Hypomagnesemia (hMg) is a common side effect of important anti-cancer therapies such as epidermal growth factor receptor inhibitors (EGFRIs) and platinum-containing anti-cancer drugs. EGFRIs, including cetuximab (cmab) and panitumumab (pmab), have been estimated to cause hMg in over 18% and 27% of patients respectively1, while 90% of patients receiving cisplatin will develop hMg if left untreated. The development of severe hMg may result in increased symptoms such as fatigue, neuromuscular changes, mental status changes and cardiac arrhythmias which could result in treatment delays and may compromise treatment efficacy. Despite the common occurrence of this toxicity, little is known regarding the optimal magnesium management strategy. As physicians do not know what the "best" treatment for patients is, genuine uncertainty ("clinical equipoise") exists. Physicians will choose between different "standards" of magnesium replacement in their personal practice, using idiosyncratic decision making processes, without the physician or the patient knowing the optimal option. This is not good for patients, physicians and society as a whole. Determining the optimal treatment remains an important medical issue for patients, physicians and society. This study will use a novel method to allow comparisons of established standard of care prophylactic treatment using the "integrated consent model" as part of a pragmatic clinical trial7. By integrating medical and clinical practices, physicians will be able to inform their patients about the randomized control trial, akin to a typical conversation between the physician and patient, without written informed consent. This clinical interaction would then be documented, as ordinarily done in practice. Medical and clinical practice will be intertwined with the patients' welfare at the forefront of our best interests.

Inclusion Criteria:

• • Palliative-intent treatment with Cisplatin, Carboplatin, Panitumumab or Cetuximab and expected to receive ≥ 2 months of further therapy.

  • Potassium level within normal limits
  • Developed grade ≥1 hMg (Mg < lower limit of normal)
  • ECOG less than or equal to 2
  • ≥19 years of age
  • Able to swallow tablets/capsules
  • Able to provide verbal consent

Exclusion Criteria:

• baseline creatinine >1.5x upper limit of normal ULN
• Current use of oral or IV magnesium supplementation (patients who receive 1 gram of magnesium with their standard Cisplatin/Carboplatin chemotherapy regimens are eligible).