Rational Fixed Dose Drug Combinations

Rational Fixed Dose Drug Combinations

Write A Short Note On Rational Fixed Dose Drug Combinations (FDCs).
Answer:

Rational Fixed Dose Drug Combinations

Fixed dose combination refers to the combination of two or more therapeutic drugs in the fixed-dose ratio in a single formulation.

Criteria For Choosing Fixed-Dose Drug Combinations

• FDCs must be based on convincing therapeutic rationalization and be carefully justified and clinically relevant.
• They are safe and effective for claimed indications and it cannot be assumed that the benefits of FDC outweigh its risks.
• As for new medicine, the risks and benefits must be defined and compared. Attention should be drawn to the doses of each active substance in FDC.

Examples Of FDCs

• A combination of levodopa and carbidopa is used in Parkinsonism
• Combination of amoxicillin and clavulanic acid as antimicrobial
• Combination of isoniazid and rifampicin and pyrazinamide in tuberculosis
• Combination of estrogen and progesterone as oral contraceptives.

Rational Fixed Dose Drug Combinations  Advantages

• Convenience and better patient compliance when all the components present in a formulation are actually needed by the patient. It may also be cost-saving compared to both all the components administered separately.
• Certain drug combinations are synergistic, for Example. sulfamethoxazole + trimethoprim, combination oral contraceptives.
• The therapeutic effect of two components being the same may add up while the side effects being different may not.
  For Example. amlodipine + atenolol as antihypertensive.
• The side effect of one component may be counteracted by the other, for Example. a thiazide + a potassium sparing diuretic.
  However, the amount of the latter may not be sufficient in all cases.
• The combined formulation ensures that a single drug will not be administered.
  This is important in the treatment of tuberculosis and HIV-AIDS.
• Cost is reduced.

Rational Fixed Dose Drug Combination Disadvantages

• The patient may not actually need all the drugs present in a combination. He is subjected to additional side effects and expenses.
• The dose of most drugs needs to be adjusted and individualized. When a combined formulation is used, this cannot be done without altering the dose of the other components.
• The time course of action of the components may be different: administering them at the same intervals may be inappropriate.
• The altered renal or hepatic function of the patient may differently affect the pharmacokinetics of the components.
• An adverse effect, when it occurs, cannot be easily ascribed to the particular drug causing it.
• Contraindication to one component contraindicates the whole preparation.
• Confusion of therapeutic aims and a false sense of superiority of two drugs over one is fostered, especially in the case of antimicrobials whose combinations should be avoided.
• Corticosteroids should never be combined with any other drug meant for internal use.