Questions from practice: G6PD deficiency
QuestionsMy teenage son is at home in bed with a cold and cough. He has G6PD deficiency. I know he can’t take aspirin but can he take these Actifed tablets (pseudoephedrine and triprolidine)?
A Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymatic defect to occur in humans, affecting around 400 million people worldwide. G6PD plays an important role in the protection of cells from oxidative stress, through generating NADPH (nicotinamide adenine dinucleotide phosphate) in the pentose phosphate pathway.
Deficiency of the enzyme leaves red blood cells unprotected from sources of oxidative stress, including infection, certain drugs and some foods (typically broad beans). The most common clinical presentations of G6PD deficiency are acute haemolytic anaemia and neonatal jaundice.
G6PD deficiency is most common among people whose ethnic origins are African, Middle Eastern, Asian, Oceanian or Mediterranean. This pattern has some similarities to the distribution of malaria and led to the hypothesis that G6PD deficiency confers some protection against this disease.
Despite migration, many countries in these areas continue to have the highest prevalence of G6PD deficiency (eg, the World Health Organisation reports rates in Egypt and Nigeria as about 20 per cent).
G6PD deficiency is an X-linked hereditary disease, in which there are mutations in the gene encoding the enzyme, and the condition is classified by the WHO according to enzyme activity levels as follows:
Class I Severely G6PD deficient, associated with chronic non-spherocytic haemolytic anaemia
Class II Severely G6PD deficient (1–10 per cent activity), associated with acute haemolytic anaemia
Class III Moderately G6PD deficient (10–60 per cent activity)
Class IV Normal activity (60–150 per cent)
Class V Increased activity (>150 per cent)
Most people with G6PD deficiency are asymptomatic throughout life. Of those who are symptomatic most are male.
Management focuses on avoiding triggers for haemolysis, in particular drugs. Examples of drugs available in the UK linked with G6PD deficiency mediated haemolysis include:
- ascorbic acid
- methylthioninium chloride
- vitamin K analogues
Although some drugs are consistently reported as being problematic (eg, nitrofurantoin), for others the information is inconsistent and, in some cases, contradictory. This probably reflects the fact that a drug that is safe in one patient with G6PD deficiency may not be safe in another and explains the lack of guidance on which drugs may be safely used.
Many of the drugs listed above are rarely used or are second- or third-line choices. Nonetheless, there may be situations where they are the only option (eg, a fluoroquinolone in a resistant infection).
In such circumstances treatment decisions should be based on assessment of clinical risk and on considerations that the hazards are invariably dose related.
Cold and cough remedies
The father is correct that aspirin should generally be avoided because of potential risk in G6PD deficiency (and also given the link with Reye’s disease if his son is under 16 years). If an analgesic or antipyretic is required, some sources suggest that paracetamol or ibuprofen are not problematic, while others classify them as low risk.
In terms of antihistamines in G6PD deficiency, there is limited information available, with just one source suggesting that antazoline and diphenhydramine are low risk. None of the information sources refers to decongestants.
For patients with G6PD deficiency who request over-the-counter treatment, it is important to identify known triggers for haemolysis.
Further clarification of the exact nature of the symptoms that are troubling the teenager is advisable to guide recommendations. If a product, such as Actifed, is indicated based on further discussion, it would be advisable to highlight that there is no clear information on the safety or otherwise of the constituents in G6PD deficiency.
If a patient decides to use such a product, it would be appropriate to advise him or her to be alert for emerging signs or symptoms of haemolysis or jaundice, such as dark urine, which usually appear 24 to 72 hours after exposure. An alternative remedy would be to consider a simple demulcent and steam inhalation for cough and cold symptoms.
Pharmacists can play a useful role in guiding patients with G6PD towards useful information, such as that available from Great Ormond Street Hospital or Patient.co.uk
Cappellini MD and Fiorelli G. Glucose-6-phosphate dehydrogenase deficiency. Lancet 2008;371:64–74.
Angus Thompson, lecturer in therapeutics and pharmacy practice at the School of Pharmacy, University of Tasmania, Hobart, Australia, and part-time community pharmacist
Citation: The Pharmaceutical Journal URI: 11068923
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