Effects of Selective Serotonin Reuptake Inhibitors and Ondansetron on Urinary Tract Infections in Pregnancy

Abstract

Urinary tract infections (UTIs) are prevalent during pregnancy and pose risks of adverse outcomes. Recent research suggests that urethral serotonin signaling may protect against ascending uropathogens. With the common use of Selective Serotonin Reuptake Inhibitors (SSRIs) and ondansetron, a serotonin receptor antagonist, during pregnancy, it is essential to explore their interactions with serotonin mechanisms to improve maternal health care. This study examines the relationship between SSRIs and ondansetron use in pregnancy and the incidence of UTIs and other negative outcomes. A retrospective analysis of data from 7,023 pregnant women in the PeriBank database (IRB ID: 2023-0263), from February 2020 to April 2023, revealed that 1,019 received ondansetron and 316 were on SSRIs, including fluoxetine, sertraline, escitalopram, and citalopram. An experimental component involving pregnant mice treated with ondansetron or saline before E. coli infection further assessed UTI severity. Findings indicated that pregnant women using ondansetron had significantly increased odds of developing UTIs, while no significant association was noted for those on SSRIs. Additionally, pregnant mice administered ondansetron exhibited more severe bladder infections compared to those given saline. These results suggest SSRIs are not linked to an increased UTI risk or adverse outcomes, whereas ondansetron is associated with higher UTI risk and pre-term birth. Thus, careful use of ondansetron during pregnancy is recommended to avoid potential risks to maternal and fetal health.

1. Introduction

Urinary tract infections (UTIs) affect approximately 5–10% of expecting mothers [1]. UTIs are associated with heightened risks of adverse pregnancy outcomes, including preeclampsia, fetal growth restriction, preterm birth, and low birth weight [2–4]. Timely and appropriate antibiotic treatment is the current standard of care for UTIs during pregnancy to mitigate these risks [5].

A rise of antibiotic-resistant bacterial strains poses a growing challenge, particularly in the context of pregnancy and birth, where maternal bacteria can be transmitted to the fetus [5, 6]. Thus, there is an urgent need to understand risk factors for the development of UTIs in order to decrease antibiotic use and mitigate associated complications.

It was recently shown that the urethra mediates an innate response to ascending uropathogens by releasing serotonin (5-HT), inducing urethral contraction, and expelling bacteria from the urinary tract [7]. 5-HT is synthesized locally in the urethra by neuroendocrine cells (UNECs) and is released to act upon HTR2B and HTR3 receptors on Interstitial Cells of Cajal (ICCs). These cells depolarize smooth muscle cells to expel ascending microbes in the female urethra. This defense mechanism suggests that drugs targeting the serotonergic system may influence urethral contraction and susceptibility to UTIs[7].

Selective serotonin reuptake inhibitors (SSRIs), commonly prescribed for anxiety and depression, increase extracellular 5-HT by inhibiting the serotonin transporter (SERT - solute carrier family 6 member 4). This results in an increase in plasma serotonin levels and thus serotonin signaling [8–10], stimulating specific 5-HT receptors in the bladder [8].

Conversely, ondansetron, a serotonin 5HTR3 antagonist commonly prescribed for nausea and vomiting, may potentially affect the serotonergic system [9, 10]. Approximately 75% of pregnant women experience nausea and vomiting [11]. Ondansetron is a widely prescribed treatment and is first line therapy for some obstetric and emergency providers. [12]. Additionally, up to 6% of pregnant individuals are treated with SSRIs [13]. Therefore, it is crucial to explore the potential implications of augmenting (SSRIs) or selectively blocking (ondansetron) serotonergic signaling during pregnancy on UTI incidence adverse pregnancy outcomes.

5-HT levels, besides their direct influence on urethral response, can also affect the growth of gut bacteria, which interact with the host’s serotonergic system [14]. Recent research has shown that SSRI medications can affect gut microbiome composition in adult humans [15], and gut microbiome can alter the host’s secretory response to 5-HT, in part by affecting 5HTR3 expression via acetate production [16]. It is important to consider that the gut microbiome can influence both the vaginal and urinary microbiomes, which are interconnected and interact with each other [17]. The exchange of organisms between these microbiomes can contribute to urinary tract infections (UTIs) [17]. Thus, serotonergic drugs, including SSRIs and ondansetron, may impact the gut, vaginal, and urinary microbiomes, potentially influencing UTI risk.

We used electronic medical records from a perinatal database (PeriBank) to conduct a retrospective cohort analysis of pregnant women and conducted additional prospective studies in pregnant mice. Our objective was to investigate potential associations between the use of SSRIs or ondansetron during pregnancy and the incidence of urinary tract infections UTIs and adverse pregnancy outcomes. Specifically, we hypothesized that women who took SSRIs during pregnancy would experience lower incidence of UTIs and adverse pregnancy outcomes, whereas those who took ondansetron would face higher incidence of UTIs and adverse pregnancy outcomes. We also tested whether ondansetron worsens bladder infections in pregnant mice given an ascending infection with E. coli UTI89. Our findings demonstrate that SSRI use during pregnancy showed no apparent link to UTIs risk or adverse outcomes. However, Ondansetron exposure was associated with a higher risk of UTIs and pre-term birth. This correlation was supported by experiments on pregnant mice treated with ondansetron, which showed worsened bladder infections.

2. Methods

2.1. Subjects

Study data were obtained by accessing PeriBank database (Institutional Review Board No. 2023-0263). PeriBank is a de-identified perinatal database maintained by Baylor College of Medicine and Texas Children’s Hospital in Houston, Texas [18, 19]. The PeriBank database is maintained by trained personnel and does not rely on volunteers to self-identify or enter data. To ensure the quality of the recorded data, a subset was regularly verified by a board-certified Maternal-Fetal Medicine physician. [18].

In the current study, all participants with a history of infections and prescribed medications, as well as information regarding pregnancy outcomes such as gestational hypertension (preeclampsia), preterm birth, fetal growth restriction (FGR), chorioamnionitis, and birth weight, were queried. To ensure the quality of the recorded data, a subset was regularly verified by a board-certified Maternal-Fetal Medicine physician. Patients were interviewed on labor and delivery to obtain information following informed consent. Further data on birth and neonatal outcomes were abstracted by trained obstetric research coordinators following delivery, using electronic medical record (EMR) information. All interviews were conducted after the subjects were assessed by a physician to ensure optimal patient comfort and care [18].

2.1.1. Inclusion criteria

Criteria for inclusion were live deliveries occurring between February 2020 – April 2023. Patients with sickle cell disease, type I or type II diabetes, human immunodeficiency virus, or multifetal gestations were excluded. Patients with unavailable or incomplete information in the PeriBank database were also excluded. Pre-specified data abstracted for this study included demographic information and maternal outcomes. The primary outcome was the rate of urinary tract infection, (defined as both cystitis or pyelonephritis), among pregnant patients receiving SSRI or ondansetron treatment compared to those who did not receive these medications during pregnancy. SSRIs investigated in this study included fluoxetine, sertraline, escitalopram, and citalopram.

Secondary outcomes included birth weight, the presence of fetal growth restriction, preterm birth (delivery prior to 37 weeks), pregnancy-related hypertension or preeclampsia and the incidence of chorioamnionitis.

The cohort was classified into four groups based on their UTI history and prescription status for SSRIs: UTI positive with SSRI prescribed (UTI+ SSRI+), UTI positive without SSRI prescribed (UTI+ SSRI−), UTI negative with SSRI prescribed (UTI− SSRI+), and UTI negative without SSRI prescribed (UTI− SSRI−).

Similarly, patients were categorized based on their UTI history and prescription status for ondansetron (OD): UTI positive with OD prescribed (UTI+ OD+), UTI positive without OD prescribed (UTI+ OD−), UTI negative with OD prescribed (UTI− OD+), and UTI negative without OD prescribed (UTI− OD−).

2.2. Mice

All experiments were conducted in strict adherence to the approved protocol from the University of Wisconsin Animal Care and Use Committee, following the guidelines outlined in the National Institutes of Health Guide for the Care and Use of Laboratory Animals (ID: V005096-R03-A02). All mice were from Jackson Laboratories (Bar Harbor, ME) and maintained on a C57BL/6J genetic background (Jackson stock #000664). Mice used in this study were pregnant adult females, aged 8 and 10 weeks. Pregnancy was determined by visual plug observation and weight gain; all mice used in this study were staged between the 3^rd and 7^th day of pregnancy. A total of 12 pregnant mice were included in the study, with 6 mice in the Ondansetron-treated group and 6 mice in the saline control-treated group.

Mice were housed in Udel^® Polysulfone microisolator cages placed on racks or in Innocage^® disposable mouse cages on an Innorack^®. Room lighting was maintained on a 12-hour light-dark cycle, with room temperature set at a consistent 20.5 ± 5°C and humidity ranging from 30% to 70%. The mice were provided with 8604 Teklad Rodent Diet (Harlan Laboratories, Madison, WI) and had access to feed and water ad libitum. Cages were furnished with corn cob bedding.

2.3. Ondansetron treatment and induction of ascending urinary tract infection with E. coli

C57BL/6J pregnant female starting on pregnancy days 3–7, were injected interperitoneally with ondansetron (2 mg/kg/day × 3 days) or saline alone (5 mL/kg × 3 days, vehicle control).

On the same day as the third ondansetron or saline (control) injection, mice were given an ascending infection of uropathogenic E. coli as described previously [7]. The experiments utilized E. coli UTI89 [20], a uropathogenic strain of Escherichia coli (UPEC) originally isolated from a human patient with cystitis [21]. The bacteria were genetically modified with a pCOMGFP plasmid [22] to enable the expression of green fluorescent protein and confer kanamycin resistance. UTI89 was obtained from J. Barasch (Columbia University) and originally reported [21]. Before inoculation, E. coli UTI89 was cultured statically for 18 hours in antibiotic-free Luria-Bertani broth at 37°C. The optical density (OD) was measured before inoculating mice. The culture was centrifuged for 15 minutes at 1157 rcf and the resulting pellet was suspended in sterile phosphate buffered saline (PBS) for instillation.

A transurethral catheter (0.6 cm, PE-10) was inserted, and sterile PBS containing E. coli UTI89 (1–8.2 × 10⁷ CFU/mL) was instilled into the urethra, with a volume of 10 μL per instillation, as previously described [7]. It is important to highlight that, as described in our previous study, the bacteria were delivered into the urethra rather than the bladder, to replicate the natural course of urinary tract infection. All mice underwent catheterization only once.

To quantify severity of bladder infection, mice were euthanized 4 hours after instillation, placed on sterile surgical drape, and drenched in 70% ethanol. Because our goal was to determine the distribution and severity of E. coli infection, great care was taken during dissection to reduce the risk of cross-contaminating organs or surgical instruments. Sterile scissors were used to open the body cavity and expose the lower urinary tract (bladder and urethra). Intestines were moved aside with a sterile gloved finger. The female urethra was lying immediately to the vagina is approximately 11 mm in length and opens independently of the vagina, it passes through and almost adjacent to the pubic symphysis, from which it is separated by a small amount of adipose tissue. A suture was placed in the bladder neck and bladder and urethra were dissected by resecting the adipose tissue and pubic symphysis. The bladder and urethra were separated at the level of the bladder neck with a single transverse cut. The bladder was placed in a sterile 1.5-mL tube with 1 mL of sterile PBS and hand ground with a sterile pestle and vortex. Serial dilutions were made and plated on LB agar containing kanamycin (50 mg/mL). Scissors and forceps were sterilized between mice using a bead sterilizer, and a new sterile surgical drape, sterile suture, and sterile PBS were used for each mouse. CFU values were calculated per milliliter by 10-fold serially diluting tissue homogenates in 1000 μl sterile saline and 10 μl were cultured on agar plates. Plates were incubated at 37 °C for 18–24 h and CFUs were counted for each sample [23, 24]

2.4. Variables Measured in Serum and Urine

Serum and urine samples were collected from pregnant mice treated with ondansetron or saline 4 hours post-UEPC infection. Serotonin concentrations in serum were determined using a commercial 5-HT ELISA kit (IM1749, Beckman Coulter GmbH, Sinsheim, Germany). Similarly, concentrations of urinary 5-Hydroxyindoleacetic acid (5-HIAA), the main metabolite of serotonin were determined using a commercial 5-HIAA ELISA kit (17-5HIHU-E01, ALPCO Diagnostics, USA).

2.5. Statistical analysis

Statistical analyses were performed with GraphPad Prism 8.0.2 (GraphPad Software, La Jolla, CA). The statistical analysis included t-tests for colony-forming units (CFU), serum 5-HT, and urine 5-HIAA for quantitative variables. Fisher’s exact tests were employed for categorical variables to assess the significance of differing outcomes between groups. Logistic regression was used to control demographic differences between groups. A p-value of < 0.05 was considered statistically significant.

3. Results

3.1. Demographic Characteristics

Demographics were assessed among subjects with and without a diagnosis of UTI during pregnancy. Subjects were more likely to be of Hispanic ethnicity (p = 0.0016), with an average age of 31 years. Pregnant women diagnosed with mental health disorders had a higher incidence of UTIs compared to the control group (p = 0.0269) (Table 1).

Table 1.

Demographic characteristics of women diagnosed with a Urinary Tract Infection (UTI) during pregnancy or not diagnosed with a UTI during pregnancy (Control). An unpaired t-test was used for numerical values (age) and a Fisher’s exact test for categorical values (ethnicity and mental health issues).

	Control	UTI	p-value
N	6580	443
Ethnicity (% Not Hispanic/Latino)	46%	39%	p=0.00l6
Mean maternal age (median, IQR)	31 (32,9)	31 (31,10)	p=0.1644
Diagnosed with mental health disorder (%)	17%	21%	p=0.0269

IQR= Interquartile range.

3.2. SSRI Prescription During Pregnancy and UTI Diagnosis During Pregnancy

The incidence of one or more UTIs diagnosed during pregnancy among women prescribed an SSRI (SSRI+) did not significantly differ from that of one or more diagnosed UTIs among those who were not treated with SSRIs (SSRI−) (p = 0.8124) (Table 2). In the study population, 4.5% were prescribed SSRIs (n=316). In this group of subjects receiving SSRIs, 21 were diagnosed with a UTI (UTI+SSRI+). There were 6,707 subjects who were not prescribed SSRIs during pregnancy. Of these, 422 were diagnosed with a UTI (UTI+SSRI−) (Fig. 1).

Table 2.

Incidence of one or more urinary tract infection (UTI) diagnoses during pregnancy among women who were prescribed an SSRI during pregnancy (SSRI+) and who were not prescribed an SSRI during pregnancy (SSRI−). Fisher’s exact test was used.

	SSRI+	%	SSRI−	%	p-value	OR	95%CI
Pregnancies (N)	316		6,707
UTI	21	6.6	422	6.3	0.8124	0.9432	0.6040 to 1.484

Figure 1.

Patient selection, selective serotonin reuptake inhibitor (SSRIs) use, and UTI flow chart. Study participants 7,023 pregnant women among them 316 patients treated with SSRIs and 6,707 patients not treated with SSRI. In this study, outcomes of the SSRIs exposure group (SSRI/UTI) are compared to the two unexposed groups (no SSRI/UTI) and the control group (no SSRI/no UTI).

Pregnancy outcomes in those diagnosed with a UTI and prescribed an SSRI (UTI+SSRI+) compared to those diagnosed with a UTI and not prescribed an SSRI (UTI+SSRI−) are presented in Table 3A. Pregnancy outcomes in women diagnosed with a UTI and prescribed an SSRI (UTI+SSRI+) did not significantly differ from pregnancy outcomes in women who were not diagnosed with a UTI during pregnancy and not prescribed an SSRI during pregnancy (UTI−SSRI−; Control group) (Table 3B). The pregnancy outcomes for women prescribed an SSRI during pregnancy did not significantly differ from those of women who were not prescribed an SSRI during pregnancy.

Table 3A.

Pregnancy outcomes of women diagnosed with one or more UTIs during pregnancy and prescribed an SSRI (UTI+SSRI+) or not prescribed an SSRI (UTI+SSRI−). Fisher’s exact test was used for all categorical values.

	SSRI+	%	SSRI−	%	p-value	OR	95%CI
Pregnancies (N)	21		422
Outcome
Fetal growth restriction	2	10	8	2	0.0766	0.1836	0.03931 to 0.9139
Preeclampsia/gestational hypertension	5	24	82	19	0.5797	0.7718	0.2743 to 1.969
Chorioamnionitis	0	0	22	5	0.6147	+infinity	0.2969 to +infinity
Preterm Birth	3	14	53	13	0.7388	1.16	0.3512 to 3.760
Low birth weight <2500g	2	10	34	8	0.6839	1.447	0.3708 to 5.650
Very low birth weight <1500g	1	5	6	1	0.2893	4.7	0.7540 to 29.30
Extremely low birth weight <1000g	0	0	4	1	>0.9999	0	0.000 to 21.65

SSRI+ (Prescribed a selective serotonin reuptake inhibitors).

SSRI− (Not prescribed a selective serotonin reuptake inhibitor).

Table 3B.

Pregnancy outcomes of women diagnosed with one or more UTIs during pregnancy and prescribed an SSRI (UTI+SSRI+) or not diagnosed with a UTI during pregnancy and not prescribed SSRI (UTI−SSRI−). Fisher’s exact test was used for all categorical values.

	SSRI+	%	SSRI−	%	p-value	OR	95%CI
Pregnancies (N)	21		6,285
Outcome
Fetal growth restriction	2	10	115	2	0.0572	0.1774	0.04576 to 0.7792
Preeclampsia/gestational hypertension	5	24	1125	18	0.5655	0.6977	0.2634 to 1.742
Chorioamnionitis	0	0	290	5	0.6226	+infinity	0.2971 to +infinity
Preterm Birth	3	14	554	9	0.4257	1.948	0.6194 to 6.126
Low birth weight <2500g	2	10	467	7	0.6676	1.589	0.4245 to 5.949
Very low birth weight <1500g	1	5	86	1	0.2542	5.224	0.9821 to 27.79
Extremely low birth weight <1000g	0	0	50	1	>0.9999	2.86	0.1709 to 47.87

SSRI+ (Selective serotonin reuptake inhibitors exposure).

SSRI− (not exposed to Selective serotonin reuptake inhibitors).

3.3. Ondansetron Prescription During Pregnancy and UTI Diagnosis During Pregnancy

Patients prescribed ondansetron were more likely to report urinary tract infections during pregnancy than those who did not. Notably, the incidence of one or more diagnosed UTIs during pregnancy among women prescribed ondansetron during pregnancy (OD+) was significantly greater (p < 0.0001) than the incidence of one or more diagnosed UTIs among women who were not prescribed ondansetron (OD−) (Table 4). In the study population, 14% were prescribed ondansetron (n = 1019). In this group, 105 subjects were diagnosed with a UTI (UTI+OD+). Conversely, 6,004 pregnant women were not prescribed ondansetron but 338 were diagnosed with a UTI (UTI+OD−) (Fig. 2).

Table 4.

Urinary tract infections (UTIs) of women who were prescribed ondansetron (OD+) or were not prescribed Ondansetron (OD−) during pregnancy. Fisher’s exact test was used.

	O+	%	O−	%	p-value	OR	95%CI
Pregnancies (N)	1019		6,004
UTI	105	10.3	338	5.6	<0.0001	1.926	1.525 to 2.421

Figure 2.

Patient selection, antiemetic use (ondansetron) and UTI flow chart. Study participants 7,023 pregnant women, among them was reported on 1,019 pregnancies treated with ondansetron and 6,004 pregnancies that were not treated with ondansetron. In this study, outcomes of the ondansetron exposure group (ondansetron/UTI) are compared to the two unexposed groups (no ondansetron/UTI) and the control group (no ondansetron/no UTI).

Women who were diagnosed with one or more UTI and prescribed ondansetron (UTI+OD+) had significantly more preterm births (p = 0.0021), neonates with very low birth weight <1500g (p = 0.0009), and extremely low birth weight <1000 g (p = 0.0031) compared to those who were diagnosed with one or more UTIs but were not prescribed ondansetron (UTI+OD−) (Table 5A).

Table 5A.

Pregnancy outcomes of women diagnosed with one or more UTIs during pregnancy and prescribed ondansetron (UTI+OD+) or not prescribed ondansetron (UTI+OD−). Fisher’s exact test was used for all categorical values.

	O+	%	O−	%	p-value	OR	95%CI
Pregnancies (N)	105		338
Outcome
Fetal growth restriction	2	2	8	2	>0.9999	1.248	0.3013 to 5.921
Preeclampsia/gestational hypertension	24	23	63	19	0.3986	0.7732	0.4597 to 1.298
Chorioamnionitis	6	6	16	5	0.6149	0.8116	0.3150 to 2.061
Preterm Birth	23	22	33	10	0.0021	2.592	1.473 to 4.575
Low birth weight <2500g	13	12	23	7	0.1	1.921	0.9541 to 3.871
Very low birth weight <1500g	6	6	1	0	0.0009	14.6	2.439 to 87.36
Extremely low birth weight <1000g	4	4	0	0	0.0031	29.81	1.592 to 558.3

O+ (ondansetron exposure).

O− (not exposed to ondansetron).

Women who were diagnosed with one or more UTIs and prescribed ondansetron (UTI+OD+) had a significantly higher preterm birth rate (p < 0.0001) and neonates with a very low birth weight <1500 g (p = 0.0021) or an extremely low birth weight <1000 g (p = 0.0064) compared to women who were not diagnosed with a UTI and not prescribed ondansetron (UTI−OD−; Control group) (Table 5B).

Table 5B.

Pregnancy outcomes of women diagnosed with one or more UTIs during pregnancy and prescribed ondansetron (UTI+OD+) or not diagnosed with a UTI during pregnancy and not prescribed ondansetron (UTI−OD−). Fisher’s exact test was used for all categorical values.

	O+	%	O−	%	p-value	OR	95%CI
Pregnancies (N)	105		5,666
Outcome
Fetal growth restriction	2	2	100	2	0.7087	0.9234	0.2445 to 3.873
Preeclampsia/gestational hypertension	24	23	996	18	0.1569	0.7198	0.4611 to 1.144
Chorioamnionitis	6	6	273	4.8	0.6422	0.8333	0.3685 to 1.783
Preterm Birth	23	22	468	8	<0.0001	3.164	1.982 to 5.053
Low birth weight <2500g	13	12	393	7	0.0511	1.937	1.085 to 3.458
Very low birth weight <1500g	6	6	67	1	0.0021	5.37	2.345 to 12.30
Extremely low birth weight <1000g	4	4	37	1	0.0064	6.596	2.434 to 17.88

O+ (ondansetron exposure).

O− (not exposed to ondansetron).

3.4. Ondansetron worsens bladder infection in a pregnant mouse model of ascending UPEC infection.

While our retrospective cohort study provided valuable insights into the association between SSRI/Ondansetron use during pregnancy and UTI incidence, there are several limitations. Firstly, although we could identify patients diagnosed with UTIs and those prescribed SSRIs or Ondansetron, the exact timing of UTI occurrence in relation to SSRI/Ondansetron use during pregnancy is not known. This lack of temporal information limits our ability to establish causality and discern the direct influence of these medications on UTI development. Furthermore, the possibility of cryptic infections exists, as they may not be documented in electronic medical records. Additionally, while SSRIs and ondansetron were prescribed, details regarding the specific dosage and participant compliance were not available. To address these limitations and explore the potential influence of ondansetron on 5-HT mediated urethral innate defense mechanism against E. coli and UTI severity in a more controlled manner, we conducted further experiments.

To assess the in vivo effect of ondansetron, we treated pregnant wild-type female mice between days 3 and 7 of gestation (length of mouse gestation is typically 19 days). This timeframe was chosen to mimic the first trimester, during which nausea and vomiting of pregnancy typically occur and ondansetron is typically prescribed [29, 30].

After three days of treatment (ondansetron or saline), pregnant mice were anesthetized and UPEC was instilled into the distal urethra to initiate an ascending infection. Bladders were collected four hours after UPEC instillation to quantify bacterial burden. Ondansetron treated pregnant mice had more severe bladder infections (median CFU = 32,500, n = 6) compared to saline control treated pregnant mice (median CFU = 2,500, n = 6, p = 0.0022) (Fig. 3A). These data support the hypothesis that ondansetron treatment during pregnancy (days 3–7) increases the severity of bladder infection from ascending UPEC.

Figure 3.

Ondansetron increases the severity of an ascending E. coli infection and elevates serum serotonin (5HT) and urinary 5-hydroxyindoleacetic acid (5-HIAA) concentrations. A catheter was placed into the distal urethra of adult female wild-type pregnant mice (on days 3–7 of pregnancy) were injected intraperitoneally with ondansetron (2 mg/kg/day for 3 days) or saline alone, followed by delivery of E. coli UTI89 to initiate an ascending infection. Bladders were removed 4 h later, and bacteria burden was determined by counting colonies on Kanamycin agar plates. (A) Ondansetron-treated pregnant mice bladders contained significantly more E. coli CFUs (p = 0.0022, n=6) than control mouse bladders. Additionally, blood and urine were collected from these animals, and ELISA was used to determine the concentration of serum 5-HT and 5-HIAA in the urine. (B) Ondansetron-treated pregnant mice exhibited elevated serum serotonin levels (p=0.0321, n=6), and increased 5-HT metabolism, as evidenced by (C) elevated 5-HIAA levels in urine (p=0.0038, n=6). *p < 0.05 ** p < 0.01.

3.5. Ondansetron increases serum serotonin and urinary 5-hydroxyindoleacetic (5HIAA) concentrations in pregnant mice.

Studies have shown the involvement of 5-HT receptors in the regulation of 5-HT release from the small intestine [25, 26]. HTR3 receptor activation increases 5-HT release in animal models [25, 26]. By measuring serum serotonin and urinary 5-HIAA concentrations, we aimed to investigate whether ondansetron administration during pregnancy affected 5-HT blood concentration and 5-HIAA urinary concentration in pregnant mice.

We collected serum and urine from pregnant UPEC infected mice that were treated with saline or ondansetron. Ondansetron-treated mice had higher serum 5-HT concentrations (p = 0.0321) and higher urinary 5-HIAA concentrations (p = 0.0038) compared to saline-treated, UPEC-infected pregnant mice (Fig. 3B and 3C, respectively). These findings are consistent with previous research [27], which demonstrated that peripheral HTR3 receptor blockade inhibits 5-HT degradation by monoamine oxidase A (MAOA).

4. Discussion

The current study investigates relationships between urinary tract infections during pregnancy and drugs that influence 5-HT signaling during pregnancy through a retrospective cohort analysis of human women in Texas (labor and delivery at unit Ben Taub Hospital and the Texas Children’s Hospital Pavilion for Women) [18] and a small prospective study in pregnant female mice.

Our analysis of PeriBank records revealed higher rates of UTIs among pregnant Hispanic/Latino women compared non-Hispanic/Latino women (American Indian/Alaska Native, Asian, Native Hawaiian, Black or African, and White). This finding aligns with previous a previous study by Schwartz et al. [28], which documented an increased UTI risk among individuals of Hispanic ethnicity. Moreover, we found a higher incidence of UTIs among pregnant individuals diagnosed with mental health disorders, consistent with previous research linking anxiety and depression to UTIs occurrence in female patients [29].

Approximately 7–13% of mothers experience depression during pregnancy and 6–10% of pregnant women are prescribed antidepressants [13]. SSRIs are the most commonly used antidepressants during pregnancy [30]. We hypothesized that SSRIs, which are known to increase 5-HT signaling in peripheral tissues [8, 31], would reduce the rate of UTIs in pregnant women. Moreover, 5-HT can influence the microbiome [15] and modulate the immune system, as its receptors are expressed on immune cells. SSRIs have been shown to impact immune cell functions, including proliferation, cytokine secretion, and lymphocyte viability [32]. These effects could enhance the host’s immune response to urinary pathogens. However, contrary to our hypothesis, the rate of diagnosed UTIs among women prescribed SSRIs during pregnancy did not significantly differ from that of pregnant women who were not prescribed SSRIs during pregnancy.

Furthermore, SSRIs are generally considered safe for use during pregnancy [30], and the incidence of adverse pregnancy outcomes in women prescribed SSRIs during did not significantly differ from that of pregnant women who were not prescribed SSRIs during pregnancy, regardless of UTI status. It’s important to note the lack of detailed information in our study regarding the precise sequencing of UTI occurrence in relation to SSRI/ondansetron use during pregnancy. This lack of temporal information hinders our ability to establish causality and accurately determine the direct influence of these medications on UTI development. Furthermore, the potential for cryptic infections exists, as they might not be documented in electronic medical records as diagnosed UTIs. Additionally, while SSRIs and ondansetron were prescribed, the specific dosage and participant compliance details were unavailable, potentially impacting the observed outcomes.

Ondansetron is commonly prescribed for the management of nausea and vomiting during pregnancy [12]. Pregnant women prescribed ondansetron exhibited significantly higher odds of developing UTIs (OR = 1.926, 95% CI = 1.525, 2.421). To address the limitations outlined in this study, we exposed female mice to ondansetron (2mg/kg for 3 days) prior to transurethral infection with E. coli UTI89, to assess the impact of ondansetron on UTI severity. Pregnant mice treated with ondansetron exhibited more severe bladder infections compared to those treated with saline, thus corroborating the findings from the retrospective study in pregnant women. Additionally, ondansetron-treated mice showed elevated serum serotonin levels and increased urinary 5-HIAA, indicating broader effects on serotonin metabolism and signaling pathways.

This heightened risk may arise from ondansetron’s potential interference with the physiological urethral defense mechanism, particularly by blocking HTR3 receptors expressed by urethral ICCs, as observed in our study and previous research [7, 33]. This interference could disrupt 5-HT mediated urethral contraction, potentially impeding the expulsion of ascending pathogens and increasing susceptibility to UTIs.

Our previous research demonstrated that 5-HT, likely originating from UNECs, contributes to the protective mechanism against ascending UPEC infections in female mice. This mechanism is likely mediated by the activation of 5-HT receptors on urethral ICCs, leading to urethral smooth muscle contraction and pathogen expulsion. We previously localized 5-HT-positive cells to the urethral epithelium (UNEC) and HTR3 to ICCs in the urethra of humans and mice [7]. In vitro experiments showed that 5-HT drives urethral smooth muscle contraction, while ondansetron blocked 5-HT-mediated contraction, potentially disrupting urethral defense and impeding pathogen expulsion [7].

Additionally, ondansetron may influence the gut microbiome[16], and, consequently, the vaginal and urinary microbiomes, potentially contributing to UTIs [17]. Beyond these microbiome effects, ondansetron, exhibit anti-inflammatory properties by potentially reducing pro-inflammatory cytokine release through serotonin receptor blockade on macrophages, although the mechanisms remain incompletely understood [34]. While reducing inflammation may be beneficial in some contexts, it could impair the immune response to urinary pathogens by limiting pro-inflammatory cytokines needed for pathogen clearance.

We found higher rates of preterm birth and low birth weight among pregnant patients with a history of UTIs treated with ondansetron compared to control groups. The timing of UTIs during pregnancy is critical, as early infections have been associated with disruptions in placental vascularization and adverse outcomes, such as preterm birth and low birth weight [35, 36]. However, given the consistent association between UTIs and adverse pregnancy outcomes, drawing definitive conclusions about the causal relationship between ondansetron and these outcomes is challenging. Also, the absence of detailed temporal data in our study, particularly regarding the sequencing of UTI occurrence relative to medication use, limits our ability to fully assess causality.

In conclusion, our study provides compelling evidence of an association between ondansetron use and increased UTI risk during pregnancy. This underscores the importance of cautious prescribing practices and ongoing monitoring of maternal health outcomes. Further clinical research is warranted to confirm our findings and ensure optimal maternal and fetal health outcomes.

Availability of Data and Material:

Data available on request.