What blood work would you recommend to investigate increased sweating in a patient on duloxetine (Cymbalta) and Wellbutrin (bupropion)?

Blood Work for Investigating Increased Sweating in a Patient on Duloxetine and Wellbutrin

The most appropriate initial blood work for a patient with increased sweating who is taking duloxetine and wellbutrin should include thyroid function tests (TSH, free T4), complete blood count, comprehensive metabolic panel, and HbA1c to rule out the most common medical causes, as medication side effects are the most likely explanation.

Medication-Induced Sweating: Primary Consideration

Increased sweating is a well-documented side effect of both medications this patient is taking:

• Bupropion (Wellbutrin): Sweating is listed as a common adverse reaction occurring in at least 5% of patients treated with bupropion at therapeutic doses 1. The FDA label specifically mentions sweating as one of the adverse reactions that occurred at a rate at least twice that of placebo.

• Duloxetine (Cymbalta): Excessive sweating is a frequently reported side effect of duloxetine 2. When combined with other medications, the risk of sweating may increase.

• Combination effect: The combination of duloxetine and bupropion has been specifically documented to cause increased sweating in some patients 3. One study reported increased sweating in patients receiving this combination therapy for treatment-resistant depression.

Essential Laboratory Tests

Despite the high likelihood of medication-induced sweating, it's important to rule out other medical causes:

1. Thyroid Function Tests

   • TSH and free T4
   • Rationale: Both hyperthyroidism and hypothyroidism can cause sweating abnormalities 4
   • Thyroid disorders are common and can present with increased sweating, particularly hyperthyroidism

2. Complete Blood Count (CBC)

   • Rationale: To evaluate for infection, anemia, or other hematologic abnormalities that may cause sweating 4

3. Comprehensive Metabolic Panel (CMP)

   • Glucose, electrolytes, renal and liver function
   • Rationale: To assess for metabolic disorders, diabetes, renal dysfunction, or liver abnormalities

4. Glycemic Assessment

   • Fasting glucose and HbA1c
   • Rationale: Diabetes or hypoglycemia can present with sweating 4

Additional Considerations Based on Clinical Suspicion

If the initial workup is negative and symptoms persist:

• Plasma metanephrines or 24-hour urinary fractionated metanephrines

  • Rationale: To rule out pheochromocytoma if patient has paroxysmal hypertension, palpitations, or other suspicious symptoms 4

• Plasma aldosterone/renin ratio

  • Rationale: If hypertension and hypokalemia are present, consider primary aldosteronism 4

Management Approach

1. If laboratory tests are normal: Consider medication-related sweating as the most likely cause

   • Options include:
     • Dose reduction of one or both medications
     • Switching to an alternative antidepressant with lower risk of sweating
     • Adding an agent to control sweating (e.g., anticholinergics like benztropine) 5

2. If laboratory tests identify an underlying cause: Treat the specific condition accordingly

Important Caveats

• Excessive sweating from duloxetine and bupropion can occur even months after starting the medications 5
• The combination of these two medications may have synergistic effects on sweating 3
• Sweating may be more pronounced at higher doses of either medication
• Resolution of medication-induced sweating may take several weeks after dose reduction or discontinuation 5

Remember that while medication side effects are the most likely explanation, underlying medical conditions should still be ruled out with appropriate testing.