What is Methicillin?

Methicillin, called meticillin in some countries, is a narrow-spectrum antibiotic in the penicillin family. It was developed in 1959, and given intravenously to treat staphylococcus areus infections. Sometimes it is also referred to as staphicillin because of its use against staph bacteria, including those strains resistant to other penicillin drugs. Methicillin is no longer used in the United States because of its side effects, and not regularly used in other countries. It is still used in laboratories, however, to gauge resistance of bacterial strains.

The most worrying side effect of methicillin is interstitial nephritis. Symptoms include fever, blood in the urine, nausea, vomiting, rash, and weight gain. This occurs in up to 33 percent of patients treated with the drug, and can cause kidney failure. Mild cases may go unnoticed, and elderly patients usually have a more severe form of the condition. The risk of interstitial nephritis is the main reason methicillin is no longer used.

Methicillin-resistant staphylococcus areus (MRSA) is a strain of staphylococcus infection that is resistant to drugs in the penicillin family, and is becoming resistant to other drugs as well. The original term is still used, even in countries where methicillin is no longer in clinical use. MRSA infection can be mild or serious, depending upon the systems affected. Symptoms of a MRSA skin infection include an abscess and fever. Systemic MRSA infection symptoms include chills, fever, chest pain, cough, fatigue, headache, muscle aches, and rash.

MRSA is becoming more and more difficult to treat, since it develops resistance to antibiotics commonly used to treat it. Doxycycline, daptomycin, and vancomycin are some drugs that it still responds to. Treatment takes place either on an in-patient or out-patient basis, depending upon the location and severity of the disease.

Staphylococcus areus infection of the central nervous system (CNS) is still treated with methicillin in some countries. It provides better penetration of the CNS than other drugs. Cloxacillin is commonly used to treat these conditions in the United States.

Methicillin is sometimes confused with the drug metacycline, which is a tetracycline antibiotic. Metacycline is also not used clinically in the United States, although it is used industrially in the synthesis of doxycycline hyclate. In some countries, it is used to treat bacterial infections and acne vulgaris.

The penicillin drugs oxacillin and nafcillin are now the most commonly used antibiotics in the treatment of staph infection. Some strains of MRSA are resistant to these drugs, but others are not. These are both given intravenously. Oxacillin, however, carries a risk of hepatitis, which occurs in up to 22 percent of patients treated.