Which classification of drugs is used to treat itching?

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.

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
• Vasodilation
• Phototoxicity
• 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
• Amoxicillin/clavulanate
• Ampicillin
• Cefotaxime
• Ceftazidime
• Erythromycin
• Ciprofloxacin
• Vancomycin
• Clindamycin
• Tetracyclines
• Minocycline
• Metronidazole
• Rifampicin
• Trimethoprim/sulfamethoxazole
• Oral antifungal agents
• Antimalarial agents (chloroquine and amodiaquine)

Cardiovascular medicines

Cardiovascular medicines that can cause pruritus include:

• Amlodipine
• Diltiazem
• Verapamil
• Clonidine
• Methyldopa
• Amiodarone
• Captopril
• Enalapril
• Lisinopril
• Candesartan
• Irbesartan.

Metabolic medicines

Metabolic medicines that can cause pruritus include:

• Metformin
• Gliclazide
• Allopurinol.

Neuroleptic and psychotropic drugs

Neuroleptic and psychotropic drugs (used to treat psychosis) that can cause pruritus include:

• Amitriptyline
• Citalopram
• Fluoxetine
• Paroxetine
• Sertraline
• Carbamazepine
• Phenytoin
• Topiramate
• Chlorpromazine
• Phenothiazine
• Risperidone.

Opioids and analgesics

Opioids and analgesics that can cause pruritus include:

• Morphine
• Codeine
• Fentanyl
• Oxycodone
• Tramadol
• Aspirin.

Steroids and hormones

Steroids and hormones that can cause pruritus include:

• Danazol
• Some oral contraceptive pills.

Chemotherapeutics and biological agents

Chemotherapeutic and biological agents that can cause pruritus include:

• Chlorambucil
• Gemcitabine
• Nilotinib
• Vemurafenib
• Temsirolimus
• Ipilimumab
• Cetuximab
• Rituximab
• Panitumumab
• Gefitinib [2,6]
• The tumour necrosis factor-alpha blockers adalimumab and infliximab [7].

Other drugs

Other drugs that can cause pruritus include:

• Enoxaparin
• 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.