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Tissue distribution of methotrexate in rats. A comparison between intravenous injection as bolus or drip infusion
Abstract:
Concentrations of methotrexate (MTX, 30 mg/kg) in rat sera and tissues were compared after the drug was administered by i.v. route as bolus injection or by drip infusion. Plasma and tissue specimens were collected after 1 h and 4 h and assayed for MTX by RIA. After 1 h the continuous infusion gave higher MTX levels in plasma, liver, bowel, lung, kidney, testicle and muscle; bolus injection gave higher levels in brain. No differences in levels were found in fat. After 4 h the differences between the two methods of administration were still appreciable only in liver, testicle and muscle. The differences were confirmed by determination of AUC for sera and tissue levels (1-4 h). These data suggest that continuous infusion may be more useful to obtain the highest levels of MTX in tissues with low or medium blood flow (as is probably the case in cancer tissue). Bolus injection, on the other hand, promotes the flow of the drug across the blood-brain barrier.
Insights
Continuous infusion of methotrexate (MTX) increases tissue drug levels, except in the brain, compared to bolus injection. This suggests infusion may be better for targeting cancer tissues with lower blood flow.
Area of Science:
- Pharmacology
- Oncology
- Drug Delivery
Background:
- Methotrexate (MTX) is a critical chemotherapy agent.
- Understanding MTX distribution is key for optimizing cancer treatment.
- Different administration routes can significantly alter drug pharmacokinetics.
Purpose of the Study:
- To compare MTX concentrations in rat sera and tissues after intravenous bolus injection versus continuous drip infusion.
- To evaluate the impact of administration route on MTX distribution in various organs.
- To determine the optimal administration strategy for maximizing MTX efficacy in specific tissues, including potential tumor sites.
Main Methods:
- Rats were administered MTX (30 mg/kg) via intravenous bolus injection or continuous drip infusion.
- Serum and tissue samples (plasma, liver, bowel, lung, kidney, testicle, muscle, brain, fat) were collected at 1 hour and 4 hours post-administration.
- Methotrexate concentrations were quantified using radioimmunoassay (RIA).
- Area Under the Curve (AUC) was calculated to assess overall drug exposure from 1-4 hours.
Main Results:
- After 1 hour, continuous infusion resulted in higher MTX levels in plasma and most tissues (liver, bowel, lung, kidney, testicle, muscle), while bolus injection yielded higher brain MTX levels.
- No significant differences in MTX levels were observed in adipose tissue at 1 hour.
- After 4 hours, notable differences persisted in liver, testicle, and muscle MTX concentrations between the two administration methods.
- AUC analysis confirmed these observed differences in serum and tissue MTX levels.
Conclusions:
- Continuous MTX infusion may be advantageous for achieving higher drug concentrations in tissues with low to medium blood flow, potentially including cancerous tissues.
- Bolus MTX injection appears more effective at facilitating drug penetration across the blood-brain barrier.
- The choice of administration route (infusion vs. bolus) significantly influences MTX tissue distribution and has implications for therapeutic strategies.