [1.3.2]. It is effective against a range of common bacterial eye pathogens, including Staphylococcus aureus and Streptococcus pneumoniae [1.3.2].
The Path from Eye to Gut: Systemic Absorption
Ordinarily, a medicine applied to the eye is expected to act locally. However, medications can be absorbed into the bloodstream and have effects elsewhere in the body—a process known as systemic absorption [1.3.6]. The eye is connected to the nasal cavity via the nasolacrimal duct (tear duct). Excess eye drops can drain through this duct into the back of the throat, where they are swallowed. Once in the gastrointestinal tract, the drug can be absorbed into the bloodstream, similar to an oral medication, albeit at a much lower concentration [1.3.6, 1.7.7]. This systemic exposure is the primary reason a topical medication like eye drops can cause side effects typically associated with oral drugs [1.3.6].
Can Chloramphenicol Eye Drops Cause Diarrhea?
Yes, it is possible for chloramphenicol eye drops to cause diarrhea, though it is considered a less common side effect [1.2.2, 1.4.2]. Multiple medical resources list diarrhea, nausea, and vomiting as potential side effects of chloramphenicol, even when not taken orally [1.2.1, 1.2.2, 1.2.3, 1.4.3].
The mechanism is linked to the systemic absorption discussed above. When the antibiotic reaches the gut, it can disrupt the natural balance of gut flora (the microbiome). As a broad-spectrum antibiotic, chloramphenicol doesn't just target the harmful bacteria causing the eye infection; it can also affect the beneficial bacteria in your digestive system. This disruption can lead to gastrointestinal distress, including abdominal pain and diarrhea [1.2.1]. While these symptoms are usually temporary, persistent or severe diarrhea should be reported to a healthcare provider [1.2.1, 1.2.6].
Other Potential Side Effects of Chloramphenicol Eye Drops
While diarrhea is a possibility, there are other side effects to be aware of, ranging from common and mild to rare and extremely serious.
Common and Localized Side Effects
The most frequently reported adverse reactions are local to the eye itself [1.7.1, 1.7.2]. These are generally mild and transient:
- Burning or stinging upon application [1.7.4]
- Temporary blurred vision [1.5.4]
- Itching and redness (conjunctival hyperemia) [1.7.1]
- Sensitivity to light [1.7.2]
Serious Systemic Side Effects
The most significant risk associated with chloramphenicol, regardless of its administration route, is its potential to cause serious and sometimes fatal blood dyscrasias (blood disorders) [1.5.1].
- Aplastic Anemia: This is a rare but often fatal condition where the bone marrow stops producing enough new blood cells [1.5.3, 1.7.1]. Cases have been reported following both long-term and short-term topical use of chloramphenicol [1.5.7]. The risk is lower with eye drops compared to oral administration but is significant enough that the drug is reserved for serious infections [1.5.3].
- Bone Marrow Suppression: This is a more common, dose-related toxic effect on the bone marrow that is usually reversible upon stopping the medication [1.5.3, 1.3.2]. Symptoms can include unusual tiredness, pale skin, sore throat, fever, and unusual bleeding or bruising [1.3.3, 1.5.1].
- Gray Baby Syndrome: This is a serious condition that occurs in newborn infants (especially premature ones) who cannot metabolize the drug effectively. Symptoms include a swollen stomach, low blood pressure, and a gray skin color [1.5.2, 1.4.5]. This is primarily a concern with systemic administration but highlights the drug's potency.
Comparison of Common Antibiotic Eye Drops
| Feature | Chloramphenicol | Ciprofloxacin (Fluoroquinolone) | Ofloxacin (Fluoroquinolone) |
|---|---|---|---|
| Spectrum | Broad-spectrum [1.7.6] | Broad-spectrum, good against Pseudomonas | Broad-spectrum, similar to Ciprofloxacin |
| Primary Use | Serious bacterial conjunctivitis [1.3.2] | Bacterial conjunctivitis, corneal ulcers | Bacterial conjunctivitis, corneal ulcers |
| Common Side Effects | Stinging, burning, blurred vision [1.7.4] | Local irritation, white crystalline deposits (with ulcer use) | Eye irritation, stinging, redness |
| Key Systemic Risks | Rare but fatal aplastic anemia, bone marrow suppression [1.5.1, 1.5.3] | Potential for tendonitis/tendon rupture (very rare with eye drops) | Similar to Ciprofloxacin |
Conclusion
To answer the central question: yes, chloramphenicol eye drops can cause diarrhea. This occurs due to systemic absorption of the drug, which can disrupt the gut microbiome [1.2.1]. While gastrointestinal issues are considered a less common side effect, they are a documented possibility [1.2.2]. It is far more critical, however, to be aware of the rare but potentially fatal risk of aplastic anemia and other blood disorders associated with chloramphenicol use, even in its topical form [1.5.1, 1.5.3]. Because of these risks, chloramphenicol is typically reserved for infections where other antibiotics are not suitable [1.3.2]. Always use this medication exactly as prescribed and immediately report any concerning side effects—such as persistent diarrhea, severe weakness, unusual bruising, or fever—to your healthcare provider.
For further reading on this medication, you can visit the NHS page on Chloramphenicol.
