Introduction to Radio Pharmaceuticals
Radio pharmaceuticals are special pharmaceutical preparations that contain radioactive isotopes. They can be in the form of solutions, capsules, or injections and are primarily used for diagnostic imaging and therapeutic purposes.
In India, most radio-pharmaceuticals are developed and supplied by the Bhabha Atomic Research Centre (BARC), Mumbai, to approved hospitals and laboratories. Each preparation is named according to its radioactive component, for example, sodium-radio-iodide injection or sodium-iodide I-131 capsules. BARC produces more than 40 different radioactive preparations, kits, and generators.
Important Radio-Pharmaceutical Preparations
| Product | Radionuclide | Shelf Life | Half-Life | Application |
|---|---|---|---|---|
| Ammonium bromide injection | Br-82 | 36 hrs | 36 hrs | Measurement of extracellular water |
| Calcium chloride solution | Ca-45 | 180 days | 160 days | Study of calcium metabolism |
| Chromic chloride injection | Cr-51 | 90 days | 27.7 days | Protein loss and absorption studies |
| Colloidal gold injection | Au-198 | 65 hrs | 56 hrs | Treatment of cancer and RES studies |
| Cyanocobalamin preparation | Co-57 / Co-58 | 60 / 270 days | 71 days | Diagnosis of pernicious anemia |
| Ferric chloride solution | Fe-59 | 120 days | 44.6 days | Study of iron metabolism |
| Indium chloride | In-113m / Sn-113 | 8 hrs / 99.5 min | – | Diagnosis of placental and cardiac diseases |
| Potassium chloride injection | K-42 | 12.5 hrs | 12.5 hrs | Potassium exchange studies |
| Rubidium chloride injection | Rb-86 | 45 days | 18.6 days | Determination of myocardial blood flow |
| Sodium chloride injection | Na-24 | 15 hrs | 15 hrs | Sodium exchange studies |
| Sodium iodide capsules | I-131 | 30 days | 8.06 days | Thyroid function study |
| Sodium orthophosphate solution | P-32 | 30 days | 14.3 days | Treatment of polycythemia |
| Sodium sulphate solution | S-35 | 180 days | 87.4 days | Extracellular fluid volume measurement |
| Sodium pertechnetate | Tc-99m | 24 hrs | 6.02 hrs | Various diagnostic applications |
Designing Radio Pharmaceuticals
The design of radio-pharmaceuticals focuses on choosing compounds that selectively accumulate in target organs or tissues. The goal is to ensure that adding the radioactive isotope does not alter the chemical or biological behavior of the molecule.
Similar to Structure-Activity Relationship (SAR) in drug development, the Structure-Distribution Relationship (SDR) helps predict how the compound will distribute in the body. The main objective is to optimize delivery to the target site before testing in animals or humans.
Technetium-99m (Tc-99m) Radio Pharmaceuticals
Technetium-99m (Tc-99m) is the most widely used radionuclide in diagnostic medicine, present in about 75% of all radio-pharmaceuticals. It has excellent imaging characteristics:
- Half-life of 6 hours (ideal for short diagnostic procedures)
- Emits a 140 keV gamma photon suitable for imaging
- Forms stable complexes with various ligands due to flexible chemistry
Tc-99m compounds are used to study organs such as the heart, brain, lungs, liver, kidneys, and bones.
Sodium Iodide I-131 (Solution and Capsules)
Form: Clear, colorless solution (pH 7.5–9.0) for oral or IV administration. Capsules are made by evaporating the radioactive solution onto inert fillers.
Uses:
- Diagnosis of thyroid structure and function
- Treatment of thyroid cancer, hyperthyroidism, and hypothyroidism
- Evaluation of thyroid-related cardiac conditions
Half-life: 8.08 days
It is prepared with minimal impurities and carefully processed for stability and safety.
Safe Storage and Handling of Radioactive Materials
- Store radioactive materials in restricted, shielded areas using lead or thick glass.
- Monitor radiation levels regularly in both storage and working areas.
- Use protective equipment such as gloves, tongs, and lab coats.
- Follow national safety regulations for handling, disposal, and personnel monitoring.
- Avoid eating, drinking, or smoking in handling areas.
- Waste should be stored securely until radiation decays to safe levels.
Pharmaceutical Applications of Radioactive Substances
Radioactive isotopes have been used in medicine since the early 20th century. Radium was the first radionuclide used medically (1901–1946). Today, more than 50 radionuclides are available for diagnosis, therapy, and calibration.
In diagnostics, radio-pharmaceuticals act as tracers — pharmacologically inactive compounds that help image specific organs or biological processes. Therapeutic isotopes, on the other hand, deliver controlled doses of radiation to treat diseases such as cancer.
Common Applications Include:
- Gold-198: Used for treating malignant effusions and carcinomas.
- Cobalt-57 / 58: Used in vitamin B12 labeling for diagnosing anemia.
- Sodium Iodide I-131: Used for thyroid disorder diagnosis and treatment.
- Ferric Citrate: Used in hematological studies.
- Calcium Isotopes: Used for studying bone metabolism.
- Strontium-90: Used for superficial carcinoma treatment.
- Deuterium and Tritium: Used to measure total body water content.
In addition, strong gamma radiation sources like Cobalt-60 and Cesium-137 are used for sterilizing pharmaceutical products and surgical instruments.
Detailed Notes:
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