Antibiotics Health Article

Definition

Antibiotics are drugs that are used to treat infections caused by bacteria and other organisms, including protozoa, parasites, and fungi.

Purpose

Many treatments for cancer destroy disease-fighting white blood cells, thereby reducing the body's ability to fight infection. For example, bladder, pulmonary, and urinary tract infections may occur with chemotherapy. Single-celled organisms called protozoa are rarely a problem for healthy individuals. However, they can cause serious infections in individuals with low white blood cell counts. Because of the dangers that infections present for cancer patients, antibiotic treatment often is initiated before the exact nature of the infection has been determined; instead, the choice of antibiotic may depend on the site of the infection and the organism that is likely to be the cause. Often, an antibiotic that kills a broad spectrum of bacteria is chosen and several antibiotics may be used together.

Description

The common antibiotics that are used during cancer treatment include:

• Atovaquone (Mapren): antiprotozoal drug used to prevent and treat a very serious type of pneumonia called Pneumocystis carinii pneumonia (PCP), in individuals who experience serious side effects with SMZ-TMP (Sulfamethoxazole/Trimethoprim, brand name Bactrim).
• Aztreonam (Azactam): monobactam antibiotic used to treat gram-negative bacterial infections of the urinary and lower respiratory tracts and the female organs, and infections that are present throughout the body (systemic infections or septicemia).
• Cefepime (Maxipime), ceftazidime (Ceptaz, Fortaz, Tazicef, Tazidime), and ceftriaxone sodium (Rocephin): members of a group of antibiotics called cephalosporins used to treat bacterial infections of the urinary and lower respiratory tracts, and infections of the skin, bones, joints, pelvis, and abdomen.
• Ciprofloxacin (Cipro): fluoroquinolone antibiotic used to treat certain gram-negative and gram-positive bacteria and some mycobacteria.
• Clindamycin phosphate (Cleocin): used to treat gram-positive and gram-negative bacterial infections and, in individuals who are allergic to sulfadiazine, toxoplasmosis caused by a parasitic protozoa.
• Gentamicin (gentamycin) sulfate (generic name product, Garamycin, G-Mycin, Jenamicin): aminoglycoside antibiotic used to treat serious infections by many gram-negative bacteria that cannot be treated with other medicines.
• Metronidazole hydrochloride (Flagyl, Metric 21, Metro I.V., Protostat): used for anaerobic bacteria and protozoa.
• Pentamidine (generic name product, Pentam 300): used to treat PCP if serious side effects develop with SMZTMP.
• Pyrimethamine (Daraprim): antiprotozoal medicine used together with sulfadiazine to treat toxoplasmosis; or in combination with other medicines for treating mild to moderate PCP, in individuals who cannot tolerate the standard treatment.
• Sulfadiazine (generic name product): sulfonamide antibiotic used with pyrimethamine to treat toxoplasmosis.
• Sulfamethoxazole-Trimethoprim (SMZ-TMP) (generic name product, Bactrim, Cofatrim Forte, Cotrim, Septra, Sulfatrim): the sulfonamide antibiotic, sulfamethoxazole, used in combination with trimethoprim, to prevent and treat PCP and bacterial infections, such as bronchitis and middle ear and urinary tract infections.
• Trimethoprim (generic name product, Proloprim, Trimpex): primarily used to prevent or treat urinary tract infections.
• Vancomycin hydrochloride (generic name product, Vancocin): glycopeptide antibiotic used to treat a variety of serious gram-positive bacterial infections for which other medicines are ineffective, including strains of Staphylococcus that are resistant to most oral antibiotics.

Most of these antibiotics kill bacteria by preventing them from making protein for their cell walls. Ciprofloxacin and metronidazole prevent bacteria from reproducing by interfering with their ability to make new DNA. All of these drugs are approved for prescription by the U.S. Food and Drug Administration.

Recommended dosage

Dosages of antibiotics depend on the individual, the infection that is being treated, and the presence of other medical conditions. For children, the dosage usually is based on body weight and is lower than the adult dosage. To be effective, an entire treatment with antibiotics must be completed, even if the symptoms of infection have disappeared. Furthermore, it is important to keep the level of antibiotic in the body at a constant level during treatment. Therefore, the drug should be taken on a regular schedule. If a dose is missed, it should be taken as soon as possible. If it is almost time for the next dose, the missed dose should be skipped. Doubling up doses is generally not recommended.

Average adult dosages of common antibiotics for cancer patients are as follows:

• Atovaquone: for PCP treatment, 750 mg oral suspension twice a day, or tablets three times per day, for 21 days; for PCP prevention, 1, 500 mg oral suspension, once a day; must be taken with balanced meals.
• Aztreonam: 1-2 gm every 6-12 hours, injected into a vein, over a 20-60 minute-period.
• Cefepime: 500 mg to 2 gm, injected into a vein or muscle, every 8-12 hours for 7-10 days.
• Ceftazidime: 250 mg to 2 gm, injected into a vein or muscle, every 8-12 hours.
• Ceftriaxone: 1-2 gm, injected into a vein or muscle, every 24 hours.
• Ciprofloxacin: 500-750 mg of the tablet or suspension, every 12 hours, for 3-28 days, taken two hours after meals with 8 oz of water; bone and joint infections usually are treated for at least 4-6 weeks; 200-400 mg injected every 8-12 hours.
• Clindamycin: 150-300 mg of capsule or solution, every six hours; 300-600 mg every six to eight hours or 900 mg every eight hours, injected into a vein or muscle.
• Gentamicin: dosage determined by body weight, every 8-24 hours for at least 7-10 days, injected into a vein or muscle.
• Metronidazole: for bacterial infections, 7.5 mg per kg (3.4 mg per lb) of body weight up to a maximum of 1 gm, every six hours for at least seven days (capsules or tablets); 15 mg per kg (6.8 mg per lb) for the first dose, followed by half that dosage every six hours for at least seven days (injected into a vein); for protozoal infections caused by amebas, 500-750 mg of oral medicine, three times per day for 5-10 days; for trichomoniasis, 2 gm for one day or 250 mg three times per day for seven days (oral medicine); extended-release tablets for vaginal bacterial infections, 750 mg once a day for seven days.
• Pentamidine: for treating PCP, 4 mg per kg (1.8 mg per lb) of body weight, once per day for 14-21 days, injected into a vein over one to two hours, while lying down.
• Pyrimethamine: for toxoplasmosis, 25-200 mg tablets, taken with other medicine, for several weeks.
• Sulfadiazine: for bacterial and protozoal infections, 2-4 gm for the first dose, followed by 1 gm every four to six hours (tablets).
• SMZ-TMP: 800 mg of sulfamethoxazole and 160 mg of trimethoprim, (tablet or oral suspension), every 12 hours for bacterial infections and every 24 hours for prevention of PCP; dosage based on body weight for PCP treatment; injections based on body weight, every six, eight or 12 hours for bacterial infections and every six hours for PCP treatment.
• Trimethoprim: 100 mg tablet every 12 hours for 10 days; for prevention of urinary tract infections, once a day for a long period.
• Vancomycin: 7.5 mg per kg (3.4 mg per lb) of body weight, or 500 mg-1 gram, injected or taken orally, every 6-12 hours.