Why I Prescribe Antibiotics
By 
Gabe Mirkin M.D.

The latest information for you and your doctor on the treatment of:

Rheumatoid or Reactive Arthritis
Fibromyalgia
Chronic Fatigue Syndrome
Multiple Chemical Sensitivities
Late-Onset Asthma
Ulcerative Colitis
Chrohn’s Disease
Stomach Problems
Prevention of Heart Attacks
Infertility
Sexually Transmitted Disease 
Yeast Infections

Why I Prescribe Antibiotics to My Patients with Rheumatoid or Reactive Arthritis, Late-onset Asthma, Crohn’s Disease, Fibromyalgia, and Other Autoimmune Diseases. 

Before I prescribe any medication, I ask myself whether it will help or hurt. All of the autoimmune diseases cause severe disability. Conventional medications neither cure these diseases nor stop the progressive destruction that they cause. Doctors prescribe immune suppressives that sometimes have deadly effects. Antibiotics are far safer that the drugs conventionally used to treat these diseases. So, if antibiotics can be shown to help control these diseases, they should be used long before a doctor thinks of using the conventional immune suppressives.
When a germ gets into your body, you are supposed to produce cells and proteins called antibodies that attach to and kill that germ. These diseases are felt by many doctors to be caused by your own immunity. Instead of doing its job of killing germs, your immunity attacks your own tissue. If it attacks your joints, its is called reactive arthritis; if it attacks your intestines, it’s called Crohn’s disease; your colon, it’s called ultra ulcerative colitis; and if it fills your lungs with mucous, it’s called late onset asthma. I do not believe that your immunity is that stupid. Accumulating data show that all of these conditions can be caused by infection. Many diseases that were thought to be autoimmune turn out to be infections: stomach ulcers are caused by bacterium, helicobactor pylori and others; multiple sclerosis may be caused by HHS-6 virus; rheumatic fever is caused by the bacterium, beta streptococcus, group A; Gillian-Barre syndrome may be caused by the bacterium, campylobacter; Crohn’s disease and ulcerative colitis by E. Coli, Klebsiella and Bacteroides; and so forth.

Shouldn’t We Be Concerned About Resistant Bacteria? 

The argument that giving antibiotics causes bacteria to be resistant to that antibiotic is reasonable, but it has no place in discouraging people with these diseases from taking them. First, these people have serious diseases that cause permanent damage life and death. Second, the treatments that are available are toxic, shorten life, cause cancer, and have to be followed by frequent blood tests. On the other hand, I prescribe derivatives of tetracycline and erythromycin. These are extraordinarily safe and do not require drawing frequent blood tests. If you were to become infected subsequently with bacteria that are resistant to these antibiotics, you would have lost nothing. No reasonable doctor would prescribe erythromycin or tetracycline for acute serious diseases, such as meningitis, pneumonia, or an abscess, because tetracyclines and erythromycins do not kill germs, they only stop them from multiplying. Instead, doctors prescribe far more bacteriocidal antibiotics that kill bacteria.
Many doctors criticize my use of antibiotics, but many antibiotics are far safer than conventional treatment, cost less, can be administered by a general practitioner, and often cure the condition, rather that just suppressing symptoms. I know that most physicians who develop these conditions will treat themselves with antibiotics because they know that conventional treatments with prednisone, chloroquine, azathioprine, and methotrexate are toxic and my treatments with erythromycins and tetracyclines are safe.

The Hidden Epidemic—Mycoplasma, Chlamydia, and Ureaplasma

	Mycoplasma, chlamydia, and ureaplasma are the smallest of free-living organisms. They are unlike all other all other bacteria because they have no cell walls and therefore must live inside cells. They are unlike viruses because they can live in cultures outside of cells and can be killed by certain antibiotics. However, they cannot be killed by most antibiotics, as most antibiotics work by damaging a bacteria’s cell wall. They can be killed by antibiotics such as tetracyclines or erythromycins that do not act on a cell wall. 
If you feel sick and your doctor is unable to make a diagnosis because all laboratory tests and cultures fail to reveal a cause, you could be infected with one or more of these bacteria. The only way that you will be cured is for your doctor to suspect an infection with these germs and for you to take long-acting erythromycin or tetracyclines for several weeks, months or years. They are the most common cause of venereal diseases and are a common cause of muscle and joint pains, burning in the stomach, a chronic cough, and chronic fatigue. They can cause transverse myelitis (paralysis of the spine); gall stones; a chronic sore throat; red itchy eyes, pain on looking at light and blindness; arthritis; brain and nerve damage with symptoms of lack of coordination, headaches and passing out; spotting between periods or uterine infections; kidney stones; testicular pain; asthma; heart attacks; strokes; cerebral palsy; premature birth; high blood pressure; nasal polyps; stuffy nose in newborns; chronic fatigue; belly pain; muscle pain; confusion; passing out and death; coughing; bloody diarrhea; and anal itching and bleeding.
Mycoplasma, chlamydia, and ureaplasma infections are extraordinary difficult to diagnose and treat. No dependable tests are available to most practicing physicians that will rule infections with these bacteria in or out, and most doctors will not prescribe antibiotics to patients unless they have results of a laboratory test that confirms a specific infection. If you feel sick and your doctor unable to make a diagnosis because all laboratory test and cultures fail to reveal a cause, you could be infected with mycoplasma, chlamydia, or ureaplasma and will be cured only by taking long-acting erythromycin or tetracyclines for many months. 
Usually the first symptoms from chlamydia, ureaplasma and mycoplasma are burning on urination, a feeling that you have to urinate all the time, terrible discomfort when the bladder is full and vaginal itching, odor or discharge. Other first symptoms include itchy eyes, a cough or a burning in your nose. The bacteria are transmitted through sexual contact, or you can be infected when an infected person coughs in your face or you touched nasal or eye secretions from an infected person and put your finger in your nose or eye. Your chances for a cure are high if you are treated when you have only local symptoms; but after many months the infection can spread to other parts of your body and make you sick or damage nerves, joints and muscles.
 	Once these infections are allowed to persist for months or years, they are extraordinarily difficult to cure and often require treatment for many months. Even if your doctor is willing to prescribe antibiotics, treatment can be difficult. Often patients do not take the medication long enough to be cured, or they may have a close contact with an infected person and become reinfected.  One patient in four takes of medication as prescribed and almost all women who had chlamydia one month after treatment had been reinfected by new or old partners. 
My recommended treatment: I often prescribe 500 mg of azithromycin twice a week and/or doxycycline 100-mg twice a day. Many physicians disagree with these recommendations, so check with your doctor to see if you may be a candidate for this treatment.

Reactive and Rheumatoid Arthritis

 	Most rheumatologist refuse to treat their rheumatoid arthritis patients with antibiotics even though all five controlled prospective studies conducted to date show that minocycline drops the rheumatoid factor towards zero and helps to alleviate the pain and destruction of cartilage of rheumatoid arthritis. There are two major types of arthritis: osteoarthritis, also called degenerative arthritis; and reactive arthritis, which includes rheumatoid arthritis. Osteoarthritis means that cartilage wears away and doctors don’t have the foggiest idea why. There is no effective treatment. Doctors usually prescribe non-steroidal pills that help to block pain but do not stop or even slow down the destruction of cartilage. 
Most scientists agree that an infection initiates rheumatoid and other reactive arthritides and most think that the germ is still there when the symptoms start. Short-term antibiotics are ineffective, but if antibiotics are started before the joint is destroyed, many months and years of antibiotics are effective in reducing and preventing joint damage. Your arthritis is likely to be classified as reactive arthritis if you have: 1) positive blood tests for arthritis (all tests used to diagnose arthritis are measures of an overactive immunity); 2) swelling of the knuckles and middle joints of your fingers, causing them to look like cigars; 3) a history of a long-standing infection such as a chronic cough, burning on urination or pain when the bladder is full, chronic diarrhea, burning in the stomach, throat or nose, or gum disease; and 4) symptoms that begin before age 50.
Rheumatoid arthritis is characterized by pain in many muscles and joints and is thought to be caused by a person’s own antibodies and cells and cells attacking and destroying cartilage in joints. Rheumatoid arthritis may be triggered by infection and antibiotics may help to prevent and treat this joint destruction. Most rheumatologists treat rheumatoid arthritis with immune suppressants, which are extraordinarily expensive, highly toxic and, in my opinion, far less effective in controlling rheumatoid arthritis than antibiotics. Antibiotics are effective in controlling the symptoms of rheumatoid arthritis and higher doses are more effective. Short-term antibiotics are ineffective. Doxycycline may prevent joint destruction by stabilizing cartilage in addition to clearing the germ from the body.
How do germs cause arthritis? When a germ gets into your body, you manufacture cells and proteins called antibodies that attach to and kill that germ. Sometimes, the germ has a surface protein that is similar to the surface protein in your cells. Then, not only do the antibodies attach to and kill the germ, they also attach to and kill your own cells that have the same surface membranes. People with rheumatoid arthritis have high antibody titre to E. Coli, a bacteria that lives normally in everyone’s intestines. It has the same surface protein as many cells in your body. Normal intestines do not permit E. Coli to get into your bloodstream. The people who get rheumatoid arthritis may be those whose intestines allow E. Coli to pass into the blood stream and cause the immune reaction that destroys muscles and joints. The same type of reaction applies to several other bacteria and viruses that can pass into your blood stream. Venereal diseases, such as gonorrhea, chlamydia, mycoplasma, and ureaplasma have been found in the joint fluid of many people with arthritis. People with rheumatoid arthritis are more likely to have staph aureus in their noses and carry higher antibody titer against that germ. Many people with rheumatoid arthritis have had chronic lung infections, caused by mycoplasma and chlamydia, prior to getting rheumatoid arthritis.
I have seen antibiotics reduce high rheumatoid factors to zero, alleviate symptoms and stop the progressive destruction of cartilage in joints. The lead paper at a recent meeting of the American Academy of Rheumatology showed that Minocycline is the safest and least expensive drug that effectively stops progressive joint damage caused by rheumatoid arthritis. It is most effective when given before extensive cartilaginous damage occurs. 
I treat my reactive arthritis patients with Minocycline 100 mg twice a day, (sometimes azithromycin 500-mg twice a week). This must still be considered experimental because most doctors are not yet ready to accept antibiotics as treatment. There is also concern about a rare, serious side effect of lupus. However, other papers show that even osteoarthritis may respond to antibiotics. 

Late-Onset Asthma May Be Caused by Infection.

	A recent issue of the Journal of the American Medical Association reviews articles showing that asthma that starts after puberty can be caused by an infection. At the 37th Interscience Conference on Antimicrobial Agents and Chemotherapy in Toronto, papers were presented showing that mycoplasma is a common cause of pneumonia in young adults and children, a common cause for meningitis, nerve damage, heart and muscle infection, (myocarditis) and arthritis, and a common cause of asthma in young adults. One paper showed that a significant number of young adults who develop asthma caused by mycoplasma fail to develop antibodies to kill that bacteria, so they continue to be infected for the rest of their lives. Another paper showed that another intracellular bacteria called ureaplasma is a common cause of asthma in young children. Since practicing physicians usually do not have an available laboratory test to find chlamydia, ureaplasma and mycoplasma, doctors should consider prescribing antibiotics for some people with persistent wheezing and coughing (azithromycin, clarithromysin, dirithromycin, minocycline or doxycycline).

Fibromyalgia, Chronic Fatigue Syndrome or Multiple Chemical Sensitivities 

	Fibromyalgia means that a previously healthy person develops unexplained exhaustion, fatigue and muscle aches and pains that last for more that six months; all blood tests are normal and doctors can’t find a cause. One recent report shows that a large number of people who were diagnosed with having fibromyalgia really had polymyalgia rheumatica, which does have abnormal blood tests. A recent report shows that many sufferers have low spinal fluid levels of vitamin B12 can be treated with 1000mcg of B12 each day.
	The diagnosis of fibromyalgia should be made only after all other causes have been ruled out. Many infections can cause fatigue and muscle pain. The evaluation should include tests for infectious diseases; such as Lyme disease and Hepatitis B or C, cytomegalovirus, toxoplasmosis or the helicobactor that causes stomach ulcers; autoimmune diseases, such as rheumatoid arthritis, lupus, Crohn’s disease or ulcerative colitis; hidden cancers such as those of the breast and prostate; hormonal diseases such as low thyroid; or side effects from a medication or illicit drug. Around 20 percent will be depressed. Most people miss work and complain of illness long before their diagnosis, but the majority will not have a known cause.
	Chronic fatigue means that the primary symptom is exhaustion, but most also have constipation and diarrhea. Fibromyalgia usually means that muscle and joint pains are major symptoms, but muscle biopsies are normal, pressure points are not reproducible and ultra sound is normal. Multiple chemical sensitivities means that patients think that their symptoms are caused by factors in their environment or they consult doctors who think the same thing. Untreated, the symptoms that that lead to any of these diagnoses will usually continue in adults for the rest of their lives. I have prescribed doxycycline 100-mg twice a day for several months, and sometimes azithromycin 500-mg twice a week, and some of my patients get better. However, this treatment is not accepted by most doctors. Please check with your doctor.

Prevention of Heart Attacks

	Myriad scientific papers show that heart attacks may be caused by infection with chlamydia and other bacteria and viruses. Most mainstream heart specialists feel that infection with chlamydia can cause heart attacks, but most doctors are afraid to prescribe new treatments. Most people who develop fatty plaques in their arteries have been infected with chlamydia and many people with arteriosclerotic heart disease carry chlamydia in their mouths.
	Previous studies show that chlamydia is associated with and has been found repeatedly in plaques that form in arteries to causes heart attacks, high blood pressure and strokes. Antibodies combine with chlamydia to form immune complexes that convert the bad LDL cholesterol to oxidized cholesterol to form plaques in arteries. People with high blood levels of C-reactive protein, an indicator of infection are the ones most likely to suffer heart attacks and strokes. Aspirin reduces inflammation caused by infection in the inner lining of arteries and prevents heart attacks. People who have had heart attacks are more likely to die if they have had high levels of C-reactive protein. Being infected with chlamydia is associated with increased risk for heart attacks and having chlamydia increases a heart attack victim’s chances of suffering another heart attack fourfold, presumably by increasing susceptibility clotting. Treating with azithromycin, an antibiotic that kills chlamydia helped relieve symptoms in people with agina chest pain. Herpes simplex and cytomegalovirus have been associated with heart attacks. 
	To prevent heart attacks, eat a low-fat, high-fiber diet and treat chronic infections. I recommend a short course of doxycycline or azithromycin to people who have heart attacks or strokes, or who are at high risk for heart attacks because of extensive arteriosclerosis; and have a positive antibody blood test for chlamydia or mycoplasma. I predict that soon most physicians will do the same, but now most physicians disagree with me even though studies show that antibiotics prevent heart attacks.

Ulcerative Colitis and Crohn’s Disease
	
When a person has bloody diarrhea and doctors find ulcers in the intestines, they look for cancer, infection or parasites. When they can’t find a cause, they should say that they don’t have the foggiest idea why the person has intestinal ulcers. Instead, they deceive their patients by saying that the person has Chrohn’s disease and explaining that the person’s immunity is so stupid that it punches holes in the intestines, rather than doing its job of killing germs. They prescribe medications that suppress immunity or cut out parts of intestine. 
Normal intestines are so loaded with bacteria that doctors can’t possibly tell which belong there and which may be causing disease. The conventional treatment offers no cure and is associated with many complications that shorten life. Exciting research from France show that a variant of E. Coli, a bacteria that lives in normal intestines, sticks to the intestinal lining and produces an alpha hemolysis that punches holes in the intestines to cause at least some cases of Crohn’s disease. Further studies show that heat shock protein can be removed from the common intestinal bacteria, E. Coli, and when given to mice, causes terrible bloody ulcers to form in the intestines. Under the microscope, intestines looked exactly the same as those of people who suffer from ulcerative colitis or Crohn’s disease. Extensive data show that people with this condition have leaky intestines that allow germs to pass into the bloodstream and their immunities are trying to kill these germs. 
Antibiotics can reduce swelling and ulcers in Crohn’s disease. Dr. Joel Taurog of the University of Texas has shown that a bacteria called bacteroides causes ulcerative colitis and Crohn’s disease in mice who are genetically programmed to have an HLA-B27, a special gene that causes arthritis. Special tissue staining techniques show that tissue taken from patients with Crohn’s disease and ulcerative colitis contain parts of two common bacteria called E. Coli and streptococci. Many studies show that infections may cause Crohn’s disease and that antibiotics, particularly Cipro with or without metronidazole, control ulcerative colitis and Crohn’s disease. Although many doctors disagree, I treat Crohn’s disease with Cipro 500-mg twice a day continuously and metronidazole 250-mg four times a day on alternate weeks and check liver tests monthly. I tell patients to stop the metronidazole if they feel any strange nerve sensations.

Stomach Problems 

	If you have belching, burping, a sour taste in your mouth, mouth odor, a white-coated tongue or a burning pain in your stomach or chest that gets worse when you are hungry and better when you eat, you probably have too much stomach acid. Doctors may say you have ulcers, esophagitis, gastritis, duodenitis, achalasia, chalazia, hiatal hernia or reflux. These terms mean that stomach acid is burning your gastrointestinal tract. Most people who have these symptoms have an infection with a bacteria called helicobactor pylori.
	If you have these symptoms, you need blood tests to see if you have helicobactor and a special x-ray called an upper GI series to rule out a cancer. Since there are several bacteria that cause stomach cancers ulcers, a negative blood test does not rule out an infection. I usually treat all people with gastritis symptoms with a one-week course of antibiotics: metronidazole four times a day, clarithromycin 500-mg twice a day and omeperazole 20-mg once a day for one week. At least 12 weeks later, you need a follow up blood test for helicobactor. If your symptoms are gone and the titre drops, you are probably cured. If your helicobactor titre is still high, your helicobactor is probably resistant to metronidazole and your need to be treated for at least ten days with amoxacillin 500-mg four times a day, tetracycline 500-mg three times a day and omeperazole 20-mg once a day. If you have regurgitation of stomach acid into your esophagus (reflux, hiatal hernia), you may need to be treated with 20-mg omeperazole once a day and 10-mg cisapride four times a day. Virtually all physicians have now accepted the infectious causes of stomach problems. Only the manufacturers of over-the-counter remedies still try to make you believe that stomach pain is caused by stress.

Infertility   

	Recent reports from the University of Maryland and Germany show that before you consult an infertility doctor to help you become pregnant, you should take antibiotics to treat a possible hidden infection. Many other studies show that the most common cause of infertility is a uterine infection. Of women being evaluated for infertility, 40 percent are infected with chlamydia, mycoplasma or ureaplasma, as are 36 percent of those with a previous history of uterine infection and 50 percent of those with tubule blockage. More than 60 percent had evidence of a past infection. The more partners you have, the more likely you are to be infected, although you can be infected by one contact. An infection can prevent pregnancy by blocking the uterine tubes. It can damage sperm so that they can’t swim toward the egg, and it can cause abortions, premature birth and low birth weight. Infected people may have burning on urination, discomfort when the bladder is full, or an urgency to void. Women may have only spotting between periods. Men and women can be infected with mycoplasma or ureaplasma, even though all available tests can’t find them and they may have no symptoms at all. A dipstick urine test may diagnose the infection. Semen from 91 percent of infertile men contain contains types of bacteria that grow without oxygen. Before infertile couples spend between $10,000 and $150,000 for infertility evaluations and treatments, they should ask their gynecologist to treat them with the newer erythromycins, Zithromax (250-mg once a day for eight days) or Biaxin (500-mg BID for 10 days), for chlamydia and mycoplasma infections. 
	Other tests for evaluation of infertility: Female: FSH (menopause), TSH (thyroid disease), Prolactin (brain tumor), Progesterone (7 days after expected ovulation, around 21 days after start of menstruation), HSG (to check if uterine tubes are open). If masculinization: testosterone, DHEAS, 17-oh progesterone, sonogram of ovaries. Male: semen analysis.

You Should Be Afraid to Have Casual Sex!

	If you have unprotected sex with a person who is having sex with someone else, you are at extraordinarily high risk for getting venereal diseases that can make you sick and even kill you. A report from Johns Hopkins shows that 25 percent of girls between 12 and 19 who show up at school based and sexually transmitted disease clinics are infected with chlamydia, a venereal disease that cause infertility, terrible pelvic infections, horrible urinary symptoms, joint pains, a sore throat, a cough, heart attacks and even death. Other studies show that 50 percent of young people with more than three sexual partners a year have sexually transmissible diseases and 40 percent of sexually active adolescent females in a large American city have chlamydia and or gonorrhea. 
	If you have discomfort when your bladder is full, get up in the middle of the night to urinate, have spotting between periods, feel like there is a hair in your urinary tube or have unexplained pelvic pain, you may have a venereal disease that can be cured with antibiotics. You should get urine and vaginal cultures and tests for venereal diseases. Even if none is found, if you are sexually active and have symptoms, both you and your partner still should be treated with the newer erythromycins or tetracyclines for several weeks. If you still have symptoms, you need a thorough evaluation.
	The most common causes of burning on urination in young men are venereal diseases caused by mycoplasma, chlamydia and ureaplasma. If you are a man who has burning on urination, a feeling that you have to urinate all the time, a sense of urgency to urinate when your bladder is full and have to get up frequently in the middle of the night to urinate, you probably have an infection. Your doctor may do urethral smear for chlamydia and gonorrhea, but negative tests do not rule out these infections. Bladder infections rarely occur in men, but your doctor can order a urinalysis and urine culture. If the culture grows out a bacterium, you should be treated with the appropriate antibiotic. If, as expected, no germ grows from the culture and your urine has a positive nitrite or leukocyte esterase test, the odds are overwhelming that you have a mycoplasma, chlamydia or ureaplasma infection and you and your partner should be treated with azithromycin 500-mg the first day and 250-mg each day for the next 7 days, or doxycycline 100-mg twice a day for several weeks.
	If that doesn’t cure you, you are in big trouble. Your doctor may order a semen culture, but semen cultures can grow germs that are not causing your symptoms, but it may be the only clue you have. Prostate infections can be extraordinarily difficult to cure so you may have to be treated with injections of very high doses of antibiotics or with antibiotic pills for several months. Your doctor may also check you for other causes of urinary symptoms such as prostate and bladder cancer.

Yeast Infections

	Some yeasts cause vaginal itching and discharge, particularly after a woman takes antibiotics or birth control pills. A doctor diagnoses yeast by inserting a cotton swab into the vagina, placing it in a drop of water and examining the fluid for yeast under a microscope. Cultures should not be used to diagnose yeast as most healthy women harbor harmless yeast in their vaginas, mouths and intestines.
	Yeast infections often follow taking antibiotics or birth control pills, but when yeast cause a rash on the genitals, it is often acquired through heterosexual contact or it can be caused by immune defects associated with diabetes or HIV. When normal healthy people develop rashes caused by yeast, doctors should look for a cause. Genital infections caused by yeast are often associated with a special type of yeast that is able to break through the skin to cause a red, itchy rash. Men and women with genital rashes caused by yeast usually have several sexual partners and therefore, are at increased risk for picking up this special yeast through sexual contact.  Since yeast is a normal inhabitant in the vagina, it is often diagnosed as the cause of vaginal itching when it is only an innocent bystander. When a physician takes cultures for many different types of infections and finds only a yeast, he usually prescribes suppositories (over–the-counter clotrimazole vaginal suppository, once a day for three days) to kill yeast and the patient feels better for a week or so because the suppository lubricates the irritated area. Then the itching returns because these women often are infected with mycoplasma, which is extraordinarily difficult to find on culture. They can be cured when they and their partners take azithromycin (250-mg once a day for 9days) to kill the mycoplasma. If a woman really has a vaginal yeast infection, she usually clears up with a pill called fluconazole (150-mg/day for 4 days).

Doxycycline, Minocycline and Tetracycline

	Many doctors have asked why I treat some of my patients with acne, arthritis, chronic fatigue syndrome, and late on-set asthma with antibiotic, doxycycline, when minocycline is probably more effective. Doxycycline is a fairly safe drug, although it can cause a sore throat, sunlight sensitivity, pigmentation and abnormal liver tests. It causes sore throat and heartburn when it gets stuck in your esophagus, so take it with large amounts of water to wash it down to your stomach. To prevent sunburn, avoid excessive exposure to the sun. Minocycline is fairly safe, but it can cause more serious serum sickness-like reaction, hypersensitivity syndrome reaction, and drug-induced lupus: characterized by fever, joint pain, a rash, a feeling of being sick, hives itching and severe pain. Other reported side effects include dark colored eyeballs, and liver damage.
	Minocycline is more effective than doxycycline because it achieves much higher concentrations in the tissues where it does work in reducing swelling, killing germs, and stopping pain. Although minocycline and doxycycline are in the same class of antibiotics as tetracycline, we rarely use tetracycline because it does not achieve high tissue concentrations. Doxycycline achieves much higher tissue concentrations than tetracycline, while minocycline penetrates tissue far more effectively than doxycycline.