Page 814 - Basic _ Clinical Pharmacology ( PDFDrive )

800 SECTION VIII Chemotherapeutic Drugs

TABLE 43–1 Guidelines for dosing of some commonly used penicillins.

Adjusted Dose as a Percentage of
Normal Dose for Renal Failure Based
on Creatinine Clearance (Cl cr )

Antibiotic (Route of Clcr Approx Clcr Approx
Administration) Adult Dose Pediatric Dose 1 Neonatal Dose 2 50 mL/min 10 mL/min
Penicillins
6
Penicillin G (IV) 1–4 × 10 units 25,000–400,000 units/kg/d 75,000–150,000 units/ 50–75% 25%
q4–6h in 4–6 doses kg/d in 2 or 3 doses
Penicillin V (PO) 0.25–0.5 g qid 25–75 mg/kg/d in 4 doses None None
Antistaphylococcal penicillins
Cloxacillin, 0.25–0.5 g qid 15–25 mg/kg/d in 4 doses 100% 100%
dicloxacillin (PO)
Nafcillin (IV) 1–2 g q4–6h 100–200 mg/kg/d in 50–75 mg/kg/d in 100% 100%
4–6 doses 2 or 3 doses
Oxacillin (IV) 1–2 g q4–6h 50–100 mg/kg/d in 50–75 mg/kg/d in 100% 100%
4–6 doses 2 or 3 doses
Extended-spectrum penicillins
Amoxicillin (PO) 0.25–0.5 g tid 20–40 mg/kg/d in 3 doses 66% 33%
Amoxicillin/potassium 500/125 mg tid– 20–40 mg/kg/d in 3 doses 66% 33%
clavulanate (PO) 875/125 mg bid
Piperacillin/ 3.375–4.5 g q4–6h 300 mg/kg/d in 4–6 doses 3 150 mg/kg/d in 50–75% 25–33%
tazobactam (IV) 2 doses 3
1
The total dose should not exceed the adult dose.
2 The dose shown is during the first week of life. The daily dose should be increased by approximately 33–50% after the first week of life. The lower dosage range should be used
for neonates weighing less than 2 kg. After the first month of life, pediatric doses may be used.
3 Dose is based on piperacillin component.

Clinical Uses Penicillin V, the oral form of penicillin, is indicated only in
minor infections because of its relatively poor bioavailability, the
Except for amoxicillin, oral penicillins should be given 1–2 hours need for dosing four times a day, and its narrow antibacterial spec-
before or after a meal; they should not be given with food to mini- trum. Amoxicillin (see below) is often used instead.
mize binding to food proteins and acid inactivation. Amoxicillin Benzathine penicillin and procaine penicillin G for intra-
may be given without regard to meals. Blood levels of all penicil- muscular injection yield low but prolonged drug levels. A single
lins can be raised by simultaneous administration of probenecid, intramuscular injection of benzathine penicillin, 1.2 million units,
0.5 g (10 mg/kg in children) every 6 hours orally, which impairs is effective treatment for β-hemolytic streptococcal pharyngitis.
renal tubular secretion of weak acids such as β-lactam compounds. Given intramuscularly once every 3–4 weeks, it prevents reinfec-
Penicillins, like all antibacterial antibiotics, should never be used tion. Benzathine penicillin G, 2.4 million units intramuscularly
for viral infections and should be prescribed only when there is once a week for 1–3 weeks, is effective in the treatment of syphilis.
reasonable suspicion of, or documented infection with, susceptible Procaine penicillin G was once a commonly used treatment for
organisms.
pneumococcal pneumonia and gonorrhea; however, it is rarely
used now because many gonococcal strains are penicillin-resistant,
A. Penicillin and many pneumococci require higher doses of penicillin G or the
Penicillin G is a drug of choice for infections caused by strep- use of more potent β-lactams.
tococci, meningococci, some enterococci, penicillin-susceptible
pneumococci, staphylococci confirmed to be non-β-lactamase-
producing, Treponema pallidum and certain other spirochetes, B. Penicillins Resistant to Staphylococcal Beta-
some Clostridium species, Actinomyces and certain other Gram- Lactamase (Methicillin, Nafcillin, and Isoxazolyl Penicillins)
positive rods, and non-β-lactamase-producing Gram-negative These semisynthetic penicillins are indicated for infections caused
anaerobic organisms. Depending on the organism, the site, and by β-lactamase-producing staphylococci, although penicillin-
the severity of infection, effective doses range between 4 and susceptible strains of streptococci and pneumococci are also sus-
24 million units per day administered intravenously in four to ceptible to these agents. Listeria monocytogenes, enterococci, and
six divided doses. High-dose penicillin G can also be given as a methicillin-resistant strains of staphylococci are resistant. In recent
continuous intravenous infusion. years the empirical use of these drugs has decreased substantially