Understanding What Chloramphenicol Is Used to Treat: A Full Pharmacological Review

October 6, 2025 •

4 min read

First isolated from the bacterium Streptomyces venezuelae in 1947, chloramphenicol is a broad-spectrum antibiotic with a history of treating severe, life-threatening infections [1.2.5]. This article explains what chloramphenicol is used to treat, its mechanism, and significant risks associated with its use.

Quick Summary

Chloramphenicol is a potent antibiotic for serious infections like meningitis, plague, cholera, and typhoid fever when safer drugs are ineffective [1.2.5]. It is also commonly used topically for bacterial conjunctivitis [1.2.3].

Key Points

Primary Use: Chloramphenicol is used for serious infections like meningitis, typhoid fever, and cholera, and topically for eye infections [1.2.1, 1.2.3].
Mechanism of Action: It is a bacteriostatic antibiotic that works by inhibiting protein synthesis in bacteria [1.3.1].
Systemic Use Warning: Systemic (oral or IV) use is restricted to life-threatening infections where safer antibiotics are ineffective due to severe side effect risks [1.2.2].
Aplastic Anemia Risk: Carries a risk of irreversible and fatal aplastic anemia, a serious blood disorder, especially with oral use [1.4.3, 1.3.5].
Gray Baby Syndrome: Can cause a fatal toxicity in newborns called Gray Baby Syndrome if dosage is not carefully managed [1.4.4, 1.4.5].
Topical Formulation: Eye drops and ointments are common for treating bacterial conjunctivitis and generally considered safe for short-term use [1.6.3, 1.6.4].
Global Health Role: Remains a WHO Essential Medicine due to its effectiveness and low cost in treating severe infections in developing nations [1.2.5].

The Role of Chloramphenicol in Modern Medicine

Chloramphenicol is a broad-spectrum antibiotic that functions by inhibiting bacterial protein synthesis [1.3.1]. Discovered in 1947, it was the first synthetically mass-produced antibiotic [1.4.5]. Its use, however, is now significantly restricted, especially in developed nations. Systemic use (oral or intravenous) is reserved for serious, life-threatening infections where other, safer antibiotics are ineffective or contraindicated [1.2.2, 1.2.5]. This is primarily due to its potential for severe side effects, including a US Boxed Warning for serious and fatal blood dyscrasias [1.4.3].

Despite the risks, it remains on the World Health Organization's List of Essential Medicines because of its effectiveness and low cost, particularly in low-income countries for conditions like meningitis [1.2.5].

How Chloramphenicol Works

The primary mechanism of action for chloramphenicol is bacteriostatic, meaning it stops bacteria from multiplying rather than killing them outright, though it can be bactericidal at high concentrations against specific bacteria [1.3.2, 1.3.5]. It achieves this by binding to the 50S subunit of the bacterial ribosome, which effectively blocks the peptidyl transferase step of protein synthesis. This action prevents the formation of peptide bonds, halting the creation of proteins essential for bacterial survival and replication [1.3.2, 1.7.1]. Its high lipid solubility allows it to penetrate effectively into nearly all body tissues, including the brain and cerebrospinal fluid, making it historically useful for treating meningitis [1.3.5, 1.7.2].

Systemic Infections Treated by Chloramphenicol

Intravenous or oral chloramphenicol is only recommended for severe infections when the benefits outweigh the significant risks. Patients undergoing systemic treatment require hospitalization and close monitoring of blood levels [1.2.5, 1.4.3].

Meningitis: Due to its excellent penetration of the blood-brain barrier, chloramphenicol has been a key treatment for bacterial meningitis, especially in low-income nations. An oily, single-injection formulation has been demonstrated as a highly effective and inexpensive option [1.7.1].
Typhoid Fever: Historically, chloramphenicol was the drug of choice for typhoid fever caused by Salmonella typhi [1.7.1]. The emergence of multidrug-resistant strains has reduced its first-line use, but it remains an option if the bacteria is proven to be sensitive [1.5.1, 1.7.1].
Cholera and Plague: It is used to treat cholera and plague (Yersinia pestis) [1.2.1, 1.2.5]. It can be an alternative antibiotic for treating pregnant patients with various forms of plague [1.4.3].
Rickettsial Infections: This includes diseases like scrub typhus, where it was first proven highly effective in field trials in 1948 [1.7.3].
Drug-Resistant Infections: There has been a re-evaluation of chloramphenicol for treating infections caused by multidrug-resistant organisms, such as vancomycin-resistant enterococci (VRE) [1.2.5].

Topical Applications of Chloramphenicol

The most common and safer application of chloramphenicol today is in topical forms for localized infections.

Bacterial Conjunctivitis (Pink Eye): Chloramphenicol eye drops and ointments are widely used to treat superficial eye infections like bacterial conjunctivitis and blepharitis [1.2.3, 1.6.5]. It is effective against common culprits like Staphylococcus aureus and Streptococcus pneumoniae [1.2.5]. For most eye infections, improvement is typically seen within 2 days [1.2.3].
Otitis Externa (Outer Ear Infections): Prescription ear drops containing chloramphenicol are used to treat bacterial infections of the outer ear canal [1.2.1, 1.2.3].

Significant Risks and Side Effects

The use of systemic chloramphenicol is limited by its severe adverse effects. All patients on systemic therapy require regular blood tests [1.4.3].

Aplastic Anemia: This is the most serious side effect. It is a rare, often fatal condition where the bone marrow stops producing enough new blood cells [1.4.3, 1.7.1]. This reaction is idiosyncratic (not related to dose) and can occur weeks or months after treatment has ended [1.3.5, 1.7.1]. The risk is highest with oral administration, estimated at 1 in 24,000 to 40,000 treatment courses [1.3.5]. While the risk from eye drops is exceedingly low (less than 1 in 224,716 prescriptions), isolated cases have been reported [1.6.5, 1.7.1].
Bone Marrow Suppression: This is a more common, dose-related, and reversible side effect [1.3.5]. It results from the drug's toxic effect on mitochondria and manifests as anemia, low white blood cell count, or low platelet count. It typically resolves after the drug is discontinued [1.7.1].
Gray Baby Syndrome: This is a life-threatening condition of circulatory collapse that occurs in newborns and premature infants treated with excessively high doses of chloramphenicol [1.4.2, 1.4.4]. Infants lack the necessary liver enzymes to metabolize the drug, leading to toxic accumulation. Symptoms include an ashen-gray skin color, abdominal swelling, low blood pressure, and circulatory collapse [1.4.2, 1.4.5].

Topical Antibiotic Comparison

For superficial eye infections, several alternatives to chloramphenicol exist. The choice depends on the suspected bacteria, local resistance patterns, and patient factors.


Feature	Chloramphenicol	Ciprofloxacin	Gentamicin
Antibiotic Class	Amphenicol	Fluoroquinolone	Aminoglycoside
Spectrum	Broad-spectrum, effective against many gram-positive and gram-negative bacteria [1.2.5].	Broad-spectrum, including Pseudomonas aeruginosa [1.10.5].	Primarily targets gram-negative bacteria, with some gram-positive coverage [1.10.3, 1.10.5].
Primary Use	Bacterial conjunctivitis, blepharitis [1.6.5].	Bacterial conjunctivitis, corneal ulcers [1.10.3, 1.10.4].	Bacterial conjunctivitis, keratitis [1.10.5].
Key Consideration	Rare risk of aplastic anemia even with topical use [1.6.5].	Generally safe; may cause a white precipitate on the eye with corneal ulcers [1.10.3, 1.10.4].	Can cause localized irritation [1.10.3].

Conclusion

Chloramphenicol is a powerful antibiotic whose role has evolved significantly since its discovery. While its topical formulations remain a common and effective treatment for bacterial eye and ear infections, its systemic use is strictly reserved for severe, life-threatening infections where no safer alternatives are available [1.2.2, 1.2.3, 1.6.5]. The serious risks of aplastic anemia and Gray Baby Syndrome necessitate extreme caution and diligent patient monitoring [1.4.3, 1.4.5]. The medical community continues to weigh its efficacy against its toxicity, solidifying its status as a last-resort but sometimes essential, life-saving medication.

Authoritative Link: For more detailed information on chloramphenicol, consult the U.S. National Library of Medicine's entry on StatPearls. [1.2.1]

Frequently Asked Questions

Systemically, it treats severe infections like meningitis, plague, cholera, and typhoid fever when other antibiotics fail [1.2.5]. Topically, it is commonly used for bacterial eye infections, such as conjunctivitis, and ear infections [1.2.3].

Yes, it is a potent, broad-spectrum antibiotic. However, due to its potential for serious side effects, its use is often restricted to infections that cannot be treated with safer alternatives [1.2.2, 1.2.5].

In some countries, chloramphenicol eye drops and ointments are available over the counter or from a pharmacy for adults and children over 2 years old for treating acute bacterial conjunctivitis [1.8.1, 1.8.2, 1.8.3]. Systemic forms (capsules, injections) always require a prescription [1.2.3].

The most serious side effect is aplastic anemia, a rare but often fatal condition where the bone marrow fails to produce blood cells. This has led to a US Boxed Warning for the drug [1.4.3, 1.7.1].

Gray Baby Syndrome is a rare but life-threatening reaction in newborns exposed to high doses of chloramphenicol. Their immature liver cannot process the drug, leading to a toxic buildup causing symptoms like an ashen-gray skin color, abdominal distention, and cardiovascular collapse [1.4.4, 1.4.5].

For most bacterial eye infections like conjunctivitis, you should start to see an improvement within about two days of starting treatment with chloramphenicol eye drops [1.9.1].

The manufacture of oral chloramphenicol for human use stopped in the U.S. in 1991 because the vast majority of cases of the fatal side effect, aplastic anemia, were associated with the oral preparation [1.2.5].