Sulfa and G6PD deficiency.
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X-linked enzyme disorder more common in some Mediterranean, African, Middle Eastern, and South/Southeast Asian populations. Affected people can develop haemolytic anaemia under oxidative stress. Within the sulfa family, dapsone is the real risk, and pre-prescription G6PD testing before it is standard. Sulfamethoxazole, sulfadiazine and sulfasalazine are classified as low-to-no risk by current pharmacogenomic guidance, despite decades of teaching to the contrary.
Educational reference — not medical advice. This page describes what is generally known about a drug family. It cannot account for your history, your other medicines, or your circumstances. Decisions about your own treatment belong with your doctor or pharmacist.
- Inheritance
- X-linked. Most severely affected are male, but X-inactivation means heterozygous women span the range from normal to fully deficient. How the enzyme defect works.
- Higher prevalence
- Mediterranean, African, Middle Eastern, South/Southeast Asian populations.
- Testing first
- Required before tafenoquine, primaquine and
rasburicase; standard beforedapsone. Not recommended before TMP-SMX by any guideline. - Commonest triggers
- Fava beans and infection account for the overwhelming majority of severe episodes — medication for very few.
Where G6PD comes up clinically
For sulfa-family drugs, G6PD considerations matter most prominently in these scenarios:
Before starting dapsone. Dapsone is among the highest-risk drugs for hemolysis in G6PD deficiency. Pre-prescription testing is standard in many settings, particularly when long-term use is planned (leprosy, dermatitis herpetiformis, PCP prophylaxis as an alternative to TMP-SMX).
Before starting sulfasalazine in patients from higher-prevalence populations or with a relevant family history. The risk is real but lower than with dapsone.
In patients with active hemolysis on a sulfa antibiotic. Unexpected anemia, jaundice, dark urine, or back pain on TMP-SMX may be drug-induced hemolysis in a previously undiagnosed G6PD-deficient patient. The drug is stopped and supportive care given.
In neonates from higher-prevalence populations. Newborn screening for G6PD deficiency is performed in some countries; identified infants are managed accordingly.
Geographic and ethnic prevalence
G6PD deficiency is one of the most common enzyme disorders in humans — hundreds of millions of people worldwide carry a deficient variant. Prevalence is notably higher in regions with historical malaria endemicity. The protective effect of partial G6PD deficiency against malaria is the leading evolutionary explanation for the high carrier rates in those populations.
Different geographic regions are associated with different G6PD variants, with different clinical severity. The Mediterranean variant tends to produce more severe hemolysis on triggering than the African (A−) variant. The clinical implications are important: a patient labelled "G6PD-deficient" without further information is in a heterogeneous group, and the specific variant matters when dapsone or another higher-risk drug is being considered.
Practical implications for sulfa prescribing
For patients with known G6PD deficiency:
Avoid dapsone where possible. If dapsone is the only suitable option (some specific dermatologic conditions, leprosy regimens), use is at specialist discretion with close hematologic monitoring.
Sulfasalazine and the sulfa antibiotics do not require the same caution. Current guidance rates sulfamethoxazole, sulfadiazine and sulfasalazine as low-to-no risk, on the grounds that the evidence linking them to haemolysis is weak and heavily confounded — typically by the infection being treated, which is itself one of the commonest triggers of haemolysis in G6PD deficiency. No guideline recommends G6PD testing before prescribing TMP-SMX. Haemolysis remains dose-related, so a high-dose or prolonged course warrants more attention than a short course for a urinary infection. The evidence behind this shift.
Watch the substitution. Nitrofurantoin, the usual alternative to TMP-SMX for urinary infection, carries a higher G6PD risk rating than TMP-SMX does. Switching away from a sulfa antibiotic on G6PD grounds can land the patient on something less safe.
The non-antibiotic sulfonamides (furosemide, HCTZ, celecoxib, sulfonylureas, acetazolamide) are not generally G6PD-related concerns in routine practice.
dapsone — particularly in anyone from a higher-prevalence population, or where status is unknown — is widely recommended, and it is required before tafenoquine, primaquine and rasburicase. Don't assume it has been done; ask. It is not a prerequisite for a course of TMP-SMX. More on the hemolysis mechanism.
What hemolysis looks like
Drug-induced hemolysis in G6PD deficiency typically begins one to three days after starting the drug. Symptoms can include pallor, fatigue, jaundice, dark urine, back or abdominal pain, breathing difficulty in severe cases. Laboratory findings include anemia, raised reticulocytes, raised indirect bilirubin, low haptoglobin, and (sometimes) hemoglobinuria. Severity ranges from self-limiting to life-threatening.
If hemolysis is suspected, the offending drug is stopped, and supportive care (hydration, monitoring, transfusion in severe cases) is provided. Diagnosis of G6PD deficiency is confirmed once the patient has recovered — measurement during acute hemolysis can give falsely normal results because the deficient older red cells have already been destroyed and the remaining younger cells have higher enzyme activity.
Family and population considerations
G6PD deficiency is heritable. After a new diagnosis, family screening — particularly for boys and for relatives planning pregnancy — may be appropriate. Newborn screening programs exist in some countries with higher prevalence. Patients with G6PD deficiency should be aware of:
Drugs to avoid where possible: dapsone, primaquine, rasburicase, certain antimalarials, methylene blue, and others. Foods and exposures: fava beans (favism — sometimes severe in some variants), naphthalene exposure (mothballs), some commercially used dyes.
Carry the information. A clear medical record entry, and in some cases a wearable allergy alert or medical bracelet, helps in unfamiliar care settings (emergency rooms, foreign travel, after major surgery). Medical ID and bracelets covers this.