Is enteral administration of fluorine-18-fluorodeoxyglucose (F-18 FDG) a palatable alternative to IV injection? Pre-clinical evaluation in normal rodents

Oral Administration of [18F]MC225 for Quantification of P-glycoprotein Function: A Feasibility Study

PURPOSE

This preclinical study explored the feasibility of assessing P-glycoprotein (P-gp) function in both brain and gastrointestinal (GI) tract of rats using positron emission tomography (PET) following oral administration of [18F]MC225. Different oral administration protocols were evaluated, and radioactivity uptake was compared with uptake following intravenous administration.

PROCEDURES

Twelve male Wistar rats were divided into four groups and subjected to intravenous or oral [18F]MC225 administration protocols: G1 (intravenous route), G2 (oral administration without fasting), G3 (oral administration with fasting), and G4 (oral administration with fasting following administration of the P-gp inhibitor tariquidar). Dynamic brain imaging, late abdominal imaging, ex vivo biodistribution, and metabolite analysis were conducted to assess tracer distribution.

RESULTS

In the brain, oral administration yielded lower values compared with intravenous administration, resulting in a reduction in the tissue-to-plasma ratio by approximately 51% for the cortex and 45% for the midbrain and cerebellum. Fasting improved radioactivity uptake, aiding brain visualization. Unexpectedly, administration of the P-gp inhibitor tariquidar did not increase brain concentration, suggesting a signal that was dominated by non-specific uptake, possibly due to instability of [18F]MC225 in the GI tract. Metabolite analysis in G4 indicated a significant presence of polar metabolites.

CONCLUSIONS

Oral administration of [18F]MC225 faces challenges and, at this stage, cannot be used to quantify P-gp function. Further research to assess tracer stability and metabolism in the stomach and intestine will be essential for advancing the feasibility of oral tracer administration.

Human Radiation Dosimetry for Orally and Intravenously Administered 18F-FDG

Intravenous access is difficult in some patients referred for ¹⁸F-FDG PET imaging. Extravasation at the injection site and accumulation in central catheters can lead to limited tumor ¹⁸F-FDG uptake, erroneous quantitation, and significant image artifacts. In this study, we compared the human biodistribution and dosimetry for ¹⁸F-FDG after oral and intravenous administrations sequentially in the same subjects to ascertain the dosimetry and potential suitability of orally administered ¹⁸F-FDG as an alternative to intravenous administration. We also compared our detailed intravenous ¹⁸F-FDG dosimetry with older dosimetry data. Methods: Nine healthy volunteers (6 male and 3 female; aged 19-32 y) underwent PET/CT imaging after oral and intravenous administration of ¹⁸F-FDG. Identical preparation and imaging protocols (except administration route) were used for oral and intravenous studies. During each imaging session, 9 whole-body PET scans were obtained at 5, 10, 20, 30, 40, 50, 60, 120, and 240 min after ¹⁸F-FDG administration (370 ± 16 MBq). Source organ contours drawn using CT were overlaid onto registered PET images to extract time-activity curves. Time-integrated activity coefficients derived from time-activity curves were given as input to OLINDA/EXM for dose calculations. Results: Blood uptake after orally administered ¹⁸F-FDG peaked at 45-50 min after ingestion. The oral-to-intravenous ratios of ¹⁸F-FDG uptake for major organs at 45 min were 1.07 ± 0.24 for blood, 0.94 ± 0.39 for heart wall, 0.47 ± 0.12 for brain, 1.25 ± 0.18 for liver, and 0.84 ± 0.24 for kidneys. The highest organ-absorbed doses (μGy/MBq) after oral ¹⁸F-FDG administration were observed for urinary bladder (75.9 ± 17.2), stomach (48.4 ± 14.3), and brain (29.4 ± 5.1), and the effective dose was significantly higher (20%) than after intravenous administration (P = 0.002). Conclusion: ¹⁸F-FDG has excellent bioavailability after oral administration, but peak organ activities occur later than after intravenous injection. These data suggest PET at 2 h after oral ¹⁸F-FDG administration should yield images that are comparable in biodistribution to conventional clinical images acquired 1 h after injection. Oral ¹⁸F-FDG is a palatable alternative to intravenous ¹⁸F-FDG when venous access is problematic.

Comparison of the Intraperitoneal, Retroorbital and per Oral Routes for F-18 FDG Administration as Effective Alternatives to Intravenous Administration in Mouse Tumor Models Using Small Animal PET/CT Studies

PURPOSE

We compared alternative routes for (18)F-fluorodeoxyglucose (FDG) administration, such as the retroorbital (RO), intraperitoneal (IP) and per oral (PO) routes, with the intravenous (IV) route in normal tissues and tumors of mice.

MATERIALS AND METHODS

CRL-1642 (ATCC, Lewis lung carcinoma) cells were inoculated in female BALB/c-nu/nu mice 6 to 10 weeks old. When the tumor grew to about 9 mm in diameter, positron emission tomography (PET) scans were performed after FDG administration via the RO, IP, PO or IV route. Additional serial PET scans were performed using the RO, IV or IP route alternatively from 5 to 29 days after the tumor cell injection.

RESULTS

There was no significant difference in the FDG uptake in normal tissues at 60 min after FDG administration via RO, IP and IV routes. PO administration, however, showed delayed distribution and unwanted high gastrointestinal uptake. Tumoral uptake of FDG showed a similar temporal pattern and increased until 60 min after FDG administration in the RO, IP and IV injection groups. In the PO administration group, tumoral uptake was delayed and reduced. There was no statistical difference among the RO, IP and IV administration groups for additional serial PET scans.

CONCLUSION

RO administration is an effective alternative route to IV administration for mouse FDG PET scans using normal mice and tumor models. In addition, IP administration can be a practical alternative in the late phase, although the initial uptake is lower than those in the IV and RO groups.

Oral administration of F-18 FDG to evaluate a single pulmonary nodule by positron emission tomography in a patient with poor intravenous access

F-18 fluorodeoxyglucose (FDG) is typically administered intravenously for positron emission tomography. The authors present a case of oral administration of FDG for evaluation of a pulmonary nodule and review the limited literature on this subject. Oral administration of FDG is a useful alternative to intravenous administration in patients with difficult intravenous access when the alimentary tract is not involved in the clinical diagnosis.