What is drug-induced pruritus?
Pruritus is the medical name for itching. Drug-induced pruritus is an itch caused or triggered by medication. There are various itchy drug eruptions, but generally, the term ‘drug-induced pruritus’ implies that no primary rash is present — just scratch marks.
- Pruritus can begin within hours or up to several weeks after the drug responsible has first been administered.
- Pruritus can be classified as acute (ie, present for < 6 weeks) or chronic (ie, present for > 6 weeks).
- It can be localised or generalised.
- Following the cessation of the causative drug, the itch may persist for days to months before resolving.
Scratching due to drug-induced pruritus
Who gets drug-induced pruritus?
The epidemiology of drug-induced pruritus is unknown. Generally, adverse drug reactions are more common in older patients and in patients taking multiple medicines.
What is the cause of drug-induced pruritus?
The cause of drug-induced pruritus is often unknown and depends on the drug. It may involve:
- A genetic predisposition
- Neural pathways
- Cutaneous deposition of drugs or their metabolites
- Dry skin
- Cholestatic liver injury
- Another unknown mechanism [1,2].
Which drugs cause pruritus?
The most commonly reported drugs to cause pruritus are opioids (especially during spinal anaesthesia), chemotherapeutic agents, and chloroquine (affecting 60–70% of black Africans prescribed this medicine).
The main groups of drugs that cause pruritus through various mechanisms are listed below.
Antimicrobials and antibiotics
Antimicrobials and antibiotics that cause pruritus include:
- Penicillin G
- Oral antifungal agents
- Antimalarial agents (chloroquine and amodiaquine)
Cardiovascular medicines that can cause pruritus include:
Metabolic medicines that can cause pruritus include:
Neuroleptic and psychotropic drugs
Neuroleptic and psychotropic drugs (used to treat psychosis) that can cause pruritus include:
Opioids and analgesics
Opioids and analgesics that can cause pruritus include:
Steroids and hormones
Steroids and hormones that can cause pruritus include:
- Some oral contraceptive pills.
Chemotherapeutics and biological agents
Chemotherapeutic and biological agents that can cause pruritus include:
- Gefitinib [2,6]
- The tumour necrosis factor-alpha blockers adalimumab and infliximab .
Other drugs that can cause pruritus include:
- Hydroxyethyl starch (a plasma volume expanders)
- Radiopaque contrast agents [1–3].
What is the treatment of drug-induced pruritus?
The cessation of the causative drug is an immediate priority [1,4–6]. Treatment depends on how the causative drug triggered the itching and its severity.
- If the pruritus is associated with dry skin or secondary dermatitis, topical steroids and moisturisers may be of benefit.
- Topical capsaicin has been reported as useful for treating localised drug-induced pruritus.
- Oral antihistamines are effective if the pruritus is associated with an urticaria-like mechanism.
- Systemic corticosteroids may be effective if there is an inflammatory pathway suspected to be involved.
- Naloxone or naltrexone is used for pruritus caused by the activation of mu receptor in the nervous system (in the case of opioids and plasma volume expanders).
- Ursodeoxycholic acid and cholestyramine can reduce pruritus due to cholestatic liver injury.
- Doxepin, amitriptyline, gabapentin, paroxetine, and ondansetron can also be used as second- or third-line antipruritic agents.
- Phototherapy can also be of benefit.