Medication Dosing in Transgender Patients

Medication Dosing in Transgender Patients
Txia Xiong, Pharm.D., Minnesota Community Care 

Background: The term transgender describes people whose gender identity differs from their sex assigned at birth. They are a unique population and are often the targets of discrimination and harassment. This may lead to higher instances of comorbid conditions including depression, substance abuse, and suicide compared to their cisgender counterparts. Unsurprisingly, access to quality healthcare may be limited in this population because of the lack of confidence transgender patients and providers have in each other to provide adequate care. Guidelines for transgender care do exist; however, they do not include guidance on how to calculate creatinine clearance (CrCl) or ideal body weight (IBW) necessary to dose many medications. The consequences of overdosing or underdosing medications in transgender patients include drug toxicity or therapeutic failure especially if they receive doses inconsistent with their current physiology. 

Evidence: A literature review from Webb et al. looked at the current evidence on the effect of gender-affirming hormone therapy on serum creatinine concentration and lean body mass to inform a recommendation for drug dosing. Four studies were found on the effect of hormone therapy on biometric laboratory values. One study reported a range of values that more closely resembled those associated with sex at birth while still overlapping with values associated with gender identity. However, Webb et al. concluded that the results from this study were difficult to interpret since normal ranges for cisgender men and women already overlap. 

Three studies reported that the values of transgender patients more closely resembled the standard values of their gender identity versus sex at birth after hormone therapy. The first study, an observational cross-sectional study, found that median lean body mass (LBM) was lower in transgender women than in cisgender men (51.2 kg versus 61.8 kg, P<0.001). Median serum creatinine (SCr) was also lower in transgender women than in cisgender men (0.78 mg/dL versus 0.94 mg/dL, P<0.001). A retrospective cohort study comparing laboratory values between baseline, three to six months, and six to 18 months revealed that both transgender women and transgender men experienced changes in biomarkers used to calculate CrCl and IBW as soon as three months after hormone therapy initiation. Transgender women did not experience a significant change in body mass index (BMI), but their SCr decreased from a baseline mean of 0.9 mg/dL to 0.85 mg/dL at follow-up (P<0.05). Mean BMI of transgender men increased from 28.1 to 30.1 (P<0.05) and mean SCr increased from 0.73 mg/dL to 0.87 mg/dL (P<0.05). Lastly, a prospective cohort trial compared LBM, BMI, and SCr before and after transgender women and transgender men had been on gender-affirming hormone therapy for four months. Relative to baseline values, mean SCr decreased in transgender women from 0.97 mg/dL to 0.89 mg/dL (P<0.001), whereas LBM remained mostly unchanged from 56.9 kg to 56.6 kg (P=0.56). In transgender men, mean LBM increased from 44 kg to 48.1 kg (P<0.001). Both groups experienced an increase in mean total BMI, from 21 to 21.9 (P=0.005) in transgender women and from 21.9 to 23.2 (P<0.001) in transgender men. 

Discussion: The literature indicates that after hormone therapy, transgender patients’ physiology more closely reflects their gender identity than their sex at birth. Furthermore, considerations to start using biometric laboratory values based on gender identity was suggested after six months of hormone therapy due to amenorrhea commonly occurring at that time in transgender men. Despite the lack of literature and the small number of participants in these studies, the findings are useful because they offer guidance to pharmacists regarding medication dosing in transgender patients. Dosing medications based on CrCl and IBW calculations consistent with gender identity after a patient has been on hormone therapy for six months or longer supports safe and effective treatment for transgender patients.

Reference

  1. Webb AJ, McManus D, Rouse GE, Vonderheyde R, Topal JE. Implications For Medication Dosing For Transgender Patients: A Review Of The Literature And Recommendations For Pharmacists.Am J Health Syst Pharm. 2020;77:427-433.