Percentage solutions

The concentration of a solution may be expressed on the basis of weight per unit volume (w/v) or volume per unit volume (v/v).

% w/v = number of grams of a substance in 100 ml of a liquid

% v/v = number of ml of a substance in 100 ml of liquid

% Solution g or ml/100 ml mg/ml Solution strength
100 100 1000 1:1
10 10 100 1:10
1 1 10 1:100
0.1 0.1 1 1:1000
0.01 0.01 0.1 1:10,000

Drugs usage in renal and hepatic insufficiency

With failure of liver or kidney, the excretion of some drugs may be impaired, leading to increased serum concentrations. Note: this information is based on mammals and may not be directly applicable to birds, reptiles, amphibians and fish.

Renal failure
  1. Double the dosing interval or halve the dosage in patients with severe renal insufficiency. Use for drugs that are relatively non-toxic.
  2. Increase dosing interval 2-fold when creatinine clearance (Ccr) is 0.5–1.0 ml/min/kg, 3-fold when Ccr is 0.3–0.5 ml/min/kg and 4-fold when Ccr is <0.3 ml/min/kg.
  3. Precise dose modification is required for some toxic drugs that are excreted solely by glomerular filtration, e.g. aminoglycosides. This is determined by using the dose fraction Kf to amend the drug dose or dosing interval according to the following equations:

    Modified dose reduction = normal dose × Kf

    Modified dose interval = normal dose interval/Kf

    where Kf = patient Ccr/normal Ccr

    Where Ccr is unavailable, Ccr may be estimated at 88.4/serum creatinine (μmol/l) (where serum creatinine is <350 μmol/l). Kf may be estimated at 0.33 if urine is isosthenuric or 0.25 if the patient is azotaemic.

Drug Nephrotoxic Dose adjustment in renal failure
Amikacin Yes c
Amoxicillin No a
Amphotericin B Yes c
Ampicillin No a
Cefalexin No b
Chloramphenicol No N, A
Digoxin No c
Gentamicin Yes c
Oxytetracycline Yes Cl
Penicillin No a
Streptomycin Yes b
Tobramycin Yes c
Trimethoprim/sulphonamide Yes b, A

a, b, c = Refer to section above on dose adjustment; A = Avoid in severe renal failure; CI = Contraindicated; N = normal dose.

Hepatic insufficiency

Drug clearance by the liver is affected by many factors and thus it is not possible to apply a simple formula to drug dosing. The table below is adapted from information in the human literature.

Drug DI CI
Aspirin X
Azathioprine X
Cefotaxime X
Chloramphenicol X
Clindamycin X
Cyclophosphamide X
Diazepam X
Doxorubicin X
Doxycycline X
Furosemide X
Hydralazine X
Lidocaine X
Metronidazole X
Morphine X
Oxytetracycline X
Pentazocine X
Pentobarbital X
Phenobarbital X
Propranolol X
Theophylline X
Vincristine X

CI = Contraindicated; avoid use if at all possible. DI = A change in dose or dosing interval may be required.

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