Infectious Disease Compendium

Penicillin G


CrCl Formula

CrCl > 80: 500-4 million units IV q 4 - 6 h.

CrCl 80-50: normal dose.

CrCl 50-10: 75% of dose.

CrCl < 10: 20-50% of dose.

Hemodialysis: 20-50% of dose.

Peritoneal dialysis: 20-50% of dose.

Obesity dosing

Important side effects

Seizures if you are dumb enough not to dose for CrCl. Immune mediated cytopenias, allergic reactions, eosinophilia, hemolytic anemia, hyperkalemia, interstitial nephritis, seizures.

Important drug interactions

Chloramphenicol, cholestyramine, ethinyl estradiol, mestranol, methotrexate, norelgestromin, norethindrone, norgestrel.

Rants and Screeds

When alternative antibiotics are given instead of a penicillin because of some usually half-assed allergy, outcomes are worse and poste-op infections increase. Most patients who think they are allergic to penicillin are not (from):

Only 10% to 20% of patients reporting a history of penicillin allergy are truly allergic when assessed by skin testing. Taking a detailed history of a patient's reaction to penicillin may allow clinicians to exclude true penicillin allergy, allowing these patients to receive penicillin. Patients with a concerning history of type I penicillin allergy who have a compelling need for a drug containing penicillin should undergo skin testing. Virtually all patients with a negative skin test result can take penicillin without serious sequelae.

And in the old days it was contamination that led to the allergic reactions as well as penicillin break down products. I cannot find data to suggest if Type 1 antibiotic allergies fade with time. How often does penicillin allergy cross react with ampicillin? Reasonably often, but not always:

Thirty subjects with a history of allergic reactions to penicillins were studied. In vivo and in vitro specific IgE antibodies were determined to different penicillin determinants. Fifteen subjects developed anaphylactic responses and the remainder urticaria and angioedema. The drug most frequently involved in the patients' allergic reactions was ampicillin (AMP). The benzylpenicilloyl (BPO) skin test was positive in 16 (53.3%) patients, whereas 23 (76.6%) patients were positive to minor determinant mixture (MDM), benzylpenicillin (PG), AMP, or amoxicillin. (AX).

And as best I can tell, there are (understandably) no clinical trials giving ampicillin to penicillin Type 1 allergic patients.

I also put the code cart in the room. My only superstition: put the emergency equipment in the patients room and you will never have to use it.

BTW: in the era of home antibiotic infusion, be aware of the spouses allergy history: We present a case of an immediate allergic reaction in a penicillin-sensitive spouse of a patient receiving parenteral mezlocillin sodium therapy. A seminal level of 42 μg/mL of mezlocillin was documented by bioassay.

Here is a nice bit of penicillin history: (PubMed). Read it instead of looking at your Facebook page next time you are on the toilet.

Treatment of choice for

Actinomycosis, Streptococci, Syphilis

Use for

Actinomyces, anaerobic infections, Anthrax, Aphthous ulcers, Bronchitis, Cellulitis, Clostridium infections, Diptheria - prevention of carrier state, Bites, animal, Empyema, Endocarditis, Endophthalmitis - bacterial, Enterococcus, Fusobacterium infections, Gonorrhea, Lactobacillus casei, Leptospira infections, Listeria monocytogenes, Lyme Disease, Meningitis, Neisseria meningiditis meningitis, Moraxella catarrhalis, Neisseria, Osteomyelitis, Pasteurella infections, Pharyngitis - streptococcal, Streptococcus pneumoniae infections, Pneumonia, Rat Bite Fever, Rheumatic Fever prophylaxis, scarlet fever, Spirillum minor, Streptobacillus moniliformis, Streptococci, surgical prophylaxis, Sydenham's chorea, Syphilis, umbilical cord infection, Whipples disease, wound infection prophylaxis, Yaws.


Hmmmm. I wonder.