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A Bacterial Infectio
Causative organisms
MAC is comprised of two predominant species, M. avium
and M. intracellulare.
Symptoms of active infection
Most patients with AIDS and MAC disease have disseminated
multiorgan involvement. Most frequently described symptoms
are fever, night sweats, weight loss, wasting, fatigue,
diarrhoea and abdominal pain. Common physical findings
include hepatomegaly or splenomegaly. Intraabdominal
lymphadenopathy may be demonstrated by radiographic
imaging procedures. Laboratory abnormalities include
anaemia and an elevated alkaline phosphatase.
Diagnosis
Diagnosis of disseminated MAC disease is generally based
on recovery of MAC in culture of blood or bone marrow.
A positive AFB smear of blood, tissue or secretions
is non-specific.
Treatment
Patients with AIDS and disseminated MAC disease have
reduced survival compared with those who do not have
disseminated MAC disease; appropriate treatment improves
survival (Ives et al AIDS 1995; 9: 261). Patients with
AIDS and MAC bacteremia or disseminated MAC disease
should be treated with a multiple-drug regimen consisting
of 2 or more drugs known to be active against MAC to
delay or prevent the emergence of resistance (Masur
N Engl J Med 1993; 329: 898). Most patients require
2 to 8 weeks of treatment before a substantial reduction
in clinical symptoms can be demonstrated.
Oral clarithromycin, 500 mg b.i.d. forms the cornerstone
of multiple-drug regimens for the treatment of MAC disease.
Ethambutol 15 mg/kg/day has been widely recommended
as a second drug. A third or fourth drug selected from
among rifabutin 300 mg o.d., ciprofloxacin 500-750 mg
b.i.d. or parenteral amikacin 10-15 mg/kg/day may be
added for patients with more severe or extensive symptoms
or disease. Initiation of potent antiretroviral therapy
dramatically improves outcome.
Prophylaxis
Secondary prophylaxis
Patients who have been treated for disseminated MAC
should continue to receive full therapeutic doses of
antimycobacterial agents for life.
Primary prophylaxis
All adults with HIV infection should receive primary
prophylaxis for disseminated MAC once their CD4 count
drops below 50 cells/ l. Before initiating prophylaxis,
active MAC disease should be ruled out. The preferred
regime is azithromycin 1200 mg/wk or clarithromycin
500 mg b.i.d. An alternative is rifabutin 300 mg/day.
Drug interactions
Clarithromycin
Avoid terfenadine and astemizole
Rifampin
Concomitant use of rifampin and protease inhibitors
is contraindicated.
Rifabutin
Clarithromycin and fluconazole increase concentrations
of rifabutin, increasing the risk of developing rifabutin-associated
uveitis. Concomitant use of rifabutin and delavirdine
is contraindicated. If rifabutin is used in conjunction
with indinavir, nelfinavir or amprenavir, a dose of
150 mg o.d. should be used.
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