C H A P T E R 9
Antibiotics
109
of the cell wall, and the bacteria with weakened cell
walls swell and then burst from osmotic pressure within
the cell. Because human cells do not use the biochemical
process that the bacteria use to form the cell wall, this
effect is a selective toxicity.
The penicillins are indicated for the treatment of
streptococcal infections, including pharyngitis, ton-
sillitis, scarlet fever and endocarditis; pneumococcal
infections; staphylococcal infections; fusospirochetal
infections; rat-bite fever; diphtheria; anthrax; syphilis;
and uncomplicated gonococcal infections. At high
doses, these drugs are also used to treat meningococcal
meningitis. See Table 9.5 for usual indications for each
agent.
Pharmacokinetics
Most of the penicillins are rapidly absorbed from the
GI tract, reaching peak levels in 1 hour. They are sensi-
tive to the gastric acid levels in the stomach and should
TABLE 9.5
DRUGS IN FOCUS Penicillins and penicillinase-resistant antibiotics
Drug name
Dosage/route
Usual indications
Penicillins
benzathine penicillin
(Bicillin)
675 mg–1.8 g IM
Mild to moderate URTI, streptococcal
infections, syphilis, rheumatic fever
benzylpenicillin (BenPen)
Adult and paediatric >10 years: 300 mg IM or
IV q 6 hours
Paediatric 3–10 years: 150–300 mg IM or IV q
6 hours
Paediatric: <3 years: 60 mg IM or IV q 6 hours
Treatment of infections caused by
sensitive organisms; treatment of syphilis,
prevention of bacterial endocarditis, wound
infection and sepsis
dicloxacillin (Diclocil,
Distaph)
Adult: 250–500 mg IV or 250 mg PO q 6 hours
Paediatric: 25–50 mg/kg/day IV q 6 hours
Severe staphylococcal and other
gram-positive coccal infections; skin
and wound infections, pneumonia,
osteomyelitis
flucloxacillin (Flopen,
Staphylex)
Adult: 250 mg PO of IV q 6 hours
Treatment of staphylococcal or other gram-
positive coccal infection; pneumonia,
osteomyelitis skin and wound infection
phenoxymethylpenicillin
benzathine (Abbocillin,
Cilicaine V )
Adult: 250–500 mg PO q 4–6 hours
Paediatric: 15–50 mg/kg/day in 3–6 divided
doses
Treatment of mild to moderate infections
due to sensitive organisms
phenoxymethylpenicillin
potassium (Abbocillin
VK, Cilicaine VK)
Adult: 250–500 mg PO q 4–6 hours
Treatment of mild to moderate infections
due to sensitive organisms
procaine penicillin
(Cilicaine)
Adult: 1.5 g/day IM for 2–5 days
Moderately severe infections due to
organisms sensitive to penicillin
Broad-spectrum penicillins
amoxycillin (Amoxil,
Augmentin, Cilamox)
Adult: 250–500 mg PO q 8 hours
Paediatric: 20 mg/kg/day PO in divided doses
q 8 hours
Broad spectrum of uses for adults and
children
ampicillin (Amicyn,
Ibimicyn)
Adult: 250–500 mg IM or IV q 6 hours, then
500 mg PO q 6 hours when oral use is
feasible
Paediatric: 60 mg/kg/day IM or IV in 4–6
divided doses, then 250 mg PO q 6 hours
Broad spectrum of activity; useful form
if switch from parenteral to oral is
anticipated; monitor for nephritis
piperacillin (Tazocin,
Tazopip)
Adult and paediatric >12 years: 4 g IV q 8 hours
Paediatric <12 years: 100 mg/kg IV q 8 hours
Treatment of serious bacterial infections
caused by sensitive organisms; lower
respiratory tract infection, skin and
intra-abdominal infection, bacterial
septicaemia, gynaecological infection
ticarcillin (Timentin)
Adult: 1 g IM or direct IV q 6 hours; reduce
dose with renal impairment
Paediatric: 50–100 mg/kg/day IM or direct IV
q 6–8 hours
Severe infections caused by susceptible
bacteria
