The unexpected burden of hypomagnesaemia in gynae-oncology chemotherapy clinics

Carboplatin and hypomagnesemia: Is it really a problem?

BACKGROUND

Carboplatin has largely replaced cisplatin in ovarian/peritoneal/tubal cancer (OC) due to comparable activity and reduced toxicity, particularly nephrotoxicity and hypomagnesemia. Anecdotally hypomagnesemia occurs commonly with carboplatin, however there are limited data available regarding frequency or severity.

AIMS

To quantify incidence and severity of hypomagnesemia in patients receiving carboplatin-based chemotherapy for OC; to explore a dose-response relationship with carboplatin and assess potential confounding variables.

METHODS

A retrospective single-center review of all OC patients receiving carboplatin-based chemotherapy as first/subsequent line between 2012 and 2018 was performed. Data on patient/disease characteristics, potential confounders (gastrointestinal/renal impairment, premorbid hypomagnesemia and concomitant medications), dose, electrolytes, and magnesium replacement were collected.

RESULTS

One hundred four of 144 (72%) patients had at least one hypomagnesemia event, 11 of 104 (11%) grade 2, and 11 of 104 (11%) grade 3/4 in severity. Multivariate analysis showed a significant association between hypomagnesemia and treatment duration (P < .001). Premorbid hypomagnesemia was associated with a significantly longer duration and higher grade of hypomagnesemia (P = .021 and P < .001, respectively). Vomiting, diarrhea, and confounding medications were associated with hypomagnesemia (P = .019 and P = .028, respectively). Fourteen percent of hypomagnesemia events never resolved suggesting a significant cohort post-carboplatin are at risk of long-term renal toxicity. The effect of magnesium replacement could not be accurately assessed due to limited documentation of replacement.

CONCLUSION

Hypomagnesemia is common in patients receiving carboplatin-based chemotherapy for OC, and although generally mild, a significant minority were severe. Several high-risk groups were identified including patients with premorbid hypomagnesemia, vomiting, diarrhea, or taking certain medications. Further research is warranted to understand when hypomagnesemia is clinically relevant and determine the impact of interventions.

Phase I study of metformin in combination with carboplatin/paclitaxel chemotherapy in patients with advanced epithelial ovarian cancer

Background Metformin use is associated with reduced cancer risk in epidemiological studies and has preclinical anti-cancer activity in ovarian cancer models. The primary objective of this phase I study was to determine the recommended phase II dose (RP2D) of metformin in combination with carboplatin/paclitaxel in patients with ovarian cancer. Secondary objectives were to describe safety and pharmacokinetics. Methods In this single-center trial the RP2D of metformin in combination with carboplatin area under the concentration-time curve (AUC) 6 and paclitaxel 175 mg/m2 every 3 weeks (q3w) in patients with advanced epithelial ovarian cancer was determined using a 3 + 3 escalation rule at three fixed dose levels: 500 mg three times daily (tds), 850 mg tds and 1000 mg tds. Metformin was commenced on day 3 of cycle 1 and continued until 3 weeks after the last chemotherapy administration. The RP2D was defined as the dose level at which 0 of 3 or ≤ 1 of 6 evaluable subjects experienced a metformin-related dose-limiting toxicity (DLT). Safety was assessed according to CTCAE v4.0. Plasma and serum samples for pharmacokinetic (PK) analyses were collected during treatment cycles 1 and 2. Results Fifteen patients with epithelial ovarian cancer and an indication for neo-adjuvant (n = 5) or palliative (n = 10) treatment were included. No DLTs were observed. Three patients discontinued study treatment during cycle 1 for other reasons than DLT. Six patients were treated at the RP2D of metformin 1000 mg tds. The most frequent low-grade toxicities were anemia, hypomagnesemia and diarrhea. Grade 3 adverse events (AEs) occurred in ten patients, most common were leucopenia (n = 4), thrombocytopenia (n = 3) and increased GGT (n = 3). There were no grade 4 AEs. Metformin increased the platinum (Pt) AUC (Δ22%, p = 0.013) and decreased the Pt clearance (Δ-28%, p = 0.013). Metformin plasma levels were all within the therapeutic range for diabetic patients (0.1-4 mg/L). Conclusion The RP2D of metformin in combination with carboplatin and paclitaxel in advanced ovarian cancer is 1000 mg tds. This is higher than the RP2D reported for combination with targeted agents. A potential PK interaction of metformin with carboplatin was identified.