Doryx MPC (doxycycline)

Doxycycline is a tetracycline antibiotic, usually taken by mouth, that the CDC lists among the antibiotics that work against Bartonella bacteria^[4][5]. The only Bartonella use on the doxycycline FDA label is bartonellosis caused by Bartonella bacilliformis, a South American infection spread by sand flies^[8][6]. Doxycycline use for other Bartonella infections such as cat scratch disease or Bartonella endocarditis is off-label, meaning the FDA has not approved it for them^[8]. For Bartonella endocarditis, a 2025 American Heart Association statement prefers doxycycline 100mg every 12 hours for 12 weeks combined with rifampin for 6 weeks^[9]. Cat scratch disease usually clears up on its own, but the CDC says severe cases and people with weakened immune systems should get antibiotics^[4]. Lyme-literate physicians, many trained through ILADS, also treat what they describe as persistent Bartonella infection alongside Lyme disease^[1]. Richard Horowitz and colleagues have published case series of multi-drug combinations that can include doxycycline, rifampin and azithromycin, based on chart reviews rather than randomized trials^[1].

Doxycycline stops bacteria from making the proteins they need by binding to a part of the bacterial ribosome called the 30S subunit^[8]. Doxycycline slows bacterial growth rather than killing bacteria outright, which the label calls bacteriostatic activity^[8]. Bartonella bacteria grow slowly, and for serious infections the CDC notes that more than 1 antibiotic is often used together^[5][4][6]. Columbia University's Lyme center notes that case reports from one research group suggest some Bartonella species may cause a chronic bloodstream infection lasting months to years^[2].

Doxycycline does not carry a boxed warning^[8]. Stomach and gut effects such as nausea, vomiting and diarrhea can occur^[8]. Throat irritation and ulcers have been reported, mostly in people who took the pills right before going to bed^[8]. Doxycycline can cause an exaggerated sunburn reaction, so the label advises limiting sun exposure^[8]. Taking doxycycline during the second half of pregnancy or in childhood up to age 8 can permanently stain teeth yellow-gray-brown^[8]. Clostridioides difficile diarrhea can range from mild to fatal colitis and has been reported more than 2 months after antibiotics end^[8]. Severe skin reactions such as Stevens-Johnson syndrome and DRESS have been reported, and the label says doxycycline is stopped right away if one occurs^[8]. Raised pressure inside the skull can cause headache, blurred or double vision and vision loss, and overweight women of childbearing age are at higher risk^[8]. Overgrowth of yeast or other resistant germs can occur^[8]. For long-term therapy, the label advises periodic blood counts plus kidney and liver tests^[8]. The label says doxycycline should not be used by people who have had an allergic reaction to any tetracycline^[8].

The FDA label gives general adult and child doses rather than a Bartonella-specific schedule, and Doryx MPC is dosed differently from other doxycycline products^[8]. For Bartonella endocarditis, the 2025 AHA statement lists doxycycline 100mg by mouth every 12 hours for 12 weeks, combined with rifampin for 6 weeks^[9]. Azithromycin can take the place of doxycycline in that AHA regimen^[9]. The AHA statement says gentamicin also works against Bartonella but is not preferred because of a higher risk of a type of kidney inflammation called glomerulonephritis^[9]. For other Bartonella infections, the CDC does not give a set dose and recommends consulting an infectious disease specialist^[5][6]. Doxycycline is swallowed with plenty of fluid to lower the risk of throat irritation and ulcers, and it can be taken with food or milk if it upsets the stomach^[8]. In children 8 years and younger, the label limits doxycycline to severe or life-threatening conditions where benefits outweigh the risk of permanent tooth staining^[8].

Yes, Doxycycline (Doryx MPC) is FDA approved (1967) for the treatment of Bartonellosis.