What Is Streptomycin?
Streptomycin is an aminoglycoside antibiotic, a class of drugs that function by inhibiting protein synthesis in bacteria. It was first isolated by Albert Schatz in 1943, marking a significant advancement in the treatment of diseases previously considered incurable. Unlike broad-spectrum antibiotics, streptomycin is typically reserved for severe, multi-drug resistant bacterial infections where other, less toxic alternatives are ineffective. Due to its poor oral absorption, it is usually administered via deep intramuscular or intravenous injection in a hospital or clinic setting.
Key Uses of Streptomycin
While its use has diminished since its discovery due to the development of other, less toxic antibiotics, streptomycin remains a critical treatment for certain conditions. Its applications are limited to specific, severe infections.
Tuberculosis (TB)
One of the most important answers to the question "What is streptomycin for?" is the treatment of tuberculosis, caused by Mycobacterium tuberculosis.
- Initial Treatment: For active TB, it is often included as a fourth drug in the initial regimen, especially when there is a risk of resistance to first-line agents like isoniazid or rifampin.
- Multi-Drug Resistant (MDR-TB): In cases of MDR-TB, where the bacteria are resistant to isoniazid and rifampin, streptomycin may be a valuable component of a longer, more complex treatment plan.
- Combination Therapy: Streptomycin is never used alone to treat TB due to the rapid development of resistance when used as a monotherapy.
Plague (Yersinia pestis)
Streptomycin has historically been the first-line treatment for all forms of plague, a rare but severe bacterial infection. While other effective antibiotics like gentamicin and tetracyclines are now used, streptomycin is still approved by the U.S. Food and Drug Administration (FDA) for this purpose.
Tularemia (Francisella tularensis)
Also known as rabbit fever, tularemia is a bacterial infection for which streptomycin is a traditional and highly effective treatment. It has proven curative in many cases of this serious infection.
Enterococcal Endocarditis
In cases of bacterial endocarditis caused by Enterococcus faecalis, streptomycin is sometimes used in combination with other antibiotics like penicillin or vancomycin to achieve a synergistic effect, meaning the combined effect is greater than the sum of their individual effects.
How Streptomycin Works
Streptomycin functions as a bactericidal agent, meaning it kills bacteria rather than just inhibiting their growth. The mechanism of action is dependent on its ability to bind irreversibly to the 16S rRNA component of the bacterial 30S ribosomal subunit. This binding disrupts the ribosome's ability to synthesize proteins correctly, leading to several cellular failures:
- Codon Misreading: It causes the ribosome to misread the genetic code from the messenger RNA (mRNA), resulting in the production of faulty proteins.
- Inhibition of Protein Synthesis Initiation: It interferes with the very start of protein synthesis, preventing the formation of the initial protein complex.
- Destabilization of Ribosomal Complex: The binding also causes instability in the ribosome-mRNA complex, leading to premature termination of protein synthesis.
Potential Side Effects and Risks
Streptomycin's potent antibacterial action comes with significant potential for serious side effects, particularly affecting the ears and kidneys. Due to these risks, patients on streptomycin are closely monitored, often with regular hearing and kidney function tests.
Major Side Effects
- Ototoxicity: This is the most serious and common risk associated with streptomycin. It can manifest as damage to the vestibular system (affecting balance, leading to vertigo, nausea, and unsteadiness) or the cochlear system (leading to hearing loss or tinnitus). This damage can be permanent and is more likely in older patients, infants, those with kidney problems, or with prolonged, high-dose use.
- Nephrotoxicity: Though less nephrotoxic than other aminoglycosides, streptomycin can still impair kidney function. This risk increases with pre-existing kidney disease, and dosages must be adjusted accordingly.
- Neuromuscular Blockade: In high doses, streptomycin can cause muscle weakness and potentially respiratory paralysis. This risk is heightened in patients with neuromuscular disorders like myasthenia gravis.
Other Adverse Reactions
- Allergic reactions such as rash, fever, or swelling.
- Gastrointestinal upset, including nausea and vomiting.
- Fever, chills, or headache.
- Numbness or tingling sensation in the face.
Streptomycin vs. Other Antibiotics
To understand streptomycin's current role, it's helpful to compare it to other antibiotics used for similar purposes. For example, gentamicin is another aminoglycoside, and newer TB treatments offer different profiles. This table compares streptomycin with gentamicin and a common TB drug, Isoniazid.
| Feature | Streptomycin | Gentamicin | Isoniazid |
|---|---|---|---|
| Class | Aminoglycoside | Aminoglycoside | Isonicotinic acid derivative |
| Primary Uses | TB, plague, tularemia, enterococcal endocarditis | Serious infections (sepsis, pneumonia), plague | Tuberculosis |
| Mechanism | Inhibits protein synthesis by binding to 30S ribosomal subunit | Inhibits protein synthesis by binding to 30S ribosomal subunit | Inhibits synthesis of mycolic acids (key component of mycobacterial cell wall) |
| Administration | Deep Intramuscular (IM) or Intravenous (IV) injection | Intravenous (IV) or Intramuscular (IM) injection | Oral |
| Major Side Effects | Ototoxicity (vestibular damage), nephrotoxicity | Ototoxicity (cochlear damage), nephrotoxicity | Liver damage (hepatotoxicity), peripheral neuropathy |
| Role in TB | Second-line or combination therapy for MDR-TB | Less common for TB, used for other serious infections | First-line, cornerstone of TB treatment |
Drug Interactions
Streptomycin's toxicity can be exacerbated by interactions with other drugs. It is crucial to inform healthcare providers about all medications being taken. Significant drug interactions include:
- Loop Diuretics (e.g., furosemide): Increases the risk of ototoxicity.
- Other Aminoglycosides (e.g., gentamicin, tobramycin): Additive risk of both nephrotoxicity and ototoxicity.
- Nephrotoxic Agents (e.g., NSAIDs, cisplatin): Increases the risk of kidney damage.
- Neuromuscular Blocking Agents (e.g., succinylcholine): Potentiates neuromuscular blockade, which can cause breathing difficulties.
The Rise of Resistance
Like many antibiotics, the widespread use of streptomycin has led to the development of bacterial resistance. Resistance to streptomycin can be genetically determined, either through mutations in chromosomal genes like rpsL (encoding ribosomal protein S12) or through plasmid-borne genes like strA and strB that encode inactivating enzymes. The emergence of resistance is why streptomycin is often used in combination with other drugs to treat conditions like TB, reducing the chance of treatment failure.
Conclusion
Streptomycin, a historic and potent antibiotic, has been instrumental in treating serious bacterial diseases, most notably tuberculosis and plague. The answer to what is streptomycin for today involves a targeted approach, using it primarily for severe infections and in combination therapies, particularly when resistance to other drugs is a concern. However, its significant potential for ototoxicity and nephrotoxicity, along with the issue of bacterial resistance, necessitate careful administration and close patient monitoring. Despite its limitations, streptomycin remains an essential medicine in specific clinical situations, highlighting the continued importance of older antibiotics in modern medicine. For additional information on streptomycin, consider consulting reliable medical resources such as the NCBI's StatPearls on Streptomycin.
