What could be causing water-filled pimple-like patches on my left hand and shoulder after taking paracetamol (acetaminophen), aceclofenac (diclofenac), and thiocolchicoside for left shoulder pain?

Drug-Induced Vesiculobullous Eruption: Likely NSAID Hypersensitivity Reaction

You are experiencing a delayed cutaneous hypersensitivity reaction to one of the medications in your combination therapy, most likely aceclofenac (diclofenac), which is a well-documented cause of vesiculobullous (water-filled blister) drug eruptions. 1

Immediate Action Required

Stop taking the aceclofenac + paracetamol + thiocolchicoside combination immediately. 1

• NSAIDs, particularly acetic acid derivatives like aceclofenac (diclofenac), are among the most common causes of delayed drug hypersensitivity reactions that manifest as vesiculobullous eruptions occurring days to weeks after drug initiation 1
• The temporal relationship between starting the medication for shoulder pain and developing water-filled lesions strongly suggests drug-induced pathology 1
• Paracetamol (acetaminophen) can also cause severe skin reactions including blistering, though this is less common 2

Critical Warning Signs to Monitor

Seek emergency medical attention immediately if you develop any of the following: 1

• Fever accompanying the skin lesions
• Involvement of mucous membranes (mouth, eyes, genitals)
• Rapid spread of blistering beyond the hand and shoulder
• Skin reddening that becomes widespread
• Painful lesions that begin to peel or slough off

These could indicate progression to Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), a life-threatening condition where acetic acid NSAIDs like diclofenac are highly implicated 1

Diagnostic Approach

You need urgent evaluation by a dermatologist or your primary physician within 24-48 hours 1

• Document the exact timeline: when you started the medication and when the vesicles appeared 1
• The physician should perform a thorough skin examination to assess the extent and morphology of the eruption 1
• Consider lesional patch testing after the acute reaction resolves to confirm the culprit drug, though this has variable sensitivity 1
• Biopsy may be indicated if the diagnosis is uncertain or if severe cutaneous adverse drug reaction is suspected 1

Treatment Protocol

For localized vesicular eruptions (current presentation): 1

• Apply high-potency topical corticosteroids (such as betamethasone valerate 0.1% or mometasone furoate 0.1% ointment) to affected areas twice daily 1, 3
• Use non-sedating oral antihistamines for daytime symptom control: loratadine 10 mg daily or cetirizine 10 mg daily 1, 3
• Consider sedating antihistamines at night if itching interferes with sleep: hydroxyzine 25-50 mg or diphenhydramine 25-50 mg 1, 3
• Maintain skin hydration with regular emollient application 1, 3

If the reaction is more extensive or worsening: 1

• Systemic corticosteroids may be required (typically oral prednisone)
• Hospitalization may be necessary for severe or rapidly progressive cases

Future Medication Safety

Absolute avoidance recommendations: 1

• Never take aceclofenac (diclofenac) or any other acetic acid NSAIDs again (including indomethacin, ketorolac, etodolac, sulindac, tolmetin) 1
• Cross-reactivity within the same chemical class is well-described, and rechallenge risks recurrence of potentially severe reactions 1
• Document this reaction prominently in your medical records and inform all healthcare providers 3

Safe alternatives for future pain management: 1

• Paracetamol (acetaminophen) alone may be used cautiously if it was not the culprit, though it should be stopped now as part of the combination 1, 2
• NSAIDs from different chemical classes may be tolerated: consider propionic acid derivatives (ibuprofen, naproxen) or selective COX-2 inhibitors (celecoxib) only after the reaction completely resolves and under medical supervision 1
• A graded challenge to an alternative NSAID class should only be performed by an allergist if NSAIDs are medically necessary 1

Common Pitfall to Avoid

Do not assume this is a simple skin infection or contact dermatitis 1

• The distribution pattern (hand and shoulder—sites of the original pain complaint) combined with recent medication initiation strongly points to drug reaction rather than infection 1
• Antibiotic treatment would be inappropriate and could cause additional drug reactions 1
• The vesicular presentation following NSAID use is a recognized pattern of delayed hypersensitivity 1

Follow-Up Timeline

Reassess symptoms after 2 weeks of stopping the medication and starting topical treatment 1, 3

• If lesions are improving, continue topical therapy until complete resolution
• If lesions persist, worsen, or new symptoms develop, return for dermatology evaluation immediately 3
• Complete resolution may take several weeks after drug discontinuation 1