This post is about antibiotic toxicities from A to Z!
Authored by: Timothy P. Gauthier, Pharm.D., BCPS, BCIDP
Posted 9 June 2022
This article identifies an antibiotic toxicity for every letter in the alphabet. It does not list every antibiotic side effect. It is meant to highlight that antibiotic use does not come without risk. Use antibiotics with caution and only when indicated. Do not share antibiotics. Only use antibiotics under the direction of a licensed medical professional.
Be the first to use an antibiotic and you risk toxicity. Be the last to use an antibiotic and you risk efficacy.
A is for arrhythmia
B is for bronchospasm
Inhaled antibiotics can cause bronchospasm. For example, inhaled tobramycin. 
C is for C difficile associated diarrhea (CDAD)
D is for dysgeusia
E is for eosinophilic pneumonia and electrolyte abnormalities
F is for foamy urine
G is for glycemic changes
Fluoroquinolones can cause hypoglycemia and hyperglycemia. 
H is for hypersensitivity reaction
Almost all antibiotics can cause hypersensitivity reactions. Did you know that about 10% of patients in the United States report a penicillin allergy, but less than 1% of people are actually penicillin allergic!?! 
I is for infusion reactions
Several antibiotics can cause infusion-related reactions. One example is vancomycin infusion reaction (formerly referred to as “red man” or “red neck” syndrome) which happens when vancomycin is infused too fast causing histamine release. 
J is for Joint Pain
Usage of sulphonamides and trimethoprim, is associated with a 70% increased risk of rheumatoid arthritis flare at 1–3 months, which can cause significant joint pain. 
K is for kernicterus
L is for liver enzyme elevation
Penicillinase-resistant penicillin oxacillin may be a go-to IV antibiotic for some MSSA infections, but it is also notorious for causing liver enzyme elevation. I found an article from 1973 that talks about it. We’ve been dealing with oxacillin liver issues for over 50 years!  Numerous other antibiotics can do this as well. Trovafloxacin (a fluoroquinolone antibiotic) was even removed from the market for causing liver injury! 
M is for mental health side effects
Mental health side effects of fluoroquinolones include disturbances in attention, disorientation, agitation, nervousness, memory impairment, and serious disturbances in mental abilities called delirium.  The label on systemic fluoroquinolones also includes suicide as a warning as part of the potential central nervous effects. 
N is for nephrotoxicity and neurotoxicity
O is for optic neuropathy and ototoxicity
Aminoglycosides are known to cause ototoxicity and can additionally cause balance problems. 
P is for pulmonary fibrosis and pancreatitis
Q is for QTc prolongation
R is for rhabdomyolysis
S is for Steven Johnsons Syndrome (SJS) and seizures
SJS is a horribly unfortunate disease in which to put it simply, skin peels off the body. Many antibiotics have been flagged for causing SJS, including sulfonamides, aminopenicllins (most common antibiotic cause), fluoroquinolones, tetracyclines, macrolides, cephalosporins, and metronidazole. 
Carbapenems have been implicated in causing seizures. 
T is for tendon rupture, thrombocytopenia, and toxic epidermal necrolysis (TEN)
Fluoroquinolones have a FDA boxed warning for tendon rupture. 
TEN is a worse form of SJS and many antibiotics can cause it. 
U is for uveitis and urine discoloration
Fluoroquinolone antibiotics have been associated with uveitis, but maybe they are really just associated systemic illnesses. 
V is for vomiting
Virtually all antibiotics can cause vomiting and nausea, but tigecycline deserves particular note as it caused nausea and vomiting in 30% of older male patients in phase 3 clinical trials.  Tolerability is a major issue for tigecycline.
W is for weakness
Aminoglycoside antibiotics, when given to patients with neurological conditions such as myasthenia gravis or Lambert Eaton myasthenic syndrome, can worsen neuromuscular weakness. 
X is for xerostomia
Y is for yellowing of the eyes and skin
Z is for zygote toxicity
A zygotę is another name for a fertilized egg. I must admit nobody says “zygote toxicity” in the medical world, but fetal toxicity is legit and needs to be in here somewhere. There are a number of antibiotics that can cause fetal harm, including fluoroquinolones and tetracyclines 
Did you notice fluoroquinolones were mentioned 11 times!?! While they still have a role for some infectious diseases – proceed with caution!!
With all of these potential antibiotic toxicities (and many more not listed here), it certainly should give us all pause to truly consider whether antibiotics are indicated and worth the risk, before taking/ prescribing/ continuing them.
Indeed antibiotics are a miracle of modern medicine and can save lives when given to the right patients. However, their benefits must be balanced against their risks and the threat of antibiotic resistance.
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Disclaimer: The opinions and perspectives presented in this article are that of the author and do not necessarily represent the position or policy of any former, current, or potential future employer.
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